Acids polyamino

Protein-Based Adhesives. Proteia-based adhesives are aormaHy used as stmctural adhesives they are all polyamino acids that are derived from blood, fish skin, caseia [9000-71 -9] soybeans, or animal hides, bones, and connective tissue (coUagen). Setting or cross-linking methods typically used are iasolubilization by means of hydrated lime and denaturation. Denaturation methods require energy which can come from heat, pressure, or radiation, as well as chemical denaturants such as carbon disulfide [75-15-0] or thiourea [62-56-6]. Complexiag salts such as those based upon cobalt, copper, or chromium have also been used. Formaldehyde and formaldehyde donors such as h exam ethyl en etetra am in e can be used to form cross-links. Removal of water from a proteia will also often denature the material. 

The tendencies of the amino acids to stabilize or destabilize a-helices are different in typical proteins than in polyamino acids. The occurrence of the common amino acids in helices is summarized in Table 6.1. Notably, proline (and hydroxyproline) act as helix breakers due to their unique structure, which fixes the value of the —N—C bond angle. Helices can be formed from either... 

S. Fox, K. Harada, and D. Rohlfmg, Polyamino Acids, Polypeptides and Proteins, (M. Stahman, ed.), U. Wisconsin Press, Maddison, Wisconsin (1952). 

Komori and Nonaka132,133 electrochemically oxidized methyl, isopropyl, n-butyl, isobutyl, r-butyl and cyclohexyl phenyl sulfides (108) and cyclohexyl p-tolyl sulfide (109) to their sulfoxides using a variety of polyamino acid-coated electrodes to obtain the range of e.e. values shown in parentheses. The highest enantiomeric purities were obtained using an electrode doubly coated with polypyrrole and poly(L-valine), an electrode which also proved the most durable of those prepared. 

Schaffert D, Badgujar N, Wagner E (2011) Novel Fmoc-polyamino acids for solid-phase synthesis of defined polyamidoamines. Org Lett 13 1586-1589... 

Dunnick, J.K., McDougall, R., Aragon, S., Coris, M., and Kriss, J. (1975) Vesicle interactions with polyamino acids and antibody in vitro and in vivo studies./. Nucl. Med. 16, 483-487. 

However, the two methods of choice for the oxidations of a, (B-unsaturated ketones are based on lanthanoid-BINOL complexes or a biomimetic process based on the use of polyamino acids as catalysts for the oxidation 1"1. 

The biomimetic protocol was invented by Julia and Colonna, and involves the use of polyamino acids (such as poly-(L)-leucine) as the catalysts for peroxide oxidation of chalcones, styryl alkyl ketones and conjugated alkenones. The substrate range is broad, especially when using immobilized catalysts and an organic solvent containing the substrate, urea-hydrogen peroxide and an organic base (Scheme 22)[101]. 

Fandrich, M., and Dobson, C. M. (2002). The behaviour of polyamino acids reveals an inverse side chain effect in amyloid structure formation. EMBOJ. 21, 5682-5690. Fandrich, M., Fletcher, M. A., and Dobson, C. M. (2001). Amyloid fibrils from muscle myoglobin. Nature 410, 165-166. 

POLYAMINO ACIDS Aliphatic polyamino acids irradiated in the solid state have been reported to undergo N-Ctf, main-chain, bond scission on gamma radiolysis (9) and the stable radical intermediates formed following radiolysis at 303 K are alpha carbon radicals, as observed in the N-acetyl amino acids. 

Polyacetylene, vibrational spectra, 42 196 Poly acids, defined, 41 117 Polyalkenamers,24 134,135 Polyamino acids, thermal, 20 374-377 catalysis by, 20 379... 

Polyamino acids are easy to prepare by nucleophUe-initiated polymerisation of amino acid JV-carboxyanhydrides. Polymers such as poly-(L)-leucine act as robust catalysts for the epoxi-dation of a wide range of electron-poor alkenes, such as y-substituted a,Ji-unsaturated ketones. The optically active epoxides so formed may be transformed into heterocyclic compounds, polyhydroxylated materials and biologically active compounds such as dUtiazem and taxol side chain. 

Keywords Polyamino acids. Optically active epoxyketones. Synthesis of dUtiazem and taxol side-chain. Asymmetric oxidation. 

Two key points were made in the latter paper. First the polyamino acid-catalysed reactions could be conducted on a substantial scale (250 g). Secondly, the catalyst could be recovered and recycled with no loss in yield or enantioselec-tivity. In addition, the SK F group emphasised the need to pre-swell the polymer with organic solvent and aqueous sodium hydroxide for about 20 h prior to its employment in the reaction. 

In this review, recent advances in the preparation and use of polyamino acid catalysts are included these latest results are a result of developments utilising as a starting point the seminal studies undertaken earlier by the research groups described above. 

A number of amines have been investigated for their suitability as polymerisation initiators, including aliphatic amines (such as butylamine [17] and 1,3-diaminopropane [18]), polymer supported amines (such as cross-linked aminomethyl polystyrene [CLAMPS], Fig. 1, giving rise to immobilised polyamino acids [19]) and resin-bound amines. 

While immobilised polyamino acids can be recovered from a reaction and re-used in subsequent operations, it has been found that after repeated recycling the quality of the catalyst declines, resulting in increased reaction times and reduced stereoselectivity. The quality of the catalyst declines particularly quickly when it is used in the recently developed biphasic epoxidation conditions (see Sect. 4.1.2). This gradual decay of the polyamino acid catalyst led to the development of a regeneration procedure. 

A suspension of the recycled polyamino acids in toluene is stirred vigorously with 4.0 M aqueous sodium hydroxide solution for 16 h. The procedure may be repeated to ensure optimum regeneration. The polyamino acid recovered from this procedure shows catalytic activity and stereoselectivity comparable to the freshly made polyamino acid. 

A second regeneration procedure, similar to the above but using small amounts of aqueous hydrogen peroxide in addition to the sodium hydroxide solution, has also been developed. This latter procedure regenerates the recycled polyamino acid so effectively that usually only one treatment is required. 

The mechanism behind the polyamino acid-catalysed asymmetric epoxidation is particularly difficult to understand. The active catalyst exists as a paste or a gel following treatment with the organic solvent. Thus, studies on the helix/)8-sheet structure of the amorphous solid, the form of the polyamino acid in the absence of solvent, are probably not meaningful in this context. 

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