Construction and functionality as membrane of bundle polypeptides

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Hexaarmed poly (beta-benzyl-L-glutamates) (S-PBLG) with cyclotriphosphazene core were prepared by the polymerization of N-carboxy anhydride of b-benzyl-L-glutamate (BLG-NCA) with hexakis (4-benzylamino-1-oxy) cyclotriphosphazene (AMOP), and the conformation and the functionality as an enatioselctive membrane of resulting polymers were investigated. The molecular weights of S-PBLG determined by the combination of GPC and light scattering method were consistent with calculated values from the feed ratio, [BLG-NCA]/[AMOP], and conversion, and their distributions were narrow (M_w/M_n=1.1-1.3). When AMOP was added to BLG-NCA in CDCl_3 ([BLG-NCA]/[AMOP]=10), ^1H NMR spectra showed that the peak at 3.8 ppm assignable to benzyl proton disappeared immediately, together with the conversion of BLG-NCA of ca.57%. From these results, it appears that all of amino group in AMOP initiate the polymerization of BLG-NCA without delay and that the lengths of polymer chains diverging from the phosphazene c … More ore are well controlled. As expected, IR and CD spectra of S-PBLG film showed peaks at 1653 and 1550cm^<-1> and a negative peak at 226nm, respectively, indicating that the hexaarmed polyglutamates take a right handed a-helical structure. The organic group in phenoxycyclotriphosphazenes is known to be aligned approximately perpendicular to the almost planar cyclotriphosphazene. If this geometrical arrangement holds for S-PBLG,it seems reasonable to assume that the rigid polyglutamate chains from 3 alpha-helix bundle structure on both sides of phosphazene ring. This was supported by the behavior of the formation of excimer of pyrene which was introduced at terminal amino groups of S-PBLG.The membrane was prepared by displacement of benzyl group with triethylene glycol monomethyl ether (TEG). This polyglutamate again takes an alpha-helical structure, as evidenced by CD and IR spectra. The enantioselective permeation of tryptophan (Trp) through the membrane was examined. The membrane permeates only D-Trp and a complete optical resolution is achieved for over 200h. Control experiments showed that the conventional polyglutamate with triethylene glycol monomethyl ether units has no ability to resolve the recemate. These results indicate that the structural change from linear to hexaarmed polyglutamates with short oxyethylene chains brings about excellent abilities of molecular recognition of the optical isomer, i, e., the assembly of the helical structure with short side chains is important to attain a high enantioselectivity of the membrane. Less