Search results for "Divalent"
showing 10 items of 102 documents
Fabrication of soft-etched nanoporous polyimide membranes for ionic conduction and discrimination
2021
Abstract Ionic selectivity in nanopores is usually based either on steric or charge exclusion mechanisms. By simultaneously incorporating both mechanisms into a functionalized membrane, an improved control over selectivity can be achieved. We describe the fabrication and experimental characterization of alkali metal cation-selective nanopores in heavy ion-tracked polyimide (PI) membranes using the soft-etching (SE) technique. The latent ion tracks in the PI membrane are selectively dissolved by an organic solvent to form tiny pores without affecting the bulk material. The ionic transport properties of SE-PI membranes are characterized using different electrolyte solutions containing alkali …
Mn(II) complexes with sulfonamides as ligands.
2012
Abstract Sulfonamides derived from 8-aminoquinoline react with Mn(II) and Mn(III) salts to form Mn(II) complexes; the Mn(III) species are reduced to the divalent state in the presence of 1,10 phenanthroline and bipyridine. Their molecular structure, determined by single crystal X‐ray diffraction, show that all the complexes present a distorted octahedral geometry, in which the deprotonated sulfonamide acts as a bidentate ligand. UV–visible spectroscopy and changes in the melting temperature (Tm) of calf thymus DNA show a strong interaction of these complexes with DNA. The significant hypochromicity of the charge transfer transition at 370 nm without an appreciable change in wavelength and t…
Proton-dependent kinetics of citrate uptake in growing cells ofLactococcus lactissubsp.lactisbv.diacetylactis
1995
The kinetic analysis of citrate uptake in growing cells of Lactococcus lactis subsp. lactis biovar. diacetylactis identified a proton-dependent transport and suggested the divalent anionic species as the form of citrate transported across cell membranes. The reaction followed Michaelis-Menten kinetics for a two-substrate reaction. The limiting steps were the formation of the ternary complex and the rate of transport. Temperature modified the activity of the permease, increasing the uptake rate.
Biotechnological characterisation of exocellular proteases produced by enologicalHanseniasporaisolates
2014
Summary Twenty-six enological Hanseniaspora isolates were identified by ITS PCR-RFLP and D1/D2 domain of 26S rDNA sequencing and assayed for exocellular protease production. Based on qualitative data, six isolates, belonging to H. guilliermondii, H. valbyensis and H. occidentalis species, were selected to continue the study. Analytical procedure was optimised, and protease activities were quantified and characterised on the basis of different biotechnological factors. Protease activity was quite glucose, fructose and ethanol content independent, but divalent cation affects activity; these data support that they were aspartic proteases. The effect of 2-mercaptoethanol suggests the importance…
Structure and Yielding of Colloidal Silica Gels Varying the Range of Interparticle Interactions.
2016
The relationship between interaction range, structure, fluid-gel transition, and viscoelastic properties of silica dispersions at intermediate volume fraction, Φv ≈ 0.1 and in alkaline conditions, pH = 9 was investigated. For this purpose, rheological, physicochemical, and structural (synchrotron-SAXS) analyses were combined. The range of interaction and the aggregation state of the dispersions were tuned by adding either divalent counterions (Ca(2+)) or polycounterions (PDDA). With increasing calcium chloride concentration, a progressive aggregation was observed which precludes a fluid-gel transition at above 75 mM of calcium chloride. In this case, the aggregation mechanism is driven by s…
Highly Luminescent Half-Lantern Cyclometalated Platinum(II) Complex: Synthesis, Structure, Luminescence Studies, and Reactivity.
2012
The half-lantern compound [{Pt(bzq)(μ-C 7H 4NS 2-κN,S)} 2]•Me 2CO (1) was obtained by reaction of equimolar amounts of potassium 2-mercaptobenzothiazolate (KC 7H 4NS 2) and [Pt(bzq)(NCMe) 2]ClO 4. The Pt(II)•••Pt(II) separation in the neutral complex [{Pt(bzq)(μ-C 7H 4NS 2-κN,S)} 2] is 2.910 (2) Å, this being among the shortest observed in half-lantern divalent platinum complexes. Within the complex, the benzo[h]quinoline (bzq) groups lie in close proximity with most C•••C distances being between 3.3 and 3.7 Å, which is indicative of significant π-π interactions. The reaction of 1 with halogens X 2 (X 2 = Cl 2, Br 2, or I 2) proceeds with a two-electron oxidation to give the corresponding d…
Rare earth metal complexes that contain linked amido-cyclopentadienyl ligands: ansa-metallocene mimics and “constrained geometry” catalysts
2003
A survey of group 3 metal complexes that contain a linked amido-cyclopentadienyl ligand is given. Originally designed as ansa-metallocene analogues for the development of single-component olefin polymerization catalysts, variations in the metals and ligand substituents have allowed the synthetic access to new rare earth metal complexes including olefin polymerization initiators, divalent complexes and heterobimetallic metallocenes. The linked amido-cyclopentadienyl ligands have made half-sandwich complexes of group 3 metals accessible in a more systematic manner and provided a better understanding of the electronic and steric constraints of chelating ligands for the larger rare earth metal …
Ion transport through membranes: A computer experiment
1983
Abstract Gramicidin-A is a linear pentadecapeptide antibiotic, which forms transmembrane channels; these have a number of interesting conductance characteristics [1, 2 and Refs. therein], as for example high specific ion fluxes (a single channel carries about 10 7 sodium ions/sec at 25 °C, 1 M NaCl and 100 mV transmembrane d.d.p.) have a remarkable ion selectivity among the monovalent cations. The permeability ratios with respect to sodium were found to be in following order H + (150) > NH 4 + (8.9) > Cs + (5.8) > Rb + (5.5) > K + (3.9) > Na + (1.0) > Li + (0.33). The channel is impermeable to anions and to divalent cations and it exhibits saturation and maxima in conductance as a function …
Mono(cyclopentadienyl) Complexes of the Rare-Earth Metals
2002
I. Introduction 1953II. Overview of Synthesis, Structure, and Properties 1954A. Synthetic Methods 1954B. Ligands and Structures 1955III. Halo Complexes 1956A. General 1956B. Divalent Halo Complexes 1956C. Trivalent Halo Complexes 1957IV. Chalcogenido Complexes 1958A. General 1958B. Divalent Chalcogenido Complexes 1958C. Trivalent Chalcogenido Complexes 1959V. Pnicogenido Complexes 1960A. General 1960B. Divalent Amido and Phosphido Complexes 1960C. Trivalent Pnicogenido Complexes 19611. Bis(amido) Complexes 19612. Mixed Halo and Chalcogenido Complexes 1962VI. Hydrocarbyl and Silyl Complexes 1963A. General 1963B. Divalent Complexes 19631. Metallacarbaboranes 19632. Bimetallic Naphthalene Comp…
Modification of commercial UF membranes by electrospray deposition of polymers for tailoring physicochemical properties and enhancing filtration perf…
2020
Abstract The main challenge for a widespread use of nanoporous membranes in the removal of ionic contaminants lies in the adjustment of their physicochemical properties to allow adequate ion rejection and mitigate fouling based on the targeted application. Most of the commercial membranes are negatively charged and their use is thus not necessarily relevant for divalent cation rejection. The main objective for researchers is therefore to provide novel tailored membranes by developing specific synthesis or modifying available membranes. It is proposed here to tailor physicochemical properties of a commercial low molecular weight cut-off ultrafiltration membrane by electrospray deposition of …