PubMed · 4445188
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F Langenbucher. 1974. Material and method parameters in dissolution rate studies.. https://pubmed.ncbi.nlm.nih.gov/4445188/
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Partition properties, that is partition coefficients and enthalpies (delta Hp degree) and entropies (delta Sp degree) of partition, have been measured for 50 benzoic acids in the 1-octanol/water system, and their role in QSAR (quantitative structure-activity relationship) analysis examined. The novel hydrophobic parameters have been introduced as a result of the separation of the Gibbs free energy term into the corresponding enthalpy and entropy terms. Application of these novel parameters to some available biological activity data supported the usefulness of these parameters in QSAR analysis. Relative contributions of the enthalpy and entropy terms are also discussed.
Ca2+.2C7H3O2F2-.2H2O, M(r) = 390.3, monoclinic, C2/c, a = 17.584 (4), b = 10.771 (3), c = 7.887 (2) A, beta = 91.28 (2) degrees, V = 1493 A3, Z = 4, Dm = 1.75, Dx = 1.74 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 4.92 cm-1, F(000) = 792, T = 293 K, final R = 0.037 for 2415 unique observed reflections. The eight-coordinate Ca2+ ion is linked to six carboxylate O atoms from four different 2,6-difluorobenzoate ions and two water molecules. Each 2,6-difluorobenzoate ion chelates one Ca2+ ion and forms unidentate bridging linkages to two other Ca2+ ions leading to a polymeric structure. Unlike the situation in calcium 2-fluorobenzoate, the two F atoms in this structure are not involved in significant C-F...H-O hydrogen bonding.
Porous microparticulate zirconium oxide shows very different selectivities and pH dependencies for the separation of benzoic acid derivatives than do conventional bonded-phase anion-exchange supports. This results from a very significant ligand-exchange contribution to the retention of hard Lewis bases on the surface of transition-metal oxide supports. We have found that the capacity factors of a wide variety of derivatives of benzoic acid are closely correlated with their Bronsted acidities. The eluent pH is also a critical factor in determining the magnitude of the capacity factor, but it does not have much influence on chromatographic selectivity. The differential selectivity of this phase in comparison to conventional polymeric and bonded-phase anion exchangers can be attributed to complexation and steric effects which profoundly alter the elution patterns of certain solutes.