Poly conformational forms

The microtubule-bound complex of 74 revealed the F-F distance to be 6.5 0.5 A (Figure 6), which is larger than that observed in the poly crystalline form by ca. 1 A. It is very likely that the microtubule-bound conformation of 74 is achieved by a small distortion of the solution conformation (the recognition conformation), the latter being described by either conformer B or C (Figure 4). 

Nakano et al) reported a C CP/MAS NMR study on poly(L-Alanine) (PLA)/Polyglycine (PC) blends. The comparison between the C CP/MAS spectra of the blends and those of the parent polymers discloses that upon blending, new conformations of PLA and PC are fonned, which is closely related to the presence of intermolecular hydrogen-bonding interactions. Tip measurements demonstrate that the major parts of PC and PLA in the blends, which are in 3i-helix and a-helix conformation forms respectively, are phase separated. On the other hand, the p-sheet forms of PC and PLA, which are newly formed upon blending, exhibit similar values, demonstrating that these two parts are miscible at the scale of 3-4 nm. 

Poly-L-proline exists in two different conformations form I, which assumes a right-handed helix and has each peptide bond in the cis configuration (Traub and Shmueli, 1963) and form II, which is a left-handed helix and has its peptide bonds in the trans configuration (Sasisekharan, 1959 Cowan and McGavin, 1955). Isemura et at. (1968) have differentiated these two forms of poly-L-proline by characteristic far-infrared bands. Form I has two broad bands near 280 and 160cm" and form II... 

The semi-empirical conformational energy calculations of poly-cis-5-ethylproline (PC5EP) predict that the helical structure may exist in two conformational forms such as I and II. Experimental results confirmed that in solution two major conformations may be assumed by the poly-cis-5-ethyl-D-proline. However, the calculations for poly-trans-5-ethyl-D-proline indicated that only one form may be allowed.Spectroscopic data (Circular Dichroism, NMR) showed the polypeptide exists in a poly-L-proline form-I-type helix and changes slowly to some intermediate conformation. The slow muta-rotation is partially due to the steric interactions of the ethyl group with the carbonyl group of the amide during the mutarotation. 

The relative stability of poly-L-proline helices may be altered so that one conformation form becomes energetically unfavorable and thus not allowable, e.g., poly-2-methyl-L-proline, poly-trans-5-ethyl-L-proline, and poly-trans-3-ethyl-D-proline. 

In some cases, vibration bands are also conformation-sensitive. In particular, when a polymer exists in several crystal forms, different chain conformations may exist in these crystal modifications one example is poly(vinyhdene fluoride) (PVDF). At least four types of crystal modifications are known forms I, II, Hpoiar, and III (26). Form I has nearly a zig-zag chain conformation. Forms II and Ilpoiar exhibit the glide-type TGTG conformation, while form HI has a TTTGTTTG conformation. The ir spectra of these crystal modifications are shown in Fig. 9 (27). For example, the intensive bands observed in the spectra of form I are 1275, 840, and 510 cm and others correspond to the vibration modes intrinsic to long trans sequences of. .. TTTT. The bands at 800, 766, 610, and 530 cm and others in the spectra of form II are attributed to the conformation sequence of TG. On the other hand, in form III, the TG and TT bands coexist in addition to the bands characteristic of the TTTG sequence (27). 

The CD spectrum of poly(rA) changes with pH, chain length and temperature. At neutral pH, poly(rA) is unprotonated and forms a single-stranded helix. At acidic pH, poly(rA) forms dimers. Depending on the pH there are two conformational forms, one where poly(rA) is fully protonated, and one where it is half-protonated. Figure 8B shows the... 

The most possible reason may be in the higher free energy of the protein adsorption on PolyPROPYL A materials. Chemisorbed neutral poly(succinimide) of molecular weight 13000 apparently forms a diffuse interface as predicted by theory (see Sect. 2.2). Controversially, a short polyethyleneimine exists on a surface in a more flat conformation exhibiting almost no excluded volume and producing... 

It is typical, for instance, of syndiotactic polystyrene (s-PS) [7-9] and syndiotactic poly- p-methylstyrene (s-PPMS) [10] to present crystalline forms with a transplant conformation of the chains (shown for s-PS in Fig. 1) as well as crystalline forms with sequences of dihedral angles of the kind TTG+G+ (or the equivalent G G TT), corresponding to a s(2/l)2 helical symmetry of the chains (shown for s-PS in Fig. 1). 

An analogous case, of identical chain conformations as well as of similar unit cell dimensions, have been described for the two crystalline forms of poly-p-phenylene terephtalamide [33-36] (better known with the trade name of Kevlar). The projections along the c axis of the packing of the chains proposed for the two forms [36] has been sketched in Fig. 8, corresponding to the localization of the chain axes in (0,0, z) and (1/2,1/2, z) for the more common polymorph, in (0, 0, z) and (1/2,0, z) for the other polymorph. 

When rfc = 0, the polymeric structure is considered to be open enough (i = 0) that any subsequent oxidation will not occur under conformational relaxation control, hence P = 1. Every polymeric chain at the poly-mer/solution interface acts as a nucleus a planar oxidation front is formed that advances from the solution interface toward the metal/polymer interface at the diffusion rate. 

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