Electrochemical studies of porphyrin-appended dendrimers

The electrochemical properties of porphyrin-appended dendrimers containing 2-, 4-, 8-, 16-, 32- and 64-porphyrin macrocycles in their free-base and zinc(II) forms have been investigated. Both series gave diffusional based voltammetric responses in dichloromethane. There was minimal effect of dendrimer generation on the redox potentials. Multiple pi-cation and anion radicals as well as dications and dianions were formed on the surface of the dendrimers on oxidation or reduction as appropriate, with each cyclic voltammetric wave representing electron transfer to or from multiple non-interacting porphyrin sites. Electrostatic interactions in the higher generation dendrimers result in kinetic effects being observed for the highly charged species generated when each porphyrin unit is doubly or triply oxidised. The number of electrons transferred on reduction or oxidation of the dendrimers was evaluated using steady-state microelectrode voltammetry. For the lower generations of species a good correlation was observed between numbers of electrons transferred and number of porphyrin entities per molecule; for the dendrimers containing 32 and 64 units, however, slight negative deviations were observed, possibly due to electrostatic interactions as the porphyrins become closer packed.     

Electrochemical deposition of copper phosphides

Summary Methods for preparation of copper phosphides at ambient temperatures by electrodeposition are presented. From P₄/PCl₃/Acetonitrile/TBA-BF₄/Cu⁺ (solvated) Cu₃P and Cu₃P₂ can be obtained at different deposition potentials.

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Elektrochemische Abscheidung von Kupferphosphiden

Zusammenfassung Es werden Verfahren zur Herstellung von Kupferphosphiden bei ambienten Temperaturen beschrieben. Aus der Anordnung P₄/PCl₃/Acetonitril/TBA-BF₄/Cu⁺ (solvatisiert) können Cu₃P und Cu₃P₂ bei verschiedenen Abscheidungspotentialen erhalten werden.

     

Electrochemical behavior of copper in thiocarbamide solutions

It is shown that the kinetics of electrochemical processes in a copper-thiocarbamide solution is of mixed character. The effective cathodic and anodic transfer coefficients Β = 0.25 and α = 0.4, reactions orders with respect to the ligand 0.7 and 1.5, and the exchange current densityi ₀ ≅10^-4 A/cm² are determined. Using the literature data on the thiocarbamide adsorption on copper, the results are interpreted as evidence for the involvement of one thiocarbamide molecule from the bulk solution, along with the adsorbed ligands, in an elementary act of copper dissolution.     

Electrochemical synthesis of copper sulfide nanoparticles

Cu₂S nanoparticles were electrosynthesized by cyclic voltammetry between 0.10 and 1.50 V in the presence of polyvinylalcohol as stabilizer. The structure and nature of the resulting Cu₂S poly (vinyl alcohol) composite were characterized by transmission electron microscopy and X-ray diffraction. The results show that electrochemically synthesized Cu₂S nanoparticles are homogeneously dispersed and well separated from one another with a mean diameter of about 12 nm.     

Electrochemical processes on the copper electrode in water-ethanol solutions of copper sulfate

The system Cu/H₂O-C₂H₅OH-CuSO₄ was studied in a wide range of organic component concentrations by the impedance spectroscopy method. In the studied range of ethanol concentrations the diffusion of ions to an electrode is the limiting stage of the electrode process. An increase in the ethanol concentration results in a decrease in the double electrical layer capacity, which is caused by a change in the double electrical layer structure at the electrode-solution boundary.     

Electrochemical behaviour of alkaline copper complexes

A search for non-cyanide plating baths for copper resulted in the development of alkaline copper complex baths containing trisodium citrate [TSC] and triethanolamine [TEA]. Voltammetric studies were carried out on platinum to understand the electrochemical behaviour of these complexes. In TSC solutions, the deposition of copper involves the slow formation of a monovalent species. Adsorption of this species obeys Langmuir isotherm. In TEA solutions the deposition involves the formation of monovalent ions obeying the non-activated Temkin isotherm. Conversion of divalent to monovalent copper is also slow. In TEA and TSC alkaline copper solutions, the predominant species that undergo stepwise reduction contain only TEA ligands.     

Dynamics and thermodynamics of water in PAMAM dendrimers at subnanosecond time scales

Atomistic molecular dynamics simulations are used to study generation 5 polyamidoamine (PAMAM) dendrimers immersed in a bath of water. We interpret the results in terms of three classes of water: buried water well inside of the dendrimer surface, surface water associated with the dendrimer-water interface, and bulk water well outside of the dendrimer. We studied the dynamic and thermodynamic properties of the water at three pH values: high pH with none of the primary or tertiary amines protonated, intermediate pH with only the primary amines protonated, and low pH with all amines protonated. For all pH values we find that both buried and surface water exhibit two relaxation times: a fast relaxation ( approximately 1 ps) corresponding to the libration motion of the water and a slow ( approximately 20 ps) diffusional component related to the escaping of water from one domain to another. In contrast for bulk water the fast relaxation is approximately 0.4 ps while the slow relaxation is approximately 14 ps. These results are similar to those found in biological systems, where the fast relaxation is found to be approximately 1 ps while the slow relaxation ranges from 20 to 1000 ps. We used the 2PT MD method to extract the vibrational (power) spectrum and found substantial differences for the three classes of water. The translational diffusion coefficient for buried water is 11-33% (depending on pH) of the bulk value while the surface water is about 80%. The change in rotational diffusion is quite similar: 21-45% of the bulk value for buried water and 80% for surface water. This shows that translational and rotational dynamics of water are affected by the PAMAM-water interactions as well as due to the confinement in the interior of the dendrimer. We find that the reduction of translational or rotational diffusion is accompanied by a blue shift of the corresponding libration motions ( approximately 10 cm(-1) for translation, approximately 35 cm(-1) for rotation), indicating higher local force constants for these motions. These effects are most pronounced for the lowest pH, probably because of the increased rigidity caused by the internal charges. From the vibrational density of states we also calculate the enthalpies and entropies of the various waters. We find that water molecules are enthalpically favored near the PAMAM dendrimer: energy for surface water is approximately 0.1 kcal/mol lower to that in the bulk, and approximately 0.5-0.9 kcal/mol lower for buried water. In contrast, we find that both the buried and surface water are entropically unfavored: buried water is 0.9-2.2 kcal/mol lower than the bulk while the surface water is 0.1-0.2 kcal/mol lower. The net result is a thermodynamically unfavored state of the water surrounding the PAMAM dendrimer: 0.4-1.3 kcal/mol higher for buried water and 0.1-0.2 kcal/mol for surface water. This excess free energy of the surface and buried waters is released when the PAMAM dendrimer binds to DNA or metal ions, providing an extra driving force.     

Electrochemical screening of biomembrane-active compounds in water

Interactions of biomembrane-active compounds with phospholipid monolayers on microfabricated Pt/Hg electrodes in an on-line high throughput flow system are demonstrated by recording capacitance current peak changes as rapid cyclic voltammograms (RCV). Detection limits of the compounds’ effects on the layer have been estimated from the data. Compounds studied include steroids, polycyclic aromatic hydrocarbons, tricyclic antidepressants and tricyclic phenothiazines. The results show that the extent and type of interaction depends on the—(a) presence and number of aromatic rings and substituents, (b) presence and composition of side chains and, (c) molecular shape. Interaction is only indirectly related to compound hydrophobicity. For a selection of tricyclic antidepressants and tricyclic phenothiazines the detection limit in water is related to their therapeutic normal threshold. The sensing assay has been tested in the presence of humic acid as a potential interferent and in a tap water matrix. The system can be applied to the screening of putative hazardous substances and pharmaceuticals allowing for early detection thereof in the water supply. The measurements are made in real time which means that potentially toxic compounds are detected rapidly within <10 min per assay. This technology will contribute greatly to environment safety and health.     

Electrochemical reduction of copper(II) galacturonate

The complexes formed in the interaction between copper(II) anda-andβ-galacturonic acid, in the pH range 2.5–11.0, have been investigated by means of d.c. polarography and cyclic voltammetry. Witha-galacturonic acid, no complex is formed with copper up to pH 6. Between pH 6 and about 9.5, a complex is formed in solution. Above pH 9.5, the complex appears to break up releasing the ligand. In the case of β-galacturanic acid, no complex is formed until pH 3.5, and persists in solution up to a pH of about 9.5. A second complex forms above pH 6.9 and co-exists with the first complex up to pH 9.5. The complexes formed with both forms of galacturonic acid were studied and the stability constant of the coppera-galacturonate determined.     

Electrochemical synthesis of copper(II) carboxylates

A number of copper(II) carboxylates have been synthesized by anodic oxidation of copper. The reactions were found to proceed with current efficiencies of 0.95 to 1.00 eq./Faraday. Reaction products have been characterized by infrared spectral studies and analysis of copper.     

Electrochemical studies of copper fatty amides complex in organic medium

The electrochemical behavior of complexes of fatty amides, synthesized from vegetable oil, with Cu(II) has been investigated. In this study, a platinum electrode was used in presence of DMSO as a medium. Reduction of Cu(II)/fatty amides complex was found with quasi-reversible reaction. The peak potential of voltammetric behavior of fatty amides is about ?0.77 V at a scan rate v = 0.1 V s^?1 versus Ag|Ag⁺ electrode. This study shows that Cu(II)-fatty amides complex is poorly adsorbed on the electrode surface. Additionally, the copper complex form of fatty amides has a more stable structure than pure fatty amides to form the electrochemical reduction of the complex.     

Electrochemical deposition of a copper carboxylate layer on copper as potential corrosion inhibitor

Carboxylic acids and sodium carboxylates are used to protect metals against aqueous and atmospheric corrosion. In this paper, we describe the application of a layer of copper carboxylate on the surface of a copper electrode by means of cyclic voltammetry technique and tests which measure the corresponding resistance to aqueous corrosion. Unlike the soaking process, which also forms a film on the surface, the use of cyclic voltammetry allows one to follow the deposition process of the copper carboxylates onto the electrode. The modified electrodes have been characterised with infrared spectroscopy. In addition, the corrosion resistance of the film has been investigated using polarisation resistance and Tafel plot measurements.     

Electrochemical, spectroelectrochemical, and molecular quadratic and cubic nonlinear optical properties of alkynylruthenium dendrimers

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.     

Electrochemical growth of nickel hollow nanostructures on copper substrates

We have shown hollow Ni nanonodules with outer diameters of 80-200 nm and wall thicknesses of 5-25 nm could be prepared by electrochemical deposition in the NiCl2 + dimethyl sulfoxide + C2H4O3 + H2O system, and the products were high purity. In particular, Ni hollow nanonodule structures or highly assembling Ni hollow nanostructures can be selected by varying the compositions of the solvent mixture. Apart from the hollow grain size, the wall thickness can also easily be controlled by varying the electrochemical parameters, salt concentration, and deposition time. The typical coercivity of Ni hollow nanostructures with particle sizes of about 100-150 nm was much bigger than that of the bulk Ni.     

Electrochemical reactions at a copper electrode in copper-conducting solid electrolytes

Potentiostatic measurements are used to show that, depending on the overvoltage sign, either electrochemical deposition or dissolution of copper occurs at the Cu/Cu₄RbCl₃I₂ interface at overvoltages η > 8–10 mV. At η = 10–100 mV, the reaction rate is limited by the formation and expansion of dissolution centers at the copper surface during anodic polarization and crystallization centers, during cathodic polarization. At η > 120 mV, the reaction rate is limited by charge transfer; the exchange current density is 2.7 mA cm^?2 and the anodic transfer coefficient is ～0.45. Under anodic polarization, formation of electron holes in the electrolyte occurs in parallel with the copper anodic dissolution. Therefore, nonstoichiometry of the electrolyte emerges in the near-electrode layer and divalent copper accumulates there.     

铜表面烯丙基硫脲自组装膜的电化学行为

为阐明金属Cu在含稀丙基硫脲NaCl溶液中的腐蚀行为和规律,利用自组装技术在铜表面制备了烯丙基硫脲自组装膜,并在中性氯化钠体系中测试了该自组装膜的电化学行为和缓蚀效率.电化学测定表明,烯丙基硫脲自组装膜对阴极过程有明显的抑制,并且发现自组装膜的保护性质与腐蚀电位、烯丙基硫脲的浓度和溶液中Cl-浓度密切相关.烯丙基硫脲的...     

Electrochemical and spectral characterization of blue copper protein models

Blue copper proteins play a central role in various enzymatic anabolic/catabolic pathways in living cells by virtue of the integrated metal ions. These ions may exist in variable oxidation states, with suitable reduction potentials and fast electron-transfer rates which in turn is a manifestation of their unusual geometry and co-ordination. We report the electrochemical and spectral characterization of three novel complexes of copper (II) with N₂S type tridentate chelating agent 2,2′-dithiodianiline (dta), having structural similarities to the active site of Type I copper proteins. High positive redox potentials in the range of 0.5–0.6 V vs Ag/AgCl electrode of the complexes and the absorption maxima at ～550 nm, with high extinction coefficients, correspond well with typical blue copper proteins. The IR and EPR studies support the assigned pseudo tetrahedral structures to the complexes. The diffusion coefficient and rate constant for heterogeneous charge transfer for Cu²⁺/Cu⁺ coordinated in a potentially bio-mimetic Type I site is reported.