Conformations and hydrogen bonding

X-ray crystallographic studies (59) have defined the conformations and hydrogen bonding of the tetracyclines under nonpolar and polar conditions. These are shown ia Figure 3. It is beheved that the equiUbrium between the 2witterionic and nonioni2ed forms is of importance for the broad-spectmm antibacterial activity, membrane permeation, and pharmacokinetic properties. 

Detection of the dA N1 and dC N3 adducts may not in one sense be particularly important for DNA based on their central position within the helical conformation and hydrogen bonding network.37,38 Still, the deoxynucleoside studies helped to focus attention on the reversibility of alkylation by QM and provided insight into the reactions of duplex DNA described below in Section 9.3. Reaction at the deoxynucleoside level also provided an essential system for developing a theoretical treatment of QM reaction.50-52 Computations based on density functional theory well rationalized the published results on d A and correctly anticipated the results on dG and dC reviewed above and described in more detail in Chapter 2 (Freccero). 

El Tayar, N., Mark, A. E., Vallat, P., Bmnne, R. A., Testa, B. and van Gunsteren, W. E. Solvent-dependent conformation and hydrogen-bonding capacity of cyclosporin A evidence from partition coefficients and molecular dynamics simulations, J.Kled. Chem., 36 (1993), 3757-3764... 

Conformational and Hydrogen-Bonding Characteristics of the Nucleosides and Nucleotides... 

Ramanadham M, Chidambaram R (1978) Amino acids systematics of molecular structure, conformation and hydrogen bonding. In Srinivasan R (ed) Adv. Crystallogr., Invited Rev Lect Natl Conf Crystallogr 1977, Oxford and IBH, New Delhi, pp 81-103... 

Pascher, I. (1976). Molecular arrangements in sphingolipids. Conformation and hydrogen bonding of ceramides and their implication on membrane stability and permeability. Biochim. Biophys. Acta 455 433. 

A new crystal structure with tilted chains has recently been found in pentamer of nylon-6 and nylon-8, termed A-phase.108 Molecules are in the all-trans conformation and hydrogen bond to antiparallel neighbors to form the usual nylon 6 hydrogen-bonded sheets. However, in this structure, the sheets stack with progressive c-axis shear, and consequently, the molecular layer thickness is noticeably reduced. 

Berkovitch-Yellin, Z. and Leiserowitz, L. (1984) The role played by C-H- - -O and C-H- - -N interactions in determining molecular packing and conformation, Acta Cryst. B40, 159-165. Parthasarathy, R., Fridey, S.M., and Srikrishnan, T. (1989) Conformation and hydrogen bonding of A-formylmethionyl peptides. II. Crystal and molecular structure of iV-formyl-L-methionyl-L-phenylalanine, Int. J. Peptide Protein Res. 33, 308-312. 

Sadlej-Sosnowska, N., Dobrowolski, J.C., Oziminski, W.P., and Mazurek, A.P. (2002) On conformation and hydrogen bonding in vigabatrin amino acid molecule, J. Phys. Chem. A... 

Wang F, Polavarapu PL. Vibrational circular dichroism, predominant conformations, and hydrogen bonding in )-3-butyn-2-ol. J Phys Chem A 2000 104 1822-1826. 

Cellulose polymorphy was studied by comparing the spectra of Valonia, ramie, and mercerized ramie. It appears that the conformation of the cellulose backbone is the same in Valonia and ramie celluloses, but that the hydrogen bonding patterns are different. Mercerized cellulose and native celluloses differ in both their backbone conformations and hydrogen bonding patterns. 

C-H- -Ourea synthon. The molecular conformation and hydrogen bonding are different from one structure to another but the urea tape is conspicuously absent. The urea tape is absent in Af-phenyl-Af-3-pyridylurea (a phenyl-pyridyl urea example) but the C-H- -O synthon is present. 

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