Catalytic Wave Research Articles

Enhancement of direct electron transfer by aromatic thiol modification with truncated d-fructose dehydrogenase

A heterotrimeric membrane-bound d-fructose dehydrogenase (FDH) from Gluconobacter japonicus, composed of subunits L, C, and S, shows strong direct electron transfer (DET)-type bioelectrocatalytic performance in the two-electron oxidation of d-fructose. The electrode-active site of the enzyme is the heme c moiety in the subunit C. A previous study reported the construction of the subunit L/S subcomplex (ΔC FDH) lacking the subunit C. In this work, we attempted to realize the DET-type reaction of ΔC FDH using porous gold electrodes functionalized with several thiols, and investigated the influence of the thiols on DET. Kinetic analysis of the steady-state catalytic waves revealed that the electrode-active site of ΔC FDH is the [3Fe-4S] iron-sulfur cluster in the L subunit. The experimental results demonstrated that uncharged aromatic thiols on the electrode enhance the DET-type reaction of ΔC FDH. Based on the pH-dependent profile of the DET-type activity and the surface conditions of the modified thiols evaluated by electrochemical reductive desorption, we suggest an enhancement mechanism for DET by aromatic thiols.

Electrocatalytic facets of a newly designed cobalt(III) complex towards sustainable hydrogen evolution

A hybrid cobalt complex (C7H10ON)[Co(L)2].CH3OH (Co-complex) bearing an organic cation and anionic cobalt complex has been designed, synthesized, and structurally characterized. The tridentate chelator, 2-((2-hydroxybenzylidene)amino)-4-methylphenol (H2L), was prepared by the condensation reaction between salicylaldehyde and 4-methyl-2-amino phenol. Crystal structure analysis reveals a slight distortion in the octahedral coordination geometry of the cobalt(III) centre. This complex was evaluated in the hydrogen evolution reaction (HER) using a glassy carbon working electrode in acetonitrile (ACN), using tBu4NClO4 as the supporting electrolyte. The catalyst exhibited heightened catalytic activity when acetic acid was introduced, leading to a significant elevation in the catalytic wave at −1.6 V (V vs. Ag wire). The most pronounced activity was observed by adding 15 mM acetic acid, with a turnover number (TON) of 10.1. The catalyst’s durability was confirmed through controlled potential electrolysis (CPE) at −1.6 V for 2 h, displaying a steady current for the initial 20 min, followed by a gradual increase over the subsequent 2 h. A negligible amount of deposited metallic cobalt on the surface of the glassy carbon electrode through a ligand dissociation was evident during the electrocatalytic studies, as ensured by X-ray Photoelectron Spectroscopy (XPS) analysis. Further, the presence of ligand-centric reduction wave in the complex signifies the synergistic effect of the M−L cooperation and offers a plausible ECEC mechanistic route for the release of molecular hydrogen.

Phenoxide coordination to Fe(III) tetraphenylporphyrin: Exploring antibacterial and electrocatalytic HER activity

Herein, we report synthesis, solid and solution state structure as well as properties of three five coordinate (unsubstituted, 4-NO2 substituted and 2,4,6 trinitro substituted) phenoxide axially ligated to Fe(III)-tetraphenyl porphyrins. Spectroscopic characterization revealed high-spin (S = 5/2) nature of the phenoxide bound Fe(III) porphyrins (Fe1 and Fe2). However, the 2,4,6 trinitro substituted phenoxide axially ligated Fe(III) porphyrin (Fe3) demonstrate spin admixed nature (S = 5/2, 3/2) with predominate high spin contribution. (Phenolato)(porphinato)iron(III) complexes merit attention owing to structural analogy with the catalase enzyme. In this study we investigated their antibacterial as well as electrocatalytic hydrogen evolution reaction (HER) activity. Fe1 demonstrate potent antibacterial activity against gram-negative E. coli (MTCC 443) and gram-positive Staphylococcus aureus (MTCC 3160) human pathogenic bacteria. It also produce catalytic current for electrocatalytic HER activities upon gradual addition of PTSA (para-tolunesulphonic acid) as proton source. Compounds Fe2 and Fe3 also produce enhanced catalytic wave which originate possibly from reduction of proton coupled with reduction of –NO2 group.

A CRISPR/Cas13a-powered catalytic hairpin assembly evanescent wave fluorescence biosensor for target amplification-free SARS-CoV-2 detection

The end of the coronavirus disease 2019 (COVID-19) pandemic still drives the development of rapid and accurate detection technology to prepare for diverse viral infections and emerging pandemics in the future. Herein, a CRISPR/Cas13a-powered catalytic hairpin assembly evanescent wave fluorescence biosensor (CAPABLE) was developed for amplification-free detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). With the ingenious design of trigger, the presence of SARS-CoV-2 activated the trans-cleavage activity of Cas13a, followed by the initiation of a catalytic hairpin assembly (CHA) system that exhibited excellent signal amplification efficiency. By integrating the biotin-avidin system, the detection sensitivity of the portable fluorescence platform was greatly improved. Quantitative SARS-CoV-2 detection was realized with a detection limit of 18.6 copies/μL within 50 min based on a fast extraction method. The proposed method exhibited a 100% positive detection rate for environmental water samples spiked with SARS-CoV-2 pseudovirus, which was consistent with standard RTqPCR results. Benefiting from amplification-free performance, the CAPABLE method holds great promise for rapid SARS-CoV-2 detection in field laboratories and primary facilities in resource-limited areas. With the inherent flexibility of the CRISPR/Cas system, the proposed method has the potential to be applied in the diagnosis of various infectious diseases.

Carboxamide Fe(III) complex as the electrocatalyst of water oxidation reaction: WNA and I2M O–O bond formation pathways

A single-site Fe(III) carboxamide complex, [Fe(HbpH) (Cl)2] (1), (HbpH‾ = N,N′-Bis(picolinoyl)hydrazine) anion), was synthesized and used as the electrocatalyst of water oxidation reaction. Complex 1 catalyzes the oxidation of water to O2 at the pH of 8 in phosphate buffer solution with the onset of a catalytic wave at about 0.45 V versus RHE with the turnover frequency (TOF) of 5.8 s−1 at room temperature. The stability of the catalyst in water oxidation processes by electrochemical and UV–vis measurements, demonstrated the realistic molecular electrocatalysis of 1. Differential pulse voltammetry (DPV) of 1 in different pH values showed the dependency of oxidation potential to the pH of the environment, establishing the fact that the catalytic cycle involves the proton-coupled electron transfer (PCET) process. Density functional theory (DFT) calculations on the mechanism of water oxidation process of 1 shows that the oxygen evolution reaction is carried out through the water nucleophilic attack (WNA) to the metal center ion, resulted to the formation of FeIV(O) species. Also, DFT calculations showed that the formation of an O–O bond proceeds through the interaction two molecular mechanism (I2M), which compete with the WNA mechanism following from experimental analysis. The electroactivity of the metal centre and carboxamide ligand and the ability of the ligand to stabilize the high oxidation numbers of the metal-ion centre during the oxidation process, provide different oxidation pathways for an OER process.

Electrocatalytic hydrogen evolution with a copper porphyrin bearing meso-(o-carborane) substituents.

A newly designed copper complex of 5,15-bis(pentafluorophenyl)-10,20-bis(o-carborane)porphyrin (1) was synthesized and tested for the electrocatalytic hydrogen evolution reaction (HER). In acetonitrile, 1 was much more efficient than Cu 5,15-bis(pentafluorophenyl)-10,20-diphenylporphyrin (2) for electrocatalytic HER by shifting the catalytic wave to the anodic direction by 190 mV. In aqueous media, 1 also outperformed 2 by achieving higher current densities under smaller overpotentials. This enhancement was attributed to the aromatic and the strong electron-withdrawing properties of o-carborane groups. This work is significant to address the crucial effects of meso-(o-carborane) substituents of metal porphyrins on boosting the electrocatalytic HER.

A Spectroscopically Observed Iron Nitrosyl Intermediate in the Reduction of Nitrate by a Surface-Conjugated Electrocatalyst.

We report an iron-based graphite-conjugated electrocatalyst (GCC-FeDIM) that combines the well-defined nature of homogeneous molecular electrocatalysts with the robustness of a heterogeneous electrode. A suite of spectroscopic methods, supported by the results of DFT calculations, reveals that the electrode surface is functionalized by high spin (S = 5/2) Fe(III) ions in an FeN4Cl2 coordination environment. The chloride ions are hydrolyzed in aqueous solution, with the resulting cyclic voltammogram revealing a Gaussian-shaped wave assigned to 1H+/1e- reduction of surface Fe(III)-OH surface. A catalytic wave is observed in the presence of NO3-, with an onset potential of -1.1 V vs SCE. At pH 6.0, GCC-FeDIM rapidly reduces NO3- to ammonium and nitrite with 88 and 6% Faradaic efficiency, respectively. Mechanistic studies, including in situ X-ray absorption spectroscopy, suggest that electrocatalytic NO3- reduction involves an iron nitrosyl intermediate. The Fe-N bond length (1.65 Å) is similar to that observed in {Fe(NO)}6 complexes, which is supported by the results of DFT calculations.

Bulky oxadithiolate-bridged [FeFe]‑hydrogenase mimics [Fe2(μ-R2odt)(CO)4(κ2-diphosphine)] (R = Ph and H) with chelating diphosphines

In order to develop an attractive generation of bulky oxadithiolate-bridged [FeFe]‑hydrogenase mimics with chelating diphosphines, two new series of asymmetrically diphosphine-substituted diiron model complexes [Fe2(μ-R2odt)(CO)4(κ2-diphosphine)] (3–5) with bulky Ph2odt bridge and their reference counterparts (6–8) with common odt bridge were obtained from the Me3NO-assisted substitutions of diiron hexacarbonyl precursors [Fe2(μ-R2odt)(CO)6] (R2odt = (SCHR)2O, R = Ph (1) and H (2)) with different diphosphines such as (Ph2P)2NBn (labelled PNBnP, Bn = benzyl), (Ph2PCH2)2NBn (PCNBnCP), and (Ph2PCH2)2CH2 (DPPP)), respectively. All the as-prepared complexes have been characterized by elemental analysis, IR plus NMR spectroscopies, and particularly by X-ray crystallography for 3–8. It is interesting to note that complexes 3 and 6 chelating by small bite-angle PNBnP diphosphine have the favorable dibasal isomer whereas analogues 4, 5 and 7, 8 chelating by flexible backbone PCNBnCP or DPPP ligands possess the main apical-basal isomer in solution or in the solid state. Further, the electrochemical properties of two pairs of representative complexes 3, 6 and 5, 8 are explored and compared by cyclic voltammetry (CV) in the absence and presence of trifluoroacetic acid (CF3CO2H) as proton source, indicating that the complete protonations of 3, 6 and 5, 8 with higher concentration of CF3CO2H lead to two new catalytic waves for the electrocatalytic proton reduction to hydrogen (H2).

Chemical and electrochemical water oxidation catalyzed by heteroleptic Ru(III) complexes of anionic 2,6 pyridine dicarboxylate ligand: Experimental and theoretical study

Herein we report two new mononuclear heteroleptic Ruthenium complexes, 1 and 2 with anionic N, O donor pyridine dicarboxylate (pdc2-) ligand along with neutral bipyridine moieties. The general formula of the complexes are [RuIII(pdc2-)(L1)Cl](1), [RuIII(pdc2-)(L2)Cl](2) (Where L1 = bipyridine, L2 = 4,4′-dimethylbipyridine). Synthesis, characterization and water oxidation catalytic properties of both complexes were investigated. A combined theoretical (DFT) and experimental study were carried out to investigate the catalytic (in presence of CAN) and electrocatalytic activity of 1 and 2 for water oxidation in aqueous solution at pH ∼ 1. During electrocatalysis, the catalytic activity wave has been detected in acetonitrile/water 1:9 (v/v) solution in the range 1.39–1.41 V vs SCE. pH based electrochemistry reveals that, water oxidation (at pH = 1) takes place via sequential proton-electron transfer process to form a RuV = O moiety, which oxidises water through I2M pathway. For water oxidation by CAN, both the molecules show appreciably high TOF values 3.47971 x10-4 s−1 and 1.183 × 10–3 s−1 for 1 and 2 respectively in comparison to similar molecules [1,2].

Effects of N-linked glycans of bilirubin oxidase on direct electron transfer-type bioelectrocatalysis

Bilirubin oxidase from Myrothecium verrucaria (mBOD) is a promising enzyme for catalyzing the four-electron reduction of dioxygen into water and realizes direct electron transfer (DET)-type bioelectrocatalysis. It has two N-linked glycans (N-glycans), and N472 and N482 are known as binding sites. Both binding sites located on opposite side of the type I (T1) Cu, which is the electrode-active site of BOD. We investigated the effect of N-glycans on DET-type bioelectrocatalysis by performing electrochemical measurements using electrodes with controlled surface charges. Two types of BODs with different N-glycans, mBOD and recombinant BOD overexpressed in Pichia pastoris (pBOD), and their deglycosylated forms (dg-mBOD and dg-pBOD) were used in this study. Kinetic analysis of the steady-state catalytic waves revealed that both size and composition of N-glycans affected the orientation of adsorbed BODs on the electrodes. Interestingly, the most favorable orientation was achieved with pBOD, which has the largest N-glycans. Furthermore, the effect of the orientation control by the N-glycans is cooperative with electrostatic interaction.

A Strongly Coupled Biruthenium Complex as Catalyst for the Water Oxidation Reaction

AbstractThe catalytic activity towards water oxidation of a strongly coupled bimetallic ruthenium complex, trans‐[Ru(tpy)(bpy)(μ‐CN)Ru(py)4(OH2)]3+ (RuIIRuIIOH2), where tpy=2,2′:6′,2’’‐terpyridine, bpy=2,2′‐bipyridine and py=pyridine are presented. At pH 1 the first two oxidation reactions are centred at the aquo fragment and result in the RuIIRuIIIOH2 and RuIIRuIVO redox states as confirmed by its spectroscopy and DFT calculations. Oxidation by an additional electron is followed by an irreversible step and a catalytic wave associated with the water oxidation reaction. At pH 1 the reaction with an excess of Ce(IV) results in the generation of an stoichiometric amount of oxygen based on molar amounts of the added Ce(IV). The dominant species during the catalytic cycle is the three‐electron oxidized product, RuIIIRuIVO. The reduction of the concentration of Ce(IV) monitored at 370 nm follow the rate equation, −d[Ce(IV)]/dt=kox[Ce(IV)][RuIIRuIIOH2] with a kox=82±3 M−1s−1 at T=298 K. The RuIIIRuIVO species is not stable and reacts to give RuIIRuIVO.

Determination of Manganese(II) using Catalytic Hydrogen Wave (CHW) Technique in Environmental and Biological Samples

Background: A simple, low cost and highly sensitive catalytic hydrogen wave (CHW) method has developed for the investigation of Manganese(II) in ammonium 4-phenylpiperazine-1- dithiocarbamate and ammonium 4-benzylpiperidine-1-dithiocarbamate in various environmental and biological samples using D.C. polarography. This procedure was based on the reaction of Mn(II) in APP-DTC/ABP-DTC in the presences of NH4Cl-NH4OH medium at pH 6.6 and 7.2 respectively. The resulting oxidation signals were obtained at -0.78 V and -0.64 V vs SCE, owing to the CHWs. Different experimental conditions such as pH effects, background electrolyte (NH4Cl-NH4OH) effects and DTCs and Mn(II) ion effects have been studied. The current method was effectively employed for the testing of Mn(II) in different environmental and biological samples and attained recovery percentages (95-99%) are comparable to the Atomic Absorption Spectrophotometry (AAS) method. Methods: Direct current polarography, model CL-357 and CL-25 (Elico Private Ltd, Hyderabad, India), Shimadzu AA 6300 spectrometer furnished thru a deuterium background corrector and hollow cathode lamp, at corresponding wavelengths (resonance line) with an air acetylene flame. The experimental guidelines remained those suggested by the makers. Results: The effect of NH4Cl between 0.1 to 0.7 M on the nature of CHW at DME, maintaining the concentrations of Mn(II) at 4.0 ppm and DTC at 3.0 mM (APP-DTC/ABP-DTC) then adjusting the pH to 6.6/7.2 (APP-DTC/ABP-DTC). The polarograms were well-defined in NH4Cl of 0.4/0.5 M for APP-DTC/ABP-DTC. The peak height decreased beyond this concentration and therefore 0.4/0.5 M (APP-DTC/ABP-DTC) concentrations was kept for more analysis. At fixed concentration of DTC, (3.0 mM APP-DTC/ABP-DTC) and (0.4/0.5 M for APP-DTC/ ABP-DTC) NH4Cl adjusting the pH to 6.6/7.2 respectively the metal ion concentration of the Mn(II) was adjusted between 0.05 to 7.0 ppm and results of CHWs were studied. The peak current increased linearly with Mn(II) concentration in the range 0.05 to 4.0 ppm for both DTCs. However, the sensitivity of the method was more with APP-DTC/ABP-DTC because of strong complex of Mn(II) and increased catalytic activity. Conclusion: The developed CHW method is highly sensitive, simple and spontaneous for the analysis of Mn(II) in environmental and biological samples. The polarographic reduction of Mn(II) in aqueous solutions in the attendance of DTC displays a catalytic wave as a role of pH, concentration of supporting electrolyte and metal ion. The graphs of catalytic signals as a role of the concentration of dithiocarbamate shows that the signals do not vary linearly with the concentration of dithiocarbamate which the characteristic of Brdicka CHWs. It is presumed that the dithiocarbamate complexes with metal ions involve adsorption process and can be described by a Langmuir adsorption isotherm and the plot of CL/ip Vs CL should be linear. The CHW method is free from interference effect avoiding the removal stages which made towards placing among utmost sensitive methods for the analysis of Mn(II) in different Environmental and Biological samples.

Proton reduction by phosphinidene-capped triiron clusters

Bis(phosphinidene)-capped triiron carbonyl clusters, including electron rich derivatives formed by substitution with chelating diphosphines, have been prepared and examined as proton reduction catalysts. Treatment of the known cluster [Fe3(CO)9(µ3-PPh)2] (1) with various diphosphines in refluxing THF (for 5, refluxing toluene) afforded the new clusters [Fe3(CO)7(µ3-PPh)2(κ2-dppb)] (2), [Fe3(CO)7(µ3-PPh)2(κ2-dppv)] (3), [Fe3(CO)7(µ3-PPh)2(κ2-dppe)] (4) and [Fe3(CO)7(µ3-PPh)2(µ-κ2-dppf)] (5) in moderate yields, together with small amounts of the corresponding [Fe3(CO)8(µ3-PPh)2(κ1-Ph2PxPPh2)] cluster (x = -C4H6-, -C2H2-, -C2H4-, -C3H6-, -C5H4FeC5H4-). The molecular structures of complexes 3 and 5 have been established by X-ray crystallography. Complexes 1–5 have been examined as proton reduction catalysts in the presence of p-toluenesulfonic acid (p-TsOH) in CH2Cl2. Cluster 1 exhibits two one-electron quasi-reversible reduction waves at –1.39 V (ΔE = 195 mV) and at –1.66 V (ΔE = 168 mV; potentials vs. Fc+/Fc). Upon addition of p-TsOH the unsubstituted cluster 1 shows a first catalytic wave at –1.57 V and two further proton reduction processes at –1.75 and –2.29 V, each with a good current response. The diphosphine-substituted derivatives of 1 are reduced at more negative potentials than the parent cluster 1. Clusters 2–4 each exhibit an oxidation at ca. +0.1 V and a reduction at ca. –1.6 V; for 4 conversion to a redox active successor species is seen upon both oxidation and reduction. Clusters 2–4 show catalytic waves in the presence of p-TsOH, with cluster 4 exhibiting the highest relative catalytic current (icat/i0 ≈ 57) in the presence of acid, albeit at a new third reduction process not observed for 2 and 3. Addition of the dppf ligand to the parent diphosphinidene cluster 1 gave cluster 5 which exhibited a single reduction process at –1.95 V and three oxidation processes, all at positive values as compared to 2–4. Cluster 5 showed only weak catalytic activity for proton reduction with p-TsOH. The bonding in 4 was investigated by DFT calculations, and the nature of the radical anion and dianion is discussed with respect to the electrochemical data.

Unsymmetrical Dinuclear RuII Complexes with Bridging Polydentate Nitrogen Ligands as Potential Water Oxidation Catalysts

AbstractMononuclear RuII complex [RuCl(κ3N‐tpm)(κ2N‐bptz)]Cl, [1]Cl [tpm=tris(1‐ pyrazolyl)methane; bptz=3,6‐di(2‐pyridyl)‐1,2,4,5‐tetrazine], and dinuclear complexes [RuCl(κ3N‐tpm)(μ‐κ2N:κ2N‐bptz)Ru(κ2N‐bipy)2][PF6]3, [3][PF6]3, [RuCl(η6‐p‐cymene)(μ‐κ2N:κ2N‐dpp)Ru(κ2N‐bipy)2][PF6]2, [4][PF6]2, and [RuCl(η6‐p‐cymene)(μ‐κ2N:κ2N‐dpp)Ru(κ2N‐biqn)2][PF6]3, [5][PF6]3 [dpp=2,3‐bis(2′‐pyridyl)‐pyrazine; bipy=2,2′‐bipyridine; biqn=2,2′‐quinoline], incorporating both potentially catalytic and photosensitive subunits, were synthesized and characterized by means of elemental analysis, mass spectrometry, and spectroscopic methods. The molecular structures of the new compounds were also investigated and compared by means of DFT calculations. The absorption spectra of all the compounds are dominated by metal‐to‐ligand charge‐transfer bands in the visible (which in most cases largely extend over the red portion of the spectrum) and ligand‐centered bands in the UV region. The oxidation behavior is based on metal‐centered RuII to RuIII oxidation processes, which in phosphate buffer solution are followed by a catalytic water oxidation wave for [1]Cl and [3][PF6]3. For these compounds, the mechanism of water oxidation is proposed to consist in water nucleophilic attack, according to chemical experiments with Ce(IV) salts, so demonstrating for the first time that the bptz ligand can be profitably used to build ruthenium(II) complexes with catalytic properties. On the contrary, no catalytic process is observed for 4 and 5, most likely due to the high positive potential for RuII oxidation induced by the presence of the p‐cymene moiety.

Modulating alkene reactivity from oxygenation to halogenation via electrochemical O2 activation by Mn porphyrin.

Oxidation of organic substrates is achieved in nature under mild conditions thanks to metalloenzymes but remains a challenge for chemists. Herein we show by UV-Vis spectroelectrochemistry that when MnIIITPPCl is electrochemically reduced to MnII in CH2Cl2 under O2, a MnIIO2˙ species is generated. Benzoic anhydride reacts with the latter triggering a catalytic current in cyclic voltammetry. Electrolysis on the catalytic wave in the presence of cyclooctene leads to its oxygenation or halogenation depending on the axial ligand present as reported here for the first time.

Synthesis, structure, and hydrogen evolution studies of a heteroleptic Co(III) complex

[Co(tpy)(phen)Cl](PF6)2•0.25CH3CN (where tpy = 2,2′;6′,2″-terpyridine and phen = 1,10-phenanthroline) was prepared from a one pot mixture involving stoichiometric quantities of tpy and phen. The structure of [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN was confirmed by elemental analysis, high resolution mass spectroscopy (HRMS), various spectroscopic analyses, and X-ray crystallography. Density functional theory calculations were also carried out. The crystal structure of [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN, which was grown from acetonitrile, revealed a monoclinic crystal system with a C2/c space group. The cyclic voltammogram which was acquired in acetonitrile revealed reversible CoIII/II, CoII/I, and CoI/0 mixed with ligand-based redox couples at E½ = +0.35, –0.81, and –1.37 V (vs Ag/AgCl), respectively. In the presence of p-cyanoanillinium tetrafluoroborate with acetonitrile as the solvent, [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN displayed electrocatalytic hydrogen evolution activity at a 830 mV overpotential, as evidenced by a catalytic wave which was observed in the voltammogram, and by the detection of hydrogen in the headspace of the reaction vessel of a controlled potential electrolysis experiment. Photocatalytic hydrogen evolution studies with [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN produced a turnover frequency (TOF) of 3300 mmol H2 mol−1CAT min−1 when compared to [Co(dmgH)2(py)Cl] (where dmgH = dimethylglyoximato), which had a TOF of 4500 mmol H2.mol−1CAT min−1 under the same conditions. [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN produced a turnover number (TON) of 79 when compared to 141 for [Co(dmgH)2Cl(py)] in DMF in ca 3 h.

Downscale transfer of quasigeostrophic energy catalyzed by near-inertial waves

Abstract

Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

A series of [Re(N^N)(CO)3(Cl)] (N^N = diimine) complexes based on 4-(pyrid-2-yl)-1,2,3-triazole (1), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2), and 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3) diimine ligands were prepared and their photophysical and electrochemical properties were characterized. The ligand-based reduction wave is shown to be highly sensitive to the nature of the triazole-based ligand, with the peak potential shifting by up to 600 mV toward more positive potential from 1 to 3. All three complexes are phosphorescent in solution at room temperature with λmax ranging from 540 nm (1) to 638 nm (3). Interestingly, the complexes appear to show inverted energy-gap law behaviour (τ = 43 ns for 1 versus 92 ns for 3), which is tentatively interpreted as reduced thermal accessibility of metal-centred (3MC) states from photoexcited metal to ligand charge transfer (3MLCT) states upon stabilisation of the N^N-centred lowest unoccupied molecular orbital (LUMO). The photophysical characterisation, supported by computational data, demonstrated a progressive stabilization of the LUMO from complex 1 to 3, which results in a narrowing of the HOMO–LUMO energy gap (HOMO = highest occupied molecular orbital) across the series and, correspondingly, red-shifted electronic absorption and photoluminescence spectra. The two complexes bearing pyridyl (1) and pyrimidyl (2) moieties, respectively, showed a modest ability to catalyse the electroreduction of CO2, with a peak potential at ca. −2.3 V versus Fc/Fc+. The catalytic wave that is observed in the cyclic voltammograms is slightly enhanced by the addition of water as a proton source.

A Ru-bda Complex with a Dangling Carboxylate Group: Synthesis and Electrochemical Properties.

Ruthenium complexes containing the tetradentate 2,2'-bipyridine-6,6'-dicarboxylato (bda2-) equatorial ligand and ortho-subsituted pyridines in the axial position have been prepared and characterized using spectroscopic, crystallographic and electrochemical techniques. Complexes [Ru(Hbda)(DMSO)(pyC)] (1) and [Ru(bda)(DMSO)(pyA)] (2) (where pyC is 2-pyridinecarboxylate, pyA is pyridine-2-ylmethanol and DMSO is dimethyl sulfoxide) have been isolated in moderate to high yields. The solid state structures of (1-H)- and 2 reveal the strong chelate effect of the axial pyridine ligand that coordinates in a bidentate fashion leaving the bda2- equatorial ligand coordinating in a tridentate mode. In solution, compound 2 shows a dynamic equilibrium between different coordination modes of the bda2- and pyA ligands. This phenomenon does not occur for 1 because the carboxylate binds stronger than the labile alcohol in 2. Cyclic voltammetry analysis of 1 reveals a complex behavior with a pH-independent wave at E1/2 = 1.12 V that is tentatively associated with the two-electron RuIV/II couple. In sharp contrast, complex 2 shows a pH-dependent one-electron wave at E1/2 = 0.83 V (pH 1), assigned to the proton-coupled electron transfer process of the RuIII/II couple and a pH-independent wave at E1/2 = 1.06 V assigned to the RuIV/III couple. Compound 2 is used to prepare complex [Ru(bda)(pic)(pyA)] (4). This complex is air sensitive and converts to complex [Ru(bda)(pic)(pyE)] (5) (where pyE is methyl 2-pyridine carboxylate) in the presence of methanol. This oxidation also occurs by applying a positive potential to an aqueous solution of 4, producing the derivative [Ru(bda)(pic)(pyC)] (3). Cyclic voltammetry of 3 shows two pH-independent one-electron oxidation waves at E1/2 = 0.64 V and E1/2 = 1.0 V, corresponding to the RuIII/II and RuIV/III couples, respectively. In addition, a water oxidation catalytic wave appears at Eonset ≈ 1.4 V. Foot-of-the-wave analysis of this catalytic wave based on a water nucleophilic attack accounts for a TOFmax = 0.63-0.74 s-1.

Direct electron transfer-type bioelectrocatalysis of FAD-dependent glucose dehydrogenase using porous gold electrodes and enzymatically implanted platinum nanoclusters

The direct electron transfer (DET)-type bioelectrocatalysis of flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (GDH) from Aspergillus terreus (AtGDH) was carried out using porous gold (Au) electrodes and enzymatically implanted platinum nanoclusters (PtNCs). The porous Au electrodes were prepared by anodization of planar Au electrodes in a phosphate buffer containing glucose as a reductant. Moreover, PtNCs were generated into AtGDH by an enzymatic reduction of hexachloroplatinate (IV) ion. The modification was confirmed by native polyacrylamide gel electrophoresis and sodium dodecyl sulfate polyacrylamide gel electrophoresis analyses. The AtGDH-adsorbed porous Au electrode showed a DET-type bioelectrocatalytic wave both in the presence and absence of PtNCs; however, the current density with PtNCs (~1 mA cm−2 at 0 V vs. Ag|AgCl|sat. KCl) was considerably higher than that without PtNCs. The kinetic and thermodynamic analysis of the steady-state catalytic wave indicated that inner PtNCs shortened the distance between the catalytic center of AtGDH (=FAD) and the conductive material, and improved the heterogeneous electron transfer kinetics between them.