ChemComm
Dynamic Article Links
Cite this: Chem. Commun., 2011, 47, 1961–1975
FEATURE ARTICLE
www.rsc.org/chemcomm
‘Supramolecular wrapping chemistry’ by helix-forming polysaccharides: a powerful strategy for generating diverse polymeric nano-architectures Munenori Numataa and Seiji Shinkai*bc Received 9th August 2010, Accepted 25th November 2010 DOI: 10.1039/c0cc03133j We have exploited novel supramolecular wrapping techniques by helix-forming polysaccharides, b-1,3-glucans, which have strong tendency to form regular helical structures on versatile nanomaterials in an induced-fit manner. This approach is totally different from that using the conventional interpolymer interactions seen in both natural and synthetic polymeric architectures, and therefore has potential to create novel polymeric architectures with diverse and unexpected functionalities. The wrapping by b-1,3-glucans enforces the entrapped guest polymer to adopt helical or twisted conformations through the convergent interpolymer interactions. On the contrary, the wrapping by chemically modified semi-artificial b-1,3-glucans can bestow the divergent self-assembling abilities on the entrapped guest polymer to create hierarchical polymeric architectures, where the polymer/b-1,3-glucan composite acts as a huge one-dimensional building block. Based on the established wrapping strategy, we have further extended the wrapping techniques toward the creation of three-dimensional polymeric architectures, in which the polymer/b-1,3-glucan composite behaves as a sort of amphiphilic block copolymers. The present wrapping system would open several paths to accelerate the development of the polymeric supramolecular assembly systems, giving the strong stimuli to the frontier of polysaccharide-based functional chemistry.
Graduate School of Life and Environmental Science, Kyoto Prefectural University, Shimogamo, Sakyo-ku, Kyoto 606-8522, Japan b Institute of Systems, Information Technologies and Nanotechnologies (ISIT), 203-1, Motooka, Nishi-ku, Fukuoka 819-0385, Japan. E-mail:
[email protected] c Department of Nanoscience, Faculty of Engineering, Sojo University, 4-22-1, Ikeda, Kumamoto 860-0082, Japan
1. Introduction
Munenori Numata was born in Osaka, Japan (1970). He received his MS degree from Kyoto Institute of Technology, and his PhD from Kyushu University under the supervision of Prof. Seiji Shinkai (2000). After postdoctoral work with Prof. Kazuhisa Hiratani at the National Institute of Advanced Industrial Science and Technology, he joined JST SORST project (2002), led by Prof. Shinkai, as a group leader at Kyushu Munenori Numata University. Then, he became an associate professor at Ritsumeikan University in the group of Prof. Hitoshi Tamiaki, and began his independent career at Kyoto Prefectural University (2008). His current research interests include molecular self-assembly, macromolecular architectures, and nanomaterials.
Seiji Shinkai was born in 1944 in Fukuoka, Japan, and received his PhD in 1972 from Kyushu University, where he became a lecturer soon afterwards. After postdoctoral work at the University of California, Santa Barbara, he joined Kyushu University in 1974 and became a full professor there in 1988. He had been acting as a leader of several national projects and COE projects. He retired from Kyushu University in Seiji Shinkai 2008 and moved to Sojo University. Besides, he is also serving as a President of Institute of Systems, Information Technologies and Nanotechnologies. His research interests focus on sugar sensing, allosteric functions, organogels, sol–gel transcription, polysaccharide–polynucleotide interactions.
a
This journal is
c
The Royal Society of Chemistry 2011
In nature, polymeric nanoarchitectures, constructed by weak inter- or intrapolymer interactions of versatile biopolymers, play central roles to control all biological events such as storing molecular information, supporting molecular assembly, transportation and chemical conversion of
Chem. Commun., 2011, 47, 1961–1975
1961
molecules, etc. A specific feature of the polymeric interactions in the natural system is to create homogeneous and monodispersive polymeric architectures such as higher-order structures of proteins and double-stranded DNA structures, which are essentially governed by ubiquitous inter- or intrapolymer interactions. Over the last decade, the strategy of ‘supramolecular chemistry’ has widely spread to the selfassemblies of synthetic functional polymers, which have potential to create various polymeric nanoarchitectures with desired structures as well as diverse functionalities that have never been produced in natural polymeric systems.1 To date, this concept has enabled us to create numerous polymeric architectures, which are based on the combination of a variety of weak interpolymer interactions that are important to explain the final functionalities of the polymer assemblies.2 From the standpoint to create precise artificial polymeric architectures, control of the interpolymer interactions, which generally result in extended two- or three-dimensional structures in an uncontrollable way, is essentially important and still a challenging research subject. The specific interpolymer interaction that has potential to form regular polymeric architectures in a convergent manner is to wrap a polymer chain with another polymer in a helical fashion, which results in spatially closed one-dimensional supramolecular polymeric architectures. The polymer wrapping is thus characterized as unique and uncommon interpolymer interactions, which have never been seen in natural systems and even in supramolecular systems of small molecules, and therefore, has great potential to create novel polymeric architectures with diverse and unexpected functionalities (Fig. 1).3–5 Firstly, the surface of the resultant polymer composite is covered with a wrapping agent, which governs the total surface properties of the composite, where the wrapping agent acts as a huge one-dimensional host for the incorporated guest
Fig. 1 Schematic illustration of the conventional inter- or intrapolymer interactions. The polymer wrapping can be characterized as a unique interpolymer interaction to create convergent polymeric architectures.
1962
Chem. Commun., 2011, 47, 1961–1975
polymers. From the alternative viewpoint, the size or shape of the resultant composite can be basically affected by the morphological feature of the guest polymers. In addition, the entrapped guest polymers are isolated by the wrapping agent, and in some cases, functionalities of guest polymers are tuned through the interpolymer interactions. The supramolecular interactions between the wrapping agent and the guest polymers are basically reversible; wrapping and peeling of the wrapping agent would be controllable by external stimuli. Furthermore, if the surface of the wrapping agent can be selectively decorated by interactive groups, the resultant one-dimensional composites acquire the self-assembling ability toward two- or three-dimensional divergent architectures. Herein, we will review our recent research on the supramolecular wrapping by natural helix-forming polysaccharides, b-1,3-glucans, which can form water-soluble one-dimensional composites incorporating hydrophobic polymers. This approach is totally different from the conventional approach to construct polymeric nanoarchitectures. Particularly, we would like to highlight a novel self-assembling system of the resultant one-dimensional composites as building blocks toward two- or three-dimensional nanoarchitectures, where self-assembling capabilities of guest polymers can be bestowed through the wrapping by semiartificial b-1-3-glucans having molecular recognition abilities. The lineup of these examples will establish that the one-dimensional composites will be useful as versatile building blocks for huge and diverse hierarchical superstructures.
2. Structural aspects of b-1,3-glucans Nature produces really numerous kinds of polysaccharides and X-ray diffraction patterns of various natural polysaccharides have revealed that some of them adopt well-defined helical nanoarchitectures, which have encouraged us to use them as natural wrapping agents. b-1,3-Glucans are produced in fungi and are essentially linear polymers of (1 - 3) linked b-D-glucose units and known as a series of b-1,3-glucans distinguished by the number of side-groups (Fig. 2).6 Among them, curdlan (CUR) is known as the simplest b-1,3-glucan. X-Ray diffraction patterns of CUR in the anhydrous form revealed that it adopts a right-handed 61 triple helix with a diameter of 2.3 nm and a pitch of 1.8 nm. In contrast to the simple CUR structure, schizophyllan (SPG) has side glucose groups linked at every third main-chain glucose (Fig. 2). The side glucose groups endow SPG with the water-solubility, whereas they do not affect the helical conformation of the main-chain. For both CUR and SPG, in their triple helix structures, the side glucose or the 6-OH group always exists on the exterior surface of the triple helix, making them recognition tags for further chemical modification. In 1968, Atkins and Parker revealed the detailed inner structure of CUR by X-ray diffraction patterns: in the triple helix, three glucoses composed of different chains are bound together through the hydrogen bonds among the three 2-OH groups.7 This means that there is no enough space to accommodate even small guest molecules in the b-1,3-glucan triple helix. Although the b-1,3-glucan triple helix has no ability to accept guest molecules, the single-stranded b-1,3-glucan chain is expected to act as a wrapping agent because it is This journal is
c
The Royal Society of Chemistry 2011
Fig. 2 Chemical structures of schizophyllan (SPG) and curdlan (CUR) and their calculated triple-helix structures.
rather flexible and can adopt various conformations. Unique conformational transition from the flexible random coil to the rigid triple helix was reported for b-1,3-glucans in 1981. Norisuye et al. revealed that denature and renature of the triple helix can take place reversibly; that is, b-1,3-glucans dissolve in water as a triple helix (t-SPG or t-CUR), whereas as a single chain in DMSO (s-SPG or s-CUR). When water is added to the DMSO solution, however, renature of the single-stranded b-1,3-glucan is promoted, resulting in the formation of the original triple helix.8 As we describe in this review article, the drastic conformational transition is essential for b-1,3-glucans to exert the unique wrapping properties. As a foregoing preliminary result, it is already known that b-1,3-glucans can form one-dimensional complexes with some polynucleotides during their denature/renature processes.9 These complexes are characterized by a hetero-triple helix consisting of two b-1,3-glucan chains and one polynucleotide chain. This fact apparently suggests that b-1,3-glucans have inherent potential to interact with different kinds of polymers to form helical one-dimensional complexes. It should be noted here that the hetero-triple helix formation can be recognized as a result of the supramolecular wrapping toward specific helical polymers, in which the helical pitch and the diameter are consistent with those of b-1,3-glucans. Therefore, this co-helix formation between b-1,3-glucans and helical polymers should be strictly differentiated from the simple wrapping toward conventional polymer guests.
effort has been paid to exploit the effective synthetic route to introduce the functional group into the desired OH group. Chemical modification of b-1,3-glucans has been independently developed by several research groups including us.10,11 In order to prepare the functionalized wrapping agent based on b-1,3-glucans, the selective modification targeting the sideglucose in SPG or the 6-OH group in CUR should be exploited, because the 2- or 4-OH groups connected to the main-chain are indispensable for stabilization of the inherent helical structure. To solve this requirement, we successfully established a versatile synthetic route to introduce various functional groups selectively into the side-glucose of SPG or the 6-OH group of CUR, without affecting the inherent helix-forming property of b-1,3-glucans (Schemes 1 and 2). CUR has one primary OH group in its repeating unit, i.e., 6-OH group, which would be an active nucleophile under appropriate reaction conditions, making the selective modification possible. Moreover, the quantitative reaction can be achieved through the azideation reaction of 6-OH, followed by ‘click chemistry’, which involves a Cu(I)catalyzed chemoselective coupling between organic azides and terminal alkynes.11f,g This newly exploited strategy has allowed us to directly introduce various functional groups into the 6-OH group of CUR, leading to the creation of CUR-based functional materials. The advantageous point of this method is that a series of reactions proceed quantitatively and selectively. In addition, by adjusting the feed acetylene
Scheme 1 Synthetic strategy toward semi-artificial CUR: selective and quantitative modification of CUR 6-OH groups.11f–i
3. Synthetic strategies toward the selective modification of b-1,3-glucans Many studies on polysaccharides have focused on exploiting the functional materials through chemical modification of polysaccharides. The particular problem occurring from the chemical modification is the similar reactivity of the OH groups, making selective functionalization difficult. Accordingly, much This journal is
c
The Royal Society of Chemistry 2011
Scheme 2 Synthetic strategy toward semi-artificial SPG: selective modification of SPG side glucose groups.11a–e
Chem. Commun., 2011, 47, 1961–1975
1963
molar ratio, different functional groups can be easily introduced into the same CUR chain in a step-wise manner. SPG has two primary OH groups in the main chain and one in the side glucose group, so that the selective modification targeting the primary OH group seems to be difficult. On the other hand, the side glucose group of SPG has 1,2-diols at 2-OH, 3-OH and 4-OH positions, whereas the main chain glucose has no such a 1,2-diol due to the glicoside linkage between 1-OH and 3-OH positions. Therefore, one may expect that the oxidative cleavage of these 1,2-diols by NaIO4 would proceed selectively only at the side glucose unit. Combining this oxidative cleavage of the 1,2-diols with the reductive amination reaction, these classical synthetic strategies can become a powerful tool for the selective modification of the native SPG chain. So far, we have demonstrated that a series of chemically modified SPGs bearing various molecular recognition tags can be obtained according to this synthetic route.11a,c–e Here, it is worthy to address the basic discrepancy between these chemically modified CURs and SPGs: 6-OH groups of CUR can be converted to functional groups ‘quantitatively’, whereas the side glucose groups of SPG can be ‘partially’ functionalized because excessive oxidation of the side glucoses results in the insoluble aggregate probably due to the interpolymer cross-linking between the 6-OH and the aldehyde group thus formed. The modification percentage of the side glucose groups is, at most, 30%.
Fig. 3 Nano-surface-fabrication by wrapping: (a) a proposed wrapping mode of b-1,3-glucan on the SWNT surface, schematic illustration of the wrapping by (b) natural b-1,3-glucan and (c) semiartificial b-1,3-glucan; introduced functional groups exist on the exterior surface of the composite.
4. Supramolecular wrapping by b-1,3-glucans toward nano-surface-fabrication The supramolecular wrapping by b-1,3-glucans has been evolved as a precise surface modification technique. The surface properties of wrapped guest polymers are totally governed by those of b-1,3-glucans, which have inherent water-solubility and bio-compatibility leading to novel artificial functionalities (Fig. 3). The first idea was to wrap a single-walled carbon nanotube (SWNT) as a guest polymer,12 expecting that the SWNT surface would acquire the hydrophilic properties due to the wrapping SPG. As a preliminary experiment to investigate whether b-1,3-glucans can really wrap SWNTs, an s-SPG (Mw = 150 KDa) DMSO solution was directly added to an aqueous solution containing cut SWNTs (c-SWNTs) that were cut into an appropriate length (1–2 mm) by the acid treatment.13 Several lines of evidence that SWNTs are really entrapped into the SPG cavity were obtained by atomic force microscopy (AFM); that is, the surface of the fibrils showed a periodical structure with inclined stripes, reflecting the strong helix-forming nature of the b-1,3-glucan main-chain (Fig. 4).14 Although natural CUR is scarcely soluble in water due to the lack of side glucoses, low molecular-weight CURs obtained after hydrolysis by formic acid treatment become water-soluble.15 These findings have led us to conclude that the b(1 - 3) glucose linkage is indispensable for helix formation that brings forth the unique wrapping capabilities of b-1,3-glucans. Another goal for preparing SWNT hybrid materials is to directly solubilize solid SWNTs into water. We have successfully demonstrated that SWNT powder can be directly dispersed into water by the same wrapping technique with the aid of 1964
Chem. Commun., 2011, 47, 1961–1975
Fig. 4 AFM images of (a) c-SWNTs, (b) SWNTs/SPG composite, (c) c-SWNT/CUR composite and (d) magnified image of the c-SWNT/ SPG composite. Adapted with permission from ref. 14. Copyright 2004, Chemical Society of Japan.
sonication, suggesting that the wrapping by SPG is effective even for solid materials.16 To characterize the obtained SWNTs/SPG composite, it was subjected to VIS-NIR measurements in the D2O solvent. The characteristic sharp bands assignable to individual SWNTs can be observed in the VIS-NIR region, supporting the view that one or only a few pieces of SWNTs are included in the SPG helical structure. High-resolution TEM (HRTEM) revealed that two s-SPG chains wrap one SWNT which is clearly recognized from the Fourier filtered image (Fig. 5). This journal is
c
The Royal Society of Chemistry 2011
Fig. 5 TEM images of (a) ag-SWNT/SPG composite, (b) magnified Fourier filtered image of (a) and (c) pictures of aqueous solution containing the ag-SWNT/SPG composite (left) and that taken after addition of 50% of DMSO (right). Adapted with permission from ref. 16. Copyright 2005, American Chemical Society.
The wrapping behavior of b-1,3-glucans is characterized by the non-covalent interaction with guest polymers. If b-1,3-glucans maintain their helix-forming nature even on the SWNT surface, the dissociation from SWNTs would be promoted by addition of DMSO or NaOH, in which b-1,3-glucans tend to exist as a single chain. As shown in Fig. 5c, when DMSO was added to the aqueous solution dissolving the composite up to the final composition of 50 v/v%, the entrapped SWNTs were dissociated and immediately precipitated out. This result indicates that the resultant composite is stabilized by the non-covalent interactions which make the reversible association–dissociation possible. Although the further detail of the interaction mechanism between the SWNT surface and the b-1,3-glucan main chain remains unclear, we consider that the a-face of the glucose main-chain unit would play a crucial role probably due to the hydrophobic interaction or the CH–p interaction. If this is the case, the original b-1,3-glucan conformation, in which the three 2-OH groups constitute triangle interpolymer hydrogenbonds, should be modified so that they can enjoy the effective interaction with the SWNT surface. In other words, the flexible nature of the b-1,3-glucan main chain makes it possible to take various conformations suitable to accept different sizes and shapes of guest polymers. In addition to the excellent water-solubility, desired functionalities can be bestowed to the SWNT surface when it is wrapped by SPG derivatives carrying various functional appendages. For example, when SWNT is wrapped by
lactoside-appended SPG (SPG-Lac), the composite acquires a specific lectin-affinity.17 The specific lectin-affinity of the SWNT/SPG-Lac composite was confirmed by the confocal laser scanning microscopic (CLSM) observation using the fluorescein(FITC)-labeled lectin. The SWNT/SPG-Lac composite incubated with FITC-RCA120 showed that the fluorescence image and microscopic image are precisely overlapped with each other, indicating that FITC-RCA120 is clustered around the SWNT/SPG-Lac composite. This system has further extended to the construction of a layer-by-layer structure composed of the SWNT/SPG-Lac composite and RCA120. Quartz crystal microbalance (QCM) measurements using the RCA120-immobilized Au-surface revealed that an alternative deposition of the SWNT/SPG-Lac composite and RCA120 caused a step-by-step decrease in the frequency, supporting the construction of the expected layer-by-layer structure on the Au-surface. It is undoubted, therefore, that the wrapping approach toward SWNTs can be a new and potential alternative way to functionalize the SWNT surface, comparing to the conventional functionalization through covalent bonding. The supramolecular wrapping of SWNT by b-1,3-glucans has led us to a few important conclusions: (1) the periodical stripe structure, which stems from a helical wrapping mode characteristic of b-1,3-glucans, can be confirmed and (2) b-1,3-glucans would have the latent ability to accommodate various guest polymers bearing different sizes and shapes because of their flexible main-chain conformation.
5. b-1,3-Glucans as a chiral wrapping agent for achiral guest polymers b-1,3-Glucans show a strong tendency to form a right-handed helical structure, so that the entrapped polymers are enforced to be twisted into the same right-handed direction by the wrapping. We have extended the wrapping system to conventional functional polymers and have found that most polymers adopt a helical conformation in the 1D-shaped hollow space constructed by b-1,3-glucans (Fig. 6). Poly(aniline) (PANI) is one of the most promising and widely studied conductive polymers owing to its high
Fig. 6 Schematic illustration of the supramolecular wrapping by chiral b-1-3-glucan for achiral guests and the chemical structures of used guest polymers and oligomers.
This journal is
c
The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 1961–1975
1965
Fig. 7 Picture of aqueous solution containing the PANI/SPG composite and its TEM image obtained without staining. Adapted with permission from ref. 19. Copyright 2004, American Chemical Society.
chemical stability, high conductivity and unique redox properties.18 Based on the results obtained from the foregoing c-SWNT/SPG composite system, one can expect that b-1,3-glucans would be able to fabricate some PANI’s nanofiber structures.19 The expected PANI/SPG nanocomposite was prepared through gradual dilution of a DMSO solution containing commercially available PANI (emerardine base, Mw = 10 kDa) and s-SPG (Mw = 150 kDa) with water followed by purification through repeating centrifugations. TEM observations showed that the fibrous architecture is formed from the PANI/SPG composite whose length is apparently consistent with that of the used SPG (Fig. 7). In the TEM images, the observed nanofibers show clear contrast, without treatment by any staining reagent, due to the absorption of the electron beam. Importantly, the contrast ascribable to the incorporated PANIs exists continuously all through the obtained 1D-shaped composite. Since the length of used PANIs is shorter than that of s-SPG, the incorporated PANIs should be continuously bundled up as the onedimensional fibers in the SPG cavity. The diameter of the smallest fiber is estimated to be around 10 nm, indicating that the several PANI strands are co-entrapped within the SPG one-dimensional cavity. From the CD spectra of the composite, we confirmed that the SPG/PANI composite solution affords a positive Cotton effect at 370 nm and a negative Cotton effect at 330 nm. The appearance of this weak but important CD signals implies that the PANI fibers strongly interact with the cavity wall and are twisted in the right-handed direction. On the other hand, the mixture containing t-SPG and PANIs did not give any CD signal in the same wavelength region. This result also supports the view that the renaturating process is indispensable for the effective inclusion of PANIs in the SPG cavity. To explore the further possibility of semi-artificial b-1,3glucans as a wrapping agent, the mannose-modified SPG was synthesized and used for PANIs, expecting that the resultant composite acquires the lectin affinity as demonstrated in the SWNT/SPG-Lac composite system. The specific interaction between the composite and ConA was also estimated by a CLSM using a FITC-labeled ConA. The CLSM observation clearly showed that PANIs and ConA coexist in the same domain, indicating that (1) the mannose-modified SPG can also wrap PANIs and (2) the mannose group introduced into the side group exists on the exterior surface of the composite. Next, we tried to extend the guests to the conjugated polymers. First, we adopted water-soluble cationic poly(thiophene) 1966
Chem. Commun., 2011, 47, 1961–1975
Fig. 8 (a) UV-VIS spectra of PT–N+ (black line) and PT–N+/SPG composite (red line), (b) CD spectrum of the PT–N+/SPG composite and (c) photo images of aqueous solutions containing PT–N+ (left) and PT–N+/SPG composite (right) and schematic illustration of the PT–N+/SPG composite. Adapted with permission from ref. 20. Copyright 2005, American Chemical Society.
(PT–N+) because its interaction mode with b-1,3-glucans can be easily monitored by the drastic color change. The composite formation between SPG and an individual PT chain is of interest not only from the specific interpolymer interactions but also from a new approach leading to the novel chiral molecular wires.20 In Fig. 8, absorption and emission spectra are compared between PT–N+ itself and the PT–N+/SPG composite. The absorption maximum of PT–N+ appears at 403 nm, whereas that of the PT–N+/SPG composite is drastically red-shifted to 454 nm by ca. 50 nm. The findings reveal that SPG forces the PT backbone to adopt a more planar conformation with increasing the effective conjugation length. The CD spectra of the composite show an intense split-type ICD in the p–p* transition region (Fig. 8b). This fact clearly indicates that PT–N+ would be chirally twisted through the interaction with the helical SPG chain. The observed ICD pattern is characteristic of a right-handed helix of the PT backbone, reflecting the right-handed helical structure of SPG. The stoichiometry of the composite was determined by means of continuous variation plots (Job plots) of the CD spectra. Consequently, the molar ratio of glucose residues along the main chain to the repeating unit of PT–N+ can be determined to be ca. 2. Therefore, the PT–N+/SPG composite consists of one PT–N+ chain and two SPG chains, being similar to the polynucleotide/SPG composite. The finding has led us to conclude that SPG tends to form triplestranded hetero-macromolecular complexes by replacing one glucan chain in t-SPG with one water-soluble guest polymer. One of the most interesting features arising from conjugated polymers is circularly polarized luminescence (CPL), which is one of the most fascinating applications leading to the novel LED design. In principle, it becomes possible to design such CPL materials by directly introducing chiral substituents into conjugated polymers, resulting in the chirally twisted polymeric structure.21 In the PT–N+/SPG composite, on the other hand, the appearance of CPL is expected because the achiral luminescent PT chain is chirally twisted by supramolecular wrapping by SPG and the intensity is enhanced owing to the restricted molecular motion occurring upon complexation.22 In the PT–N+/SPG composite, the This journal is
c
The Royal Society of Chemistry 2011
Fig. 9 CPL (solid line) and intensity (dash line) in the fluorescence spectrum of the PT–N+/SPG composite dispersed in acetone/water mixed solvent; acetone : water = 70 : 30 (v/v), lex = 410 nm, 25 1C. Adapted with permission from ref. 22. Copyright 2009, Chemical Society of Japan.
strong positive CPL signal appeared in the p–p transition region of PT–N+. The CPL maximum was observed at 560 nm, which is well in accord with the maximum of the fluorescence. The g values of absorption (gabs) and luminescence (glum), which are defined as gabs = 2 (eL eR)/(eL + eR) and glum (IL IR)/(IL + IR), were estimated to be +7.7 10 3 (525 nm) and 4.5 10 3 (561 nm), respectively. These values are very close to each other, indicating that both of the CD and the CPL originate from the same chiral structural origin, that is, the right-handed helical structure of the PT–N+ backbone (Fig. 9). These trends consistently indicate that SPG can form a supramolecular chirally-twisted polymer complex with PT–N+, which serves as a unique candidate for superior CPL materials. We have also confirmed that in addition to the optical activity in solution, the (chir)optical properties of the PT–N+/SPG composite are also presented in the powder state. The positive CPL signals were observed and the glum still maintained the order of 10 3, indicating that the PT–N+/SPG composite keeps the supramolecular chiral insulated molecular structure even in the powder state. Oligosilanes have been investigated as attractive functional materials since they have unique s-conjugated helical structures and show unique optoelectric properties.23 Their fabrication by the b-1,3-glucan wrapping technique would provide various applications such as (1) preparation of water-soluble oligosilane composites, (2) regulation of their helical conformation and (3) hierarchical assemblies from their composites, etc.24 The triple strand of SPG is dissociated into the single strand at pH > 12, whereas it retrieves the original triple strand by pH neutralization.6a A NaOH solution containing s-SPG was neutralized by acetic acid in the presence of hexane droplets This journal is
c
The Royal Society of Chemistry 2011
containing permethyldecasilane (PMDS), expecting that the renature process from s-SPG to t-SPG would extract PMDS into the aqueous phase through complexation with SPG. Firstly, a hexane solution containing PMDS and an aqueous NaOH solution containing s-SPG were well homogenized by sonication. Aqueous acetic acid was then added to the resultant mixture to give two layers, where the renature from s-SPG to t-SPG would occur on the water/hexane interface. The hexane layer showed a broad UV-VIS absorption band with full-width-half-maximum (FWHM) of 40 nm at around 280 nm, which is characteristic of the s–s* transition of flexible, random-coiled PMDS. The aqueous PMDS/SPG composite thus formed through the extraction showed an intense red-shifted fluorescence band with FWHM of 18 nm at 323 nm when excited at the s–s* transition band (280 nm), which is comparable with the fluorescence band at 310 nm of free PMDS in hexane. When the resultant aqueous layer showed the broad absorption band, no detectable CD signal was observed in this wavelength region. This indicates that the PMDS chain adopts a flexible, random-coiled conformation in the onedimensional SPG cavity. The 1H NMR study of the aqueous layer showed that hexane molecules were extracted with PMDS, suggesting that the PMDS chain in the composite is still ‘wet’ with hexane molecules. Once the aqueous layer was dried in vacuo and then re-dissolved into the fresh water, the resultant PMDS/SPG composite showed a sharp absorption band at 290 nm with a narrow FWHM of 12 nm as well as a positive CD signal at 283 nm and a negative one at 293 nm (Fig. 10). These results suggest that the ‘dry’ PMDS chain has a very rigid, extended conformation and interacts strongly with the helical SPG environment in the PMDS/SPG composite. In general, the conformational studies on PMDS have been performed by UV-VIS and CD spectroscopic methods. Accordingly, it is worthy to compare the spectral features of the PMDS/SPG composite with those of PMDS itself, because the comparison would give us the information on how the PMDS chain behaves when wrapped by SPG. The bisignate CD spectral profile is rationalized on the basis of two origins: (1) a mixture of two different helices with the opposite screw senses and different pitches and (2) the exciton couplet due to
Fig. 10 (a) UV-VIS (bottom) and CD (top) and (b) fluorescence spectra of the PMDS/SPG composite in water (lex = 290 nm, red solid line), the PMDS/t-SPG mixture in water (lex = 290 nm, blue solid line) and free PMDS in hexane (lex = 280 nm, black dotted line): [s-SPG]/ [PDMS] = 1.2 in molar ratio, 0.5 cm cell, 25 1C. Adapted with permission from ref. 24. Copyright 2005, American Chemical Society.
Chem. Commun., 2011, 47, 1961–1975
1967
chirally-twisted PMDS aggregates. Kunn’s dissymmetry ratio defined as gabs = De/e = CD (in mdeg)/32980/Abs is a dimensionless parameter to semi-quantitatively characterize the helical structure of oligosilanes and other chromophoric chiral molecules. The absolute magnitude in their small gabs values (+3.3 10 4 at 283 nm and –1.7 10 4 at 293 nm) is almost comparable with the gabs value of (2.0–2.5) 10 4 at 323 nm observed for the rigid rod-like poly(silane) (PS) chain with a single-screw helix. PMDS incorporated in the helical cavity of s-SPG, therefore, exists as a mixture of diastereomeric helices with the opposite screw senses. From these spectral studies, it was found that the UV-VIS and CD spectral features of the PMDS/SPG composite are very similar to those of the PMDS/g-cyclodextrine complex.25 The foregoing results clearly show that the supramolecular wrapping by b-1,3-glucans enforces the entrapped polymer or oligomer to adopt the helical or twisted conformation depending on the intrinsic compatibility of their repeating units. Therefore, the SPG wrapping technique is useful as a versatile tool to create various insulated functional polymers.26
6. Novel wrapping properties emerging form semi-artificial CURs Even though the selective modification of 6-OH of CUR scarcely affects its inherent helix-forming ability, the renature and denature properties as well as the solubility of the modified CURs are strongly affected by the introduced groups, because they always exist on the outer surface of the helical structure. Among various functional groups introduced into 6-OH groups, ionic groups such as trimethylammonium and sulfonium groups particularly impart interesting behaviours to semi-artificial CUR: as the ionic groups are located at a distance of approximately 6 A˚ when they adopt the regular triple helix, the electrostatic repulsion among the ionic groups would have a strong influence on its conformation in water. Consequently, the electrostatic repulsion would destabilize the triple helix, which could be transformed to a loosely tied triple strand or to a single strand in water. This conjecture implies that the chemically modified CURs have a potential to act as a new wrapping agent useful without the troublesome renature treatment in water (Fig. 11).11h To estimate the conformational properties of trimethylammonium modified CUR (CUR–N+), we measured the optical rotatory dispersion (ORD) spectra under the various conditions. In the triple-stranded helical form, the ORD spectra of b-1,3-glucans such as SPG and CUR have positive values in the wavelength region from 600 nm to 200 nm. However, CUR–N+ in water shows a negative sign in this wavelength region. The negative sign can be ascribed to the single-stranded form. In addition, we evaluated the effect of added NaCl on the ORD sign of CUR–N+, expecting that it may reduce electrostatic repulsion. Interestingly, the intensity of ORD increased gradually with increasing the NaCl concentration but did not reach the positive value observed for SPG in water. This difference implies that formation of the triple helix from CUR–N+ is energetically disadvantageous because of electrostatic repulsion among the cationic charges in the side chains. Besides, formation of the triple helix from 1968
Chem. Commun., 2011, 47, 1961–1975
Fig. 11 Schematic illustration of the composites formation between b-1,3-glucans ((a) CUR–N+ and (b) SPG) and a hydrophobic guest polymer. Adapted with permission from ref. 11h. Copyright 2007, American Chemical Society.
CUR–SO3 is also difficult because of the electrostatic repulsion among the anionic charges. These results suggest that ionic CURs would be able to accommodate hydrophobic polymers into the inner hydrophobic domain in water without the denature/renature processes. This simplified wrapping system was applied to the polymeric or oligomeric guests such as polycytidylic acid (poly(C)), singlewalled carbon nanotubes (SWNTs) and permethyldecasilane (PMDS), which are known to be incorporated into SPG and CUR only through the denature/renature processes, as already described in foregoing sections. Upon just mixing these guest polymers with CUR–N+ (or CUR–SO3 ) in water, clear aqueous solutions were readily obtained. Characterizations by UV-VIS and CD spectroscopic measurements and AFM and TEM observations revealed that these polymeric guests are entrapped into the hydrophobic domain of semi-artificial CURs to give the nanosized fibrous structures. In the case of poly(C) with CUR–N+, the complexation can be driven by the cooperative action of three different forces: the hydrogenbonding interaction between the 2-OH group in CUR–N+ and the cytosine ring in poly(C), the electrostatic interaction between the ammonium cation and the phosphate anion and the background hydrophobic interaction. This journal is
c
The Royal Society of Chemistry 2011
SWNT powder can be easily dispersed into water in the presence of CUR–N+ or CUR–SO3 with the aid of sonication, the solution color becoming dark as the sonication time increases. The resultant aqueous solution is stable for more than one month without forming any precipitate probably due to the electrostatic repulsion among the composites. The NIR-VIS spectra are similar to those of the SWNT/SPG composite, suggesting that CUR–N+ is also capable of wrapping an individual SWNT fiber in the helical cavity. This conclusion is also supported by TEM and AFM observations. In the case of PMDS with CUR–N+, only 5% of PMDS in feed can be solubilized into water by CUR–N+. This value indicates that approximately 0.8 eq. of PMDS against CUR–N+ in their monomer units (SiMe2 unit for PMDS and glucose unit for CUR–N+, respectively) is included in the PMDS/CUR–N+ composite. Further conformational investigation on PMDS by CD spectroscopy reveals that the dissymmetry ratios (g) of the PMDS/CUR–N+ composite are smaller by a factor of ca. 4 than those of the PMDS/SPG composite. This difference indicates that the PMDS included in CUR–N+ exists as a mixture of a few different conformations. Together with the broad absorption band of the PMDS/CUR–N+ composite compared with the narrow absorption band of the PMDS/SPG composite, these findings allow us to propose that strong electrostatic repulsion among the cationic side-chains of CUR–N+ prevents the PDMS/CUR–N+ composite from forming a rigid helical structure as in the case of the neutral PMDS/SPG composite.
7. One-dimensional composite as a building block for hierarchical organization Creation of highly-ordered huge assemblies utilizing functional polymers as building blocks would be an expeditious way to design new materials having novel chemical and physical properties. The self-assembling methodology for small molecules has been well established, whereas only a limited number of attempts have been reported for the self-assembling of polymers.27 The difficulty in the polymeric system arises from two questions: how one can impart the self-assembling
capability to the polymer backbone without losing its inherent functionality and how one can assemble polymers through ‘specific’ interpolymer interactions without the influence of the ‘nonspecific’ polymer bundling. In addition, to tune their physicochemical properties in nanoscale, individual polymers must be finely manipulated during their self-assembling processes. As described in the previous sections, modified SPG can bestow the lectin affinity to SWNT and PANI fibers through the wrapping method. Thus, the polymer wrapping using the chemically modified b-1,3-glucans can be regarded as a novel approach to attain this purpose through a supramolecular manner. In this approach, as introduced functional groups are regularly aligned on the composite surface, the control of specific interpolymer interactions also becomes possible. In particular, the quantitative conversion of CUR 6-OH groups to desired new functional groups allows us to self-organize the composites in a finely tuned way through the surface-tosurface recognition among the composites. Accordingly, one can expect that one-dimensional composites would act as building blocks for the creation of further divergent architectures, in which each guest polymer is still isolated from each other and maintains its original functionality (Fig. 12). As a preliminary example, two kinds of semi-artificial CURs, i.e., CUR–N+ and CUR–SO3 were utilized as wrapping agents for SWNTs, expecting that the mixture of these two composites in an appropriate ratio would result in a higherorder SWNT architecture due to their mutual electrostatic interaction.28 The mixture of the SWNT/CUR–N+ composite and the SWNT/CUR–SO3 composite was prepared according to the procedure described in the previous section. The z-potential value of an aqueous solution containing only the SWNT/CUR–N+ composite was estimated to be +48.9 mV, whereas an aqueous solution containing only the SWNT/CUR–SO3 composite showed 49.5 mV. When these two solutions were mixed in the same volume under the very diluted condition, the z-potential value of the resultant mixture showed 0.53 mV without precipitate formation, indicating that the potential charges on these composites are almost neutralized to give a self-assembling composite through
Fig. 12 Polymer wrapping using semi-artificial b-1,3-glucans and divergent self-assembly of one-dimensional composites: introduced functional groups are regularly aligned on the composite surface and the control of specific interpolymer interactions becomes possible.
This journal is
c
The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 1961–1975
1969
Fig. 13 TEM images of (a) sheet-like structure (inset: electron diffraction pattern), (b) elemental analysis of the sheet based on EDS, (c) magnified image of (a) and (d) Fourier translation image of (c) (inset: extracted periodical patterns). Adapted with permission from ref. 28. Copyright 2008, Wiley.
the electrostatic interaction. AFM images revealed that the resultant solution contains a well-developed sheet-like structure with micrometre-scale length, which is entirely different from the very fine fibrous structures observed for individual SWNT/CUR–N+ and SWNT/CUR–SO3 composites. In the TEM images shown in Fig. 13, one can recognize that the sheetlike structure is composed of highly ordered fibrous assemblies. Furthermore, the electron diffraction pattern revealed that the assembly has some crystalline nature, suggesting that the cationic and anionic composites are regularly packed through the electrostatic interaction. The periodicity of the dark layer is estimated to be ca. 2 nm, which is almost consistent with the diameter of the individual composite obtained by the AFM height profile. The resultant higher-order architectures as well as the selfassembling processes are strongly affected by the initial [CUR–N+/SWNT]/[CUR–SO3 /SWNT] ratio; that is, upon mixing the same concentration of composites, the welldeveloped sheet-like structure is formed, whereas an excess amount of one composite over the other results in the bundle structure with the uniform diameter. It is particularly worthy to mention here that the VIS-NIR spectral feature of the obtained sheet-like architecture is almost the same as those of the CUR–N+/SWNT composite and the CUR–SO3 /SWNT composite. This result supports the view that CUR–N+ and CUR–SO3 act as a sheath for SWNTs, where the direct 1970
Chem. Commun., 2011, 47, 1961–1975
interaction among SWNTs can be suppressed even in the tightly-packed sheet-like structure. Supramolecular nanofiber structures constructed from small molecules carrying anionic or cationic charges also act as complementary one-dimensional building blocks for CUR–N+ or CUR–SO3 composites to form higher-order architectures through electrostatic interactions. For example, the two nitrogens of tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4 ) are protonated to generate the di-acid form (H4TPPS2 ) under the acidic conditions, which tends to selfassemble into the well-regulated fibrous structure (J-aggregate) through the electrostatic interaction.29 Thus, the mixture of the H4TPPS2 J-aggregate and the cationic CUR–N+/SWNT composite results in the self-assembled SWNT sheet, in which the H4TPPS2 J-aggregate acts as a supramolecular adhesive agent for the sheet formation. The effective interpolymer interactions between the H4TPPS2 J-aggregate and the CUR–N+/SWNT composite were examined by UV-VIS and CD spectroscopic measurements. When the [trimethylammonium]/[sulfonate] ratio was increased from 0.0 to 0.67, the Soret- and Q-bands of monomeric H4TPPS2 gradually decreased and new peaks assignable to J-aggregate appeared at 490 nm and 710 nm, as shown in Fig. 14. The finding implies that the J-aggregate formation from H4TPPS2 is assisted by the opposite charge array of fibrous SWNT composites. The CD spectral change strongly supports the view that H4TPPS2 molecules are linearly arranged between the CUR–N+/SWNT composites. TEM observation revealed that the mixture of H4TPPS2 J-aggregate and the CUR–N+/SWNT composite ([trimethylammonium]/[sulfonate] = 0.50) creates the sheetlike nanostructure with about 20 nm width, which corresponds to an aggregate of several tens of CUR–N+/SWNT composites. In the present system, the H4TPPS2 J-aggregate also assists the self-assembling of CUR–N+/SWNT composites. Formation of the H4TPPS2 J-aggregate is sensitive to a pH change. In fact, the absorption peaks assignable to the H4TPPS2 J-aggregate were dramatically decreased with increasing medium pH, and a new peak assignable to monomeric H2TPPS4 appeared at 414 nm. The split-type ICD also disappeared during this treatment, suggesting that H2TPPS4 molecules no longer interact with the cationic CUR–N+/SWNT composites. TEM observation reveals that the sheet-like nanostructure is decomposed and transformed to the individual fibrous assemblies of CUR–N+/SWNT composites. Interestingly, when the medium pH was restored to 3.4, the sheet-like nanostructure was reconstructed and the original absorption spectral peaks assignable to the J-aggregate emerged again. As explained above, we have established a new methodology for self-assembled nanoarchitectures consisting of cationic polymeric composites and anionic low molecular-weight supramolecular assemblies. As a result, the dynamic association/ dissociation processes can occur in a reversible manner, which can be realized only by noncovalent-bond-based polymeric components. We consider, therefore, that this system leads to further creation of various hierarchical polymer/supramolecular co-assemblies.30 This journal is
c
The Royal Society of Chemistry 2011
Fig. 14 (a) Chemical structures of H4TPPS2 and H2TPPS4 , (b and d) UV-VIS and CD spectral changes of H4TPPS2 upon addition of only CUR–N+ and (c and e) upon addition of the CUR–N+/ SWNT complex, respectively: 1.0 cm cell, 25 1C.30b
8. Construction of 3D polysaccharide composites from polymeric assembly systems The alternative packing of SWNT/CUR–N+ and SWNT/ CUR–SO3 composites results in the sheet-like two-dimensional structure. If the packing occurs on an appropriate template surface, the sheet-like structure would memorize the threedimensional shape of the used template.31 This intriguing idea was tested by a layer-by-layer approach on the silica particle surface, expecting that the spherical shape can be transcribed to the layer-by-layer assemblies. As a result, we have found that the layer-by-layer method leads to the creation of SWNT-based hollow capsules (in this case, spherical hollow assemblies) with the controlled layer thickness after dissolution of silica particles by HF etching. Layer-by-layer assembling on the silica particle surface was performed by using silica particles with ca. 5.0 mm diameter. The z-potentials of the particles at each adsorption step were measured by microelectrophoresis to monitor the layerby-layer growth of the CUR–N+/SWNT composite and the CUR–SO3 /SWNT composite on the silica particle. The This journal is
c
The Royal Society of Chemistry 2011
z-potentials of the silica particle shifted to +23.6 (3.4 mV) when the outer surface is coated with the CUR–N+/SWNT composite and to 24.0 (3.2 mV) when it is coated with the CUR–SO3 /SWNT composite. These alternate changes in the z-potential are characteristic of the layer-by-layer adsorption of SWNT multi-layers on the silica particle. SEM images of the silica particle surface revealed that CUR–SO3 /SWNT composite layers still maintain the original morphologies of SWNTs with a knitting pattern. TEM observations were also performed for CUR/SWNT-coated silica particles having nine SWNT layers in total. The total thickness of the SWNT layers on the silica particle was estimated to be 20–40 nm. This strategy was applied to an alternate layer-bylayer adsorption of the CUR–SO3 /SWNT composite and the CUR–N+/DWNT (double-walled carbon nanotube) composite on the silica particle surface. Consequently, two different composites could be assembled alternately just by changing the guest compounds wrapped by functionalized b-1,3-glucans. After HF treatment of the resultant silica particles, the creation of hollow capsules with 4–6 mm average diameters could be confirmed. The capsule size was almost consistent with the average diameters of the silica particles used as the template. Another challenge toward the construction of spherical b-1,3-glucan architectures is to use O/W emulsion as a temporal template. This approach is expeditious and versatile to create spherical b-1,3-glucan architectures, because the supramolecular wrapping can work efficiently in the aqueous phase of the O/W emulsion interface. We have successfully extended the wrapping target to one piece of polymeric chain: if the target polymer exists more than SPG, then the polymer chain should be wrapped only partially (Fig. 15).32 It should be emphasized that in this case, the SPG-wrapped chain behaves as a hydrophilic segment whereas the naked polymeric chain behaves as a hydrophobic segment: as a result, the composite should become a sort of ‘amphiphile’. One may consider that this is a supramolecular version of amphiphilic block copolymers.33 As a preliminary system, combination of SPG and poly(styrene) (PS) was selected for preparing a well-regulated spherical structure. The sample was prepared by adding a DMSO solution containing s-SPG to an O/W emulsion solution containing PS. The DLS measurement of the resultant aqueous solution revealed that it contains selfaggregated assemblies with 100–300 nm size in diameter. The result suggests that the partially SPG-wrapped PS acts as a giant amphiphile to form the aggregate structure. The direct interaction between SPG and PS was further evidenced by the appearance of the CD (ICD) band. By comparing with UV-VIS and CD spectra, one can confirm that this CD (ICD) band appears in the PS absorption region, indicating that the PS chain is chirally twisted. The morphological images of the formed polymer micelles were obtained by microscopic observations. The TEM images revealed that the sphere consists of two different phases; that is, the core with 50–100 nm diameter is surrounded by the outer shell with 25–50 nm thickness (Fig. 16). These findings unambiguously support the view that the created spherical structure has an amphiphilic core–shell structure. Chem. Commun., 2011, 47, 1961–1975
1971
Fig. 15 Construction of 3D polysaccharide composites by the wrapping on the emulsion template: the resultant composite acts as a sort of ‘amphiphile’. Adapted with permission from ref. 32. Copyright 2009, Wiley.
Fig. 16 (a) SEM and (b) TEM images of the spherical structures (s-SPG: Mw = 3.5 103, PS: Mw = 1.1 106), (c) magnified TEM image of (b) and (d) TEM image of the fused spherical structure obtained by the combination of s-SPG with PS having Mw = 2.1 107. Adapted with permission from ref. 32. Copyright 2009, Wiley.
We examined whether the hydrophobic domain can dissolve hydrophobic molecules, using a hydrophobic porphyrin (5,10,15,20-tetrakis(4-methoxycarbonylphenyl)porphyrin: TMPP) as a probe molecule. In CLSM images shown in Fig. 17, TMPP gave the blue fluorescence with a globular shape under UV light irradiation at 488 nm. In the optical microscopic image, the micelles appeared as the toroidal shape, suggesting that the micelle has the amphiphilic structure. Importantly, the fluorescence image arising from TMPP is perfectly overlapped with the core domain in the optical microscopic image. The result clearly proves the view that TMPP molecules exist in the hydrophobic domain constructed by PS. To explore a new application of this system, the chemically modified SPG was utilized as a wrapping agent for the PS-containing O/W emulsion. We synthesized biotinmodified SPG and used it as a wrapping agent. The presence of the biotin group in the shell would enable us to introduce various avidin-linked functional groups. When we used avidinlinked FITC, the blue fluorescent ring arising from FITC appeared. This image is in sharp contrast to the globularshaped porphyrin fluorescence image as seen in Fig. 17d. These results support the view that biotin-modified SPG exists only in the exterior shell of the micelles and can be easily recognized by avidin-linked functional groups. The weak interactions between the phase-separated domains, e.g., core and shell, can endow the dynamic properties arising 1972
Chem. Commun., 2011, 47, 1961–1975
Fig. 17 CLSM images of the spherical structure containing TMPP: (a) fluorescence image, (b) optical image, (c) overlap of (a) and (b). CLSM images obtained by using FITC-avidin/biotin-modified SPG as a wrapping agent: (d) fluorescence image (inset: magnified image), (e) optical image, (f) overlap of (d) and (e). Adapted with permission from ref. 32. Copyright 2009, Wiley.
from non-covalent interactions within the micellar structures. This feature would allow us to design new reaction environments and energy transfer systems. We believe that the present system becomes an alternate method to generate novel polymer micelles with dynamic properties under the regulated conditions and would be widely applied to molecular containers, delivery vesicles and reactive nanovessels. This journal is
c
The Royal Society of Chemistry 2011
9. Summary Most interpolymer interactions, except those occurring in biological systems, have been considered to take place in a random fashion and to produce morphologically uninteresting polymeric aggregates. In contrast, b-1,3-glucans can interact with polymers or molecular assemblies in a specific fashion and construct well-regulated one-dimensional superstructures. In this process, the supramolecular wrapping by b-1,3-glucans occurs in an induced-fit manner, so that various functional nanocomposites can be created, reflecting the inherent size, shape and functionality of the entrapped guest materials. These unique features of b-1,3-glucans mostly stem from the strong helix-forming nature and the reversible interconversion between the single-stranded random coil and the triplestranded helix. The wrapping by the chemically modified b-1,3-glucans also provides a novel strategy to create functional polymer composites with various molecular recognition tags attached on the strand surface. These composites can be arranged according to the further interpolymer interactions on the composite surfaces. In particular, the quantitative conversion of 6-OH groups of CUR to various functional groups allows us to design new polymeric assemblies having the twodimensional and three-dimensional hierarchical structures. Finally, it should be emphasized again that polysaccharides are the most abundant organic materials existing on the earth. Hence, to utilize them as industrial resources is very important from the viewpoint of green chemistry and exploitation of novel strategies to attain this purpose in nanotechnology has been strongly desired. From the standpoint to exploit such useful nanomaterials based on polysaccharides, the present system would open several new paths to accelerate the development of the polymeric assembly systems, giving the strong stimuli to the frontier of polysaccharide-based functional chemistry.
Acknowledgements The present works were performed in cooperation with many project members; Mr. T. Matsumoto, Ms. M. Umeda, Dr T. Hasegawa, Dr C. Li, Dr A.-H. Bae, Mr. T. Fujisawa, Dr S. Haraguchi, Dr S. Tamesue, Dr M. Ikeda and Dr K. Sugikawa. The authors express their gratitude for all the members. The authors thank Mitusi Sugar Co., Japan, for providing the schizophyllan samples. This work was supported by the SORST of the Japan Science and Technology Agency. This work was partially supported by the MEXT, Grant-in-Aid for Scientific Research on Innovative Areas ‘Emergence in Chemistry’. M. N. thanks Mitsubishi Chemical Corporation Fund, Izumi Science and Technology Foundation, Kansai Research Foundation for Technology Promotion, Tokuyama Science Foundation, Iketani Science Technology Foundation and Sumitomo Foundation for partial financial supports.
Notes and references 1 (a) R. P. Sijbesma, F. H. Beijer, L. Brunsveld, B. J. B. Folmer, J. H. K. K. Hirschberg, R. F. M. Lange, J. K. L. Lowe and E. W. Meijer, Science, 1997, 278, 1601; (b) V. Percec, C. -H. Ahn,
This journal is
c
The Royal Society of Chemistry 2011
G. Ungar, D. J. P. Yeardley, M. Mo¨ller and S. S. Sheiko, Nature, 1998, 391, 161; (c) O. Ikkala, M. Knaapila, J. Ruokolainen, M. Torkkeli, R. Serimaa, K. Jokela, L. Horsburgh, A. Monkman and G. Brinke, Adv. Mater., 1999, 11, 1206; (d) D. J. Hill, M. J. Mio, R. B. Prince, T. S. Hughes and J. S. Moore, Chem. Rev., 2001, 101, 3893; (e) L. Brunsveld, B. J. B. Folmer, E. W. Meijer and R. P. Sijbesma, Chem. Rev., 2001, 101, 4071; (f) H. Goto and E. Yashima, J. Am. Chem. Soc., 2002, 124, 7943; (g) S. Fo¨rster and T. Plantenberg, Angew. Chem., Int. Ed., 2002, 41, 688; (h) S. Zahn and T. M. Swager, Angew. Chem., Int. Ed., 2002, 41, 4225; (i) H. Hofmeier and U. S. Schubert, Chem. Commun., 2005, 2423. 2 Recent reviews see: (a) T. F. A. De Greef, M. M. J. Smulders, M. Wolffs, A. P. H. J. Schenning, R. P. Sijbesma and E. W. Meijer, Chem. Rev., 2009, 109, 5687; (b) M. M. Caruso, D. A. Davis, Q. Shen, S. A. Odom, N. R. Sottos, S. R. White and J. S. Moore, Chem. Rev., 2009, 109, 5755; (c) E. Yashima, K. Maeda, H. Iida, Y. Furusho and K. Nagai, Chem. Rev., 2009, 109, 6102; (d) B. M. Rosen, C. J. Wilson, D. A. Wilson, M. Peterca, M. R. Imam and V. Percec, Chem. Rev., 2009, 109, 6275. 3 (a) B. Z. Tang and H. Xu, Macromolecules, 1999, 32, 2569; (b) A. Star, J. F. Stoddart, D. Steuerman, M. Diehl, A. Boukai, E. W. Wong, X. Yang, S.-W. Chung, H. Choi and J. R. Heath, Angew. Chem., Int. Ed., 2001, 40, 1721; (c) M. Zheng, A. Jagota, M. S. Strano, A. P. Santos, P. Barone, S. G. Chou, B. A. Diner, M. S. Dresselhaus, R. S. Mclean, G. B. Onoa, G. G. Samsonidze, E. D. Semke, M. Usrey and D. J. Walls, Science, 2003, 302, 1545; (d) M. Zheng, A. Jagota, E. D. Semke, B. A. Diner, R. S. Mclean, S. R. Lusting, R. E. Richardson and N. G. Tassi, Nat. Mater., 2003, 2, 338; (e) N. Nakashima, S. Okuzono, H. Murakami, T. Nakai and K. Yoshikawa, Chem. Lett., 2003, 456; (f) V. Zorbas, A. O. Acevedo, A. B. Dalton, M. M. Yoshida, G. R. Dieckmann, R. K. Draper, R. H. Baughman, M. J. Yacaman and I. H. Musselman, J. Am. Chem. Soc., 2004, 126, 7222; (g) V. V. Didenko, V. C. Moore, D. S. Baskin and R. E. Smalley, Org. Lett., 2005, 5, 1563; (h) C. Zhi, Y. Bando, C. Tang, R. Xie, T. Sekiguchi and D. Golberg, J. Am. Chem. Soc., 2005, 127, 15996; (i) K. S. Chichak, A. Star, M. V. P. Altoe´ and J. F. Stoddart, Small, 2005, 1, 452; (j) B. Gigliotti, B. Sakizzie, D. S. Bethune, R. M. Shelby and J. N. Cha, Nano Lett., 2006, 6, 159; (k) W. Z. Yuan, J. Z. Sun, Y. Dong, M. Ha¨ussler, F. Yang, H. P. Xu, A. Qin, J. W. Y. Lam, Q. Zheng and B. Z. Tang, Macromolecules, 2006, 39, 8011; (l) C. Zhi, Y. Bando, C. Tang, S. Honda, K. Sato, H. Kuwahara and D. Golberg, J. Phys. Chem. B, 2006, 110, 1525; (m) W. Zhao, Y. Gao, M. A. Brook and Y. Li, Chem. Commun., 2006, 3582; (n) A. Ikeda, K. Nobusawa, T. Hamano and J. Kikuchi, Org. Lett., 2006, 8, 5489; (o) J. Kumaki, T. Kawauchi, K. Okoshi, H. Kusanagi and E. Yashima, Angew. Chem., Int. Ed., 2007, 46, 5348; (p) M. Naito, K. Nobusawa, H. Onouchi, M. Nakamura, K. Yasui, A. Ikeda and M. Fujiki, J. Am. Chem. Soc., 2008, 130, 16697; (q) H. Qian, P. T. Araujo, C. Georgi, T. Gokus, N. Hartmann, A. A. Green, A. Jorio, M. C. Hersam, L. Novotny and A. Hartschuh, Nano Lett., 2008, 8, 2706; (r) H. Cathcart, V. Nicolosi, J. M. Hughes, W. J. Blau, J. M. Kelly, S. J. Quinn and J. N. Coleman, J. Am. Chem. Soc., 2008, 130, 12734; (s) F. Zhang, H. Zhang, Z. Zhang, Z. Chen and Q. Xu, Macromolecules, 2008, 41, 4519; (t) Y. Chen, L. Yu, X.-Z. Feng, S. Hou and Y. Liu, Chem. Commun., 2009, 4196; (u) Y. K. Kang, O.-S. Lee, P. Deria, S. H. Kim, T.-H. Park, D. A. Bonnell, J. G. Saven and M. J. Therien, Nano Lett., 2009, 9, 1414; (v) Y. Liu, C. Chipot, X. Shao and W. Cai, J. Phys. Chem. B, 2010, 114, 5783. 4 Wrapping by polysaccharides see: (a) J. Kadokawa, Y. Kaneko, H. Yagaya and K. Chiba, Chem. Commun., 2001, 449; (b) A. Star, D. W. Steuerman, J. R. Heath and J. F. Stoddart, Angew. Chem., Int. Ed., 2002, 41, 2508; (c) O.-K. Kim, J. Je, J. W. Baldwin, S. Kooi, P. E. Phehrsson and L. J. Buckley, J. Am. Chem. Soc., 2003, 125, 4426; (d) C.-Y. Lii, L. Stobinski, P. Tomasik and C.-D. Liao, Carbohydr. Polym., 2003, 51, 93; (e) A. Star, V. Joshi, T.-R. Han, M. V. P. Altoe, G. Gru¨ner and J. F. Stoddart, Org. Lett., 2004, 6, 2089; (f) T. Sanji, N. Kato, M. Kato and M. Tanaka, Angew. Chem., Int. Ed., 2005, 44, 7301; (g) T. Sanji, N. Kato and M. Tanaka, Chem. Lett., 2005, 1144; (h) M. Ikeda, Y. Furusho, K. Okoshi, S. Tanahara, K. Maeda, S. Nishino,
Chem. Commun., 2011, 47, 1961–1975
1973
5
6
7 8 9 10
11
12 13 14 15 16 17 18
19 20
T. Mori and E. Yashima, Angew. Chem., Int. Ed., 2006, 45, 6491; (i) T. Kida, T. Minabe, S. Okabe and M. Akashi, Chem. Commun., 2007, 1559; (j) M. J. Frampton, T. D. W. Claridge, G. Latini, S. Brovelli, F. Cacialli and H. L. Anderson, Chem. Commun., 2008, 2797. Recent reviews see: (a) K. Sakurai, K. Uezu, M. Numata, T. Hasegawa, C. Li, K. Kaneko and S. Shinkai, Chem. Commun., 2005, 4383; (b) M. J. Frampton and H. L. Anderson, Angew. Chem., Int. Ed., 2007, 46, 1028; (c) M. Numata and S. Shinkai, Adv. Polym. Sci. Self-Assembled Nanomaterials II, ed. T. Shimizu, Springer-Verlag, Berlin, Heidelberg, 2008, vol. 220, p. 65. (a) T. Yanaki, T. Norisuye and H. Fujita, Macromolecules, 1980, 13, 1462; (b) T. Yanaki, W. Ito, K. Tabata, T. Kojima, T. Norisuye, N. Takano and H. Fujita, Biophys. Chem., 1983, 17, 337; (c) B. T. Stokke, A. Elgsaeter, D. A. Brant and S. Kitamura, Macromolecules, 1991, 24, 6349; (d) J. A. Bohn and J. N. BeMiller, Carbohydr. Polym., 1995, 28, 3. E. D. T. Atkins and K. D. Parker, Nature, 1968, 220, 784. T. Sato, T. Norisuye and H. Fujita, Carbohydr. Res., 1981, 95, 195. K. Sakurai and S. Shinkai, J. Am. Chem. Soc., 2000, 122, 4520. (a) S. Demleitner, J. Kraus and G. Franz, Carbohydr. Res., 1992, 226, 239; (b) T. Yoshida, Y. Yasuda, T. Mimura, Y. Kaneko, H. Nakashima, N. Yamamoto and T. Uryu, Carbohydr. Res., 1995, 276, 425; (c) Y. Gao, K. Katsuraya, Y. Kaneko, T. Mimura, H. Nakashima and T. Uryu, Macromolecules, 1999, 32, 8319; (d) K. Katsuraya, H. Nakashima, N. Yamamoto and T. Uryu, Carbohydr. Res., 1999, 315, 234; (e) K. Na, K. H. Park, S. W. Kim and Y. H. Bae, J. Controlled Release, 2000, 69, 225; (f) T. Ikai and Y. Okamoto, Chem. Rev., 2009, 109, 6077. (a) M. Numata, T. Matsumoto, M. Umeda, K. Koumoto, K. Sakurai and S. Shinkai, Bioorg. Chem., 2003, 31, 163; (b) K. Koumoto, M. Umeda, M. Numata, T. Matsumoto, K. Sakurai, T. Kunitake and S. Shinkai, Carbohydr. Res., 2004, 339, 161; (c) T. Hasagawa, M. Umeda, T. Matsumoto, M. Numata, M. Mizu, K. Koumoto, K. Sakurai and S. Shinkai, Chem. Commun., 2004, 382; (d) T. Hasegawa, T. Fujisawa, M. Numata, T. Matsumoto, M. Umeda, R. Karinaga, M. Mizu, K. Koumoto, T. Kimura, S. Okumura, K. Sakurai and S. Shinkai, Org. Biomol. Chem., 2004, 2, 3091; (e) T. Hasegawa, T. Fujisawa, S. Haraguchi, M. Numata, R. Karinaga, T. Kimura, S. Okumura, K. Sakurai and S. Shinkai, Bioorg. Med. Chem. Lett., 2005, 15, 327; (f) T. Hasegawa, M. Umeda, M. Numata, T. Fujisawa, S. Haraguchi, K. Sakurai and S. Shinkai, Chem. Lett., 2006, 82; (g) T. Hasegawa, M. Umeda, M. Numata, C. Li, A.-H. Bae, T. Fujisawa, S. Haraguchi, K. Sakurai and S. Shinkai, Carbohydr. Res., 2006, 341, 35; (h) M. Ikeda, T. Hasegawa, M. Numata, K. Sugikawa, K. Sakurai, M. Fujiki and S. Shinkai, J. Am. Chem. Soc., 2007, 129, 3979; (i) M. Ikeda, J. Minari, N. Shimada, M. Numata, K. Sakurai and S. Shinkai, Org. Biomol. Chem., 2007, 5, 2219. (a) S. Iijima, Nature, 1991, 354, 56; (b) S. Iijima and T. Ichihashi, Nature, 1993, 363, 603. M. Sano, A. Kamino, J. Okamura and S. Shinkai, Science, 2001, 293, 1299. M. Numata, M. Asai, K. Kaneko, T. Hasegawa, N. Fujita, Y. Kitada, K. Sakurai and S. Shinkai, Chem. Lett., 2004, 232. T. Kimura, K. Koumoto, K. Sakurai and S. Shinkai, Chem. Lett., 2000, 1242. M. Numata, M. Asai, K. Kaneko, A.-H. Bae, T. Hasegawa, K. Sakurai and S. Shinkai, J. Am. Chem. Soc., 2005, 127, 5875. T. Hasegawa, T. Fujisawa, M. Numata, M. Umeda, T. Matsumoto, T. Kimura, S. Okumura, K. Sakurai and S. Shinkai, Chem. Commun., 2004, 2150. (a) F. L. Lu, F. Wudl, M. Nowak and A. J. Heeger, J. Am. Chem. Soc., 1986, 108, 8311; (b) H. S. Woo, D. B. Tanner, W. S. Huang and A. G. MacDiarmid, Phys. Rev. Lett., 1987, 59, 1464; (c) J. P. Pouget, M. Laridjani, M. E. Jozefowicz, A. J. Epstein, E. M. Scherr and A. G. MacDiarmid, Synth. Met., 1992, 51, 95. M. Numata, T. Hasegawa, T. Fujisawa, K. Sakurai and S. Shinkai, Org. Lett., 2004, 6, 4447. C. Li, M. Numata, A.-H. Bae, K. Sakurai and S. Shinkai, J. Am. Chem. Soc., 2005, 127, 4548.
1974
Chem. Commun., 2011, 47, 1961–1975
21 (a) B. M. W. Langeveld-Voss, R. A. J. Janssen, M. P. T. Christiaans, S. C. J. Meskers, H. P. J. M. Dekkers and E. W. Meijer, J. Am. Chem. Soc., 1996, 118, 4908; (b) E. Peeters, M. P. T. Christiaans, R. A. J. Janssen, H. F. M. Schoo, H. P. J. M. Dekkers and E. W. Meijer, J. Am. Chem. Soc., 1997, 119, 9909; (c) S. H. Chen, D. Katsis, A. W. Schmid, J. C. Mastrangelo, T. Tsutsui and T. N. Blanton, Nature, 1999, 397, 506; (d) S. C. J. Meskers, E. Peeters, B. M. W. Langeveld-Voss and R. A. J. Janssen, Adv. Mater., 2000, 12, 589; (e) M. Oda, H.-G. Nothofer, G. Lieser, U. Scherf, S. C. J. Meskers and D. Neher, Adv. Mater., 2000, 12, 362; (f) A. Satrijo, S. C. J. Meskers and T. M. Swager, J. Am. Chem. Soc., 2006, 128, 9030; (g) H. Goto and K. Akagi, Angew. Chem., Int. Ed., 2005, 44, 4322; (h) H. Goto, Macromolecules, 2007, 40, 1377. 22 S. Haraguchi, M. Numata, C. Li, Y. Nakano, F. Michiya and S. Shinkai, Chem. Lett., 2009, 254. 23 (a) M. Fujiki, J. Am. Chem. Soc., 1994, 116, 6017; (b) Y. Ichino, N. Minami, T. Yatabe, K. Obata and M. Kira, J. Phys. Chem. B, 2001, 105, 4111; (c) H. Nakashima, M. Fujiki, J. R. Koe and M. Motonaga, J. Am. Chem. Soc., 2001, 123, 1963; (d) W. Peng, M. Motonaga and J. R. Koe, J. Am. Chem. Soc., 2004, 126, 13822. 24 S. Haraguch, T. Hasegawa, M. Numata, M. Fujiki, K. Uezu, K. Sakurai and S. Shinkai, Org. Lett., 2005, 7, 5605. 25 H. Okumura, Y. Kawaguchi and A. Harada, Macromolecules, 2003, 36, 6422. 26 (a) T. Hasegawa, S. Haraguchi, M. Numata, T. Fujisawa, C. Li, K. Kaneko, K. Sakurai and S. Shinkai, Chem. Lett., 2005, 40; (b) T. Hasegawa, S. Haraguchi, M. Numata, C. Li, A.-H. Bae, T. Fujisawa, K. Kaneko, K. Sakurai and S. Shinkai, Org. Biomol. Chem., 2005, 3, 4321; (c) C. Li, M. Numata, T. Fujisawa, S. Haraguchi, K. Sakurai and S. Shinkai, Chem. Lett., 2005, 1532; (d) Wrapping of PPE see: M. Numata, T. Fujisawa, C. Li, S. Haraguchi, M. Ikeda, K. Sakurai and S. Shinkai, Supramol. Chem., 2007, 19, 107. 27 (a) L. Yang, H. J. Liang, T. E. Angelini, J. Butler, R. Coridan, J. X. Tang and G. C. L. Wong, Nat. Mater., 2004, 3, 614; (b) Y. Kubo, Y. Kitada, R. Wakabayashi, T. Kishida, M. Ayabe, K. Kaneko, M. Takeuchi and S. Shinkai, Angew. Chem., Int. Ed., 2006, 45, 1548; (c) K. K. Ewert, H. M. Evans, A. Zidovska, N. F. Bouxsein, A. Ahmad and C. R. Safinya, J. Am. Chem. Soc., 2006, 128, 3998; (d) K. K. Ewert, H. M. Evans, A. Zidovska, N. F. Bouxsein, A. Ahmad and C. R. Safinya, J. Am. Chem. Soc., 2006, 128, 3998; (e) P. J. Yoo, K. T. Nam, J. Qi, S.-K. Lee, J. Park, A. M. Belcher and P. T. Hammond, Nat. Mater., 2006, 5, 234. 28 M. Numata, K. Sugikawa, K. Kaneko and S. Shinkai, Chem.–Eur. J., 2008, 14, 2398. 29 (a) R. Purrello, E. Bellacchio, S. Gurrieri, R. Lauceri, A. Raudio, L. M. Scolaro and A. M. Santoro, J. Phys. Chem. B, 1998, 102, 8852; (b) A. D. Schwab, D. E. Smith, C. S. Rich, E. R. Young, W. F. Smith and J. C. De Paula, J. Phys. Chem. B, 2003, 107, 11339; (c) C. Escudero, J. Crusats, I. Diez-Perez, Z. El-Hachemi and J. M. Ribo, Angew. Chem., Int. Ed., 2006, 45, 8032; (d) K. Hosomizu, M. Oodoi, T. Umeyama, Y. Matano, K. Yoshida, S. Isoda, M. Isosomppi, N. V. Tkachenko, H. Lemmetyinen and H. Imahori, J. Phys. Chem. B, 2008, 112, 16517. 30 (a) S. Tamesue, M. Numata, K. Kaneko, T. D. James and S. Shinkai, Chem. Commun., 2008, 4478; (b) K. Sugikawa, M. Numata, D. Kinoshita, K. Kaneko, K. Sada, A. Asano, S. Seki and S. Shinkai, Org. Biomol. Chem., 2011, 9, 146. 31 K. Sugikawa, M. Numata, K. Kaneko, K. Sada and S. Shinkai, Langmuir, 2008, 24, 13270. 32 M. Numata, K. Kaneko, H. Tamiaki and S. Shinki, Chem.–Eur. J., 2009, 15, 12338. 33 (a) H.-A. Klok, J. F. Langenwalter and S. Lecommandoux, Macromolecules, 2000, 33, 7819; (b) J. M. Hannink, J. J. L. M. Cornelissen, J. A. Farrera, P. Foubert, F. C. Schryver, N. A. J. M. Sommerdijk and R. J. M. Nolte, Angew. Chem., Int. Ed., 2001, 40, 4732; (c) K. Velonia, A. E. Rowan and R. J. M. Nolte, J. Am. Chem. Soc., 2002, 124, 4224; (d) M. J. Boerakker, J. M. Hannink, P. H. H. Bomans, P. M. Frederik, R. J. M. Nolte, E. M. Meijer and N. A. J. M. Sommerdijk, Angew. Chem., Int. Ed., 2002, 41, 4239;
This journal is
c
The Royal Society of Chemistry 2011
(e) M. Morikawa, M. Yoshihara, T. Endo and N. Kimizuka, Chem.–Eur. J., 2005, 11, 1574; (f) D. M. Vriezema, M. C. Aragone´s, J. A. A. W. Elemans, J. J. L. M. Cornelissen, A. E. Rowan and R. J. M. Nolte, Chem. Rev., 2005, 105, 1445; (g) F. Fikri, M. S. Alemdaroglu, W. Jie, B. Ru¨diger and H. Andreas, Chem. Commun., 2007, 1358; (h) T. Francisco, Jr., R. Per and V.-N. Corinne, Chem. Commun., 2007, 1130;
This journal is
c
The Royal Society of Chemistry 2011
(i) K. Ding, F. E. Alemdaroglu, M. Bo¨rsch, R. Berger and A. Herrmann, Angew. Chem., Int. Ed., 2007, 46, 1172; (j) C. Schatz, S. Louguet, J.-F. L. Meins and S. Lecommandoux, Angew. Chem., Int. Ed., 2009, 48, 2572; (k) I. C. Reynhout, J. J. L. M. Cornelissen and R. J. M. Nolte, Acc. Chem. Res., 2009, 42, 681; (l) S. F. M. van Dongen, H.-P. M. de Hoog, R. J. R. W. Peter, M. Nallani, R. J. M. Nolte and J. C. M. van Hest, Chem. Rev., 2009, 109, 6212.
Chem. Commun., 2011, 47, 1961–1975
1975