Retention modeling and adsorption mechanisms in reversed-phase liquid chromatography.

To interpret the dependence of solute retention behavior on modifier content in reversed-phase liquid chromatography, a theoretical framework, based on the concentration dependence of solvophobic forces imposed on solutes and the competitive adsorptions of solutes and solvent modifiers, was proposed. The generality of the developed model was demonstrated by comparing the model with conventional retention models. The linear dependence of the Gibbs energy change of solute adsorption with respect to the modifier concentration was assumed, and the model was fitted to the experimental results, with good agreement demonstrated between the experimental data and the model. Retention behaviors were inferred to be determined by two key dimensionless groups that represented the reductions in the retention factors resulting from a weakened solvophobic interaction and modifier competitive adsorption. The retention behaviors were successfully deconvoluted for each contribution as a function of the modifier concentration by using the fitted parameters. The effects of both contributions on the retention behaviors were enhanced for the solutes with aromatic groups. The standard Gibbs energy change SLo of benzene adsorption was found to depend linearly on the number of modifier molecules present but independent of modifier identity. For the solutes associated with hydrogen-bonding groups, the degree of reduction in the solvophobic interactions was considerably reduced. Hence, the relative contributions of both mechanisms to solute retention depend greatly on the solute structure. Perturbation method was performed to investigate the modifier adsorption mechanisms. The results show that the standard Gibbs energy change SLo for the first-layer adsorption of modifiers changed linearly with the carbon number of modifier molecule. These results demonstrated that the proposed model can offer a physically consistent quantitative description of retention when solvent composition is varied.

2,6-Bis(1H-benzimidazol-2-yl)pyridine butyric acid monosolvate dihydrate.

In the title compound, C(19)H(13)N(5)·C(4)H(8)O(2)·2H(2)O, the mol-ecular skeleton of the 2,6-bis-(benzimidazol-2-yl)pyridine (bbip) mol-ecule is essentially planar (r.m.s. deviation = 0.023 Å). An extensive three-dimensional network of inter-molecular N-H⋯O, O-H⋯O and O-H⋯N hydrogen bonds consolidates the crystal packing, which also exhibits π-π inter-actions between the five- and six-membered rings from neighbouring bbip mol-ecules.

Adipic acid-2,6-bis-(1H-benzimidazol-2-yl)pyridine-water (1/2/4).

The asymmetric unit of the title hydrated co-crystal, 2C19H13N5·C6H10O4·4H2O, consists of one 2,6-bis-(1H-benzimidazol-2-yl)pyridine mol-ecule, half of an adipic acid mol-ecule (bis-ected by an inversion center) and two water solvates. In the crystal, N-H⋯O, O-H⋯O and O-H⋯N hydrogen bonds and π-π inter-actions [centroid-centroid distances = 3.769 (2) and 3.731 (2) Å] form a three-dimensional supra-molecular structure.

Glutaric acid-2-(pyridin-4-yl)-1H-benzimidazole (1/1).

The crystal structure of the title co-crystal, C(12)H(9)N(3)·C(5)H(8)O(4), N-H⋯O and O-H⋯N hydrogen bonds link the components. There are also π-π stacking inter-actions between the imidazole rings, between the imidazole and pyridine rings and between the pyridine and benzene rings [centroid-centroid distances = 3.643 (2), 3.573 (2) and 3.740 (1)Å, respectively].

4-[(9-Ethyl-9H-carbazol-3-yl)imino-meth-yl]phenol.

In the title compound, C(21)H(18)N(2)O, the dihedral angle between the phenol ring and the carbazole system is 39.34 (2)°. Inter-molecular O-H⋯N hydrogen bonds and C-H⋯π and π-π inter-actions [centroid-centroid distances = 3.426 (2) and 3.768 (2) Å] stabilize the crystal structure.

{2-Hydr-oxy-N'-[1-(2-oxidophenyl)ethyl-idene]benzohydrazidato}morpholinecopper(II).

The Cu(II) ion in the title complex, [Cu(C(15)H(12)N(2)O(3))(C(4)H(9)NO)], is coordinated by one carbonyl O atom, one hydrazine N atom and one phenolate O atom from the doubly deprotonated tridentate ligand and one N atom from a morpholine mol-ecule, forming a distorted trans-CuN(2)O(2) square-planar coordination geometry. An intra-molecular O-H⋯N hydrogen bond occurs within the ligand, generating an S(6) ring.

(E)-3-[4-(Dimethyl-amino)phen-yl]-1-(2-pyrid-yl)prop-2-en-1-one.

In the title mol-ecule, C(16)H(16)N(2)O, the pyridine ring and non-H atoms of the =CH-C(=O)- unit are coplaner, the largest deviation being 0.045 (2) Šfor the O atom. The dihedral angle between this plane and the benzene ring is 2.79 (2)°. The mol-ecular structure is stabilized by inter-molecular C-H⋯π and inter-actions.