Structural conformation studies

IR data are of no importance for the characterization and structural elucidation of azepines. NMR Spectra and Conformational Studies... 

Maser, F., Bode,K., Pillai, V. N. R. and Mutter, M. Conformational Studies on Model Peptides. Their Contribution to Synthetic, Structural and Functional Innovations on Proteins. Vol. 65, pp. 177 — 214. 

Although perhaps not strictly a conformational study, the structure of the gem-disulfoxide 184 was determined by X-ray crystallography169. A comparison of the structural parameters so measured with 1H and 13C NMR chemical shifts led the authors to conclude that chemical shifts should allow configurational assignments to be made to related sulfoxides. 

The preparation and investigation of the thietane oxide system (5a) is largely associated with stereochemical and conformational studies . The investigation of the thietane dioxides (5b) is substantially related to the chemistry of sulfenes , the [2 -I- 2] cycloaddition of which with enamines is probably the method of choice for the synthesis of 5b . The study of the thiete dioxide system (6) evolved, at least in part, from the recognition that the unstable thiete system 183 can be uniquely stabilized when the sulfur in the system is transformed into the corresponding sulfone , and that the thiete dioxide system is very useful in cycloadditions and thermolytic reactions. The main interest in the dithietane oxides and dioxides (7) appears to lie in the synthetic challenge associated with their preparation, as well as in their unique structural features and chemical behavior under thermolytic conditions . ... 

Dipole moments of azolides have been reviewed, with emphasis on the conformation of the acyl group. 441 Unfortunately, structural and conformational studies on azolides by X-ray structure analysis are almost totally lacking, although they would be of great interest with regard to the conformations and to the bond lengths and bond orders in these systems. Only an X-ray analysis of V-acetyl-4-bromopyrazole 451 has been reported. 

However, X-ray diffraction data show [68,69] that in K2[Tc2C16], the Tc-Tc bond distance is 0.1 A shorter than that in an analogous d4-d4 chloride technetium complex, although its main structural fragment [Tc2C18]4- has a staggered structural conformation. That is why a study of the electronic... 

This procarcinogen undergoes metabolic conversion to benzo[a]pyrene diol epoxides, BPDEs (5,28-31), which have been the focus of structural and conformational studies by theoretical and experimental methods. These chemically reactive BPDEs are involved in covalent binding to DNA (13-22). 

Dicko, C., Knight, D., Kenney, J. M., and Vollrath, F. (2004c). Structural conformation of Spidroin in solution A synchrotron radiation circular dichroism study. Biomacromo-leculesB, 758—767. 

The purpose of this brief survey was to demonstrate that, despite the criticisms which may be made of the use of any semi-empirical quantum technique for structural and conformational studies, the CNDO/2 and Extended CNDO/2 formalisms are definitely reliable tools for theoretical conformational analyses in inorganic and coordination chemistry. Moreover, if these tools are combined with the most suitable experimental techniques (i.e. microwave spectroscopy and electron diffraction) in that field, many problems of geometry and conformation can be solved in a way that neither of these approaches could have accomplished alone. 

A similar approach was used in the synthesis of the sialyl Lewis X mimetics of type 85 (Scheme 13.22).66 Protein crystallization,67 conformational studies of sLex in solution68 and in bound form to E- and P-selectin69 as well as the study of structure-function relationships70,71 gave information about the functional groups of the sLex-epitope essential for the binding to the selectins. Synthesized mimetics must contain the three essential hydroxyl functions of the fucose. Sialic acid, galactose, and... 

The introduction of additional techniques such as Pulsed Fourier Transform NMR spectroscopy (PFT-NMR) has considerably increased the sensitivity of the method, allowing many magnetic nuclei which may be in low abundance, including 13C, to be studied. The additional data available from these methods allow information on polymer structure, conformation and relaxation behaviour to be obtained (1.18.20). 

In the following pages, the results of conformational studies of important classes of push-pull ethylenes will be reviewed, after which experimental and theoretical results bearing on the electronic structure of these compounds will be discussed. 

How do proteins fold into their native structures To study the mechanism of protein folding is to seek an answer to this question. The astronomically large number of possible conformations suggests that proteins use some sort of directed mechanisms to fold. Under evolutionary pressure, these mechanisms have been refined such that proteins can fold reasonably quickly to well-defined functionally useful structures. We will review briefly the history of protein folding studies and discuss the theoretical studies in more detail. We will concentrate on recent developments and give a brief perspective of the future. 

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