Theoretical study on CO2 reduction catalyzed by formate dehydrogenase using the cation radical of a bipyridinium salt with an ionic substituent as a co-enzyme.

Formate dehydrogenase from Candida boidinii (CbFDH; EC.1.2.1.2) is a useful enzyme for CO2 reduction to formate in the photoredox system of a visible-light sensitizer and an electron mediator in the presence of an electron donor. The electron mediator, cation radicals of 4,4'-bipyridinium salts (4,4'-BPs) act as the co-enzyme for CbFDH in the CO2 reduction to formate. We found that the CbFDH-catalyzed CO2 reduction to formate could be controlled by the ionic substituents introduced into the cation radical of 4,4'-BPs [Y. Amao, Sustainable Energy Fuels, 2018, 2, 1928-1950]. By using 1,1'-diaminoethyl-4,4'-bipyridinium salt (DABP), 1-aminoethyl-1'-methyl-4,4'-bipyridinium salt (AMBP), 1,1'-carboxymethyl-4,4'-bipyridinium salt (DCBP), and 1-carboxymethyl-1'-methyl-4,4'-bipyridinium salt (CMBP), the introduction of an amino-group into 4,4'-BP accelerates the CbFDH-catalyzed CO2 reduction to formate, while the introduction of a carboxy-group into 4,4'-BP slows the CO2 reduction to formate. This work clarified the direct interaction of the cation radicals of DABP, DCBP, AMBP, CMBP, and MV in the substrate-binding site of CbFDH by the docking simulation. In addition, a mechanistic investigation for the CbFDH-catalyzed CO2 reduction to formate with cation radicals of DABP, DCBP, AMBP, CMBP, and MV was carried out based on the energy of molecular orbitals calculated by density functional theory (DFT).

How does methylviologen cation radical supply two electrons to the formate dehydrogenase in the catalytic reduction process of CO2 to formate?

Formate dehydrogenase from Candida boidinii (EC.1.2.1.2; CbFDH) is a commercially available enzyme and can be easily handled as a catalyst for the CO2 reduction to formate in the presence of NADH, single-electron reduced methylviologen (MV+˙) and so on. It was found that the formate oxidation to CO2 with CbFDH was suppressed using the oxidized MV as a co-enzyme and the single-electron reduced MV (MV+˙) was effective for the catalytic activity of CbFDH for the CO2 reduction to formate compared with that using the natural co-enzyme of NADH [Y. Amao, Chem. Lett., 2017, 46, 780-788]. The CO2 reduction to formate catalyzed by CbFDH requires two molecules of the MV+˙. In order to clarify the two-electron reduction process using MV+˙ in the CO2 reduction to formate catalyzed with CbFDH, we attempted enzyme reaction kinetics, electrochemical and quantum chemical analyses. Kinetic parameters obtained from the enzymatic kinetic analysis metric revealed an index of affinity of MV+˙ for CbFDH in the CO2 reduction to formate. From the results of the electrochemical analysis, it was predicted that only one molecule of MV+˙ was bound to CbFDH, and the MV bound to CbFDH was to be necessarily re-reduced by the electron source outside of CbFDH to supply the second electron in the CO2 reduction to formate. From the results of docking simulation and density functional theory (DFT) calculations, it was indicated that one molecule of MV bound to the position close to CO2 in the inner part of the substrate binding pocket of CbFDH contributed to the two-electron CO2 reduction to formate.

Proton Transfer vs Complex Formation Channels in Ionized Formic Acid Dimer: A Direct Ab Initio Molecular Dynamics Study.

Photoirradiation to a hydrogen-bonded system plays an important role in the initial DNA and enzyme damage processes. The formic acid (FA) dimer is a model compound of double proton transfer systems, such as DNA base pairs. In the present study, the reactions of the FA dimer cation, formed upon ionization of the neutral dimer, have been investigated by the direct ab initio molecular dynamics method. Two reaction channels were identified for the FA dimer cation: complex formation and proton transfer (PT). In the complex formation channel, the carbonyl oxygen atoms of the two FA monomers were bound symmetrically, and a face-to-face complex was formed. In the PT channel, the proton of FA+ was transferred to FA, forming the H+(HCOOH)--HCO2 radical cation as product. At low temperature, the complex channel was dominant, whereas the PT channel increased with increasing temperature. The asymmetric spin distribution on the FA dimer cation exhibited a strong correlation with the PT channel.

Reactivity of a biomimetic W(iv) bis-dithiolene complex with CO2 leading to formate production and structural rearrangement.

A mononuclear W(iv) bis-dithiolene complex stabilized by an oxo ligand shows a reductive reactivity toward CO2, from which formate and a dinuclear W(v) complex are generated. An unusual structural rearrangement was observed during the reaction. Structural and spectroscopic characterization for a novel triply bridged dinuclear W(v) complex is reported.

Hitting on the move: Targeting intrinsically disordered protein states of the MDM2-p53 interaction.

Intrinsically disordered proteins are an emerging class of proteins without a folded structure and currently disorder-based drug targeting remains a challenge. p53 is the principal regulator of cell division and growth whereas MDM2 consists its main negative regulator. The MDM2-p53 recognition is a dynamic and multistage process that amongst other, employs the dissociation of a transient α-helical N-terminal ''lid'' segment of MDM2 from the proximity of the p53-complementary interface. Several small molecule inhibitors have been reported to inhibit the formation of the p53-MDM2 complex with the vast majority mimicking the p53 residues Phe19, Trp23 and Leu26. Recently, we have described the transit from the 3-point to 4-point pharmacophore model stabilizing this intrinsically disordered N-terminus by increasing the binding affinity by a factor of 3. Therefore, we performed a thorough SAR analysis, including chiral separation of key compound which was evaluated by FP and 2D NMR. Finally, p53-specific anti-cancer activity towards p53-wild-type cancer cells was observed for several representative compounds.

Liquid chromatography-tandem mass spectrometry based method development and validation of S016-1271 (LR8P), a novel cationic antimicrobial peptide for its application to pharmacokinetic studies.

S016-1271 (LR8P) is a broad spectrum novel cationic antimicrobial peptide. The objective of the present study was to develop a selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) based bioanalytical method of S016-1271 peptide in mice and human plasma in order to uncover its pharmacokinetic aspects. The chromatographic separation of S016-1271 (FR8P as internal standard) was achieved on a Waters™ X select CSH-C18 column (75 × 3.0 mm, 2.5 µ) using mixture of acetonitrile and triple distilled water (TDW) both containing 0.05% formic acid as mobile phase. A seven minute linear gradient method was designed to separate analytes from ion suppression at a flow rate of 0.3 mL/min. The extraction of analytes from mice and human plasma was performed through solid phase extraction technique using mixed mode weak cation exchange cartridge (Thermo SOLA WCX 10 mg 1CC) with an extraction recovery of analytes about 75%. Mass spectrometric detection of S016-1271 and FR8P was performed with optimized multiple reaction monitoring (MRM) transitions (Q1/Q3) at 658.8 [M+3H] 3+/653.2 [M+3H-NH3] 3+ and 443.4 [M+5H]5+ /434.7 [y12-NH3]4+,respectively in positive electrospray ionization (ESI) mode. The linearity in mice and human plasma was established over a concentration range of 7.81-250 ng/mL with regression coefficient (r2 > 0.99). The currently developed method was validated as per US-FDA guidelines and found to be within the acceptable limits. The method was successfully applied to intravenous (IV) pharmacokinetic study in mice wherein the levels were detected upto 24 h. The peptide demonstrated poor distribution characteristics which were demonstrated through volume of distribution at steady state (202.71 ± 47.02 mL/kg less than total body water of mice; 580 mL/kg). The clearance of the peptide predominantly occurred through central compartment (central clearance is 25 fold greater than peripheral clearance). Also, the in vitro pharmacokinetic studies demonstrated the stability of S016-1271 in plasma and high plasma protein binding in mice and humans.

Efficient and Selective Electrochemically Driven Enzyme-Catalyzed Reduction of Carbon Dioxide to Formate using Formate Dehydrogenase and an Artificial Cofactor.

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.

Aluminum formate (AF): Synthesis, characterization and application in dye wastewater treatment.

Aluminum formate (AF), a degradable and non-corrosive coagulant, was synthesized from aluminum hydroxide and formic acid. Polyamidine (PA), as a coagulation aid, was combined with AF for dye wastewater treatment. AF was characterized by XPS, FT-IR, viscosity, zeta potential, mass spectrum and XRD, and the flocculation properties of the dual-coagulation system were characterized by FT-IR and SEM. The results showed that COOH, Al2O3-Al and O2-Al bonds were formed in the AF synthesis process, and AF had a higher molecular weight and higher charge neutralization ability than PAC. The hydrolysates of AF were determined to contain Al13 Al11 and Al2, and the components of AF were confirmed to comprise a mixture including aluminum formate (C3H3AlO6) and its hydrate. When the color removal efficiency reached 100% in jar tests, the optimized dosage of AF/PA was 18.91/0.71mg/L, while the optimized dosage of PAC/PA was 21.19/0.91mg/L. According to the variance analysis, the interaction between AF/PA and PAC/PA were insignificant in macroscopic view. FT-IR spectrum indicated AF captured pollutant by means of CCO bond, PAC captured pollutant by δ CH, CC and δ CH. Overall, although the coagulation mechanism of AF was different from that of PAC, AF/PA showed better coagulation efficiency than PAC/PA in dye wastewater treatment.

Synthesis, Molecular Docking and in Vitro Screening of Some Newly Synthesized Triazolopyridine, Pyridotriazine and Pyridine⁻Pyrazole Hybrid Derivatives.

A series of novel pyridine and fused pyridine derivatives have been prepared starting from 6-(3,4-dimethylphenyl)-2-hydrazinyl-4-(thiophen-2-yl)-pyridine-3-carbonitrile 1 which on treatment with appropriate formic acid, acetic acid/ acetic anhydride, benzoyl chloride and/or carbon disulfide afforded the corresponding triazolopyridine derivatives 2⁻5. Also, treatment of hydrazide 1 with diethyloxalate, chloroacetyl chloride, chloroacetic acid and/or 1,2-dichloroethane yielded the corresponding pyridotriazine derivatives 7⁻10. Further transformation of compound 1 with a different active methylene group, namely acetyl acetone, diethylmalonate, ethyl cyanoacetate, ethyl benzoylacetate and/or ethyl acetoacetate, produced the pyridine⁻pyrazole hybrid derivatives 11⁻15. These newly synthesized compounds (1⁻15) were subjected to in silico molecular docking screenings towards GlcN-6-P synthase as the target protein. The results revealed moderate to good binding energies of the ligands on the target protein. All the newly prepared products exhibited antimicrobial and antioxidant activity.

Providing reducing power by microalgal photosynthesis: a novel perspective towards sustainable biocatalytic production of bulk chemicals exemplified for aliphatic amines.

A biotechnological process is reported, which enables an enzymatic reduction without the need for addition of an organic co-substrate for in situ-cofactor recycling. The process is based on merging the fields of enzymatic reductive amination with formate dehydrogenase-based in situ-cofactor recycling and algae biotechnology by means of the photoautotrophic microorganism Chlamydomonas reinhardtii, providing the needed formate in situ by formation from carbon dioxide, water and light. This biotransformation has been exemplified for the synthesis of various aliphatic amines known as bulk chemicals.

Synthesis and physicochemical characterization of (6S)-5-formiminotetrahydrofolate; a reference standard for metabolomics.

The one-carbon carrier of the formate oxidation level derived from the interaction of tetrahydrofolate and formiminoglutamate, which has been tentatively identified as 5-formiminoltetrahydrofolate, has been prepared by chemical synthesis. Treatment of a solution of (6S)-tetrahydrofolate in aqueous base with excess ethyl formimidate in the presence of anti-oxidant under anaerobic conditions afforded a gummy solid which, based on mass spectral analysis, conformed to a monoformimino derivative of tetrahydrofolate. Further physicochemical characterization by validated methods strongly suggested that the product of chemical synthesis was identical to the enzymatically produced material and that it was, in fact, (6S)-5-formiminotetrahydrofolate. Conditions and handling methods toward maintaining the integrity of this highly sensitive compound were identified and are described, as is analytical methodology, useful for research studies using it.

Hydroperoxyl radical and formic acid formation from common DNA stabilizers upon low energy electron attachment.

2-Amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) and ethylenediaminetetraacetic acid (EDTA) are key components of biological buffers and are frequently used as DNA stabilizers in irradiation studies. Such surface or liquid phase studies are done with the aim to understand the fundamental mechanisms of DNA radiation damage and to improve cancer radiotherapy. When ionizing radiation is used, abundant secondary electrons are formed during the irradiation process, which are able to attach to the molecular compounds present on the surface. In the present study we experimentally investigate low energy electron attachment to TRIS and methyliminodiacetic acid (MIDA), an analogue of EDTA, supported by quantum chemical calculations. The most prominent dissociation channel for TRIS is through hydroperoxyl radical formation, whereas the dissociation of MIDA results in the formation of formic and acetic acid. These compounds are well-known to cause DNA modifications, like strand breaks. The present results indicate that buffer compounds may not have an exclusive protecting effect on DNA as suggested previously.

Towards Sustainable Production of Formic Acid.

Formic acid is a widely used commodity chemical. It can be used as a safe, easily handled, and transported source of hydrogen or carbon monoxide for different reactions, including those producing fuels. The review includes historical aspects of formic acid production. It briefly analyzes production based on traditional sources, such as carbon monoxide, methanol, and methane. However, the main emphasis is on the sustainable production of formic acid from biomass and biomass-derived products through hydrolysis and oxidation processes. New strategies of low-temperature synthesis from biomass may lead to the utilization of formic acid for the production of fuel additives, such as methanol; upgraded bio-oil; γ-valerolactone and its derivatives; and synthesis gas used for the Fischer-Tropsch synthesis of hydrocarbons. Some technological aspects are also considered.

ZrO2 Nanocrystals As Catalyst for Synthesis of Dimethylcarbonate from Methanol and Carbon Dioxide: Catalytic Activity and Elucidation of Active Sites.

The catalytic activity of zirconium oxide (ZrO2) nanocrystals for the reaction of carbon dioxide (CO2) with methanol to form dimethylcarbonate (DMC) was investigated. ZrO2 nanocrystals prepared by hydrothermal synthesis at various temperatures were compared. The size of the ZrO2 nanocrystals monotonically increased with the hydrothermal temperature, according to specific surface area, transmission electron microscope measurements, and their X-ray diffraction peak widths. The ZrO2 nanocrystals prepared by hydrothermal synthesis were found to exhibit high catalytic activity owing to their high surface area and catalytically active surfaces arising from their high crystallinity. Next, adsorbed species generated from CO2 on the ZrO2 surfaces were measured using CO2 temperature-programmed desorption (TPD) and in situ FT-IR spectroscopy. The results confirmed the presence of several kinds of adsorbed species including bidentate bicarbonate (b-HCO3-), bidentate carbonate (b-CO32-), and monodentate carbonate (m-CO32-). The relationship between the amounts of these surface species and the catalytic activity of the ZrO2 was investigated for the first time. The amount of the bidentate species (b-HCO3- and b-CO32-) was found to correlate well with the catalytic activity, demonstrating that the surface sites that afford these species contribute to the catalytic activity for this reaction.

Selective oxidation of lignocellulosic biomass to formic acid and high-grade cellulose using tailor-made polyoxometalate catalysts.

The main goal of this project was to identify and optimize tailor-made polyoxometalate catalysts for a fractionated oxidation of lignocellulosic biomass (i.e. wood and residues from sugar or paper industries) to produce formic acid (FA) and high-grade cellulose for further processing e.g. in white biotechnology to provide bio-ethanol. Homogeneous vanadium precursors like sodium metavanadate and vanadyl sulfate as well as Keggin-type polyoxometalates (POMs) and more exotic structures like Anderson-, Wells-Dawson- and Lindqvist-type POMs were screened for the desired catalytic performance. The most promising behaviour was found using the Lindqvist-type POM K5V3W3O19, showing for the first time in the literature a selective oxidation of only hemicellulose and lignin to formic acid, while the cellulose fraction was untrapped. However, this can only be a first step towards the project goal as low product yields were obtained.

Asymmetric Radical Bicyclization of Allyl Azidoformates via Cobalt(II)-Based Metalloradical Catalysis.

Cobalt(II)-based metalloradical catalysis has been successfully applied to radical bicyclization of allyl azidoformates to construct aziridine/oxazolidinone-fused bicyclic structures. The Co(II) complex of D2-symmetric chiral amidoporphyrin 3,5-DitBu-QingPhyrin has been identified as an effective metalloradical catalyst for the intramolecular radical aziridination of this type of carbonyl azides, allowing for high-yielding formation of synthetically useful chiral [3.1.0]-bicyclic aziridines with high diastereo- and enantioselectivity.

Challenges in the development of bio-based solvents: a case study on methyl(2,2-dimethyl-1,3-dioxolan-4-yl)methyl carbonate as an alternative aprotic solvent.

Many traditional solvents have drawbacks including sustainability and toxicity issues. Legislation, such as REACH, is driving the move towards less hazardous chemicals and production processes. Therefore, safer bio-based solvents need to be developed. Herein, a 10 step method has been proposed for the development of new bio-based solvents, which utilises a combination of in silico modelling of Hansen solubility parameters (HSPs), experimental Kamlet-Abboud-Taft parameters, a selection of green synthetic routes followed by application testing and toxicity measurements. The challenges that the chemical industry face in the development of new bio-based solvents are highlighted through a case study on methyl(2,2-dimethyl-1,3-dioxolan-4-yl)methyl carbonate (MMC), which can be synthesised from glycerol. Although MMC is an attractive candidate as a replacement solvent, simply being bio-derived is not enough for a molecule to be regarded as green. The methodology of solvent development described here is a broadly applicable protocol that will indicate if a new bio-based solvent is functionally proficient, and will also highlight the importance of early stage Kamlet-Abboud-Taft parameters determination and toxicity testing in the development of a green solvent.

Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol at Room Temperature Using Imidazolium Hydrogen Carbonate Ionic Liquid as a Recyclable Catalyst and Dehydrant.

The direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3 OH was achieved at room temperature with 74 % CH3 OH conversion in the presence of an imidazolium hydrogen carbonate ionic liquid ([Cn Cm Im][HCO3 ]). Experimental and theoretical results reveal that [Cn Cm Im][HCO3 ] can transform quickly into a CO2 adduct, which serves as an effective catalyst and dehydrant. Its dehydration ability is reversible. The energy barrier of the rate-determining step for the DMC synthesis is only 21.7 kcal mol-1 . The ionic liquid can be reused easily without a significant loss of its catalytic and dehydrating ability.

Alkyl Formate Ester Synthesis by a Fungal Baeyer-Villiger Monooxygenase.

We investigated Baeyer-Villiger monooxygenase (BVMO)-mediated synthesis of alkyl formate esters, which are important flavor and fragrance products. A recombinant fungal BVMO from Aspergillus flavus was found to transform a selection of aliphatic aldehydes into alkyl formates with high regioselectivity. Near complete conversion of 10 mm octanal was achieved within 8 h with a regiomeric excess of ∼80 %. Substrate concentration was found to affect specific activity and regioselectivity of the BVMO, as well as the rate of product autohydrolysis to the primary alcohol. More than 80 % conversion of 50 mm octanal was reached after 72 h (TTN nearly 20 000). Biotransformation on a 200 mL scale under unoptimized conditions gave a space-time yield (STY) of 4.2 g L-1 d-1 (3.4 g L-1 d-1 extracted product).

Aqueous Biphasic Systems for the Synthesis of Formates by Catalytic CO2 Hydrogenation: Integrated Reaction and Catalyst Separation for CO2 -Scrubbing Solutions.

Aqueous biphasic systems were investigated for the production of formate-amine adducts by metal-catalyzed CO2 hydrogenation, including typical scrubbing solutions as feedstocks. Different hydrophobic organic solvents and ionic liquids could be employed as the stationary phase for cis-[Ru(dppm)2 Cl2 ] (dppm=bis-diphenylphosphinomethane) as prototypical catalyst without any modification or tagging of the complex. The amines were found to partition between the two phases depending on their structure, whereas the formate-amine adducts were nearly quantitatively extracted into the aqueous phase, providing a favorable phase behavior for the envisaged integrated reaction/separation sequence. The solvent pair of methyl isobutyl carbinol (MIBC) and water led to the most practical and productive system and repeated use of the catalyst phase was demonstrated. The highest single batch activity with a TOFav of approximately 35 000 h-1 and an initial TOF of approximately 180 000 h-1 was achieved in the presence of NEt3 . Owing to higher stability, the highest productivities were obtained with methyl diethanolamine (Aminosol CST 115) and monoethanolamine (MEA), which are used in commercial scale CO2 -scrubbing processes. Saturated aqueous solutions (CO2 overpressure 5-10 bar) of MEA could be converted into the corresponding formate adducts with average turnover frequencies up to 14×103  h-1 with an overall yield of 70 % based on the amine, corresponding to a total turnover number of 150 000 over eleven recycling experiments. This opens the possibility for integrated approaches to carbon capture and utilization.