Conformational change, temperature

Probably the main utilization of low-temperature spectroscopic studies in biophysics has been to trap short-lived intermediate chemical states of a protein. Typically the chromophore alone is the object of study, and the protein is viewed basically as a structure which simply holds the chromophore in place or may contribute some critical amino acids in close proximity to the chromophore. The protein is not believed to play an overtly dynamic role, a dynamic role being one where the reaction process is steered by time-dependent protein conformational changes. Temperature is used to slow down or arrest the reaction kinetics occurring at the chromophore and perhaps to discover additional chemical states which have too short a lifetime to be observed at room temperature. Such kinds of kinetic arrest studies have been successfully used in studies of heme... 

Limiting Conformational Changes during High Temperature Simulations... 

High temperature searches of conformational space (see Quenched Dynamics" on page 78), can produce unwanted conformational changes, such as cis-tmnx peptide flips, ring inversions, and other changes that you cannot reverse easily by geometry optimization. You can use restraints to prevent these changes. 

Structures A and A are nonsuperimposable mirror images of each other Thus although as 1 2 dichloro cyclohexane is chiral it is optically inactive when chair-chair interconversion occurs Such interconver Sion IS rapid at room temperature and converts opti cally active A to a racemic mixture of A and A Because A and A are enantiomers interconvertible by a conformational change they are sometimes re ferred to as conformational enantiomers... 

Experimental results corroborate that shifts of 1.2 eV are always present if any of the variables acting on the electrochemical process are changed the solvent, the salt, or the temperature of work. We cannot attribute the observed shift to solvatochromic, counter-ion-chromic, or thermochromic effects taking place inside the film during oxidation-reduction processes. So, as predicted, these shifts are a consequence of the way the chains store or relax energy through conformational changes stimulated by electrochemical oxidation or reduction, respectively. 

The ability to detect discrete rovibronic spectral features attributed to transitions of two distinct conformers of the ground-state Rg XY complexes and to monitor changing populations as the expansion conditions are manipulated offered an opportunity to evaluate the concept of a thermodynamic equilibrium between the conformers within a supersonic expansion. Since continued changes in the relative intensities of the T-shaped and linear features was observed up to at least Z = 41 [41], the populations of the conformers of the He - lCl and He Br2 complexes are not kinetically trapped within a narrow region close to the nozzle orifice. We implemented a simple thermodynamic model that uses the ratios of the peak intensities of the conformer bands with changing temperature in the expansion to obtain experimental estimates of the relative binding energies of these complexes [39, 41]. 

Lowering the temperature in the lipase-catalyzed resolution usually enhances the enantioselectivity. The phenomenon does not come from the temperature-induced conformational change of lipase, but it is understandable on the basis of the theory of physical organic chemistry as explained below. ... 

Flacche, L. S., Washington, G. E., and Brant, D. A., Light scattering investigation of the temperature-driven conformation change in xanthan, Macromolecules, 20, 2179, 1987. 

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