Organometallic complexes in ascidian embryonic development: II. Effects on different stages and larvae

The effects of the organometallic compounds Bu₂Sn-D -(?;)sorbitol, Bu₂Sn-D -(+)glucose, Bu₂Sn-D -(?)fructose and Bu₂Sn-D -(+)glyceraldehyde were tested in vivo on different stages of Ascidian development, larval movement and metamorphosis. Organotin(IV) complexes are organometallic compounds widely used as industrial biocides, antifouling agents and agricultural fungicides and are toxic to a range of organisms. Two-cell stage embryos, if incubated for one hour in the organotin (IV) solutions, stopped the cleavage, which was restored when they were transferred into normal sea water. The gastrula stage was seriously affected in 10^?4mol dm^?3 solutions of the above-mentioned complexes: 85% of the embryos were anomalous neurulae with open neural folds, 5% were twisted larvae. The gastrulae, when incubated for 1 h in 10^?5mol dm^?3 solutions, developed twisted larvae in ovular envelopes and immobile larvae with twisted tails. Larvae treated with 10^?4mol dm^?3 and 10^?5 mol dm^?3 Bu₂Sn-D -(?)sorbitol, Bu₂Sn-D -(+)glucose and Bu₂Sn-D -(+)glyceraldehyde solutions stopped swimming, did not metamorphose and afterwards underwent cytolysis. An initial hyperactivity of circular movements, followed by immobility, was observed in the larvae incubated in Bu₂Sn-D -(?;)fructose.     

Metal complexation of crosslinked polyacrylamide-supported dithiocarbamates: Effect of the molecular character and extent of crosslinking on complexation

Dithiocarbamate functions were incorporated into different polyacrylamide matrices crosslinked with a flexible and hydrophilic crosslinking agent, tetraethyleneglycol diacrylate (TEGDA), and their complexation behaviours were investigated. Crosslinked polyacrylamides with varying extents of the tetrafunctional TEGDA crosslinks were prepared by free radical solution polymerization at 60°C using potassium persulphate as initiator in ethanol. The dithiocarbamate functionality was incorporated into these polyacrylamides by a two-step polymer-analogous reaction involving (i)trans-amidation with ethylenediamine and (ii) dithiocarbamylation of the aminopolyacrylamide with carbon disulphide and alkali. The complexations of dithiocarbamate with Cu(II), Ni(II), Zn(II), Co(II) and Hg(II) ions were followed under different conditions. The metal ion intake varied with the extent of the crosslinking agent and the observed trend in complexation is Hg(II) > Cu(II)> Zn(II)> Co(II)> Ni (II). The time-course of complexation, the possibility of recycling, swelling characteristics, and spectral and thermal analyses were carried out. The thermal stability increases upon complexation with metal ions.     

Mimicking catalase and catecholase enzymes by copper(II)-containing complexes

An imidazolate-bridged copper(II)-zinc(II) complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(2-aminoethyl)amine perchlorate (denoted as “Cu,Zn complex”) and a simple copper(II) complex (Cu(II)-tris(2-aminoethyl) amine chloride (“Cu-tren”) were prepared and immobilised on silica gel (by hydrogen or covalent bonds) and montmorillonite (by ion exchange). The immobilised substances were characterised by FT-IR spectroscopy and their thermal characteristics were also studied. The obtained materials were tested in two probe reactions: catalytic oxidation of 3,5-di-tert-butyl catechol (DTBC) (catecholase activity) and the decomposition of hydrogen peroxide (catalase activity). It was found that the catecholase activity of the Cu,Zn complex increased considerably upon immobilization on silica gel via hydrogen bonds and intercalation by ion exchange among the layers of montmorillonite. The imidazolate-bridged copper(II)-zinc(II) complex and its immobilised versions were inactive in hydrogen peroxide decomposition. The Cu(II)-tris(2-aminoethyl)amine chloride complex displayed good catalase activity; however, immobilisation could not improve it.     

Solvent-dependent host–guest complexation of two homologous merocyanines by a water-soluble calix[8]arene: Spectroscopic analysis and structural calculations

The sulfonated calixarene I₈C₁₂ acts as a host for homologous merocyanines Mc1 and Mc2 in organic solvents, exhibiting neither selectivity towards the guest dyes nor solvent dependence of the complexation equilibria. In water, on the contrary, only the lower homologue, Mc1, is solubilized in the presence of the calixarene. A combination of UV–visible and fluorescence spectroscopic and photophysical analysis and MD structural simulation of the calixarene-dye complexes was employed to account for the observations, and suggests that a radical change in the complexation mode occurs upon moving from an organic to an aqueous environment.     

Finite-Type Invariants of Cubic Complexes

The paper is for a general audience and may serve as a preliminary introduction to the theory of finite-type invariants.     

Effect of the environment on the stability of surfactant–polypeptide self‐assembled complexes: Molecular dynamics simulations of stoichiometric complexes formed by N‐dodecyltrimethylammonium and poly(α,L‐glutamate) in chloroform,methanol, and water

A series of molecular dynamics simulations have been performed to study the supramolecular structure of self‐assembled complexes formed by N‐dodecyltrimethylammonium cations and the synthetic polypeptide poly(α,L ‐glutamate). The influence of the type of solvent has been investigated, considering explicit environments of chloroform, water, and methanol on a stoichiometric complex containing 15 residues. In chloroform, the complex stabilizes in a regular structure: the polypeptide adopts an α‐helix conformation that is regularly surrounded by surfactant molecules to form electrostatic interactions through a multiple interaction pattern. However, this structure destabilizes in methanol and water: (a) the α‐helix unfolds in the two solvents and (b) the electrostatic links between the surfactant molecules and the polyanion are disrupted in aqueous solution, although these interactions are still preserved in methanol. The role of the solvent environment in stabilizing or destabilizing the polypeptide secondary structure, the organization of the surfactant molecules, and predominantly the surfactant–polypeptide supramolecular organization is discussed in detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1122–1133, 2006     

Absorbance spectra of polycrystalline samples and twinned crystals of oligothiophenes

We propose optical absorption technique at oblique incidence as one of the spectroscopic tools that allow experimentally recognizing the macroscopic order and structural features of molecular solids of conjugated molecules, from single crystals to polycrystalline or twinned samples. We apply this spectroscopy to quaterthiophene as representative of a wide class of materials that usually possess optical transitions of Frenkel exciton origin with strong directional dispersion. The comparison between experimental and simulated data gives evidence of the high sensitivity of this technique for determining quantitatively the polycrystallinity of the measured samples, whose domains may show mirror-like orientation of the unit cell with respect to one of its faces.Frenkel exciton; Oligothiophene, Optical properties