Tetradentate Copper Research Articles

Thermodynamic study of axial coordination reaction of zinc porphyrin with metal Schiff base and imidazole complex

AbstractA thermodynamic study is reported for the coordination reaction of ZnT ( m‐X)PP derivatives (X = NO2, Cl, OCH3, H or CH3) with various ligands L (L= imidazole (Im), 2‐methylimidazole (Melm), clotrimidazole (CIM), imidazol‐4‐carboxaldehyde (4‐CHOIm), unsymmetrical tetradentate copper Schiff base, Culm(p‐C1), Ch(p‐Br), and nickel Schiff base, Nilm(p‐CI)), in dichloromethane solvent. Conversion of the four‐coordinated ZnT( m‐X)PP to the five‐coordinated species is followed and isosbestic behavior is exhibited in the region among 450 and 700 nm. The reaction of a copper(II) or nickel(II) imidazolate Schiff base with ZnT( m‐X)PP results in the formation of an imidazolate bridged heterobinuclear complex. The stochiometric number is unity for all axial ligands. The equilibrium constants were determined using the β band of ZnT( m‐X)‐PP in the 293–308 K range by the method of Rose and Drago. It increases with decrease in temperature, and ΔH0 0, Δ09 0. The stronger the nucleophilic ability of the axial ligand is, the larger the stability of the axial coordination product is. Hammet linear relationships and isoequilibrium relationships exist in the system studied.

On the chemical basis of the Lowry protein determination

The copper-catalyzed oxidation of peptides and proteins by phosphomolybdic/phosphotungstic acid (Folin phenol reagent) was studied with respect to redox stoichiometry of color formation and nature of the oxidation products. From peptides without reducing side chains two reducing equivalents were transferred under ideal conditions to Mo 6+ W 6+ for each unit of tetradentate copper complex with concomitant formation of an imino peptide. Tyrosine and tryptophan side chains contributed four additional reducing equivalents. Oxidation of proline-containing peptides was greatly impaired as judged from color formation due to the interference of the imino acid with complex formation. Reaction of the oxidized peptides with 2,4-dinitrophenyl (DNP)-hydrazine gave a peptide amide and the DNP-hydrazone of a 2-oxoacyl peptide. The oxidation products from tetraalanine were identified as dialanine amide and pyruvoylalanine DNP-hydrazone. From the time course of the development of the blue color on reduction of Folin reagent with tetraalanine it was inferred that the reaction consisted of an initial (<5 s) oxidation to a Cu 3+ peptide complex followed by slow changes in absorbance, especially above 0.2 m m. Due to these complications the two-electron stoichiometry has to be considered only as a limiting case for peptide concentrations below 0.02 m m.

On the differing acidities of tri- vs. tetradentate copper(II) chelates and its effects on their catalytic properties

Hydroxo complex formation constants for a series of Cu(II) chelates have been determined, and Bronsted plots of the log of the rate constants of Cu(L) x+ promotion of methyl glycinate hydrolysis vs. the log of the hydroxo complex formation constants indicate that the different catalytic activities of tri vs. tetradentate Cu(II) chelates are mainly due to ground state effects, i.e., differences in the Lewis acidities of the two sets of metal chelates. Previously proposed rate profiles for Cu(L) x+ promotion of methyl glycinate hydrolysis are in agreement with these data and are also dicsussed in terms of the differing Lewis acidities of the Cu(II) chelates. Correlations of λ max values for tridentate Cu(II) chelates were found with both the log of the rate constant for Cu 2+ complex-catalysis of methyl glycinate hydrolysis and with the log of the hydroxometal-complex formation constants.

Applications of dexsil and other gas chromatographic porous-layer open tubular columns to metal compound separations and pyrolysis

Stainless-steel porous-layer open tubular (PLOT) columns have been made with Dexsil and other stationary phases suitable for the separation of a range of volatile metal chelates and organometallic compounds. Integrity of the substrate is assured by multiple coating of the stationary phase. Structural isomers of chromium β-diketonates and mixed ligand redistribution products are resolved and eluted without sample loss to flame ionization detection limits. A family of tetradentate copper β-ketoamine chelates are separated and the pyrolysis products of analogous tetradentate salicylaldimine complexes are resolved. Vapor phase infra-red spectrophotometry is used on-line with the PLOT column eluent for peak identification. A range of metallocene organometallics are separated including ferrocene, ruthenocene and osmocene, and substituted ferrocenes are resolved with iron specific detection by d.c. argon plasma emission spectroscopy. Cyclopentadienylmanganese tricarbonyls and cyclopentadienylchromium nitrosyl carbonyl species are also chromatographed.

Synthesis and electron spin resonance study of a tetradentate copper(II) mercaptobenzaldimine complex

The X-band e.s.r, spectrum of a copper(II) Schiff-base complex, 2,2?- [ethylenebis(nitrilomethylidyne)]-bis(benzenethiolato-S,N)copper(II) (Cu(mben)), has been determined in frozen toluene-chloroform solutions. The complicated line shape has been simulated by a computer program incorporating symmetry around the copper lower than axial, together with a nitrogen hyperfine pattern calculated for two cis nitrogen atoms. The e.s.r parameters are compared with those obtained for two other thio Schiff-base chelates and with those for the salicylaldimine analogue, Cu(salen). Metal-ligand covalency parameters estimated from the e.s.r. parameters are discussed briefly.