Poly helical structure

Poly(7-benzyl-L-glutamate) is known to possess a helical structure in certain solvents. As part of an investigationf of this molecule, a fractionated sample was examined in chloroform (CHCI3) and chloroform saturated ( 0.5%) with dimethyl formamide (DMF). The following results were obtained ... 

Fig. 2.2 Most favored helical structures proposed for two crystal forms of poly(a-n-butyl-/ -L-aspartate) (7, R=Bu) [28]. (A) Model of a (P)-3.25i4-helix. (B) Model of a (P)-4is-helix...

Iso tactic poly(methyl methacrylate) (it-PMMA) can form a stereocomplex with st-PMMA. Recent X-ray studies 179) of this material indicate that the two polymer chains probably interact to form a double helical structure. The it-PMMA chain forms the inner helix and is surrounded by the st-PMMA helical chain which winds around it. If subsequent work confirms this model, this material would constitute a most unusual inclusion compound involving only one monomeric substance. 

There are two levels of self-assembly in the formation of tetra-, penta-and hexa-nuclear products from the poly-bipyridyls (L) 20 and 21 and iron(II) salts FeCl2, FeBr2 or FeS04 - the products are anion-dependent. The coordination of three bpy units, from different ligand molecules, to the Fe2+ centers produces a helical structure interaction of these helical strands with anions results in further molecular organization to form the final toroidal product. The discussion draws parallels between the helical and toroidal structures here and secondary and tertiary structure in biological systems (482). Thermodynamic and kinetic intermediates have been characterized in the self-assembly of a di-iron triple stranded helicate with bis(2,2/-bipyridyl) ligands (483). 

Kishimoto T, Morihara Y, Osanai M, Ogata S-1, Kamitakahara M, Ohtsuki C, Tanihara M. Synthesis of poly(Pro-Hyp-Gly)n by direct polycondensation of (Pro-Hyp-Gly)n, where n = 1, 5, and 10, and stability of the triple-helical structure. Biopolymers 2005 79 163-172. 

Poly(19-< (9-15) and poly(19 -co-2 )) undergo helix-helix transition upon temperature change. All the co-polymers exhibit no optical activity at certain temperatures, which depends on the co-polymer composition. The helical structure of poly(19-/ o-15) carrying long alkyl chains is much affected compared to poly(19-/ o-20). The thermodynamic parameters of helix transition also depend on solvent. 

The secondary structure of poly(iV-alkynylamides) is influenced by the position of the chiral center and amide group.The position of the chiral center mainly affects the helical pitch, which becomes short when the chiral center is positioned away from the main chain. The stability of the helical structure is also influenced by the position of the amide group. Based on molecular orbital study, it is concluded that poly(iV-propargylamides) with right-handed helical structure display a plus Cotton effect around 390 nm. This is also confirmed by the exciton chirality method using porphyrin as a chromophore. ... 

The co-polymerization of D-alanine-derived A-propargylamide 22, L-valine-derived 23, and pyrene-based monomer 24 gives helical poly(22 -< o-23-c -24) carrying pyrene. The secondary structure of the co-polymer is tunable by the composition of the optically active amino acid units and solvent, which makes it possible to control the direction of the pyrene groups in the side chain. The interaction between the pyrene groups is small when the co-polymer takes a helical structure. The pyrene groups are regularly positioned in the polymer side chain. The co-polymer emits weak... 

Hatano et aL U7) studied the poly(L-lysine)(PLL)- and poly(DL-lysine)-Cu(II) complexes as catalysts in the oxidation of 3,4-dihydroxyphenylalanine. The catalytic activity of PLL-Cu was found to be greater than that of ethylenediamine-Cu. The oxidation was asymmetrically catalyzed by PLL-Cu the D-isomer of the substrate coordinated to PLL-Cu more strongly and its oxidation rate was greater than that of the L-enantiomer. The asymmetrical oxidation was ascribed to the helical structure of PLL-Cu in an aqueous solution of pH 10.5118. ... 

Conformational calculations are carried out on poly(di-n-hexylsilanes). The most significant finding from the energy calculations is that the a -trans conformation is not the lowest energy structure for the symmetrically alkyl-substituted silane polymers. A helical structure is preferred for the isolated molecule. 

N 017 "Conformational Analysis of Macromolecules. IV. Helical Structures of PolyfL-alanine), Poly(L-valine), Poly(p-methyl-L-aspartate), Polyly-methyl-l.-glutamate),... 

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