Molecular mechanisms of yielding

The relation of the plastic deformation of MGIMx copolymers with the corresponding ft transition motions is based on the molecular mechanism of yielding developed for PMMA in Sect. 3.1.1.6. 

A considerable number of experimental extensions have been developed in recent years. Luckliam et al [5] and Dan [ ] review examples of dynamic measurements in the SFA. Studying the visco-elastic response of surfactant films [ ] or adsorbed polymers [7, 9] promises to yield new insights into molecular mechanisms of frictional energy loss in boundary-lubricated systems [28, 70]. 

The large region of yield in materials that fail by tough fracture arises as the molecules of the polymer rearrange themselves in response to the applied stress. This is different from the mechanism of yield in metals, where planes of metal atoms slide over one another. In polymers, the molecular movement... 

Despite the many decades amyl nitrite and glyceryl trinitrate have been used in therapy, it is only in recent years that the molecular mechanism of action of the nitrovasodilators has begun to be understood [3-5]. The drugs act by releasing nitric oxide (NO, a neutral radical usually written simply as NO), which produces smooth muscle relaxation in blood vessels and exhibits a range of other biological effects [6]. Thus, bioactivation to yield NO precedes the main therapeutic effect of nitrovasodilators and would justify their classifica-... 

Raman difference spectroscopy has also been used to understand the molecular mechanism of viral core assemblies yielding information on viral subunits from precursor and mature states. Benevides et al. employed Raman difference spectroscopy to investigate conformational changes of the protein building blocks of the icosahedral core of a double-stranded RNA (p6 virus during viral procapsid and capsid assembly [18],... 

Well-defined nickel-sulfur complexes that enable a stepwise combination of CO, alkyl, and thiol groups to give thioesters can be anticipated to yield deeper insight into the molecular mechanism of the acetyl-CoA synthesis (142, 149). The complex [Ni(C3Me2—S4)] afforded an example for such a thioester synthesis. In principle, it is even catalytic and Scheme 36 summarizes the individual steps (10). 

The yeast cell cycle has also been analyzed at this high level of chemical detail [17]. The molecular mechanism of the cycle in the form of a series of chemical equations was described by a set of ten nonlinear ordinary differential kinetic rate equations for the concentrations of the cyclins and associated proteins and the cell mass, derived using the standard principles of biochemical kinetics. Numerical solution of these equations 3uelded the concentrations of molecules such as the cyclin, Cln2, which is required to activate the cell cycle, or the inhibitor, Sid, which helps to retain the cell in the resting Gi phase. The rate constants and concentrations ( 50 parameters) were estimated from published measurements and adjusted so that the solutions of the equations yielded appropriate variations, i.e., similar to those experimentally measured, of the concentrations of the constituents of the system and the cell mass. The model also provides a rationalization of the behavior of cells with mutant forms of various system constituents. 

The first step of the catalytic cycle constitutes the oxidative addition of the organic halide to the Pd catalyst, yielding a c/5-palladium(Il) species, which subsequently isomerizes to the more stable trans form [8]. Theoretical studies so far have focused on the molecular mechanism of C-X bond activation and the influ-... 

Kyle DJ (1987) The biochemical basis for photoinhibition of Photosystem II. In Kyle DJ, Osmond CB and Arntzen CJ (eds) Photoinhibition. Photoinhibition, Topics of Photosynthesis, pp 197-226. Elsevier, Scientific Press, Amsterdam KyleDJ, Ohad I and Arntzen CJ (1985) Molecular mechanisms of compensation to light stress in chloroplast membranes. In Key JL and Kosuge T (eds) Cellular and Molecular Biology of Plant Stress, pp 51-69. Liss, New York Laisk A, Oja V, Rasulov B, Eichelmann H and Sumberg A (1997) Quantum yields and rate constants of photochemical and non-photochemical excitation quenching—Experiment and model. Plant Physiol 115 803-815 Lancaster CRD and Michel H (1996) Three-dimensional stmetures... 

---