Alcoholic Solvents Research Articles

One‐pot synthesis of graphene oxide/poly(furfuryl alcohol) in deep eutectic solvent: A metal‐free electrocatalyst for non‐enzymatic glucose sensor application

AbstractA facile strategy is presented for the preparation of poly(furfuryl alcohol) functionalized graphene oxide (GO‐f‐PFA) by using Diels‐Alder (DA) click chemistry in deep eutectic solvent (DES), and its application in glucose sensing. The GO‐f‐PFA hybrid was obtained in a one‐pot procedure involving the polymerization reaction of furfuryl alcohol (FA) and subsequent DA reaction of poly(furfuryl alcohol) (PFA) with graphene oxide (GO). Both reactions were conducted in DES formed by the mixture of choline chloride: zinc chloride under assistance of ultrasonication without any catalyst. The highest percentage of grafted PFA in GO‐f‐PFA was 82.1 % at the DES/FA feeding weight ratio of 10. GO‐f‐PFA materials were analyzed by TGA, FTIR, XRD, Raman, SEM‐EDX and dispersion capacities were evaluated in various solvents such as water, ethanol, N,N’‐dimethylformamide, tetrahydrofuran, chloroform, and p‐xylene. GO‐f‐PFA was used as a free‐metal electrocatalytic material to fabricate the electrode for the recognition of glucose. The highest current density of GO‐f‐PFA was achieved to be 0.252 mA·cm‐2 using 10 mM glucose recorded at the potential of 0.7 V. These results have suggested the potential application of bio‐based materials for the fabrication of glucose biosensor.

Fabrication of oxygen doped g‐C3N4 through the formation of a supramolecular precursor for the enhanced photocatalytic degradation of sulfonamides

AbstractBACKGROUNDGraphitic carbon nitrate (g‐C3N4) is considered a promising metal‐free photocatalyst. However, the applications of pristine g‐C3N4 are subject to the high recombination of electron‐hole pairs and low solar utilization. This study aimed to develop a unique and effective method to synthesize oxygen‐doped g‐C3N4 with enhanced photocatalytic activity for pollutant treatment.RESULTSOxygen‐doped g‐C3N4 photocatalysts (CN(M), CN(E), CN(I), and CN(P)) were successfully synthesized via the thermal polycondensation of a novel supramolecular precursor based on urea and monobasic alcohol, in which the urea and alcohol solvent can fully interact through a cross‐linking network fabricated by H‐bonding. The as‐prepared catalysts exhibited enhanced catalytic activity compared with g‐C3N4 on the photocatalytic oxidation of sulfanilamide antibiotics (SMR). The structure of alcohol has an influence on the amount of oxygen doping and on the catalytic activity of oxygen‐doped g‐C3N4; the optimized photocatalytic performance was achieved on CN(I). By combining characterization results, the improved catalytic activity was mainly ascribed to a certain amount of highly electronegative O atoms being doped into the tri‐s‐triazine units of g‐C3N4, which can optimize the basic chemical structure, thus improving light‐harvesting and increasing the separation rate of electron‐hole pairs. In addition, trapping experiments indicated that •O2− is the main active species in the photocatalytic degradation of sulfamethazine.CONCLUSIONThis work provides a facile and efficient approach for the fabrication of an O doped g‐C3N4 catalyst with promising photocatalytic performance on SMR degradation. © 2022 Society of Chemical Industry.

Screening, packing systematics, Hansen solubility parameters and desolvation of resmetirom (MGL-3196) solvates

Resmetirom (MGL-3196) can form masses of solvates with a variety of solvents. In this study, a series of solvates, including those reported in patents and newly discovered solvates, were prepared by experimental screening. Hansen solubility parameters (HSPs) were used to investigate the formation rules of MGL-3196 solvates, and the results showed that the formation of MGL-3196 solvates was most related to the parameterΔδt. When the Δδt value between MGL-3196 and solvent was less than 14.23 MP0.5 a, MGL-3196 tended to form solvate with an accuracy of 84.09%. The precise crystal structures of six solvates and one solvent-free form (form A) were acquired by single crystal X-ray diffraction (SCXRD). After analyzing the structures of obtained solvates in-depth from the aspects of conformation, dimeric synthon, molecular packing, porosity and isostructuralism, the six solvates were classified into alcohol solvates (group 2), ester solvates (group 3) and other types of solvates (group 1). Generally, these three groups of solvates had completely different crystal structures. The solvates in group 1 and group 3 were channelized and isostructural in which solvents could be substituted without great influence on the structure, while in the alcohol solvates (group 2) solvents were fixed by strong hydrogen bonds to be a part of the crystal structure. Moreover, when solvates were desolvated, two metastable solvent-free forms (i.e., B and C) were crystallized and then transformed to form A through a structural rearrangement. The possible mechanisms for the phase transformation during different desolvation processes were finally proposed. All results shall provide an understanding and inspiration on the screening and production of polymorphic and pseudopolymorphic forms of MGL-3196 for the pharmaceutical industry.

Lubrication Performance and Mechanism of Electrostatically Charged Alcohol Aqueous Solvents with Aluminum–Steel Contact

Alcohol aqueous solvents were prepared by individually adding n-propanol, isopropanol, 1,2-propanediol, and glycerol to deionized water for use as lubricants for the electrostatic minimum quantity lubrication (EMQL) machining of aluminum alloys. The tribological characteristics of those formulated alcohol solvents under EMQL were assessed using a four-ball configuration with an aluminum–steel contact, and their static chemisorption on the aluminum surfaces was investigated. It was found that the negatively charged alcohol lubricants (with charging voltages of −5 kV) resulted in 31% and 15% reductions in the coefficient of friction (COF) and wear scar diameter (WSD), respectively, in comparison with those generated using neutral alcohol lubricants. During the EMQL, static charges could help dissociate the alcohol molecules, generating more negative ions, which accelerated the chemisorption of those alcohol molecules on the aluminum surfaces and thereby yielded a relatively homogeneous-reacted film consisting of more carbon and oxygen. This lubricating film improved the interfacial lubrication, thus producing a better tribological performance for the aluminum alloys. The results achieved from this study will offer a new way to develop high-performance lubrication technologies for machining aluminum alloys.

Critical Review of the Various Reaction Mechanisms for Glycerol Etherification

This review provides in-depth coverage of numerous mechanisms available for the etherification process of glycerol, including alcohol solvent, olefin solvent and solvent-free routes along with products that are formed at various stages of the reaction. Mono tert-butyl glycerol ether (MTBG), di tert-butyl glycerol ether (DTBG), and tri tert-butyl glycerol ether (TTBG) are the three general ether compounds obtained through tert-butyl alcohol (TBA) etherification. Glycerol etherification with n-butanol results in the formation of glycerol ether products that are linked to the substituted butyl groups. These products include two mono-butyl glycerol ethers, two di-butyl glycerol ethers and a tri-butyl glycerol ether. Two mono-benzyl glycerol ether isomers, two di-benzyl glycerol ether isomers and tri-benzyl glycerol ether are the most reported results when benzyl alcohol is used as a solvent in the etherification reaction. The etherification of glycerol with 1-butene involves a series of equilibrium reactions to produce mono-ethers, di-ethers, and tri-ethers, whereas the etherification of glycerol with isobutene is carried out via tert-butylation of glycerol, yielding similar glycerol ether products when TBA is used as a solvent. As the by-product may be easily removed, the solvent-free glycerol etherification approach may have several advantages over the other conventional methods. Therefore, further studies on base-catalyzed glycerol etherification that employs a solvent-free reaction route may reveal a method for improving the conversion, selectivity, and yield of reaction products. This review study is crucial in improving knowledge of numerous mechanisms and how they relate to the effectiveness of the product’s catalytic process.

Excellent Adsorption of Dyes via MgTiO3@g-C3N4 Nanohybrid: Construction, Description and Adsorption Mechanism

This report investigates the elimination of hazardous Rhodamine B dye (RhB) from an aqueous medium utilizing MgTiO3@g-C3N4 nanohybrids manufactured using a facile method. The nanohybrid MgTiO3@g-C3N4 was generated using an ultrasonic approach in the alcoholic solvent. Various techniques, including HRTEM, EDX, XRD, BET, and FTIR, were employed to describe the fabricated MgTiO3@g-C3N4 nanohybrids. RhB elimination was investigated utilizing batch mode studies, and the maximum removal was attained at pH 7.0. The RhB adsorption process is more consistent with the Langmuir isotherm model. The highest adsorption capacity of MgTiO3@g-C3N4 nanohybrids for RhB was determined to be 232 mg/g. The dye adsorption followed a pseudo-second-order model, and the parameters calculated indicated that the kinetic adsorption process was spontaneous. Using ethanol and water, the reusability of the nanomaterial was investigated, and based on the results; it can be concluded that the MgTiO3@g-C3N4 nanohybrids are easily regenerated for dye removal. The removal mechanism for the removal of RhB dye into MgTiO3@g-C3N4 nanohybrids was also investigated.

Ligand-enabled Ni-catalyzed hydroarylation and hydroalkenylation of internal alkenes with organoborons

The transition metal-catalyzed hydrofunctionalization of alkenes offers an efficient solution for the rapid construction of complex functional molecules, and significant progress has been made during last decades. However, the hydrofunctionalization of internal alkenes remains a significant challenge due to low reactivity and the difficulties of controlling the regioselectivity. Here, we report the hydroarylation and hydroalkenylation of internal alkenes lacking a directing group with aryl and alkenyl boronic acids in the presence of a nickel catalyst, featuring a broad substrate scope and wide functional group tolerance under redox-neutral conditions. The key to achieving this reaction is the identification of a bulky 1-adamantyl β-diketone ligand, which is capable of overcoming the low reactivity of internal 1,2-disubstituted alkenes. Preliminary mechanistic studies unveiled that this reaction undergoes an Ar-Ni(II)-H initiated hydroarylation process, which is generated by the oxidative addition of alcoholic solvent with Ni(0) species and sequential transmetalation. In addition, the oxidative addition of the alcoholic solvent proves to be the turnover-limiting step.

Performance of alcoholic solvents in the continuous countercurrent spent coffee grounds oil extraction

Ethanol and isopropanol, absolute (ET0, IPA0) and hydrated with 6 and 12 water mass% (ET6, IPA12), were evaluated as solvents in the oil extraction from spent coffee grounds (SCGO). Alcohols' performance evaluation was based on the SCGO partitioning between extract and raffinate phases and the extractor design. An SCGO concentration limit in systems containing ET indicates extract phase saturation. In this case, a Langmuir-type equation provided a satisfactory SCGO partitioning data mathematical description, while the IPA data presented a linear behavior. The increase in temperature from 60 to 80 °C did not affect SCGO partitioning when IPA0 was used as a solvent. ET6 required higher solvent proportions concerning SCG, leading to extractors with a higher number of theoretical stages. The minimum flow rates of ET6 were 1.9 times higher than those required by ET0 and IPA12 and up to 3.2 times higher than the IPA0 flow rate at 60 °C. At 80 °C, the SCGO extraction performance with ET0 and IPA0 was similar. A solvent-to-feed ratio of at least five must be used when an extractor with five theoretical stages operating at 80 °C is considered. In this case, extracts with about 5 mass% of SCGO are obtained.

Pd/C embedded crosslinked polystyrene fibers as an efficient catalyst for Heck reactions

AbstractPd/C embedded polystyrene fibers were successfully prepared by electrospinning. The polystyrene molecules were then cross‐linked by paraformaldehyde in sulfuric acid to improve the solvent resistance of composite fibers. SEM images conformed the preparation of uniform and smooth composite fibers. FT‐IR spectra demonstrated that the polystyrene molecules inside fibers have been sulphonated and crosslinked. Heck reactions were used to evaluate the catalytic performance of these novel composite fibers. The catalysis results show that this composite fiber mat catalyzed Heck reactions could be evidently promoted by using preferred reducing alcohol agent and solvent. Under the optimized reaction conditions, this composite fiber mat could effectively catalyze the Heck reactions of aromatic iodides with n‐butyl acrylate to afford the products with satisfied yields. Especially, compared with the particulate Pd/C catalyst, the separation and recycling of this fibrous catalyst from the reaction mixture were significantly improved due to the larger fibrous structure. At last, this fiber catalyst was successfully reused for eight times with little loss of initial catalytic activity, which was even better than the pristine Pd/C catalyst. Hence, embedment of particulate supported metal catalysts inside the crosslinked polystyrene fibers can effectively improve their catalytic performance and handiness.

Simultaneous adsorptive removal of three fluoroquinolones using humic acid modified hydrogel beads.

This study elaborates the simultaneous removal of three different fluoroquinolones (FQs), i.e., Norfloxacin (NOR), Lomefloxacin (LOM), and Enrofloxacin (ENR) from water using hydrogel beads of humic acid coated biochar (HA-BC) and chitosan. In our previous study, this adsorbent has already achieved tremendous results for the removal of a single FQ, i.e., ciprofloxacin. Now, initial concentrations of all FQs were set 100mg/L each, and the maximum adsorbed amounts were 38.08mg/g (NOR), 25.03mg/g (LOM), and 29.72mg/g (ENR). Adsorption attained equilibrium after 24h, which obeyed the pseudo-second-order kinetic model. The mutation of humic acid-biochar/chitosan hydrogel beads (HBCB) with alcoholic solvents, i.e., methanol and ethanol to replace water decreased its sorption capacities from 38.08mg/g (NOR) to 34.91mg/g and 32.19mg/g, respectively. Similarly, from 25.03mg/g (LOM) to 22.81mg/g and 19.91mg/g, and 29.72mg/g (ENR) to 26.52mg/g and 24.64mg/g. Adsorption isotherm data for all FQs were up to both Langmuir and Freundlich, but it suited more to that of Langmuir adsorption isotherm model. Sorption capacities, for all FQs, had a minor decline due to addition of NaCl, NaNO3, and Na2SO4. However, there was a huge decline when Na3PO4 was added into the adsorption system. Adsorbent was desorbed and regenerated for consecutive removal, and it showed good adsorption in the 4th cycle, i.e., 47mg/g net adsorption. These results prove that HBCB is not only effective for adsorption removal of ciprofloxacin but also for other FQs too.

Physico-chemical parameters for the assembly of moxifloxacin hydrochloride and cetyltrimethylammonium chloride mixture in aqueous and alcoholic media

The aggregation behavior of the mixture of cetyltrimethylammonium chloride (CTAC), a cationic surfactant, and moxifloxacin hydrochloride (MFH), a fourth-generation fluoroquinolone antibiotic drug, has been studied using the conductivity technique in aqueous and alcoholic (EtOH, 1-PrOH, and 2-BuOH) media. The study was performed at several temperatures between 298.15 and 323.15 K at 5 K intervals. The assembly has been characterized by evaluating the micellar parameters, such as the critical micelle concentration (CMC) and the counter ion binding (β), of the CTAC + MFH mixture. The values of the CMC for the assembly of the CTAC + MFH mixture were reliant on the composition of alcohols in the mixed solvents and the temperature. The CMC values of the CTAC + MFH mixture increased with increasing temperature; that is, assembly was delayed by increased temperature. The micellization of the CTAC + MFH mixed system was delayed in alcoholic media. The observed -ΔGm0 values for the association of the CTAC + MFH mixed system demonstrated a spontaneous aggregation process under all study conditions. Based on the -ΔHm0 and +ΔSm0 values, the association of the CTAC + MFH mixture is exothermic and the interaction forces acting between the CTAC and MFH species are hydrophobic, ion–dipole, and electrostatic interactions. The transfer properties and enthalpy–entropy compensation were also assessed and described comprehensively.

Modeling hydrogen solubility in alcohols using group method of data handling and genetic programming

Having accurate information about the solubility of hydrogen (H2) in alcoholic solvents is crucial for the design and implementation of numerous chemical processes. In this communication, two robust correlative techniques, Genetic programming (GP) and Group method of data handling (GMDH) were used to estimate H2 solubility in alcohols. For the mentioned purpose, 673 laboratory data of H2 solubility for 26 distinct alcoholic solvents were collected over a broad interval of operating pressure from 0.101 MPa to 110.3 MPa and temperature from 213.15 K to 524.9 K. These solvents include fatty alcohols, aliphatic alcohols, diols, glycols, and hydroxypolyether with molecular weights ranging from 32.042 to 242.446 g/mol. The algorithms' input parameters were selected to be molecular weight of alcohol, the temperature and pressure of the solubility system, critical temperature and pressure of alcohols. According to the graphical and statistical assessments, the GMDH model was shown to be the best choice for estimating H2 solubility in alcoholic solvents, with a root mean square error of 0.00482 and a coefficient of determination of 0.9841. Furthermore, according to sensitivity analysis, the greatest influence on H2 solubility in alcoholic solvents is dedicated to pressure, temperature, and molecular weight of alcohols. Furthermore, the Leverage technique was used to identify the application domain of the GMDH model and outlier data, with the findings indicating that GMDH has a high credit for estimating H2 dissolution in alcoholic media.

Solubility measurement and correlation of 2-aminoterephthalic acid in eight alcoholic solvents at different temperatures

This research experimentally measured the solubility of 2-aminoterephthalic acid in eight pure alcoholic solvents – methanol, ethanol, 1-propanol, 1-butanol, 2-propanol, 2-butanol, 2-methyl-2-propanol, and 3-methyl-1-butanol – from 303.15 to 338.15 K at normal pressure p = 0.1 MPa by the excess solid method. The measured solubility of 2-aminoterephthalic acid in these pure organic solvents was found to increase with the rise of temperature in the following order: 3-methyl-1-butanol (lowest solubility) < 1-butanol < 2-butanol < 1-propanol < 2-methyl-2-propanol ≈ 2-propanol < ethanol < methanol (highest solubility). The experimental solubility was correlated by the Van’t Hoff equation and the λh (Buchowski) equation. The apparent thermodynamic properties (Δ0Gsol, Δ0Hsol and Δ0Ssol) were calculated by the Van’t Hoff equation, from which it was concluded that the dissolution process is entropy-motivated and endothermal. In addition, the solvent effects on 2-aminoterephthalic acid solubility were studied by the KAT-LSER model, where the results showed that the polarizability accounts for 47.9 ± 4.2 % of the total solvent effect.A volcano-type relation between the dissolution entropy and enthalpy versus the solvent boiling point is reported, showing maximal values of 55.3 J mol−1 K−1 and 29.2 kJ mol−1, respectively, for intermediate molecular interactions of solute and solvent.

α-Carbonyl Radicals from N-Enoxybenzotriazoles: De Novo Synthesis of 9-Phenanthrols.

Visible-light-induced energy transfer to N-enoxybenzotriazoles in the presence of hydrogen atom donors or alcoholic solvents led to α-carbonyl radicals. The utility of the α-carbonyl radicals was demonstrated in intramolecular tandem cyclization and in the synthesis of 9-phenanthrols and their analogues. The mechanistic experiments suggested that quenching of the reactive benzotriazolyl radical by the alcohol was accompanied by the formation of an α-hydroxy radical that mediated hydrogen atom transfer or, itself, oxidized into aldehydes.

Recrystallization and grain growth by intense pulsed light with mixed solvent annealing for efficient perovskite solar cells

A novel processing technique using a two-step intense pulsed light (IPL) with a mixed solvent annealing method to increase the grain size of perovskite film was investigated. Three annealing methods [thermal, IPL, and IPL with mixed solvent] were contrasted in the perovskite recrystallization procedure. The grain size of the recrystallized perovskite films according to the composition of the mixed solvent [a mixed solvent of chlorobenzene (a non-solvent) and isopropyl alcohol (a solvent)] was determined through atomic force microscope and X-ray diffraction (XRD), and compared with those of produced using the traditional annealing method (thermal and IPL). The surface roughness of the films made with IPL with mixed solvent was significantly increased compared to previous techniques. The grain size of the perovskite films was obtained through the analysis of scanning electron microscope images; the average grain sizes of thermal, IPL, and IPL with mixed solvent annealing were 217, 351 and 381 nm, respectively. The grain orientation of the formed perovskite films was investigated through XRD analysis, and the alignment of the grains could be discovered through the peak intensity ratio analysis of these grain planes. Through this structural and spatial alignment analysis, it was found that the new annealing process produces a larger (converted to monocrystalline-like grains) and anisotropic (normal to the substrate plane) perovskite grains than the traditional annealing method. The power conversion efficiency of the device fabricated in an ambient condition by the new annealing approach was 11.39 ± 0.36% (maximum value was 11.86%), which was nearly 8% higher than that of the device fabricated by the traditional annealing method. • Developed a novel process for perovskite recrystallization. • Used a combined process of mixed solvent and intense pulsed light annealing. • Formed highly oriented anisotropic large perovskite grains.

In-situ catalytic hydro-liquefaction of Delonix regia lignocellulosic biomass waste in hydrogen-donor solvent

Wastes from forestry residues and tree felling have been a major waste management concern since a long time. This issue had been addressed in this work where utilization of waste Delonix regia biomass by hydro-liquefaction in a hydrogen-donor solvent (methanol) and in presence of Ni–Al co-precipitation catalyst at different temperatures and a fixed pressure have seen to provide synergistic results not only in terms of yield of liquid products but also their higher heating values. To the best of authors’ knowledge, no studies have been testified in the literature using such co-precipitation catalyst for Delonix regia biomass liquefaction. The hydrogen donating capability of alcoholic methanol solvent in the hydro-liquefaction process along with existence of hydrogen rich environment, caused by supply of initial external hydrogen pressure, explained high yield of liquid products. A maximum higher heating value (HHV) of 26.31 MJ/kg for biocrude, obtained at 200 °C and 80 bar final reactor pressure for 60 min reaction time, depicted the potentiality of Ni–Al catalyst in reducing oxygen content of biocrude by partial hydrogenation during the liquefaction process. Apart from this, biocrude showed presence of long chain alkanes, esters, aldehydes and ketones in them. The low phenol content of the biocrude as found from Gas Chromatography-Mass Spectrometry (GC-MS) results were an indication of its less hazardous and toxic nature. The free-flowability and porous nature of solid biochar from this hydro-liquefaction process was a sign of their effectiveness in soil remediation processes and wastewater treatment. Finally, physical properties and fuel potential of biocrude obtained in this process were superior compared to those of bio-oil obtained by catalytic, non-catalytic and hydro-catalytic pyrolysis of same biomass conducted at elevated temperature of 600 °C.

Catalytic synthesis of sucrose‐6‐acetate by lipase in DMF composite solvent

AbstractBACKGROUNDHigh selectivity, fewer reaction steps, and energy conservation are the most important advantages of the enzymatic synthesis of sucrose‐6‐acetate. To improve the enzymatic synthesis efficiency, a solvent system involving N,N‐dimethylformamide (DMF) for lipase‐catalyzed synthesis of sucrose‐6‐acetate was studied.RESULTSUsing Lipozyme TL IM as the catalyst, tert‐amyl alcohol was screened out as the auxiliary solvent and complexed with DMF at 1/1 (v/v) ratio. The optimized technology conditions for the enzymatic synthesis of sucrose‐6‐acetate in the above solvent system were as follows: 100 ml composite solvent with sucrose (2.0%, w/v), vinyl acetate (2.90 M), and Lipozyme TL IM (20 mg/ml) was oscillated at 160 rpm in a water bath at 45 °C for 16 h. The esterification rate and the 6‐position esterification rate of sucrose were 88.9 ± 1.3% and 94.2 ± 1.2%, respectively. Raising the sucrose concentration to 7.0% and reacting by mechanical stirring at 45 °C in 1000 ml composite solvent could also achieve ideal esterification effects (esterification rate: 87.2 ± 1.0%, 6‐position esterification rate: 90.7 ± 1.6%).CONCLUSIONSAs a reaction medium for the enzymatic synthesis of sucrose‐6‐acetate, the DMF/tert‐amyl alcohol solvent was significantly more efficient than the DMSO composite solvent reported in the literature; therefore, the studied solvent could be an ideal application prospect. © 2022 Society of Chemical Industry (SCI).

Divergent regioselective Heck-type reaction of unactivated alkenes and N-fluoro-sulfonamides

The control of regioselectivity in Heck-type reaction of unactivated alkenes represents a longstanding challenge due to several detachable hydrogens in β–H elimination step, which generally afford either one specific regioisomer or a mixture. Herein, a copper-catalyzed intermolecular Heck-type reaction of unactivated alkenes and N-fluoro-sulfonamides with divergent regioselectivities is reported. The complete switch of regioselectivity mainly depends on the choice of different additives. Employment of alcohol solvent gives access to vinyl products, while the addition of carboxylate leads to the formation of allylic products. In addition, exclusion of these two promoting factors results in β-lactams via a C–N reductive elimination. This protocol shows a broad substrate scope for both alkenes and structurally diverse N-fluoro-sulfonamides, producing the corresponding products with excellent regio- and stereoselectivities. Further control experiments and DFT calculations provide in-depth insights into the reaction mechanism, highlighting the distinct effect of the additives on a bidentate auxiliary-stabilized Cu(III) intermediate.

Dissolution of 5-azacytidine in aqueous solution of alcohols at various temperatures: Preferential solvation and thermodynamic analysis

In this work, the dissolution process of 5-azacytidine in mixtures of (methanol + water), (ethanol + water), (n-propanol + water) and (isopropanol + water) at several temperatures was studied and correlated by Jouyban-Acree model and CNIBS/R-K model. In pure solvent, the maximum solubility is observed in water (1.862 × 10-3) followed by isopropanol (1.025 × 10-4), ethanol (5.804 × 10-5), methanol (4.280 × 10-5) and n-propanol (3.478 × 10-5) at 318.15 K. In the mixed solvent, with the increasing water molecules around the solute molecules, the polarity of the solvent system increases, which is conducive to the dissolution of solute molecules. According to the preferential solvation results in water-rich mixtures, it is possible that 5-azacytidine is acting as a Lewis acid due to the more basic alcoholic solvent molecules respect to water. –OH and –NH2 in 5-azacytidine provide hydrogen protons to form hydrogen bonds with oxygen atoms on alcohol molecules. While in the mixtures with compositions of 0.30 < x1 < 1 for methanol, 0.20 < x1 < 1 for ethanol, 0.15 < x1 < 1 for n-propanol and isopropanol, 5-azacytidine molecule is preferential solvation by water and acting as a Lewis base in front to alcohols. The calculation of thermodynamic properties for the whole composition range of aqueous binary mixtures indicates the dissolution process is endothermic and entropy-increasing. Moreover, the enthalpy is the main contributor to Gibbs energy of the solution process in each binary mixtures. The experimental solubility data and thermodynamic parameters of 5-azacytidine achieved in present work could be very useful in drug development method, purification and crystallization.

(Digital Presentation) A Two-Electron Transition Metal Based Redox Mediator for Dye-Sensitized Solar Cells

Since the first report of a Dye Sensitized Solar Cells (DSSC), I3 -/I- has been as staple redox mediator because of its efficient 2e- redox cycle. However, tuning this mediator is challenging given its atomic nature. Here we present the combination of a multielectron redox cycle with a tunable transition metal complex as an alternative redox mediator in DSSCs. This research focuses on using the [NiIV(R2dtc)3]+/NiII(R2dtc)2 redox couple, where dtc- is a bidentate dithiocarbamate ligand with R = ethyl and butyl groups. DSSC device measurements under low light intensity and 1 sun illumination showed the highest efficiency of 8% at 10,000 lux for [NiIV/II(Et2dtc)3/2]+/0, whereas [NiIV/II(Bu2dtc)3/2]+/0 displayed a high of 20% at 4660 lux. To investigate the individual roles of reduced and oxidized mediators, comparative photoelectrochemical studies between reduced mediators, Ni(dtc)2 and I- were performed in a photoelectrochemical cell with an external white light LED along with a photoanode consisting of FTO/TiO2 sensitized with the N3 dye. Ni(Et2dtc)2 and Ni(Bu2dtc)2 showed 75 μA and 100 μA more photocurrent respectively than iodide in the case of the highest irradiance (100 mW/cm2). These studies show the NiII(R2dtc)2 is a superior mediator for dye regeneration. Likewise, the photovoltage was much greater in the case of nickel mediators, NiII(Et2dtc)2 (800 mV) and NiII(Bu2dtc)2 (860 mV) than iodide (560 mV), consistent with ERedox = 0.02 V for the Ni(IV/II) couple, which is 0.32 V greater than ERedox for I3 -/I-. Surprisingly, as [NiIV(R2dtc)3]+ was introduced into the electrolyte the observed photocurrent became dynamic with time and continued to show photoanodic current even at 100% NiIV. These results are consistent with [NiIV(R2dtc)3]+ photodissociation to yield NiII(dtc)2. Preliminary studies on this photodissociation have been done by a UV-Vis kinetic analysis in various solvents. [NiIV(R2dtc)3]+ showed a prolonged dissociation in dichloromethane and chloroform while dissociation was much quicker in acetonitrile. An unknown intermediate was observed in the case of alcohol solvents which suggests a two-step mechanism for dissociation. Taken together, NiIV/II represents alternative redox mediator with outstanding dye regeneration capabilities, but complications due to photodissociation of [NiIV(R2dtc)3]+. Further studies are underway to investigate the impact of photodissociation on the redox cycle and electron-hole recombination in DSSCs.