Proton-acceptor Properties Research Articles

Chiral Diselenophosphoric Acids for Ion Pair Catalysis: A Novel Approach to Enhance Both Proton Donating and Proton Accepting Properties.

The activation of poorly reactive substrates via strong chiral acids is a central topic in asymmetric ion pair catalysis these days. Despite highly successful scaffolds such as N-triflylphosphoramides, these catalysts either lack C2-symmetry or provide multiple H-bond acceptor sites, leading to lower ee values for certain reactions. We present BINOL-based diselenophosphoric acids (DSA) as an extremely promising alternative. Using an intertwined approach of synthesis and NMR studies, we developed a synthetic approach to DSA with up to 98 % NMR yield. The obtained acids provide both very high proton donor and proton acceptor properties, a bifunctionality, which is key to catalytic applications. Indeed, first reactivity test proved the much higher acidity of DSA and its ability to initiate Mukaiyama-Mannich reaction and protodesilylation of silyl ethers. Together with their C2-symmetry, the single donor and single acceptor situation, the decreased tendency of self-association, and the straightforward synthesis with potential 3,3'-substitution, the DSA provide all features ideal for the further development of ion pair catalysis.

Modified quantum mechanical approach for the estimation of single-electron reduction potential of nitroaromatic compounds in aqueous medium

The midpoint single-electron reduction potential of nitroaromatic compounds in aqueous medium at pH 7.0 (potential of ArNO2/ArNO2 · – couple, E m7) frequently determines their therapeutic and/or toxic properties. However, its estimation remains a complex problem. We propose a modified method of E m7 estimation by quantum mechanical calculations, based on the use of the dielectric continuum model together with a certain number of H2O molecules at the vicinity of nitro group. The optimal number of H2O molecules corresponds to a minimal difference between the experimentally determined and calculated values of E m7, and/or the most negative value of calculated E m7. This enabled us to calculate the E m7 values for a number of ArNO2 (n = 19) with the average deviation of 0.027 V from the experimentally determined ones. Apart from nitrobenzene derivatives, the application of this approach for the representatives of nitropyridines, nitrofurans, nitrothiophenes, and nitrothiazoles was demonstrated. In this case, nitroimidazole derivatives are an exception, evidently due to a strong proton accepting properties of N3 atom of their free radicals.

A natural deep eutectic solvent - protonated L-proline-xylitol - based stationary phase for gas chromatography

The paper presents a new kind of stationary phase for gas chromatography based on deep eutectic solvents (DES) in the form of a mixture of L-proline (protonated with hydrochloric acid) as a hydrogen bond acceptor (HBA) and xylitol as a hydrogen bond donor (HBD) in a molar ratio of HBA:HBD 5:1. DES immobilized on a silanized chromatographic support was tested by gas chromatography (GC) in order to determine its resolving power for volatile organic compounds. Studies have demonstrated the suitability of this type of DES as a stationary phase for GC. The Rohrschneider-McReynolds constants were determined for the synthesized DES, revealing that it is a polar stationary phase (Σ(ΔI) = 1717). The selectivity of DES is influenced by the presence of hydroxyl groups in the xylitol structure capable of forming hydrogen bonds of a donor nature and the proton acceptor properties of the protonated L-proline structure. The presence of additional interactions is brought about by the presence of the carboxyl group. As a result, the retention of alcohols is several times higher (200-670%) than the expected value based on their boiling points. A significant increase in retention (400-970%) was also found for pyridine derivatives. The developed DES stationary phase is characterized by very good repeatability of retention and stability (up to 140°C). The efficiency of the prepared columns (6300-11300 theoretical plates/m) and the selectivity of the DES stationary phase are competitive with the commercial products.

Analysis of Weak Interactions in Crystals of Fenamic Acids–Ethacridine Complexes

While searching for new drugs based on combinations of fenamic acid and its derivatives with other pharmaceutically active substances, the syntheses of complexes of fenamic, flufenamic, mefenamic, and tolfenamic acids with ethacridine lactate were performed, and obtained complexes were characterized by X-ray diffraction. The inter- and intramolecular interactions were determined. An analysis of hydrogen bonds and other weak interactions was performed using Quantum Theory of Atoms in Molecules and noncovalent interaction approaches. The main force building the hydrogen-bond system are proton-accepting properties of the carboxylate group. Also, the presence of molecules of solvents in crystals results in the formation of interaction networks.

Redox‐Active Dendrimer‐Like Oligoguanidines and Their Use in a Proton‐Coupled Electron Transfer Reaction

AbstractRedox‐active organic dendrimers are of interest for a variety of applications, e. g. as components in optoelectronic devices and energy‐storage (battery) materials, and were also used to model enzymatic reactivity. Here, we report the first synthesis of redox‐active dendrimer‐like oligoguanidines, assembling six or twelve guanidino groups attached to aromatic cores in one molecule. The novel oligoguanidines, being strong electron donors, are characterized in their stable (neutral and dicationic) redox states. Redox processes occur preferrentially at the core, while the periphery provides highly Brønsted basic sites. The combined electron and proton acceptor properties of the molecules in their stable oxidized dicationic redox state motivate applications in proton‐coupled electron transfer (PCET) processes. In this work, we test their application in a representative intramolecular oxidative aryl‐aryl coupling reaction.

Comparison of Proton Acceptor and Proton Donor Properties of H2O and H2O2 in Organic Crystals of Drug-like Compounds: Peroxosolvates vs. Crystallohydrates.

Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (H2O2) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (H2O) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by H2O2 as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by H2O. In the case of H2O2 as a proton acceptor in H-bonds, the ratio appeared reversed. The neutral O∙∙∙H-O/O∙∙∙H-N bonds formed by the lone electron pair of the oxygen atom of water were the strongest H-bonds in the considered crystals. In the paper, it was found out that the low-frequency Raman spectra of isomorphous crystalline hydrate and peroxosolvate of N-(5-Nitro-2-furfurylidene)-1-aminohydantoin are similar. As for the isostructural hydrate and peroxosolvate of the salt of protonated 2-amino-nicotinic acid and maleic acid monoanion, the Raman spectra are different.

Spectral and proton acceptor properties of chloramphenicol

The absorption spectra of chloramphenicol aqueous solution were obtained experimentally. The absorption spectra of chloramphenicol isomers and the effect on the spectra of the formation of H-bonded complexes were calculated and interpreted using quantum chemistry methods. Calculation results showed that the absorption spectrum of chloramphenicol by position of bands and their nature is largely determined by the nitrobenzene fragment with little participation of propanol and dichloroacetamide fragments of chloramphenicol. The proton acceptor properties of individual chloramphenicol fragments and the effect of the formation of H-bonded complexes on them have been analyzed. Keywords: chloramphenicol, enantiomers, electronic absorption spectrum.

Спектральные и протоноакцепторные свойства хлорамфеникола

The absorption spectra of chloramphenicol aqueous solution were obtained experimentally. The absorption spectra of chloramphenicol isomers and the effect on the spectra of the formation of H-bonded complexes were calculated and interpreted using quantum chemistry methods. Calculation results showed that the absorption spectrum of chloramphenicol by position of bands and their nature is largely determined by the nitrobenzene fragment with little participation of propanol and dichloroacetamide fragments of chloramphenicol. The proton acceptor properties of individual chloramphenicol fragments and the effect of the formation of H-bonded complexes on them have been analyzed.

Perfluorosulfonic Acid Membranes Thermally Treated and Modified by Dopants with Proton-Acceptor Properties for Asparaginate and Potassium Ions Determination in Pharmaceuticals.

The influence of incorporation of the dopants with proton-acceptor properties into perfluorosulfonic acid cation exchange membranes (MF-4SC and Nafion), and their treatment conditions on the characteristics of Donnan potential (DP)-sensors (analytical signal is the Donnan potential) in the aqueous solutions containing asparaginate and potassium ions in a wide pH range was investigated. A silica, surface modified by 3-aminopropyl and 3-(2-imidazolin-1-yl)-propyl groups, was used as the dopant. The membranes were subjected to mechanical deformation and thermal treatment at various relative humidities. The relationship between water uptake and diffusion permeability of membranes subjected to modification and treatment and the cross sensitivity of DP-sensors based on them to counter and co-ions was studied. The multisensory systems for the simultaneous determination of asparaginate and potassium ions in a concentration range from 1.0 × 10−4 to 1.0 × 10−2 M and pH range from 4 to 8 were developed. An array of cross-sensitive DP-sensors based on MF-4SC membranes containing 3 wt.% SiO2 modified by 10 mol.% 3-aminopropyl and 3-(2-imidazolin-1-yl)-propyl was used for the potassium asparaginate hemihydrate and magnesium asparaginate pentahydrate determination in Panangin® (with an error of 2 and 4%, respectively).

Spectral Response and Diagnostics of Biological Activity of Hydroxyl-Containing Aromatic Compounds

Using IR Fourier spectra and employing quantum-chemical calculations of electronic structure, spectra, and proton-acceptor properties, synthetic derivatives of aminophenol exhibiting biological activity in the suppression of herpes, influenza, and HIV viruses have been investigated from a new perspective, with the aim of establishing the spectral response of biological activity of the molecules. It has been experimentally established that the participation of the aminophenol hydroxyl group in intramolecular hydrogen bonds is characteristic of structures with antiviral properties. A quantum-chemical calculation of the proton-acceptor ability of the investigated aminophenol derivatives has shown that biologically active structures are characterized by a high proton-acceptor ability of oxygen of the hydroxyl group. A correlation that has been obtained among the formation of an intramolecular hydrogen bond, high proton-acceptor ability, and antiviral activity of substituted aminophenols enables us to predict the pharmacological properties of new medical preparations of the given class of compounds.

The effect of the nitrogen-containing base nature on the kinetic of zinc complex formation with octa(m-trifluoromethylphenyl)porphyrazine in benzene

The effect of morpholine and piperidine on the kinetics of complex formation between zinc acetate and octa(m-trifluoromethylphenyl)porphyrazine in benzene has been studied. Possible scheme of the complex formation has been suggested. The effect of proton-accepting properties of the additive on the rate constants has been demonstrated.

Features of the electronic structure and photophysical processes in asymmetric and symmetric (dicyanomethylene)-pyran dyes

The electronic structure and photophysical processes in (dicyanomethylene)-pyran dyes, DCM and bis-DCM, have been studied by methods of quantum chemistry and optical spectroscopy. The spectral-luminescence and proton-acceptor properties for trans and cis conformers are investigated theoretically. The influence of the pyran ring geometry on the aforementioned properties and the efficiency of intramolecular photophysical processes in these molecules are analyzed. Simulation of trans-cis photoisomerization is performed, and its influence on the spectral-luminescence properties is studied.

Electropolymerization of non-substituted Mg(II) porphine: Effects of proton acceptor addition

Electropolymerization of unsubstituted magnesium porphine in acetonitrile solutions possessing various proton-accepting properties has been studied. The overall rate of the polymer-product accumulation on the electrode surface has been established to be limited by the deprotonation step of intermediate species. This conclusion is based on the observed influence of proton-accepting additives, water or 2,6-dimethylpyridine (lutidine), on the Mg-porphine electrooxidation process. Lutidine addition into the polymerization bath enables one to enhance strongly the rate of the film growth and the efficiency of this process increases more than by a factor of two, redox, electric conductivity and spectral properties of thus obtained polyporphine films remaining unchanged, while this non-coordinating agent, lutidine, is not included inside such films.Measurement of the electric resistance of magnesium polyporphine film obtained with lutidine addition has been carried out for its various redox states. Correlation between the redox and electron-conductive properties of the polyporphine film for various potential ranges has been observed.

Infrared Spectroscopy of Hydrogen Bonds in Benzoic Acid Derivatives

We have measured the Fourier transform IR spectra of CCl4 solutions of benzoic acid and its biologically active derivatives. We investigated the proton-acceptor properties of the studied molecules theoretically by the molecular electrostatic potential method. The calculations are compared with experimental results. Based on an estimate of the proton-acceptor properties, we give an interpretation of the specific features of the IR spectra of benzoic acid and its derivatives in the region of the O–H and C = O vibrations. The mechanisms for interactions of the molecules are determined by the nature of substituents which are added to the benzene ring in positions para and meta to the carboxyl group. We identify the conditions for appearance of intermolecular hydrogen bonds of O–H · · · O = C, O–H · · · O–H types with formation of cyclic and linear dimers. We show that intramolecular hydrogen bonds of the type O–H · · · O–CH3 prevent the hydroxyl groups from participating in intermolecular interactions.

Spectroscopic and proton-acceptor properties of biologically active molecules of benzoic acid and its derivatives

We have measured the absorption, fluorescence, fluorescence excitation spectra, fluorescence quantum yields, and IR Fourier-transform spectra of aromatic acids in solutions. We have considered spectroscopic particular features of benzoic acid, its hydroxylated and methoxylated derivatives. Using quantumchemistry methods, we have calculated and interpreted electronic spectra. Data of calculations have been compared with experimental results. We have ascertained the main channels and mechanisms of photophysical relaxation processes in the molecules under study. Proton-acceptor properties of molecules of aromatic acids have been evaluated. We have analyzed in detail mechanisms by which hydrogen bonds are formed, intramolecular charge redistribution is realized, and the electron density of oxygen atoms changes. Spectroscopic indications of participation of oxygen-containing groups in intramolecular interactions and in intermolecular interactions with the formation of cyclic dimers have been revealed.

Stability and efficiency of supported liquid membranes in electromembrane extraction—a link to solvent properties

The current work presents a large systematic screening of 61 possible organic solvents used as supported liquid membranes (SLM) in electromembrane extraction (EME). For each organic solvent, recovery, current across the SLM, and stability considerations have been investigated and correlated to relevant solvent properties through partial least square regression analysis. The five unpolar basic drugs pethidine, haloperidol, methadone, nortriptyline, and loperamide were used as model analytes. Efficient EME solvents were found to have a low water solubility (<0.5 g L(-1)) and belonged to cluster 2 of a Kamlet-and-Taft-based solvent classification system (high dipole moments and proton acceptor properties). These parameters were especially found in nitroaromatic compounds and ketones. Small molecules with low log P value and high water solubility were unsuitable, as they tended to give unstable extractions, caused by a high current across the SLM. This was often combined with substantial solvent-related interferences and the generation of an electroosmotic flow across the SLM, with resulting acceptor solution expansion. Large molecules with a high log P value were classified as inefficient. For these solvents, no current was measured across the SLM and no analytes were extracted. This is the first time systematic knowledge on the SLM in EME has been gathered and investigated, and the presented results could be highly beneficial for future development and optimization of EME.

Hybrid materials based on MF-4SC perfluorinated sulfo cation-exchange membranes and silica with proton-acceptor properties

Hybrid materials based on perfluorinated sulfo cation-exchange MF-4SC membranes with silica nanoparticles in the pores, whose surface is modified by hydrocarbon fragments containing amino groups [3-aminopropyl and 3-(2-imidazolin-1-yl)propyl] that impart it with proton-acceptor properties, were obtained. In has been shown that this modification results in a decrease in ion exchange capacity, water uptake and diffusion permeability of the membranes, whereas the ionic conductivity of the membranes with low content of modifying groups increases in comparison with the membrane that contains only SiO 2 . The observed phenomenon, non-typical of ion-exchange materials, was explained using the model of the semielacticity of membrane pore walls.

Quantum-chemical and ir spectroscopic analysis of aminophenol derivatives with antiviral activity

Bioactive carbonyl- and sulfonyl-derivatives of aminophenols were studied. The proton-acceptor abilities of the aminophenols were estimated using a molecular electrostatic potential method. IR Fourier spectra of the aminophenols with different substituents on the amine were measured in solutions and crystals. Molecular functional groups that participate in the formation of H-bonds of the O-H⋅⋅⋅O=C, N-H⋅⋅⋅O=C, O-H⋅⋅⋅O=S=O, and N-H⋅⋅⋅O=S=O types were identified. The aminophenol antiviral activity correlated with the ability to form the H-bonds. A correspondence between the proton-acceptor properties of the hydroxyl oxygen in the amino- phenols and their antiviral activity was revealed. Introduction. The ability of viruses to acquire drug resistance necessitates the targeted discovery of new compounds that exhibit high antiviral activity and low toxicity and; therefore, are promising for developing new drugs. Such compounds could be aminophenol (AP) derivatives. It was found that AP exhibit antiviral properties against Her- pes and influenza A viruses (1-4) and are also capable of suppressing HIV infection in cell culture (5). A systematic and detailed investigation of the electronic structure using quantum-chemical and optical methods was carried out in order to find the chemical structure-pharmacological activity relationship of AP derivatives. The spectral and luminescence properties of N-aryl AP derivatives possessing antiviral activity were studied (6-8). It was found that intramolecular H-bonds (IHB) of the O-H⋅⋅⋅N or N-H⋅⋅⋅O types could form in ortho-AP be- tween NH and OH groups, both of which could be either a proton donor or acceptor. Two sterically different confor- mations with planar and non-planar amines could form as a result of the structural features of these types of H-bonds. Introducing t-butyl groups into the phenyl ring facilitated a shift of the conformational equilibrium toward non-planar conformations and strengthened the O-H⋅⋅⋅N bond. This led to an increase in the antiviral activity of the compounds. Herein results from quantum-chemical and IR spectroscopic studies of AP derivatives with C=O and SO2 groups are reported. The AP exhibited activity against Herpes, influenza A, and HIV viruses. A comprehensive study of compounds exhibiting activity against various virus species seemed necessary in order to reveal relationships of electronic structure, spectroscopic properties, and pharmacological activity. Theoretical Calculations and Experimental Method. The studied AP derivatives were synthesized according

Electronic structure and spectroscopic properties of anti-HIV active aminophenols

We have measured the absorption and fluorescence spectra and fluorescence quantum yields of sulphone-containing anti-HIV active o-aminophenol molecules in an inert solvent, hexane, and in a polar solvent, acetonitrile. We have studied IR Fourier-transform spectra and examined structural features of o-aminophenols with different substituents in solutions and crystals. Functional groups of molecules that are involved in the formation of hydrogen bonds have been revealed. Proton acceptor properties of o-aminophenol molecules have been theoretically evaluated using the method of molecular electrostatic potential. Using quantum chemistry methods, we have calculated and interpreted absorption and fluorescence spectra of o-aminophenols. Calculation data are compared with experimental results. We have determined the main channels and mechanisms of photophysical relaxation processes in o-aminophenols.

Spectral and luminescent properties of 1-substituted naphthalenes

Spectral, luminescent, and proton-acceptor properties of 1-substituted naphthalenes containing a CO group were investigated. Photophysical rate constants and quantum yields of fluorescence were calculated. The ability of the carbonyl oxygen to form a hydrogen bond was estimated for 1-naphthaldehyde, methyl 1-naphthoate, and 1-naphthyl acetate.