Organic Solvent Molecules Research Articles

A quantitative discrimination between reversible Li +-insertion and irreversible solvent oxidation at a lithium/manganese-spinel electrode

Oxidic Li +-insertion compounds of the donor type in aprotic Li +-electrolytes are of high practical importance as positives in rechargeable Li +-ion batteries. The manganese oxides MnO x are of special interest as host lattices due to their high reversibility and to the relatively positive potentials. However, these materials may induce irreversible anodic decomposition of the organic solvent molecules, especially towards the end of the charging process. Protons are injected into the electrolyte in this case. It is possible to evaluate these side reactions quantitatively through a measurement at the rotating ring/disk-electrode (RRDE). The disk was made of a 1 μm thick layer of MnO 2 (anodic deposit) on Pt (I) or a ceramic layer of the spinel LiMn 2O 4 on Ti, which was fabricated after Beers’s method at a firing temperature of 400 (II) and 600°C (III). The ring was made of Pt. At the ring, protons were reduced to H 2 at a half wave potential of −0.25 V versus saturated sodium chloride electrode (SSCE). The electrolytes were 0.1 M LiClO 4 in propylenecarbonate (PC) and acetonitrile (MeCN). These measurements showed that the novel MnO x -layers behave similar to the conventional porous battery electrodes which are much thicker and are made of powdery materials. Charge stoichiometry y in Li y Mn 2O 4 is found to increase from I to III from 0.2 to 2.0. No solvent oxidation could be detected at the potentials of the reversible Li +-intercalation peaks in cyclic voltammogram. The irreversible side reaction can be excluded therefore with a margin of error of 1–2%. This is in contrast to the former results obtained from the graphite intercalation compounds of the acceptor type (A-GIC), albeit at potentials more positive by 1 V. However, just behind the reversible Li +-deintercalation peak, i.e. charge direction, the positive end of the electrochemical window is attained. The current rises steeply. Abundant protons are injected into the electrolyte. The potentials are by 0.5–1 V more negative than at Pt due to the electrocatalytic activity of MnO x with respect to the irreversible anodic oxidation of the solvent molecules PC and MeCN.

Potential-Independent Electron Transfer Rate at the Liquid/Liquid Interface

Electron transfer (ET) from neutral zinc porphyrin (ZnPor) molecules in various organic solvents to aqueous redox species (e.g., Ru(CN)63-) was probed by the scanning electrochemical microscope (SECM). Unlike previous studies in which organic redox species were charged, the ET rate was found to be essentially independent of the potential drop across the interfacial boundary. This difference is explained by diffuse double-layer effect predicted by known models of the liquid/liquid interface. The effect of solvent dynamics on the rate of ET at the liquid/liquid interface was observed for the first time. The high precision and sensitivity of the SECM allow one to detect complexity in an interfacial reaction that may not be obvious from other electrochemical measurements and select a suitable system for checking the ET theory.

Synthesis and Characterization of Stacked and Quenched Uridine Nucleotide Fluorophores

Intramolecular aromatic interactions in aqueous solution often lead to stacked conformation for model organic molecules. This designing principle was used to develop stacked and folded uridine nucleotide analogs that showed highly quenched fluoroscence in aqueous solution by attaching the fluorophore 1-aminonaphthalene-5-sulfonate (AmNS) to the terminal phosphate via a phosphoramidate bond. Severalfold enhancement of fluorescence could be observed by destacking the molecules in organic solvents, such as isopropanol and dimethylsulfoxide or by enzymatic cleavage of the pyrophosphate bond. Stacking and destacking were confirmed by 1-H NMR spectroscopy. The extent of quenching of the uridine derivatives correlated very well with the extent of stacking. Taking 5-H as the monitor, temperature-variable NMR studies demonstrated the presence of a rapid interconversionary equilibrium between the stacked and open forms for uridine-5'-diphosphoro-beta-1-(5-sulfonic acid) naphthylamidate (UDPAmNS) in aqueous solution. DeltaH was calculated to be -2.3 Kcal/mol, with 43-50% of the population in stacked conformation. Fluorescence lifetime for UDPAmNS in water was determined to be 2.5 ns as against 11 ns in dimethyl sulfoxide or 15 ns for the pyrophosphate adduct of AmNS in water. Such a greatly reduced lifetime for UDPAmNS in water suggests collisional interaction between the pyrimidine and thefluorophore moieties to be responsible for quenching. The potential usefulness of such stacked and quenched nucleotide fluorophores as probes for protein-ligand interaction studies has been briefly discussed.

Hydrodynamic, optical and spectroscopic studies of some organic-aqueous binary systems

Abstract The peculiar occurrence of pseudoplastic behaviour of protein solutions in certain organic-aqueous media has been subject of previous studies [Areas et al., J. Coll. Interface Sci., 180 (1996), 578]. The role of the solvent in these events has been shown to be determinant, suggesting that particular configurations of the solvent/water microstructure are able to induce an extensive change in the folding of proteins such as lysozyme and cytochrome c, experimentally observed. In this work, we present a study on the rheology, refractivity and spectroscopic (Raman scattering and 1H and 13C nuclear magnetic resonance) behaviour of some of such binary organic-aqueous systems, as a function of the organic component mass fraction in water. Results obtained are consistent with the occurrence of a solution configurational transition at characteristic critical concentrations of the binary mixtures. The transition is apparent through several physico-chemical parameters monitored, including Raman frequency, 1H and 13C spin-lattice relaxation times, refractive index and viscosity. The effect has been observed for a few binary systems where protein was found to form stable solutions, including certain amides and urea derivatives, such as tetramethylurea, hexamethylphosphotriamide and dimethylformamide, some alcohols and for dimethylsulfoxide. All systems presenting the effect were found to contain coexistent polar/apolar molecular domains in their organic component. The effect is not observed for systems where the organic solvent molecule lacks a significative apolar moiety, such as formamide. Results were consistent with the view of a discontinuous liquid structure for those organic/aqueous binary mixtures.

Phospholipid monolayers at water∣oil interfaces: theoretical modelling of surface pressure–molecular area isotherms

Abstract The phospholipid adsorption and surface pressure–molecular area isotherms at interfaces are interpreted theoretically from two-dimensional (2D) lattice and real gas models that incorporate a minimum number of adjustable parameters. The first model is based on the lattice statistics of binary solutions and the molecular parameters introduced are the energy changes involved in the mixing process of the phospholipid and organic solvent molecules and the effective phospholipid head area. The surface pressure is interpreted in terms of the difference between the two liquid surface tensions. The second model makes use of (i) a non-localised adsorption model with a square-well potential energy term for the calculation of the surface concentration of the phospholipids at the interface as a function of the volume concentration of the phospholipids in the organic solvent phase, and (ii) a 2D hard disc gas model with a mean-field term accounting for the attractive interactions between the tails of the adsorbed phospholipids. The molecular parameters introduced in this model are the interfacial phospholipid adsorption energy, the effective hard disc diameter of the phospholipid head and the interaction energy between the phospholipid tails. The surface pressure is interpreted in terms of a 2D gas pressure in this model. The theoretical results obtained are compared with experimental data for the water ∣ 1,2-dichloroethane and water ∣ air interfaces. The two models predict correctly the typical order of magnitude for surface concentration and pressure values, as well as some qualitative features of the experimental isotherms, for low phospholipid surface concentrations.

Organic Solvent Binding to Crystalline Subtilisin1in Mostly Aqueous Media and in the Neat Solvents

The X-ray crystal structures of the protease subtilisin Carlsberg in 40% acetonitrile and in 20% dioxane have been determined to at least 2.3 Å resolution, and their solvent binding patterns have been compared to those observed in the neat organic solvents. The structures of the protein in the two aqueous-organic mixtures are essentially the same as in pure water, acetonitrile, and dioxane. Interestingly, the enzyme-bound organic solvent molecules tend to congregate in the active site. Three of the five bound acetonitrile molecules observed in the structure of subtilisin in 40% acetonitrile are situated in the enzyme active site, as is the single enzyme-bound dioxane molecule observed in 20% dioxane (whose location is distinct from that of any bound acetonitrile molecule). Furthermore, the organic solvent molecules detected in the enzyme active site in the aqueous-organic mixtures are in the same locations as in the structures in the corresponding neat organic solvents.

Movement of water in fish otoliths

The diffusion of small organic and inorganic solvent molecules and larger dye molecules into fish otoliths has long been utilized in clearing and staining otoliths to facilitate age estimation studies. This study quantifies the diffusivity of water into otoliths of Beryx splendens as a general analog of small molecule diffusivity in otoliths. The effects on the optical properties of otoliths of the diffusion of solvent and dye molecules into otoliths are also discussed.

The structure and properties of 12-heteropolyacid of molybdenum and tungsten (H 3PMo 6W 6O 40) solvated by dimethyl ether

The crystal structure of H 3PMo 6W 6O 40 3C 2H 6O was determined by X-ray crystallography and refined to R = 0.0698 based on 2279 observed reflections to give unit cell parameters a = 16.48(2) ( A ̊ ) , c = 25.205(5) A ̊ , γ = 120°, hexagonal, space group R3̄. The organic solvent molecules were characterized also by IR, 1H NMR spectra. Weak interaction existed between the organic solvent and the heteropoly acid in the secondary structure. The novel compound showed different behaviours in solubility, oxidizability and photosensitivity in comparison with classical dodeca heteropolyacid of molybdenum and tungsten.

Thermal gravimetry, mass spectrometry and solid-state 13C NMR spectroscopy—simple and efficient methods to characterize the inclusion behaviour of p-tert-butylcalix[n]arenes

The solid state inclusion of various organic solvent molecules in p-tert-butylcalix[4]arene and p-tert-butylcalix[6]arene has been studied by thermal gravimetry and electron impact mass spectrometry (EI-MS). The host–guest ratio varies from 1∶2 to 4∶1 and the nature of included guest has been determined by EI-MS. Thermal gravimetric analysis of solvent–p-tert-butylcalix[n]arene complexes gives a qualitative order of intramolecular forces involved. Structural information obtained by cross-polarization magic angle spinning (CP-MAS) 13C NMR spectroscopy is in good agreement with known data from single-crystal X-ray diffraction analysis.

Attractive potential effect on the self-diffusion coefficients of a solitary water molecule in organic solvents

H 1 -Fourier-transform pulsed field-gradient spin-echo NMR method is applied at 30 °C to measure the self-diffusion coefficients of water, acetonitrile, and benzene in dilute organic solutions of carbon tetrachloride, benzene, chloroform, dichloromethane, acetonitrile, acetone, and water. The dependence of the translational friction coefficients ζT of the apolar solute molecule, benzene, on solvent viscosity η is linear as predicted by the simple hydrodynamic theory. The η dependence of ζT of the polar solute molecule, acetonitrile, is linear, though the slope is different in apolar and polar solvents. The η dependence of ζT of the hydrogen-bonding solute molecule, water, is nonlinear and dependent on the strength of the solvent as a proton acceptor. The breakdown of the hydrodynamic theory is discussed in terms of the attractive part of the solute–solvent interaction. The role of the attractive interaction is illustrated through a linear relationship between the proton chemical shift of water and the residual friction coefficient, which is defined by removing the repulsive component from the overall translational friction coefficient.

Polarization phenomena at the water|o-nitrophenyl octyl ether interface Part II. Role of the solvent viscosity in the kinetics of the tetraethylammonium ion transfer

Abstract The kinetics of the tetrahylammonium ion transfer from water to o -nitrophenyl octyl ether has been studied by impedance measurements at the equilibrium cell potential. Enhanced capacity of the interface points to a significant specific adsorption of the tetraethylammonium ion, probably via forming the interfacial ion pairs. In spite of the coupling between the ion transfer and the ion adsorption, a non-linear least squares fitting of impedance data to the Randles-type equivalent circuit or to an impedance model accounting for the specific ion adsorption yields similar values of the kinetic parameters. The most important finding is that the ratio of the rate constants of the tetraethylammonium ion transfer from water to nitrobenzene and to o -nitrophenyl octyl ether correlates with the inverse ratio of the organic solvent viscosities. The low viscosity of 1,2-dichloroethane can then be responsible for rather fast ion transfer kinetics at the water|1,2-dichloroethane interface. The viscosity effect is likely to be associated with the friction exerted by the organic solvent molecules on the hydrated ion penetrating the organic solvent to some depth prior to the ion transfer step.

Organic solvents identify specific ligand binding sites on protein surfaces.

Enzymes frequently recognize substrates and pharmaceutical drugs through specific binding interactions in deep pockets on the protein surface. We show how the specificity-determining substrate binding site of hen egg-white lysozyme (HEWL) can be readily identified in aqueous solution by nuclear magnetic resonance spectroscopy using small organic solvent molecules as detection probes. Exchange of magnetization between the 1H nuclei of the protein and the ligands through dipole-dipole interactions is observed which allows the modeling of their position and orientation at the binding site. Combined with site-specific binding constants measured by titration experiments with different organic solvents, the method can provide important information for rational drug design. In addition, the lifetime of nonspecific interactions of HEWL with organic solvents is shown to be in the sub-nanosecond time range.

Inclusion of Volatile Organic Compounds into Natural Cyclodextrins and Their Branched Cyclodextrins in the Gaseous Phase

The adsorption isotherms of water, the differential heat of adsorption, and the entropy of adsorbed water were investigated to elucidate the structure of stability of cyclodextrins (CyD) and branched CyD's. The amount adsorbed on branched CyD's increased with increasing relative humidity. The steep rise in the amount adsorbed at higher relative humidities indicated that the structure of branched CyD's was affected by the water molecules at these higher relative humidities. The bonding force between α-CyD's and water molecules was stronger than that between their branched CyD's and water, while that between β-CyD's and water was weaker than that between their branched CyD's and water. We have used activated carbons for the recovery of organic solvents. There are polar groups on the activated carbon surface. Therefore, the recovered organic solvents were degraded by these groups. However, such polar groups are not expected for the hydroxyl groups of the CyD's. The amounts of 1,1,1-trichloroethane, benzene, and toluene included in natural CyD's and their branched CyD's were measured. The amounts of organic solvents included in the CyD's depended upon the cavity radii and the glucosyl and maltosyl functional groups of the CyD's and the radii of the organic solvent molecules.

Electrical double layer on renewed iron electrodes in solutions based on a number of organic solvents

Dependences were obtained of the current and impedance component transients on the potential for Fe electrodes renewed by cutting in the solutions based on certain organic solvents: tetra-methylurea, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, hexamethylphosphortriamide, dimethylsulfoxide (DMSO), and acetonitrile (AN). It was found that the renewed iron electrode in LiClO 4 or KBF 4 solutions in a certain potential region behaves in the first approximation as an ideally polarizable electrode (with the exception of DMSO and AN solutions). The values of potentials of zero charge (pzc) of Fe were determined from the capacitance minimum in dilute electrolyte solutions. The relationship between the double-layer capacitances corresponding to the positive and negative charges strongly depends on the solvent nature. A similarity was found in the behaviour of Fe and Pt electrodes, which is associated with the chemisorptive interaction between these metals and organic solvent molecules. Literature data on the Fe pzc in aqueous solutions are analyzed in comparison with the data for organic solvents and from the standpoint of the correlation with the work functions W of metals. It is concluded that the values of Fe pzc obtained earlier by Leikis, Rybalka, and Zelinskii for renewed Fe electrodes in aqueous electrolyte solutions correspond most closely to the active iron surface free from any oxides.

AC-impedance-based chemical sensors for organic solvent vapors

A type of chemical sensor based on impedance spectroscopy (IS) measurements utilizing an interdigital transducer structure on a glass substrate is investigated for the detection of organic solvent molecules, such as chloronated hydrocarbons, in the gas phase. The IDT structures were coated with sensitive material such as soluble tetrakis-t-butyl phthalocyaninatonickel(II), ethylcellulose, poly(ethyl acrylate), and poly(etherurethane). The target organic solvent molecules are dichloromethane, chloroform, trichloroethene, tetrachloroethene, toluene, and ethanol. The sensor responses were monitored by measuring changes in the transducer/coating composite properties upon exposure to the organic solvent molecules. The sensor parameters of interest include the electrostatic capacitance, the resistance of the composite and the relaxation time, which will lead to the implementation of a multi-information sensor. Results are presented and compared for selected samples with completely reversible sensor signals at room temperature. Based on the measurements, use of metal complexes can improve sensitivity and increase the signal-to-noise ratio.

Polymer-coated QCR sensors for the detection of organic solvents in water

Poly(ethyl acrylate) (PEA), poly(epichlorohydrin) (PECH) and a silicon-based copolymer of trimethoxypropylsilane/octadecyltrimethoxysilane (TMPS/ODTMS) were used as sensitive materials for the detection of organic solvent molecules in water. Quartz crystal resonators (QCR) with modified electrode configurations are used to monitor the changes in mass and in electrical properties by measuring the shifts in series resonance frequency ( f s), parallel resonance frequency ( f p), and frequency of maximum admittance ( f m), respectively. The result is a multi-information chemical sensor. The sensor signals are completely reversible at room temperature with the response and recovery time in the order of minutes under our measurement conditions. The sensitivities obtained from the measurements of f m for all organic solvents investigated are generally larger than those obtained from f s and f p. It is also found that there is no correlation between the measured sensitivities of the series resonance frequency and the boiling point temperatures of the organic solvents investigated in the liquid phase under our experimental conditions, as is generally obtained in the gas phase.

Detection of organic solvent vapours and studies of thermodynamic parameters using quartz crystal microbalance sensors modified with siloxane polymers

Quartz crystal microbalance (QCM) sensors were modified by a series of siloxane polymer coatings, including polydimethyldiphenylsiloxane, polymethylhydrosiloxane and PS-086. These sensors were exposed to different concentrations of various organic solvent molecules, including related chlorinated hydrocarbons, alcohols and other organic vapours. The results showed that the responses of frequency changes to concentration changes exhibited linear relationships within the concentration range studied. The thickness of the above three coatings was in the range 3.04–4.24 nm. Thermodynamic parameters of polymer–gas interactions were determined. Partition coefficients (K) of the modified polysiloxane layers obtained from frequency changes at different concentrations of the detected solvents showed good reproducibility (about 0.77–5.45% relative standard deviation) at room temperature. The selectivity and sensitivity of the polysiloxane-based sensors were correlated with the solvent boiling points, Ostwald solubility coefficients and the different molecular interactions between the functional groups of polysiloxanes and organic solvent molecules.

Heterocalixarenes featuring the benzimidazol-2-one subunit. Synthesis and X-ray structural studies of solvent inclusions

The heterocalixarenes 4a,b and 5a–f have been synthesized. Compounds 4a,b and 5a–d were obtained by two-step fragment condensation from benzimidazol-2-one and 1,3-bis(bromornethyl)benzene building elements using blocking/deblocking, high dilution and template (Cs2CO3) techniques to give 4a/5a and 4b/5b in an approximate 1 : 2 or 1 : 3 ratio of the cyclo oligomers. The cleavage of the methyl ether groups of 5a and 5b yielded the tetraphenols 5e and 5f, respectively. The calix hosts 4a, 5a–c and 5f form crystalline inclusion compounds with organic solvent molecules. X-Ray crystal structures of the solvent inclusions 5a·methylene chloride (1 : 1), 5b·toluene·water (1 : 2 : l), Sc·acetone·methylene chloride (1 : 1 : 1) and 5f·toluene (1 : 3) have been studied. The molecular structures show a general trend of having enhanced calix-forming ability compared with conventional calix[8]arenes of the same ring size. The shape of the host molecules appear to be determined by the packing of the symmetry centres of related host molecules on either one of the benzimidazolone rings yielding basket-like hosts (5a–c) or on one of the phenol rings resulting in a chair-like host shape (5f), always exhibiting base-stacking characteristics between the aromatic planes concerned.

17O-NMR Evidence on the Isolated Water Molecule in Hydrophobic Organic Solvents

Abstract 17O-NMR spectra of H217O molecules in benzene, chloroform, ethylacetate, dimethylformamide, and 1-butanol were measured. For hydrophobic benzene and chloroform, the 17O-NMR spectra give two peaks consisting of the triplet and singlet lines, which are assingned to the isolated monomeric and clustered water molecules, respectively. The observed triplet splitting due to the spin - spin coupling of J17O-H gives an evidence that the isolated water molecule can not exchange the protons between water molecules seperated far away during the measurement time of NMR phenomenon.

Effect of solvent, temperature, and pressure on hydrogen bonding and reorientation of water molecules

On the basis of the study of the solvent, temperature, and pressure effects, we show how the NMR rotational correlation times τ 2R for a heavy water molecule in neat liquid and organic solvents are correlated with the strength of solute-solvent interactions, in particular, H bonds. At room temperature (30 °C), the correlation time is 2.1 ps in the random H-bond network in heavy water, whereas it is as small as 0.1 ps in such an apolar, hydrophobic solvent as carbon tetrachloride because of the absence of the H bonds between water molecules. Pressure distorts H bonds and accelerates the orientational motion of water molecules in neat liquid. Firm evidence is collected for the limitations of the Stokes-Einstein-Debye (SED) law in solution.