Circular dichroism of diglycosyl dichalcogenides in solution and solid state

Abstract

Solution and solid-state CD spectra of nine peracetylated and deacetalyted diglycosyl disulfides were measured to study the relationship between the low-energy CD transitions (n1-->sigma*(S--S) and n2-->sigma*(S--S)) and helicity of the inherently chiral disulfide chromophore as perturbed by chiral carbohydrate moieties. The solid-state CD spectra were directly correlated with the reported X-ray structures of Ac4GlcSSGlcAc4 and Ac4GlcSSGalAc4, and the CD data revealed that all the disulfides have M helicity with C1--S--S--C1' dihedral angles -90 degrees < phi < 0 degrees both in solution and in the solid state. A TDDFT CD study was carried out on dimethyl diselenide which confirmed that the same quadrant rule is relevant between the signs of the low-energy CD transitions and the diselenide torsional angle as formulated previously for the disulfide chromophore. The CD spectra of Ac4GlcSeSeGlcAc4 measured in solution and in the solid state were correlated with its X-ray structure and reproduced well by TDDFT CD calculations performed on its tetra-O-acetyl derivative.

On the Complementarity of ECD and VCD Techniques

“…An analysis of the MO transitions that determine this band has shown that this band is mostly determined by the so‐called n 1 →σ* S−S transition (where n 1 is an antiphase combination of the two p‐type sulfur lone‐pair atomic orbitals—the HOMO in this particular case). While the intensity of this band is overestimated by our BP86/TZP calculations, the sign of the band is in agreement with the quadrant rule formulated by Linderberg and Michl and also with the conclusions drawn elsewhere …”

“…While the intensity of this band is overestimated by our BP86/TZP calculations, the sign of the band is in agreement with the quadrant rule formulated by Linderberg and Michl 29 and also with the conclusions drawn elsewhere. 30,31…”

Crystal and molecular structures of diglycosyl disulfide derivatives

“…In solution both M and P forms can occur in equilibrium. Our preliminary NOE studies have, however, indicated 17 Pinto and co-workers 2 came to a similar conclusion for (1!4)-linked disulfide-and selenosulfide disaccharides. The C2-C1-S1-S2 and S1-S2-C21-C22 torsions indicate syn and anti geometry, respectively, the latter displaying more deviation from the ideal value (157°rather than 180°) just as in the symmetrical molecule 2.…”

Experimental aspects of solid state circular dichroism

“…Pellet techniques have been used in many laboratories, for a variety of samples including biomolecules, [32][33][34][35][36][37][38][39][40][41][42][43] both in the UV-vis (ECD) and in the IR (VCD).…”