Non-aqueous Media Research Articles

A Preliminary Assessment of the ‘Greenness’ of Halide-Free Ionic Liquids—An MCDA Based Approach

With the growing interests in non-aqueous media for diversified applications, ionic liquids (ILs) are frequently considered as green solvents. While the environmental, health, and safety assessments of the commercially developed ILs and their ‘greenness’ status are in debate, research focus is shifting towards the application of halide-free ILs for diversified applications. To clarify the situation on their greenness, and to understand if they really possess safe characteristics, we performed an initial assessment of 193 halide free ionic liquids composed of four groups of cations (imidazolium, pyridinium, pyrrodilinium, piperidinum) and 5 groups of anions (acetate, propionate, butyrate, alkanesulfonates, alkylsulfates). The ‘Technique for Order of Preference by Similarity to Ideal Solutions’ (TOPSIS), a multi-criteria decision analysis (MCDA) tool that allows ranking many alternatives is applied by carrying out the assessment against 14 criteria that includes hazard statements, precautionary statements, biodegradability, and toxicity towards different organisms. The ranking results obtained against the set of criteria considered show that the halide free ILs placed between recommended polar solvents: methanol and ethanol can be considered to be safer alternatives in terms of ‘greenness’. The study in this work provides an initial assessment of the halide-free ionic liquids evaluated against 14 criteria in terms of their safety characteristics (“green character”) using the MCDA-TOPSIS approach.

Synthesis, structural characterization and binding ability of A2B cobalt(III) corroles with pyridine

A series of five A2B type bis-pyridine ligated cobalt complexes Co[(p-NO2Ph)2RCor](py)2, has been synthesized where R belongs to different electron withdrawing or electron donating substituent at meso position for different complexes. The synthesized complexes were fully characterized through 1H NMR, HRMS, UV–Visible and single crystal X-ray Spectroscopy. The effect of meso substituents were studied through NMR spectroscopy. The single crystal X-ray structure was obtained for the p-trifluoromethylphenyl substituents (Co-2) located at C10-meso position and indicated that cobalt corroles exist in Co(III) form. In these compounds, the axial pyridines were observed to be labile, and the complexes were almost entirely dissociated in the five coordinated cobalt corrole monopyridine complexes in dilute solutions such as in dichloromethane. Mono- and bis- pyridine ligation behavior was studied by UV–Visible spectroscopy. These complexes were also examined in different non-aqueous media such as dichloromethane, benzonitrile, and pyridine. The effect of substituent behavior present at meso position was also tested through the Hill equation. This provided the fact that the lower the electron density on corrole macrocycle, more the tendency of the complex to bind the ligands axially as the highest binding constant was found for the Co-1 complex, with more electronegative groups on meso position.

Methylcellulose/tannic acid complex particles coated on alginate hydrogel scaffold via Pickering for removal of methylene blue from aqueous and quinoline from non-aqueous media

Adsorbents reported for liquid phase decontamination under both aqueous and non-aqueous media are all dispersed phase sorbents that further require a tedious separation step post adsorption. Herein, a monolith, highly porous, and mechanically robust scaffold was synthesized for the adsorption of pollutants from both aqueous and non-aqueous media with facile separation and regeneration. Methylcellulose-tannic acid complex particles were prepared and systematically decorated on the surface of interpenetrating polymer network (IPN) scaffold via Pickering emulsion. Due to the surface coating of the particles, plausible amphiphilic adsorption of quinoline (QUI) and methylene blue (MB) was achieved from fuel and water, respectively. The hydroxyl (OH-) and carboxyl (COOH-) groups of tannic acid, alginate, and polyacrylic acid created hydrogen bonding, electrostatic interaction, acid-base interaction, and π-π stacking. Maximum adsorption capacity of 791.17 mg/g MB and 460.92 mg/g QUI was recorded with facile separation, excellent adsorbent regeneration, and reusability. Although both followed the pseudo-second-order adsorption kinetic model, a different mechanism was identified to govern the adsorption under aqueous and non-aqueous environment i.e. only the surface particles were active for QUI adsorption while the scaffold was also involved for MB adsorption.

Highly persistent triphenylamine-based catholyte for durable organic redox flow batteries

Organic redox flow batteries (ORFBs) have recently drawn significant attention as cost-effective and scalable energy storage systems, utilizing the distinct features of redox-active organic materials (ROMs), which offer chemical diversity and potential mass-scalability. Nevertheless, their inferior cycle performance compared with that of conventional inorganic-based RFBs is one of the major drawbacks limiting their practical application, which is often attributable to the chemical instability of charged ROMs during long-term operation. Herein, we present an ultra-stable triphenylamine-based molecule, tris(4-methoxyphenyl)amine or 3MTPA, which exhibits a highly stable redox reaction and rapid kinetics as a catholyte in non-aqueous media. It is demonstrated that the 3MTPA catholyte exhibits exceptionally robust radical cation stability, enabling its retention of near the theoretical capacity even after 168 h of high temperature storage in a fully charged state, while most known ROMs have not been able to achieve it and suffer from the significant degradation. Moreover, a flow cell exploiting 3MTPA is capable of delivering an unprecedentedly high capacity retention of 99.998% per cycle over 1400 cycles, opening up a new pathway toward highly durable ORFBs.

Voltammetric study of itraconazole an antifungal drug at glassy carbon electrode in acidic medium: A simple plus cost-effective detection method

In this study, the electro-oxidative behaviour and determination of itraconazole at a glassy carbon electrode have been investigated using cyclic voltammetry, differential pulse anodic stripping voltammetry (DPASV), and square wave anodic stripping voltammetric (SWASV) techniques, under different experimental conditions. The voltammetric peak current for the oxidation of itraconazole has been analyzed at different pH, scan rate and concentrations. The voltammograms have exhibited irreversible oxidation of ITRA in B.R. buffer of pH 3.0. The oxidation of itraconazole gives a well-defined irreversible peak at glassy carbon electrode vs. Ag/AgCl as reference electrode. The oxidation process is adsorption controlled. A linear response has been obtained between 26.7×10–6 to 152.8×10–6 M in non-aqueous media for all the techniques. The analyzed square wave anodic voltammetric and differential pulse anodic stripping voltammetric methods show limit of detection at 27.28 µM and 65.16 µM respectively. Ultimately, the proposed validated method has been effectively applied for the determination of the antifungal drug which is commercially available in solid form.

Solvent and moleculer structure effects on acidity strength in non-aqueous medium

The acidic properties of ten 3-alkyl(aryl)-4-[3-hydroxy-4-methoxy benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-one derivatives were investigated. In this study, isopropyl alcohol and tert‐butanol were used as an amphiprotic solvent. Aceton and N,N‐ dimethylformamide (DMF) were preferred as a dipolar aprotic solvent. Compounds were titrated with tetrabuthylamonnium hydroxide (TBAH) in isopropyl alcohol and titrimetric analyses were used potentiometric method determining the end-points, half-neutralization method determining acidity. Typical S-shaped titration graphs excepted were determined. The acidity strengths of 4,5-dihydro-1H-1,2,4-triazol-5-one derivatives in amphiprotic and dipolar aprotic solvents were calculated using tables and graphs. The pKa values obtained in the solvents were found to be differentiated. The effects of solvent, molecular structure, autoprotolysis constant dielectric constant, and leveling‐differentiation effects of the solvents upon acidity strength of the compounds were discussed.

Constructing a selective blocked-nanolayer on nanofiltration membrane via surface-charge inversion for promoting Li+ permselectivity over Mg2+

The separation of Li+ and Mg2+ is a decisive step for achieving high-grade lithium extraction from salt-lake brines to circumvent the lithium supply shortage and sustainability. However, polymer nanofiltration membranes suffer from low lithium selectivity and are hindered by complicated preparation and miniaturized scales. Here, we report a facile surface charge-inversion strategy via a unique secondary non-aqueous medium interfacial reaction of polyethyleneimine to construct a selective positive-nanolayer on nanofiltration membranes surface for selective separation of lithium ions from concentrated magnesium/lithium mixtures. The introduction of amine moieties not only increases the Donnan potential but also improves the compactness of the membrane, which simultaneously enhances the Donnan exclusion and size sieving for the Mg2+ ion with higher valence and larger hydration ion size. The surface interaction theory (DLVO) verified that the high positive-charge density provided an excellent selectivity to allow passage of Li + but reject Mg2+, and the separation factor (SLi/Mg) achieved 12.37 at a high Mg2+/Li+ mass ratio of 150. Such highly positive transmembrane potential barrier simultaneously endowed the membrane surface with the anti-fouling performance against Ca2+. We anticipate that our facile and scalable surface charge-inversion will greatly advance lithium ions permselectivity membranes design and application in lithium extraction.

Validation of quantitative determination of original substance of dipeptide threonylthreonine

Validation of the quantitative determination of the threonylthreonine substance was carried out in terms of specificity, linearity, correctness, precision, including repeatability and reproducibility. The linearity correlation coefficient of the method was 0.99998 in the range of 80–120 % of the standardized value. The calculated Student’s coefficients for the range 80, 100, 120 % are respectively equal to 1.32; 0.31; 0.55 and do not exceed the permissible limit values. The open rate was 100.07 %. The repeatability limit for one measurement group was – 0.20; for two – 0.366 in accordance with the eligibility criteria. The calculated Student’s (t = 1.34) and Fisher’s (F = 2.00) criteria for two groups of measurements did not exceed the permissible values. The developed technique for potentiometric titration of the threonylthreonine substance in a non-aqueous medium is valid.

Efficient chemical hydrophobization of lactic acid bacteria – One-step formation of double emulsion

A novel concept of stabilizing multiple-phase food structure such as emulsion using solely the constitutional bacteria enables an all-natural food grade formulation and thus a clean label declaration. In this paper, we propose an efficient approach to hydrophobically modifying the surface of lactic acid bacteria Lactobacillus rhamnosus (LGG) using lauroyl ahloride (LC) in non-aqueous media. Compared to the unmodified bacteria, cell hydrophobicity was dramatically altered upon modification, according to the higher percentages of microbial adhesion to hexadecane (MATH) and water contact angles (WCA) of LC-modified bacteria. No evident changes were found in bacterial surface charge before and after LC modification. By using one-step homogenization, all the modified bacteria were able to generate stabile water-in-oil-in-water (W/O/W) double emulsions where bacteria were observed on oil–water interfaces of the primary and secondary droplets. Modification using high LC concentrations (10 and 20 w/w%) led to rapid autoaggregation of bacteria in aqueous solution. A long-term lethal effect of modification primarily came from lyophilization and no apparent impact was detected on the instantaneous culturability of modified bacteria.

Online Stability Investigations of Platinum Electrodes in Nonaqueous Media

In the process of developing novel electrocatalysts, the focus mainly lies on finding highly active and selective materials. The stability of electrodes is often underestimated, even though a poor stability is inextricably related to economic losses. Fundamental understanding of electrode dissolution processes in nonaqueous media is not only crucial for applications like nonaqueous battery systems, sensors, capacitors but also for organic electrosynthesis. The reasons for electrode degradation are among others anodic dissolution, cathodic dissolution or cathodic corrosion. Enhanced knowledge of dissolution mechanisms, especially understanding the influence of factors like composition or structure of electrodes, electrolytes and temperature, is important to optimize the operation conditions of reactors, and with that limit electrode degradation and increase the lifetime of devices and improve processes.Coupling electrochemical measurements with an inductively coupled plasma mass spectrometer (ICP-MS), allows online stability studies and gives valuable insights into degradation mechanisms of different electrodes and catalyst materials, which are relevant in various applications. We have developed an electroanalytical flow cell (EFC) coupled to an ICP-MS, which is suitable for the use in aggressive nonaqueous electrolytes. Furthermore, the EFC is operated in an argon filled glovebox, which allows otherwise unattainably strict control of experimental conditions, like the water content of electrolytes [1,2].In order to demonstrate the capabilities of this novel method, dissolution of platinum as an ideal model system will be depicted first: this metal has excellent electrocatalytic activity and somewhat falsely supposed inertness. It is widely used in various fields of applications and its behavior in aqueous media is fairly well known. New aspects of its stability in different nonaqueous electrolytes are unveiled together with dependences on the chemical properties of the solvents and the conducting salts. While the dissolution behavior of completely water-free protic and aprotic electrolytes is very similar, the dissolution behavior changes markedly upon temperature variation or in presence of trace amounts of water.Different platinum dissolution profiles in several nonaqueous electrolytes will be discussed and dissolution mechanisms will be proposed, based on studies with changing water content. The dissolution of this electrode material has been followed during a running electrosynthesis. The correlation of possible reaction intermediates with the stability will be illustrated for a Kolbe electrolysis.Literature:[1] J. Ranninger, et al., Electrochem. Comm., 2020, 114 (106702), [2] J. Ranninger, et al., J. Electrochem. Soc., 2020, 167 (121507)

Electrochemical, EPR and Quantum Chemical Study of Pyrene-Cyclobutene Conjugates

Various biodegradable organic semiconductors are currently searched and developed for e.g. thin film transistors (OTFTs), organic light-emitting diodes (OLEDs), photovoltaic cells, sensors, radiofrequency identification tags etc. This work is focused on precursors for organic field-effect transistors – OFETs which would be based on a tetrasubstituted double bond serving as the central organic "core" (without heavy metals) and bearing photo- or redox active centers interconnected by π-conjugated bridges. These variably delocalized systems exhibit intramolecular electronic communication (charge transfer, polarizability) depending on the oxidation or excitation state.In the first part of the project, the tetrasubstituted double bond as the core was substituted by cyclobutene and cyclohexene. These "central" molecules bear various aromatic and/or unsaturated pendants, where dominating redox centre(s) are pyrene derivatives.Pyrene represents here an important structural unit which could be involved in π-delocalized systems. It can be electrochemically (and reversibly) oxidized and reduced, therefore it represents important redox center which can be used as a redox probe for more detailed investigations of electron distribution. In addition to this, pyrene exhibit fluorescence properties.For this aim, an extended series of pyrene conjugates based on the cyclobutene and cyclohexene as model precursors was synthesized and their redox properties as well as the relationship between their structure and delocalization (electron distribution) were electrochemically investigated using rotation disk voltammetry, polarography and cyclic voltammetry and their in-situ combination with simultaneously recorded EPR spectra. The experiments were performed in non-aqueous media using AN and DMF as solvents and glassy carbon and mercury (DME, HMDE) as working electrodes in order to obtain thermodynamically relevant data not influenced by solvent or electrode material. The experiments were accompanied by comparison – correlation with quantum chemical calculations.For the fundamental redox characterization, the first oxidation (Eox1) and the first reduction (Ered1) potentials are the most important. In addition to this, their difference correlates with HOMO-LUMO gap and reflects also the spectroscopic - photophysical properties. Nevertheless, we tried to analyze and interpret even the other redox steps in order to outline the redox mechanism and to understand the fate of the molecule after the primary electron transfer, that means follow-up reactions and the geometry changes connected with the changing extent of electron delocalization. Detailed analysis of electrochemical data gives information about intramolecular electron communication and reveals relationship between structure and redox properties, which is important for their tuning and further application.Although pyrene and cyclobutene derivatives seem to be totally explored, their redox properties and ET-initiated reaction mechanisms are not clear and the respective literature is missing. It is generally accepted that pyrene being reduced forms reversibly a stable radical anion and at more negative potentials unstable dianion. However, even the primary radical anion undergoes follow-up reaction yielding the same product like the dianion exhibiting thus most probably disproportionation. As the final product, we expect the 4,5-dihydro derivative, but its proof was not still successful. Gradual reduction of two directly interconnected pyrenes (1,1-dimer) involves partial irreversibility due to the slow intramolecular electron transfer caused by mutual twisting and thus limited electron communication.Similarly, electrochemical reduction of cyclobutene ring was not performed, up to now. Theoretically (based on the analogy) the ring should be reductively open giving rise the cis-disubstituted double bond, our experiments, however, point to the saturation of the double bond preserving the cyclobutane ring. In any case, it was proved that the cyclobutene bridging unit represents extension of delocalized system showing partial reversibility of its first reduction step.Whereas electrochemical oxidation of pyrenes and other aromatic substituents results in anodic polymerization and blocking of the electrode surface, the detailed reduction mechanisms are still under investigation.AcknowledgementsThis work is supported by grant GAČR 18-12150 S. The authors are grateful to Tomáš Tobrman and Peter Polák (University of Chemistry and Technology Prague) for organic synthesis of the compounds. Figure 1

(Invited) Photoelectrode Materials Design for Solar Fuels: Where Are We Now?

Solar water splitting offers an attractive solution for renewable energy storage. Ternary metal vanadates have drawn attention for use in photoelectrochemical (PEC) water oxidation due to their low band gap and photostability.1 For example, Cu2V2O7 with a ratio of CuO: V2O5 stoichiometry (2:1) is a visible light active n-type semiconductor with a low band gap (see below), and has seen use in PEC devices because of its high stability for PEC water oxidation.2 This paper describes the development of a hybrid electrochemical/thermal route for the preparation of metal vanadate thin films. Electrodeposition is a facile, low temperature method which can be deployed to prepare thin films of a target semiconductor. Also, the optoelectronic parameters (e.g., photocurrent, flat band potential) of the thin film semiconductors prepared by electrodeposition can be measured easily without any more processing steps. In addition, the thickness of a given thin film semiconductor, a crucial factor for PEC reactions, can be controlled easily in an electrodeposition process.A two-step electrodeposition strategy for ternary oxides3 was deployed in this study. Results will be presented for M-V-O ternary films (e.g., Cu2V2O7) on fluorine doped tin oxide (FTO) substrate. In the first step, a copper thin film was deposited cathodically from copper(II) nitrate in a non-aqueous medium to preclude copper oxide formation. In the second step, the copper thin film was stripped anodically in ammonium metavanadate (NH4VO3) aqueous solution to generate Cu+ and subsequent in situ precipitation with VO3 - species to yield a green CuVO3 film on the substrate. Electrochemical quartz crystal microgravimetry confirmed two- and one-electron stoichiometry for the first and second steps respectively.Finally, aspects related to film stability and charge transfer efficiency as they relates to solar water splitting, will be reviewed in the light of data from our group.

Role of Catalyst in Controlling N2 Reduction Selectivity: A Unified View of Nitrogenase and Solid Electrodes

The Haber–Bosch process conventionally reduces N2 to ammonia at 200 bar and 500 °C. Under ambient conditions, i.e., room temperature and ambient pressure, N2 can be converted into ammonia by the nitrogenase molecule and lithium-containing solid electrodes in nonaqueous media. In this work, we explore the catalyst space for the N2 reduction reaction under ambient conditions. We describe N2 reduction on the basis of the *N2 binding energy versus the *H binding energy; we find that under standard conditions, no catalyst can bind and reduce *N2 without producing H2. We show why a selective catalyst for N2 reduction will also likely be selective for CO2 reduction, but N2 reduction is intrinsically more challenging than CO2 reduction. Only by modulating the reaction pathway, like nitrogenase, or by tuning chemical potentials, like the Haber–Bosch and the Li-mediated process, N2 can be reduced.

Heme Detoxification in the Malaria Parasite: A Target for Antimalarial Drug Development.

Over the last century, malaria deaths have decreased by more than 85%. Nonetheless, there were 405 000 deaths in 2018, mostly resulting from Plasmodium falciparum infection. In the 21st century, much of the advance has arisen from the deployment of insecticide-treated bed nets and artemisinin combination therapy. However, over the past few decades parasites with a delayed artemisinin clearance phenotype have appeared in Southeast Asia, threatening further gains. The effort to find new drugs is thus urgent. A prominent process in blood stage malaria parasites, which we contend remains a viable drug target, is hemozoin formation. This crystalline material consisting of heme can be readily seen when parasites are viewed microscopically. The process of its formation in the parasite, however, is still not fully understood.In early work, we recognized hemozoin formation as a biomineralization process. We have subsequently investigated the kinetics of synthetic hemozoin (β-hematin) crystallization catalyzed at lipid-aqueous interfaces under biomimetic conditions. This led us to the use of neutral detergent-based high-throughput screening (HTS) for inhibitors of β-hematin formation. A good hit rate against malaria parasites was obtained. Simultaneously, we developed a pyridine-based assay which proved successful in measuring the concentrations of hematin not converted to β-hematin.The pyridine assay was adapted to determine the effects of chloroquine and other clinical antimalarials on hemozoin formation in the cell. This permitted the determination of the dose-dependent amounts of exchangeable heme and hemozoin in P. falciparum for the first time. These studies have shown that hemozoin inhibitors cause a dose-dependent increase in exchangeable heme, correlated with decreased parasite survival. Electron spectroscopic imaging (ESI) showed a relocation of heme iron into the parasite cytoplasm, while electron microscopy provided evidence of the disruption of hemozoin crystals. This cellular assay was subsequently extended to top-ranked hits from a wide range of scaffolds found by HTS. Intriguingly, the amounts of exchangeable heme at the parasite growth IC50 values of these scaffolds showed substantial variation. The amount of exchangeable heme was found to be correlated with the amount of inhibitor accumulated in the parasitized red blood cell. This suggests that heme-inhibitor complexes, rather than free heme, lead to parasite death. This was supported by ESI using a Br-containing compound which showed the colocalization of Fe and Br as well as by confocal Raman microscopy which confirmed the presence of a complex in the parasite. Current evidence indicates that inhibitors block hemozoin formation by surface adsorption. Indeed, we have successfully introduced molecular docking with hemozoin to find new inhibitors. It follows that the resulting increase in free heme leads to the formation of the parasiticidal heme-inhibitor complex. We have reported crystal structures of heme-drug complexes for several aryl methanol antimalarials in nonaqueous media. These form coordination complexes but most other inhibitors interact noncovalently, and the determination of their structures remains a major challenge.It is our view that key future developments will include improved assays to measure cellular heme levels, better in silico approaches for predicting β-hematin inhibition, and a concerted effort to determine the structure and properties of heme-inhibitor complexes.

Chalcogenide Dopant-Induced Lattice Expansion in Cobalt Vanadium Oxide Nanosheets for Enhanced Supercapacitor Performance

We explore the effect of sulfur doping in Co3V2O8 on the electrochemical performance of supercapacitors in terms of enhanced lattice spacing, electrochemical surface area (ECSA), electronic conductivity, and density of states. The sulfur-doped Co3V2O8 (S-Co3V2O8) nanosheets were grown in situ as a binder-free synthesis on nickel foam by the hydrothermal method. The electrochemical performance was analyzed in an aqueous alkaline electrolyte where the S-Co3V2O8 electrode exhibited a specific capacity of 410 mAh/g at 2 A/g with enhanced rate capability and capacity retention of 94.2% at 5 A/g specific currents after 4000 cycles, whereas the undoped Co3V2O8 electrode exhibited a specific capacity of 337.8 mAh/g at 2 A/g. The high capacity of S-Co3V2O8 is attributed to the enhanced ECSA (by ∼45%) and improved electrical conductivity (by ∼22%) upon doping with sulfur. Furthermore, these results corroborated with density functional theory results. The calculations suggest an increase in lattice parameters and the introduction of additional density of states near the valence-band edge due to the doping of sulfur, resulting in a decrease in charge-transfer resistance. An asymmetric supercapacitor was fabricated, using S-Co3V2O8 nanosheets as the cathode and activated carbon as the anode, which shows a high specific capacity (or capacitance) value of 485 mAh/g, an energy density of 36.4 W h/kg, and a power density of 740 W/kg at 2 A/g with 98.4% specific capacity retention after 4000 consecutive charge–discharge cycles. Furthermore, the analysis was extended in a nonaqueous medium for Li-ion storage where S-Co3V2O8 exhibits a specific capacity of 994 mA h/g and a specific energy density of 828 W h/kg at 1 A/g making it a promising candidate for future high-energy storage systems. The concept of doping is extended to other chalcogenide (e.g., selenium) doping (Se-Co3V2O8), which also shows improved device performance and makes this a versatile approach for high-performance devices.

An insight into the solvatochromic and photophysical behaviours of biowaste-origin carbon nanodots

In this work, C-dots were synthesised inexpensively, using hydrothermal, one-step pathway from persimmon peel biowaste. The prepared C-dots were investigated by UV–Vis spectroscopy, photoluminescence spectroscopy, XRD, TEM, CHN, FE-SEM and FT-IR. It was found that the C-dot is amorphous in nature, spherical in shape, narrow-sized, monodispersed, polar functionalised with average 2 nm size and highly dispersible in aqueous and non-aqueous media. Optical study in wide range of solvents, exhibited excitation wavelength dependency of photoluminescence, bathochromic and hypsochromic shifts in absorption and emission spectra and incredibly high quantum yields ranging from 10% to 60%. It was shown that the C-dot could be exploited as nanoprobe for polarity of medium in addition as fluorescent chemical sensing platform for some metal ions. Analyses resulted in different functional groups on the surface (carboxylic, carbonyl, amine, amide and hydroxyl) and led us to treat the solvatochromic method as convincing argument to resolve the dilemma of whether or not which functional groups are responsible for the intriguing observed optical properties. The increasing trend of emission efficiencies of homologues alcohols was interpreted in terms of exoergic (specific and non-specific) interaction parameters included in Kamlet-Taft’s equation along with the endoergic solubility parameters and correspondingly the stiffness of solvent.

Electrochemical characterization of β,β′-butanoporphyrins containing sterically hinderedmeso-2,6-dihalogenophenyl substituents and first-row transition metal ions in nonaqueous media

Six [Formula: see text],[Formula: see text]-butano substituted metalloporphyrins containing sterically hindered meso-dihalogenophenyl substituents and first-row transition metal ions were synthesized and their electrochemical and spectroelectrochemical properties were characterized in nonaqueous media. The investigated compounds have the general formula butano(Y2Ph)4PorM, where Por is a dianion of the porphyrin, M = Mn[Formula: see text]Cl, Fe[Formula: see text]Cl, Co[Formula: see text], Ni[Formula: see text], Cu[Formula: see text] or Zn[Formula: see text]and Y2Ph is a sterically hindered 2,6-F2Ph or 2,6-Cl2Ph group on each of the four meso-positions of the macrocycle. The electrochemistry of each porphyrin was examined in CH2Cl2or pyridine containing 0.1 M tetra-[Formula: see text]-butylammonium perchlorate. The first one-electron reduction is metal-centered for the manganese(III), iron(III) and cobalt(II) porphyrins to generate the Mn(II), Fe(II) and Co(I) porphyrins, but it is porphyrin ring-centered for the other examined M(II) porphyrins to give porphyrin [Formula: see text]-anion radicals under the given solution conditions. The effect of the [Formula: see text],[Formula: see text]-butano and sterically hindered meso-Y2Ph substituents on redox potentials and electron transfer mechanisms are discussed and compared to what was previously reported for butano-substituted tetraarylporphyrins without hindered meso-substituents.

Pentadentate Copper(II)-amidate complex as a precatalyst for electrocatalytic proton reduction

Electrochemical reduction studies of a mononuclear Cu(II) complex bearing a pentadentate amidate ligand under both aqueous and non-aqueous media revealed the deposition of a heterogeneous film on the electrode. The heterogeneous film was grown on an FTO working electrode by control potential electrolysis (CPE) at −0.9 V vs. NHE for 3 h (pH 3.0, phosphate buffer). Characterization of the electrodeposited film by SEM, EDX and XPS indicates the preferential formation of Cu2O. The FTO/Cu2O cathode, thus formed, exhibits electrocatalytic proton reduction in acidic aqueous medium (pH 3.0) with 95% Faradaic efficiency at moderate overpotential (η = 320 mV at onset). The overpotential required to reach 1 mA/cm2 is 530 mV. The FTO/Cu2O cathode maintained a current density of 2.5 mA cm−2 for a period of 3 h and showed stability after 200 scan cycles.

Thermodynamic properties of cotton dyeing with indigo dyes in non-aqueous media of liquid paraffin and D5

On the basis of investigation into the dyeing equilibrium of cotton fibers with indigo dyes in decamethylcyclopentasiloxane (D5), liquid paraffin and water, the thermodynamic properties of cotton dyeing with indigo dyes in non-aqueous medium systems were studied in comparison with aqueous dyeing. The main works involved are as follows: firstly, the adsorption isotherms were created; then, the three theoretical adsorption models of Nernst, Langmuir and Freundlich were used to fit the adsorption isotherms created; finally, the thermodynamic parameters were calculated. The results showed that the adsorption isotherms were all in line with the Freundlich model. The order of dyeing affinity was in the sequence: liquid paraffin > D5 > water. The dyeing entropy in the three media showed positive values, which is mainly attributed to the adsorption of both indigo-leuco and water onto cotton fibers, thus reducing the ice-like structure formed among the water molecules in the dyeing system and the hydrophobic bonding structure formed among the non-aqueous medium molecules, then leading to an increase in the system disorder. The dyeing heat in the three media also showed positive values, due mainly to the absorption of thermal energy to “melt” the ice-like structure and to “break” the hydrophobic bonding structure. These dyeing thermodynamic properties are conducive to understanding and interpreting the dyeing performance and behavior of indigo dyes in non-aqueous dyeing systems.

The Hydrophobic Effect in Chemistry, Biology and Medicine: An Update

The roots of the hydrophobic effect (HE) apparently lie in certain chemical principles, although it has far-reaching implications across a swath of chemical biology. In particular, the HE drives the formation of micelles, the catalytic properties of which are believed to model the action of enzymes. The HE is also believed to be the key to drug-receptor interactions as captured in the Hansch equation and enshrined in QSAR.
 Yet, the HE remains paradoxical: The attributed medium effects apparently contravene normal experience, as apolar solvents are rarely (if ever) the preferred choice in practice! Indeed, the HE is complex and varied in its manifestations, affecting both structure and reactivity. The latter “kinetic hydrophobic effect” itself exists as “Types 1 and 2”, referring to reactions in water (e.g., Diels Alder) and non-aqueous media (e.g., micelles) respectively.
 Micellar reactivity also remains mysterious as, apparently, the HE only facilitates the formation of the micelles. The idea that micellar reactivity arises from concentration effects, in fact, appears simplistic for several reasons. Furthermore, reactions may well occur on the micellar surface, particularly with ionic reagents that would be poorly soluble in the core.
 There are important differences between micelles and enzymes: Enzymes are pre-configured with catalytic groups and charge-relay systems, although the contribution of the HE to activity remains uncertain. Micelles also form a separate phase, hence defining the thermodynamic ground state of the reactants (contrasting with enzymes).
 Certain aspects of the Hansch equation, particularly the decline of drug activity beyond the “Goldilocks zone” peak, are intriguing. However, a kinetic model of drug-receptor interactions based on the rates of drug binding and release, offers an explanation for the observations, also leading to further insights into the nature of the binding itself.