Random-phase calculation of the low-energy circular dichroism in glucans

✍ Scribed by B. K. Sathyanarayana; E. S. Stevens; J. Texter

• Publisher: Wiley (John Wiley & Sons)
• Year: 1985
• Tongue: English
• Weight: 1004 KB
• Volume: 24
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360240719

✦ Synopsis

The CD of the long-wavelength electronic transition in the a41 -Ihlinked glucan dimer (maltose) and polymer (amylose), and in the p-(1 -. 6hlinked dimer (gentiobiose) and polymer (pustulan), are calculated in the random-phase approximation using timedependent Hartree theory. This long-wavelength transition (180-190 nm) is assumed to be localized on the linkage oxygen atom and to be of a c * / 3 s + n character. The zerothorder cr8/3sn magneticdipole transition moment is coupled to the CC, CO, and CH bond density of states via a polarizability approximation. We assume this coupling is dominated energetically by the electricdipole, electricdipole interaction terms in the context of Schellman's pL.-pmcoupling mechanism of rotatory power. The CD is calculated as a function of rotation about the two single bonds of the linkage oxygen atom and also as a function of rotation about the C(5)6( 6) bond. For maltose, four rotational isomers are considered, resulting from combinations of the gg and gt C(6)H,OH group rotational isomers. The calculated CD values were then Boltzmann-averaged over an empirical potential, and the resulting CD was found to compare satisfactorily with experiment. In the case of the polymers, only structures having periodicity (helicity) were examined.