Diffusion-controlled Electron Transfer Process Research Articles

Octahedral Copper(II) Carboxylates with 1,10-Phenanthroline: Synthesis, Structural Characterization, DNA-Binding and Anti-Fungal Properties

Two mono-nuclear axially distorted octahedral copper(II) complexes have been prepared and characterized via FT-IR, UV–Visible, elctrochemical, electron spin resonance and powder and single crystal XRD techniques. The complexes consist of a phenanthroline and two carboxylate ligands each bonded in bidentate fashion. Carboxylates are ortho-nitro-2-phenyl acetate (L1) and para-chloro-2-phenyl acetate (L2). Structural study showed that both complexes possess Jahn–Teller distorted octahedral geometry. The bulk purity was assessed from the matching experimental and simulated powder XRD spectra. The results of spectroscopic techniques are consistent with each other. ESR data revealed single electron occupancy of dx2 − y2 orbital with 2B1g as ground state typical of tetragonally distorted octahedral geometry. Electrochemical solution study showed diffusion controlled electron transfer processes with diffusion co-efficient values of 10.323 × 10–8 cm2s–1 and 0.972 × 10–8 cm2s–1 for 1 and 2. Complexes exhibited excellent DNA-binding activity studied via UV–Visible spectroscopy, cyclic voltammetry, florescence spectroscopy and viscometry yielding Kb values of 1.871 × 104 M–1 (1) and 1.577 × 104 M–1 (2), 0.38 × 104 M–1 (1) and 6.39 × 104 M–1 (2) and 2.1 × 106 M–1 (1) and 2.0 × 06 M–1 (2), respectively, for the first three techniques. Complexes possess good antifungal activity against three fungal strains.

Dinuclear Ternary Copper(II) Complex: Synthesis, Characterization, Structure and DNA-Binding Studies

A dinuclear centrosymmetric copper(II) complex has been prepared and characterized via FT-IR, UV-Visible and electron spin resonance spectroscopy, electrochemical method, and powder and single crystal XRD techniques. The two copper(II) ions are connected by two μ-1,1-O atoms belonging to para-fluorophenyl acetate ligands. Each copper(II) ion is coordinated by two other carboxylate ligands in monodentate and a 2,2'-bipyridine molecule in bidentate manner. Thus the geometry around each penta-coordinated copper(II) ion is square pyramidal with distortion factor τ = 0.04. Purity and uniform crystalline nature of the complex was assessed from powder XRD spectrum. ESR signal consisted of partially resolved hyperfine splitting pattern while electrochemical studies revealed diffusion controlled electron transfer processes with diffusion co-efficient of 1.628×10-7 cm2 s-1. The results of all spectroscopic experiments support each other. The complex afforded mixed binding mode with DNA yielding DNA-binding constant values of 3.667×104and 1.438×104 M-1 using cyclic voltammetry and absorption spectroscopy, respectively. The preliminary studies heralded good structural and biological importance of the synthesized complex.

Polymeric Copper(II) Paddlewheel Carboxylate: Structural Description, Electrochemistry, and DNA‐binding Studies

A polymeric complex of copper(II) was isolated and purified from the self‐assembly of CuSO4 and 2‐phenyl acetate in aqueous medium. It was characterized through FT‐IR, UV/Vis, electron spin resonance, electrochemical solution studies, and powder and single crystal XRD techniques. The structure was revealed to consist of directly interconnected dimeric paddlewheel building units without any intervening ligand. This type of polymeric paddlewheel structures are found very rarely. Each copper is lying in a CuO5 square pyramid coordinated by four oxygen atoms in the square base while the axial oxygen belongs to the neighboring paddlewheel. Purity and uniform crystalline nature of the complex was assessed from matching theoretical and experimental powder XRD spectra. ESR spectrum consisted of a broad signal with g value = 2.2427, whereas electrochemical studies revealed diffusion controlled electron transfer processes with diffusion co‐efficient = 1.628 × 10–7 cm2·s–1. The results of spectroscopic techniques support each other. The complex afforded mixed binding mode with DNA yielding DNA‐binding constant values of 1.384 × 104 m–1 and 8.845 × 104 m–1 using absorption spectroscopy and cyclic voltammetry, respectively. The complex also exhibited significant activity against anti‐fungal strain Helminthosporium solani by inhibiting its 75 % ± 2.5 growth. The preliminary studies heralded excellent biological potential of the synthesized complex.

In Stationary Regime, Electron Transfer Rates in RTIL Media Are Diffusion Controlled: Experimental Evidence from Pulse Radiolysis Study

We report electron transfer (ET) process from the long-lived radical anions of pyrene and benzophenone to molecular acceptors, e.g., benzophenone and fluorenone, respectively, in two RTIL media, namely, [BMIM][PF6] and [BMIM][BF4], as well as a few other conventional organic solvents using the nanosecond pulse radiolysis technique. Decay of the donor radical anion and concomitant formation of the acceptor radical anion ensure a bimolecular ET process. The rate constants for the bimolecular ET process in both normal organic solvents and RTILs have been found to be nearly equal to diffusion controlled rate calculated for the corresponding solvent. For long-lived anions, having lifetimes longer than a few hundred nanoseconds, quenching occurs mainly in the stationary regime. In this regime, the ET rate is fully controlled by the rate of diffusion of the reactive species in those solvents. To the best of our knowledge, this is the first experimental evidence of the diffusion controlled ET process occurring in the stationary regime in RTIL media.

Electrokinetic and Impedimetric Dynamics of FeCo-Nanoparticles on Glassy Carbon Electrode

The electrochemical dynamics of a film of FeCo nanoparticles were studied on a glassy carbon electrode (GCE). The film was found to be electroactive in 1 M LiClO4 containing 1:1 v/v ethylene carbonate dimethyl carbonate electrolyte system. Cyclic voltammetric experiments revealed a diffusion-controlled electron transfer process on the GCE/FeCo electrode surface. Further interrogation on the electrochemical properties of the FeCo nanoelectrode in an oxygen saturated 1 M LiClO4 containing 1:1 v/v ethylene-carbonate-dimethyl carbonate revealed that the nanoelectrode showed good response towards the electro-catalytic reduction of molecular oxygen with a Tafel slope of about 120 mV which is close to the theoretical 118 mV for a single electron transfer process in the rate limiting step; and a transfer coefficient (α) of 0.49. The heterogeneous rate constant of electron transfer (ket), exchange current density (io) and time constant (τ) were calculated from data obtained from electrochemical impedance spectroscopy and found to have values of 2.3 x 10-5 cm s-1, 1.6 x 10-4 A cm-2 and 2.4 x 10-4 s rad-1, respectively.

Quenching studies of pyrenoyl glutamic acid derivatives

The preparation and full characterization of fluorescent labeled N-pyrenoyl–L-glutamic acid diethyl ester (2) and 4-(N-Boc–L-glutamide(O-benzyl ester))–N,N-dimethylaniline (3) by the DCC–HOBT protocol is described. The benzyl group in 3 was removed by hydrogenation giving the free acid 4-(N-Boc–L-glutamide(OH))–N,N-dimethylaniline (4). The steady-state and time-resolved fluorescence quenching studies were performed in order to distinguish ground state quenching taking place in a hydrogen-bonded complex and dynamic quenching. Weak molecular interactions between the fluorophore 2 and the quencher 4 leading to a 1∶1 complex were detected by 1H-NMR titration experiments. The association constants were determined by fluorescence methods to be in the order of 3.8–4.0 × 103 M–1 for all systems investigated. The bimolecular quenching constants kq are in the order of 1.0–1.28 × 1010 M–1 s–1, indicating a diffusion controlled electron transfer process.

Electrochemical studies on cobalt tris (acetylacetone)

The electrochemical reduction of cobalt acetylacetonate (Co(acac)3) at the mercury electrode in propylene carbonate anddmso has been carried out using dc polarography, controlled potential coulometry, chronoamporometry and cyelic voltammetry. In propylene carbonate, polarograms showed two well defined waves, one wave being an adsorption pre-wave, the other an irreversible, diffusion-controlled electron transfer process. From chronoamperometry the diffusion coefficient was determined. Cyclic voltammetry confirmed the polarographic results, although additional adsorption waves were found. Indmso, results were similar to those in propylenecarbonate. However, polarograms showed no adsorption pre-wave and additional adsorption waves found in propylene carbonate in the cyclic voltammograms were absent. The mechanism of the reduction process in both solvents is discussed.