Conformation of poly

Several years ago Makino et al. 86) studied the influence of anions on the conformation of poly-[L-methionine-S-methylsulfonium] salts in solution. They found that especially perchlorate will induce a-helix formation whereas Cl- and Br do not. Since then several authors 87 92) have found a similar a-helix inducing effect in the case of poly-L-lysine (Lys) and other BPAA at low pH-values where the polymer molecules usually attain an extended conformation due to the electrostatic repulsion of the ammonium groups. Therefore, the a-helix inducing effect is obviously an... 

In order to develop compounds that can selectively target duplex RNA, Sinha et al. [ 194] studied the interaction of berberine with two different conformations of poly(rC) poly(rG) structures. Poly(rC) poly(rG) has been shown [15,215] to exist in two conformations depending on the pH of the solution, the A-form at physiological pH and the protonated form at pH 4.3. These two conformations have been characterized to have clearly defined but distinctly different circular dichroic and absorption spectral characteristics. Both the A-form and the protonated form of the RNA induced moderate hypochromic change and bathochromic shifts in the absorption maxima peaks at 344 nm and 420 nm of the alkaloid with three isosbestic points centered around 357,382 and 448 nm. Binding of berberine to both forms enhanced the fluorescence intensity, which was higher with the protonated form than with the A-from, suggesting clear differences in the nature of orientation... 

The Pn conformation of poly-L-proline (PP) or collagen in the solid state could be identified from X-ray fiber diffraction results (Cowan and McGavin, 1955). Persistence of this basic structure in solution was inferred from the resemblance between the CD spectra of solutions and films of the polypeptide. The CD spectra of the charged forms of PGA and PL closely resemble that of Pn (compare Fig. IB, 1C, and ID) however, these spectra differ significantly from those of PP peptides at high temperature or in the presence of high concentration of salts... 

An illustrative example is the work of Clark et al, on the conformation of poly(vinyl pyrrolidone) (PVP) adsorbed on silica 0). These authors determined bound fractions from magnetic resonance experiments. In one instance they added acetone to an aqueous solution of PVP in order to achieve theta conditions for this polymer. They expected to observe an increase in the bound fraction on the basis of solvency effects as predicted by all modern polymer adsorption theory (2-6), but found exactly the opposite effect. Their explanation was plausible, namely that acetone, with ability to adsorb strongly on silica due to its carbonyl group, would be able to partially displace the polymer by competing for the available surface sites. 

Figure 19 Conformations of poly(methyl-3,3,3-trifluoropropylsilylene), 87, in coordinating and non-coordinating solvents.

These facts can be explained by a simple comparison of the stretched conformations of poly(p-phenylene terephthalamide) and poly(m-phenylene iso-phthalamide). Whereas the all-para linked polyamide can build up many hydrogen bonds to the neighboring molecules, this is less possible for the all-wcta linked polymer ... 

Figure 11.38 (Left) Fourth generation monodendron with a hexaethylene glycol tail. (Right) Proposed conformations of poly(benzyl ethyl ether) monodendrons oriented at the air-water interface.

Kampf JP, Frank CW, Malmstroem EE, Hawker CJ. Stability and molecular conformation of poly(benzyl ether) monodendrons with oligo(ethylene glycol) tails at the air-water interface. Langmuir 1999 15 227-233. 

The term tertiary electroviscous effect is applied to the changes in the conformation of poly electrolytes that are caused by //t/ramolecular double-layer interactions. It is customary to extend this definition to include all effects in which the geometry of the system is altered as a result of double-layer interactions. 

What is the explanation for the effect of the pH changes on the conformations of poly(Glu) and poly(Lys) Why does the transition occur over such a narrow range of pH ... 

Further investigations in this field will probably lead to interesting conclusions on the conformation of poly-acrylamides in solution. 

Figure 2.33 Distorted cis-trans planar conformation of poly(dichlorophosphazene).70-72 Reproduced by permission of...

We have carried out a computational and experimental study on the "random coil" conformation of poly-L-Tyr to answer the question about the local order in the "random coil" conformation which had been addressed before by researchers in a number of fields [39,40]. This study was made possible by our successful application of the DECO model (cf. Section 3) to interpret VCD spectra of model compounds. Our efforts to deduce a structure for the "random coil conformation of (homo)-polyamino acids was prompted by the observation by us and others [41] that the "random coil" in systems (such as poly-L-Tyr) produces VCD features which are nearly equal in magnitude, and opposite in sign, to those produced by the a-helical conformation (cf. Figure... 

Figure 28 Diagrams of a sequence of conformations of poly(L-alanine) encountered at various successive stages on a conformational pathway during a folding simulation, starting from a fully extended conformation.190 The final structure is the same as shown in Figure 29e.

S. Tanaka and H. A. Scheraga, Macromolecules, 8, 516 (1975). Theory of the Cooperative Transition Between Two Ordered Conformations of Poly(L-proline). III. Molecular Theory in the Presence of Solvent. 

The effect of base stacking interaction on the conformation of poly-VAd was also studied by osmometry, intrinsic visosity and light-scattering measurements24). 

Conformations of the polymers were studied by CD and optical rotation measurements. Poly-L-lysine is known to exist in disordered, helical and -conformation, depending on the temperature, pH of the system and the solvent used. The side chain of the polymer has a significant effect on the backbone conformation. At neutral pH, poly-L-lysine exists in a random coil structure while at pH above 10, the e-amino group becomes a neutral form and the polymer undergoes transition to a helical structure. In order to elucidate the effect of base substituents on the conformation of poly-L-lysine, CD spectra of the copolymer were measured. 

Fig. 7 Possible conformations of poly(cyclopent-1 -enylene-1 -vinylene)s and poly(cyclohex-l-ene-3-methylidene)s...

Fig. 4-4. A schematic illustration of the conformation of poly(4-vinylimidazole) in ethanol-water.

Fig. 11-4. Possible conformations of poly inerchains al the surfaces of chain-folded single crystals, (a) Adjacent reentry model with smooth, regular chain folds, (b) adjacent reentry model with rough fold surface, and (c) random reentry (switchboard) model.

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