ABSTRACT
The ability of the COSMO-RS method to predict the relative stability of different conformers of the same species in solution was evaluated by comparing computational results with experimental conformer data for 105 molecules from 20 literature sources. The solvents CDCl3, CD2Cl2, benzene, toluene, ethyl ether, tetrahydrofuran, acetone, dimethylformamide, DMSO (and DMSO-d6), water, and ethanol were used (dictated by the solvents used in the literature). In the case of 16 molecules the quantitative conformer abundances were also available and were compared with the data from computations. The results show that although COSMO-RS reproduces the conformer abundances only very approximately, the most stable conformer is determined correctly in 103 cases out of 105. This result validates the use of COSMO-RS in a number of applications (distribution coefficients, vapor pressures, solubilities, etc.) where the most stable conformer of a molecule can be different in different phases and accounting for this difference is important for obtaining meaningful results.
ABSTRACT
The binding constants (log Kass ) of small synthetic receptor molecules based on indolocarbazole, carbazole, indole, urea and some others, as well as their combinations were measured for small carboxylate anions of different basicity, hydrophilicity and steric demands, that is, trimethylacetate, acetate, benzoate and lactate, in 0.5 % H2 O/[D6 ]DMSO by using the relative NMR-based measurement method. As a result, four separate binding affinity scales (ladders) including thirty-eight receptors were obtained with the scales anchored to indolocarbazole. The results indicate that the binding strength is largely, but not fully, determined by the strength of the primary hydrogen-bonding interaction. The latter in turn is largely determined by the basicity of the anion. The higher is the basicity of the anion the stronger in general is the binding, leading to the approximate order of increasing binding strength, lactate
ABSTRACT
The ability of the Conductor-like Screening Model for Realistic Solvation (COSMO-RS) computational method to model hydrogen bond (HB) formation in solution is examined by comparing computational data with experimental data from literature. This is the first study of this kind where mixed solvents are also involved. Hydrogen bond formation is examined between neutral molecules, between acids and their anions, and between various anion receptor molecules and different anions in a number of aprotic solvents. HB formation equilibrium constants, the corresponding Gibbs' free energies and, when available from the literature, enthalpies were calculated. The supermolecule (SM) approach and the contact probability (CP) approach were used. Both in the case of the SM and CP approach, good to very good correlations between the experiment and computations are found for complexes formed from neutral species, enabling quantitative predictions. When the HB acceptor is an anion, the correlations are poor and in some cases even qualitative predictions fail.
