Thermal stability of products prepared by the combination of cyclodextrins and zeolites

Derivatographic and calorimetric measurements were used to study the thermal properties of combined inclusion compounds of zeolite-cyclodextrin type and of zeolite-cyclodextrin-pharmaceutical type. There were differences in the characteristic decomposition temperature intervals and in the modes of cyclodextrin and pharmaceutical liberation from the products. Calorimetric measurements revealed that the process in the newly-formed complex host is connected with a glass transition. The products are intended for use in veterinary medicine.     

Crystalline Inclusion Compounds Derived from Derivatives of Mandelic Acid. Host Synthesis, Inclusion Formation, and X-Ray Structures of a Free Host Compound and of DMSO Inclusion Complexes in Both Racemic and Optically Resolved Forms

New chiral host compounds based on mandelic acid derivatives having methyl (6a, b and 8a, b) or bromo substituents (7a, b) attached to the phenyl ring of mandelic acid and involving additional aromatic groups were synthesized. The inclusion properties of both the racemic and the optically resolved host species are reported, including solvent co-crystallization as well as chiroselective and vapour sorptive inclusion. The structures of the free racemic host compound 6b and of the DMSO inclusion compounds of optically resolved and racemic 8 (8a and 8b, respectively) have been determined by X-ray analysis. Enantiomeric pairs of molecules in 6b form centro-symmetric dimers by mutual hydrogen bonding of one hydroxyl group while the other is involved in O-–H ... interactions. The guest molecules in the DMSO complexes of 8a and 8b are bound via hydrogen bonds to two host molecules related by translation along crystallographic axes. Parallels to previous hosts of this type are drawn.     

Vibrational Spectroscopic Investigations of M(Imidazole)2Ni(CN)4·2 Dioxane Clathrates

Four new clathrates of the formula M(Im)2Ni(CN)4·2·Dioxane (where M = Co, Ni, Cu, Cd; Im = Imidazole) have been prepared in powder form and their FT-IR and laser-Raman spectra are reported for the first time. These clathrates are analogues to the previously reported classical Hofmann type clathrates except for the copper clathrate. The Cu clathrate has different spectral features in comparison with its analogues due to the Jahn-Teller effect.     

Complexation of Fluvastatin Sodium with β-Cyclodextrin: NMR Spectroscopic Study in Solution

¹H NMR spectroscopic study of fluvastatin sodium (FLU), β-Cyclodextrin (β-CD) and their mixtures confirmed the formation of FLU/β-CD inclusion complex in solution. The stoichiometry of the complex was determined to be 1:1 and the overall binding constant (K _s) was calculated to be 340 M⁻¹. Two dimensional COSY, ROESY and DEPTO experiments were performed for the unambiguous assignment of aromatic proton resonances and it was found that two isomeric forms of FLU are present in solution. It was confirmed with the help of ROESY spectral data that only F-substituted aromatic ring penetrates the β-CD cavity and there is chiral differentiation by the β-CD as one of the isomer binds more strongly, which is indicated by the intensity of correlation peaks. The mode of penetration of the guest into the β-CD cavity was also established and structure of the complex has been proposed.     

Phase Separation in Sol-Gel System Containing Mixture of 3- and 4-Functional Alkoxysilanes

The phase separation behavior of gelling systems containing the mixture of 3-functional and 4-functional alkoxysilanes has been investigated. The relation between the starting composition and resultant macroporous morphology was examined using tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as starting alkoxysilanes, formamide (FA) as an additive, under an acidic condition. Up to TMOS:VTMS molar ratio of 0.5:0.5, the phase relation remained almost unchanged from that of pure TMOS system which exhibits morphology with well-defined co-continuous macropores in a very limited concentration region. On the VTMS-rich side typically TMOS:VTMS = 0.2:0.8, however, the co-continuous macroporous morphology was obtained in a broader composition range than those of either pure TMOS or VTMS system. A dome-like pseudo binary region was obtained with the two-phase region extending toward FA-rich direction. The domain size and pore volume of the gels with macroporous morphology could be controlled by alkoxide:water ratio and total solvent fraction, respectively.     

An Investigation of Inclusion Complexes of Cyclodextrins with Phenylurea Herbicides by Photochemically-Induced Fluorescence. Analytical Applications

The effect of -cyclodextrin (-CD) and hydroxypropyl--cyclodextrin (HP--CD) upon the photochemically-induced fluorescence (PIF) properties of four phenylurea herbicides, including linuron, diuron, isoproturon and neburon has been studied. Photochemical conversion of these nonfluorescent herbicides into strongly fluorescent photoproducts was shown to occur in -CD and HP--CD aqueous media. The influence of pH, UV irradiation time and photoproduct stability on the fluorescence intensity was also investigated. In addition, the stoichiometry and formation constants of the complexes formed between herbicides and -cyclodextrin (-CD) or 2-hydroxypropyl--cyclodextrin (HP--CD) were determined. The formation constant values, ranging from 184 ± 40 to 1498 ± 245 M^-1, were calculated by applying the iterative nonlinear regression (NLR) approach to the PIF data. Linear calibrations graphs were established in the interval 1–12 g/mL, for diuron, linuron and neburon. The IUPAC limits of detection ranged between 580 and 700 ng/mL, according to the compound. Application to the analysis of phenylurea herbicides in spiked river water was also described.     

Circular dichroism spectra of the inclusion complexes of phlorizin in cyclodextrins

Two aromatic rings of a phlorizin molecule form inclusion complexes with -CD and -CD. Induced circular dichroism spectra of these complexes have been measured to estimate the orientation of the two aromatic rings in the hydrophobic space of CDs. Apparent complex formation constants have been also estimated for each complex. It is concluded that phlorizin forms a stronger inclusion complex with -CD than with -CD.     

The inclusion complex of piromidic acid with dimethyl-β-cyclodextrin in aqueous solution and in the solid state

Inclusion complex formation of piromidic acid (PA) with dimethyl--cyclodextrin (DM--CD) in aqueous solution and in the solid state was confirmed by the solubility method, differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The apparent stability constant,K _c , of the complex was estimated to be 244 M^–1. The stoichiometry of the complex was given as the ratio 1:2 of PA to DM--CD. The dissolution rate of the PA/DM--CD complex was much greater than that of intact PA.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Synthesis of Ultrafine SiC Powders from Carbon-Silica Hybridized Precursors with Carbothermic Reduction

Inorganic-organic hybrid gels were prepared by simultaneous condensation of the liquid mixture of ethyl silicate, ethyl borate and water soluble phenol resin with low molecular weight. The liquid mixtures were changed into lightly colored transparent gels after a catalyst addition and stirring. The obtained gels were crushed, dried and fired in controlled conditions to yield the inorganic precursors. Since the tailored inorganic precursors mainly consisted of SiO2 and carbon, silicon carbide was formed with the heat treatments in an Ar atmosphere beyond 1773 K with carbothermic reduction. The properties and morphology of the formed silicon carbide powders in terms of the starting precursor compositions and the conditions of the carbothermic reduction were investigated with SEM, XRD and TG-DTA analysis.