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

Reman 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 Reman assignments for nucleoside conformers: C3′-endo/syn C, 623±1; C2′-endolsyn C, 671±2; C end C, 782±1; C2′endo/anti T, 650±5 and a. 750; C3′-endolsyn A, 729±1 cm . These results show that (i) the 670 cm line of syn G is highly 1 sensitive to the change from C3-endo to Cr′-endo pucker, (ii) the 729 cm^-1 line of A is affected neither by furanose pucker nor glycosidic bond orienta tion and (iii) the 1200-1500 cm^-1 region of the Reman 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.