Angular Relations between Two Polypeptides in Hinged Polymers (original) (raw)
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Physical Review Letters, 1983
A rod-to-coil conformational transition is demonstrated for polydiacetylene, 4-butozycarbonylmethylurethane, in solution. With use of quasielastic light scattering, a coillike structure with relatively small hydrodynamic radius is indicated for the polymer in a good solvent, CHC13. As the proportion of nonsolvent (hexane) is increased, the hydrodynaxnic radius increases abruptly to a value consistent with the molecule being a rigid rod.
Helix-Coil transition in polypeptides: A microscopical approach
Biopolymers, 1990
ABSTRACT In the framework of an earlier constructed model [N.S. Ananikyan et al. (1990) Biopolymers, Vol. 30, pp. 357-367], some analytical estimates for the correlation length and degree of helicity near the transition point were obtained in the case of an arbitrary topology of hydrogen bond closing (delta). It was shown that the Zimm-Bragg cooperativity parameter sigma is determined by the set of (delta-1) amino acid residues and so is nonlocal. An analytic expression for cooperativity parameters in a heteropolypeptide chain was obtained and numerical calculations showed that in case of heteropolypeptide with random primary structure the nonlocality of cooperativity parameter influenced the temperature dependence of helicity degree.
Extension of Rod-Coil Multiblock Copolymers and the Effect of the Helix-Coil Transition
Physical Review Letters, 2000
The extension elasticity of rod-coil mutliblock copolymers is analyzed for two experimentally accessible situations. In the quenched case, when the architecture is fixed by the synthesis, the force law is distinguished by a sharp change in the slope. In the annealed case, where interconversion between rod and coil states is possible, the resulting force law is sigmoid with a pronounced plateau. This last case is realized, for example, when homopolypeptides capable of undergoing a helix-coil transition are extended from a coil state. PACS numbers: 61.25.Hq, 61.41. + e, 87.15.He With the advent of single molecule mechanical measurements it became possible to study the force laws characterizing the extension of individual macromolecules [1]. In turn, these provide a probe of internal degrees of freedom associated with intrachain self-assembly or with monomers that can assume different conformational states. A molecular interpretation of the force laws thus obtained requires appropriate theoretical models allowing for the distinctive "internal states" of each system. The formulation of such models is a challenging task in view of the complexity and diversity of the systems investigated. These include DNA [2], the muscle protein titin [3] and the extracellular matrix protein tenascin [4], the polysaccharides dextran [5] and xanthan , as well as the synthetic polymer poly(ethelene-glycol) .
Journal of the American Chemical Society, 1976
Measurements of the macroscopic properties of synthetic polypeptide liquid crystals indicate that the helix-coil pretransition behavior parallels that reported in dilute solution studies. As varying amounts (I l O % by volume) of TFA were added to PBLG in dioxane (24 mg/cm3 dioxane), observations were made on the pitch in zero magnetic field; in orientated nematic structures of the same liquid crystals, measurements of the diamagnetic susceptibility anisotropy, Ax. and the reorientation rate in a magnetic field were made. The results obtained indicate that the asymmetric part of the intermolecular potential increases across the pretransition range while the twist elastic constant K 2 2 remains unchanged. Even small amounts of TFA (-1% by volume) are sufficient to induce a sharp increase in the fluidity, reminiscent of the behavior of dilute, isotropic solutions of PBLG (i.e., breakdown of an aggregated network). In addition, this work demonstrates that extracting microscopic polypeptide side chain structural information from A x measurements is feasible. Specifically, the average orientation of the PBLG side chain as well as its mobility can be monitored as TFA is added to the liquid crystal. The sum of evidence supports the idea that, in the pretransition region, the helix remains rodlike while there is an increased mobility of the side chain as T F A is added. phase transitions with provisions for fitting the abruptness of the transition "cooperativity" to experimental observations of the helix-coil transition.3a And, as new physical parameters become experimentally accessible, the measurement and usefulness of such parameters are frequently demonstrated via
On the Rigidity of the α-Helix as Measured by Dielectric Studies
Polymer Journal, 1972
The persistence length and flexural rigidity of the a-helix of poly(rbenzyl-L-glutamate) have been found to be 1000± 100A and 4±0.4 x 10-19 dyn/cm 2 , respectively, from a dielectric study in m-cresol. Since the electric dipole moment of the a-helix is expected to be proportional to the end-to-end distance, flexural rigidity can be estimated in the theoretical framework of the stiff-chain model. The effect of side-chain moment is also discussed.