Copper Complexes In Solution Research Articles

SCN as a local probe of protein structural dynamics.

The dynamics of lysozyme is probed by attaching -SCN to all alanine residues. The one-dimensional infrared spectra exhibit frequency shifts in the position of the maximum absorption of 4 cm-1, which is consistent with experiments in different solvents and indicates moderately strong interactions of the vibrational probe with its environment. Isotopic substitution 12C → 13C leads to a redshift by -47 cm-1, which agrees quantitatively with experiments for CN-substituted copper complexes in solution. The low-frequency, far-infrared part of the protein spectra contains label-specific information in the difference spectra when compared with the wild type protein. Depending on the position of the labels, local structural changes are observed. For example, introducing the -SCN label at Ala129 leads to breaking of the α-helical structure with concomitant change in the far-infrared spectrum. Finally, changes in the local hydration of SCN-labeled alanine residues as a function of time can be related to the reorientation of the label. It is concluded that -SCN is potentially useful for probing protein dynamics, both in the high-frequency part (CN-stretch) and in the far-infrared part of the spectrum.

Cycloalkane Oxidation Catalyzed by Copper‐based Catalysts with H2O2 under Mild Conditions

AbstractCopper‐catalyzed cycloalkane oxidation using H2O2 as an oxidant was investigated under mild conditions. The copper catalysts studied in this work ranged from commercially‐available copper(II) salts to copper(II) complexes containing polypyridyl ligands. Various factors that affected catalytic activity of copper catalysts were elucidated. It was found that geometry of the copper complex in solution and coordinated anions played important roles in catalytic activity. The copper(II) complex generated in‐situ by mixing Cu(OAc)2 and TMPA ligand (TMPA=tris(2‐pyridylmethyl)amine) adopted trigonal bipyramidal geometry and was competent to catalyze cyclohexane oxidation with higher yields, compared to those of other Cu2+ species used in this work. The optimal catalytic condition was achieved using 1.0 % mol of Cu(OAc)2/TMPA and 10 equivalents of H2O2 with respect to cyclohexane in CH3CN at 33–35 °C for 3 hours, resulting in the total product yield of 44 %. Moreover, since cyclohexyl hydroperoxide was detected as a major product, the Fenton‐like mechanism via one electron process was proposed as a plausible mechanism in this cycloalkane oxidation. In addition, our catalytic system was further demonstrated to be applicable for oxidation of various cycloalkane substrates with moderate yields and relatively short time.

Stereochemical Properties of Multidentate Nitrogen Donor Ligands and Their Copper Complexes by Electronic CD and DFT.

UV-Vis and electronic circular dichroism (ECD) spectroscopy, complemented with Density Functional Theory (DFT) calculations, were used to elucidate the structural diversities of three multidentate nitrogen donor ligands and two associated copper complexes in solution directly. The three chiral salen ligands all consist of trans-cyclohexane-1,2-diamine as a chiral scaffold and also of pyridine rings as chromophores, differing only in the linking groups between the two functional groups mentioned above. Very different ECD intensities and somewhat different ECD patterns were observed for these ligands and satisfactorily interpreted theoretically. For the geometry optimization and spectral simulation of the open-shell metal complexes, the LANL2DZ basis set with effective core potential for the Cu and Cl atoms and pure cc-pVTZ for the rest of the atoms was utilized. The performance of the same calculations with the polarization functions (f,g) from the cc-pVTZ basis added to the LANL2DZ basis was compared. While the three ligands exhibit different conformational flexibility, the associated copper complexes show great rigidity imposed by the metal-ligand coordination, taking on a single structure in each case. In addition, dispersion interactions were shown to change the conformational stability ordering of the ligands noticeably and to exert considerable influence on the simulated UV-Vis and ECD spectra. Chirality 28:545-555, 2016. © 2016 Wiley Periodicals, Inc.

Cu(II) complexes of pyridine-2,6-dicarboxylate and N-donor neutral ligands: Synthesis, crystal structure, thermal behavior, DFT calculation and effect of aromatic compounds on their fluorescence

Two copper(II) complexes [Cu(pdc)(im)] (1) and {[Cu(pdc)(2-ap)(H2O)]·2H2O} (2) [pdc, pyridine-2,6-dicarboxylate; im, imidazole and 2-ap, 2-aminopyridine] have been synthesized and characterized by elemental analysis, IR spectroscopy, X-ray crystallography, and thermal analysis. Complexes 1 and 2 show a square planar and square pyramidal Cu(II) coordination sphere, respectively, and in solid state form hydrogen bonded 3D supramolecular networks. Both the complexes exhibit fluorescence in water–methanol solution at room temperature [λex=261nm, λem=317 and 361nm, quantum yield=0.0149 for 1; λex=278nm, λem=351nm, quantum yield=0.0031 for 2]. The effect of the presence of different aromatic compounds such as m-toluidine, aniline, nitrobenzene, p-cresol, phenol, etc., on the fluorescence of these copper complexes in solution has been inspected. Results indicate that complex 2 behaves as a fluorescence sensor for p-cresol, but loses its fluorescent properties in association with phenol. The optimized geometry from density functional theory (DFT) study shows a good agreement with the X-ray structural data. The electronic and IR spectra of these compounds are compared with results obtained by employing DFT and time-dependent density functional theory (TD-DFT) calculations.

Complexation of Cu(II) with Hetarylformazanes in Solutions, Polycrystals, and Modified Anionite

The Cu(II) complexes with hetarylformazanes (HF) formed in solutions, polycrystals, and AN-18 polymeric ionite modified with HF were studied by EPR method and were found to have almost identical structures. The configuration of the Cu2+ coordination surrounding (square-planar or pseudotetrahedral) is specified by the substituents at N1 in formazane fragments. Complexes with coordination unit Cu(4N) were formed mainly, when the ligands were taken in excess, while in the case of the ligand deficiency and with the coordinating OH group in benzene ring, the complexes with the Cu(3NO) coordination unit were formed. The covalence of in-plane metal-ligand σ-bond was found to be affected by the substituents. The formation of binuclear copper complexes in solutions and polycrystals was established in the case of deficiency of the ligand with SO3H substituent in benzene ring.

Atom-transfer radical polymerization of methyl methacrylate (MMA) using CuSCN as the catalyst

The effect of CuSCN as a catalyst in atom-transfer radical polymerization (ATRP) was investigated. CuSCN can successfully be used for the ATRP of MMA. Substituted bipyridines as well as imines can be used to stabilize the copper complex in solution. CuSCN induces faster polymerization compared to CuBr and CuCl when tosylchloride is used as the initiator. However, the polydispersity is larger than that obtained in the cases of CuCl and CuBr.

Spectroscopic Study of the Structure of Bis(oxazoline)copper Complexes in Solution and Immobilized on Laponite Clay. Influence of the Structure on the Catalytic Performance

A bis(oxazoline)copper complex is immobilized in a synthetic Laponite clay by cationic exchange in different conditions. The structure of the exchanged complex is studied by several spectroscopic methods, mainly EPR and EXAFS, and compared with the homogeneous precursors in both solid state and solution. The exchanged copper complexes are isolated species with an almost square-planar structure with the clay surface acting as a counterion of the cationic complex. The strength of the copper−anion interaction, conditioned also by the solvent, allows one to explain the differences in catalytic activity and selectivities between the different homogeneous and supported catalysts.

Rotational Motion of Square Planar Copper Complexes in Solution and Phospholipid Bilayer Membranes

Electron spin resonance (ESR) spectra of 3-ethoxy-2-oxobutyraldehydebis(N,N-dimethylthiosemicarbazonato)copper(II) (CuKTSM2) and copper(II) tetraphenylporphyrin (CuTPP), in paraffin oil at various temperatures, as well as in oriented dimyristoylphosphatidylcholine bilayer membranes, at 25 °C, were simulated using the stochastic Liouville equation formalism and a postconvolution method. It has been recognized that because nitrogen hyperfine couplings are nearly isotropic, they can be easily introduced after a simulation that omits ligand nuclear parameters, by convoluting a stick diagram for the nitrogen splitting with the copper spectrum. For the whole range of temperatures studied (from −10 to +120 °C for CuTPP and from −60 to +120 °C for CuKTSM2), the line shapes of ESR spectra for these square planar copper complexes can be accounted for by motion. The ESR spectra of Cu(II) in oriented bilayers are well reproduced for the magnetic field both perpendicular and parallel to the membrane plane. Spectra, fo...

A molecular model for the structure of copper complexes on hydrous oxide surfaces: An ENDOR study of ternary Cu(II) complexes on δ-Alumina

An ENDOR study of ternary copper(II) complexes on δ-alumina is reported. From EPR results, it is concluded, that copper has a pseudo square planar coordination geometry. The presence of protons of both axially and equatorially coordinated water is indicated by proton ENDOR data, the corresponding CuO(H 2O) distances are estimated to be 2.6(1) and 2.0(1) Å, respectively. The observed nitrogen hyperfine couplings in the ternary complexes are typical for equatorially coordinated ligands. These ENDOR data together with the EPR results allow the development of a model for the molecular structure of the surface complex. The copper and nitrogen hyperfine data are interpreted in terms of an LCAOMO model. The resulting spin density distribution is similar to that found in related copper complexes in solution or diamagnetic host matrices. The nitrogen quadrupole data are discussed in the framework of the Townes-Dailey theory.

Reactions of (polyhaloaryl)copper compounds with aryl, alkyl and allyl halides

(Polyhaloaryl)copper complexes in solution were reacted with some aryl and alkyl iodides and allyl halides to give the coupled products. The composition of some isolated complexes is reported.

Exchange coupling in copper complexes in solution

An exchange interaction was found between copper ions when bromide ions were added to a solution of copper bis-acetylacetonate in methylene chloride. The magnetic moments as well as the electronic and ESR spectra of these solutions were measured. The magnetic moment, exchange integral (− J) and D value show that the type of mechanism through which the exchange coupling occurs is superexchange via a bromide bridge. The assignment of the changed electronic spectrum is discussed.

Spectrometric Investigation of Complexes of Copper(II) and anti-2-Aminobenzophenone Oximes, and Characterization of the syn and anti Forms

Nine bivalent cations were examined spectrophotometrically for a color reaction with anti-2-amino-5-chlorobenzophenone oxime, using aqueous ethanol as solvent. Only Cu++ gave a positive color change owing to the formation of complexes. The syn isomer gave a negative result with all of the cations. This test also distinguished the two isomeric forms of eight additional pairs of analogous oximes. In the case of the anti-2-amino-5-chloro-derivative, the nature of the copper complexes in solution was explored; a crystalline complex, formulated as [(C13H11CIN2O)2Cu.H2O]2++2SO4−, was isolated. The proton-resonance signals given by the hydroxyl and amino groups for the whole set of oximes provide evidence for a significant structural difference between the two isomeric forms. The infrared spectra show lower symmetric NH stretching frequencies for the anti forms than for the syn forms. These differences are attributed to the presence of an intramolecular N-H…N=C hydrogen bond in the anti forms and to its absence in the case of the syn forms. The ultraviolet spectra of the anti forms show an increased intensity of absorption and a maximum at lower wavelength in the 220–250 mμ, range when compared to the syn forms. The situation is similar with regard to intensity, but there is a shift to a higher wavelength, for the broad absorption maximum in the 300–350 mμ range. It is concluded that these latter two regularities stem mostly from the differences in molecular geometry of the anti and syn isomers, with only a small contribution resulting specifically from the difference in hydrogen bonding.

Visible Absorption Spectra of Copper-ethylene-diamine-bis(acetylacetone) in the Crystalline State

FOR square planar copper complexes the crystal field theory predicts a splitting of the five-fold degenerate d-orbital energy-levels into four energetically different levels, d xy, d z 2, d x 2–y 2, and d zx(d yz), in the order of diminishing energy1. The visible absorption in these systems is associated with the transitions from d Zx to d xy (w 1, from d x 2–y 2 to d xy (w 2)and from d z 2 to d xy (w 3), where w 1 is the shortest wave-length and w 3 the longest wave-length band with w 2 in between. The absorption spectra of square planar copper complexes in solution invariably consist of one broad absorption band in the visible region, which, however, could be resolved into three component bands by Gaussian analysis2. With the object of finding if these split levels could be detected in the absorption spectra of the single crystal of a square planar copper complex, the present investigation was undertaken on the absorption spectra of an elongated platelet of copper-ethylene-diamine-bis(acetylacetone).