Poly-L-alanine

These polymers, typical of polyamides with fewer than four main chain carbon atoms in the repeating unit, decompose before melting and have to be processed from solution. Several of the polymers may, however, be spun into fibres. Over thirty years ago Courtaulds produced silk-like fibres on an experimental commercial scale from poly-(L-alanine) and from poly-(a-methyl-L-glutamate). The latter material is also said to be in use as a synthetic leather in Japan. The... 

Further evidence for these a-helix ROA band assignments in the extended amide III region comes from the ROA spectrum of poly-L-alanine dissolved in a mixture of chloroform (70%) and dichloracetic acid (30%), known to promote a-helix formation (Fasman, 1987), which shows strong positive ROA bands at 1305 and 1341 cm-1 (unpublished results), and of the cv-helix forming alanine-rich peptide AK21 (sequence Ac-AAKAAAAKAAAAKAAAAKAGY-NHg) in aqueous solution which shows strong positive ROA bands at 1309 and 1344 cm-1 (Blanch et al., 2000). 

Takano, M., Yamato, T., FligoJ., Suyama, A., andNagayama, K. (1999). Molecular dynamics of a 15-residue poly(L-alanine) in water Flelix formation and energetics. / Am. Chem. Soc. 121, 605-612. 

Malcolm (1973, 1975) reported possible observable differences between the pressure-area curves of poly(L-alanine) mixed with poly(D-a-amino-n-butyric acid) and the corresponding mixture containing poly(D-alanine). Shafer (1974) observed differences in the film pressure between (/ )-phosphatidyl serine with poly-L-lysine and the corresponding film with poly-D-lysine injected under the film. 

Arnott, S., Dover, S. D., and Elliott, A. (1967). Structure of / -poly-L-alanine Refined atomic co-ordinates for an anti-parallel /(-pleated sheet./. Mol. Biol. 30, 201-208. 

Scheuermann, T., Schulz, B., Blume, A., Wahle, E., Rudolph, R., and Schwarz, E. (2003). Trinucleotide expansions leading to an extended poly-L-alanine segment in the poly (A) binding protein PABPN1 cause fibril formation. Protein Sci. 12, 2685-2692. 

Shinchuk, L. M., Sharma, D., Blondelle, S. E., Reixach, N., Inouye, H., and Kirschner, D. A. (2005). Poly-(L-alanine) expansions form core /1-sheets that nucleate amyloid assembly. Proteins 61, 579-589. 

The results of a comprehensive 13 C CP/MAS NMR study of the structure of solid polypeptides, prepared by polymerization of amino acid N-carboxyanhydrides under various conditions, have been reported105,107. In the case of poly(L-alanine) it was found that... 

In the early 1980 s Julia and Colonna published a series of papers which, to some extent, filled the gap left by the natural biocatalysts. The Spanish and Italian collaborators showed that a, -unsaturated ketones of type 1 underwent asymmetric oxidation to give the epoxide 2 using a three-phase system, namely aqueous hydrogen peroxide containing sodium hydroxide, an organic solvent such as tetrachloromethane and insoluble poly-(l)-alanine, (Scheme 1) [12]. The reaction takes place via a Michael-type addition of peroxide anion (the Weitz-Scheffer reaction). 

Julid and Colonna showed that, as expected, poly-(L)-leucine and poly-(i)-isoleucine could be employed in place of poly-(L)-alanine, while poly-(L)-valine gave poorer results in terms of yields and stereoselectivity [13]. Some other eno-nes were tried without success and nucleophiles other than peroxide anion were... 

Scheme 1. Reagents and Conditions (i) H2O2, H2O, NaOH, CCI4, poly-(L)-alanine...

A research team from Bloemfontein (South Africa) have also taken advantage of the Julia and Colonna oxidation in elegant research aimed at the synthesis of optically active flavonoids. Bezuidenhoudt, Ferreira et al. have oxidised a range of chalcone derivatives using poly-(L)-alanine in the three phase system to afford optically active epoxides 4 which were readily cyclised to target compounds of the dihydroflavinol type 5, (Scheme 3) [16]. 

From such a background, some kinds of polypeptide blend samples have been studied by solid state NMR.27,72 74 Especially, detailed information for four kinds of blend samples such as poly(L-alanine) (PLA)/poly(L-valine) (PLV), PLA/poly(L-isoleucine) (PLIL), poly(D-alanine) (PDA)/PLV and polyglycine (PG)/PLV blends, have been reported. Here, let us describe some reasons why PLA/PLV, PDA/PLV, PLA/PLIL and PG/PLV blends are interesting systems. PLA and PDA in the solid-state can take the a-helix and (3-sheet forms due to intra- and intermolecular HBs, respectively. PG in the solid-state can take the 3j-helix (PG-II) and (3-sheet (PG-I) forms due to intra- and intermolecular HBs, respectively. However, PLIL and PLV in the solid state can predominantly take the (3-sheet form as the stable conformation. For this reason, it is interesting to know whether an isolated a-helix or 3i-helix form polypeptide surrounded by a major polypeptide in the (3-sheet form can take the helical conformation, or not, due to the balance between intramolecular and intermolecular hydrogen bonds. In addition, we would like to know whether a polypeptide in the (3-sheet form surrounded by a major polypeptide in the a-helix or 3 -helix form can take the (3-sheet form. 

Similarly, good results were obtained with poly-(L)-alanine, poly-(L)-leucine and poly-(L)-isoleucine, whereas with poly-(L)-valine or random copolymers reduced chemical yields as well as asymmetric induction were obtained. Chemical and optical yields are closely related in all cases. The enantiomeric excesses obtained increased as the average chain length of the catalyst increased varying from 10 to 30 amino acids (ee values between 50 to 99%). For high ee values it seems to be essential that the polymer chain is at least 10 units154. The degree of asymmetric induction decreases as the temperature is raised. The amount of catalyst only influences the chemical yield, not the optical yield of... 

PHEG = poly-N5-(2-hydroxyethyl)L-glutamine PHPG = poly-N5-(3-hydroxypropyl)L-glutamine PHBG = poly-N5-(4-hydroxybutyl)L-glutamine PLA = poly-L-alanine... 

Gratzer and Doty (30) showed that when poly-DL-glutamic add was attached to the chain ends of water-insoluble poly-L-alanine (PLA), the resulting block... 

A partition function is derived for a simple model of interacting helices in a short (20 residues) chain of poly-L-alanine. It Is found that interhelical hydrophobic bonds effect a marked stabilization of helical forms, and give rise to a sharp transition of the type found in many polymers. 

N 058 "Moments and Distribution Functions for Polypeptide Chains. Poly(L-alanine) ... 

RIS theory, in the form appropriate for branched molecules, is used to calculate the mean-square unperturbed radius of gyration, < s2>0, for cross-linked polyglycine, poly(L-alanine),poly(L-proline),poly(i-alanyl-D-alanine),poly(i.-prolyl-L-pro lylglycine),poly(L-prolyl-i.-alanylglycine ,poly(glycyl-L-alanyl-L-pro line), andpoly(L-aianyl-L-alanylgIycine).Thecentral amino acid residue in each polypeptide chain is replaced by the L-cysteinyl residue involved in cross-link formation. Each cross-linked molecule is considered to contain two trifunctional branch points, the a-carbon atoms of the two... 

The synthetic polypeptides poly-L-alanine (—NH. CH(CH3). CO—)p (a form) and poly-y-methyl-L-glutamate... 

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