Polypeptides copolypeptides

Fig. 1. A scheme of conformational generation of polypeptides, copolypeptides and proteins.

The polymerizations initiated by HMDS and N-TMS amines usually complete within 24 h at ambient temperature with quantitative monomer consumption. These polymerizations in general are slower than those mediated by Deming s Ni(0) or Co (0) initiators (about 30-60 min at ambient temperature) [19, 24, 25], but are much faster than those initiated by amines at low temperature or using amine hydrochloride initiators [20]. These HMDS and N-TMS amine-mediated NCA polymerizations can also be applied to the preparation of block copolypeptides of defined sequence and composition [22]. This organosilicon-mediated NCA polymerization, which was also shown by Zhang and coworkers to be useful for controlled polymerization of y-3-chloropropanyl-L-Glu NCA [43], offers an advantage for the preparation of polypeptides with defined C-terminal end-groups. 

Fig. 1 Vesicle construct formed from poly(L-lysine)-i)-poly(L-leucme) polypeptides where the poly(L-leucine) block corresponds to the a-helical hydrophobic segments and the poly (L-lysine) block corresponds to the random coil hydrophilic segments. Note that this is one specific example and not all vesicle constructs have a-helical and random coil blocks. Moreover, the amphiphilic copolymer can be comprised of either a pure block copolypeptide or a macromolecule consisting of a polypeptide and another type of polymer. Adapted from [20] with permission. Copyright 2010 American Chemical Society...

These transformations arise from the energetical stability caused by intramolecular or intermolecular hydrogen bond (HB) interactions. Thus, by the balance of intramolecular and intermolecular HB interactions in polypeptide blends, it is expected that the strength of intermolecular interaction in the blends is different from those in homopolypeptides then new conformations can be formed by intermolecular HB interactions that do not exist originally in homopolypeptides. There are many studies on intermolecular HB interactions in homopolypeptides and copolypeptides in the solid state, but to the best of our knowledge there is little study on intermolecular HB interactions in polypeptide blends except for our previous studies. 

A mean-square helical hydrophobic moment,

, is defined for polypeptides in analogy to the mean-square dipole moment, , for polymer chains. For a freely jointed polymer chain, is given by X rr , where mi denotes the dipole moment associated with bond /. In the absence of any correlations in the hydrophobic moments of individual amino acid residues In the helix,

is specified by X Wj2, where H denotes the hydrophobicity of residue /, Matrix-generation schemes are formulated that permit rapid evaluation of

and . The behaviour of

I

is illustrated by calculations performed for model sequential copolypeptides. 

Polymeric polypeptides have long been the focus of many research groups and are, therefore, covered in Section 14.2. Early on, these polymers were considered to be protein model structures. Discussions of homopolypeptides prepared by a-amino acid TV-carboxy-anhydride (NCA) polymerizations are an important part of the volume (Sections 14.2,14.2.1, and 14.2.1.1). 19,20 Copolypeptides are prepared by routes which lead to random or sequential copolymer structures (Sections 14.2.2 and 14.2.3).[21,22 ... 

The recent studies on the structure and properties of polypeptide liquid crystals, which are formed in solution as well as in the solid state, are reviewed in this article. Especially the cholesteric pitch and the cholesteric sense (right-handed or left-handed), which are characteristic factors of cholesteric liquid crystals, are discussed in detail in relation to the effects of temperature, concentration, and solvent. Further cholesteric liquid crystalline structure retained in cast fdms and thermotropic mesomorphic state in some copolypeptides are also discussed. 

Abstract The aggregation behaviour of biomimetic polypeptide hybrid copolymers and copolypeptides is here reviewed with a particular eye on the occurrence of secondary structure effects. Structure elements like a-helix or / -sheet can induce a deviation from the classical phase behaviour and promote the formation of vesicles or hierarchical superstructures with ordering in the length-scale of microns. Polypeptide copolymers are therefore considered as models to study self-assembly processes in biological systems. In addition, they offer a great potential for a production of novel advanced materials and colloids. 

This review covers the literature on the aggregation of (homo)polypeptide hybrid copolymers and copolypeptides in dilute solution, which was published up to June 2005 a recent review on amphiphiles consisting of peptide sequences is given elsewhere in [12]. It was a particular concern to give a comprehensive overview on secondary structure effects in the self-assembly of these copolymers. Briefly presented are also structures in concentrated solutions (lyotropic phases) and in heterophase systems (see also [14]). 

Besides the polypeptide hybrid block copolymers described earlier, there exist a few examples of purely peptide-based amphiphiles and block/random copolymers (copolypeptides) (Fig. 10). In the latter case, both the core and corona of aggregates consist of a polypeptide. Any of the studies reported so far dealt with aggregation in aqueous media. 

There are several ways to prepare peptides, polypeptides, and artificial proteins carrying these aromatic amino acids as their constituents. Homopolypeptides can be prepared by the polymerization of amino acid N-carboxyanhydrides (NCAs) derived from the corresponding amino acids ( ). Sequential polypeptides of the form (ABC...W) are prepared by the polymerization of the corresponding oligopeptide active esters ABC...W-X. Small peptides of any sequence can be synthesized by a step-by-step procedure (5). Finally, cultivation of some bacteria in the presence of artificial amino acids will possibly incorporate them into the proteins produced by the bacteria. In the following, attention will be focused on homopolypeptides and sequential copolypeptides carrying one type of chromophore on a chain. 

Can H cramps NMR become an effective means for conformational analysis of polypeptides and proteins in the solid state In order to answer this question, in this section, we focus on and discuss a study on correlation between the H chemical shifts and the main-chain conformation (secondary structure) of synthetic polypeptides.Homopolypeptides and copolypeptides are useful as models for structural analysis of natural proteins. Homopolypeptide is the simplest and the most basic model polypeptide for NMR studies of proteins. 

The linear polypeptide hybrid block copolymers and block copolypeptides reported to form vesicles in aqueous solution are listed in Fig. 1. 

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