Water-acetonitrile Solutions Research Articles

Extraction of amitraz and its metabolites with organic solvents

The distribution constants of amitraz and its three main metabolites (DMFF, DMF, DMA) for water–organic solvent (n-hexane, toluene, dichloromethane, chloroform) extraction systems were estimated. Based on the analysis of the substances distribution in the studied systems, it was established that dichloromethane is the optimal choice for amitraz and its metabolites liquid-liquid extraction for method development for their simultaneous determination in honey. Amitraz stability study in water-acetonitrile solutions with various additives demonstrated that 50 mM ammonia solution in water– acetonitrile mixture (1 : 1, vol.) should be used as solvent for the samples final solutions.

IONIZATION OF ETHANOLAMINES IN WATER- ORGANIC MEDIA

In this paper, the ionization constants (pKa) of some nitrogen-containing organic bases (monoethanolamine, diethanolamine and triethanolamine) in water-ethanol, water-acetone and water-acetonitrile solutions at various concentrations of organic solvent in the studied systems have been determined by the potentiometric titration method. It was found that the values of pKa of monoethanolamine, diethanolamine and triethanolamine in aqueous-organic solutions naturally decreases with increasing concentration of organic solvent in the system. It was shown that their nature and the physico-chemical properties of the medium are significantly influenced by the nature and degree of change in the electron donor ability of the studied nitrogen-containing organic bases. It should be noted that for the studied nitrogen-containing organic bases (monoethanolamine, diethanolamine and triethanolamine), when passing from an aqueous medium to an organic one (ethanol or acetone or acetonitrile), the pKa values naturally decrease with an increase in the content of the organic solvent in the system. In general, in the transition from an aqueous medium to an organic one (ethanol or acetone or acetonitrile), a change in pKa can reach 1.73 units. It was established that the dependence of the values of pKa of nitrogen-containing organic bases which were determinate via potentiometric titration method on the inverse of the dielectric constant of water-ethanol and water-acetone or water-acetonitrile solutions tends to be linear, consistent with Izmailov’s theory. Thus, we can conclude that the change in the ratio of the mixed solvent components and, as a result, in general, dielectric permeability of the medium does not lead to a significant change in the solvation characteristics of the studied nitrogen-containing organic bases.

Selective Photocatalytic Transformation of Lignin to Aromatic Chemicals by Crystalline Carbon Nitride in Water–Acetonitrile Solutions

The photocatalytic conversion of lignin to aromatic compounds in aqueous solutions is a promising approach. We herein report a crystalline carbon nitride prepared by high-temperature thermal polymerization and alkali-metal molten salt treatment, which was then applied in the selective conversion of lignin to aromatic compounds. The results showed that the tri-s-tri-C3N4 presented a relatively high activity and selectivity for the conversion of lignin in aqueous solutions. In a 95% water-acetonitrile solution, it achieved a relatively high conversation rate of lignin, reaching 62.00%, and the selectivity of the C-C bond cleavage was high, at 86.8%. The characterization results obtained by TEM, UV-vis/DRS, PL, and transient photocurrent response showed that the ultra-high activity of tri-s-tri-C3N4 was mainly due to the improvements in crystallinity and light absorption. Mechanism studies showed that the dispersion of the catalyst and the combination of lignin and catalyst in aqueous solvents with different acetonitrile ratios were the main factors affecting lignin conversion. As the water content in the solutions increased, the primary active sites were converted from h+ to ·O2-. This study revealed the interactions between lignin, photocatalysts, and reaction solutions, providing a theoretical basis for the photocatalytic conversion of lignin in aqueous solutions.

Pediatric Brain Tumors: Signatures from the Intact Proteome.

The present investigation aimed to explore the intact proteome of tissues of pediatric brain tumors of different WHO grades and localizations, including medulloblastoma, pilocytic astrocytoma, and glioblastoma, in comparison with the available data on ependymoma, to contribute to the understanding of the molecular mechanisms underlying the onset and progression of these pathologies. Tissues have been homogenized in acidic water–acetonitrile solutions containing proteases inhibitors and analyzed by LC–high resolution MS for proteomic characterization and label-free relative quantitation. Tandem MS spectra have been analyzed by either manual inspection or software elaboration, followed by experimental/theoretical MS fragmentation data comparison by bioinformatic tools. Statistically significant differences in protein/peptide levels between the different tumor histotypes have been evaluated by ANOVA test and Tukey’s post-hoc test, considering a p-value > 0.05 as significant. Together with intact protein and peptide chains, in the range of molecular mass of 1.3–22.8 kDa, several naturally occurring fragments from major proteins, peptides, and proteoforms have been also identified, some exhibiting proper biological activities. Protein and peptide sequencing allowed for the identification of different post-translational modifications, with acetylations, oxidations, citrullinations, deamidations, and C-terminal truncations being the most frequently characterized. C-terminal truncations, lacking from two to four amino acid residues, particularly characterizing the β-thymosin peptides and ubiquitin, showed a different modulation in the diverse tumors studied. With respect to the other tumors, medulloblastoma, the most frequent malignant brain tumor of the pediatric age, was characterized by higher levels of thymosin β4 and β10 peptides, the latter and its des-IS form particularly marking this histotype. The distribution pattern of the C-terminal truncated forms was also different in glioblastoma, particularly underlying gender differences, according to the definition of male and female glioblastoma as biologically distinct diseases. Glioblastoma was also distinguished for the peculiar identification of the truncated form of the α-hemoglobin chain, lacking the C-terminal arginine, and exhibiting oxygen-binding and vasoconstrictive properties different from the intact form. The proteomic characterization of the undigested proteome, following the top-down approach, was challenging to originally investigate the post-translational events that differently characterize pediatric brain tumors. This study provides a contribution to elucidate the molecular profiles of the solid tumors most frequently affecting the pediatric age, and which are characterized by different grades of aggressiveness and localization.

Ternary palladium(II) complexes with N-benzyliminodiacetic acid derivatives and 2,2′-bipyridine: Preparation, thermogravimetric, vibrational spectroscopic, DFT, NMR studies and biological activity in vitro

The reactions of N-benzyliminodiacetic acid (BnidaH2) and its para-substituted derivatives, namely: N-(p-chlorobenzyl)iminodiacetic acid (p-ClBnidaH2), N-(p-nitrobenzyl)iminodiacetic acid (p-NO2BnidaH2) and N-(p-methoxybenzyl)iminodiacetic acid (p-MeOBnidaH2) with paladium(II) chloride and 2,2′-bipyridine, were performed in water-acetonitrile solutions. Four new prepared complexes [Pd(Bnida)(bipy)]∙2H2O (1), [Pd(p-ClBnida)(bipy)]∙4H2O (2), [Pd(p-NO2Bnida)(bipy)]∙2H2O (3) and [Pd(p-MeOBnida)(bipy)]∙3H2O (4) were identified by means of chemical analysis and mass spectrometry, and characterized by infrared spectroscopy and thermal analysis (TG/DTA). The molecular geometry and infrared spectra of these four complexes were modelled using DFT calculations at the BP86/def2-TZVP (Pd: ECP) level of theory. Extensive NMR studies have shown the presence of two isomers in solution (DMSO). The characterized palladium(II) complexes demonstrate valuable antiproliferative activity against Caco-2, SW620, NCI-H358 and MDCK I reducing cell growth from 71.7% to 79.9% (10−4 M) (1; 4). PANC-1 display mild sensitivity and slow reduction in cell growth (less than 50%) while BJ present higher viability range and proliferative status. BJ proliferation after exposure to palladium complexes at 10−4 M concentration ranged from 55.2% to 83.5% (1–4). In descending order, antiproliferative effect of tested palladium complexes is, as follows: 4 > 1 > 2 > 3.

Chromatographic behavior of benzimidazole derivatives on hypercrosslinked polystyrene by reverse-phase HPLC

An important part in the research of separation of various compound classes is the study of relationship between structure and property by describing the effect of structure on compounds’ chromatographic retention. The aim of this work was to study the chromatographic retention of the firstly synthesized benzimidazoles from water-acetonitrile and water-methanol solutions on hypercrosslinked polystyrene (HCP) by high-performance liquid chromatography (HPLC). The effect of water-methanol and water-acetonitrile solutions’ composition on the benzimidazole derivative retention factors on HCP was studied. The thermodynamic characteristics of sorption of benzimidazoles’ transition from water-organic solutions onto the surface of HCP phase were obtained. The thermodynamic compensation effects were studied. It has been shown that the benzimidazole nitro derivative realizes additional specific interactions with the aromatic network of HCP. The slope ratio of the Soczewiński–Wachtmeister equation was calculated. It was shown that 1-hydroxymethylbenzimidazole and 2-aminobenzimidazole characterized by small volumes and containing hydrophilic substituents do not subordinate Soczewiński–Wachtmeister model under ranging from 75 to 85% concentrations of acetonitrile.

Carbon monoxide oxidation by oxygen in water-acetonitrile solutions of palladium(II) bromide complexes in the presence of Co(II), Fe(II) and Mn(III) phthalocyaninates

Objectives. The objective of this paper was to compare acetylene oxidative dicarbonylation that leads to maleic anhydride with a side reaction of CO oxidation by oxygen in a PdBr 2 -LiBr-H 2 C-CH 3 CN system and in the presence of insoluble (Co) and soluble (Co, Fe, and Mn) phthalocyaninates (PcM). Methods. To study the oxidation of CO to CO 2 , a kinetics method was used; UV and IR spectroscopy was used to determine the concentrations of initial and intermediate compounds. Results . The knetics of CO to CO 2 oxidation were investigated and the reactivity series of PcM in CO oxidation and maleic anhydride synthesis was characterized. A satisfactory correlation was observed between reaction rates and PcM concentration, as well as the nature of metal, in both processes. The IR measurements of concentrations of Pd(II) and Pd(I) intermediate carbonyl complexes, and CO 2 concentrations, have made it possible to hypothesize the mechanism of CO 2 generation. The effect of PcM concentration on the concentrations of Pd(II)(CO) in CO oxidation has been shown. Conclusions. Based on the data regarding CO oxidation and acetylene oxidative dicarbonylation, certain conditions have been proposed to effectively produce double-labeled maleic anhydride with 13 C (from 13 CO).

The Influence of Water–Acetonitrile Solvent Composition on Thermodynamic Characteristics of Adsorption of Aromatic Heterocycles on Octadecyl-Bonded Silica Gels

The thermodynamics of adsorption of some substituted 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from water–acetonitrile solutions with acetonitrile volume fraction varying within a range of 0.35–0.90 on chemically modified Luna C18 and Discovery C18 silica gels has been studied within a temperature range of 313.15–333.15 K. The thermodynamic characteristics of the adsorption of these compounds on Luna C18 and Discovery C18 silica gels have been determined as depending on solution composition. In the case of Discovery C18, the character of the dependences of different thermodynamic characteristics of the adsorption on liquid phase composition is similar to that of the corresponding dependences previously observed for modified Ascentis®Phenyl silica gel. A similarity has also been found for the dependences of the thermodynamic characteristics of the adsorption on Luna C18 and modified Diasfer-110-C18 silica gel studied previously. The mechanism of the liquid-phase adsorption of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on Luna C18 is changed within a range of acetonitrile volume fractions of 0.60–0.75, as it is in the case of Diasfer-110-C18. At acetonitrile volume fractions of higher than 0.75, the studied heterocycles are adsorbed on Luna C18 surface dynamically modified with acetonitrile without a direct interaction with the grafted layer of the chemically modified silica gel. At the same time, the mechanism of their adsorption on Discovery C18 remains unchanged while acetonitrile concentration is increased in the liquid phase.

On the Differences in the Mechanisms of Adsorption of Aromatic Heterocycles from Water–Acetonitrile Solutions on Octadecyl-Bonded Silica Gels

Adsorption of some 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from water–acetonitrile solutions on Luna C18 and Discovery C18 silica gels with grafted octadecyl groups has been studied in a wide range of compositions at temperatures of 313.15–333.15 K. The comparative analysis of the liquid-phase adsorption of the heterocycles has revealed a number of differences between the mechanisms of binding molecules of the studied compounds by the surfaces of these octadecyl-derivatives of silica gel. The log–log dependences of the retention factor on the molar fraction of acetonitrile in the solutions are strictly linear only for adsorption on Luna C18 silica gel, which is characterized by an increased hydrophobicity. For the adsorption of the studied heterocycles on Discovery C18 silica gel, the concentration dependences of the retention at low and high acetonitrile concentrations in the solution are described by quadratic functions and characterized by higher retention values as compared with those for the linear dependence because of the lower hydrophobicity of this silica gel. It has been found that the surface layer of Luna C18 modified silica gel is enriched with acetonitrile molecules to a higher extent than the surface layer of Discovery C18 silica gel. It has been shown that one adsorbed molecule of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines displaces three and two molecules of pre-adsorbed acetonitrile from the surfaces of Luna C18 and Discovery C18 silica gels, respectively. Linear correlation equations have been proposed for calculating the retention of the studied heterocycles on Luna C18 and Discovery C18 silica gels from mobile phases of arbitrary compositions at different temperatures of chromatographic columns.

Comparative Study of Quinolines and Tetrahydroquinolines Sorption on Various Sorbents from Water-Acetonitrile Solutions.

The retention of 16 quinoline and tetrahydroquinoline derivatives was investigated under liquid chromatography conditions using porous graphitized carbon (PGC), octadecyl silica (ODS) and hypercrosslinked polystyrene (HCLP) stationary phases. For most of the analytes, retention on PGC was greater than on ODS, while retention on HCLP was even greater than on both ODS and PGC. The non-linearity of retention dependencies on acetonitrile content in the eluent was observed for compounds containing carboxy, hydrazo and methoxy groups. The relationships between quinolines structure and their retention factors were investigated. It was found that sorption on different sorbents correlated with different descriptors. Retention on ODS was found to be highly correlated with lipophilicity only while on HCLP it depended on both lipophilicity and polarizability of the sorbates. The feature of PGC was a good correlation of retention factors with topological and geometrical parameters. Additionally, ability of PGC to form OH…π bonds with hydroxymethylquinolines was found. The observed regularities allow one to rationally optimize the chromatographic analysis of structurally similar compounds, which is very important for bioactive substances.

Intermolecular Interactions in Water–Acetonitrile Solutions of Quinoline

The structure of water–acetonitrile solutions of derivatives of quinoline and tetrahydroquinoline is investigated by means of аb initio molecular dynamics. It is shown that the propensity of molecules to form different types of hydrogen bonds depends largely on both the nature of the functional groups and on steric factors. When porous graphitic carbon is used as a sorbent, a linear correlation is observed between the fraction of configurations with hydrogen bonds and the logarithm of the retention factor under conditions of reverse-phase liquid chromatography.

Elucidating the Formation and Transformation Mechanisms of the Switchable Metal-Organic Framework ELM-11 by Powder and Single-Crystal EPR Study.

The effect of the synthesis conditions on the structure and guest-responsive properties of a "gate pressure" metal-organic framework (MOF) with composition [Cu(4,4'-bipy)2(BF4)2] n (4,4'-bipy = 4,4'-bipyridine), also known as ELM-11 (ELM = elastic layer material) was investigated. Two different batches of ELM-11, synthesized from water-methanol and water-acetonitrile solutions, have been entirely characterized by PXRD, nitrogen (77 K) and carbon dioxide (195 K) physisorption, elemental analysis, DRIFT, TG, and SEM. Both ELM-11 samples were studied by electron paramagnetic resonance (EPR) spectroscopy in order to follow the change in the local structure of the copper ion during the activation and resolvation. Continuous wave X-band EPR measurements on powder samples provided an elongated octahedral coordination symmetry of the cupric ions and revealed different axial ligands in the as-synthesized and activated forms in both bulk samples of ELM-11. One of the procedures was amended in order to slow down the crystallization that allows isolation of single crystals of two polymorphic modifications of Cu-4,4'-bipyridine coordination polymers, namely [Cu(4,4'-bipy)2(CH3CN)2](BF4)2 and [Cu2O(4,4'-bipy)3(CH3CN)4](BF4)2, one of which shows a crystal structure similar to that of ELM-11. Further single-crystal EPR experiments on the as-synthesized material [Cu(4,4'-bipy)2(CH3CN)2](BF4)2 revealed the orientation of the g tensor of the cupric ions and proved that layers of acetonitrile-synthesized ELM-11 are arranged perpendicularly to the crystallographic c axis.

Studying the Sorption of Certain Benzimidazoles on Octadecyl Silica Gel from Water–Acetonitrile Solutions via Liquid Chromatography

The effect the composition of a water–acetonitrile eluent has on the sorption of benzimidazoles by octadecyl silica gel is studied using the Snyder–Soczewinski model. Three-parameter equations associating retention factors and certain physicochemical characteristic of the molecules of benzimidazoles are obtained via linear regression analysis. Standard changes in the enthalpy of the transfer of benzimidazoles from the water–acetonitrile phase to the layer of octadecyl silica gel and entropic components of the process are calculated from the temperature dependences of the retention factors. The enthalpy–entropy dependences of sorption are discussed.

Influence of the Structure of Molecules of Derivatives of 1,2,4-Triazole and 1,2,4-Triazine on Chromatographic Retention Under Conditions of Reversed Phase HPLC

The dependence of the chromatographic retention of 1,2,4-triazine and 1,2,4-triazole derivatives from water–acetonitrile solutions over octadecyl silica on the structure of sorbate molecules is studied. The effect the physicochemical parameters and topology of heterocycle molecules have on the retention characteristics under RP HPLC conditions is analyzed.

Photochemical Reaction Between 1,2‐Naphthoquinone and Adenine in Binary Water‐Acetonitrile Solutions

The photochemical reaction between 1,2-naphthoquinone (NQ) and adenine was investigated using nanosecond time-resolved laser flash photolysis. With photolysis at 355nm, the lowest triplet state T1 of NQ was produced via intersystem crossing from its singlet excited state. The triplet-triplet absorption of the state contributes three bands of transient spectra at 374, 596 and 650nm, respectively, in pure acetonitrile and binary water-acetonitrile solutions. In the presence of adenine, the observation of A·+ (at 363nm) and NQ+H· radical (at 343 and 485nm) indicates a multistep mechanism of electron transfer process followed by a proton transfer between 3 NQ* and adenine. By fitting with the Stern-Volmer relationship, the quenching rate constant kq of 3 NQ* by adenine in binary water-acetonitrile solutions (4/1, volume ratio, v/v) is determined as 1.66×109 m-1 s-1 . Additionally, no spectral evidence confirms the existence of electron transfer between 3 NQ* with thymine, cytosine and uracil.

Sorption of adamantane phenylamide derivatives on hyper-cross-linked polystyrene from water–acetonitrile eluents

Study of the main physicochemical features of the sorption of phenylamide adamantane derivatives on hyper-cross-linked polystyrene from water–acetonitrile solutions shows that both hydrophobic and electronic interactions make a large contribution to retention, especially for a chlorine-containing derivative in which there are π–p and π–d interactions between the outer-shell electrons of the chlorine atom in addition to π–π interactions between aromatic fragments of the sorbate and sorbent.

Investigation of adsorption of phenols on detonation nanodiamonds using liquid column chromatography

Adsorption of phenols on microdisperse sintered detonation nanodiamond (MSDN) from water–acetonitrile solutions was investigated using high performance liquid chromatography (HPLC). Parabolic dependence between retention and organic solvent content in mobile phase was observed. The influence of physicochemical characteristic solutes including molecular volume (V), dipole moment (μ), hydrophobicity (logP), polarizability (α) and molecular refractivity (MR)) of phenols on their adsorption from water–acetonitrile solutions was investigated. Single- and multi-parameter correlations between retention factor and various physicochemical characteristics of sorbates were obtained. The effect of column temperature on adsorption of phenols on UDD was investigated. The changes in ΔH and ΔS for competitive adsorption of the test sorbates were determined.

Reaction kinetics and solubility in water-organic binary solutions are governed by similar solvation equilibria

The solvation effects observed in water-organic solutions were studied by combining data for reaction kinetics and dissolution equilibria by means of a linear free-energy (similarity) analysis. Kinetic data for the pH-independent hydrolysis of (4-methoxyphenyl)-2,2-dichloroacetate measured in this work and solubility data for naphthalene, and other substrates of low polarity, in aqueous binary mixtures of methanol, ethanol, acetonitrile, dimethyl sulfoxide (DMSO), and 1,4-dioxane were used. Linear similarity relationships were discovered for these data over the full range of solvent compositions studied. To gain insight into the similarities observed between these different phenomena, molecular dynamics simulations were carried out for naphthalene and an ester in water–acetonitrile solutions. The results revealed considerable preferential solvation of these substrates by the co-solvent. Linear relationships between the experimental data and the mole fractions of acetonitrile in the solvation shells of substrates were found. Surprisingly, a linear relationship was found between the mole fractions of acetonitrile in the solvation shells of the ester and naphthalene. This linearity indicated that a similar solvation mechanism governs even such different phenomena as dissolution and reaction kinetics. The relationships between the experimental data and the results of the molecular dynamics calculations found in this work explained the solvent effect observed in water-organic solutions on the molecular level. Copyright © 2015 John Wiley & Sons, Ltd.

Enthalpies of dissolution of ionic liquids in water-acetonitrile solutions at 298.15 K

Enthalpies of dissolution of ionic liquids [C4mim]OTf, [C4mim]NTf2, and [C4mpy]NTf2 are measured in studying the thermodynamic characteristics of solvation and ion association for ionic liquids in nonaqueous and mixed solvents in acetonitrile-water of three compositions at 298.15 K. Standard enthalpies of solution are determined.

Thermodynamics of the sorption of 1,3,4-oxadiazole and 1,2,4,5-tetrazine derivatives from solutions on hypercrosslinked polystyrene

The sorption of a series of aromatic heterocycles on neutral hypercrosslinked polystyrene from maximally dilute acetonitrile and water.acetonitrile solutions of them is investigated by high-performance liquid chromatography in a range of column temperatures from 308 to 348 K at 5 K intervals. It is found that for all heterocycles, the logarithm of the retention factor versus the reciprocal of the temperature dependences can be approximated by linear functions with r 2 ≥ 0.999. It is established that the true compensation effect (which does not result from the correlation between enthalpy and entropy determination errors) occurs during the sorption of heterocycles on hypercrosslinked polystyrene from both acetonitrile and water-acetonitrile solutions. It is shown that in the compensation diagram, the points corresponding to sorbates are grouped together according to the type of sorbate-sorbent interactions. It is found that changes in the Gibbs energy, enthalpy, and entropy of sorption from acetonitrile solutions and for sorption from water-acetonitrile solutions are related to one another by linear dependences.