X-ray structure of physiological copper(II)-bis(L-histidinato) complex

The isolation and the X-ray crystal structure of physiological copper(II)-L-histidine complex are reported. The neutral five-coordinate complex shows distorted square pyramidal geometry with bidentate and tridentate L-histidine ligands. The basic character of the pendent imidazole group and H-bonding interactions of bidentate L-histidine ligand are important for copper transport. The unique structural features help explain the origin of its thermodynamic stability and kinetic reactivity in human blood along with the ternary copper(II)-amino acid complexes. The role of L-histidine in interaction with copper(II)-albumin, in cellular uptake of copper, and in treatment of Menkes disease can be studied using these results.     

EXAFS studies of cobalt oxides and oxide glasses

The exafs of Co²⁺ has been studied in rare earth cobaltites and in sulphate and borate glasses. It has been found that the environment of Co²⁺ ions is very similar in these cases. It appears feasible to study local structures in glasses using probe ion exafs. Communication No. 151 from the Solid State and Structural Chemistry Unit.     

Oxidative verdoheme formation and stabilization by axial isocyanide ligation

The effect of isocyanides as axial ligands on the formation and stability of verdoheme by oxidation has been examined. The reaction of [Fe(III)(OEPO)]2 with t-butyl isocyanide under dioxygen-free conditions results in the formation of (t-BuNC)2Fe(II)(OEPO*) with an electron paramagnetic resonance at g=2.009 with a peak-to-peak separation of 23.5 G at 4 K. (OEPO is the trianion of octaethyloxophlorin and OEPO* is the radical dianion obtained from OEPO by one-electron oxidation.) Exposure of chloroform solutions of either (2,6-xylylNC)2Fe(II)(OEPO*) or (t-BuNC)2Fe(II)(OEPO*) to dioxygen followed by the addition of ammonium hexafluorophosphate results in their transformation into the diamagnetic verdohemes, [(2,6-xylylNC)2Fe(II)(OEOP)](PF6) and [(t-BuNC)2Fe(II)(OEOP)](PF6), yields 68 and 70%, respectively. (OEOP is the anion of octaethyl-5-oxaporphyrin.) The oxidation reactions of (2,6-xylylNC)2Fe(II)(OEPO*) and (t-BuNC)2Fe(II)(OEPO*) have also been monitored by 1H NMR spectroscopy. No resonances due to paramagnetic products could be detected, the reactions appear to result only in the formation of the diamagnetic verdohemes, and the products are not susceptible to further oxidation.     

Synthesis and characterization of crosslinked polydiacetylene and its two-component interpenetrating polymer networks

The synthesis of crosslinked polydiacetylenes and its two-component interpenetrating polymer networks (IPNs) was carried out utilizing its polar and flexible substituent groups. Polydiacetylenes were crosslinked by the formation of allophanate linkages utilizing urethane groups in the substituent groups of the polydiacetylenes. Elemental analysis, DSC, TMA, solvent resistance, and IR spectra are presented as evidence for the formation of crosslinked polydiacetylenes. IPNs of polydiacetylenes and an epoxy resin (diglycidyl ether of bisphenol A) were synthesized by using simultaneous and sequential methods of synthesis. A study of phase morphology of the simultaneous and sequential IPNs was carried out using electron microscopy, TMA, and DSC.     

A new and rapid titration of antimony(III) with potassium dichromate, with iron(II) as inductor

The optimum conditions for the titration of antimony(III) with dichromate, and diphenyl-aminesulphonic acid as indicator, have been established. No iodine catalyst is used; the analytical reaction is based on an induced reaction with iron(II) as inductor. The titration can be done as easily as an iron(II) titration and the end-point is equally sharp. Titrations are possible with 0.01N solutions.     

Direct Barbier-type allylation of aromatic acetals and dioxolanes in the presence of β-cyclodextrin in water

A new and convenient procedure for the synthesis of homoallylic alcohols directly from aromatic acetals and dioxolanes has been developed with very good yields under biomimetic conditions using a Zn-mediated Barbier-type allylation in the presence of β-cyclodextrin in water.     

Gold nanoshells on polystyrene cores for control of surface plasmon resonance

A method is presented for synthesizing core-shell structures consisting of monodisperse polystyrene latex nanospheres as cores and gold nanoparticles as shells. Use of polystyrene spheres as the core in these structures is advantageous because they are readily available commercially in a wide range of sizes, and with dyes or other molecules doped into them. Gold nanoparticles, ranging in size from 1 to 20 nm, are prepared by reduction of a gold precursor with sodium citrate or tetrakis(hydroxymethyl)phosphonium chloride (THPC). Carboxylate-terminated polystyrene spheres are functionalized with 2-aminoethanethiol hydrochloride (AET), which forms a peptide bond with carboxylic acid groups on their surface, resulting in a thiol-terminated surface. Gold nanoparticles then bind to the thiol groups to provide up to about 50% coverage of the surface. These nanoparticles serve as seeds for growth of a continuous gold shell by reduction of additional gold precursor. The shell thickness and roughness can be controlled by the size of the nanoparticle seeds as well as by the process of their growth into a continuous shell. By variation of the relative sizes of the latex core and the thickness of the gold overlayer, the plasmon resonance of the nanoshell can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum, for applications ranging from the construction of photonic crystals to biophotonics. The position and width of the plasmon resonance extinction peak are well-predicted by extended Mie scattering theory.     

Physico-chemical properties of the sodium salts of some fatty acids in formamide solution in the temperature range 15–45°C

The thermal stability of some boracites, CuB₇O₁₃Cl, NiB₇O₁₃Br and FeB₇O₁₃I, was investigated using thermogravimetry in air up to 1000°, DTA in air to 1200° and evolved gas analysis in vacuum to 1200°C. Only the FeI compound showed weight loss below 1000°C. The endothermic peaks associated with melting were CuCl (1025°C), NiBr (1150°C) and FeI) (965°C). Evolved gas analysis indicated major differences in the decomposition products of the three materials.     

The effects of axial ligands on electron distribution and spin states in iron complexes of octaethyloxophlorin, intermediates in heme degradation

The results presented here show that the nature of the axial ligand can alter the distribution of electrons between the metal and the porphyrin in complexes where there is an oxygen atom replacing one of the meso protons. The complexes (1-MeIm)(2)Fe(III)(OEPO) and (2,6-xylylNC)(2)Fe(II)(OEPO(*)) (where OEPO is the trianionic octaethyloxophlorin ligand and OEPO(*) is the dianionic octaethyloxophlorin radical) were prepared by addition of an excess of the appropriate axial ligand to a slurry of [Fe(III)(OEPO)](2) in chloroform under anaerobic conditions. The magnetic moment of (2,6-xylylNC)(2)Fe(II)(OEPO(*)) is temperature invariant and consistent with a simple S = (1)/(2) ground state. This complex with an EPR resonance at g = 2.004 may be considered as a model for the free-radical like EPR signal seen when the meso-hydroxylated heme/heme oxygenase complex is treated with carbon monoxide. In contrast, the magnetic moment of (1-MeIm)(2)Fe(III)(OEPO) drops with temperature and indicates a spin-state change from an S = (5)/(2) or an admixed S = (3)/(2),(5)/(2) state at high temperatures (near room temperature) to an S = (1)/(2) state at temperatures below 100 K. X-ray diffraction studies show that each complex crystallizes in centrosymmetric form with the expected six-coordinate geometry. The structure of (1-MeIm)(2)Fe(III)(OEPO) has been determined at 90, 129, and 296 K and shows a gradual and selective lengthening of the Fe-N(axial bond). This behavior is consistent with population of a higher spin state at elevated temperatures.     

EPR and optical absorption studies on Cr3+ ions doped in KZnClSO4 x 3H2O single crystals

EPR and optical absorption spectra of Cr3+ ions doped in KZnClSO4 x 3H2O single crystals have been studied at room temperature. The EPR spectrum exhibits a group of three fine structure transitions characteristic of Cr3+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in an octahedral symmetry. From the observed band positions, the crystal field parameters have been evaluated.