Complexation study of midazolam hydrochloride with beta-cyclodextrin: NMR spectroscopic study in solution

(1)H NMR spectroscopic study of midazolam hydrochloride (MDL), beta-cyclodextrin (beta-CD) and their mixtures confirmed the formation of beta-CD-MDL inclusion complex in aqueous solution. The stoichiometry of the complexes was determined by Scott's method to be 1:1, and the association constant (K(a)) was calculated to be 108 M(-1). It was confirmed on the basis of 2D ROESY spectral data that only a fluorine-substituted aromatic ring acted as guest in complexation. Most of the aromatic signals of MDL exhibited induced shift changes as well as splitting, in the presence of beta-CD, indicating chiral differentiation of MDL by beta-CD.     

Complexation study of diclofenac with beta-cyclodextrin and spectrofluorimetric determination

The inclusional complexation between the anti-inflammatory pharmaceutical diclofenac and beta-cyclodextrin (beta-CD) was studied by potentiometry, spectrophotometry and spectrofluorimetry, in both acid and neutral pH. Guest-host 1:1 stoichiometries for the complexes in both media were determined, and their equilibrium constants were calculated. The values obtained from the different methods used are in very good agreement and are in the order of 10(3). From the analysis of the pKa value for diclofenac in both the absence and presence of beta-CD (4.84 and 4.90 respectively), it was inferred that in the inclusion complex the carboxylic group is located outside the cavity. Further structural characterization of the inclusate was carried out by means of 1H NMR spectra and AM1 semiempirical calculations. Based on the obtained results, a spectrofluorimetric method for the determination of diclofenac in the presence of beta-CD was developed in the range of 0-5 micrograms ml-1. Better limits of detection (0.03 microgram ml-1) and quantification (0.1 microgram ml-1) were obtained in this latter case with respect to those obtained in the absence of beta-CD. The method was satisfactorily applied to the quantification of diclofenac in pharmaceutical preparations.     

Iridium-catalyzed asymmetric hydrogenation of imines in supercritical carbon dioxide using phosphite-type ligands

A series of chiral phosphite-type ligands has been evaluated in the iridium-catalyzed asymmetric hydrogenation of acyclic arylimines in supercritical CO₂. High reactivities (100% conversion in 50-120 min) and enantioselectivities (up to 95%) were obtained.     

Raman spectroscopic determination of equilibrium constants of uranyl sulphate complexes in aqueous solutions

Raman spectra are used to determine the formation constants of uranyl sulphate complexes in aqueous solutions at 20 degrees and remedy the confusion existing in this area in the available literature. Solutions with a varying total sulphate concentration and an ionic strength lower than 0.4M are analysed. The species UO(2)SO(4) and UO(2)(SO(4))(2-)(2) are characterized by a resolved Raman band at 861 cm(-1) and an unresolved one at 852 cm(-1), corresponding to the uranyl symmetrical stretching vibration. The equilibrium constants, in term of activity (standard state 1M), are found to be about 1400 and 11, respectively, for the consecutive reactions: UO(2+)(2)(aq)+SO(2-)(4)(aq)=UO(2)SO(4)(aq) and UO(2)SO(4)(aq)+SO(2-)(4)(aq)=UO(2)(SO(4))(2-)(2)(aq).     

Fluorinated phenylated polyphenylenes with nanoporous structures and ultralow dielectric constants formed in supercritical carbon dioxide

New fluorinated bis(tetraarylcyclopentadienones) are synthesized, and their compositions and structures are investigated by elemental analysis and IR, Raman, ¹H, ¹³C, and ¹⁹F NMR spectroscopy. The fluorinated bis(tetraarylcyclopentadienones) are used to prepare a number of new fluorinated phenylated polyphenylenes that combine high thermal and mechanical characteristics and low dielectric constants (2.54?C2.74) with solubility in organic solvents. With the use of supercritical carbon dioxide, thermally stable nanoporous materials with ultralow dielectric constants (1.58?C1.97) are designed on the basis of phenylated polyphenylenes. For phenylated polyphenylenes, the described approach to the synthesis of nanoporous structures with the use of supercritical carbon dioxide is developed for the first time. This approach provides the basis for creation of new breakout technologies in the field of microelectronics.     

Coating carbon nanotubes with polymer in supercritical carbon dioxide

A facile and efficient method has been developed for coating MWNTs with solvent resistant polymer in scCO2, which permits the selective deposition of high molecular weight fluorinated graft poly(methyl vinyl ether-alt-maleic anhydride) polymer onto MWNTs in scCO2 under 100-170 bar at 40 degrees C and forms quasi one-dimensional nanostructures with conducting cores and insulating surfaces.     

Pyrazoles as ligands for the Rh-catalyzed hydroformylation of alkenes in supercritical carbon dioxide

Activity of pyrazole ligands in hydroformylation of a number of unsaturated terminal substrates in supercritical carbon dioxide (scCO₂) in the presence of Rh-catalyst was studied. The ligands without free NH group at position 1 of the pyrazole ring were found to be active. The use of scCO₂ as the reaction medium served to reach a higher conversion and regioselectivity of hydroformylation as compared to those in toluene.     

在超临界CO2流体中的化学反应

超临界CO2流体中的化学反应是继超临界流体应用于萃取分离过程之后进一步将其应用于化学反应的新尝试。本文重点综述了超临界CO2流体中的化学反应研究进展, 并对其发展前景作了展望。     

The use of carboranylphosphite ligands in Rh-catalyzed hydroformylation of alkenes in supercritical carbon dioxide

Novel carborane-containing phosphites were synthesized. The efficiency of the ligands was tested in the Rh-catalyzed hydroformylation of styrene, hept-1-ene, and oct-1-ene in super-critical carbon dioxide (scCO₂) and toluene. The use of scCO₂ as the reaction medium allows one to attain higher conversions and regioselectivities compared to toluene.     

Spectrophotometric determination of equilibrium constants in solution

This paper reviews critically a number of published methods for using ultraviolet or visible spectrophotometric data for the determination of equilibrium constants in solution. Single-stage or overlapping equilibria are considered, and a number of ways in which the experimental data can be handled by electronic computers are suggested.     

Dissolution of uranium dioxide in supercritical fluid carbon dioxide

Uranium dioxide can be dissolved in supercritical CO2 with a CO2-philic TBP-HNO3 complexant to form a highly soluble UO2(NO3)(2).2TBP complex; this new method of dissolving UO2 that requires no water or organic solvent may have important applications for reprocessing of spent nuclear fuels and for treatment of nuclear wastes.     

Monoacetylferrocene crystallization in supercritical carbon dioxide

An organometallic compound, monoacetylferrocene, was for the first time obtained as single crystals by crystallization from supercritical carbon dioxide. This offers the possibility of utilizing supercritical media for efficient crystallization and purification of organometallic compounds without using organic solvents. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 555–557, March, 2006.     

超临界二氧化碳介质中有机化学反应研究

综述了本研究小组近年来在超临界二氧化碳介质中过渡金属催化的有机化学反应的研究结果,主要包括烯烃和炔烃的羰基化反应、氧化反应、自由基反应、低聚反应。     

Solubility of a spiroindolinonaphthoxazine photochromic dye in supercritical carbon dioxide: Experimental determination and correlation

The measurement and correlation of the experimental solubility of a spiroindolinonaphthoxazine photochromic dye (1,3-dihydro-3,3-dimethyl-1-isopropyl-6′-(2,3)-(dihydroindole-1-yl)spiro[2H-indole-2,3′-3H-naphtho[2,1-b] [1,4] oxazine]) in supercritical carbon dioxide (scCO₂) is reported. Results were obtained using a static analytical method, at 308.0, 318.0 and 328.0 K, and in a pressure range from 10.0 to 26.0 MPa. Solubility experimental data were correlated with three density-based models (Chrastil, Bartle and Méndez-Santiago–Teja models), with the Ziger–Eckert semi-empirical correlation and with two cubic equation-of-state (EOS) models, namely the Peng–Robinson EOS (PR-EOS) and the Soave–Redlich–Kwong EOS (SRK-EOS), together with the conventional van der Waals mixing and combining rules. Good correlation results were obtained between the calculated and experimental solubility, to all fitted models. Solubility results clearly indicate the feasibility of processing this dye, and possibly this class of photochromic dyes, using supercritical fluid technologies and processes, for example, supercritical fluid dye impregnation of polymer host materials.     

In situ infrared spectroscopic study of brucite carbonation in dry to water-saturated supercritical carbon dioxide

In geologic carbon sequestration, whereas part of the injected carbon dioxide will dissolve into host brine, some will remain as neat to water saturated supercritical CO(2) (scCO(2)) near the well bore and at the caprock, especially in the short term life cycle of the sequestration site. Little is known about the reactivity of minerals with scCO(2) containing variable concentrations of water. In this study, we used high-pressure infrared spectroscopy to examine the carbonation of brucite (Mg(OH)(2)) in situ over a 24 h reaction period with scCO(2) containing water concentrations between 0% and 100% saturation, at temperatures of 35, 50, and 70 °C, and at a pressure of 100 bar. Little or no detectable carbonation was observed when brucite was reacted with neat scCO(2). Higher water concentrations and higher temperatures led to greater brucite carbonation rates and larger extents of conversion to magnesium carbonate products. The only observed carbonation product at 35 °C was nesquehonite (MgCO(3)·3H(2)O). Mixtures of nesquehonite and magnesite (MgCO(3)) were detected at 50 °C, but magnesite was more prevalent with increasing water concentration. Both an amorphous hydrated magnesium carbonate solid and magnesite were detected at 70 °C, but magnesite predominated with increasing water concentration. The identity of the magnesium carbonate products appears strongly linked to magnesium water exchange kinetics through temperature and water availability effects.     

Olefin metathesis in supercritical carbon dioxide

Liquid or supercritical carbon dioxide (scCO(2)) is a versatile reaction medium for ring-opening metathesis polymerization (ROMP) and ring-closing olefin metathesis (RCM) reactions using well-defined metal catalysts. The molybdenum alkylidene complex 1 and ruthenium carbenes 2 and 3 bearing PCy(3) or N-heterocyclic carbene ligands, respectively, can be used and are found to exhibit efficiency similar to that in chlorinated organic solvents. While compound 1 is readily soluble in scCO(2), complexes 2 and 3 behave like heterogeneous catalysts in this reaction medium. Importantly, however, the unique properties of scCO(2) provide significant advantages beyond simple solvent replacement. This pertains to highly convenient workup procedures both for polymeric and low molecular weight products, to catalyst immobilization, to reaction tuning by density control (RCM versus acyclic diene metathesis polymerization), and to applications of scCO(2) as a protective medium for basic amine functions. The latter phenomenon is explained by the reversible formation of the corresponding carbamic acid as evidenced by (1)H NMR data obtained in compressed CO(2). Together with its environmentally and toxicologically benign character, these unique physicochemical features sum up to a very attractive solvent profile of carbon dioxide for sustainable synthesis and production.     

Rheology of polydimethylsiloxane swollen with supercritical carbon dioxide

Viscosity curves were measured for polydimethyl siloxane (PDMS) melts swollen with dissolved carbon dioxide at 50 and 80°C for shear rates ranging from 40 to 2300 s⁻¹, and for carbon dioxide contents ranging from 0 to 21 wt %. The measurements were performed with a capillary extrusion rheometer modified for sealed, high-pressure operation to prevent degassing of the melt during extrusion. The concentration-dependent viscosity curves for these systems are self-similar in shape, exhibiting low-shear rate Newtonian plateau regions followed by shear-thinning “power-law” regions. Considerable reduction of viscosity is observed as the carbon dioxide content is increased. Classical viscoelastic scaling methods, employing a composition-dependent shift factor to scale both viscosity and shear rate, were used to reduce the viscosity data to a master curve at each temperature. The dependence of the shift factors on polymer chain density and free volume were investigated by comparing the shift factors for PDMS-CO₂ systems to those obtained by iso-free volume dilutions of high molecular weight PDMS. This comparison suggests that the free volume added to PDMS upon swelling with dissolved carbon dioxide is the predominant mechanism for viscosity reduction in those systems. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 523–534, 1997     

Lewis acids catalyzed ring-opening reactions of methylenecyclopropanes and epoxides in supercritical carbon dioxide or modified supercritical carbon dioxide with perfluorocarbon

The reactions of methylenecyclopropanes (MCPs) and epoxides with alcohols and aromatic amines can be carried out in supercritical carbon dioxide (scCO₂) or modified scCO₂ with perfluorocarbon which offer a way to synthesize various alcohols, amino-alcohols, homoallylic ethers, and amines under an environmentally benign condition.