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In the present work, a simple supramolecular approach was used to spontaneously form nanoparticles from sodium carboxymethylcellulose and viologen calix[4]resorcinol as a result of joint self-assembly in water at room temperature. Supramolecular interactions between them led to the formation of nanoparticles, the morphology and properties of which depend on polymer/macrocycle ratio. When there is excess of macrocycle, the nanoparticles bind lipophilic oleic acid, and when there is excess of polymer, they bind hydrophilic doxorubicin. Interestingly, the solubilization of lipophilic quercetin into these nanoparticles was significantly increased compared to the pure polymer and macrocycle, regardless of their ratio. The nanoparticles of triple composition (polymer/macrocycle/drug) have a more effective penetration ability in tumorcells than those of double composition (polymer/drug). The presented results are the first step towards the creation of new nanotechnologies to improve the bioavailability and delivery of bioactive components., (© 2024 Wiley-VCH GmbH.)

Asymmetric hydrogenation of alkene moieties is important for the synthesis of chiral molecules, but achieving high stereoselectivity remains a challenge. Biocatalysis using ene-reductases (EReds) offers a viable solution. However, the need for NAD(P)H cofactors limits large-scale applications. Here, we explored an electrochemical alternative for recycling flavin-containing EReds using methyl viologen as a mediator. For this, we built a bio-electrocatalytic setup with an H-type glass reactor cell, proton exchange membrane, and carbon cloth electrode. Experimental results confirm the mediator's electrochemical reduction and enzymatic consumption. Optimization showed increased product concentration at longer reaction times with better reproducibility within 4-6 h. We tested two enzymes, Pentaerythritol Tetranitrate Reductase (PETNR) and the Thermostable Old Yellow Enzyme (TOYE), using different alkene substrates. TOYE showed higher productivity for the reduction of 2-cyclohexen-1-one (1.20 mM h -1 ), 2-methyl-2-cyclohexen-1-one (1.40 mM h -1 ) and 2-methyl-2-pentanal (0.40 mM h -1 ), with enantiomeric excesses ranging from 11 % to 99 %. PETNR outperformed TOYE in terms of enantioselectivity for the reduction of 2-methyl-2-pentanal (ee 59 % ± 7 % (S)). Notably, TOYE achieved promising results also in reducing ketoisophorone, a challenging substrate, with similar enantiomeric excess compared to published values using NADH., (© 2024 The Authors. ChemBioChem published by Wiley-VCH GmbH.)

Oxidoreductase enzymes, used for a variety of applications including organic synthesis and pharmaceutical industry, require reduced nicotinamide adenine dinucleotide (NADH) as reducing equivalents. Methods for regenerating NAD + to NADH are of significant interest due to the high cost and stoichiometric amounts of cofactor required. Diaphorase/redox mediator systems have shown promise for this purpose, but suitable mediators are few due to the low redox potential required, necessary downstream processing and stability issues. A novel amino-functionalized viologen is presented in this work which, upon immobilization with diaphorase, yields bioactive NADH with high selectivity (99 %) and faradaic efficiency (99 %). This system was tested with NADH-dependent formate dehydrogenase, showing a 21-fold improvement in formate yield compared to an enzymatic negative control without NADH regeneration. The findings underscore the potential of this novel amino-functionalized viologen polymer to advance sustainable and efficient NADH regeneration at very low overpotential., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

The systematic study of two ionic porous organic polymers (iPOPs) based on viologens and their first applications in the electrochromic field are reported. The viologen-based iPOPs are synthesized by electrochemical polymerization with cyano groups, providing a simple and controllable method for iPOPs that solves the film preparation problems common to viologens. After the characterization of these iPOPs, a detailed study of their electrochromic properties is conducted. The iPOP films based on viologens structure exhibit excellent electrochromic properties. In addition, the resulting iPOP films show high sensitivity to electrolyte ions of different sizes in the redox process. Electrochemical and electrochromic data of the iPOPs explain this phenomenon in detail. These results demonstrate that iPOPs of this type are ideal candidates as electrochromic materials due to their inherent porous structures and ion-rich properties., (© 2024 Wiley‐VCH GmbH.)

The structure of the Viologen-Phenylene-Imidazole (VPI) guest, previously shown to be bound by cucurbit[7]uril (CB[7]) with binding modes depending on pH and silver ions, has been extended by adding hydrophobic groups on the two extremities of VPI before investigations of CB[7] binding by NMR, ITC, X-ray diffraction, UV-vis and fluorescence spectroscopies. With an imidazole station extended by a naphthalene group (VPI-N), binding modes of CB[7] are similar to those previously observed. However, with the viologen extended by a tolyl group (T-VPI), CB[7] preferentially sits on station T, shuttling between the T and P stations at acid pH or after Ag + addition. The CB[7] ⋅ T-VPI complex thus behaves as a metal-actuated thermodynamic stop-and-go molecular shuttle featured by fast and autonomous ring translocation between two stations and a continuum for fractional station occupancy solely and easily controlled by Ag + concentration., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Aqueous-organic redox flow batteries (RFBs) have gained considerable interest in recent years, given their potential for an economically viable energy storage at large scale. This, however, strongly depends on both the robustness of the underlying electrolyte chemistry against molecular decomposition reactions as well as the device's operation. With regard to this, the presented study focuses on the use of in situ IR spectroscopy in combination with a multivariate curve resolution approach to gain insight into both the molecular structures of the active materials present within the electrolyte as well as crucial electrolyte state parameters, represented by the electrolyte's state of charge (SOC) and state of health (SOH). To demonstrate the general applicability of the approach, methyl viologen (MV) and bis(3-trimethylammonium)propyl viologen (BTMAPV) are chosen, as viologens are frequently used as negolytes in aqueous-organic RFBs. The study's findings highlight the impact of in situ spectroscopy and spectral deconvolution tools on the precision of the obtainable SOC and SOH values. Furthermore, the study indicates the occurrence of multiple viologen dimers, which possibly influence the electrolyte lifetime and charging characteristics., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Paramagnetic metallohost systems can bind guest molecules and find application as biomimetic catalysts. Due to the presence of the paramagnetic metal center, rigorous characterization of these systems by NMR spectroscopy can be very difficult. We report here that metallohost-guest systems can be studied by using the paramagnetic relaxation enhancement (PRE) effect. Manganese(III) porphyrin cage compounds are shown through their PRE to thread and bind viologen guests, including a polymeric one. The binding constants and dethreading activation parameters are lower than those of the metal-free porphyrin cage compounds, which is proposed to be a result of charge repulsion of the trivalent metal center and dicationic viologen guest. The threading rate of the manganese(III) porphyrin cage onto the polymer is more than 10 times faster than that of the non-metallated one, which is ascribed to initial binding of the cage to the polymer chain prior to threading, and to an entron effect., (© 2022. The Author(s).)

Water serves as an inert environment for the dispersion and application of many kinds of herbicides. Viologen compounds, a type of widely used but highly toxic herbicide, are stable in bulk water, whose half-life can be up to 23 weeks in natural water, imposing a severe health risk to mammals. In this study, we present the striking results of the spontaneous and ultrafast reduction-induced degradation of three viologen compounds in water microdroplets and provide the concentration, time, temperature dependence, mechanism, and scale-up of the reactions. We postulate that the electrons existing at the air-water interface of the microdroplets due to the unique redox potential therein initiate the reduction, from which further degradation occurs. The host-guest complexation between cucurbit[7]uril and viologens only slightly changes the redox potential of viologens in the bulk but completely inhibits the reactions in microdroplets, adding to the uniqueness of the redox potentials at the air-water interfaces of microdroplets. Taken together, microdroplets might have been functioning as naturally occurring ubiquitous tiny electrochemical cells for a plethora of unique redox reactions that were thought to be impossible in the bulk water.

In only a few decades, lithium-ion batteries have revolutionized technologies, enabling the proliferation of portable devices and electric vehicles 1 , with substantial benefits for society. However, the rapid growth in technology has highlighted the ethical and environmental challenges of mining lithium, cobalt and other mineral ore resources, and the issues associated with the safe usage and non-hazardous disposal of batteries 2 . Only a small fraction of lithium-ion batteries are recycled, further exacerbating global material supply of strategic elements 3-5 . A potential alternative is to use organic-based redox-active materials 6-8 to develop rechargeable batteries that originate from ethically sourced, sustainable materials and enable on-demand deconstruction and reconstruction. Making such batteries is challenging because the active materials must be stable during operation but degradable at end of life. Further, the degradation products should be either environmentally benign or recyclable for reconstruction into a new battery. Here we demonstrate a metal-free, polypeptide-based battery, in which viologens and nitroxide radicals are incorporated as redox-active groups along polypeptide backbones to function as anode and cathode materials, respectively. These redox-active polypeptides perform as active materials that are stable during battery operation and subsequently degrade on demand in acidic conditions to generate amino acids, other building blocks and degradation products. Such a polypeptide-based battery is a first step to addressing the need for alternative chemistries for green and sustainable batteries in a future circular economy.

A new conjugated ionic porous organic polymer (AN-POP), incorporated with anthracene-extended viologen, has been rationally designed and prepared to explore its dual functions in photocatalytic oxidation and bacterial killing. Compared with its anthracene-free counterpart (BD-POP), AN-POP showed a superior photocatalytic oxidation performance and antibacterial activity demonstrating the critical role of an anthracene-extended viologen structure.

Donor-acceptor (DA) π-interactions are weak attractive forces that are exploited widely in molecular and supramolecular chemistry. They have been characterized extensively by ensemble techniques, providing values for their energies that are useful for the design of soft materials. For implementation of motions or operations based on these DA π-interactions in wholly synthetic molecular machines, the mechanical strength and force associated with their out-of-equilibrium performance are the key parameters, in addition to their energies obtained at thermodynamic equilibrium. In this context, we have used single-molecule force spectroscopy as a nonequilibrium technique to determine the mechanical strength of individual DA π-interactions in solution. We designed and synthesized a molecular tweezer that is able to encapsulate π-donors and also demonstrated a precise opening extension. The mechanical breaking of the noncovalent interactions between viologen units-π-acceptors commonly employed in mechanically interlocked molecules-and several π-donors afforded a characteristic force-distance signature, revealing the opening of individual viologen tweezers with an unambiguous extension. Single-tweezer host-exchange experiments performed in situ demonstrated the sensitivity of the technique. This simple design could be exploited in quantifying the force of a large range of weak noncovalent bonding interactions as well as the potential work that molecular machines can generate at the single-molecule level.

A novel viologen-based multifunctional Eu-MOF was obtained by integrating a luminescent component Eu(NO 3 ) 3 ·6H 2 O and a viologen-functionalized ligand. The Eu-MOF not only exhibited reversible photochromic and electrochromic properties, but also displayed photoluminescent and electroluminochromic properties.

Helquats (HQs) are structurally linked to helicenes and viologens, and they represent an attractive field of research in chemistry and medicinal chemistry. In the present work they were used as catalysts for the synthesis of 1,2,3,4-tetrahydroquinolines in good yields by the Povarov reaction. The substrate scope and the capability of different helquats to promote Povarov reactions are demonstrated. Studies to elucidate mechanistic details revealed that helquats act as single-electron transfer oxidants through a cation-radical mechanism. The screening of the catalytic activity of HQs confirmed that an active HQ must have a LUMO energy below -8.67 eV and the standard redox potential higher (less negative) than -1.2 V vs. the ferrocene/ferrocenium redox couple., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The development of a highly effective photosensitizer (PS) that can be activated with a low-power single light is a pressing issue. Herein, we report a PS for synergistic photodynamic and photothermal therapy constructed through self-assembly of poly(selenoviologen) on the surface of core-shell NaYF 4 :Yb/Tm@NaYF 4 upconversion nanoparticles. The hybrid UCNPs/PSeV PS showed strong ROS generation ability and high photothermal conversion efficiency (∼52.5%) under the mildest reported-to-date irradiation conditions (λ = 980 nm, 150 mW/cm 2 , 4 min), leading to a high efficiency in killing methicillin-resistant Staphylococcus aureus (MRSA) both in vitro and in vivo . Remarkably, after intravenous injection, the reported PS accumulated preferentially in deep MRSA-infected tissues and achieved an excellent therapeutic index. This PS design realizes a low-power single-NIR light-triggered synergistic phototherapy and provides a simple and versatile strategy to develop safe clinically translatable agents for efficient treatment of deep tissue bacterial inflammations.

A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by 1 H and 13 C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-smectic A (SmA) transitions, T m s, and SmA-to-isotropic transitions, T i s. Those with longer length of alkoxy chains had relatively low T m s at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330-370 °C. Their light-emitting properties in methanol were also included.

Self-propelled micro- and nanomachines are at the forefront of materials research, branching into applications in biomedical science and environmental remediation. Cationic frameworks enabling the collection and delivery of anionic species (A - ) are highly required, due to the large variety of life-threatening pollutants, such as radioactive technetium and carcinogenic chromium, and medicines, such as dexamethasone derivatives with negative charges. However, such autonomous moving carriers for active transport of the anions have been barely discussed. A polymeric viologen (PV ++ )-consisting of electroactive bicationic subunits-is utilized in a tubular autonomous microswimmer to selectively deliver A - of different sizes and charge densities. The cargo loading is based on a facile anion exchange mechanism. The packed crystal structure of PV ++ allows removal of an exceptionally high quantity of anions per one microswimmer (2.55 × 10 -13 mol anions per microswimmer), a critical factor often neglected regarding the real-world application of microswimmers. Notably, there was virtually no leakage of anions during the delivery process or upon keeping the loaded microswimmers under ambient conditions for at least 4 months. Multiple release mechanisms, compatible with different environments, including electrochemical, photochemical, and a metathesis reaction, with high efficiencies up to 98% are introduced. Such functional autonomous micromachines provide great promise for the next generation of functional materials for biomedical and environmental applications.

Background: Continuous glucose monitors (CGMs) enable people with diabetes to proactively manage their blood glucose and reduce the risk of hypoglycemia. Commercially available CGMs utilize percutaneous electrodes that, after days to weeks of implantation, are subjected to the foreign body response that severely reduces sensor accuracy. The previous work demonstrated the use of hydrogels containing a glucose-responsive viologen that quenches a nearby fluorophore. Here, we investigate the immobilization of this sensing motif onto a nanoparticle surface and optimize local surface concentrations for optical glucose sensing., Methods: A viologen quencher-fluorescent dye system was incorporated into poly(2-hydroethyl methacrylate) hydrogels in varying quantities to assess the effect of quencher-fluorophore concentration on glucose responsiveness. The sensing motif was then immobilized onto silica nanoparticles by carbodiimide chemistry. Nanosensors with a range of dye and quencher concentrations were challenged for glucose responsiveness to determine the optimal sensor formulation., Results: When incorporated into a hydrogel, high concentrations of viologen quencher and fluorophore were required to permit electron transfer between the two components and yield a detectable glucose response. Immobilization of this glucose-responsive system onto a silica nanoparticle facilitated this electron transfer to yield detectable responses at even low concentrations. Increasing quencher concentration on the nanoparticle, relative to the fluorophore, resulted in the greatest apparent glucose response., Conclusion: The nanoparticle sensors demonstrated excellent glucose response in the physiological range and are a promising tool for real-time glucose tracking.

Mono- and di-quaternized 4,4'-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4'-bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium- and environment-responsive 4,4'-bipyridine derivatives. Two important classes of 4,4'-bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N , N' -disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4'-bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure-property relations are discussed in connection to the role of these derivatives in various novel applications., Competing Interests: The author declares no conflict of interest.

The utilization of the light-harvesting and electron-transferring function of chlorophylls (Chls) has received attention for visible-light driven hydrogen production. In this work, a series of Chl derivatives based on pyropheophorbide-a (Pyro-a) conjugated with a viologen moiety, including a Pyro-a methyl ester directly bonded with the viologen at the 3-position 1, its 31-methylene analog 2 and Pyro-a connected with the viologen in the 17-substituent 3, were synthesized from chemical modification of naturally occurring Chl-a and characterized in terms of their photochemical and photophysical properties. As the photoexcited singlet state of the Pyro-a moiety was strongly quenched by the viologen moiety in a molecule, the effective photoinduced intramolecular electron transfer from Pyro-a to the bonded viologen moiety occurred. Moreover, these molecules were applied as a photosensitizer in the system for visible-light driven hydrogen production with platinum nanoparticles via intramolecular reduction of the bonded viologen moiety. Efficient photoreduction of external methyl viologen and successive hydrogen production on platinum nanoparticles were achieved using the synthetic conjugate of Pyro-a with the viologen moiety as a photosensitizer. In particular, effective visible-light driven hydrogen production was accomplished using 3 and platinum nanoparticles via the reduction of external methyl viologen.

How to reduce the cytotoxicity of antitumor peptides to normal cells remains an ongoing challenge. Here, we designed a pH/redox-responsive supramolecular structure (Pep-V⊂P-PEG) composed of a peptide modified with viologen (Pep-V) and polyethylene glycol bearing pillar[5]arene (P-PEG) as a "helmet". By shielding the hydrophobic moiety of the peptide derivative with pillar[5]arene via host-guest interactions, its disruption on normal cells can be effectively reduced. At acidic pH, the supramolecular structure can selectively adsorb onto negatively charged lipid membranes because of electrostatic interactions. Owing to redox responsiveness of the viologen group, Pep-V could be separated from P-PEG after the addition of reductants and inserted into lipid bilayers, which leads to membrane disruption. Cargo leakage of liposome models was investigated to understand Pep-V⊂P-PEG-induced liposomal membrane disruption under different pH values and redox conditions. Results showed that Pep-V⊂P-PEG caused almost no cargo leakage from (1,2-dipalmitoyl- sn -glycerol-3-phosphocholine) liposomes at pH 7.4 but significant leakage from negatively charged (1,2-dipalmitoyl- sn -glycerol-3-phospho-(1- rac -glyerol)) liposomes at pH 5.0 under a reducing environment. Pep-V⊂P-PEG displayed low destructive effects on mimic normal cells and significant disruption to mimic tumor cells when exposed to a reducing environment that is expected to be a potential antitumor agent.

A series of viologen related redox mediators of varying reduction potential has been characterized and their utility as electron shuttles between CdSe quantum dots and hydrogenase enzyme has been demonstrated. Tuning the mediator LUMO energy optimizes the performance of this hybrid photocatalytic system by balancing electron transfer rates of the shuttle.

The photosynthetic protein complex, photosystem I (PSI), can be photoexcited with a quantum efficiency approaching unity and can be integrated into solar energy conversion devices as the photoactive electrode. The incorporation of PSI into conducting polymer frameworks allows for improved conductivity and orientational control in the photoactive layer. Polyviologens are a unique class of organic polycationic polymers that can rapidly accept electrons from a primary donor such as photoexcited PSI and subsequently can donate them to a secondary acceptor. Monomeric viologens, such as methyl viologen, have been widely used as diffusible mediators in wet PSI-based photoelectrochemical cells on the basis of their suitable redox potentials for accepting electrons. Polyviologens possess similar electronic properties to their monomers with the added advantage that they can shuttle electrons in the solid state. Depositing polyviologen directly onto a film of PSI protein results in significant photocurrent enhancement, which confirms its role as an electron-transport material. The polymer film not only improves the photocurrent by aiding the electron transfer but also helps preserve the protein film underneath. The composite polymer-PSI assembly enhances the charge-shuttling processes from individual protein molecules within the PSI multilayer, greatly reducing charge-transfer resistances. The resulting PSI-based solid-state platform demonstrates a much higher photocurrent than the corresponding photoelectrochemical cell built using a similar architecture.

A molecular switch built with cucurbit[7]uril and a 3-station viologen-phenylene-imidazole compound exhibited pH actuated ring translocation with high fatigue resistance (up to 102 cycles). The switch movement was harnessed toward selectively masking the toxicity of the viologen fragment at neutral pH near non-cancerous cells, while exposing it at acid pH near cancer cells.

Herein, a new class of polymerizable boronic acid (BA) monomers are presented, which are used to generate soft hydrogels capable of accurate determination of saccharide concentration. By exploiting the interaction of these cationic BAs with an anionic fluorophore, 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine), a two-component sugar-sensing system was realized. In the presence of such cationic BAs ( o-BA, m-BA, and p-BA), the fluorescence of pyranine becomes quenched because of the formation of a nonfluorescent BA-fluorophore complex. Upon addition of saccharides, formation of a cyclic boronate ester results in dissociation of the nonfluorescent complex and recovery of the pyranine fluorescence. The response of this system was examined in solution with common monosaccharides, such as glucose, fructose, and galactose. Subsequent polymerization of the BA monomers yielded cross-linked hydrogels which showed similar reversible recovery of fluorescence in the presence of glucose.

Standard [NiFe]-hydrogenase from Desulfovibrio vulgaris Miyazaki F (DvMF-H 2 ase) catalyzes the uptake and production of hydrogen (H 2 ) and is a promising biocatalyst for future energy devices. However, DvMF-H 2 ase experiences oxidative inactivation under oxidative stress to generate Ni-A and Ni-B states. It takes a long time to reactivate the Ni-A state by chemical reduction, whereas the Ni-B state is quickly reactivated under reducing conditions. Oxidative inhibition limits the application of DvMF-H 2 ase in practical devices. In this research, we constructed a mediated-electron-transfer system by co-immobilizing DvMF-H 2 ase and a viologen redox polymer (VP) on electrodes. The system can avoid oxidative inactivation into the Ni-B state at high electrode potentials and rapidly reactivate the Ni-A state by electrochemical reduction of VP. H 2 oxidation and H + reduction were realized by adjusting the pH from a thermodynamic viewpoint. Using carbon felt as a working-electrode material, high current densities-up to (200 ± 70) and -(100 ± 9) mA cm -3 for the H 2 -oxidation and H + -reduction reactions, respectively-were attained., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this work we present a viologen-modified electrode providing protection for hydrogenases against high potential inactivation. Hydrogenases, including O2-tolerant classes, suffer from reversible inactivation upon applying high potentials, which limits their use in biofuel cells to certain conditions. Our previously reported protection strategy based on the integration of hydrogenase into redox matrices enabled the use of these biocatalysts in biofuel cells even under anode limiting conditions. However, mediated catalysis required application of an overpotential to drive the reaction, and this translates into a power loss in a biofuel cell. In the present work, the enzyme is adsorbed on top of a covalently-attached viologen layer which leads to mixed, direct and mediated, electron transfer processes; at low overpotentials, the direct electron transfer process generates a catalytic current, while the mediated electron transfer through the viologens at higher potentials generates a redox buffer that prevents oxidative inactivation of the enzyme. Consequently, the enzyme starts the catalysis at no overpotential with viologen self-activated protection at high potentials.

We report a cross-reactive sensor array, combining a two-component probe system based upon three viologen substituted boronic acids and a poly(aryleneethynylene) (PAE) and an additional number of simple PAEs alone. This combined system discriminates 27 different honeys in aqueous solution, according to patterns in fluorescence intensity modulation, using linear discriminant analysis for data processing. The fluorescence turn-on array detects saccharide composition, while the PAEs discriminate trace colored components in the honeys., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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 CO 2 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 CO 2 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 CO 2 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.

Results of our study on ultrafast electron transfer (eT) dynamics from coumarins (coumarin-1, coumarin-480, and coumarin-153) incarcerated within octa acid (OA) capsules as electron donors to methyl viologen dissolved in water as acceptor are presented. Upon photoexcitation, coumarin inside the OA capsule transfers an electron to the acceptor electrostatically attached to the capsule leading to a long-lived radical-ion pair separated by the OA capsular wall. This charge-separated state returns to the neutral ground state via back electron transfer on the nanosecond time scale. This system allows for ultrafast electron transfer processes through a molecular wall from the apolar capsular interior to the highly polar (aqueous) environment on the femtosecond time scale. Employing femtosecond transient absorption spectroscopy, distinct rates of both forward (1-25 ps) and backward eT (700-1200 ps) processes were measured. Further understanding of the energetics is provided using Rehm-Weller analysis for the investigated photoinduced eT reactions. The results provide the rates of the eT across a molecular wall, akin to an isotropic solution, depending on the standard free energy of the reaction. The insights from this work could be utilized in the future design of efficient electron transfer processes across interfaces separating apolar and polar environments.

Organic materials have recently gained considerable attention for electronic applications, improving performance and sustainability to current technologies. Commercialized metal-based systems are generally expensive, toxic and difficult to recycle, however organic materials offer promising solutions. Viologens, N,N' di-quaternized bipyridyl salts, are a well-studied species exhibiting three reversible redox states, possessing valuable electrochromic and electron-accepting properties. These properties can be fine-tuned through synthesis by altering the nitrogen substituents and various counteranions. Currently, viologens have become of great interest as functional materials in a wide array of applications; a few to name include electrochromic devices, molecular machines, and organic batteries. This review highlights representative recent work and advances towards utilizing viologens in practical applications that currently compete with metal-based technologies. Additionally, modified viologens that can be further fine-tuned will be discussed., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Three novel solution-processable polyimides containing triphenylamine and pendant viologen moieties are prepared from the newly synthesized diamine and three commercially available dianhydrides. The thermally stable polyimide with strong donor-acceptor charge-transfer possesses write-once read-many-times memory behavior with excellent operation stability. The obtained multicolored electrochromic polymer films reveal ambipolar electrochemical behavior with high optical transmittance contrast of coloration changed from transmissive neutral state to the cyan/magenta/yellow redox states, implying great potential for application in smart window and displays., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

With the aim of discerning between different sugar and sugar alcohols of biomedical relevance, such as gut permeability, arrays of 2-component probes were assembled with up to six boronic acid-appended viologens (BBVs): 4,4'-o-BBV, 3,3'-o-BBV, 3,4'-o-BBV, 4,4'-o,m-BBV, 4,7'-o-PBBV, and pBoB, each coupled to the fluorophore 8-hydroxypyrene, 1,3,6-trisulfonic acid trisodium salt (HPTS). These probes were screened for their ability to discriminate between lactulose, l-rhamnose, 3-O-methyl-d-glucose, and xylose. Binding studies of sugar alcohols mannitol, sorbitol, erythritol, adonitol, arabitol, galactitol, and xylitol revealed that diols containing threo-1,2-diol units have higher affinity for BBVs relative diols containing erythro-1,2 units. Those containing both threo-1,2- and 1,3-syn diol motifs showed high affinity for boronic acid binding. Fluorescence from the arrays were examined by principle component analysis (PCA) and linear discriminant analysis (LDA). Arrays with only three BBVs sufficed to discriminate between sugars (e.g., lactulose) and sugar alcohols (e.g., mannitol), establishing a differential probe. Compared with 4,4'-o-BBV, 2-fold reductions in lower limits of detection (LOD) and quantification (LOQ) were achieved for lactulose with 4,7-o-PBBV (LOD 41 μM, LOQ 72 μM). Using a combination of 4,4'-o-BBV, 4,7-o-PBBV, and pBoB, LDA statistically segregated lactulose/mannitol (L/M) ratios from 0.1 to 0.5, consistent with values encountered in small intestinal permeability tests. Another triad containing 3,3'-o-BBV, 4,4'-o-BBV, and 4,7-o-PBBV also discerned similar L/M ratios. This proof-of-concept demonstrates the potential for BBV arrays as an attractive alternate to HPLC to analyze mixtures of sugars and sugar alcohols in biomedical applications and sheds light on structural motifs that make this possible.

A tetracationic pyridinium-based cyclophane with a box-like geometry, incorporating two juxtaposed alkyne functions, has been synthesized. The triple bonds are reactive through cycloadditions toward dienes and azides, promoted by the electron-withdrawing nature of the pyridinium rings, as well as by the strain inherent in the cyclophane. The cycloadditions proceeded in high yields, with the cyclophane reacting faster than its acyclic analogue. While the cyclophane contains two reactive triple bonds, there is no evidence for a stable monofunctional intermediate-only starting material and the difunctional product have been detected by (1)H NMR spectroscopy. Molecular modeling of the energy landscape reveals a lower barrier for the kinetically favored second cycloaddition compared with the first one. This situation results in tandem cascading reactions within rigid cyclophanes, where reactions at a first triple bond induce increased reactivity at a distal second alkyne.

A new single-component photocatalyst for the reduction of water to H2, a dichloro(dpbpy)platinum(ii) derivative (dpbpy = 4,4'-diphenyl-2,2'-bipyridine) tethered to four pendant viologen acceptors (1), is shown to exhibit twice higher photocatalytic efficiency than the previously reported dichloro(bpy)-platinum(ii) analog (; bpy = 2,2'-bipyridine), consistent with the higher absorptivity of at the metal-to-ligand charge transfer ((1)MLCT) band due to the larger π-conjugation in dpbpy relative to bpy.

Photoactive viologen fragments were covalently embedded within the material framework during the self-assembly and sol-gel polymerisation of phosphonate-terminated dendrimers and soluble titanium-oxo-species. The resulting porous anisotropic phosphonate-bridged-crystalline anatase materials serve as new hosts to disperse and stabilize small gold nanoparticles.

In this communication we report the synthesis of Pd nanoparticle clusters achieved via the assembly of Pd nanoparticles on the surface of a spherical polymer network. The network exhibits flexibility and adapts to the cluster formation. The nanoclusters display high catalytic activity toward p-nitrophenol reduction and the Suzuki-Miyaura coupling reaction.

We describe here the generation of new donor-acceptor disulfide architectures obtained in aqueous solution at physiological pH. The application of a dynamic combinatorial chemistry approach allowed us to generate a large number of new disulfide macrocyclic architectures together with a new type of [2]catenanes consisting of four distinct components. Up to fifteen types of structurally-distinct dynamic architectures have been generated through one-pot disulfide exchange reactions between four thiol-functionalized aqueous components. The distribution of disulfide products formed was found to be strongly dependent on the structural features of the thiol components employed. This work not only constitutes a success in the synthesis of topologically- and morphologically-complex targets, but it may also open new horizons for the use of this methodology in the construction of molecular machines.

A systematic study of the ternary complex formation process for aromatic amino acids using ucurbit[8]uril (CB[8]) and a viologen amphiphile shows that the affinity of the amino acid needs to be higher or in a comparable range to that of CB[8] for the amphiphile in order to form the ternary complex. Based on these observations, a supramolecular peptide amphiphile and its corresponding vesicle are prepared using a peptide containing an azobenzene moiety. The azobenzene group at the N-terminus of the peptide served as the second guest for CB[8]. The vesicles obtained from this peptide amphiphile show response to a number of external triggers. The trans-cis isomerization of the azobenzene group upon irradiation with UV-light of 365 nm leads to the breakdown of the ternary complex and eventually to the disruption of the vesicle. The deformation-reformation of the vesicle can be controlled by illuminating the disrupted solution with light of 420 nm as it facilitates the cis-trans isomerization. Thus, the vesicle showed a controlled and reversible response to UV-light with the ability for manipulation of the formation-deformation of the vesicle by the choice of an appropriate wavelength. The vesicle showed response to a stronger guest (1-adamantylamine) for CB[8], which displaces both the guests from the CB[8] cavity and consequently ruptures the vesicle structure. 2,6-Dihydroxynaphthalene acts as a competitive guest and thereby behaves as another external trigger for replacing the peptide from the CB[8] cavity by self-inclusion to form the ternary complex. Henceforth, it allows retaining the vesicle structure and results in the release of the peptide from the vesicle.

A pillar[5]arene-crown ether fused bicyclic host 1 was found to be able to recognize an imidazolium ion G1 by its pillar[5]arene subunit and a viologen ion G2 by its crown ether receptor discriminatively. The simultaneous binding of G1 and G2 by 1 resulted in the formation of a three-component host-guest complex G1⊂1⊃G2. Negative heterotropic cooperative effects were displayed by G1 and G2 in their binding to 1 and were investigated by stepwise bindings of G1 and G2 to 1.

The binding modes, inclusion abilities, and thermodynamic parameters for the intermolecular complexation of p-sulfonatocalix[4]arene (SC4A), p-sulfonatocalix[5]arene (SC5A), and p-sulfonatothiacalix[4]arene (STC4A), with methyl viologen (MV(2+)), ethyl viologen (EV(2+)), propyl viologen (PV(2+)), butyl viologen (BV(2+)), and benzyl viologen (BnV(2+)), were systematically investigated by NMR spectroscopy, molecular mechanics calculation, and microcalorimetry in neutral aqueous solutions. The obtained results show that all the sulfonated calixarene hosts can form stable inclusion complexes with viologen guests driven by much favorable enthalpy changes. All the viologen guests are encapsulated into the smaller SC4A cavity in their axial orientation. The larger SC5A cavity can accommodate all the viologen guests at its upper-rim midsection in the latitudinal orientation. The binding modes of more flexible STC4A with the smaller MV(2+) and EV(2+) guests are similar to those of SC5A with the two guests, while the binding modes of STC4A with the larger PV(2+) and BV(2+) guests are similar to those of SC4A with the two guests. The host selectivity for all the investigated viologen guests is the same: SC5A > SC4A > STC4A. The magnitude of the host selectivity is associated with the size of the guest. Moreover, the thermodynamic origin of the host selectivity for these viologen guests can be explained well by host-guest binding modes.

Bionanocomposites of hydrogenase and viologen-functionalized carbon nanotubes (H2ase/V-MWNTs) were prepared and characterized by using infrared spectra and scanning electron microscope. Cyclic voltammograms revealed two couples of redox waves corresponded to the electron transfer processes of viologens and [4Fe-4S]2+/1+ clusters of hydrogenase. The current intensity was enhanced in the H2 atmosphere, which suggested that the present bio-nanocomposites could be used as heterogeneous bio-catalyst to catalyze reversible reaction between protons and H2.

We report the synthesis of a series of homologous oligoviologens in which different numbers of 4,4'-bipyridinium (BIPY(2+)) subunits are linked by p-xylylene bridges, as a prelude to investigating how their radical cationic forms self-assemble both in solution and in the solid state. The strong radical-radical interactions between the radical cationic forms of the BIPY(2+) units-namely, BIPY(•+)-in these oligoviologens induce intra- or intermolecular folding of these homologues. UV/Vis/NIR spectroscopic studies and DFT quantum mechanics indicate that the folding of the shorter oligoviologens is dominated by intermolecular radical-radical interactions. In addition to intermolecular interactions, strong intramolecular radical-radical interactions, which give rise to an NIR absorption band at 900 nm, tend to play a crucial role in governing the folding of the longer oligoviologens. The solid-state superstructure of the oligoviologen with three BIPY(2+) units reveals that two intertwining chains fold together to form a dimer, stabilized by intermolecular radical-radical interactions. These dimers continue to stack in an infinite column through intermolecular radical-radical interactions between them. This research features an artificial biomimetic system which sustains delicate secondary and tertiary structures, reminiscent of those present in nucleic acids and proteins.

Threading of a polymer through a macrocyclic ring may occur directly, that is, by finding the end of the polymer chain, or by a process in which the polymer chain first folds and then threads through the macrocyclic ring in a hairpin-like conformation. We present kinetic and thermodynamic studies on the threading of a macrocyclic porphyrin receptor (H2 1) onto molecular threads that are blocked on one side and are open on the other side. The open side is modified by groups that vary in ease of folding and in bulkiness. Additionally, the threads contain a viologen binding site for the macrocyclic receptor, which is located close to the blocking group. The rates of threading of H2 1 were measured under various conditions, by recording as a function of time the quenching of the fluorescence of the porphyrin, which occurs when receptor H2 1 reaches the viologen binding site. The kinetic data suggest that threading is impossible if the receptor encounters an open side that is sterically encumbered in a similar way as a folded polymer chain. This indicates that threading of polymers through macrocyclic compounds through a folded chain mechanism is unlikely., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of two types of viologen dendrimers with peripheral carboxyl groups is described. Their interaction with plasmid DNA and CT-DNA and the influence of time evolution and electrolyte on dendriplex formation have been electrochemically investigated. A negative potential shift appearing in the cyclic voltammograms of the dendrimers indicates dendriplex formation on the time scale of 15 to 19 minutes, i.e. similar to those determined empirically for other dendrimer types. The presence or absence of the negative potential shift can be used to check the stability towards sodium chloride and different cell growth media directing to sucrose for cell incubation experiments. The electrolyte content of commercially available cell growth media inhibits the dendriplex formation in solution prior to plasmid addition. Furthermore, a low salt stability of 20 mM sodium chloride for viologen dendriplexes has been confirmed, also recommending the use of lysosomotropic sucrose. The two types of viologen dendrimers have been combined with two plasmids differing in the number of base pairs. Four immortal cell lines have been tested to check the suitability of viologen dendriplexes as gene delivery systems. Probably due to the absence of terminal amino groups and endosomolytic substances only a small transfection efficiency of dendriplexes was achieved at low pH, generally excluding in vivo applications. With the larger pHSV-eGFP plasmid (5743 bp) no transfected cells were observed indicating a preference for shorter plasmids.

Oxacalix[2]arene[2]pyrazine and functional polyether derived oxacalixcrown-6, -7, and -8 were synthesized, and their host-guest complexation with paraquat to form [2]pseudorotaxanes was studied. The [2]pseudorotaxanes were then successfully used in the construction of two oxacalixcrown-tetracationic cyclophane [CBPQT(4+)] based [2]catenanes.

The synthesis and binding properties of new porphyrin cage compounds consisting of a rigid diphenylglycoluril part, which is connected via flexible bis(ethyleneoxy) spacers to a (metallo)porphyrin "roof", are reported. Binding of viologen guests and pyridine ligands in these porphyrin cages are accompanied by significant conformational reorganizations of the hosts. Despite these structural changes, association constants are still very high, revealing that not only receptors that bind guests according to a lock-and-key mechanism but also those that bind guests by an induced-fit mechanism can exhibit strong binding., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Chemokine receptors and their ligands play a central role in cancer metastasis, inflammatory disorders, and viral infections. Viologen dendrimers (VGD) emerged recently as a promising class of synthetic polycationic ligands for chemokine receptor CXCR4. The objective of this study was to evaluate the potential of VGD as novel dual-function polycations capable of simultaneous CXCR4 antagonism and gene delivery. As part of our systematic studies, we have synthesized a library of VGD with differences in molecular architecture, number of positive charges, and type of capping group. The ability of VGD to condense DNA was evaluated, and physicochemical and biological properties of the resulting polyplexes were studied. We have evaluated the effect of VGD surface charge, size, capping group, and molecular architecture on physicochemical properties of polyplexes, transfection efficiency, CXCR4 antagonism, and cytotoxicity in human epithelial osteosarcoma (U2OS) and in human liver hepatocellular carcinoma (HepG2) cells. We found that properties and behavior of the polyplexes are most dependent on the number of positive charges and molecular weight of VGD and to a lesser extent on the type of a capping group. Using TNFα plasmid, we have demonstrated that VGD prevents CXCR4-mediated cancer cell invasion and facilitates TNFα-mediated cancer cell killing. Such dual-function carriers have potential to enhance the overall therapeutic outcomes of cancer gene therapy.

The synthesis and switching properties of two "basket handle" porphyrin isomers is described. The cis-oriented meso-phenyl groups of these porphyrins are linked at their ortho-positons via benzocrown-ether-based spacers, which as a result of slow atropisomerization are located either on the same side of the porphyrin plane (cis), or on opposite sides (trans). In solution, the cis-linked isomer slowly isomerizes in the direction of the thermodynamically more stable trans-isomer. In the presence of viologen (N,N'-dialkyl-4,4'-bipyridinium) derivatives, which have different affinities for the two isomers, the isomerization equilibrium could be significantly influenced. In addition, the presence of these guests was found to enhance the rate of the switching process, which was suggested to be caused by favorable interactions between the positively charged guest and the crown ethers of the receptor, stabilizing the transition state energies of the isomerization reaction between the two isomers.

The photolytic formation of thiyl radicals allows for the selective detection of total homocysteine (tHcy) in plasma after reduction and filtering. The mechanism is based on the reduction of viologens by the α-amino carbon centred radical of Hcy generated by intramolecular hydrogen atom transfer (HAT) of its thiyl radical.

Measuring humidity in dynamic situations calls for highly sensitive fast response sensors. Here we report, a humidity sensor fabricated using solution processed supramolecular nanofibres as active resistive sensing material. The nanofibres are built via self- assembly of donor and acceptor molecules (coronene tetracarboxylate and dodecyl methyl viologen respectively) involved in charge transfer interactions. The conductivity of the nanofibre varied sensitively over a wide range of relative humidity (RH) with unprecedented fast response and recovery times. Based on UV-vis, XRD and AFM measurements, it is found that the stacking distance in the nanofibre decreases slightly while the charge transfer band intensity increases, all observations implying enhanced charge transfer interaction and hence the conductivity. It is demonstrated to be as a novel breath sensor which can monitor the respiration rate. Using two humidity sensors, a breath flow sensor was made which could simultaneously measure RH and flow rate of exhaled nasal breath. The integrated device was used for monitoring RH in the exhaled breath from volunteers undergoing exercise and alcohol induced dehydration.