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Increasing levels of carbon dioxide in the atmosphere and the growing need for energy necessitate a shift toward reliance on renewable energy sources and the utilization of carbon dioxide. Thus, producing carbonaceous fuel by the electrochemical reduction of carbon dioxide has been very appealing. We have focused on addressing the principal challenges of poor selectivity and poor energy efficiency in the electrochemical reduction of carbon dioxide. We have demonstrated here a viable pathway for the efficient and continuous electrochemical reduction of CO2 to formate using the metal-independent enzyme type of formate dehydrogenase (FDH) derived from C andida boidinii yeast. This type of FDH is attractive because it is commercially produced. In natural metabolic processes, this type of metal-independent FDH oxidizes formate to carbon dioxide using NAD+ as a cofactor. We show that FDH can catalyze the reverse process to generate formate when the natural cofactor NADH is replaced with an artificial cofactor, the methyl viologen radical cation. The methyl viologen radical cation is generated in situ, electrochemically. Our approach relies on the special properties of methyl viologen as a "unidirectional" redox cofactor for the conversion of CO2 to formate. Methyl viologen (in the oxidized form) does not catalyze formate oxidation, while the methyl viologen radical cation is an effective cofactor for the reduction of carbon dioxide. Thus, although the thermodynamic driving force is favorable for the oxidized form of methyl viologen to oxidize formate to carbon dioxide, the kinetic factors are not favorable. Only the reverse reaction of carbon dioxide reduction to formate is kinetically viable with the cofactor, methyl viologen radical cation. Binding free energy calculated from atomistic molecular dynamics (MD) simulations consolidate our understanding of these special binding properties of the methyl viologen radical cation and its ability to facilitate the two-electron reduction of carbon dioxide to formate in metal-independent FDH. By carrying out the reactions in a novel three-compartment cell, we have demonstrated the continuous production of formate at high energy efficiency and yield. This cell configuration uses judiciously selected ion-exchange membranes to separate the reaction compartments to preserve the yields of the methyl viologen radical cation and formate. By the electroregeneration of the methyl viologen radical cation at -0.44 V versus the normal hydrogen electrode, we could produce formate at 20 mV negative to the reversible electrode potential for carbon dioxide reduction to formate. Our results are in sharp contrast to the large overpotentials of -800 to -1000 mV required on metal catalysts, vindicating the selectivity and kinetic facility provided by FDH. Formate yields as high as 97% ± 1% could be realized by avoiding the adventitious reoxidation of the methyl viologen radical cation by molecular oxygen. We anticipate that the insights from the electrochemical studies and the MD simulations to be useful in redesigning the metal-independent FDH and alternate artificial cofactors to achieve even higher rates of conversion.

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Because of the similarity of odor, appearance, and chemical structure of methanol and ethanol, measuring the low concentration of methanol in an alcoholic beverage is difficult to perform in a quick, quantitative, and repeatable fashion. However, it is important for people to monitor the content of methanol in a liquor because a high amount of methanol absorbed will result in blindness, coma, and death. In response to this need, we have developed electrolyte-free methanol electrolysis and ethanol electrolysis based on the nanogap electrochemical cells for the methanol and ethanol sensing. Upon applying a voltage, a high electric field across the nanogap cell enhances the solution ionization and the ion transport rate. Moreover, the nanoscale distance between the electrodes provides a shorter path for electrolysis to easily occur. The nanogap electrochemical cells not only make the direct electrolyte-free organic solvent electrolysis possible but also enhance the sensitivity of the chemical of interest in low-concentration solutions without the influence of the added electrolyte. The nanogap electrochemical cells have been demonstrated having high sensitivity to detect 0.15% methanol volume concentration in deionized water solutions without adding any electrolyte, and its ability for the fake alcoholic beverages' detection has successfully demonstrated.

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Owing to the low conductivity of pure water, using an electrolyte is common for achieving efficient water electrolysis. In this paper, we have fundamentally broken through this common sense by using deep-sub-Debye-length nanogap electrochemical cells to achieve efficient electrolysis of pure water (without any added electrolyte) at room temperature. A field-assisted effect resulted from overlapped electrical double layers can greatly enhance water molecules ionization and mass transport, leading to electron-transfer limited reactions. We have named this process "virtual breakdown mechanism" (which is completely different from traditional mechanisms) that couples the two half-reactions together, greatly reducing the energy losses arising from ion transport. This fundamental discovery has been theoretically discussed in this paper and experimentally demonstrated in a group of electrochemical cells with nanogaps between two electrodes down to 37 nm. On the basis of our nanogap electrochemical cells, the electrolysis current density from pure water can be significantly larger than that from 1 mol/L sodium hydroxide solution, indicating the much better performance of pure water splitting as a potential for on-demand clean hydrogen production.

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Adsorbents prepared easily by impregnation of fumed silica with polyethylenimine (PEI) are promising candidates for the capture of CO2 directly from the air. These inexpensive adsorbents have high CO2 adsorption capacity at ambient temperature and can be regenerated in repeated cycles under mild conditions. Despite the very low CO2 concentration, they are able to scrub efficiently all CO2 out of the air in the initial hours of the experiments. The influence of parameters such as PEI loading, adsorption and desorption temperature, particle size, and PEI molecular weight on the adsorption behavior were investigated. The mild regeneration temperatures required could allow the use of waste heat available in many industrial processes as well as solar heat. CO2 adsorption from the air has a number of applications. Removal of CO2 from a closed environment, such as a submarine or space vehicles, is essential for life support. The supply of CO2-free air is also critical for alkaline fuel cells and batteries. Direct air capture of CO2 could also help mitigate the rising concerns about atmospheric CO2 concentration and associated climatic changes, while, at the same time, provide the first step for an anthropogenic carbon cycle.

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Iron-based rechargeable batteries, because of their low cost, eco-friendliness, and durability, are extremely attractive for large-scale energy storage. A principal challenge in the deployment of these batteries is their relatively low electrical efficiency. The low efficiency is due to parasitic hydrogen evolution that occurs on the iron electrode during charging and idle stand. In this study, we demonstrate for the first time that linear alkanethiols are very effective in suppressing hydrogen evolution on alkaline iron battery electrodes. The alkanethiols form self-assembled monolayers on the iron electrodes. The degree of suppression of hydrogen evolution by the alkanethiols was found to be greater than 90%, and the effectiveness of the alkanethiol increased with the chain length. Through steady-state potentiostatic polarization studies and impedance measurements on high-purity iron disk electrodes, we show that the self-assembly of alkanethiols suppressed the parasitic reaction by reducing the interfacial area available for the electrochemical reaction. We have modeled the effect of chain length of the alkanethiol on the surface coverage, charge-transfer resistance, and double-layer capacitance of the interface using a simple model that also yields a value for the interchain interaction energy. We have verified the improvement in charging efficiency resulting from the use of the alkanethiols in practical rechargeable iron battery electrodes. The results of battery tests indicate that alkanethiols yield among the highest faradaic efficiencies reported for the rechargeable iron electrodes, enabling the prospect of a large-scale energy storage solution based on low-cost iron-based rechargeable batteries.

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Calcium-doped lanthanum cobalt oxide is a promising electrocatalyst for oxygen evolution and oxygen reduction in rechargeable metal-air batteries and water electrolyzers operating with alkaline electrolyte. Nanocrystalline perovskite of composition La0.6Ca0.4CoO3 with a unique cellular internal structure was prepared at 350 °C and then annealed in air at progressively higher temperatures in the range of 600-750 °C. The samples were characterized by electrochemical techniques and X-ray photoelectron spectroscopy. The area-specific electrocatalytic activity for oxygen evolution/oxygen reduction, the oxidation state of cobalt, and the crystallite size increased with annealing temperature, while the Tafel slope remained constant. These trends provide new insights into the role of the cobalt center in oxygen evolution and oxygen reduction, and how preparation conditions can be altered to tune the activity of the cobalt center for electrocatalysis. We expect these findings to guide the design of electrocatalysts for bifunctional oxygen electrodes, in general.

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Easy to prepare solid materials based on fumed silica impregnated with polyethylenimine (PEI) were found to be superior adsorbents for the capture of carbon dioxide directly from air. During the initial hours of the experiments, these adsorbents effectively scrubbed all the CO(2) from the air despite its very low concentration. The effect of moisture on the adsorption characteristics and capacity was studied at room temperature. Regenerative ability was also determined in a short series of adsorption/desorption cycles.

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Anhydrous electrolytes with high proton conductivity and adequate chemical stability in the temperature range of 120-180 °C can be very useful in electrochemical devices such as fuel cells, sensors, and electrolyzers. Developing such proton-conducting materials has been challenging. We have fabricated and characterized the performance of such membranes, based on poly-2-vinylpyridinium dihydrogenphosphate (P2VP-DHP), that can operate in the range of 105-180 °C under anhydrous conditions. The ionic conductivity of the membrane was 0.01 S cm(-1) at 140 °C. Proton conduction occurs by ionization of the quaternary ammonium group and by Grotthus-type transport that involves the rapid rotation of the dihydrogenphosphate anion. The activation energy for proton transport was 50 kJ/mol. The transport number of the proton was measured by impedance spectroscopy and potential-step techniques. The measured value was in the range of 0.17-0.20. A membrane-and-electrode assembly using the P2VP-DHP was tested as an electrochemical hydrogen pump. This demonstration shows the advantage of membranes based on a polymer amine salt in electrochemical applications that require operating under water-free conditions. Weight loss measurements at 120 °C in air confirmed the thermal and oxidative stability of the membrane. The properties of the P2VP-DHP membrane reported here provide the basis for further development of proton-conducting polymer electrolyte membranes for operating temperatures above 100 °C in anhydrous environments.

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Water and ice were investigated by ac impedance with the electrochemical properties cup in an effort to develop an in situ instrument for water characterization. In liquid water, the impedance modulus decreased with the increase in charge carriers. In the ice, the impedance measurements were characterized by the dielectric relaxation and its corresponding activation energy. The activation energy of 0.400 eV was determined for pure ice. With ice containing Cl(-) anions, the activation energy was 0.24 eV. H(+) and OH(-) doped ice has the lowest activation energy for dielectric relaxation. Results from previous works are similar to the results reported in this study.

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The need to design proton-conducting electrolytes for fuel cells operating at temperatures of 120 degrees C and above has prompted the investigation of various "water-free" polymeric materials. The present study investigates the properties of "water-free" proton-conducting membranes prepared from high-molecular-weight polymeric organic amine salts. Specifically, the properties of bisulfates and dihydrogenphosphates of poly-2-vinylpyridine (P2VP), poly-4-vinylpyridine (P4VP), and polyvinylimidazoline (PVI) have been investigated over the temperature range of 25-180 degrees C. Nanocomposites of these polymeric organic amine salts and hydroxylated silica have also been investigated in this study. These polymers are found to be stable and proton-conducting at temperatures up to 200 degrees C. In all the polymer examples studied herein, the phosphates are more conducting than the bisulfates. The activation energy for ionic conduction was found to decrease with increasing temperature, and this is associated with the increased polymer mobility and ionization of the proton. This is confirmed by the high degree of motional narrowing that is observed in proton NMR experiments. The measured values of conductivity and the differences in pKa values of the polymeric organic amine and the mineral acid are clearly correlated. This observation provides the basis for the design of other water-free acid-base polymer systems with enhanced proton conductivity. The results presented here suggest that anhydrous polymer systems based on acid-base polymer salts could be combined with short-range proton conductors such as nanoparticulate silica to achieve acceptable conductivity over the entire temperature range.

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The binding constants for racemic, R and S naproxen and ibuprofen to human serum albumin have been determined by a circular dichroic technique. The ibuprofens and naproxens show no measurable extrinsic optical activity on interaction with the protein, and so the extrinsic Cotton effect shown following the diazepam-albumin interaction is used as a probe. The presence of the drugs reduce the amount of diazepam bound as shown by the interaction is used as a probe. The presence of the drugs reduce the amount of diazepam bound as shown by the reduced size of the induced ellipticity. The calculated primary binding constants show that the S form of both drugs bind to the albumin more tightly than the R form and that the racemic forms bind less tightly than either enantiomer.

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PURPOSE: The heats of reaction between the enantiomers and racemates of ibuprofen and naproxen and human serum albumin (HSA) are to be measured with and without the addition of octanoic acid. The effects of octanoic acid on the free energies of interaction between the drugs and HSA is to be determined and compared to that estimated from theoretical equations. METHODS: The heats of reaction have been measured directly by flow microcalorimetry. RESULTS: The data showed that octanoic acid lowered the 1:1 binding constants for all the drug-HSA interactions investigated. The effect of octanoic acid was greater on the R than on the S forms of the drugs as shown by the differences in free energies of interaction in the presence and absence of octanoic acid. CONCLUSIONS: The increased free energy differences for the binding of the enantiomers of both drugs to HSA in the presence of octanoic acid is closer to the value deemed to be necessary for the separation of enantiomers by Davenkov, and shows the importance of the addition of octanoic acid to the mobile phase in the separation of these enantiomers on immobilized albumin columns.

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This review examines the role of protein-bonded chiral stationary phases (CSPs) in enantiomeric separation and investigates the performance characteristics and desired properties of protein CSPs for separation and large-scale operation. The review also discusses the ability of protein-based CSPs to examine the stereochemistry of drug metabolism processes.

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A high-performance affinity chromatography support based on silica has been developed for the immobilization of proteins containing primary amino groups. A hydrophilic polymer covalently bound to the silica surface minimizes nonspecific protein binding to the support while preserving high binding capacity. The Schiff base reaction involved in the coupling of a ligand to the affinity medium is rapid, allows the use of mild conditions during the coupling process, and results in a very stable linkage. Reaction parameters were studied for protein coupling to the affinity support to determine optimum binding conditions and dynamic capacity as a function of protein size. The stability of the ligand-matrix bond was determined. The performance and reproducibility of the affinity support are demonstrated by its use in the analysis of nitrophenyl sugar derivatives, purification of glycoproteins, and isolation of anti-bovine immunoglobulin G developed in rabbit.

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Because of its high selectivity, affinity chromatography is a preferred tool in the downstream processing of high-value proteins and peptides of therapeutic interest. This review examines the affinity supports currently available, and investigates the performance characteristics and properties required of the support matrices for improved affinity-based supports for large-scale purification of biomolecules. Parameters for optimizing an affinity chromatographic process, and the advantages of affinity-based separation for scaled-up systems are highlighted.

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S-Adenosylhomocysteine (AdoHcy) hydrolase (adenosylhomocysteinase, EC 3.3.1.1) was purified from bovine liver by conventional protein purification procedures (differential centrifugation, ammonium sulfate fractionation and DEAE-cellulose chromatography) followed by affinity chromatography on blue dextran coupled to agarose. The enzyme was eluted from the blue dextran-agarose column with adenosine and the adenosine was removed by chromatography on Sephadex G-75. The affinity chromatography step resulted in a substantial increase in total AdoHcy hydrolase activity (about 600%) suggesting either removal of some inhibitory substance or a change in the structure of the protein producing a more catalytically efficient enzyme. The isolation procedure afforded over 3400-fold purification of the enzyme, which was shown to be homogeneous by polyacrylamide gel electrophoresis. Using high pressure liquid chromatography, the nucleotide content of the freshly purified enzyme was determined to be 2 mol of nicotinamide adenine nucleotide per mol of enzyme tetramer. The ratio of the reduced to the oxidized form of the nucleotide was correlated to the activity of the enzyme preparation.

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