The Raman spectra of left-handed DNA oligomers incorporating adenine-thymine base pairs

Raman spectra were obtained from single crystals of d(CGCATGCG)2 and d(m5CGTAm5CG)2, both of which incorporate A-T pairs into Z-DNA structures and contain C2'-endo/syn conformers of deoxyguanosine at the oligonucleotide ends. Correlation with x-ray results permits the following Raman assignments for nucleoside conformers: C3'-endo/syn G, 623 +/- 1; C2'-endo/syn G, 671 +/- 2; C2'-endo/anti C, 782 +/- 1; C2'endo/anti T, 650 +/- 5 and ca. 750; C3'-endo/syn A, 729 +/- 1 cm-1. These results show that (i) the 670 cm-1 line of syn G is highly sensitive to the change from C3'-endo to C2'-endo pucker, (ii) the 729 cm-1 line of A is affected neither by furanose pucker nor glycosidic bond orientation and (iii) the 1200-1500 cm-1 region of the Raman spectrum of the A-T double helix is greatly altered by the B-to-Z transition. Conformation sensitive Raman frequencies in the 850-1700 cm-1 region are identified for both octamer and hexamer, and the Z-to-B transition of each is monitored by spectral changes which occur upon dissolving the crystal in H2O solution.