Conformational changes in solution

Silk type Function Proteins (ratio )a Predicted structure from sequence Amino acid (%r Structure in solution Conformational change in solution Fiber degree of crystallinity (%y Fiber extensibility <%)s... 

The soluble polythiophenes are the first conducting polymers that can be taken above their glass transition without decomposition and it will be interesting to study morphology-property relationships. Heeger et al.262) have recently described conformational changes in solutions of poly-3-hexylthiophene which seem to involve a coil-helix transformation as the temperature is decreased or a poor solvent is added. 

The metal-NADH distance determined by fluorescence studies on the cobalt-substituted enzyme, using binary NADH, thio-NADH, and Rose Bengal/enzyme complexes, differs from the above.242 The minimum metal-NADH distance determined by Forster calculations based on the energy transfer from bound ligand to cobalt(n) is reported as 19 A. It is thought possible that the discrepancy between this value and that determined by X-ray diffraction may be due to conformational changes in solution. 

Nickel(II) complexes have long been known to undergo several types of structural and conformational changes in solution. These include ... 

It seems possible to amplify the photostimulated conformational changes in solution at the molecular level into shape changes of polymer gels or solids at the visible macro level. The first proposal to use the structural changes at the molecular level for direct conversion of photon energy into mechanical work has been made by Merian (13.) in 1966. Since then, many materials, most of which contained azobenzene chromophores, have been reported to show photostimulated deformation(JM). Till now, however, the reported deformations were limited to less than 10%. In addition, Matejka et. al. have pointed out that in many cases photo-heating effect instead of photochemical reaction plays a dominant role in the deformation(15,16). 

The photostimulated dilation of the gel is well understood by the osmotic pressure mechanism. Although the electrostatic repulsive forces between the positive ions play an important role in the conformational changes in solution, they are considered to make a minor contribution to the gel dilation. 

Katta, V., Chait, B.T. (1993) Hydrogen/Deuterium Exchange Electrospray Ionization Mass Spectrometry A Method for Probing Protein Conformational Changes in Solution. J. Am. Chem. Soc. 115 6317-6321. 

Polysialic acid has been reported to undergo conformational changes in solution. Several left-handed helical epitopes with different pitches have been calculated and their relative occurrence in solution has been discussed [131, 132], Polysiahc acid bound to the cell surface adopts a similar average epitope as in solution [133], A sialic acid decamer is bound in an extended helix to the monoclonal antibody 735 [134], In contrast, a sialic acid pentamer has been described to bind endoNF in a compressed helical epitope [135] which has also been measured for polysialic acid in solution [132] and on the cell surface [133], Therefore, polysialic acid selectively undergoes conformational changes upon binding to endosiahdase or monoclonal antibody. 

As has been clearly recalled in the other chapters concerning optically active polymers, most of the work has been devoted to conformational studies either to show secondary structures or to observe conformational changes in solution. 

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