Trinuclear ReFePt clusters with a µ3-phenylvinylidene ligand: synthetic approaches, rearrangement of vinylidene, and redox-induced transformations.

A series of trinuclear µ3-vinylidene ReFePt clusters were synthesized by the application of two approaches: (i) reactions of the binuclear RePt µ-vinylidene complexes with Fe2(CO)9; (ii) ligand substitution or exchange reactions at the Pt atom in the synthesized ReFePt clusters. The molecular structures of CpReFePt(µ3-CCHPh)(CO)5[P(OEt)3]L [L = CO; P(OEt)3] were determined by an X-ray diffraction study. The obtained compounds were studied by IR and 1H, 13C and 31P NMR spectroscopy. The spectroscopic study revealed that the clusters CpReFePt(µ3-CCHPh)(CO)5[P(OEt)3]L [L = CO; P(OEt)3] and CpReFePt(µ3-CCHPh)(CO)6[P(OPri)3] undergo isomerization upon dissolution, resulting in three isomers with different positions of the µ3-vinylidene ligand over the ReFePt core. The redox properties of the clusters were studied by electrochemical methods. The relatively stable cation-radicals obtained by chemical oxidation of CpReFePt(µ3-CCHPh)(CO)6[P(OPri)3] and CpReFePt(µ3-CCHPh)(CO)5[P(OEt)3]2 with ferrocenium tetrafluoroborate were characterized by EPR spectroscopy.

Combination of phase-solubility method and capillary zone electrophoresis to determine binding constants of cyclodextrins with practically water-insoluble compounds.

The combined method based on phase-solubility technique and capillary zone electrophoresis (PS-CZE) was suggested for the determination of binding (stability) constants of cyclodextrins (CD) complexes with water-insoluble organic compounds that have no or weak UV chromophores. In this method, the insoluble compounds are agitated at the desired temperature in CD solutions with different concentration up to the attainment of equilibrium and then CZE is used to determine the concentration of the compounds that have passed into the solutions. To avoid precipitation and complex dissociation, the background electrolyte (BGE) for CZE should contain ethanol and, if necessary, cyclodextrin. The samples should be diluted with the BGE without CD so that the CD concentrations in BGE and samples were equal to preclude a baseline shift. Using the suggested approach, the inclusion complexes between betulinic and betulonic acids, pentacyclic lupane-type triterpenes, and hydroxypropyl-ß- and γ-cyclodextrins (HP-ß-CD and HP-γ-CD) were studied. It was found that solubility of the acids studied in HP-ß-CD solutions did not differ from their solubility in pure water. That is, the HP-ß-CD complexes of the acids studied were not formed in noticeable amount. At the same time, the acids formed inclusion complexes with HP-γ-CD, what possibly was caused by the greater size of the HP-γ-CD molecule as compared to HP-ß-CD. To determine binding constants by Higuchi and Connors method, the acids solubility was determined by CZE after their agitation in the solutions of HP-γ-CD (with 0.6 molar substitution) at 25 °C for 3 days. The dependences of acids solubility on HP-γ-CD concentration deviated from straight line in the range of high concentration (AN mode). This can be explained by a self-association of HP-γ-CD molecules. Using the linear segment of the solubility dependences on CD concentration, the binding constants were determined. Their logarithms for the HP-γ-CD complexes with betulonic and betulinic acids were 3.88 ± 0.14 and 3.82 ± 0.12, respectively.