Photochemical properties of copper complexes

Effects of Cu(I) contents on voltammetric behavior and electrodeposition mechanism of bimetallic composite ionic liquids

Effective electrochemical recovery of metal for bimetallic composite ionic liquid (IL) is related to ion species and even the reaction mechanism under different Cu(I) content, thus bimetallic composite ILs (Et3NHCl-1.54AlCl3-xCuCl,...

Nonpolar Side Chains Affect the Photochemical Redox Reactions of Copper(II)-Amino Acid Complexes in Aqueous Solutions

Photochemical redox reactions of Cu(II) complexes of eight amino acid ligands (L) with nonpolar side chains have been systematically investigated in deaerated aqueous solutions. Under irradiation at 313 nm, the intramolecular carboxylate-to-Cu(II) charge transfer within Cu(II)-amino acid complexes leads to Cu(I) formation and the concomitant decomposition of amino acids. All amino acid systems studied here can produce ammonia and aldehydes except proline. For the 1:1 Cu(II) complex species (CuL), the Cu(I) quantum yields at 313 nm (Φ_Cu(I),CuL) vary by fivefold and in the sequence (0.10 M ionic strength at 25 °C) alanine (0.094) > valine (0.059), leucine (0.059), isoleucine (0.056), phenylalanine (0.057) > glycine (0.052) > methionine (0.032) > proline (0.019). This trend can be rationalized by considering the stability of the carbon-centered radicals and the efficient depopulation of the photoexcited state, both of which are dependent on the side-chain structure. For the 1:2 Cu(II) complex species (CuL₂), the Cu(I) quantum yields exhibit a similar trend and are always less than those for CuL. The photoformation rates of ammonia, Cu(I), and aldehydes are in the ratio of 1:2.0 ± 0.2:0.7 ± 0.2, which supports the proposed mechanism. This study suggests that the direct phototransformation of Cu(II)-amino acid complexes may contribute to the bioavailable nitrogen for aquatic microorganisms and cause biological damage on cell surfaces in sunlit waters.

Elemental and Isotopic Variations of Copper and Zinc Associated with the Diel Activity of Phototrophic Biofilm

The response in metal concentrations and isotopic composition to variations in photosynthetic activity of aquatic micro-organisms is crucially important for understanding the environmental controls on metal fluxes and isotope excursions. Here we studied the impacts of two successive diel cycles on physicochemical parameters, Cu and Zn concentrations, and isotopic composition in solution in the presence of mature phototrophic biofilm in a rotating annular bioreactor. The diel cycles induced fluctuations in temperature, pH, and dissolved oxygen concentration following the variation in the photosynthesis activity of the biofilm. Diel variations in metal concentrations were primarily related to the pH variation, with an increase in metal concentration in solution related to a pH decrease. For both metals, δ(⁶⁶Zn) and δ(⁶⁵Cu) in solution exhibited complex but reproducible diel cycles. Diel variations in photosynthetic activity led to alternatively positive and negative isotope fractionation, producing the sorption of light Zn (Δ(⁶⁶Zn_{sorbed-solution}) = -0.1 ± 0.06‰) and heavy Cu isotopes (Δ(⁶⁵Cu_{sorbed-solution}) = +0.17 ± 0.06‰) during the day at high pH and the excretion of lighter Zn isotopes (-0.4‰ < Δ(⁶⁶Zn_{excreted-biofilm}) < +0.14‰) and heavy Cu isotopes (Δ(⁶⁵Cu_{excreted-biofilm}) = +0.7 ± 0.3‰) during the night at lower pH. We interpreted Zn and Cu diel cycles as a combination of a desorption of exopolymeric substance-metal complexes and a small active efflux during the night with adsorption and incorporation via an active uptake during the day. The hysteresis of metal concentration in solution over the diel cycle suggested the more important role of uptake compared to desorption and efflux from the biofilm. The phototrophic biofilm presents a non-negligible highly labile metal pool with important potential for contrasting isotopic fractionation at the diel scale.

Vibrations tell the tale. A time-resolved mid-infrared perspective of the photochemistry of iron complexes

Time-resolved infrared spectroscopies are used to elucidate multiscalar photochemical processes of iron complexes.

Characterization and photocatalytic behavior of 2,9-di(aryl)-1,10-phenanthroline copper(i) complexes

The synthesis, characterization, photophysical properties, theoretical calculations, and catalytic applications of 2,9-di(aryl)-1,10-phenanthroline copper(i) complexes are described. Specifically, this study made use of di(aryl)-1,10-phenanthroline ligands including 2,9-di(4-methoxyphenyl)-1,10-phenanthroline (1), 2,9-di(4-hydroxyphenyl)-1,10-phenanthroline (2), 2,9-di(4-methoxy-3-methylphenyl)-1,10-phenanthroline (3), and 2,9-di(4-hydroxy-3-methylphenyl)-1,10-phenanthroline (4). The 2 : 1 ligand-to-metal complexes, as PF₆^- salts, i.e., ([Cu·(1)₂]PF₆, [Cu·(2)₂]PF₆, [Cu·(3)₂]PF₆, and [Cu·(4)₂]PF₆) have been isolated and characterized. The structures of ligands 1 and 2 and complexes [Cu·(1)₂]PF₆ and [Cu·(3)₂]PF₆ have been determined by single-crystal X-ray analysis. The photoredox catalytic activity of these copper(i) complexes was investigated in an atom-transfer radical-addition (ATRA) reaction and the results showed fairly efficient activity, with a strong wavelength dependence. In order to better understand the observed catalytic activity, photophysical emission and absorption studies, and DFT calculations were also performed. It was determined that when the excitation wavelength was appropriate for exciting into the LUMO+1 or LUMO+2, catalysis would occur. On the contrary, excitations into the LUMO resulted in no observable catalysis. In light of these results, a mechanism for the ATRA photoredox catalytic cycle has been proposed.

Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy

The kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(i) bis(phenanthroline)/ruthenium(ii) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(i)-Ru(ii) analogs of the homodinuclear Cu(i)-Cu(i) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These results suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations.

Ultrafast Photochemistry of Copper(II) Monochlorocomplexes in Methanol and Acetonitrile by Broadband Deep-UV-to-Near-IR Femtosecond Transient Absorption Spectroscopy

Photochemistry of copper(II) monochlorocomplexes in methanol and acetonitrile solutions is studied by UV-pump/broadband deep-UV-to-near-IR probe femtosecond transient absorption spectroscopy. Upon 255 and 266 nm excitation, the complexes in acetonitrile and methanol, respectively, are promoted to the excited ligand-to-metal charge transfer (LMCT) state, which has a short (sub-250 fs) lifetime. From the LMCT state, the complexes decay via internal conversion to lower-lying ligand field (LF) d-d excited states or the vibrationally hot ground electronic state. A minor fraction of the excited complexes relaxes to the LF electronic excited states, which are relatively long-lived with lifetimes >1 ns. Also, in methanol solutions, about 3% of the LMCT-excited copper(II) monochlorocomplexes dissociate forming copper(I) solvatocomplexes and chlorine atoms, which then further react forming long-lived photoproducts. In acetonitrile, about 50% of the LMCT-excited copper(II) monochlorocomplexes dissociate forming radical and ionic products in a ratio of 3:2. Another minor process observed following excitation only in methanol solutions is the re-equilibration between several forms of the copper(II) ground-state complexes present in solutions. This re-equilibration occurs on a time scale from sub-nanoseconds to nanoseconds.

Diel changes in trace metal concentration and distribution in coastal waters: Catalina Island as a study case

Understanding biogeochemical cycling of trace metals in the ocean requires information about variability in metal concentrations and distribution over short, e.g., diel, time scales. Such variability and the factors that influence it are poorly characterized. To address this shortcoming, we measured trace metal concentrations in the total dissolved, colloidal, and soluble fractions every 3-4 h for several consecutive days and nights in surface waters from a coastal station. Our results show that both the concentration and the size partitioning of some biologically essential (Fe, Cu, Co, and Cd) and anthropogenic (Pb) metals are subjected to diel variations that may be related to both inorganic and biological processes (e.g., photolysis of high-molecular-weight dissolved organic matter, photoinduced reduction/oxidation of metal(hydrous)oxides, uptake by growing phytoplankton, degradation of organic matter, lysis, and grazing). The largest fluctuations were observed in the soluble and colloidal pools. Soluble Fe varied during the day-night cycle by a factor of 40, and the contribution of colloidal Pb to the total dissolved fraction increased from 6±3% during the day to as much as 70-80% during the night. Our results suggest that changes occurring over time scales of hours need to be considered when collecting and interpreting trace metal data from the surface ocean.

Photopolymerization reactions using the photoinitiated copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction

The first bulk photopolymerization of multifunctional alkyne and azide monomers using the CuAAC reaction is successfully carried out from low molecular weight, nonviscous monomer resins. Compared to other traditional step-growth bulk photopolymerization, this approach readily provides crosslinked, high glass transition temperature polymers that incorporate triazole linkages throughout the polymer structure with great temporal control.

Light-induced copper(II) coordination by a bicyclic tetraaza chelator through a ligand-to-metal charge-transfer reaction

To enable utilization of the broad potential of copper isotopes in nuclear medicine, rapid and robust chelation of the copper is required. Bowl adamanzanes (bicyclic tetraaza ligands) can form kinetically stable copper complexes, but they are usually formed at low rates unless high pH values and high temperatures are applied. We have investigated the effects of the variation in the pH, different anions, and UV irradiation on the chelation rate. UV spectra of mixtures of Cu(2+) and [2(4).3(1)]adz in water show the existence of a long-lived two-coordinated copper(II) intermediate (only counting coordinated amine groups) at pH above 6. These findings are supported by pH titrations of mixtures of Cu(2+) and [2(4).3(1)]adz in water. Irradiation of this complex in the ligand-to-metal charge-transfer (LMCT) band by a diode-array spectrophotometer leads to photodeprotonation and subsequently to formation of the four-coordinated copper(II) complex at a rate up to 7800-fold higher at 25 °C than in the dark. Anions in the solution were found to have three major effects: competitive inhibition due to Cu(II) binding anions, inhibition of the photoinduced transchelation from UV-absorbing anions, and photoredox inhibition from acido ligands capable of acting as electron donors in LMCT reactions. Dissolved O(2) was also found to result in photoredox inhibition.

Inactivation of MS2 coliphage in Fenton and Fenton-like systems: role of transition metals, hydrogen peroxide and sunlight

The inactivation of coliphage MS2 by iron- and copper-catalyzed Fenton systems was studied to assess the importance of this process for virus inactivation in natural systems and during water treatment by advanced oxidation processes. The influence of H(2)O(2) (3-50 microM) and metal (1-10 microM) concentrations, HO(*) production, and sunlight on inactivation was investigated. Inactivation was first order with respect to H(2)O(2), but the dependence on the metal concentration was more complex. In the Cu/H(2)O(2) system, the inactivation rate constant k(obs) increased with added Cu up to 2.5 microM, and then leveled off. This was consistent with Cu saturation of the solution, indicating that only soluble Cu contributed to inactivation. In contrast, inactivation in the Fe/H(2)O(2) system was governed by colloidal iron. Irradiation by sunlight only affected the Fe/H(2)O(2) system, leading to a 5.5-fold increase in k(obs) (up to 3.1 min(-1)). HO(*) production, measured by electron spin resonance, could not account for the observed inactivation in the Fe/H(2)O(2) system. Other oxidants, such as ferryl species, must therefore play a role. Experiments using bulk oxidant scavengers revealed that inactivation occurred by a caged mechanism involving oxidant production by metals located in close proximity to the virus. Overall, our results show that the Fenton/photo-Fenton process may serve as an efficient technology for virus disinfection.

Copper(I)-Purine-Phosphine Complexes. Syntheses and Molecular Structures of [Cu(2)(&mgr;-HL(1))(2)(&mgr;-dppm)(eta(1)-dppm)(2)] and {[Cu(3)(&mgr;(3)-Cl)(2)(&mgr;-dppm)(3)][Cu(HL(2))(2)]} (H(2)L(1) = 8-Mercaptotheophylline and H(2)L(2) = 8-Ethyl-3-methylxanthine)

The syntheses and molecular structures of two novel polynuclear copper(I)-purine-phosphine complexes are reported. The first one is a dinuclear [Cu(2)(&mgr;-HL(1))(2)(&mgr;-dppm)(eta(1)-dppm)(2)] complex (H(2)L(1) is 8-mercaptotheophylline). The compound crystallizes in the triclinic system, space group P&onemacr;, with cell constants a = 12.342(5) Å, b = 15.255(5) Å, c = 24.972(5) Å, alpha = 74.31(2) degrees, beta = 78.62(2) degrees, gamma = 72.51(2) degrees, and Z = 2. The structure of this complex exhibits as the most important feature the simultaneous presence of eta(1)-terminal and eta(2)-bridging dppm ligands, which is first here described for a copper complex. This complex is also of interest because of its reversible photochromic behavior in the solid state. The second compound is an ionic {[Cu(3)(&mgr;(3)-Cl)(2)(&mgr;-dppm)(3)][Cu(HL(2))(2)]} complex (H(2)L(2) is 8-ethyl-3-methylxanthine), which crystallizes in the monoclinic system, space group P2(1)/n, with cell constants a = 15.829(6) Å, b = 22.801(7) Å, c = 28.569(6) Å, beta = 97.65(4) degrees, and Z = 6. The structure of this complex consists of trinuclear copper(I) cations and mononuclear [Cu(purine)(2)](-) anions, exhibiting a linear stereochemistry. As far as we know, this compound represents the first example of a copper(I)-purine complex whose structure has been determined by X-ray crystallography.

Light-dependent reduction of copper(II) and its effect on cell-mediated, thiol-dependent superoxide production

The thiol-dependent reduction of copper(II) and associated superoxide radical production in copper(II)-treated cultures of the unicellular alga Dunaliella tertiolecta is induced by light of wavelength greater than 425 nm. We propose that the effect of light on these reactions is mediated at the copper(II) reduction step through a light-stimulated ligand to metal charge transfer reaction between sulphur and copper(II). These results suggest that light may be an important controlling factor in metal-induced lipid peroxidation reactions.