Aqueous-organic Solvent Systems Research Articles

EFFECT OF WAVELENGTH, CARBONYL GROUP AND SOLVENT ON PHOTO-INDUCED GRAFT POLYMERIZATION ONTO DIALDEHYDE CELLULOSE

Graft polymerization of various vinyl monomers onto dialdehyde cellulose (H-sample) by a photo-induced method was carried out in aqueous systems using qualz and pyrex tube, and the results were compared with those for the photo-induced graft polymerization onto purified cotton linter (C-sample).The degree of grafting of methyl methacrylate (MMA) onto H-sample contained a small amounts of carbonyl group is greater than that onto C-sample. H-sample was easily grafted by the light with the wavelength above 300nm. The chain scission in H-sample occurred with the light of 253nm wavelength. From these results, it is indicated that the graft polymerization proceeds mainly via the photolysis of carbonyl groups in cellulose, and the difference in the wavelength of absorbed light has an effect on the grafting site.In the graft polymerization of various vinyl monomers onto H-sample, the total conversion and the degree of grafting increased with increasing carbonyl group content in cellulose. The grafting activity decreased in the order of MMA, acrylamide, vinyl acetate, acrylonitrile and styrene.In the graft polymerization of MMA in aqueous organic solvent systems, the degree of grafting decreased with increase of the organic solvent concentration, but the grafting efficiency yield 85-95%. The chain transfer constants of CCl4, i-BuOH, (Me)2CO and dimethylformamide were 10.3, 3.8, 1.3 and 0.7×10-5, respectively.

Cryoenzymology: The use of sub-zero temperatures and fluid solutions in the study of enzyme mechanisms

Theoretical and experimental support for the use of sub-zero temperatures and fluid aqueous organic solvent systems in the study of enzyme mechanisms is presented. If the reaction between enzyme and substrate is initiated by mixing them at a suitably low temperature non-steady state, non-turnover conditions will result. Under such circumstances, the overall catalytic reaction will potentially appear as a series of reactions as the temperature is raised, each one corresponding to the transformation of one intermediate into a subsequent one. The technique is especially suited for the accumulation of high concentrations of intermediates which makes physical and chemical studies on their structure quite feasible. Recent investigations have shown that enzyme-substrate intermediates can be trapped in the crystalline state and that X-ray crystallographic studies can be carried out on them at sub-zero temperatures. Rate reductions of the order of 10 10 are possible using the combined effects of pH and temperature. Kinetic and thermodynamic information concerning intermediate transformations may also be obtained. Kinetic expressions for such systems are derived in the Appendix. The advantages and limitations of the method, including possible problems relating to the effects of solvent and temperature on the enzyme structure, experimental procedures, and interpretation of results are considered.

Collagen‐Poly(methyl methacrylate) graft copolymers: Effect of aqueous organic solvent system and salts on copolymer composition

AbstractCollagen‐poly(methyl methacrylate) (PMMA) graft copolymers were prepared in a number of aqueous/organic solvent systems and in the presence of neutral salts using ceric ammonium nitrate as initiator. The composition of the collagen‐methyl methacrylate graft copolymers was studied by hydrolyzing the collagen backbone and measuring the molecular weights of the grafted PMMA branches. In water/methanol grafting media the molecular weights of the PMMA branches showed a maximum at a methanol concentration of 25% and then decreased with further increase in methanol concentration. Even though the percent grafting registered a sharp fall with increasing concentration of methanol, the number of grafting sites remained more or less constant and was almost the same as that obtained in aqueous medium. Other aqueous/organic solvent systems gave more grafted chains than those prepared in water alone, and these were of lower molecular weight. Anions such as sulphate and chloride were found to have more influence than nitrate in decreasing the number of grafting sites.

Determination of vanadium and molybdenum by atomic-absorption spectrophotometry

A method is described for the determination by atomic-absorption spectrophotometry of vanadium and molybdenum, up to the milligram level, in samples of yellow cake, uranium-bearing minerals and geochemical standards. After attack with acids these two elements are separated from each other and from matrix elements by means of anion-exchange in 6M hydrochloric acid on the strongly basic anion-exchange resin Dowex 1, X8 (chloride form). Vanadium is unadsorbed and passes into the effluent while molybdenum is adsorbed on the resin. For the elution of molybdenum a mixed aqueous-organic solvent system consisting of methanol and 6M hydrochloric acid (9: 1 v/v) is used. After evaporation of the 6M hydrochloric acid effluent and of the mixed aqueous-organic eluate vanadium and molybdenum are determined by atomic-absorption spectrophotometry. The method was tested by analysing numerous samples with contents ranging from a few ppm to milligram amounts of vanadium and molybdenum. For comparison, the concentrations of these two elements were determined in a large number of samples by spectrophotometric and titrimetric procedures. In all cases very good agreement of results was obtained.

Graft copolymers of starch with mineral acid salts of dimethylaminoethyl methacrylate. Preparation and testing as flocculating agents

AbstractMineral acid salts of dimethylaminoethyl methacrylate (DMAEMA) have been graft polymerized onto starch with ferrous ammonium sulfate–hydrogen peroxide initiation. The nitric acid salt was used in most reactions, and graft polymerizations were run in both water and aqueous–organic solvent systems. Increased monomer concentration in water led to an increase in both the percentage of poly(DMAEMA · HNO3) in the graft copolymer (percent add‐on) and the molecular weight of grafted branches. Variations in initiator concentration altered the percent add‐on only slightly but affected the molecular weight of grafted polymer significantly. When swollen starch, in contrast with unswollen starch was used in graft polymerization reactions run in water, the product had a higher per cent add‐on and a larger number of grafted branches of lower molecular weight. The efficiency of starch–poly(DMAEMA · HNO3) graft copolymers as flocculants for diatomaceous silica increased with per cent add‐on; however, variations in grafting frequency and graft molecular weight had less effect on the behavior of these materials as flocculants.

Solvent effects on solubilities and partition coefficients of some copper(II)-beta-diketone complexes

The solubilities of three members of a homologous series of copper(II)-beta-diketone complexes have been measured in a number of common organic solvents at 25 ± 0·02 deg centigrade. Using these data and respective molar volumes of the solid chelates, solubility parameter values (δ) were calculated. The constancy of the calculated values was taken as evidence of the adequacy of the regular solution concept for explaining the observed solubility trends in the solvents studied. Distribution coefficients for the first member of the series were measured in a number of aqueous-organic solvent systems. The extraction data were examined by the regular solution treatment and good agreement of solubility parameter values (δ) calculated from solubility and distribution data was obtained. A comparison of results obtained by the various proposed methods is given. A verification of the validity of estimating δ values for chelate compounds from structural information was attempted.

Copolymers of Wheat Starch and Polyacrylonitrile. Effect of Aqueous-Organic Solvent Systems on Copolymer Composition

Abstract Starch-polyacrylonitrile graft copolymers prepared in a number of aqueous-organic solvent systems with ceric ammonium nitrate as the initiator had more grafted chains than those prepared in water alone, and these were of lower molecular weight. Substitution of methanol for 80% of the water produced grafted chains with a molecular weight of 15,700 and a grafting frequency of 253 anhydroglucose units per graft. The influence of catalyst concentration, increased reaction temperature, and sodium sulfate on the composition of the copolymer were investigated for the methanol-water system.

Rate laws for the U(IV)-U(VI) exchange reaction in aqueous-organic mixed solvent systems

Rate laws have been written and discussed for the U(IV)-U(VI) exchange reaction in the following mixed solvents: 30, 60, 90, and 98 volume per cent ethanol-water; 30, 60, 90, and 98 volume per cent ethylene glycol-water; and 30, 60, and 90 volume per cent acetone-water.

Studies on mono- and di- n-butylphosphoric acids—V : The extraction of nitric acid from aqueous solution by di- n-butylphosphoric acid and further results on the distribution of di- n-butylphosphoric acid in aqueous-organic solvent systems

The distribution of 32P-labelled di- n-butylphosphoric acid (HDBP) between toluene and aqueous nitric acid has been measured as a function of (i) the concentration of HNO 3 from 0·5–12 M for 0·01, 0·05 and 0·5 M HDBP, and (ii) the concentration of HDBP from 10 −5-0·5 M for 1, 6 and 10 M HNO 3. The dimerization constant and monomer distribution coefficient for HDBP in toluene-1 M HNO 3 correspond to log K 2 = 5·09 and log K d = 0·70. The amount of HNO 3 extracted by a 0·5 M solution of HDBP in toluene can be expressed by the relation C HNO 3(org) = 0·051 C HNO 3(unionized, aq) up to 12 M HNO 3 in the aqueous phase; approximately 20 per cent of the uncomplexed HDBP and 40 per cent of the HDBP·HNO 3 complex are hydrated. A third phase forms in the 0·5 M HDBP-kerosene-HNO 3 system at >4 M HNO 3 in the aqueous phase; at 12 M HNO 3 the third phase has the empirical formula HDBP·HNO 3·H 2O.

Studies on mono- and di- n-butylphosphoric acids—II The solubility and distribution of mono- and di- n-butylphosphoric acids in aqueous-organic solvent systems

The solubilities of mono- and di- n-butylphosphoric acid (H 2MBP and HDBP respectively) at 25°C in water, aqueous nitric acid, odourless kerosene and benzene have been measured using 32P-labelled acids. The net distribution coefficient ( D HDBP) for HDBP has been measured as a function of the concentration of HDBP for 1. (i) a number of organic solvents in contact with 1 M HNO 3, 2. (ii) chloroform in contact with 0·1 and 1 M perchloric acid, and 3. (iii) the kerosene-HNO 3 system from 0 to 15 M HNO 3 In TBP-kerosene-HNO 3 systems, D HDBP and D H 2MBP have been measured as functions of the concentrations of HDBP, H 2MBP, TBP, and HNO 3, and TBP has been shown to associate with both HDBP and H 2MBP. The data can be applied to the calculation of equilibrium distribution coefficients for HDBP and H 2MBP in TBP-HNO 3 systems over a range of [TBP] from 0·1–100% v/v in the diluent, of [HNO 3] from 0 to 15 M, and of [HDBP] and [H 2MBP] either separately or together in the range 10 −6 M-0·05 M. The solubility and distribution data for HDBP are qualitatively interpreted in terms of 1. (i) a series of equations for the dissociation of HDBP, the dimerization of HDBP in both aqueous and organic phases, the association of HDBP with TBP and with HNO 3, and the association of TBP with HNO 3, and 2. (ii) the distribution of the HDBP monomer and dimer, and the HDBP·HNO 3 species, between the phases. The dimerization constants of HDBP in various organic solvents, the distribution constants of the monomer and the dimer in aqueous-organic solvent systems, and the association constant between TBP and HDBP in kerosene have been calculated.