Interaction of some antibiotics with hydroxypropyl-β-cyclodextrin

The interaction between 19 antibiotics and hydroxypropyl--cyclodextrin (HPCD) was studied by reversed-phase thin-layer chromatography. HPCD formed inclusion complexes with 16 compounds, the complex always being more hydrophilic than the uncomplexed drug. The intensity of interaction significantly increased with increasing specific hydrophobic surface area of the guest molecule proving the preponderant role of hydrophobic interactions in inclusion complex formation. The intensity of the HPCD-drug interaction significantly decreased with increasing concentration of methanol in the environment indicating that methanol can also enter the cyclodextrin cavity and inhibits competitively the inclusion complex formation or the free energy of transfer from water to the HPCD cavity should be less negative at higher concentration of methanol in the aqueous medium.Dedicated to Professor József Szejtli.     

Use of full-column imaging capillary isoelectric focusing for the rapid determination of the operating conditions in the preparative-scale continuous free-flow isoelectric focusing separation of enantiomers

A rapid, simple method is proposed here for the identification of the experimental conditions that lead to satisfactory preparative-scale isoelectric focusing enantiomer separations in continuous free-flow electrophoretic units. The method first calls for the use of a commercially available, full-column imaging capillary electrophoretic system to find the background electrolyte composition that generates the largest pI difference between the bands of the enantiomers. The method then calls for the finding of the minimum residence time that permits full development of the pH gradient across the separation chamber of the continuous free-flow electrophoretic unit by measuring the pH in the sample-free carrier electrolyte fractions collected during these runs. Finally, the quality of the predicted preparative-scale separation is verified by analyzing the enantiomer-containing collected fractions by capillary electrophoresis using a 14-sulfated, single-isomer cyclodextrin as resolving agent. The pI difference values and production rate values observed in this work agree well with the literature values that were obtained by much more time-consuming methods.     

pH oscillations in the BrO3--SO3(2-)/HSO3- reaction in a CSTR

Large-amplitude pH oscillations have been measured during the oxidation of sulfur (IV) species by the bromate ion in aqueous solution in a continuous-flow stirred tank reactor in the absence of any additional oxidizing or reducing reagent. The source of the oscillation in this simple chemical reaction is a two-way oxidation of sulfur (IV) by the bromate ion: (1) the hydrogen-ion-producing self-accelerating oxidation to sulfur (VI) (SO4(2-)), and (2) a hydrogen-ion-consuming oxidation to sulfur (V) (S2O6(2-)). In such a way, both the H+-producing and H+-consuming composite processes required for a pH oscillator take place in parallel in a reaction between two reagents in this system. A simple reaction scheme, consisting of the protonation equilibria of SO3(2-) and HSO3-, the oxidation of HSO3- and H2SO3 by BrO3- to SO4(2-), and the oxidation of H2SO3 to S2O6(2-) has successfully been used to simulate the observed dynamical behavior. Simulation with this simple scheme shows that oscillations can be calculated even if only about 1% of sulfur (IV) is oxidized to S2O6(2-) along with the main product SO4(2-). Agreement between calculated and measured dynamical behavior is found to be quite good. Increasing temperature decreases both the period length of oscillations in a CSTR and the Landolt time measured in a closed reactor. No temperature compensation of the oscillatory frequency is found in this reaction.     

Preparative-scale isoelectric trapping separations in methanol-water mixtures

The typically low aqueous solubilities of small, hydrophobic organic ampholytic molecules limit the production rates that can be achieved in their isoelectric trapping (IET) separations and call for the use of hydro-organic mixtures as solvents. The compatibility of methanol-water mixtures and poly(ethylene terephthalate) substrate-supported isoelectric polyacrylamide hydrogels, developed for binary IET separations in a Gradiflow BF200IET unit, was investigated. The isoelectric polyacrylamide-based hydrogels retained their functional and mechanical integrities when the methanol concentration in the hydro-organic solvent mixture was kept at or below 25% (v/v). The utility of the hydro-organic media was demonstrated in the purification of a hydrophobic ampholytic compound, technical grade 4-hydroxy-3-(morpholinomethyl) benzoic acid. Production rates as high as 7 mg/h were achieved using small, 15 cm2 active surface area isoelectric membranes.     

Analysis of silicon carbide powder by ETV-ICP-AES

Summary A direct tandem atomic spectroscopic method for the determination of Ca, Fe and Ti impurities in SiC powders with various grain size (0.7850<48.5 m) has been developed. The method is based on high temperature halogenation of the sample with Freon 12 in a graphite furnace and ICP-AES detection of the evolved sample components. The concentration of the matrix element silicon in the ICP increased to a maximum value after 10s of heating, independent of the grain size of the powder samples. For performing a calibration with standard solutions a finegrained, purified SiC-powder was evaporated simultaneously with the solution residues. The calibration curves produced using this analyte-addition technique and using within-laboratory solid standards were identical within experimental error.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam     

Dipole-induced polymorphs of trans-2-hydroxycycloheptanecarboxylic acid with virtually the same unit cell

The polymorphs of trans-2-hydroxycycloheptanecarboxylic acid have exactly the same lattice parameters and thus mimic isomorphism. They differ only in their space group: Pna21 versus Pn21a. In form II, the screw axes turn the 18-membered rings of hydrogen-bonded tetramers around the b axis. In this way, the stacking of the layers becomes antiparallel, which cancels out the dipoles within the unit cell. In form I, the same turn around the c axis leaves the stacking of the layers parallel. Thus, the dipoles are canceled out by antiparallel domains in the crystals. Between the antiparallel domains of I, each frontier is a double layer of II. This implies that (a) a pure form of I cannot be isolated and (b) the percentage of II in I may alter from crystal to crystal.     

Synthesis,analytical characterization and initial capillary electrophoretic use in acidic background electrolytes of a new,single-isomer chiral resolving agent: hexakis(2,3-di-O-acetyl-6-O-sulfo)-alpha-cyclodextrin

The sodium salt of hexakis(2,3-di-O-acetyl-6-O-sulfo)-alpha-CD (HxDAS), the first member of the family of single-isomer, fully sulfated alpha-CDs, has been synthesized and used for the initial capillary electrophoretic separation of the enantiomers of nonionic, weak acid, weak base, and ampholytic analytes. HxDAS complexes less strongly with many of the analytes tested than the analogous beta- and gamma-cyclodextrin derivatives, namely, heptakis(2,3-di-O-acetyl-6-O-sulfo)-beta-cyclodextrin (HDAS) and octakis(2,3-di-O-acetyl-6-O-sulfo)-gamma-cyclodextrin (ODAS). Nevertheless, it facilitated the separation of the enantiomers of a large number of weak electrolyte and nonelectrolyte analytes in acidic aqueous background electrolytes. For all analytes, the effective mobilities and separation selectivities as a function of the background electrolyte concentration of HxDAS followed the trends that were found for HDAS and ODAS.     

Organotitanium carbonyls. Reaction of tetrabenzyl-titanium with carbon monoxide

Tetrabenzyltitanium and its dicyclohexylamine adduct react with carbon monoxide to form acylbenzyltitanium compounds, which have been characterized. The presence of (PhCH₂)₄Ti(CO)₂ (amine) and (PhCH₂)₄Ti(CO) (amine) as intermediates was indicated by the IR spectra.     

Preparative-scale isoelectric trapping separations using a modified Gradiflow unit

The Gradiflow BF200 preparative electrophoretic unit (Gradipore), which has been developed for size-based and charge-sign-based protein separations and in which the hydraulic flow path of the recirculating sample stream in the separation cartridge is orthogonal to the electric field, has been modified to carry out binary protein separations using the principles of isoelectric trapping. The disposable separation cartridge contained three isoelectric membranes which, along with the cartridge holder, formed the anode and cathode compartments and the anodic and cathodic separation compartments. The utility of the modified instrument was demonstrated by effecting a binary separation of chicken egg white across an isoelectric point 5.5 isoelectric membrane. The desalting and subsequent binary separation steps proved to be remarkably rapid, due to the favorable combination of short electrophoretic path, high electric field strength and large effective isoelectric membrane surface area.     

A facile synthesis of 4-, 5- and 6-chloromethyl-1H-indole-2-carboxylates: replacement of a sulfonic acid functionality by chlorine

Valuable new synthetic intermediates, 4-, 5- or 6-chloromethyl-1H-indole-2-carboxylates, were prepared by the facile elimination of SO₂ from 2-ethoxycarbonyl-1H-indole-4-, 5- or 6-methanesulfonic acids, respectively, easily accessible by Fischer-type indolization.