Protic Solutions Research Articles

Comprehensive solubility study and inter-molecular interactions on fenbendazole dissolved in some aqueous aprotic and protic co-solvent solutions

The isothermal shake-flask saturation method was used to experimentally determine the mole-fraction solubility of fenbendazole in three aqueous co-solvent blends of 1,4-dioxane/acetone/NMP encompassing the range of 283.15 to 328.15 K. The solubility of fenbendazole in various blended solvents ranks NMP + water (4.852 × 10−2) > 1,4-dioxane + water (14.81 × 10−4) > acetone + water (2.285 × 10−4) with composition of 1,4-dioxane (acetone or NMP) of 1 at 298.15 K. The solubility data rises monotonically with 1,4-dioxane/acetone/NMP concentration at the same temperature. X-ray power diffraction images show that no solvate production or crystal transition appeared throughout the studies. The solubility to solvent composition and temperature was satisfactorily associated by the modified van't Hoff-Jouyban-Acree, quantitative structure–property relationship, and Jouyban-Acree models with relative average deviations of no higher than 7.05 % and root-mean-square deviation of no higher than 1.225 × 10−3. In addition, the 1,4-dioxane/acetone/NMP + water blends studied in this paper and the methanol/ethanol/EG/DMF + water blends previously reported both used the extended Hildebrand solubility approach to quantitatively describe the solubility behavior at 298.15 K. The average relative deviations were kept under 4.06 % on both cases. As stated by the examination of the linear solvation energy relationship, the solubility parameter and dipolarity-polarizability of solutions have a significant influence on the solubility variation. The effective method of inverse Kirkwood-Buff integrals was used to investigate the preferred solvation of fenbendazole at 298.15 K. In blends with intermediate and rich ethanol/DMF/1,4-dioxane/acetone/NMP composition areas, the preferred solvation parameters of ethanol/DMF/1,4-dioxane/acetone/NMP displayed positive values, indicating the preferential solvation of fenbendazole by the co-solvents. Thermodynamic examination of the entropy-enthalpy compensation and dissolution parameters for fenbendazole dissolving in blends led to the identification of an enthalpy and/or entropy-driven mechanism as well as an endothermic process. Moreover, the average local ionization energy and electrostatic potential of molecular surface were utilized as effective instruments to demonstrate the microscopic electrostatic properties of acidity and basicity, respectively. The fenbendazole molecule's groups of –N in the five-membered ring and –NH in the straight chain serve as the main targets for electrophilic and nucleophilic assault. The weak interactions between fenbendazole and several solvents were shown using an independent gradient model based on Hirshfeld partition analysis.

Bonds over Electrons: Proton Coupled Electron Transfer at Solid-Solution Interfaces.

This Perspective argues that most redox reactions of materials at an interface with a protic solution involve net proton-coupled electron transfer (PCET) (or other cation-coupled ET). This view contrasts with the traditional electron-transfer-focused view of redox reactions at semiconductors, but redox processes at metal surfaces are often described as PCET. Taking a thermodynamic perspective, transfer of an electron is typically accompanied by a stoichiometric proton, much as the chemistry of lithium-ion batteries involves coupled transfers of e- and Li+. The PCET viewpoint implicates the surface-H bond dissociation free energy (BDFE) as the preeminent energetic parameter and its conceptual equivalents, the electrochemical ne-/nH+ potential versus the reversible hydrogen electrode (RHE) and the free energy of hydrogenation, ΔG°H. These parameters capture the thermochemistry of PCET at interfaces better than electronic parameters such as Fermi energies, electron chemical potentials, flat-band potentials, or band-edge energies. A unified picture of PCET at metal and semiconductor surfaces is presented. Exceptions, limitations, implications, and future directions motivated by this approach are described.

Structural isomerism induces pH dependent AIE-coupled ESIPT: an in-depth spectroscopic exploration with application in amine vapor sensing.

A novel excited state intramolecular proton transfer probe 3-(benzo[d]thiazol-2-yl)-4-hydroxy-5-methoxybenzaldehyde (3BTHMB) was synthesized and characterized using NMR, ESIMS and single crystal diffraction studies. The steady state and time resolved studies using the time correlated single photon counting (TCSPC) technique revealed that 3BTHMB shows ESIPT reaction with a time constant of 0.10-0.15 ns and longer local emission and anion emissions of time constants 0.5-2.0 ns and 3.0-4.0 ns, respectively, that co-exist in polar solution. In a polar protic solution like methanol, the ESIPT process is damped. Interestingly, 3BTHMB shows aggregation induced emission (AIE) solely in an acidic environment, evidenced by the enhanced quantum yield of emission (∼35%) in acidic solution as well as a long lifetime component of 7.4 ns that corresponds to the lifetime in the solid state. The AIE phenomenon was explored using the DLS technique where enhancement of the hydrodynamic radius in an acidic medium was observed. The judicious positioning of the formyl group in 3BTHMB gives the mentioned probe to show AIE in an acidic medium, as opposed to its previously reported structural isomer BTHMB, which showed no AIE phenomenon as well as its parent molecule 2-(benzo[d]thiazol-2-yl)-6-methoxyphenol (TMP), which showed AIE in neutral pH. The AIE property of 3BTHMB was exploited by successful and rapid detection of amine vapor in the solid state, qualitative ratiometric detection of aqueous pH, by observing the colour change under UV light in acidic (yellow-green) and basic to neutral (blue) medium. The above results pave the way for multiutility fluorescent probes for environmental purposes along with a deep understanding of the underlying photophysical processes which bestow the probes with such outstanding utilities.

Revisiting Disulfide-Yne and Disulfide-Diazonium Reactions for Potential Direct Modification of Disulfide Bonds in Proteins.

To find their potential use in protein research, direct addition of a disulfide compound to alkyne (namely disulfide-yne reaction) and S-arylation with arenediazonium salt (namely disulfide-diazonium reaction) were investigated in aqueous or protic solutions. The reaction of dimethyl disulfide with 5-hexynol performed best under 300 nm irradiation in the presence of sodium acetate to afford 5,6-bis(methylthio)-5-hexenol in 60% yield. Without the prior reduction of a disulfide bond to thiols, the disulfide-yne reactions have the advantage of 100% atom economy. Disulfide-diazonium reaction was triggered by sodium formate and accelerated by photoirradiation with a 450 nm LED lamp (5 W). The reaction of 3,4-dihydroxy-1,2-dithiane with 2-(prop-2-yn-1-yloxy)benzene-1-diazonium tetrafluoroborate (8b) afforded 2-(benzofuran-3-yl)-1,3-dithiepane-5,6-diol (13), confirming that both S substituents originate from the same disulfide molecule. The trastuzumab antibody was incubated with diazonium 8b, followed by α-lytic protease digestion, LC-ESI-MS/MS analysis, and Mascot search, to verify that the proximal C229 and C232 residues on the same heavy chain were reconnected with a (benzofuranyl)methine moiety that originated from 8b, unlike the expected disulfide rebridging across two heavy chains. Nonetheless, disulfide-diazonium reactions still have potential for rebridging disulfide bonds if appropriate proteins and diazonium agents are chosen.

Quantitative surface and Hirshfeld surface analysis of nicorandil molecule and further insight into its solubility in several aqueous protic and aprotic cosolvent solutions

The quantum-chemical quantities of highest negative surface electrostatic potential and lowest surface average local ionization energy as well as Hirshfeld surface were used herein to explain the electrostatic features of both basicity and acidity of nicorandil molecule. The primary electrophilic and nucleophilic sites are the -Nand > NH groups, respectively. According to the nicorandil solubility in solutions of isopropanol (1) + water (2), ethanol (1) + water (2), DMF (1) + water (2), and methanol (1) + water (2), preferential solvation of nicorandil was investigated using the famous inverse Kirkwood-Buff integrals approach. In poor water composition areas, nicorandil was surrounded preferentially by organic solvent, showing the selective solvation of nicorandil by methanol/DMF/ethanol/isopropanol. This performance was due to high basicity of organic solvents compared with water, which favors interactions with nicorandil's acidic groups. The Hansen solubility parameter was used to evaluate the performance of nicorandil solubility in depth. The derived dissolution Gibbs energy change, enthalpy and entropy indicated that the solubilization capacity improved with increasing methanol/DMF/ethanol/isopropanol compositions. As the proportions of methanol/DMF/ethanol/isopropanol rose, analysis of enthalpy–entropy compensation revealed a shift in main dissolving mechanism from enthalpy-driven to entropy-driven (alcohol solutions) or from entropy-driven to enthalpy-driven (DMF solutions).

A tetrazole-ene photoactivatable fluorophore with improved brightness and stability in protic solution

The pyrazoline fluorophore, generated by photoinduced tetrazole-ene cycloaddition, shows faint fluorescence in protic solvents. To suppress this fluorescence-quenching, we rationally designed a series of substituted diaryl tetrazoles at the N-side phenyl ring to produce a tetrazole-ene based photoactivatable fluorophore. Spectroscopic and cellular imaging studies demonstrated that the version of the fluorophore with a bis(trifluoromethyl)benzene substituent exhibited significantly enhanced brightness and photostability.

Solvatochromic study of pyridinium-acetyl-benzoyl methylid (PABM) in ternary protic solutions

A solvatochromic study is made for ternary solutions of pyridinium acetyl-benzoyl methylid in the binary solvents mixtures water (1) + ethanol (2) and water (1) + methanol (2), based on the solvatochromic Kamlet-Taft parameters and on the statistical cell model of ternary solutions, in order to obtain new information on the nature and strength of intermolecular PABM-solvent interactions in these ternary solutions. The binary solvent mixtures chosen in this study consists of two protic liquids, transparent in the visible range and able to participate in specific interactions with the ylid molecules. The contribution of non-specific and specific interactions is estimated for each binary solvent mixture (using the correlation coefficients in multi-parametric linear correlation equations based on the empirical Kamlet-Taft solvent parameters). The difference between the energies in the molecular solute-solvent pairs of the type ylid-protic solvent in the two types of binary solvent mixtures is also estimated.

Excited-State Proton Transfer in Oxyluciferin and Its Analogues.

One of the most characterized bioluminescent reactions involves the firefly luciferase that catalyzes the oxidation of the luciferin producing oxyluciferin in its first excited state. While relaxing to the ground state, oxyluciferin emits visible light with an emission maximum that can vary from green to red. Oxyluciferin exists under six different chemical forms resulting from a keto/enol tautomerization and the deprotonation of the phenol or enol moieties. The optical properties of each chemical form have been recently characterized by the investigations of a variety of oxyluciferin derivatives, indicating unresolved excited-state proton transfer (ESPT) reactions. In this work, femtosecond pump-probe spectroscopy and time-resolved fluorescence spectroscopy are used to investigate the picosecond kinetics of the ESPT reactions and demonstrate the excited state keto to enol conversion of oxyluciferin and its derivatives in aqueous buffer as a function of pH. A comprehensive photophysical scheme is provided describing the complex luminescence pathways of oxyluciferin in protic solution.

Atomic-Scale Three-Dimensional Local Solvation Structures of Ionic Liquids.

Room-temperature ionic liquids are promising media for next-generation energy devices because of their various superior characteristics. Because device performance is often dictated by the solvation structures at the solid-liquid interfaces, particularly at the local reactive sites, their atomistic pictures are in great demand. However, there has been no experimental technique for their three-dimensional solvation structures. Here, we first demonstrate the measurement of the atomic-scale ionic liquids using a recently established ultralow-noise three-dimensional frequency-modulation atomic force microscopy technique supported by molecular dynamics simulations. We conducted the experiments in protic and aprotic aqueous solutions and reveal that the aprotic solvation structure exhibits the higher site specificity, which resolves atomic-scale surface charge distribution on mica because of the absence of the H-bonding network. Our methodology is also applicable to pure liquids and would be a breakthrough for expanding their future applications.

Controllable and reversible proton transfer for inorganic cyanide visual sensing based on the deprotonation of azo-phenolic hydroxyl group

ABSTRACTMethods for optical detection of inorganic cyanide based on the single molecule sensor with high selectivity and sensitivity have attracted increasing interest recently due to the high toxicity of cyanide ions. In this work, a visual sensor (S1) containing both imidazole NH and azo-phenolic OH was synthesised and characterised. The spectral experimental data indicated that protic aqueous solution facilitated enhancing the selectivity of cyanide ions with the nanomolar-level detection limit in semi-aqueous solution. The visual sensing mechanism arising from the deprotonation of azo-phenolic OH and the enhancement of intramolecular charge transfer could be clearly demonstrated by titration experiments of 1H NMR, HR MS and energy changes between the HOMO−LUMO band gaps. Furthermore, the reversibility and reusability of S1 upon alternating addition of CN− and H+ were studied.

A series of new acid dyes; study of solvatochromism, spectroscopy and their application on wool fabric

A new series of mono azo dyes (D1-D4) was synthesized by coupling 8-anilino naphthalene-1-sulphonic acid (1) with different aromatic amines (2a-d) and applied on wool fabric. The color fastness properties of the dyed material were also studied. Spectroscopic techniques including 1H NMR, MALDI, FT-IR and UV–Visible were employed for structural characterization. The thermal gravimeteric analysis of the synthesized dyes was also carried out to determine their thermal stability. The effect of solvent and pH on colors and absorption maxima (λmax)of the synthesized dyes was examined. UV–Visible spectra of the dyes in different solvents as well as in acidic and basic alcoholic solutions revealed that these dyes exist as a mixture of two tautomers in protic solvents and acid solution.

Ultrafast photophysical properties of dimethyl amino styryl pyridine acetonitrile

The ultrafast photophysical properties of dimethyl amino styryl pyridine acetonitrile (DASPA) were studied by the femtosecond transient absorption spectra (TA). The results show no evidence of state-to-state relaxation. The excited energy is released by the interaction between DASPA and solvent molecules. The solvation relaxation in protic solutions is faster than that in aprotic solutions, which results in a rapid decay of fluorescence. An energy diagram is finally proposed to interpret the relaxation mechanism.

Theoretical insights into excited-state intramolecular and multiple intermolecular hydrogen bonds in 2-(2-Hydroxy-phenyl)-4(3H)-quinazolinone.

The photophysical properties and photochemistry reactions of 2-(2-Hydroxy-phenyl)-4(3H)-quinazolinone (HPQ) system in different solutions are studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Our theoretical investigation explores that an ultrafast barrier-free excited state intramolecular proton transfer (ESIPT) process occurs and the configuration twisting is found in the electronic excited state. In the polar protic methanol solution, the hydrogen-bonded complex composed by HPQ and two methanol molecules (HPQ-2M) could exist stably in the ground state. Upon photoexcitation the isolated HPQ is initially excited to the first excited state, while the HPQ-2M system is firstly excited to the S3 state and undergoes internal conversion (IC) to the S1 state. The intermolecular hydrogen bonds are strengthened in the excited state. The simulated electronic spectra agree well with the experimental results. The strengthening of the intermolecular hydrogen bonds is also confirmed by the calculated vibrational spectra. In addition, the intramolecular charge transfer happens in both HPQ and HPQ-2M systems from the frontier molecular orbital analysis.

Analysis of redox states of protic and aprotic solutions irradiated by low linear energy transfer carbon-ion beams using a 2,2-diphenyl-1-picrylhydrazyl radical.

The quantitative evaluation of changes in the redox state induced by low linear energy transfer (LET) radiations such as the plateau region of heavy-ion beams via formation of reactive oxygen species is of considerable importance to eliminate the adverse effects of radiation therapy on normal tissues adjacent to a tumour. In this study, a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) was used as a redox probe to estimate the redox states of protic and aprotic solutions irradiated by low LET carbon-ion (C-ion) beams. The dose dependence of the decrease in the absorption band due to DPPH˙ (which was solubilised by β-cyclodextrin (β-CD) in water) after irradiation with low LET C-ion beams (13 keV μm-1) was similar to that after X-irradiation. Similar results were obtained when H2O was replaced with methanol or acetonitrile although the slope values of the plots of the absorbance changes vs. radiation doses were twice larger as compared to the case in β-CD-containing H2O. Moreover, DPPH˙ was more susceptible to the C-ion beam than to X-rays in isopropyl myristate (IPM), which is one of the saturated fatty acid esters.

On the Proton-Coupled Electron Transfer of Urazole Derivatives in pH-Unbuffered Protic and Aprotic Solutions: The Substituent Effect

Proton-coupled electrochemical oxidation of some urazole derivatives has been investigated in pH-unbuffered N,N-dimethylformamide as an aprotic solvent to understand the role of substituent of the urazole on the electrode process. The redox chemistry of urazole is easily influenced by the presence of trace basic or acidic impurities of solvent. The voltammetric responses of the urazole derivatives affected by impurities are completely depended on the electron-donating/withdrawing properties of the functional groups. Further in the following of our previous research on the electrochemical reduction of 4-(4-nitrophenyl) urazole, the electroreduction has been examined and compared in aqueous buffered solutions and the solutions with limited concentration of proton. The mechanistic pathways display a number of similarities and differences regarding the number of involved electrons, electrode processes, reduction peaks and reversibility of the electrode processes. The mechanism of the electron transfer was surveyed in a variety of pH ranges.

Electrochemical Reduction of Protic Supercritical CO2 on Copper Electrodes.

The electrochemical reduction of carbon dioxide is usually studied in aqueous solutions under ambient conditions. However, the main disadvantages of this method are high hydrogen evolution and low faradaic efficiencies of carbon-based products. Supercritical CO2 (scCO2 ) can be used as a solvent itself to suppresses hydrogen evolution and tune the carbon-based product yield; however, it has received little attention for this purpose. Therefore, the focus of this study was on the electrochemical reduction of scCO2 . The conductivity of scCO2 was increased through the addition of supporting electrolyte and a cosolvent (acetonitrile). Furthermore, the addition of protic solutions of different pH to scCO2 was investigated. 1 m H2 SO4 , trifluoroethanol, H2 O, KOH, and CsHCO3 solutions were used to determine the effect on current density, faradaic efficiency, and selectivity of the scCO2 reduction. The reduction of scCO2 to methanol and ethanol are reported for the first time. However, methane and ethylene were not observed. Additionally, corrosion of the Cu electrode was noticed.

Catalytic activity of the Co(II)/Co(III) couple towards peptide bond cleavage and formation of molecular oxygen adducts in protic amide solutions

Formamide and N-methylformamide solutions containing variable amounts of Co(II) and Co(III) halide were employed as model systems to explain the catalytic potential of these ions towards amide bond cleavage reaction. The νCO downshifts in the IR spectra and the νCN upshifts in the Raman spectra are in agreement with the stabilization of a molecular structure near the dipolar amide form, which is considered the active species for catalysis. Quantitative analyses performed at the νCN and δOCN regions reveal the existence of four- and five-coordinate Co(II) complexes, but the addition of an oxidizing agent leads to the formation of five- and six-coordinate structures around Co(III) in 1:1 and 1:2 (O2/Co) type adducts. Attempt to correlate the electrostatic potential with the limiting canonical amide forms is also presented.

Effect of pretreatment severity on the cellulose and lignin isolated from Salix using ionoSolv pretreatment.

The ionoSolv pretreatment is a new technique employing protic low-cost ionic liquids and has previously been applied to successfully fractionate switchgrass and the grass Miscanthus giganteus. This study investigates the effect of using the protic ionic liquid solution [N2220][HSO4]80% with two different acid/base ratios (1.02 and 0.98) at 120, 150 and 170°C on the pretreatment outcome of the hardwood willow. The ionic liquid solution was able to fractionate willow, and a pulp and lignin fraction were recovered after treatment. The pretreatment success was determined via enzymatic hydrolysis of the pulp, which showed that the ionoSolv pretreatment was able to increase enzymatic glucose yields compared to untreated willow biomass. The pretreatment produced a cellulose-rich pulp with high hemicellulose and lignin removal. The pulp composition and glucose yield after saccharification were greatly influenced by the acidity of the ionic liquid solution, temperature and pretreatment time. The extracted lignin was analysed via 2-D HSQC NMR spectroscopy and GPC to investigate the changes in the lignin structure induced by the pretreatment severity. The lignin structure (in terms of inter-unit linkages and S/G ratio) and molecular weight varied significantly depending on the pretreatment conditions used.

Stabilizing Single Sites on Solid Supports: Robust Grafted Ti(IV)-Calixarene Olefin Epoxidation Catalysts via Surface Polymerization and Cross-Linking

This manuscript develops a surface polymerization and cross-linking approach for the stabilization of single-site catalysts on solid surfaces, which is demonstrated here for grafted Ti(IV)-calixarene Lewis acids on silica. Our approach relies on cationic polymerization that is initiated by an adsorbed B(C6F5)3 and uses styrene as the monomer and diisopropenylbenzene as the cross-linking agent. The mildness of this polymerization method is demonstrated by its lack of blocking micropores and only slight consumption of mesopore internal surface area on the basis of N2 physisorption data at 77 K, both of which are in contrast to previously reported surface-polymerization approaches. Catalysis of samples before and after polymerization and cross-linking was investigated with a probe reaction consisting of the epoxidation of 1-octene with tert-butyl hydroperoxide as oxidant, which is known to be catalyzed by Lewis-acid sites, and a comparison of catalyst hydrolytic stability was performed. Added water in the latter was used as a a trigger to induce site aggregation, as a stress test to determine the effectiveness of site protection by our polymerization approach. Consistent with the N2 physisorption data, catalysis data demonstrate that surface polymerization does not block small-molecule reactant and product access to Lewis-acid sites on the surface, since the conversion remains essentially unchanged before and after surface polymerization and cross-linking. DR UV–vis, TGA, and catalysis data reveal that the grafted Ti(IV)-calixarene sites on silica maintain their catalytic activity even after being treated with corrosive protic stress-test solution. In sharp contrast, grafted sites without the polymer layer leach nearly all of their calixarene and Ti contents during similar stress testing, resulting in the near complete loss of catalytic activity. We hypothesize that the surface polymer acts as a nanoreactor gatekeeper, which prevents the large Ti(IV)-calixarene site from leaching and keeps surface complexes as single sites grafted on the silica surface, by blocking access for the migration of sites from the surface to bulk solution.

Implicit and explicit solvent models to understand the d(+)-glucose solvation in aqueous protic ionic liquid solution: Volumetric and computational approach

The nature of interactions between biopolymers (polysaccharides) and ionic liquids (ILs) governs the dissolution/functionalization processes, so an understanding of these interactions demands reliable reference data on thermophysical properties of systems composed of biopolymer model compound (monosaccharide), ILs and solvent (water). In this regard, we report herein the volumetric properties of d(+)-glucose (Glu) in aqueous solutions of protic ionic liquid (propylammonium formate; PAF) at different concentrations and temperatures. The experimental results were further supported by computational studies. Structures of Glu and PAF were optimized in gas phase by employing density functional theory at CAM-B3LYP/6-311G++ (2d, 2p) level. Further, interactions between the two in presence of solvent (water) were studied by employing implicit as well as explicit solvent models. The hydrophilic-ionic interactions between Glu and PAF are significant at lower concentrations of PAF and diminish with increasing concentration of PAF as well as temperature. Overall, hydrophobic type of interactions between Glu and ions of PAF dominate the solvation behaviour at higher concentration and temperature, and these observations have been further supported by computational results.