Conformational analysis definition

The conformational behaviour in solution of a dermatan-derived tetra-saccharide has been explored by means of NMR spectroscopy, especially by NOE-based conformational analysis. RDCs were also measured for the tetrasaccharide in a phage solution and interpreted in combination with restrained MD simulations. The RDC-derived data substantially confirmed the validity of the conformer distribution resulting from the NOE-derived simulations, but allowed an improved definition of the conformational behaviour of the oligosaccharides in solution, which show a moderate flexibility at the central glycosidic linkage. Differences in the shapes of the different species with the IdoA in skew and in chair conformations and in the distribution of the sulphate groups were also highlighted.28... 

Measurements of dipole moments, Kerr constants, and dielectric absorption have been employed (81RCR336) widely to obtain information on the conformational equilibrium in acyl heterocycles. Details on conformer structures and populations depend on the choice of additive scheme, group moments, or polarizability tensor in the case of Kerr constants. Several early conclusions, especially for furan- and thiophene-2-carboxaldehyde, appeared contradictory, owing to the choice of these quantities. A more precise definition of polarizability tensors for several heterocycles and a choice of group moments and additive schemes tested on a large amount of available experimental results and supported by accurate theoretical calculations have led to more confidence in the use of experimental dipole moments and Kerr constants in conformational analysis. A limitation of the method is that the... 

Concomitant with these developments in spectroscopy, thermochemists were finding that, to a reasonable approximation, molecular enthalpies could be determined as a sum of bond enthalpies. Thus, assuming transferability, if two different molecules were to be composed of identical bonds (i.e., they were to be isomers of one kind or another), the sum of the differences in the strains of diose bonds from one molecule to the other (which would arise from different bond lengths in the two molecules - the definition of strain in this instance is the positive deviation from the zero of energy) would allow one to predict the difference in enthalpies. Such prediction was a major goal of the emerging area of organic conformational analysis. 

The following definition of computational chemistry was published in 1985 (6) quantitative modeling of chemical behavior on a computer by the formalisms of theoretical chemistry. Some quantum theoreticians naturally would like to see computational chemistry as a subset of their field (7). However, today the number of scientists employed as computational chemists well exceeds the number employed as theoreticians (8). A recent textbook author (9) views computational chemistry as encompassing not only quantum mechanics, but also molecular mechanics, [energy] minimization, simulations, conformational analysis, and other computer-based methods for understanding and predicting the behavior of molecular systems. ... 

Let US first examine current practice in nomenclature of the phenom-menon of internal rotation. Standard textbooks on conformational analysis on the one hand and those on spectroscopy on the other hand deal differently with the basic definitions. Internal rotation is measured by one or more torsion angles (dihedral angles, azimuthal angles). In the simple cases of e.g. a 1,2-disubstituted ethane the potential energy associated with the internal rotation may be written in a formal sense as a truncated Fourier expansion ... 

We define a heUx stop signal to be a residue sequence for which it is energetically more favorable to terminate the helix than to continue it. Under this definition, the two motifs are helix stop signals, as can be shown by exhaustive conformational analysis of suitable peptides. 

A detailed study was carried out on the radical anion derived from (10c) (Table 2) in connection with the conformational analysis of heteroaromatic carbonyl compounds. Notably different ESR signals could be observed originating from distinct rotational isomers. Unfortunately no information on the interconversion of the rotamers of (10c) could be definitely derived since these radicals were highly unstable at the temperature necessary for interconversion <74JCS(P2)562>. 

The terminology associated with conformational analysis is in many ways akin to the terminology used to discuss stereochemistry—namely, cis, trans, anti, syn, etc. In Chapter 6 there is a glossary of terms used in conformational analysis and stereochemistry, so if a term is used below that you are unfamiliar with, look to the end of Chapter 6 for a definition. 

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