Copper Rubeanate Research Articles

Front Cover: Self‐assembly of Soluble Nanoarchitecture using Hybrids of Diblock Copolypeptide Amphiphiles with Copper Rubeanate Hydrates in Water and Their Electrooxidation Reaction (ChemNanoMat 11/2020)

Front Cover: Self‐assembly of Soluble Nanoarchitecture using Hybrids of Diblock Copolypeptide Amphiphiles with Copper Rubeanate Hydrates in Water and Their Electrooxidation Reaction (ChemNanoMat 11/2020)

Self‐assembly of Soluble Nanoarchitecture using Hybrids of Diblock Copolypeptide Amphiphiles with Copper Rubeanate Hydrates in Water and Their Electrooxidation Reaction

AbstractA simple approach for producing supramolecular nanohybrids was developed allowing preparation of soluble hybrid two‐dimensional nanosheets in water through spontaneous organization of two‐dimensional Cu(II) rubeanate hydrate (which by itself does not dissolve in water or common organic solvents) and cationic diblock copolypeptide amphiphiles. These components self‐assembled into nanosheets with thicknesses of about several nm and widths on the order of several micrometers. Notably, the nanostructures were dependent on polypeptides containing leucine, suggesting that both cationic and hydrophobic polypeptide components are involved in generating the two‐dimensional (2D) nanosheet structures. The supramolecular hybrids exhibited excellent stability, and made it possible to control spectroscopic properties including ligand‐to‐metal‐charge‐transfer (LMCT), d‐d transition, electrochemical behavior, and electrooxidation reactions with ethanol in aqueous media.

Phase Transition and Dynamics of Water Confined in Hydroxyethyl Copper Rubeanate Hydrate

This paper reports the results of the heat capacity (Cp) and quasi-elastic neutron scattering (QENS) measurements on hydroxyethyl copper rubeanate hydrate and its deuterated analogues. These materials accommodate water in their nano-pores and exhibit large proton conductivity at room temperature. The Cp data revealed that the adsorbed water gives rise to a glass transition and a first-order transition at 170 and 260 K, respectively. The QENS data clarified that the adsorbed water consists of the free water apart from the pore wall and the bound water condensed on the pore wall. The diffusion coefficients of both waters are smaller than those of copper rubeanate hydrates owing to the steric hindrance caused by the hydroxyethyl group. The free water transforms to the condensed water through the transition at 260 K as in the case of copper rubeanate hydrates.

Electrochemical Reduction of Carbon Dioxide Using a Copper Rubeanate Metal Organic Framework

We synthesized a copper rubeanate metal organic framework (CR-MOF) which has the potential to improve the catalytic activity of electrochemical reduction of CO2 due to its characteristics of electronic conductivity, proton conductivity, dispersed reaction sites, and nanopores. Synthesized CR-MOF particles were dropped on carbon paper (CP) to form a working electrode. The onset potential for CO2 reduction of a CR-MOF electrode was about 0.2 V more positive than that observed on a Cu metal electrode in an aqueous electrolyte solution. Our analysis of the reduction products during potentiostatic electrolysis showed formic acid (HCOOH) to be virtually the only CO2 reduction product on a CR-MOF electrode, whereas a Cu metal electrode generates a range of products. The quantity of products from the CR-MOF electrode was markedly greater (13-fold at −1.2 V vs. SHE) than that of a Cu metal electrode. Its stability was also confirmed.

Quasi-Elastic Neutron Scattering Studies on Dynamics of Water Confined in Nanoporous Copper Rubeanate Hydrates

We have investigated the mechanism of the first order transition and proton conductivity in copper rubeanate hydrates from microscopic and dynamical points of view. Three different types of neutron spectrometer-time-of-flight, backscattering, and neutron spin echo-were used to cover a wide dynamic range (1 ps to 100 ns). We found that the water molecules adsorbed in the pore are divided into "free water" having diffusion coefficients similar to those of bulk water at room temperature and "condensed water" which is about 10 times slower than bulk water owing to the interaction with the pore wall. The hydrogen atoms in the pore wall exhibited no relaxation within the measured time scales. The free water has, in the framework of the jump-diffusion model, smaller activation energy, longer residence time, and longer jump distance than bulk water. The neutron spin echo measurement revealed that the first order transition is a kind of liquid-liquid transition at which the free water is condensed on the pore surface in the low temperature phase. On cooling the condensed water, the relaxation time starts to deviate from the VFT equation around 200 K as previously observed in the water confined in nanoporous silicates. The free water plays an important role as the proton carrier but the proton conductivity is mainly governed by the number of protons provided into the adsorbed water from the pore wall.

Calorimetric and Neutron Diffraction Studies on Transitions of Water Confined in Nanoporous Copper Rubeanate

Copper rubeanate (H(2)C(2)N(2)S(2)Cu) has a nanoporous structure and exhibits high proton conductivity with adsorbing water inside the pores. We have studied the phase behavior and structure of the water confined in copper rubeanate hydrates (H(2)C(2)N(2)S(2)Cu.nH(2)O, n = 0, 2.1, 3.7) by adiabatic calorimetry and neutron powder diffraction. In the hydrate samples, a glass transition and a first-order transition appeared around 150 and 260 K, respectively. The transition entropy was similar to the entropy of fusion of bulk water, indicating that the adsorbed water is disordered above the transition temperature, like bulk water, and ordered below 150 K, like bulk ice. The neutron diffraction data demonstrated that both dry and hydrated copper rubeanates have amorphous structures over the temperature range 100-340 K. The analyses on the diffraction peak owing to the adsorbed water revealed that the transition at 260 K is a liquid-liquid transition due to the condensation of water on the surface of the pores, and the condensed water molecules are gradually ordered below 260 K and frozen-in at the glass transition around 150 K.

Dentin permeability of the apical third in different groups of teeth

This ex vivo study evaluated dentin permeability of the root canal in the apical third of different human groups of teeth. Eighty teeth were used, 8 from each dental group: maxillary and mandibular central incisors, lateral incisors and canines, maxillary first premolars (buccal and palatal roots), mandibular first premolars, and maxillary and mandibular second premolars, totalizing 88 roots that were distributed in 11 groups. The root canals were instrumented, irrigated with 1% NaOCl and 15% EDTA. Roots were immersed in 10% copper sulfate for 30 min and then in 1% rubeanic acid alcohol solution for the same period; this chemical reaction reveals dentin permeability by the formation of copper rubeanate, which is a dark-colored compound. Semi-serial 100-µm-thick cross-sections were obtained from the apical third of the roots. Five sections of each apical third were washed, dehydrated, cleared and mounted on glass slides for examination under optical microscopy. The percentage of copper ion infiltration and the amount of tubular dentin were quantified by morphometric analysis. The penetration of copper ions in the apical third ranged from 4.60 to 16.66%. The mandibular central and lateral incisors presented the highest dentin permeability (16.66%), while the maxillary canines and mandibular second and first premolars presented the lowest dentin permeability (4.60%, 4.80% and 5.71%, respectively; p<0.001). The other teeth presented intermediate permeability. In conclusion, dye penetration into dentin tubules at the apical region is strongly dependent on the group of teeth evaluated.

Structural study of an iron oxalate and a copper rubeanate layer on an ultra-smooth sapphirec-face

Structural study of an iron oxalate and a copper rubeanate layer on an ultra-smooth sapphire<i>c</i>-face

Electrochemical growth,in situ optical characterization and photoelectrochemical behaviour of dithio-oxamido copper(II) films

The electrochemical growth of dithio-oxamido copper(II) (copper rubeanate, CuRA) films onto copper electrodes was investigated by voltammetric andin situ optical reflectance techniques and the photoelectrochemical behaviour of the deposits was examined. Copper oxide-free, adherent and uniform deposits are obtained in hydroalcoholic solutions of rubeanic acid by pottential steps from −0.9 to −0.75 Vvs sce up to thicknesses of several hundred manometers. Relatively high photoreduction currents (some % monochromatic quantum yield) are obtained. The presence of copper oxides chemically grown in the CuRA matrix greatly improves both the magnitude and the stability of photoresponses.

Elkctrodeposition and Photoelectrochemical Properties of Dithiooxamido Copper (II) Films Onto Copper Electrodes

Abstract Dithiooxamido copper (II)(copper rubeanate), a very insoluble and intractable coordination polymer, was successfully produced in the form of adherent films of controlled thickness (40-200 nm) by anodization of copper electrodes in aqueous solution of rubeanic acid. Under illumination the filmed electrodes show a p-type semiconducting behaviour. Though the material suffers from a short-wavelength absorption domain and possible photodecomposition processes, high quantum yields (ca.10°) were achieved.

Prevention of copper and iron turbidities in wine

A search was conducted for a satisfactory substitute for potassium ferrocyanide in removing copper from wine to prevent formation of copper casse, at present the most important problem in wine stabilization. The most promising among the relatively nontoxic organic compounds tested was rubeanic acid. Cysteine and related sulfhydryl compounds and ascorbic acid precipitate excess copper, but further tests under winery conditions are needed. Aside from potassium ferrocyanide itself, the only other material that gave satisfactory results was an adsorption complex of potassium ferrocyanide and Prussian blue. Properly prepared and used—possibly with the addition of denatured protein—this complex would avoid contamination of the wine with ferrocyanide. Neither it nor rubeanic acid was as effective as the soluble ferrocyanide in removing iron from wine; but iron casses if troublesome might be dealt with by other means. The rest of the materials tested—a number of organic chelating agents, calcium phytate, phytic acid, chlorophyll, and a number of ionexchange resins—were unsatisfactory either because they did not remove copper adequately or because they had an adverse effect on wine flavor. The results suggested, however, that it might be feasible to develop a special cation-exchange resin for this purpose. The rate of formation and precipitation of copper rubeanate and of copper and iron ferrocyanides in wine was found to depend on the proportion of reagent used, the initial copper content, and the type of wine. Sodium ethylenediaminetetraacetate was found to sequester copper and iron as soluble metal chelates in wine, but it did not bind them tight enough to prevent casse formation in some wines; and since it leaves a residue in the wine it does not appear to offer a practical solution to the casse problem. Some tests were conducted on the corrosion of various metals with and without hard chrome-plating, when stored in wine under oxidizing and nonoxidizing conditions. The preliminary results indicated that such plating would reduce copper and iron pickup during wine processing and might be a practical means of salvaging corrodible winery equipment now in use.