title: Mechanism of hydrogen-bond array isomerization in tetrahydroxycalix[4]arene and tetrahydroxythiacalix[4]arene.
abstract: Possible rearrangement mechanisms of hydrogen-bond arrays formed at the lower rim of tetrahydroxycalix[4]arene and tetrahydroxythiacalix[4]arene were studied by means of density functional theory and the resolution identity approximation modification of Møller-Plesset perturbation theory (RI-MP2). Influence of solvent to height of energy barriers was quantified by use of the conductorlike screening model (COSMO) of implicit solvent (chloroform). Generally, two types of mechanisms were investigated. The first is represented by a synchronous single-step jump of all four hydroxyl protons. Pathways of the second mechanism include the rotation of one or more hydroxyl groups around the CAr-O bond. Theoretical results, in agreement with recently published experimental data (Lang et al. J. Chem. Phys. 2005, 122, 044056), prefer a jump mechanism for the methylene-bridged calix[4]arene. Concerning the thiacalix[4]arene, results obtained by COSMO as well as RI-MP2 calculations show that the rotational mechanism is very competitive and it could even be more favorable.
authors.affiliation: National Centre for Biomolecular Research, Masaryk University, CZ-611 37 Brno, Czech Republic.
authors.forename: Jirí
authors.initials: J
authors.lastname: Matousek
authors.forename: Michal
authors.initials: M
authors.lastname: Cajan
authors.forename: Petr
authors.initials: P
authors.lastname: Kulhánek
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Koca
mesh_terms: D047250:Calixarenes / Q000737:chemistry*; D006860:Hydrogen Bonding; D006900:Hydroxylation; D007536:Isomerism; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D010636:Phenols; D013438:Sulfhydryl Compounds; C121325:calix(4)arene; D047250:Calixarenes