Simulating the interaction between amino acids and DNA: a combined matrix-isolation FT-IR and theoretical study of the 1-methyluracil·glycine H-bond complexes using a dual sublimation furnace.

The H-bond complex formation between 1-methyluracil and glycine has been investigated by theoretical calculations and the most stable complex configurations have been identified by FT-IR spectroscopy in Ar matrices. The importance of this H-bonding system is huge since all DNA biological functions are dependent on the interactions with proteins. The theoretical optimizations have revealed six different closed H-bond complexes between 1-methyluracil and glycine. The obtained energies have demonstrated that the uracil C(4)═O site is a better H-acceptor site than the C(2)═O site. The stabilization energy of the most stable complex is -47.83 (MP2) or -54.14 kJ·mol(-1) (DFT). The DFT(B3LYP)/6-31G optimized geometries have been evaluated, and the obtained energies appeared to be in agreement with the results of the computational more expensive DFT(B3LYP)6-31++G** approach. In order to identify the 1:1 complexes in an argon matrix, a new dual miniature furnace has been developed which allows to sublimate both complex partners at their optimal temperature. The presence of three different glycine·1-methyluracil complexes has been demonstrated by analysis of the H-bond shifted modes. The H-bond parameters have been evaluated and previously obtained correlations for different H-bond complexes have been confirmed.