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91.
Abstract Colloidal palladium supported on a chelate resin containing iminodiacetic acid groups was prepared by refluxing the palladium chelate resin in methanol-water. Using the resin-supported colloidal palladium as a catalyst, cyclopentadiene was hydrogenated to cyclopentene in 97.1% selectivity at 100% conversion of cyclopentadiene under 1 atm of hydrogen in methanol at 30°C. Finely dispersed metal particles ranging from 10 to 60 Å in diameter were observed in the resin by electron microscopy. Both x-ray microanalysis for palladium and elution analysis of palladium ion with an aqueous solution of ethylenediaminetetraacetic acid disodium salt demonstrated the existence of large amounts of palladium ion complexes in the resin. The amount of palladium metal in the resin was estimated to be about 5% of the total palladium. Since the resin, after removal of most of the ionic palladium, exhibited almost the same catalytic activity as before, it was concluded that the finely dispersed metal particles are the active species in the catalyst. 相似文献
92.
The purpose of these studies was to combine polydimethylsiloxane (PDMS) and polyisobutylene (PIB) sequences into novel triblock, PDMS-b-PIB-b-PDMS, and multiblock, (-PDMS-b-PIB-b-PDMS-)n, copolymers. The key toward syntheses was the definition of conditions for the initiation of living anionic polymerization of hexamethyl-cyclotrisiloxane (D3) at the CH2OLi termini of well-defined tele-chelic PIB sequences. Subsequent deactivation of living D3 polymerization charges with Me3 SiCl yielded the target triblock whereas stoichiometric amounts of Me2 SiCl2 gave the multiblock copolymer. 相似文献
93.
Pankaj Sehgal Manu Sharma Kim Lambertsen Larsen Reinhard Wimmer Daniel E. Otzen Hidekazu Doe 《Journal of Dispersion Science and Technology》2013,34(1):128-133
In this work, we have studied the influence of different concentrations of β‐Cyclodextrin (β‐CD) on the mixed micellization of anionic surfactants sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) at different SDS mole fractions (αSDS). From conductivity data, the critical micellar concentration (cmc), the equivalent ionic conductivities of the monomeric species (Λm), the associated species (Λassc) and the micelle (Λmic), the degree of counterion dissociation (α) in the presence of β‐CD were evaluated from the slope of the conductivity versus concentration plots for the pure and binary mixtures. The apparent cmc of the surfactants vary linearly with the β‐CD concentrations. From the dependence of cmc of the surfactants on β‐CD concentration, we have deduced the association constant (K) of surfactant‐β‐CD inclusion complexes assuming 1∶1 stoichiometry. Theories of Clint, Regular solution, and Motomura's have been used for the evaluation of ideality or nonideality of the mixed system. Mixed micelles were found to be rich in SDS content at the cmc in the presence and the absence of β‐CD. The cmc values have been used to evaluate the transfer of standard free energy of micelles (ΔG0 M,tr) from the aqueous medium to additive medium. 相似文献
94.
Pankaj Sehgal Manu Sharma Kim Lambertsen Larsen Reinhard Wimmer Hidekazu Doe Daniel E. Otzen 《Journal of Dispersion Science and Technology》2013,34(6):885-890
Interactions of γ-cyclodextrin (γ-CD) with the single and mixed micelles of sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) have been studied at different concentrations of γ-CD by using conductivity measurements. From conductivity data, the pure and mixed critical micellar concentration (cmc), the equivalent ionic conductivities of the monomeric species (Λ m), the associated species (Λ assc) and the micelle (Λ mic), the degree of counterion dissociation (χ) in the presence of γ-CD have been evaluated from the slope of the conductivity versus concentration plots for the pure and binary mixture of surfactants. From the dependence of cmc of the surfactantson γ-CD concentration, we have deduced the association constant (K) of surfactant-γ-CD inclusion complexes assuming 2:1 stoichiometry. Theories of Clint, regular solution, and Motomura's have been used for the evaluation of ideality or nonideality of the mixed system. Mixed micelles were found to be rich in SDS content in the presence and the absence of γ-CD. The cmc values have been used to evaluate the transfer of standard free energy of micelles (ΔG0 M,tr) from the aqueous medium to additive medium. 相似文献
95.
Molecular geometries of two structural forms of 2'-deoxyguanosine (keto-N9R and keto-N7R, R = the sugar moiety) considering both the C2'-endo and C3'-endo conformations of the sugar ring and those of the complexes of these species with two water molecules each were optimized employing the ab initio RHF procedure. A mixed basis set consisting of the 6-311+G* basis set for the nitrogen atom of the amino group and the 4-31G basis set for all the other atoms was used. The RHF calculations were followed by correlation correction of the total energy at the MP2 level. Both the structural forms of 2'-deoxyguanosine were solvated using the polarized continuum model (PCM) of the self-consistent reaction field (SCRF) theory and the corresponding RHF optimized geometries at the RHF and MP2 levels. Geometry optimization was also performed in aqueous media using the Onsager model at the RHF level using the above-mentioned mixed basis set, and subsequently, using the reoptimized geometries, single-point MP2 calculations were performed. It is found that both the keto-N9R and keto-N7R forms of 2'-deoxyguanosine as well as their complexes with two water molecules each would occur, particularly at the water-air interface. Though the normal Watson-Crick-type base pairing would not be possible with the keto-N7R form of 2'-deoxyguanosine(G*), two other (G*-C and G*-T) base pairing schemes may occur with this form of the nucleoside, which may cause mutation. The present calculated geometry of the keto-N9R form of the anti-conformation of 2'-deoxyguanosine including the dihedral angle chi(CN) agree satisfactorily with the available crystallographic results. The present results also agree satisfactorily with those obtained by other authors earlier for the keto-N9R form of 2'-deoxyguanosine using B3LYP and MP2 methods employing the 6-31G* basis set. Using transition state calculations, it is shown that tautomerism of guanine and other similar molecules where the tautomers would coexist would be facilitated by the occurrence of the H(+) and OH(-) fragments of water molecules. Further, this coexistence of the two tautomers appears to make the C8 carbon atom located between the N7 and N9 nitrogen atoms susceptible to attack by the OH(-) group. Thus, an explanation is obtained for the efficient formation of the reaction product 8-hydroxy-2'-deoxyguanosine, which serves as a biomarker for oxidative damage to DNA in biological systems. 相似文献
96.
To investigate the nature of interactive forces between sulfadiazene molecules and alumina surface the experiments were performed for the adsorption of sulfadiazene (SD) from its aqueous sulution onto the alumina surfaces at 25 ± 0.2°C and the influence of factors such as increasing concentration of SD (4.0–20.0 × 10–3 mol cm–3), the time required for adsorption equilibrium, pH (2.0–12.0) and temperature (5–45°C) of the adsorption medium, the presence of ions like Cl–, SO2–
4 and PO3–
4 (0.01–0.30 M) and organic solvents (5% v/v) were observed on the course of adsorption of SD. Various adsorption and kinetic parameters such as adsorption coefficient, the rate constants for adsorption and desorption were also evaluated. The results of the above cited studies facilitated to formulate the mechanisms of interaction between SD and alumina surfaces. From application view point the present work may be a potential tool for an effective chromatographic separation of sulfa drugs from industrial effluents. 相似文献
97.
Mixed micelles formed by zwitterionic surfactant dimethyldodecylammniopropane sulfonate and short-chain phospholipid 1,2-diheptanoyl-sn-glycero-3-phosphocholine in different proportions in an aqueous medium have been studied physicochemically at an air/water interface and in the bulk by using interfacial tension and pyrene fluorescence intensity measurements, respectively. The critical micellar concentration and free energies of micellization and of interfacial adsorption have been determined. The interfacial study reveals that a mixed monolayer is formed at the air/water interface by the adsorption of surfactant and phospholipid monomers. This has been confirmed by evaluating the interfacial parameters; the maximum surface excess, the minimum area per molecule of a surface-active compound, and the Gibbs surface excess related to surface pressure. The nonideality of mixing, expressed in the terms of the regular solution interaction parameter, #, has negative values over the whole mole fraction range. The negative # values indicate the mutual synergism between the surfactant and phospholipid monomers. The equilibrium distribution of components between micelle and monomer phases was evaluated using a theoretical treatment based on excess thermodynamics quantities evaluated by Motomura's formulation. 相似文献
98.
The preparation of polymer blends of poly(methyl methacrylate) and poly(vinylidene fluoride) in different weight percentages is described. Vickers microhardness measurements have been made to study the effects of load and compositional ratio of the two polymers in polyblend. It is observed that poly(vinylidene fluoride) acts as a plasticizer for poly(methyl methacrylate). Evidence of increasing and decreasing strength of polyblends has been obtained for different compositional ratios of the two polymers. 相似文献
99.
Constantine Tsounis Dr. Priyank V. Kumar Dr. Hassan Masood Rutvij Pankaj Kulkarni Prof. Gopalakrishnan Sai Gautam Prof. Christoph R. Müller Prof. Rose Amal Dr. Denis A. Kuznetsov 《Angewandte Chemie (International ed. in English)》2023,62(4):e202210828
MXenes, due to their tailorable chemistry and favourable physical properties, have great promise in electrocatalytic energy conversion reactions. To exploit fully their enormous potential, further advances specific to electrocatalysis revolving around their performance, stability, compositional discovery and synthesis are required. The most recent advances in these aspects are discussed in detail: surface functional and stoichiometric modifications which can improve performance, Pourbaix stability related to their electrocatalytic operating conditions, density functional theory and advances in machine learning for their discovery, and prospects in large scale synthesis and solution processing techniques to produce membrane electrode assemblies and integrated electrodes. This Review provides a perspective that is complemented by new density functional theory calculations which show how these recent advances in MXene material design are paving the way for effective electrocatalysts required for the transition to integrated renewable energy systems. 相似文献
100.
A. Ghosh K. S. Patel R. K. Mishra 《Journal of Radioanalytical and Nuclear Chemistry》1991,152(1):243-249
A new and simple method for selective spectrophotometric determination of uranium(VI) with 4-(2-pyridylazo)resorcinol (PAR) and N-octylacetamide into benzene over pH 7.0–9.0 is described. The molar absorptivity of the complex with 9 different amides is in the range of (0.40–3.2)·104 1·mol–1·cm–1 at the absorption maximum. Out of these, the most sensitive compound N-octylacetamide (OAA) was chosen for detailed studies in the present investigation. The detection limit of the method is 0.008 g U·ml–1. The system obeys Beer's law in the range of 0–5 g U·ml–1. The method is free from interferences of most of the common metal ions except vanadium(V) and copper(II), which are masked by proper masking agents. The composition of the complex is determined by curve-fitting method. The method has been applied for the recovery of the metal from rock samples and synthetic mixtures. 相似文献