Estimation of individual binding energies in some dimers involving multiple hydrogen bonds using topological properties of electron charge density

Individual hydrogen bond (HB) energies have been estimated in several systems involving multiple HBs such as adenine-thymine and guanine-cytosine using electron charge densities calculated at X center dot center dot center dot H hydrogen bond critical points (HBCPs) by atoms in molecules (AIM) method at B3LYP/6-311++G** and MP2/6-311++G** levels. A symmetrical system with two identical H bonds has been selected to search for simple relations between rho(HBCP) and individual E-HB. Correlation coefficient between E-HB and rho(HBCP) in the base of linear, quadratic, and exponential equations are acceptable and equal to 0.95. The estimated individual binding energies E-HB are in good agreement with the results of atom-replacement approach and natural bond orbital analysis (NBO). The E-HB values estimated from rho values at H center dot center dot center dot X BCP are in satisfactory agreement with the main geometrical parameter H center dot center dot center dot X. With respect to the obtained individual binding energies, the strength of a HB depends on the substituent and the cooperative effects of other HBs. (C) 2009 Elsevier B.V. All rights reserved.