Bipyridinium Salts Research Articles

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).

Tuning of the Self-Threading of Ring-in-Ring Structures in Aqueous Media.

A series of aryl-extended N-monoalkyl-4,4'-bipyridinium salts L (aryl=1,4-phenyl, 4,4'-biphenyl, 2,6-naphthyl and 9,10-anthracenyl) have been implemented by PdII /PtII -directed self-assembly into constitutionally dynamic systems (CDSs). As a result, the intended processes produced not only (en)M2 L2 (en=ethylenediamine) metallacyclic species but also (en)M4 L4 ring-in-ring aggregates, in equilibrium with the former, as a consequence of the hydrophobic nature of the aryl rings within the 4,4'-bipyridinium scaffold. The key feature of the obtained dynamic systems is the possibility of modulating their response against external stimuli by modifying the hydrophobic character of the ligand. While the different dynamic libraries follow the same trends upon changes in concentration, temperature, polarity of the medium, or addition of an aromatic chemical effector, subtle changes in the ligand hydrophobic core results in a fine-tuning of the speciation when applying a certain degree of the different stimulus. The exception is the anthracene-containing derivative, which does not form inclusion complexes or self-threaded structures.

Complexation of 2,6-helic[6]arene and its derivatives with 1,1'-dimethyl-4,4'-bipyridinium salts and protonated 4,4'-bipyridinium salts: an acid-base controllable complexation.

2,6-Helic[6]arene and its derivatives were synthesized, and their complexation with 1,1′-dimethyl-4,4′-bipyridinium and protonated 4,4'-bipyridinium salts were investigated in detail. It was found that the helic[6]arene and its derivatives could all form 1:1 complexes with both 1,1′-dimethyl-4,4'-bipyridinium salts and protonated 4,4'-bipyridinium salts in solution and in the solid state. Especially, the helic[6]arene and its derivatives containing 2-hydroxyethoxy or 2-methoxyethoxy groups exhibited stronger complexation with the guests than the other helic[6]arene derivatives for the additional multiple hydrogen bonding interactions between the hosts and the guests, which were evidenced by 1H NMR titrations, X-ray crystal structures and DFT calculations. Moreover, it was also found that the association constants (Ka) of the complexes could be significantly enhanced with larger counteranions of the guests and in less polar solvents. Furthermore, the switchable complexation between the helic[6]arene and protonated 4,4'-bipyridinium salt could be efficiently controlled by acids and bases.

A coarse-grained model of ionic liquid crystals: the effect of stoichiometry on the stability of the ionic nematic phase.

We have investigated, by means of molecular dynamics simulations, the phase behaviour of mixtures of charged ellipsoidal Gay-Berne (GB) particles and spherical Lennard-Jones (LJ) particles, as a coarse-grained model of ionic liquid crystals (ILCs). The anisotropic GB particles represent cations usually found in ILCs, for example, pyridinium or bipyridinium salts, while the spherical LJ particles are taken as a model of anions like common halides, hexafluorophosphate and tetrafluoroborate. Here we have focused our attention on the effect of the stoichiometry of the system (that is, the GB : LJ ratio n : m in the salt formula [GB]n[LJ]m) on the stability and thermal range of the ionic liquid crystal phases formed, with special attention to the ionic nematic phase. To isolate the stoichiometry effect, a comparison of four different systems with GB : LJ ratios of 1 : 3, 1 : 2, 1 : 1 and 2 : 1 is made by keeping the packing fraction and the charge of the minor component fixed. Our results suggest a way to improve the stability of the ionic nematic phase by enhancing the anisotropic van der Waals interaction compared to the Coulomb interaction, and by increasing the proportion of anisotropic particles in the mixture.

Dynamic supramolecular polymers built from cucurbit[n]urils and viologens

AbstractThis review article focuses on supramolecular assemblies involving cucurbit[n]uril‐based containers and viologen guests as key building elements. Cucurbit[n]urils (CB[n], n = 5–8,10) are fascinating hosts forming a wide range of inclusion complexes (caviplexes) with 4,4′‐bipyridinium salts, known as viologens, either as discrete 1:1 inclusion compounds with CB[7] or as ternary inclusion compounds involving two hosts or two guests (2:1 with CB[7] and 1:2 or 1:1:1 with CB[8]). This property is currently being actively exploited to design and prepare self‐assembled dynamic stimuli‐responsive supramolecular polymers including gels, vesicles, films and organized arrays of polymeric microspheres or nanoparticles. This review highlights the main benefits of such polymers and gives an overview of the achievements and progress made in this field over the past decades. © 2018 Society of Chemical Industry

Visible light-induced reduction system of diphenylviologen derivative with water-soluble porphyrin for biocatalytic carbon–carbon bond formation from CO2

Abstract From the view point of green chemistry, CO2 utilization technologies with solar energy including the photoredox system have been received a lot of attention. As one of them, photoredox system containing a photosensitizer and a catalyst catalyzing a reaction of a carbon–carbon bond formation from CO2 as a feed stock were constructed. In a recent study, we reported the visible light-induced malate (C4 compound) production from pyruvate (C3 compound) and CO2 due to carbon–carbon bond formation with the system consisting an electron donor, a photosensitizer, diphenylviologen (PV2+) derivative as an electron mediator in the presence of malic enzyme (ME). However, the interaction between a photosensitizer and PV2+ derivative has not been clarified yet. In this study, water-soluble PV2+ derivative, 1,1′-bis(p-sulfonatophenyl)-4,4′-bipyridinium salt (PSV2+) was synthesized, and its electro-, photochemical properties were evaluated. Moreover, the photoredox properties of PSV2+ with water-soluble Zn porphyrin were studied using fluorescence spectroscopy and steady state irradiation. The fluorescence of Zn porphyrin was quenched by PSV2+ and the two-electron reduced form of PSV2+ were produced with Zn porphyrin with steady state irradiation. In addition, reaction solution containing triethanolamine, tetraphenylporphyrin tetrasulfonate, pyruvate, ME, Mg2+ and PSV2+ in CO2 saturated bis-tris buffer (pH 7.4) was irradiated with visible light, the oxaloacetate and malate were produced. This result indicates that PSV2+ is an efficient electron mediator in the visible light-induced redox system for carbon–carbon bond formation with ME from CO2 as a feedstock.

Clip[5]arenes: A new family of molecular clips

Here we report the design and syntheses of two new triptycene-based rigid acyclic C-shaped hosts, clip[5]arenes C[5]OH and C[5]ME, and the strong host–guest complexation between C[5]OH and an electron-poor bipyridinium salt, paraquat G. The Ka value for the host–guest complex C[5]OH ⊃ G was calculated to be (1.09 ± 0.36) × 105 M−1 in acetone by using a non-linear curve-fitting method based on the UV–vis absorption titration experiments. Furthermore, based on this new host–guest recognition motif, a novel pseudopolyrotaxane-like supramolecular structure was constructed with C[5]OH threaded on polyviologen polymer VP-10.

Effective Artificial Co-enzyme Based on Single-Electron Reduced Form of 2,2′-Bipyridinium Salt Derivatives for Formate Dehydrogenase in the Catalytic Conversion of CO2 to Formic Acid

Abstract Formate dehydrogenase (FDH) is a useful biocatalyst for CO2 reduction to formic acid in a photoredox system consisting of a photosensitizer and an electron carrier. The electron carrier, single-electron reduced 2,2′-bipyridinium salts (2,2′-BP2+s) act as the co-enzyme for FDH in the reaction of CO2 to formic acid. An advantage of 2,2′-BP2+s is the easy change of structural geometry and the various single-electron reduction potentials. For further improvement of CO2 reduction catalytic activity of FDH, various 2,2′-BP2+s were synthesized as effective artificial co-enzymes for FDH. The effect of the structural geometry and the single-electron reduction potential in the single-electron reduced form of 2,2′-BP2+s on the CO2 reduction catalytic activity of FDH was studied by enzymatic kinetic analysis in detail for the first time. Especially, the catalytic efficiency, kcat/Km value of the single-electron reduced 1,1′-ethylene-2,2′-bipyridinium salt was c.a. 126 times larger than that of native co-enzyme, NADH. These results showed that catalytic activity of FDH can be manipulated with complete control by using 2,2′-BP2+ without changing the structure of FDH and has opened a new avenue for the approach of NAD+/NADH redox free system with FDH using an inexpensive small electron carrier molecule.

Pseudocryptand Hosts for Paraquats and Diquats.

H-bonding interaction of acidic moieties (CH2OH, COOH) at the 5- and 5'-positions of bis(1,3-phenylene)-32-crown-10 (1) with di- or tritopic anions leads to enhanced formation of inclusion complexes with N,N'-dialkyl-4,4'-bipyridinium salts ("paraquats", 2); the enforced folding of the crown ethers into pseudocryptands thus leads to pseudo-pseudorotaxanes. Strikingly, in the presence of the most effective anion (trifluoroacetate, TFA), the apparent bimolecular association constants for crown-paraquat complexation increase by more than an order of magnitude and approach those for covalent cryptands derived from the crown ether. Even though they may form pseudocryptands, the picolinate, nicotinate, and isonicotinate diesters 6 of cis-(4,4')-bis(hydroxymethyl)dibenzo-30-crown-10 do not exhibit enhanced binding of either diquat or paraquat relative to the starting diol in contrast to the picolinate ester of isomeric 5,5'-bis(hydroxymethyl)bis(m-phenylene)-32-crown-10, which displayed a higher binding constant than the starting diol. The results for the analogous reverse esters 7 derived from cis-(4,4')-dicarboxydibenzo-30-crown-10 and pyridylmethanols reveal weaker complexes with diquat than the normal esters 6; however, surprisingly, two reverse esters 7 complex paraquat more strongly than isomers 6.

The effect of the functional ionic group of the viologen derivative on visible-light driven CO2 reduction to formic acid with the system consisting of water-soluble zinc porphyrin and formate dehydrogenase.

The effect of the functional ionic group of 4,4'-bipyridinium salt derivatives (4,4'-BPs) as the electron carrier on the visible-light driven conversion of CO2 to formic acid with the system consisting of water-soluble zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) and formate dehydrogenase (FDH) in the presence of triethanolamine (TEOA) as an electron donor was investigated. 1,1'-Diaminoethyl- (DAV), 1-aminoethyl-1'-methyl- (AMV), 1-carboxymethyl-1'-methyl- (CMV) and 1,1'-dicarboxymethyl-4,4'-bipyridinium salt (DCV) were prepared as the 4,4'-BPs with the functional ionic group. Irradiation of a CO2 saturated buffer solution containing TEOA, ZnTPPS, 4,4'-BP and FDH with visible light irradiation resulted in the production of formic acid. By using 4,4'-BPs with the cationic aminoethyl-group, DAV or AMV as an electron carrier, the effective visible-light driven formic acid production based on the CO2 reduction was observed compared to the 4,4'-BPs with the anionic carboxymethyl-group, CMV or DCV. The formic acid production rate with DAV was approximately 3.2 times higher than that of the system with DCV.

Photoredox systems with biocatalysts for CO2utilization

Visible-light driven CO2reduction and utilization systems involving the photoreduction of NAD(P)+or bipyridinium salt (viologen)-based electron mediators and biocatalysts are introduced.

Abnormal co-enzymatic behavior of a one-electron reduced bipyridinium salt with a carbamoyl group on the catalytic activity of CO2 reduction by formate dehydrogenase

A carbamoyl-modified bipyridinium salt has an enhancement and deactivation behaviour on the catalytic activity of CO2 reduction by formate dehydrogenase (FDH) from Candida boidinii.

Photochromism in oxalatoniobates.

Addition of 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen) or 2-aminopyridine (2-NH2-py) to aqueous solutions of (NH4)[NbO(C2O4)2(H2O)2]·3H2O (Nb-Ox) yields tris-oxalate complexes (bpyH2)(bpyH)[NbO(C2O4)3]·2H2O (1), (phenH)3[NbO(C2O4)3]·3H2O (2), and (2-NH2-pyH)3[NbO(C2O4)3]·2H2O (3), which were characterised by XRD, IR and EA. Bipyridinium salt 1 demonstrates remarkable photoactivity even under irradiation by daylight. The nature of the photoactivity was studied by diffuse reflectance (DR) spectroscopy, ESR and quantum-chemical calculations.

Viologens for Coenzymes of Biocatalysts with the Function of CO2 Reduction and Utilization

In this review, the recent studies on 1) the visible-light-induced reduction of CO2 to formic acid catalyzed by formate dehydrogenase (FDH) via the reduction of a 4,4′- or 2,2′-bipyridinium salt (BP2+) by a photosensitizer, 2) the electrochemical properties of BP2+, and 3) the enzymatic kinetic properties of the interaction between the reduced forms of BP2+ and FDH are reviewed. Moreover, visible-light-induced biocatalytic C–C bond formation using CO2 as a feedstock via photoreduction of the phenylviologen derivative is introduced.

Complexation of Racemic 2,6-Helic[6]arene and Its Hexamethyl-Substituted Derivative with Quaternary Ammonium Salts, N-Heterocyclic Salts, and Tetracyanoquinodimethane.

Complexation of racemic 2,6-helic[6]arene 1 and its hexamethyl-substituted derivative 2 with quaternary ammonium salts, N-heterocyclic salts, and tetracyanoquinodimethane have been described in detail. It was found that host 2 could form stable complexes with acetyl choline, thiaacetyl choline, N,N,N-trimethylbenzenammonium salt, pyridinium, and 4,4'-bipyridinium salts in solution and/or in the solid state. The unsubstituted macrocycle 1 showed more significant complexation with the widely tested quaternary ammonium salts and N-heterocyclic salts, and exhibited stronger complexation towards the guests than its derivative 2. Moreover, it was found that macrocycle 1 and its derivative 2 could also complex with neutral electron-deficient tetracyanoquinodimethane (TCNQ), and the association constants were determined to be 2840±94 and 1358±46 m-1 , respectively. These results could make this new macrocycle and its derivatives find wide applications in the design and construction of functional supramolecular assemblies.

An Artificial Co‐enzyme Based on the Viologen Skeleton for Highly Efficient CO2 Reduction to Formic Acid with Formate Dehydrogenase

AbstractFormate dehydrogenase (FDH) is an attractive catalyst for the reduction of CO2 because CO2 is converted to formic acid by FDH at room temperature under normal pressure in neutral aqueous solution. The reduced form of methylviologen acts as an artificial co‐enzyme for FDH in the conversion of CO2 to formic acid. To improve the catalytic activity of FDH in reducing CO2, viologen derivatives with ionic groups were synthesized as effective artificial co‐enzymes for FDH. We used enzyme kinetic analysis to assess the effect of the ionic amino or carboxyl functional groups in the reduced form of the viologen derivatives on the catalytic activity of FDH with respect to the reduction of CO2. By using 1,1′‐diaminoethyl‐4,4′‐bipyridinium salt, which is the reduced form of a viologen derivative with two amino groups, we optimized the reduction of CO2 to formic acid with FDH. The catalytic efficiency value (kcat/Km) of the reduced form of 1,1′‐diaminoethyl‐4,4′‐bipyridinium salt was estimated to be more than 560 times larger than that of the natural co‐enzyme NADH. From the analysis result, the CO2 reduction was influenced by the ionic group of the viologen derivative.

A novel electron carrier molecule based on a viologen derivative for visible light-driven CO2 reduction to formic acid with the system of zinc porphyrin and formate dehydrogenase

An effective visible light-driven CO2 reduction to formic acid system was developed with zinc porphyrin, formate dehydrogenase and 1,1′-diaminoethyl-4,4′-bipyridinium salt.

Development of a dye molecule-biocatalyst hybrid system with visible-light induced carbon-carbon bond formation from CO2 as a feedstock.

Recently, CO2 utilization technology, including artificial photosynthesis, has received much attention. In this field, CO2 is used as a feedstock for fuels, polymers and in other chemical processes. Of note are malic enzymes (MEs) which catalyze the reaction of malic acid to pyruvic acid and CO2 with the co-enzyme NADP+, and catalyze the reverse reaction of pyruvic acid and CO2 to malic acid with the co-enzyme NADPH. Thus, MEs are also an attractive biocatalyst for carbon-carbon bond formation from CO2. Studies of the visible light-induced malic acid production from pyruvic acid and CO2 using an electron donor, a photosensitizer, an electron mediator, ferredoxin-NADP+ reductase, NADP+, and ME have been reported. However, modification of these systems is required, as they are very complicated. In this study, the visible light-induced carbon-carbon bond formation from pyruvic acid and CO2 with ME using the photoreduction of 1,1'-diphenyl-4,4'-bipyridinium salt derivatives as a novel electron mediator with water-soluble tetraphenylporphyrin tetrasulfonate (H2TPPS) in the presence of triethanolamine (TEOA) as an electron donor was developed. When a sample solution containing TEOA, H2TPPS, 1,1'-diphenyl-4,4'-bipyridinium salt derivative, pyruvic acid, and ME in CO2-saturated bis-tris buffer was irradiated, the major product was oxaloacetic acid. Thus, a visible light-induced photoredox system for carbon-carbon bond formation from CO2 with ME using 1,1'-diphenyl-4,4'-bipyridinium salt derivative as an electron mediator was developed.

Synthesis of non-symmetric viologen-containing ditopic ligands and their Pd(ii)/Pt(ii)-directed self-assembly.

We present here an efficient method for the preparation of non-symmetric viologen-containing ditopic ligands, as well as the Pd(ii)/Pt(ii)-directed self-assembly of some of these into metallacyclic receptors. The designed synthetic route, that implies the sequential alkylation and the Zincke reaction of activated bipyridinium salts, allowed us to substantially improve the yield in the preparation of three previously reported ligands. The versatility and efficiency of the method have also been tested for the preparation of four new viologen-containing ligands with very different structural features. Furthermore, the self-assembly of the new ligands around Pd(ii) and Pt(ii) centers has been tested, yielding mononuclear rectangular-shaped metallacycles of different dimensions and electronic characteristics.

Novel Artificial Coenzyme Based on the Viologen Derivative for CO2Reduction Biocatalyst Formate Dehydrogenase

Formate dehydrogenase (FDH) is an attractive biocatalyst for CO2 reduction. The reduced form of methylviologen acts as an artificial coenzyme for FDH. For further improvement in the CO2 reduction catalytic activity of FDH, a viologen derivative with two amino groups, 1,1′-diaminoethyl-4,4′-bipyridinium salt (DA2+), was synthesized as the effective artificial coenzyme for FDH. By enzyme kinetic analysis, the catalytic efficiency, i.e., kcat/Km value of the reduced form of DA2+ was estimated to be more than 560 times larger than that of NADH, the natural coenzyme for FDH.