Raman spectroscopic measurements in self-pressurized aqueous solutions above 100 degrees C: The melting of Poly(G) and Poly(G)center dot Poly(C)

We have studied by Raman spectroscopy the thermal behavior of associated po lyguanylic acid [poly(G)] and polyguanylic-polycytidylic acid [poly(G) . po ly(C)] in self-pressurized aqueous solutions contained in sealed capillary tribes. The associated polynucleotides were found to be very resistant to h eat, but evidence of thermal degradation was observed after melting of the helical structures. The cooperative melting transition of the foul-stranded complex of poly(G) was located at 141 degrees C in 0.5M KCI, 135 degrees C in 0.5M NaCl, 129 degrees C in 0.5M LiCl, 123 degrees C in 0.1M tetramethy lammonium perchlorate, and 105 degrees C in 0.1M tetraethylammonium bromide solutions. The transition was observed at 130 degrees C in poly(G) . poly( C) (in 0.5M NaCl). The results in this case show that a four-stranded poly( G) complex is formed following the melting of the double helix. (C) 1999 Jo hn Wiley st Sons, Inc.