Search results for "Divalent"
showing 10 items of 102 documents
On the stability of the 24-meric hemocyanin from Eurypelma californicum.
1998
The stability of the 24-meric hemocyanin from Eurypelma californicum towards various denaturants (GdnHCl, urea, urea derivatives and salts of the Hofmeister series) indicates that the quaternary structure is stabilized by hydrophilic and polar forces. Thus, the interaction between the seven different subunit types of this cheliceratan hemocyanin is comparable with that of the closely related crustacean hemocyanins. In contrast, no significant influence of divalent ions such as Ca2+ and Mg2+ on the stability is observed at pH 8.0 and pH 8.5 but not at pH 7.0. Studies, both in the presence of urea and GdnHCl indicate that the denaturation process consists of a dissociation of the oligomeric s…
Synthesis and characterisation of polymeric manganese and zinc 5-hydroxyisophthalates
2001
Abstract The crystallisation of 5-hydroxyisophthalic acid with divalent Mn or with Mn or Zn and either 2,2-bipyridine (2,2-bipy) or pyridine-2-(1H-pyrazol-3-yl) gave solids of composition [Mn(C8H4O5)(H2O)3]·2H2O (1), [Mn(C8H4O5)(2,2′-bipy)]·H2O (2), [Mn2(C8H4O5)2(C8H7N3)2]·H2O (3) and [Zn(C8H4O5)(2,2′-bipy)] (4). Each compound has 1D co-ordinative chains that are connected by hydrogen bonds. Compounds 2–4 contain M2C2O4 rings with pseudo-chair geometries. The Mn atoms in 2 are coupled antiferromagnetically.
Divalent metal phosphonates – new aspects for syntheses, in situ characterization and structure solution
2016
Abstract Divalent metal phosphonates are promising hybrid materials with a broad field of application. The rich coordination chemistry of the phosphonate linkers enables the formation of structures with different dimensionalities ranging from isolated complexes and layered structures to porous frameworks incorporating various functionalities through the choice of the building blocks. In brief, metal phosphonates offer an interesting opportunity for the design of multifunctional materials. Here, we provide a short review on the class of divalent metal phosphonates discussing their syntheses, structures, and applications. We present the advantages of the recently introduced mechanochemical pa…
Coamplexation of mercury(II) compounds by crown ethers in organic media
1991
Complexes between crown ethers having ring sizes of 15–24 atoms and 5 to 8 oxygens with HgX2 species (X = Cl, I, CN, SCN) have been prepared and studied. Interactions of the substituents X bound to mercury with groups or fragments in the crown compound are essential in determining the characteristics and stability of the complexes formed. Complexes with crowns of 18C6 ring sizes are the most favourable except for HgX2 compounds for which the size of X is larger than the macrocycle ring, as is the case for X = CF3.
Understanding the impact of poly(allylamine) plasma grafting on the filtration performances of a commercial polymeric membrane
2019
Abstract Commercial membranes often exhibit difficulties in rejecting specific ionic species, and especially multivalent cations, due to their usual negative charge. To face this drawback, it is proposed here to functionalize the membrane surface by allylamine plasma polymerization. The impact of this modification on both permeation flux and ion rejection is investigated for single salt solutions and ion mixtures. It is shown that the membrane behaves like a positive membrane from the point of view of cation rejection but the negative charge (and the corresponding electrical field) inside pores leads to high rejection of divalent anions like a negative membrane. This allows a high selectivi…
Structure and reactivity of a mononuclear gold(II) complex.
2017
Mononuclear gold(II) complexes are very rare labile species. Transient gold(II) species have been suggested in homogeneous catalysis and in medical applications, but their geometric and electronic structures have remained essentially unexplored: even fundamental data, such as the ionic radius of gold(II), are unknown. Now, an unprecedentedly stable neutral gold(II) complex of a porphyrin derivative has been isolated, and its structural and spectroscopic features determined. The gold atom adopts a 2+2 coordination mode in between those of gold(III) (four-coordinate square planar) and gold(I) (two-coordinate linear), owing to a second-order Jahn–Teller distortion enabled by the relativistical…
Bimodal Effect of Amphiphilic Biocide Concentrations on Fluidity of Lipid Membranes
1996
Abstract Using the spin label method (ESR) it has been shown that biologically active, amphiphilic compounds (quaternary ammonium salts -AS) containing polar heads with single and double positive charge caused, at low concentrations, decrease fluidity of liposome membranes formed with egg yolk lecithin (EYL). At higher concentrations an increase in fluidity was observed. With compounds having a single positive charge minimum fluidity of membrane structure occurs in the range of 1 to 3%, with compounds containing double positive charge -in the range of 4 -6 % . That effect does not depend on polar head size and length of alkyl chains of the AS used. Analysis of the electrostatic interaction …
A distorted honeycomb motif in divalent transition metal compounds based on 4-phosphonbenzoic acid and exchange coupled Co(II) and Cu(II): synthesis,…
2013
The first example of a two-dimensional inorganic hybrid material with cobalt as an open-shell transition metal ion and 4-phosphonbenzoic acid as a linker is presented together with its copper analogue. For both metal ions the inorganic part consists of edge-sharing metal–oxygen octahedra leading to a metal honeycomb motif. The magnetic properties of the cobalt compound are reported together with those of the corresponding copper compound based on the remarkably six-coordinated copper(II) ions.
Estimation of pKa shifts in weak polyacids using a simple molecular model: effects of strong polybases, hydrogen bonding and divalent counterion bind…
2004
Abstract The pKa values of ionizable groups in macromolecules can be significantly different than those of the isolated groups in solution. We have estimated theoretically the changes in the dissociation constant of a weak acid (a) in the vicinity of another ionizable group (b) on the basis of the theoretical approach by Hill (J. Am. Chem. Soc. 78 (1956) 3330) for matching pairs of interacting sites on two large molecules. Three cases are considered for group b: the strong base, the same weak acid as group a with hydrogen bonding between them, and the same weak acid as group a with divalent counterion binding. The pKa shifts are evaluated in each case as a function of the interaction energy…
Surface charge regulation of functionalized conical nanopore conductance by divalent cations and anions
2019
Abstract The surface charge regulation in nanoscale volumes is a subject of wide interest to biological and chemical soft matter systems. Also, electrolyte mixtures with monovalent and divalent ions are commonplace in practical applications with micro and nanoporous ion-exchange membranes. We have studied experimentally and theoretically the conductance of conical nanopores functionalized with negative and positive surface charges that are bathed by electrolyte mixtures of the monovalent ions K+ and Cl− and the divalent ions Mg2+, Ba2+, Ca2+, and SO42−. Small concentrations of these ions can modulate the nanopore selectivity and conductance because of their interaction with the charged grou…