Structural chemistry questions about structure

After the somewhat tedious parametrization procedure presented above you are basically an expert in the basic chemistry of the reaction and the questions about the enzyme effect are formally straightforward. Now we only want to know how the enzyme changes the energetics of the solution EVB surface. Within the PDLD approximation we only need to evaluate the change in electrostatic energy associated with moving the different resonance structures from water to the protein-active site. 

It is important to realize that the random-chain model need not imply an absence of residual structure in the unfolded population. Formative articles—many of them appearing on the pages of Advances in Protein Chemistry—recognized this fact. Kauzmann s famous review raised the central question about structure in the unfolded state (Kauzmann, 1959) ... 

As in any reexamination of the field, chemists and chemical engineers should ask serious questions about current practices. Does the divisional structure in academic chemistry departments discourage multi-investigator research, or encourage artificial distinctions Are the traditional divisions still the best structure... 

The reactions of boric acid solutions with diols have been used for almost a century to examine structural differences among carbohydrates. The complexity of these reactions seems to arise not only from simple structural differences but also from differences in carbohydrate configuration and conformation. The precise nature of these reactions is not clear. Recent studies of the chemistry of polyol-boric acid solutions have clarified some aspects of these reactions that have important bearing on the structure of carbohydrates in solution. Nevertheless, some of the most fundamental questions about the nature of the reaction are still unanswered. 

Site selective laser spectroscopy is a very powerful tool for studying the local environments that are present in samples. We have shown that defect structures in solids are determined by its previous history and that these structures can be measured with site selective spectroscopy. There has been no application of such techniques to geologically important questions since our work has concentrated on understanding fundamental questions about solid state defect chemistry. Our work suggests though that site selective laser spectroscopy could have important application in geological studies if it were used in the hands of people with that background. 

Tou were at Caltech from 1948 to 1951 and this was the time of the discovery of the alpha-helix. I would like to formulate a more pfeneral question about the role of structural chemistry in the emergence of molecular biology. 

A close look at the place of time within chemistry raises questions about that science s fundamental conceptual and explanatory entities. Put very simply, what is chemistry about A conventional narrative depicts chemistry, in its youth a science of substances, as reaching maturity when it metamorphosed into a science of molecules. The development of transition-state theory certainly conforms to and reinforces that narrative because the theory s successes can be ascribed to its "reduction of the dynamics problem to the consideration of a single structure" (Truhlar et al., 1983, p. 2665). Yet questions have been raised recently as to whether molecular explanations are adequate to account for all chemical phenomena (Woolley, 1978 Weininger, 1984), and the view that substances are still the primary subject matter of chemistry has by no means disappeared (van Brakel, 1997). I suggest that chemists can call on a variety of explanatory entities that are intermediate between the molecule and the substance, and these entities need not have the permanence of either molecules or substances. 

In an effort to compare descriptor distributions between compounds from different sources and synthetic paradigms, Feher and Schmidt [121] used PCA-based methods to compare property distributions from natural products, drugs, and combinatorial libraries. In this case, the authors used chemical space as a common framework to ask questions about the how the origins of compounds are manifest in their structural features at a global level. In particular, this study demonstrates the general dominance of synthetic efficiency, rather than structural diversity, in the preparation of compounds by combinatorial chemistry. The descriptors most able to distinguish natural products from those synthetic molecules studied were those that rendered the latter class easier to make, such as fewer... 

Through its ups and downs, the concept of orbital hybridization is most significative for the perspectives opened out by Quantum Chemistry from about 1930. Let us only mention all the disputes in which it was involved during almost one century with regard to tricky questions of molecular structure (i.e., the supremacy of valence-bond pictures over molecular orbitals or vice-versa, the physical content of the resonance theory, the localization versus delocalization dilemma and so on...). Furthermore, its study gives us a good example of the specificity of the scientific explanation among chemists (i.e., the rejection of reductionism to Physics [1]). 

When we presented in 1989 a systematic analysis of the hypotheses of the foundations of chirality [16], it was discovered, surprisingly, that there were at least five fundamentally different hypotheses to this seemingly simple, basic question about structures in chemistry. Their supporters barely communicated with each other. An experimental confirmation of one or the other hypothesis, then as now, was... 

Structure implemented in these research practices are as different as the scientihc objects themselves. As a matter of fact, chemical practice and theory have not spurred chemists to select one real essence of chemical structure, and, as a consequence, there have been different possibilities of classifying substances based on knowledge of molecular structure. Likewise, the classical representation of chemical composition by referring to the constituting elements of a chemical compound did not determine all aspects of classihcation. To take a very simple example from Lavoisierian chemistry, knowledge about the composition of water from hydrogen and oxygen left open the question of whether water should be ordered into the class of hydrides or oxides. 

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