Methyl Viologen Moiety Research Articles

Methyl Hexadecyl Viologen Inclusion in Cucurbit[8]uril: Coexistence of Three Host–Guest Complexes with Different Stoichiometry in a Highly Hydrated Crystal

The host–guest inclusion complexes of cucurbiturils with alkyl viologen have interesting architectures, chemical properties, and potential applications in sensors and nanotechnology. A highly hydrated triclinic crystal of cucurbit[8]uril (CB[8]) complexed by methyl hexadecyl viologen (MVC16) is characterized by the unprecedented coexistence in the crystal of three host–guest complexes with 3:2, 2:2, and 1:1 stoichiometries. In all these complexes, the hook-shaped alkyl chain of the MVC16 is hosted in the CB[8] macrocycles, while the methyl viologen moieties have various environments. In the Z-shaped 3:2 complex, a central CB[8] unit hosts two viologen heads in the cavity, while the 2:2 complex is held together by π-stacking interactions between two viologen units. In the square 2D tiling crystal packing of CB[8] macrocycles, the same site which favors the dimerization observed in the 2:2 complex is also statistically occupied by a single methyl viologen moiety of the 1:1 complex. The rational interpretation of the crystal structure represented an intriguing challenge, due to the complicated statistical disorder in the alkyl chains hosted in CB[8] units and in the methyl viologen moieties of 2:2 and 1:1 complexes. In contrast with the solution behavior dominated by the 2:1 complex, the coexistence of three host–guest complexes with 3:2, 2:2, and 1:1 ratios highlights the fundamental importance of packing effects in the crystallized supramolecular complexes. Therefore, the crystallization process has permitted us to capture different host–guest systems in a single crystal, revealing a supramolecular landscape in a single photo.

Hybrid Amyloid-Based Redox Hydrogel for Bioelectrocatalytic H2 Oxidation.

An artificial amyloid-based redox hydrogel was designed for mediating electron transfer between a [NiFeSe] hydrogenase and an electrode. Starting from a mutated prion-forming domain of fungal protein HET-s, a hybrid redox protein containing a single benzyl methyl viologen moiety was synthesized. This protein was able to self-assemble into structurally homogenous nanofibrils. Molecular modeling confirmed that the redox groups are aligned along the fibril axis and are tethered to its core by a long, flexible polypeptide chain that allows close encounters between the fibril-bound oxidized or reduced redox groups. Redox hydrogel films capable of immobilizing the hydrogenase under mild conditions at the surface of carbon electrodes were obtained by a simple pH jump. In this way, bioelectrodes for the electrocatalytic oxidation of H2 were fabricated that afforded catalytic current densities of up to 270 μA cm-2 , with an overpotential of 0.33 V, under quiescent conditions at 45 °C.

Hybrid Amyloid‐Based Redox Hydrogel for Bioelectrocatalytic H2 Oxidation

AbstractAn artificial amyloid‐based redox hydrogel was designed for mediating electron transfer between a [NiFeSe] hydrogenase and an electrode. Starting from a mutated prion‐forming domain of fungal protein HET‐s, a hybrid redox protein containing a single benzyl methyl viologen moiety was synthesized. This protein was able to self‐assemble into structurally homogenous nanofibrils. Molecular modeling confirmed that the redox groups are aligned along the fibril axis and are tethered to its core by a long, flexible polypeptide chain that allows close encounters between the fibril‐bound oxidized or reduced redox groups. Redox hydrogel films capable of immobilizing the hydrogenase under mild conditions at the surface of carbon electrodes were obtained by a simple pH jump. In this way, bioelectrodes for the electrocatalytic oxidation of H2 were fabricated that afforded catalytic current densities of up to 270 μA cm−2, with an overpotential of 0.33 V, under quiescent conditions at 45 °C.

Improved Physical Stability of an Antibody-Drug Conjugate Using Host-Guest Chemistry.

Antibody-drug conjugates (ADCs) are an emerging class of biopharmaceutical products for oncology, with the cytotoxic pyrrolobenzodiazepine (PBD) family of "warheads" well-established in the clinic. While PBDs offer high potency, they are also characterized by their hydrophobicity, which can make formulation of the ADC challenging. Several approaches have been investigated to improve the physicochemical properties of PBD-containing ADCs, and herein a supramolecular approach was explored using cucurbit[8]uril (CB[8]). The ability of CB[8] to simultaneously encapsulate two guests was exploited to incorporate a 12-mer polyethylene glycol harboring a methyl viologen moiety at one terminus (MV-PEG12), together with a PBD harboring an indole moiety at the C2' position (SG3811). This formulation approach successfully introduced a hydrophilic PEG to mask the hydrophobicity of SG3811, improving the physical stability of the ADC while avoiding any loss of potency related to chemical modification.

Two electron utilization of methyl viologen anolyte in nonaqueous organic redox flow battery

Abstract Methyl viologen (MV) as a bench-mark anolyte material has been frequently applied in aqueous organic redox flow batteries (AORFBs) towards large-scale renewable energy storage. However, only the first reduction of MV was utilized in aqueous electrolytes because of the insoluble MV0 generated from the second reduction of MV. Herein, we report that methyl viologen with bis(trifluoromethane)sulfonamide counter anion, MVTFSI, can achieve two reversible reductions in a nonaqueous supporting electrolyte. Paired with (Ferrocenylmethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide, FcNTFSI, as catholyte, the MVTFS/FcNTFSI nonaqueous organic redox flow battery (NOARFB) can take advantage of either one electron or two electron storage of the methyl viologen moiety and provide theoretical energy density of 24.9 Wh/L and a cell voltage of up to 1.5 V. Using a highly conductive LiTFSI/CH3CN supporting electrolyte and a porous Daramic separator, the NOARFB displayed excellent cycling performance, including up to a 68.3% energy efficiency at 40 mA/cm2, and more than 88% total capacity retention after 100 cycles.

Pillar[6]arene Containing Multilayer Films: Reversible Uptake and Release of Guest Molecules with Methyl Viologen Moieties.

Pillar[6]arene-containing multilayer films have been fabricated by alternating deposition of a stoichiometric complex consisting of both pillar[6]arene and methyl viologen with a photoreactive polyelectrolyte, diazoresin (DAR). After photoinduced cross-linking of the multilayer films, the guest molecule, methyl viologen, can be removed. Then, multilayer films with artificial binding sites are fabricated. The films show good properties for molecular uptake and release as well as selectivity for molecules with methyl viologen moieties. It is anticipated that this kind of multilayer films have future applications in the fields of enrichment of molecular dyes and purification of methyl viologen-polluted water.

Hybrid supramolecular and colloidal hydrogels that bridge multiple length scales.

Hybrid nanocomposites were constructed based on colloidal nanofibrillar hydrogels with interpenetrating supramolecular hydrogels, displaying enhanced rheological yield strain and a synergistic improvement in storage modulus. The supramolecular hydrogel consists of naphthyl-functionalized hydroxyethyl cellulose and a cationic polystyrene derivative decorated with methylviologen moieties, physically cross-linked with cucurbit[8]uril macrocyclic hosts. Fast exchange kinetics within the supramolecular system are enabled by reversible cross-linking through the binding of the naphthyl and viologen guests. The colloidal hydrogel consists of nanofibrillated cellulose that combines a mechanically strong nanofiber skeleton with a lateral fibrillar diameter of a few nanometers. The two networks interact through hydroxyethyl cellulose adsorption to the nanofibrillated cellulose surfaces. This work shows methods to bridge the length scales of molecular and colloidal hybrid hydrogels, resulting in synergy between reinforcement and dynamics.

Hybrid Supramolecular and Colloidal Hydrogels that Bridge Multiple Length Scales.

Hybrid nanocomposites were constructed based on colloidal nanofibrillar hydrogels with interpenetrating supramolecular hydrogels, displaying enhanced rheological yield strain and a synergistic improvement in storage modulus. The supramolecular hydrogel consists of naphthyl‐functionalized hydroxyethyl cellulose and a cationic polystyrene derivative decorated with methylviologen moieties, physically cross‐linked with cucurbit[8]uril macrocyclic hosts. Fast exchange kinetics within the supramolecular system are enabled by reversible cross‐linking through the binding of the naphthyl and viologen guests. The colloidal hydrogel consists of nanofibrillated cellulose that combines a mechanically strong nanofiber skeleton with a lateral fibrillar diameter of a few nanometers. The two networks interact through hydroxyethyl cellulose adsorption to the nanofibrillated cellulose surfaces. This work shows methods to bridge the length scales of molecular and colloidal hybrid hydrogels, resulting in synergy between reinforcement and dynamics.

Three-dimensional carbon nanotube–polypyrrole–[NiFe] hydrogenase electrodes for the efficient electrocatalytic oxidation of H 2

Hydrogenase electrodes for hydrogen oxidation are elaborated by an innovative immobilization strategy of [NiFe] hydrogenases from Desulfovibrio fructosovorans on highly porous single-walled (SWCNT) and multi-walled (MWCNT) carbon nanotube electrodes. The bioelectrode fabrication involved the adsorption of hydrogenase and amphiphilic pyrrole monomer functionalized by a methylviologen moiety on the nanotube deposits. The electropolymerization of the adsorbed monomer then leads to the enzyme entrapment in polypyrrole film surrounding the nanotubes. In addition, the redox polypyrrole achieves an efficient electrical wiring of hydrogenase on SWCNT and MWCNT electrodes via a mediated electron transfer. The latter configuration showed improved performances in catalytic responses (up to 0.30 ± 0.01 mA cm −2) at stationary electrodes due to the more appropriate wettability of MWCNTs. This led to a better coating of the nanostructured surface and thus, to an enhanced mediated electron transfer between the enzyme and the nanotubes.

Conformational and photophysical studies on porphyrin-containing donor–bridge–acceptor compounds. Charge separation in micellar nanoreactors

Photophysical studies with semi-rigid, 1, and flexible, 2, donor-bridge-acceptor (D-b-A2+) molecules with D a porphyrin and A2+ a methyl viologen moiety, were performed in neat polar solvents as well as included in surfactant (DTAB) aqueous and in reverse AOT/n-alkane micelles. The micelles acted as nanoreactors for the photoinduced electron transfer reaction upon laser excitation. In spite of the longer lifetime of the charge separated (CS) state in the semi-rigid tetrad 1(ca. 200 ns vs. ca. 100 ns for the flexible dyad 2), the CS formation quantum yield, for example in acetonitrile, was lower for the former (phi(CS) = 0.13) than for the latter (0.58). Comparison of the time-resolved fluorescence data in neat solvent and in the micelles yielded the phi(CS) values in the dilute micellar solutions. Application of laser-induced optoacoustic spectroscopy at various temperatures to 1 dissolved in a polar organic solvent (benzonitrile, BZN) included in aqueous DTAB nanoreactors afforded structural volume changes for the production in hundreds of ps of the CS state upon excitation of a polar molecule. The contraction during CS formation upon excitation of the collapsed conformer in BZN is attributed to the entering of solvent into the open molecular cavity. The opening upon formation of the CS state due to photoinduced electron transfer in the 1 collapsed conformation arises from the repulsion of the two positively charged ends in this state, as previously calculated. Inclusion of 1 in reverse AOT micelles in various n-alkanes also led to a contraction upon excitation, but the data had much more error due to the limited range of variability of the ratio of thermoelastic parameters. The data obtained with the more flexible "supermolecule" 2 showed the predicted large conformation flexibility of these molecules.

Methylviologen-pendant iron porphyrins as models of a reduction enzyme: six-electron reduction of nitrobenzene to anilineElectronic supplementary information (ESI) available: time-courses of reduction, UV-VIS spectral changes, cyclic voltammograms, EPR spectra, conversion and yield percentages for the reduction of p-nitroanisole. See http://www.rsc.org/suppdata/dt/b2/b211125j/

Methylviologen-pendant iron porphyrins, in which methylviologen was introduced to the meso-phenyl group through an amido-bridge at either the p- or m-position, were newly synthesized, in expectation that these methylviologen-pendant iron porphyrins would be good functional models of a multi-electron reductase such as nitrite reductase since the methylviologen-pendant can play the role of an electron-trapping and storage unit like the iron–sulfur cluster of the nitrite reductase. These iron porphyrins were successfully applied to the six-electron reduction of nitrobenzene to aniline, which is a model reaction of nitrite reduction to ammonia catalyzed by nitrite reductase. Both p- and m-methylviologen-pendant iron porphyrins give somewhat larger yields of aniline in the reduction of nitrobenzene and much larger yields of p-methoxyaniline in the reduction of p-nitroanisole than does normal iron tetraphenylporphyrin. Though normal iron tetraphenylporphyrin can not catalyze well the reduction of p-nitroanisole in the presence of the dioxygen molecule, these methylviologen-pendant iron porphyrins can catalyze well the reduction of p-nitroanisole and give a considerably larger yield of p-methoxyaniline even in the presence of the dioxygen molecule. These methylviologen-pendant iron porphyrins give a much larger yield of aniline in the reduction of nitrosobenzene and somewhat larger yield of aniline in the reduction of phenylhydroxylamine than does iron tetraphenylporphyrin. m-Methylviologen-pendant iron porphyrin exhibits higher catalytic activity than does the p-pendant one. The role of methylviologen moiety is discussed, based on cyclic voltammograms and UV-VIS spectra of these iron porphyrins.

Intra- and intermolecular electron transfer reactions in covalently linked donor-acceptor molecules

We synthesized a homologous series of molecules (MV nn′ Q) where a methylviologen (MV 2+) and an amino-chloronaphthoquinone (Q) are linked to each other via a flexible chain. Using the electron pulse radiolysis technique, we have measured time-resolved spectra and determined rate constants for intra- and intermolecular electron transfer (ET) between donor and acceptor site of the MV nn′ Q molecules in water and in sodium dodeeyl sulfate (SDS) micellar solution. For comparison, we also irradiated a solution containing a 1:1 mixture of methylviologen and amino-chloronaphthoquinone and measured spectra and intermolecular ET reactions between the separated electron donor and acceptor molecules. We found a remarkably slow intramolecular electron transfer from the reduced methylviologen moiety to the quinone site of all MV nn′ Q molecules both in water and in aqueous SDS micellar suspensions. The intramolecular rate constants measured in water increase with the number of intervening bonds, leading to the conclusion that electron transfer occurs by a through-space rather than through-bond mechanism. The intramolecular rate constants virtually lose their chain length dependence in SDS suspensions where, because of an extended configuration of the micellized MV nn′ Q molecules, through-space interaction is not favored.

ChemInform Abstract: Coupling Between Polypyridineruthenium(II) and Methylviologen Moieties in π-Conjugated Hybrid Systems.

The complexes (III) containing the novel 3,3'-diazamethylviologen chelate ligands are characterized by cyclic voltammetry, electronic absorption spectroscopy and ESR.

Kopplung zwischen Polypyridinruthenium(II)‐ und Methylviologen‐Einheiten in π‐konjugierten Hybridsystemen

Coupling between Polypyridineruthenium(II) and Methylviologen Moieties in n‐Conjugated Hybrid SystemsComplexes between the novel 3,3′‐diazamethylviologen chelate ligands and the [Ru(bpy)2]2+ fragment were synthesized and characterized by cyclic voltammetry, electronic absorption spectroscopy, and electron spin resonance. Incorporation into a common π system results in strong electronic coupling between the 4,4′‐bipyridinium and the tris(α‐diimine) metal chelate functions with significantly altered spectroscopic properties. The isomeric complexes with 4,4′‐diquaternized 2,2′‐bipyrazine ligands exhibit smaller electronic coupling and irreversible second reduction to a non‐Kekule system which helps to understand the superior photosensitizing properties of 2,2′‐bipyrazine complexes

Intramolecular electron transfer in a linked viologen-quinone molecule: a rate constant study

The authors synthesized a molecule MV{sup 2+}Q where a methylviologen (MV{sup 2+}) and a chloronaphthoquinone (Q) moiety are linked to each other via an aminoalkane (-NH(CH{sub 2}){sub 3}-) chain. Using the electron pulse radiolysis technique, they have determined rate constants for intra- and intermolecular electron transfer between electron donor and acceptor site of this molecule in water and sodium dodecyl sulfate (SDS) micellar solution. Measuring the decay of the absorbance at 605 nm as a function of the MV{sup 2+}Q concentration in water, they found a remarkably slow intramolecular electron transfer from the reduced methylviologen moiety to the quinone site (k{sub intra,water} = 1.4 {times} 10{sup 3} s{sup {minus}1}). Thus, even at very low MV{sup 2+}Q concentrations, intermolecular electron transfer (k = 3.8 {times} 10{sup 8} M{sup {minus}1}s{sup {minus}1}) was competing with the intramolecular reaction, and k{sub intra} was determined by extrapolation to zero MV{sup 2+}Q concentration.

Fluorescence of covalently bound zinc porphyrin—viologen complexes

A series of porphyrins covalently bound to a single methyl viologen moiety has been synthesised. Fluorescence from the porphyrin is quenched relative to the parent porphyrin; the actual yield depends markedly upon the site of attachment and the length of the chain separating the two reactants. Increasing the number of viologens attached to the porphyrin ring and using non-methylated viologen can increase the fluorescence quenching efficiency. In no case was it possible to detect long-lived redox ion products originating from the fluorescence quencing process.