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Optical resolution of racemic mixtures of amino acids through nanofiltration membrane process a
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Kripal Singh , Sadhana Devi , H. C. Bajaj , Pravin Ingole , Jayesh Choudhary & Harshad Bhrambhatt
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Reverse Osmosis Division, CSIR-Central Salt and Marine Chemicals Research Institute (CSIRCSMCRI), Gijubhai Badheka Marg, Bhavnagar, 364002(Gujarat) INDIA b
Division of Inorganic Materials & Catalysis, CSIR-Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Gijubhai Badheka Marg, Bhavnagar, 364002(Gujarat) INDIA c
Analytical Science Division, CSIR-Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Gijubhai Badheka Marg, Bhavnagar, 364002(Gujarat) INDIA Accepted author version posted online: 20 May 2014.Published online: 20 May 2014.
To cite this article: Kripal Singh, Sadhana Devi, H. C. Bajaj, Pravin Ingole, Jayesh Choudhary & Harshad Bhrambhatt (2014): Optical resolution of racemic mixtures of amino acids through nanofiltration membrane process, Separation Science and Technology, DOI: 10.1080/01496395.2014.911023 To link to this article: http://dx.doi.org/10.1080/01496395.2014.911023
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ACCEPTED MANUSCRIPT Optical resolution of racemic mixtures of amino acids through nanofiltration membrane process
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Kripal Singh1*, Sadhana Devi1, H. C. Bajaj2 , Pravin Ingole2, Jayesh Choudhary3 & Harshad bhrambhatt3 1 Reverse Osmosis Division, 2 Division of Inorganic Materials & Catalysis, 3 Analytical Science Division CSIR-Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Gijubhai Badheka Marg, Bhavnagar, 364002(Gujarat) INDIA Phone: +91-278-2567760; Fax: +91-278-2567562 *Corresponding Author E-mail:
[email protected] Abstract: Optical resolution of racemic mixtures of arginine and alanine was performed by chiral selective nanofiltration membrane. The chiral selective layer of the membrane was prepared by interfacial polymerization of metaphenylenediamine, trimesoyl chloride and S (-)-2acetoxypropionyl chloride (S-2-actoxpcl) in situ on the top of polysulfone ultrafiltration membrane. S-2-actoxpcl consists of a chiral carbon atom that has induced chiral environment in the membrane. The membranes were characterized by FTIR, scanning electron microscopy and atomic force microscopy to establish structure-performance relationship. The optical resolution was performed on membrane testing module and the effect of process parameters was determined. The results indicated that the incorporation of S-2-actoxpcl made membrane chiral selective hence membranes performed optical resolution. The resolution capacity increased by increasing S-2-actoxpcl in polymerising solution up to 0.03% but any increase beyond 0.03% reduces resolution capacity. More than 92% enantiomeric excess of D enantiomer was observed
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ACCEPTED MANUSCRIPT in permeate of membrane which was prepared from 0.07% trimesoyl chloride and 0.03% S-2actoxpcl. The membrane prepared without chain terminator exhibited less volumetric flux but more solute rejection compared to those prepared with chain terminator. The flux of the
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membrane increases as the amount of chain terminator in reaction increases. Keywords: Chiral membrane; S (-)-2-acetoxypropionyl chloride; Optical resolution; Enantioselectivity 1. Introduction: Production of chiral pure compounds is of great importance particularly in drugs and pharmaceuticals, agrochemicals and fragrances because enantiomers often show different physiological activities depending on their absolute configurations. The chiral pure compounds are prepared either by asymmetric synthesis or by optical resolution of racemic mixtures (chiral separation). Though asymmetric syntheses are widely used however these syntheses are tedious as majority of these are multistep reactions and reaction yield is very less thus products are costly [1]. The optical resolution is an important and cost-effective way to obtain optically pure substance. The optical resolution can be performed by various methods including preferential crystallization, kinetic resolution and chromatographic methods such as gas chromatography, high pressure liquid chromatography and super critical fluid chromatography [2]. The chromatographic methods mentioned above are batch processes thus very small amount can be resolved in one operation hence these methods are the best approaches at analytical scale. The liquid chromatography and preferential crystallization are most efficient methods at preparative scale however these methods require optically pure resolving agents or chiral host, or resolving columns which are highly expensive. Further resolving agents and hosts
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ACCEPTED MANUSCRIPT cannot be recovered easily and economically. Optical resolution through membrane is promising because membrane separations are continuous operations hence can resolve large quantity [3]. Moreover membrane processes are economical and eco-friendly and can be scaled up easily
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therefore optical resolution through membranes is being investigated vigorously in recent years. In the membrane separation process a membrane acts as selective barrier and transports desired molecule through it and at the same time restricts the passage of undesired molecules. Regarding chiral separation there is central dogma that chiral recognition is possible only in presence of chiral environment. Thus in order to achieve chiral separation by membrane it should possess chiral recognition mechanism. The chiral recognition mechanism would identify the desired enantiomer and would transport across the membrane preferentially [4]. The chiral recognition can be introduced in the membrane by various means such as incorporation of chiral selector in the membrane during its preparation [5], grafting chiral side chains in the polymer and then converting it into membrane [6], making membrane from a polymer having chiral backbone [78], making a chiral layer on the achiral membrane etc., [9-11]. The most commonly used membranes are either integrally skinned asymmetric membranes or thin film composite membranes. The composite membranes are considered advantageous over single layered integrally skinned asymmetric membranes [12] because each layer of composite membrane can be prepared separately thus can be optimized independently for optimum performance of each layer. Moreover the selective layer of composite membrane being extremely thin (
