Duplex stability of DNA.DNA and DNA.RNA duplexes containing 3'-S-phosphorothiolate linkages

3'-S-Phosphorothiolate (3'-SP) linkages have been incorporated into the DNA strand of both a DNA.RNA duplex and a DNA.DNA duplex. Thermal melting (T(m)) studies established that this modification significantly stabilises the DNA.RNA duplex with an average increase in T(m) of about 1.4 degrees C per modification. For two or three modifications, the increase in T(m) was larger for an alternating, as compared to the contiguous, arrangement. For more than three modifications their arrangement had no effect on T(m). In contrast to the DNA.RNA duplex, the 3'-S-phosphorothiolate linkage destabilised the DNA.DNA duplex, irrespective of the arrangement of the 3'-SP linkages. The effect of ionic strength on duplex stability was similar for both the phosphorothiolate-substituted and the unmodified RNA.DNA duplexes. The results are discussed in terms of the influence that the sulfur atom has on the conformation of the furanose ring and comparisons are also drawn between the current study and those previously conducted with other modifications that have a similar conformational effect.     

The first spectroscopic observation of germanium carbide

The gas phase spectrum of the germanium carbide radical has been observed at low temperature in emission from a corona excited supersonic expansion source. Many vibrational bands involving the Ω = 0, 1, and 2 components of the (2)³Π–X³Π system were recorded and analyzed. The equilibrium transition energy is found at 21120.3 cm⁻¹, in good agreement with theoretical predictions. The fundamental vibrational frequency for the lowest energy ground state Ω = 2 component is 795.3 cm⁻¹.