Specific puckering

Most modeling software packages do not vary puckering in increments of the C-P parameters (REFINE (2 ) is an exception) but a utility for producing rings with specific puckerings is available... 

Note 2, A more precise specification of conformation can be achieved by use of the Cremer-Pople puckering parameters [22],... 

The polypeptide chains are virtually fully extended. There is a little puckering which allows for optimum hydrogen bonding, and hence the structure is inextensible in the direction of the polypeptide chains. On the other hand, there are less specific, hydrophobic (London, dispersion) forces between the sheets, and this permits flexibility. 

The synthesis of specific sulfur allotropes is achieved by reactions of titano-cene pentasulfide Cp2TiSs with dichlorosulfanes S Cl2 ( = 2, 4, 6) or sulfuryl chloride SO2CI2 [see eqns (2.1) and (6.1)]. The X-ray structures of many of these cyclic sulfur allotropes have been determined (see Figure 6.2 in Section 6.1). In general, they adopt puckered molecular conformations, e.g. the crown-shaped cyclo-Sg, which minimise repulsions between non-bonding electron pairs on... 

The emphasis in this section is on the form of the kinetic energy operator. The choice of potential energy functions is considered in Section IV dealing with specific molecules. Emphasis is also placed on treatment of the vibrational data since a review emphasizing treatment of microwave data for ring puckering has appeared recently19). 

CPMAS solid-state NMR has been used to investigate the dependence of sugar chemical shifts on specific conformational parameters of a variety of ribonucleotides and ribonucleosides. The distinct effects of sugar puckering on the Cl, C4, and C5 resonances of Cj endo (S type) and C3 endo (N type) furanoid conformations allow us to separate them into two groups. 

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