Structural changes properties

Electronic Structure Changes, Property Changes, and Property Surfaces... 

Focuses on force field calculations for understanding the dynamic properties of proteins and nucleic acids. Provides a useful introduction to several computational techniques, including molecular mechanics minimization and molecular dynamics. Includes discussions of research involving structural changes and short time scale dynamics of these biomolecules, and the influence of solvent in these processes. 

Simmons, J.H.W., Radiation Damage in Graphite, Pergamon Press, Oxford, 1965. Kelly, B.T. and Burchell, T.D., Structure-related property changes in polycrystallinc graphite under neutron irradiation, Carbon, 1994, 32, 499 505. 

Up to this point, we have emphasized the stereochemical properties of molecules as objects, without concern for processes which affect the molecular shape. The term dynamic stereochemistry applies to die topology of processes which effect a structural change. The cases that are most important in organic chemistry are chemical reactions, conformational changes, and noncovalent complex formation. In order to understand the stereochemical aspects of a dynamic process, it is essential not only that the stereochemical relationship between starting and product states be established, but also that the spatial features of proposed intermediates and transition states must account for the observed stereochemical transformations. 

So far, we ve considered calculations which investigate a molecular system having a specified geometric structure. As we ve seen, structural changes within a molecule usually produce differences in its energy and other properties. 

Although, the heat resistance of NBR is directly related to the increase in acrylonitrile content (ACN) of the elastomer, the presence of double bond in the polymer backbone makes it susceptible to heat, ozone, and light. Therefore, several strategies have been adopted to modify the nitrile rubber by physical and chemical methods in order to improve its properties and degradation behavior. The physical modification involves the mechanical blending of NBR with other polymers or chemical ingredients to achieve the desired set of properties. The chemical modifications, on the other hand, include chemical reactions, which impart structural changes in the polymer chain. 

It is widely appreciated that the deterioration of metal and plastic implant materials within the body is one of the most important aspects of implant surgery. This particular application of materials places an almost unique demand on the resistance to deterioration. The reasons are basically twofold, for not only may the environmental effects alter the structure and properties of the material, which may itself affect the function of the implant and hence the well-being of the patient, but also the by-products of any structural change may have harmful effects on the patient... 

The careful control of electronic properties is, of course, a key motivation of such structural changes the so-called band-gap tuning being a particularly important concern. Efficiency of synthesis and structural homogeneity of the products are essential ingredients of such an approach since failure to achieve e.g. quantitative transformation of precursor polymers or to couple benzene units exclusively in a para-fashion interrupts the extensive -conjugation and hampers a reliable structure-propcrty-relalion. 

Here, of course, we may expect also an appearance of thixotropic phenomena, because a transition from the structure changed by deformation to a conventionally homogeneous structure of a filled system occurs rather slowly. And if an investigator at different moments of time deals with different structure of the medium, its properties will be different. 

In a series of remarkable papers, K. Tamao and S. Yamaguchi have shown that the physical properties of triarylboranes and triarylsilanes can be modified using structural changes induced by increasing coordination numbers [74]. In the same way, the tuning of the photophysical properties of PAr3 systems (96-99) (Scheme 27) according to the coordination number of the P-atom has been achieved [75]. 

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