THERMODYNAMIC AND SPECTROSCOPIC CHARACTERIZATION OF THE BERENIL AND PENTAMIDINE COMPLEXES WITH THE DODECANUCLEOTIDE D(CGCGATATCGCG)(2)

The dodecanucleotide d(CGCGATATCGCG)(2) was characterized by thermodyn amic and UV-spectrophotometric measurements. A van't Hoff enthalpy of Delta(v.H.)(uv) similar to -190 kJ/mol was determined for the thermal transition using UV spectroscopy. This value was confirmed by differen tial scanning calorimetry (DSC). In addition we obtained the thermodyn amic data Delta H-DSC = -405.1 kJ/mol, Delta S-DSC = -1290 J/mol . K a nd Delta G(DSC) = -53.2 kJ/mol for the helix to coil transition of the dodecanucleotide. The association of berenil and the oligonucleotide was accompanied with a stabilization of the host duplex (increase in T -m) and an increase in the van't Hoff enthalpy. The berenil binding pa rameters (Delta Delta H-DSC = -32.6 kJ/mol. Delta Delta S-DSC = -72 J/ mol . K and Delta Delta G(DSC) = -11.1 kJ/mol) revealed significant di fferences compared to those of the pentamidine aggregation (Delta Delt a H-DSC = -23.7 kJ/mol, Delta Delta S-DSC = -53 J/mol . K and Delta De lta G(DSC) = -7.8 kJ/mol). The transition of the pure oligonucleotide was characterized by a substantial amount of intermediate states (sigm a(DSC) = 0.43) which decreased significantly upon binding of the drugs (sigma(DSC) similar to 0.80). The structural features of the complexe s were analyzed by FT-IR spectroscopy. From these experiments we concl ude that the configurations in the berenil and pentamidine complexes a re different.