Dioxane-water Solvent Research Articles

Determination of Stability Constant of Flurosubstituted Chlconemines for its Medicinal Efficiency

The good activity of drug is depending upon its stability constant i.e. proton ligand stability constant and metal ligand stability constant. If the stability constant is fairly very good then it should use as a good and effective medicine .In content to this in present work the proton ligand stability constant and metal ligand stability constant of fluro substituted chalconeimines L5 = 2-Hydroxy naphthalene 4-dimethyl aniline 4- fluro chalconeimine [FN] are studied with highly reactive transition metal like (Cu (II), Co(II),Cr(II) and Fe(III)). The 70% dioxane water solvent system used in the present investigation. The presence of –OH group confirmed by using of 0.1 M ionic strength. The transition metal (Cu (II),Co (II),Cr(II)and Fe(III)) used and the ligand form 1:1 and 1:2 complex with all values of log k1 and log k2 positive.

Synthesis, spectral, thermal, potentiometric, antitumor, antimicrobial and PM3 studies of pyridazinone hydrazone metal complexes

New binary complexes with the general formula [M2(Bpsq)(NO3)n(H2O)4].yEtOH (where n = 0 or 2, y = 0 or ½, M = Cu(II), Ni(II), Co(II), VO(IV), UO2(VI) or Th(IV) ion and Bpsq = 3,4-bis[carboxy-2-hydroxy-benzyledene-5,6-diphenyl-3-(2H)pyridazinone] cyclobut-1-ene-1,2-diol), have been synthesized and characterized by elemental analysis; ESR, mass, UV-Vis and IR spectroscopies, magnetic and conductance measurements, additional to TGA and DSC thermal analysis. The acid-base interactions and their equilibrium constants with transition metal ions were investigated by potentiometric and spectrophotometric techniques in 75% (v/v) dioxane-water solvent at 30 °C. The Bpsq ligand was applied as metal indicator for determination of Cu(II) and VO(IV) by complexometric titrations. The antitumor activity was evaluated in vitro against Hepatocellular carcinoma cell line (HepG-2 cells). The Bpsq ligand exhibited stronger antitumor activity than its Cu(II)- and Ni(II)- complexes. The antimicrobial screening results showed low antimicrobial activity against Bacillus subtilis (bacteria), but moderate against Candida albicats (fungus). The molecular orbital calculations for Bpsq ligand and its complexes were performed using Hyperchem 7.52 program at PM3 level and their data are correlated with the experimental data.

The reactivity of N-phenylanthranilic acids derivatives. XXV. Kinetic parameters of activation and isoparametricity of the reaction of the alkaline hydrolysis of methyl esters of substituted 4,5-dimethoxy-N-phenylanthranilic acids in the binary dioxane-water solvent

The reactivity of N-phenylanthranilic acids derivatives. XXV. Kinetic parameters of activation and isoparametricity of the reaction of the alkaline hydrolysis of methyl esters of substituted 4,5-dimethoxy-N-phenylanthranilic acids in the binary dioxane-water solvent

Electric conductance of dispersions of metal oxides in solutions of weak acids in mixed dioxane–water solvents

The electric conductance of solutions of sulfuric, oxalic, benzoic, and salicylic acid (up to 0.02M) in dioxane–water mixed solvents (90% and 93% dioxane by mass) has been studied in the presence and absence of TiO2 and Al2O3 (0.5–5% by mass). TiO2 and Al2O3 enhanced the conductance of solutions of organic acids in aqueous dioxane. The conductance is interpreted in terms of adsorption of acid in molecular form, dissolution of ceramic oxides in form of anionic complexes, and leaching of acidic impurities from ceramic oxides.

How is the reactivity of laccase affected by single-point mutations? Engineering laccase for improved activity towards sterically demanding substrates

In spite of its broad specificity among phenols, Trametes versicolor laccase hardly succeeds in oxidizing hindered substrates. To improve the oxidation ability of this laccase towards bulky phenolic substrates, we designed a series of single-point mutants on the basis of the amino-acid layout inside the reducing substrate active site known from the crystal structure of the enzyme. Site-directed mutagenesis has addressed four phenylalanine residues in key positions 162, 265, 332, and 337 at the entrance of the binding pocket, as these residues appeared instrumental for docking of the substrate. These phenylalanines were replaced by smaller-sized but still apolar alanines. A double mutant F162A/F332A was also designed. Measurement of the oxidation efficiency towards encumbered phenols has shown that mutant F162A was more efficient than the wild-type laccase. The double mutant F162A/F332A led to 98% consumption of bisphenol A in only 5h and was more efficient than the single mutants in the aerobic oxidation of this bulky substrate. In contrast, lack of appropriate hydrophobic interactions with the substrate possibly depresses the oxidation outcome with mutants F265A and F332A. One explanation for the lack of reactivity of mutant F337A, supported by literature reports, is that this residue is part of the second coordination shell of T1 Cu. A mutation at this position thus leads to a drastic coordination shell destabilization. Thermal stability of the mutants and their resistance in a mixed water-dioxane solvent have also been investigated.

A three-phase liquid system based on orthocarboxylic acid salts

The composition of the three-phase liquid system based on potassium orthobenzoate in a water-dioxane solvent was studied. The phases were found to contain benzoic and orthobenzoic acid salts in various association states. The middle layer was considered. Its composition was indicative of the formation of a potassium complex with oxygen-containing ligands. The structure of this complex was similar to that of the associative crown ether structure.

Steady‐State and Time‐Resolved Emission Studies of 6‐Methoxy Quinoline

Steady‐state absorption, fluorescence excitation, and emission spectra of 6‐methoxy quinoline (6‐MQ) were measured at room temperature in cyclohexane, dioxane, ethanol, acetonitrile, water, and water–dioxane solvents. Absorption spectra of cyclohexane, n‐hexane, and isopentane solutions show resolved vibronic structure at room temperature. However, the excitation spectrum of cyclohexane solution is structureless and is found to be emission wavelength dependent, indicating the formation of at least two distinct species in the ground state. Similar behavior was observed in dioxane and water–dioxane solutions. For all other solutions, the fluorescence excitation spectrum of 6‐MQ was found to be the same for different emissions. Emission of 6‐MQ in all solvents consisted of two bands with their maxima around 355 nm (I) and 430 nm (II), the actual positions and the relative intensities being dependent on the solvent used. The bands I and II were respectively attributed to normal and protonated/H‐bonded species of either 1La or 1Lb states or mixed (1La/1Lb) state of ππ* character. Fluorescence decay of this dye in all solvents monitored over each emission maximum showed biexponential behavior, and the analysis yielded two different lifetime components for each emission band. The short and long fluorescence decay components were respectively in the range of 0.30–3.00 ns and 18–20 ns. The observed emission characteristics coupled with the nature of the fluorescence polarization spectra and two different decay components for each emission suggest the existence of two different conformers having two different excited electronic states.

A fluorimetric study of pindolol and its complexes with cyclodextrins

Spectrofluorimetric characteristics of pindolol have been investigated with the aim of using this technique for analytical determinations. Other monosubstituted indole derivatives, 4-methoxy and 5-methoxyindole, have been also studied for comparative purposes. Corrected excitation and emission wavelengths in different solvents are reported and the effect of solvent on the Stokes shifts of these compounds has been analysed using the Lippert equation. In addition, the Stokes shift of pindolol has been determined in dioxan–water solvent mixtures and the presence of specific solvent effects is discussed. The fluorescence of pindolol is pH dependent, the quantum yields determined in water are lower than those in other solvents. With respect to the sensitivity, it has been found that the detection limits in aqueous solutions are improved in the presence of β and methyl-β-cyclodextrin. Finally, a fluorimetric analysis of the interaction between pindolol and different cyclodextrins has been carried out in order to determine the apparent stability constants of the complexes and the thermodynamic parameters associated to complexation.

New Chromogenic Azothiacrown Ethers — Synthesis and Properties.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Thermodynamics of Complex Formation and Solvation in the System NaCl-18-crown-6-Water-Dioxane

Stability constants of Na+ complexes with 18-crown-6-ether and thermodynamic characteristics of the complex formation in water and mixed water-dioxane solvents (0.2, 0.4, 0.6, and 0.8 wt. fraction of dioxane, 283-318 K) were determined by the method of EMF of galvanic circuits without transfer. Comparative thermodynamic analysis of the complex 18-crown-6Na+ formation reactions in water-dioxane, water-acetonitrile, water-acetone, water-methanol, and water-2-propanol mixtures was carried out. Contributions of the Gibbs energies of transfer (ΔG t) of 18-crown-6Na+, Na+, and the ligand to the increase in the stability of the complexes on replacement of water by mixed water-dioxane solvents were estimated. It was shown that the increase in the stability of sodium crown ether complexes primarily depends on solvation of the complex cation and desolvation of the central cation. Changes in the conformational Gibbs energy of the ligand and quantitative parameters of selective solvation of the reagents were estimated.

Photophysical properties of 7-diethylaminocoumarin dyes in dioxane–water mixtures: hydrogen bonding, dielectric enrichment and polarity effects

The effect of water on the photophysical properties of four 7-diethylaminocoumarin dyes (AC 1, BC I, BC II and C 35) in dioxane–water solvent mixtures is studied. Dielectric enrichment of the dyes is not observed in the binary mixtures. Rate constants for bimolecular quenching are calculated. BC I and C 35 are found to undergo both static and dynamic quenching while only static quenching is observed in the case of BC II. The association constant is however found to be very small (Kb=2–5×10-2 M-1). No such dependence is observed in AC 1 where the formation of an intramolecular hydrogen bond is strongly favored. The increase in the non-radiative rate constant with the water concentration observed in the other three dyes (BC I, BC II and C 35) can be correlated to the solvent polarity and hydrogen bonding parameter ET(30). A threshold value of the solvent polarity–polarizability parameter (Pekar factor C) for the non-radiative process is observed for all these three dyes and it is nearly independent of the nature of substitution. The photophysical properties of AC 1 can be adequately explained by considering only one singlet excited state while an additional singlet excited state needs to be included to understand the photophysics of BC I, BC II and C 35 in highly polar environments.

Studies on kinetic parameters and stability of aminoacylase in non-conventional media

Catalytic properties and conformational stability of aminoacylase ( N-acylamino acid amidohydrolase, EC 3.5.1.14) were studied in water– N, N-dimethylformamide (DMF) and water–dioxane solvent mixtures. Beside the prompt inhibition the solvents caused further inactivation during incubations. In the presence of 5% DMF content the inactivation proceeds with a well-measurable rate ( t 1/2 39 min), while in the case of 20% DMF the enzyme practically lost its starting activity during 50 min incubation ( t 1/2 13 min). The K m value of the enzyme increased about three times with increasing DMF concentrations up to about 2.6 M DMF, while the V max value decreased practically to zero in the same concentration range.

Enzymatic Polymerization of Phenolic Biomonomers Derived from Cashew Nut Shell Liquid

Enzymatic polymerization of alkyl phenols derived from a renewable resource, viz., cashew nut shell, has been carried out in a dioxane-water mixture. The reaction and reaction products have been characterized by a number of spectroscopic, microscopic, and thermometric methods. These monomers have also been copolymerized with various substituted phenols. The homopolymers are soluble in organic solvents while the copolymers are crosslinked, with negligible solubility. Enzymatic polymerization in a dioxane-water solvent mixture results in spherical particles in the case of homopolymerization while structures without distinctive morphologies are obtained in the case of copolymerization. The effects of dioxane-water composition and solution pH on the polymerization reaction have also been explored.

Influence of an external magnetic field on the electrochemical behaviour of ortho, meta and para nitrobenzaldehydes and nitrobenzoic acids in water dioxane solvent

The electrochemical behaviour of ortho, meta, para nitrobenzaldehydes and nitrobenzoic acids under the influence of a magnetic field ( B = 0.45 Tesla) was examined using cyclic voltammetry. The electroreduction yield was estimated by the electric charges evolved during each cycle. It was observed that the application of the magnetic field induces an enhancement of the NO 2 group electroreduction. These yields of electroreduction seems to depend on the position of the electron withdrawing group: CHO and COOH. Two main influences are outlined: the magnetohydrodynamic effect and the magnitude of the dipole moment of each nitro compound. The case of nitrobenzoic acids appears to be more complicated because the molecular and ionic forms coexist at pH 5.5.

Nonlinear Enthalpy–Entropy Compensation for the Solubility of Phenacetin in Dioxane–Water Solvent Mixtures

The solubility of phenacetin was determined at five temperatures in solvent mixtures of aprotic–amphiprotic mixtures of dioxane and water. Enthalpy–entropy compensation analysis is used to study the effect of changing polarity of the medium on the solute. The apparent heats of solution and free energies of solution are nonlinear functions of the cosolvent (dioxane) ratio. The free energy curve goes through a minimum at 80–90% dioxane in water, whereas the apparent heat of solution displays a maximum at low cosolvent ratio (40% dioxane) and a minimum at high cosolvent ratio (90% dioxane). A plot of ΔH against ΔG shows a nonlinear compensation effect. Two different mechanisms (entropy and enthalpy) are suggested to be the driving forces to increase solubility. These two mechanisms can be related to the nonlinearity of the compensation effect. The slope changes from positive to negative at 40% dioxane. The overall nonlinear function can also be considered as two linear relationships that intersect at 40% dioxane. The results support the usefulness of enthalpy–entropy compensation analysis for a better understanding of the solubility of drugs in aqueous mixtures as related to the role of cosolvents.

Electrochemistry of polyoxometalates immobilized in ion exchange polymer films

The polyoxometalate ions PMo12O403−, PW12O403−, and SiW12O404−are incorporated in polymeric ruthenium(II)(vinyl)bipyridine (poly-Ru(vbpy)32+) films from aqueous and dioxane–water electrolytes. Despite their large mass the ions exist as freely diffusing species that compensate for up to 30% of the charge in poly-Ru(vbpy)32+. An investigation of the effect of environmental conditions on electrochemical behavior reveals that the first two one-electron reduction waves of SiW12O404−coalesce into a single two-electron reaction and those of PW12O403−shift significantly in potential upon a change from pure aqueous to 50(v/v)% dioxane/water solvent. The observation is attributed to destabilization of the one-electron reaction products as the solvent is enriched is dioxane. Incorporation of polyoxometalates in protonated poly(vinyl)pyridine and poly-Ru(vbpy)32+films from dioxane–water solvent results in differences in electrochemical behavior. Polyoxometalate anions incorporated in poly-Ru(vbpy)32+films catalyze the electrochemical reduction of hydrogen ion. Keywords: polyoxometalate, electrochemistry, poly-Ru(vbpy)32+, electrocatalysis, immobilization.

Kinetics and mechanism of hydrolysis of open-chain thioacetals derived from benzophenone and the reactivity of α-thiophenyl carbocations

In a 40%(v/v) dioxane–water solvent, in the presence of 0.3–4.0 mol dm–3 perchloric acid, the rates of hydrolysis of diethyl and diphenyl thioacetals derived from substituted benzophenones exhibit substituent effects, acidity dependencies, activation parameters and solvent isotope effects which all suggest that the hydrolyses follow the A1 mechanism. The diethyl acetals are ca. 104-fold less reactive than their O,O-analogues and ca. 104-fold more reactive than the corresponding dithanes, for both of which classes of acetal the ASE2 mechanism of hydrolysis has been suggested. In concentrated aqueous perchloric acid the diaryl thioacetals are, like the diethyl compounds, rapidly and quantitatively converted into the corresponding α-thin carbocations, which then undergo slow hydrolysis to the benzophenone. Kinetic measurements show that the α-thiophenyl carbocation Ph2C+–SPh is ca. 20-fold more reactive towards hydrolysis than is Ph2C+–SEt, but that substituents in the thiophenyl group have little effect on reactivity (ρ≃ 0.6). The detailed kinetic results are compatible with our previous suggestions about the mechanism of hydrolysis of α-thin carbocations.

Kinetics of the silver ion-promoted hydrolysis of 2-methyl-2-(substituted phenyl)-1,3-dithianes in 10% dioxane–water mixtures. Implications for cyclic acetal hydrolysis catalysed by hydrogen ions

The hydrolysis of 1,3-dithianes derived from para-substituted acetophenones is promoted by silver ions. Kinetic study using a 10%(v/v) dioxane–water solvent shows that, when [Ag+]≲ 0.2 mol dm–3, the p-NO2, -Cl, -H and -Me derivatives hydrolyse via rapidly-formed 1 Ag+ : 1 dithiane-complexes, but that the p-MeO derivative forms an unreactive 1 : 1-complex and hydrolyses via a 2 Ag+ : 1 dithiane-complex. Comparison of the kinetic parameters with those available for analogous open-chain S,S-acetals reveals that cyclisation leads to a substantial (> 104-fold) overall loss of reactivity and that this loss arises both from a lowering of acetal basicity towards Ag+ and from a slower rate of hydrolysis of the 1 : 1-complex. The implications for hydrogen ion-catalysed hydrolyses of cyclic acetals are discussed, as are the reasons for the lower reactivity of the cyclic acetals.

Kinetics of the mercury(II) ion-promoted desulfurisation of thiocarbamates in aqueous solution

In a 1% dioxane–water solvent in the presence of Hg2+ ions thiocarbamates p-RC6H4NHC(S)OEt (R = MeO, Me, H, F) rapidly form complexes of 2 thiocarbamate: 1 Hg2+ stoichiometry. In the presence of an excess of Hg2+ ions partial conversion to the 2 : 2-complexes probably occurs which decompose to the corresponding carbamates (p-RC6H4NHCO2Et) and HgS. With R = NO2 the 2 : 2 complex is dominant even at low Hg2+ ion concentrations, and desulfurisation is then independent of [Hg2+]. Electron-withdrawal by R favours the 2 : 2 complex but decreases its rate of decomposition to products. The effects of changes in the hydrogen ion concentration suggest that ionisation of N-bound protons in the complexes favours reaction. A mechanism is suggested. The kinetic behaviour is somewhat similar to that found previously for thiobenzamides, but the new results suggest the mechanism previously proposed may need revision.

Epoxidation of cyclohexene, methylcyclohexene and cis-cyclooctene by molecular oxygen using ruthenium(III) aquo ion as catalyst: a kinetic study

Kinetics of the epoxidation of cyclohexene, methylcyclohexene and cis-cyclooctene by molecular oxygen catalysed by Ru(III) ion, [RuCl 2H( 2O) 4] + at pH 2.0 in a mixed water-dioxane solvent medium are reported. The reactions were studied manometrically as a function of catalyst, substrate and dioxygen concentrations. For all the substrates studied, the rate of oxidation is first order with respect to catalyst and substrate concentrations and one-half order with respect to dioxygen concentration. The oxidations yielded epoxide as the only product in all cases; these were identified and analysed by GLC technique. Based on the kinetics, a mechanism involving homolytic cleavage of the O-O (peroxo) bond with concerted transfer of the oxygen atom to the substrate was proposed. The presence of methyl group on the cyclohexene ring (reaction 2) and an increase in the number of carbon atoms in the ring for cyclooctene (reaction 3) cause a decrease in the rates of epoxidation. The rate of epoxide formation and the corresponding yields for reactions ( 1), ( 2) and ( 3) decreases in the order: cyclohexene > methylcyclohexene > cyclooctene.