DETERMINATION OF THE HYDROGEN-BONDED STRUCTURE OF CGG TRIMERS IN CHLOROFORM SOLUTION BY VIBRATIONAL SPECTROSCOPY

Infrared and Raman spectra of 2'-deoxy-3',5'-bis(triisopropylsilyl) gu anosine (G) and its 2:1 mixture with 2'-deoxy-3',5'-bis(triisopropylsi lyl) cytidine (C) have been studied in chloroform solution. Strong int eractions occur between CG base pair and a second G whose association constant was first determined. CGG trimer is stabilized by two hydroge n bonds between a G which is in a Watson-Crick base pair and a second G. These interguanine hydrogen bonds involve the N(7) and O(6) guanine accepters and N(1)H and N(2)H guanine donors. The 1570 cm(-1) band of guanine is sensitive to hydrogen bonding at the N(3) position. Since this band is unchanged upon CGG formation, it is concluded that no bin ding at the guanine N(3) position occurs in the trimer. The pattern of hydrogen bonding in CGG trimer in chloroform solution here appears to correspond with patterns of hydrogen bonding in nucleic acid triplexe s. These spectroscopic measurements constitute the first application o f vibrational spectroscopy to the structural study of CGG trimer and s elf-associated G in a nonaqueous solvent, and these nucleosides can be used as molecular models to know the hydrogen bonding in the hydropho bic interior of nucleic acid double and triple helices. (C) 1995 John Wiley & Sons, Inc.