J Sol-Gel Sci Technol (2012) 61:119–125 DOI 10.1007/s10971-011-2600-y
ORIGINAL PAPER
Composites with photosensitive 5,10,15,20-tetrakis(Nmethylpyridinium-4-yl)porphyrin entrapped into silica gels Renata Rychtarikova • Stanislav Sabata Jiri Hetflejs • Gabriela Kuncova
•
Received: 14 July 2011 / Accepted: 26 September 2011 / Published online: 8 October 2011 Ó Springer Science+Business Media, LLC 2011
Abstract Photosensitive cationic 5,10,15,20-tetrakis(1methyl-4-pyridinio)porphyrin (TMPyP) was entrapped into microporous silica gels prepared by sol–gel method from tetrakis(2-hydroxyethoxy)silane (THES) and tetramethoxysilane (TMOS), resp., using different water and PEG 600 contents in the initial mixture. The absorption spectra of both composites showed that incorporation of TMPyP has led to a bathochomic shift (ca. 8 nm) of the Soret band and to a decrease in their molar absorption coefficient compared to TMPyP in solution. The TMPyP encapsulation kept the molecular state of the porphyrin in the free-base monomer form. In comparison to TMOS analogs, THES composites showed prolonged shape stability at least for 3 months, one-order higher rate of chemical substrate photooxidation and higher photobiocidal activity against E. coli. Keywords Sol–gel Photosensitizer Immobilization Photodynamic inactivation Escherichia coli Surfactant
1 Introduction Porphyrins are natural macrocyclic compounds playing an important role in metabolism of organisms (e.g., haemoglobin in oxygen transport or chlorophyll in photosynthesis).
R. Rychtarikova (&) S. Sabata J. Hetflejs G. Kuncova Institute of Chemical Process Fundamentals, Academy of Sciences, Rozvojova 135, 165 02 Prague 6, Suchdol, Czech Republic e-mail:
[email protected]
They are derived from porphin macrocycle, whose extended l-electron system enables considerable light absorption in visible light spectrum. Due to this property and long-lived excitation states, porphyrins are efficient sensitizers of photodynamic reaction. Illumination of porphyrins in oxygen environment leads to generation of 1O2 and other reactive oxygen species (ROS) inducing toxic events in organisms [1]. There are many places, such as hospitals and public buildings, with demands for antimicrobial surfaces of walls, floors and instruments. Therefore, porphyrins fixed in their active form into an inert and stable matrix might be of particular interest where a light induced self-sterilization surface is needed. In this respect, organic–inorganic materials prepared by sol–gel process, which offers the variable precursors and mild conditions of hydrolytic and condensation reactions, might be appropriate matrices for this purpose. Tetramethoxysilane (TMOS) has been often used to immobilize 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin (TMPyP, Fig. 1) for preparing photosensitive sol– gel composites [2–4]. Although these materials showed good light transparency and adhesion to glass, they suffered from low mechanical and chemical stability. With the aim to ensure toughness and greater stability of silica–TMPyP composites, we entrapped TMPyP into sol– gel from tetrakis(2-hydroxyethoxy)silane (THES). In these composites, changes in water content during their preparation influenced production of ROS and addition of lowmolecular poly(ethylene glycol) 600 (PEG 600) improved their flexibility. The THES composites and their TMOS analogs were characterized by BET measurements, UV– Vis absorbance and fluorescence spectra and by the production of ROS evaluated by chemical and microbiological methods.
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and (NH4)2MoO4 (1.9 mg) in deionized water in a 1,000-mL volumetric flask covered by a tinfoil for light-protection.
CH3 N
2.2 THES-TMPyP preparation
N
HN N CH3
H3C N N
NH
N CH3
Fig. 1 Structure of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin
2 Materials and methods 2.1 Chemicals 5,10,15,20-Tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-tolunesulfonate) (TMPyP) and tetramethoxysilane (TMOS) were purchased from Fluka (Switzerland). Agar–agar, TrizmaÒ Base (tris(hydroxymethyl)aminomethane, TrisBase), and TrizmaÒ Hydrochloride (TrisHCl, tris(hydroxymethyl)aminomethan hydrochloride) were obtained from Sigma (USA). Ethanol (96%), dichlormethane (DCM), sodium hydroxide, hydrochloric acid, sodium chloride, potassium phosphate dibasic, potassium phosphate monobasic, and potassium iodide in p.a. purity were obtained from P-LAB (Czech Republic). Ampicillin and ammonium molybdate were supplied by Sigma-Aldrich (USA) and isopropyl-b-D1-thiogalaktopyranosid (IPTG) by Promega (USA). Tryptone (Oxoid, UK) and yeast extract (AppliChem, BRG) were commercial products as indicated. Poly(ethylene glycol) 600 (PEG 600) was from the laboratory stock (Institute of Chemical Process Fundamentals AS CR, Prague, Czech Republic). Tetrakis(2-hydroxyethoxy)silane (THES) was prepared by transesterification of TMOS with ethylene glycol under continuous removal of the released methanol [5]. Concentration of TMPyP in deionized water was adjusted at 1 9 10-4 mol L-1 and this value was verified by absorption spectrophotometry, using an HP 8452 A spectrophotometer (USA) and the absorption coefficient of 220 L-1 mmol-1 cm-1 at 422 nm. Tris buffer (0.05 mol L-1, pH 7.2 at 25 °C) was prepared from aqueous solution of TrisHCl (7.02 g L-1) and TrisBase (0.67 g L-1). The iodometric agent [6] was prepared by mixing K2HPO4 (9.6 ml; 1.0 mol L-1), KH2PO4 (40.4 ml; 1.0 mol L-1), KI (19.9 g),
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Four THES-TMPyP composites (Table 1) were obtained by varying the volume percentage of water in an initial mixture (37 and 33 vol%) and PEG 600 content. Aqueous TMPyP solution was gradually mixed with Tris buffer ? (PEG600) ? THES, using a high-rate vortex system in a 10-mL glass tube, always for 10 s. The mixtures (500 lL) were pipetted in three parallels into plastic plates (3.5 cm2). After gelation at 103 °C for 1 h, the composites were covered by ParafilmÒ or lids and allowed to stand at 25 °C. The next day, the composites were washed by DCM:EtOH mixture in 17:3 vol ratio (1 mL) for 10 s and vacuum-dried (23.2 kPa) for 2 h. After solvents evaporation, washing of the composites was being continued in deionized water (2 mL) for 30 min at 25 °C and 100 rpm. For microbiological tests, the composites were washed only with sterile water. All composite samples were covered by ParafilmÒ or lids and stored at 4 °C. For antimicrobial tests, the control layers were prepared by addition of deionized water instead of TMPyP solution. 2.3 TMOS-TMPyP preparation TMOS, stored at 4 °C, was warmed up to laboratory temperature and weighed (8.2 g) into a beaker using a dry Pasteur pipette. Then, deionized water (4.0 mL) and a magnetic stirrer were introduced, the beaker was covered by ParafilmÒ and kept at -18 °C for 5 min. During stirring (450 rpm) of the above mixture, HCl (0.1 mol L-1; 1.0 mL) was dropwise added. After hydrolysis had started, the mixture was cooled to -18 °C for 10 min and then maintained at 4 °C. The next day, the methanol formed during TMOS polycondensation was stripped off by stirring (450 rpm) the obtained prepolymer (TMOSPP) at 25 °C for 10 min. Viscous TMOSPP was gradually mixed under vortex stirring with TMPyP solution ? (PEG 600) ? NaOH in a glass tube (Table 1). The mixtures (500 lL) were pipetted into plastic plates (3.5 cm2). After gelation (15 min), the formed composites were poured over by deionized water (1 mL), covered by lids or ParafilmÒ and stored at 4 °C. The control layers were prepared using deionized water instead of TMPyP solution. 2.4 Specific surfaces, thickness and TMPyP leaching stability Composites were dried at 103 °C for 24 h, first in an oven and then in vacuum (0.1 lPa). BET specific surface areas
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Table 1 Composition of mixtures for preparation of silica gels Samplea
VTHES (lL)
VTMOSPP (lL)
TH-W-0
1,250
TH-W-P TH-D-0 TH-D-P
nbprecursor (mmol)
VcTMPyP (lL)
nbTMPyP (nmol)
VdTris (lL)
VeNaOH (lL)
0
1.22
250
6.250
0
0
500
0
1,250
0
1.22
250
6.219
1,500
0
1.30
250
5.556
0
10
500
0
0
0
500
1,500
0
1.30
250
5.531
0
0
10
500
0
TH-W-0-c
1,250
0
1.22
0
0
250
0
500
0
TH-W-P-c
1,250
0
1.22
0
0
250
10
500
0
TH-D-0-c TH-D-P-c
1,500 1,500
0 0
1.30 1.30
0 0
0 0
250 250
0 10
500 500
0 0
TM-W-0
0
1,250
1.20
250
6.250
0
0
0
500
TM-W-P
0
1,250
1.19
250
6.219
0
10
0
500
TM-D-0
0
1,500
1.27
250
5.556
0
0
0
500
TM-D-P
0
1,500
1.27
250
5.531
0
10
0
500
TM-W-0-c
0
1,250
1.20
0
0
250
0
0
500
TM-W-P-c
0
1,250
1.19
0
0
250
10
0
500
TM-D-0-c
0
1,500
1.27
0
0
250
0
0
500
TM-D-P-c
0
1,500
1.27
0
0
250
10
0
500
VH2 O (lL)
VPEG600 (lL)
a
TH THES, TM TMOS, W materials with less THES or TMOS (weak), D materials with more THES or TMOS (dense), 0 without PEG 600, P with PEG 600, c controls with deionized water without TMPyP
b
Content in the composite
c
10-4 M solution in water
d
Tris buffer (0.05 mol L-1, pH 7.2)
e
Aqueous 0.025-M solution
of xerogels (SBET) were measured using ASAP 2010 M (Micromeritics, USA). Relative volume ratios of micropores in the porphyrin composites were evaluated as rmicro = VL/1.5468VG, where VG and VL correspond to the total volume of adsorbed gaseous nitrogen at maximal relative pressure and the volume of adsorbed liquid nitrogen in micropores, resp. Factor of 1.5468 was evaluated for nitrogen standard conditions from the Ideal Gas Phase Equation. Water content in the composite was evaluated as P P VH2 O 1 P rH2 O ¼ k 1 þ 1, where VH2 O is the total V
Thicknesses of the composites were measured with a Primostar Carl Zeiss microscope focusing on an upper and down edges of the layers. One rotation by a focusing microscrew corresponds to 300 lm. In leaching tests, the amount of TMPyP released from the composites to the deionized washing water (3 mL) was measured in a UV cuvette (optical length of 10 mm) with an HP 8452 A spectrophotometer (USA, sensitivity of 0.0022 a.u.), after shaking (100 rpm) the mixture on a Heidolph Unimax 1010 rotation shaker (BRD) at 25 °C for 1 h.
volume of water for all reaction components (TMPyP, Tris, P NaOH, and water) and Vi is the total volume of all components (including THES, TMOSPP, and PEG) in initial mixtures (Table 1). For TMOSPP, water content was
2.5 Fluorescence, absorbance and molar absorption coefficients
i
calculated as
VTMOSPP ðVH2 O þVHCl Þ VH2 O þVHCl þðmTMOS =qTMOS Þ,
where volumes or
masses of TMOSPP components are mentioned above and qTMOS = 1.023 g mL-1. The coefficient k = 1 for TMOS2 TMPyP and k ¼ 1 qm1 m VM for THES-TMPyP, where m1 H2 O
and m2 are masses of THES-TMPyP mixture before/after gelation, VM = 500 lL is the volume of THES-TMPyP mixture before gelation, and qH2 O = 0.997 g mL-1 at 25 °C.
3D-fluorescence spectra of the composites were collected with a Hitachi F-4500 spectrophotometer (Japan) at excitation/emission slits of 10/5 nm and PMT Voltage of 700 V. Fluorescence intensities of the encapsulated TMPyP at 430/650 nm were statistically evaluated. Fluorescence depth profiles of the composites were observed with an Olympus 81bx microscope with a FV1000 fluorescence unit after excitation at 405 nm. Absorption spectra of the composites were measured with an HP 8452 A spectrophotometer (resolution 2.0 nm).
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Light scatter was corrected by Scatter correction function in Advance mode of UV/Vis ChemStation software (Agillent Technol. 95-00) at 350–400 nm and 450–800 nm. Molar absorption coefficients of immobilized TMPyP samples were expressed as eC ¼ eW AAWC llWC k, where eW is the molar absorption coefficient of TMPyP in aqueous solution at 422 nm, AC and AW are the absorbances of TMPyP in the composite at 430 nm and aquoeousTMPyP solution at 422 nm, resp., lW is the optical length of a cuvette with aqueous TMPyP stock solution, and lC is the thickness of the composite. The k coefficients for TMOSTMPyP and THES-TMPyP have been defined in Sect. 2.4. 2.6 Iodometric method of 1O2 detection The iodometric method used was reported by Monsinger et al. [6]. The measurements were carried out under constant conditions (100 rpm stirring with a Heidolph Unimax 1010 rotation at 25 °C) in air atmosphere, the oxygen of which was the only source of 1O2 in the system. Before each measurement with the immobilized photosenzitizer, the solution of the iodometric reagent (3 mL, for composition see Sect. 2.1) was subjected to irradiation with a halogen lamp (10 klx), using a dish with water as an i.r. filter between the lamp and the solution. The possible I3- formation was followed for 10 min. The samples (100 lL) of the iodometric reagent were withdrawn at 1-min intervals, ten-times diluted with water, charged to a Helma 105.-201.-QS cuvette and measured with a HP 8452A spectrophotometer at 354 nm as I3- absorbance. The same procedure was used in the presence of the photosensitizer composites. The values obtained with the blank solution were subtracted from the absorbances found with the photosensitizer. In both cases the absorbance—time dependence was linear and the values for the blank did never exceed ca. 5% of those observed for the immobilized sensitizer. The resultant absorbances were recalculated to the molar amount of generated I3- ion using the Lambert–Beer Law (I3- molar absorption coefficient is 2.1 L mmol-1 cm-1 [7]). The rate of I3- production was evaluated as the slope of the linear regression n(I3-) = f(EL), where EL is the light energy emitted by the halogen lamp (J cm-2). 2.7 Microbiological test For evaluation of photomicrobicidal activity, the recently reported method was applied [2]. GMO of Escherichia coli BL21(DE3) (pET16bDsRed), producing red fluorescent protein in a medium with ampicillin and lactate, was
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obtained from Department of Biochemistry and Microbiology, Institute of Chemical Technology, Prague (Czech Republic). E. coli BL21(DE3) was cultivated in LB broth (10% tryptone, 10% NaCl, and 5% yeast extract) with ampicillin (0.2%) at 37 °C for 16 h. Inoculum was adjusted to the concentration of 106 c.f.u. mL-1 into LB agar (1%) with IPTG (1 mmol L-1). The inoculated LB agar (500 lL) was poured over the composites at the bottom of the plastic plates. The layers without porphyrins were used as controls. After illumination by a halogen lamp (10 klx for 0, 1.5, and 3 h) through a dish with water as an i.r. filter, the inoculated Petri dishes were incubated in dark at 37 °C for 48 h. After incubation, an image of each Petri dish was taken by a photocamera Canon A640. Antimicrobial activity of the composites against E. coli corresponding to bacteria growth on agar was evaluated by the computational image analysis using NIS Elements 2.60 software (Laboratory Imaging, Czech Republic). The calibration curve of logarithmic bacteria amount log c.f.u. in agar as a function of growth area SG was constructed using Origin 8.0 software (USA). The calibration equation log c.f.u. = 9.29SG/(18.47 ? SG), R2 = 0.9811 was used to recalculate bacteria growth to bacteria amount.
3 Results and discussion 3.1 Stability and texture of THES-TMPyP composites 5,10,15,20-Tetrakis(1-methyl-4-pyridinio)porphyrin (TMPyP) was encapsulated into silica gels prepared by sol gel method from tetrakis(2-hydroxyethoxy)silane (THES) and tetramethoxysilane (TMOS), resp. (Table 1). The mixtures contained 37 and 33 vol% of water, Si-TMPyP molar ratio of 1.9 and 2.3 9 105 (samples designated as weak –W– and dense –D–, resp.), and low-molecular PEG 600 (0 and 0.04 vol%; samples designated as –0 and –P, resp.). The gelation yielded the composites with the dye and water contents given in Tables 1 and 2. The thickness of THES composites was 115 and 600 lm for TMOS analogs. It was found that in both THES and TMOS gels, the cationic TMPyP vvwas firmly bound. Washing with water released only the TMPyP contra-ion, p-toluenesulfonic acid (k = 220 nm). This seems to indicate some ionic bonding between TMPyP and acidic silica gel surface. However, the low precision of the analysis does not allow quantification of the extent of this interaction. TMOS composites were glassy materials, whereas THES ones were soft gels. The THES gels were shape- and volume-stable in air at laboratory temperature for 3-month test period, unlike TMOS analogs that shrank already 2 h
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Sample
SBET [m2 g-1]a
rmicro [%]a
rH2 O [%]
TH-W-0
380
49.2
0.051
TH-W-P
350
51.1
0.059
TH-D-0
291
54.4
0.034
TH-D-P
357
54.5
0.050
TM-W-0
649
50.5
0.615
TM-W-P
640
53.6
0.615
TM-D-0
628
54.0
0.589
TM-D-P
685
49.1
0.589
a
Xerogels dried at 103 °C
after gelation, even when stored wet. This finding is of interest, since the gels prepared earlier from THES, which was free of ethylene glycol by thorough washing [8, 9], were shrink-stable only in the presence of micelles formed by addition of a cationic surface active compound. We believe that in our case the shape stability of the THES gels resulted from the positive effect of the residues of ethylene glycol released during the hydrolysis exerted most likely via hydrogen bonding of ethylene glycol with Si–O–Si network [10]. All the composites were microporous materials (Table 2). Their xerogels contained 49.1–54.5 vol% of micropores. The use of THES afforded the xerogels with BET surfaces about 50% lower (291–380 m2 g-1 vs. 628–685 m2 g-1 for TMOS). In both weak xerogels, the addition of PEG 600 decreased their BET surface, whereas the opposite effect was observed for the dense composites. In all cases, PEG 600 addition resulted in formation of the more flexible materials. 3.2 Absorption and fluorescence spectra All the composites were yellow (Fig. 2). Examples of the spectra of TMPyP immobilized into THES and TMOS gels are shown in Fig. 2. Higher hydrophobicity and lower polarity of the gels in comparison with water led to bathochromic shift of TMPyP Soret band from 422 to 430 nm [11]. In addition, the deformation of Q-bands reflects the interaction of encapsulated TMPyP with silica matrix. The presence of four Q-bands in all the spectra supports the assumption that incorporation of TMPyP was not accompanied by its protonation (the latter should have led to the occurence of only two Q bands) [11, 12]. This, along with the shape of the Soret band, speaks for immobilization of TMPyP in the free-base monomer form [13]. The sol–gel encapsulation thus did not change the molecular state of the porphyrin compared to TMPyP in solution. This is likely due to the low TMPyP concentration in the layers (5.531–6.250 nmol), as shown in Table 1.
Absorbance
Table 2 Specific surface (SBET), micropore volume ratio (rmicro), and water volume ratio (rH2 O ) of THES and TMOS composites
c b a
350
450
550
650
Wavelength (nm) Fig. 2 Absorption spectra of the composites. a Weak THES composite without PEG 600 (TH-W-0); b weak TMOS composite without PEG 600 (TM-W-0); c 10-6-M TMPyP-water solution
As already observed with other immobilized photosensitizers [14], also in this case the entrapment of TMPyP into both gels decreased its molar absorption coefficient (135–193 L mmol-1 cm-1 vs. 220 L mmol-1 cm-1 in water), the values of which were higher for the weak composites (Fig. 3a). The total fluorescence intensity of TMPyP composites at the excitation/emission maximum of 430/650 nm (Fig. 3b) was inversely proportional to the specific surface area of the gels. The values were higher for THES composites. The increased values were found with both weak composites. Several reasons might be responsible for this fact: the lower specific surface area and the higher average pore diameter, both leading to the easier light transmission, as well as the higher content of water forming a natural environment for TMPyP. On the other hand, the positive effect of PEG 600 was observed only with the dense composites. 3.3 Photosensitive and antimicrobial properties The factors influencing ROS production involve those affecting fluorescence of immobilized photosensitive dye, such as temperature or aggregates formation, limited solubility of atmospheric oxygen in polymer, the reaction of ROS with polymer during their diffusion to the outer polymer surface. The latter process is of primary importance since it has already been estimated that only ca. 50% of generated reactive species are released across illuminated polymer side [15]. Due to different hydrophobicity of sol–gels and dye solutions there proceeds phase separation. Consequently, the dye is likely preferentially deposited near the sol–gel surface and is not thus evenly distributed in the whole bulk [16]. In addition, the density of polymer network plays an important role for oxygen diffusion across the material [17–19].
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-1
(M cm )
a -1
2.5
Mol. abs. coef. × 10
-5
2.0 1.5 1.0 0.5 0.0 THES
TMOS
THES
TMOS
THES
TMOS
Fluorescence (a.u.)
b 800 600
400
200
0
dn(I3-)/dEL (nmol J -1 cm2)
c
150
100
50
0
Fig. 3 The influence of water and PEG 600 content on optical characteristics of TMPyP entrapped into the gels. a Molar absorption coefficients at 430 nm, b fluorescence intensities at excitation/ emission of 430/650 nm, c rate of I3- production (dn(I3-)/dEL) during illumination by a halogen lamp (10 klx). Vertical line bar Weak composites without PEG 600 (-W-0), horizontal line bar weak composites with PEG 600 (-W-P), left striped bar dense composites without PEG 600 (-D-0), right striped bar dense composites with PEG 600 (-D-P)
Production of ROS by photosensitive silica-TMPyP composites was tested by iodometric and microbiological methods. In the first case, the iodide solution in contact with the composite surface was oxidized to I3- (Fig. 3c). Since in comparison to TMOS composites, THES ones had the half BET surfaces (Table 2) and five-times thinner thickness, which both lead to the higher mass concentration, the I3- production was by one order of magnitude
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higher for THES (16.4–148.5 nmol cm2 J-1) than for TMOS composites (4.6–15.1 nmol cm2 J-1). The higher I3- production was also observed with the composites with PEG 600. ROS generation was further evaluated as phototoxicity of the composites against E. coli BL21(DE3) in initial concentration of 106 c.f.u. mL-1, growing in agar after illumination by 0, 7.9, and 15.8 J cm-2, resp. (Fig. 4). Whereas no antimicrobial effect was observed with gels without TMPyP, indicating high biocompatibility of the matrices, growth of E. coli in agar decreased with increasing light energy for all the composites. In general, THES composites with the lower specific surface areas were more effective than TMOS analogs. PEG 600 addition did not induce significant differences in phototoxicity. Whereas the light intensity of 7.9 J cm-2 did not avoid growth of E. coli on the dense THES composites, the double light energy led to the total growth inhibition. By contrast, the weak composites showed E. coli growth of 10–100 c.f.u., even after illumination by 15.8 J cm-2. Opposite situation has been observed for TMOS composites. The higher bactericidal effect was established for the weak composites. They showed average growth above 100 c.f.u. after illumination by 15.8 J cm-2. The composite prepared with PEG 600 was more effective, almost without growth after illumination of 15.8 J cm-2. The dense composites gave rise to a significant growth decrease from 106 to 103 c.f.u. only after light energy incidence of 7.9 J cm-2. Another light dose only led to approximately one order growth decrease. The antimicrobial activity of these composites was mainly influenced by total TMPyP content in the bulk (Table 1), BET surface areas (Table 2), and by thicknesses of the composites. Among THES composites, their flexibility brought about by PEG 600, improved O2 diffusion. As observed both visually and with a fluorescence microscope, THES composites, mainly dense ones, had the higher colour density near the surface. This fact makes them more effective antimicrobial materials than weak ones, and mainly compared to TMOS composites with more uniform TMPyP distribution.
4 Conclusions Microporous silica gels prepared by sol–gel process from tetrakis(2-hydroxyethoxy)silane (THES) have been used to immobilize photosensitive cationic 5,10,15,20-tetrakis(Nmethylpyridinium-4-yl)porphyrin (TMPyP). The composites were modified by water content and by addition of lowmolecular PEG 600. Properties of the composites were compared with their tetramethoxysilane (TMOS) analogs. All the composites showed good adhesion to glass, but
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125 THES
TMOS 6
log c.f.u.
log c.f.u.
6 4 2 0
0 TM-W-0
TM-W-P
TM-D-0
0
TM-D-P
4 2 0 TM-W-0
TM-W-P
TM-D-0
TM-D-P
Fig. 4 Antimicrobial activity of porphyrin-silica gels illuminated by halogen lamp (10 klx for 0; 1.5; and 3 h, resp.) against E. coli BL21(DE3) growing in LB agar (500 lL) with IPTG (1 mmol L-1) and ampicillin (200 mg mL-1) in dishes (3.5 cm2). Log of initial E. coli concentration of 5.87 ± 0.62. Open box Gel without TMPyP,
light shaded box TMPyP composite, 0 J cm-2, dark shaded box TMPyP composite, 7.9 J cm-2, black box TMPyP composite, 15.8 J cm-2. Squares below the composites initials correspond to designation in Fig. 3
THES ones have not shrunk at least for 3 months. As compared to the absorption spectra of TMPyP in solution, TMPyP in both composites showed a bathochomic shift (ca. 8 nm) of their Soret band and decrease in the molar absorption coefficient. However, TMPyP encapsulation did not change its molecular state that was the free-base monomer form. In all cases, the fluorescence of entrapped TMPyP depended inversely on the specific surfaces of the composites. Photosensitive and antimicrobial tests proved the higher efficiency of THES composites that exhibited by one-order higher rate of chemical substrate photoxidation and higher photobiocidal activity against E. coli compared to TMOS analogs. These properties, along with a high shape stability of THES-TMPyP composites, make them favourable photosensitive materials.
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Acknowledgments This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic, ME892 grant.
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