Derivatographic studies on transition metal complexes XV. Thermal isomerization of trans-[CrBr2pn2]Br.H2O in solid phase

The thermal trans-to-cis isomerization of [CrBr₂pn₂]Br·H₂O in a solid phase was studied by means of both derivatography and isothermal measurement. It was found that trans-[CrBr₂pn₂]Br·H₂O undergoes isomerization to the cis-complex by about 10% with complete dehydration followed by isomerization of the residual trans complex in the anhydrous state. It was characteristic of the complex, trans-[CrBr₂pn₂]Br·H₂O, that the thermal dehydration was remarkably rapid in comparison with that of the trans-[CoCl₂pn ₂](H₅O₂)Cl₂ and the isomerization of the cis complex occurred even in the anhydrous state though it did not in the corresponding cobalt(III) complex trans-[CoBr₂pn₂](H₅O₂)Br₂ in an analogous state.     

Studies on bi-heterocyclic compounds. II. 5-substituted thiazolones

Reactions of 4-methyl-2(3H)-thiazolones (5) with various N-alkoxycarbonyl pyridinium salts (6a--f) led to (N-alkoxycarbonyl dihydropyridyl)thiazolones (7a--f), oxidation of which yielded a new class of 5-pyridylthiazolones (8a--f). These reactions were applied to the synthesis of other azaarylthiazolones. Some of these azaarylthiazolones, particularly 5-(4-pyridyl)thiazolones (8b, c) and 5-(4-quinolyl)thiazolones (14a,b), showed positive inotropic activity with little chronotropic effect on guinea pig left atria.     

Synthesis of well-defined hyperbranched polymers bio-based on multifunctional phenolic acids and their structure-thermal property relationships

A number of multifunctional ABx-type monomers exist in plant metabolites, and studies on the formation of hyperbranching polymers from ABx-type monomers are very significant in the development of bio-related polymeric materials. We established a method for the preparation of well-defined structures in bio-based, hyperbranched (HB) polyarylates by the copolycondensation of caffeic acid (DHCA) as an AB₂-monomer and p-coumaric acid (4HCA) as an AB-monomer, using the highly efficient catalyst Na₂HPO₄ to regulate the polymerization speed. ¹H NMR analysis revealed the time course of the formation of the hyperbranching structures. which strongly affected the glass transition and degradation temperatures, as well as the molecular weight and composition.     

Structure and Reactivity of an Asymmetric Synthetic Mimic of Nitrogenase Cofactor

The Mo nitrogenase catalyzes the ambient reduction of N₂ to NH₃ at its M‐cluster site. A complex metallocofactor with a core composition of [MoFe₇S₉C], the M‐cluster, can be extracted from the protein scaffold and used to facilitate the catalytic reduction of CN^?, CO, and CO₂ into hydrocarbons in the isolated state. Herein, we report the synthesis, structure, and reactivity of an asymmetric M‐cluster analogue with a core composition of [MoFe₅S₉]. This analogue, referred to as the Mo‐cluster, is the first synthetic example of an M‐cluster mimic with Fe and Mo positioned at opposite ends of the cluster. Moreover, the ability of the Mo‐cluster to reduce C₁ substrates to hydrocarbons suggests the feasibility of developing nitrogenase‐based biomimetic approaches to recycle C₁ waste into fuel products.     

HYDROPHOBIZING EFFECT OF CATIONS ON ACIDIC PHOSPHOLIPID MEMBRANES

By means of contact angle measurements with water and aqueous salt solutions, it is shown that plurivalent cations increase the hydrophobicity of negatively charged phospholipid vesicle membranes (consisting of phosphatidic acid, PA, or of phosphatidylserine, PS), but does not influence the hydrophobicity of neutral phospholipid membranes, (e.g., phosphatidylcholine, PC, at up to 200 mM of CaCl₂). The hydrophobizing action of cations on PA and PS membranes is concomitant with the reduction in (negative) zeta potential with increasing cation concentrations. Trivalent cations, La³⁺, showed more effective in hydrophobizing negatively charged phospholipid membranes than divalent and monovalent cations. Except for hydrogen ions, monovalent cations do not show any appreciable hydrophobizing effect on lipid vesicle membranes at concentrations less than 1 M. The hydrophobizing effect on phospholipid membranes can also be used to explain the induction of lateral phase separation into patches of different phospholipids as well as cell fusion.     

Degradation of phenylarsonic acid and its derivatives into arsenate by hydrothermal treatment and photocatalytic reaction

The degradation of phenylarsonic acid (PA) and its derivatives by hydrothermal treatment (HTT) was examined, especially focusing on the effect of adding H₂O₂ upon the degradation efficiency. The degradation was assessed by the generation of arsenate resulting from the cleavage of As C bonds in the PA derivatives. When PA (without substituents) was subjected to an HTT with H₂O₂ (H₂O₂‐HTT; 0.5–1% H₂O₂) at 175–200 °C, PA was almost completely degraded into arsenate, whereas an HTT with NaOH (NaOH‐HTT; 3 M NaOH) at the temperatures provided almost no degradation. The H₂O₂‐HTT also worked well for the degradation of PA derivatives with hydroxy and/or nitro groups on the phenyl ring. However, the degradation of aminophenylarsonic acids was not favorably performed by the H₂O₂‐HTT. The effect of the structure of PA derivatives upon the degradation susceptibility was discussed. A photocatalytic reaction using TiO₂ was also attempted for the degradation of PA derivatives. Copyright © 2005 John Wiley & Sons, Ltd.     

Structural and thermodynamic aspects of ionic solvation in concentrated aqueous poly(ethylene glycol)

Solvation of ions in concentrated aqueous poly(ethylene glycol) (PEG) has been studied from thermodynamic and structural viewpoints using ion-transfer voltammetry at the interface between aqueous and nitrobenzene phases and X-ray absorption fine structure (XAFS). Systematic changes in the ion-transfer potential from water to aqueous PEG have been confirmed for several ions relative to the corresponding potential of tetraethylammonium ion (Et4N+), which is almost independent of PEG concentration. The results obtained for alkali cations strongly suggest the involvement of their complexation with PEG even in relatively diluted PEG solutions. It has been implied that the solvation circumstances of Br- and ClO4- are drastically altered when the PEG concentration becomes higher than particular critical values (e.g., 30-50% PEG200), where free water molecules are diminished because of the hydration of PEG. XAFS measurements have also been performed for K+ and Br- to get direct evidence for these findings. Although the spectra at the K K-edge clearly indicate the presence of a PEG complex of K+ in relatively diluted PEG solutions ( approximately 33% PEG200), an obvious increase in its ion-transfer potential has been detected at lower PEG concentrations, indicating that complexes formed at the interface rather than in bulk solution are transferred into an organic phase. Br- is fully hydrated in 0-50% PEG solutions, whereas some water molecules are replaced by PEG when the PEG concentration increases. Increasing the PEG concentration causes decreases in the coordination number from 6 in water to 2-3 in neat PEG. Thus, the present approach not only has elucidated the structural and thermodynamic aspects of ionic solvation in aqueous PEG but also has provided the information of the hydration of PEG.