Properties of the Solute-Stationary Liquid Interactions in Gas Liquid Chromatography

Abstract

Noncovalent interactions are very important in molecular recognition of biochemistry, molecular crystals, [1][2][3] and hostguest complexes. 4) In addition, they play a key role in determining the molecular orientation in molecular assemblies. The weak interaction between the C-H bond and the aromatic p system called the CH/p interaction, 5) has been determined to be a primary contributor to the electrostatic and charge-transfer terms 5,6) based on primary ab initio calculations using a small basis set. In recent years, high-level ab initio calculations of the typical CH/p complex have shown that dispersion is a major source of attraction.7-9) MP2 interaction energy depends strongly on the basis set and small basis sets (6-31G*, 6-311G** and cc-pVDZ) greatly underestimate the attraction. Therefore, MP2/cc-pVXZ (XϭT or Q) or MP2/aug-cc-pVXZ (XϭD or T) level calculations are necessary for quantitative evaluation of the dispersion energy.10) The estimated CCSD(T) interaction energy for a methane-benzene complex as an example of a typical CH/p interaction at the basis set limit (D e ) was reported to be Ϫ1. 43 ). Furthermore, DEF calculations were discussed using BLYP, B3LYP, PW91 and PBE functions were determined to be in appropriate for the quantitative evaluation of the CH/p interaction energy.12-14) The calculated energy E CCSD(T)(limit) was determined to be appropriate for a quantitative evaluation of the CH/p interaction.In the solute-staitonary liquid interaction of gas liquid chromatography, the entropy changes DDS s o of dissolution were determined to be correlated to the descriptor s M in order to evaluate a physical adsorption using Eyring's model. 15,16) These findings supported the fact that van der Waals interactions were responsible for the formation CH/p complexes between C-H bond of squalane as the stationary liquid and the aromatic p system of the solute. Herein, we discuss the physical origin of the microscopic conditions under which the descriptor s M is correlated to the CH/p interaction energy introduced into the high-level ab initio calculations. ExperimentalRelative Retention Value log g g The log g defined by Eq. 1. Where t R (A) and t R (B) are the retention times of the reference and substituted benzenes, respectively. DH s o and DS s o denote the enthalpy and entropy of dissolution of A and B. All data for log g and the thermodynamic parameters were cited in references, [18][19][20] and the regression analyses were carried out using the statistical program. 21)Descriptors s s M and s s es for Regression Analysis The descriptor s M was derived from the Eyring's method: The activated translational entropy change DDS † ABC for Eyring's equation 15) is given by the following equation, when there is the interaction between the solutes (A and B are the reference and its derivatives) and the non-polar stationary liquid (where C is constant).Where R, k, T and h are the gas constant, Boltzmann's constant, absolute temperature and Plank's constant, respectively.When T is constant, Eq. 5 is given ...