Equilibrium and NMR Studies of Noncovalent Interactions in Binary Systems:Uridine,Adenosine,Cytidine and Thymidine,and Adenosine(or Cytidine)5'-Monophosphate in Aqueous Solution

摘要

The molecular complex formation reactions of uridine(Urd)with adenosine(Ado),cytidine(Cyd),thymidine(Thd),adenosine 5'-monophosphate(AMP)and cytidine 5'-monophosphate(CMP)have been studied at 20deg C.It was found that the main positive noncovalent centers of ion-dipole and dipole-dipole type interactions are the protonated N(3)atoms of Urd,whereas the negative centers are the endocyclic atoms of the bases characterized by high electron density from the second molecule involved in the reaction.Moreover,NMR results indicate the occurrence of stacking in the complex(Urd)H(Cyd),whereas in the complex,(Urd)H_2(Thd),it is the only type of interaction.Deprotonation of the latter species brings about a change in the character of the reaction and ion-dipole interactions have been detected in the adduct,(Urd)H(Thd).Interestingly,no involvement of the phosphate groups in the formation of AMP and CMP adducts has been evidenced and the main centers of the reactions were found to be the N(7)and N(l)atoms of AMP,or the N(3)atoms of CMP and Urd.Moreover,in the Urd/CMP system the NMR results suggest stacking-type interactions.