Media Of Different Polarity Research Articles

Evolution of vibrational bands upon gradual protonation/deprotonation of arsinic acid H2As(O)OH in media of different polarity.

This computational work is devoted to the investigation (MP2/def2-TZVP) of the geometry and IR parameters of arsinic acid H2AsOOH and its hydrogen-bonded complexes under vacuum and in media with different polarity. The medium effects were accounted for in two ways: (1) implicitly, using the IEFPCM model, varying the dielectric permittivity (ε) and (2) explicitly, by considering hydrogen-bonded complexes of H2As(O)OH with various hydrogen bond donors (41 complexes) or acceptors (38 complexes), imitating a gradual transition to the As(OH)2+ or AsO2- moiety, respectively. It was shown that the transition from vacuum to a medium with ε > 1 causes the As(O)OH fragment to lose its flatness. The solvent polar medium introduces significant changes in the geometry and IR spectral parameters of hydrogen-bonded complexes too: as the polarity of a medium increases, weak hydrogen bonds become weaker, and strong and medium hydrogen bonds become stronger; in the case of a complex with two hydrogen bonds cooperativity effects are observed. In almost all cases the driving force of these changes appears to be preferential solvation of charge-separated structures. In the limiting case of complete deprotonation (or conversely complete protonation) the vibrational frequencies of νAsO and νAs-O turn into νAs-O(asym) and νAs-O(sym), respectively. In the intermediate cases the distance between νAsO and νAs-O is sensitive to both implicit solvation and explicit solvation and the systematic changes of this distance can be used for estimation of the degree of proton transfer within the hydrogen bond.

Stability of Hassi-messaoud Asphaltenes in Media of Different Polarities

The aim of this work is to explore the floculation behavior of asphaltenes (extracted from a deposit recovered from a Hassi-Messaoud oil well) in solution in toluene according to the polarity of the flocculating medium. The flocculation thresholds related to the addition of two flocculating agents of different polarities (n-heptane and acetone) for three asphaltenic concentrations are obtained by means of near infra-red absorption spectrophotometry. The Hildebrand solubility parameters of the flocculated asphaltenic fractions are deduced using the Donnagio method based on the Flory−Huggins theory. The results obtained indicate that the interactions between the flocculated asphaltenic molecules within the toluene/acetone mixture are weaker than those in the toluene/n-heptane mixture.

An Amphiphilic Pyridinoyl-hydrazone Probe for Colorimetric and Fluorescence pH Sensing.

A new pH sensor based on a substituted aroylhydrazide with a flexible side chain and a terminal trimethyl ammonium group (PHA+) was designed and synthesized. The terminal quaternary ammonium guarantees excellent solubility in water. At the same time, the probe is very soluble in hydrophobic envirornments. The pyridinoyl-hydrazone moiety acts as the pH-sensitive fluorophore/chromophore probe. Extensive physicochemical characterization has been performed on the bromide salt PHABr. DFT calculations, based on single-crystal X-ray data, permitted to rationalize the optical behavior. Molecular dynamics simulations permitted to clarify the mode of interaction with lipid membrane. The ability of the probe to change color and fluorescence in response to different pH and media of different polarity has been investigated. PHABr shows a remarkable pH-dependent behavior in both absorption and fluorescence spectra with high sensitivity and strong on-off switch effect at neutral pH, perceptible even to the naked eye.

Interaction of Titanium, Zirconium and Hafnium Metallocene Dichlorides with Styrene and Methyl Methacrylate in the Media of Different Polarity

The UV spectral study of the interaction of titanium, zirconium, and hafnium metallocene dichlorides with styrene or methyl methacrylate in the media of different polarity (carbon tetrachloride and ethanol) has been carried out using the isomolar series method. The formation of weak intermediate complexes has been shown, the solvent polarity significantly affecting the process of their formation. It has been found for the first time that charge-transfer complexes between metallocene dichlorides and styrene are formed only in polar solvent (ethanol). Possible structures of intermediate complexes have been proposed.

Effect of substituents on spectral, luminescent, and time-resolved spectral properties of 2,6-diarylidene derivatives of cyclohexanone

Spectral, luminescent, and time-resolved properties of 2,6-dibenzylidene cyclohexanone and its symmetric derivatives in the para-position of benzene ring (dimethoxy, dimethylthio, and bis-N,N-diethylamino groups) have been studied in media of different polarity (cyclohexane, acetonitrile, dimethylsulfoxide, and methanol). Introduction of electro-donating substituents to dibenzylidene cyclohexanone results in the red shift of the absorption maximum by 81–138 nm upon passing from the nonpolar to polar medium. Bis(N,N-diethylamino)dibenzylidene cyclohexanone fluoresces in polar solvents, acetonitrile, dimethylsulfoxide and methanol. The bathofluoric shift on passing from acetonitrile to methanol is 39 nm. The relative quantum yield of fluorescence in acetonitrile is seven times that in methanol. An intermediate species absorbing in the range of 400–560 nm with a maximum at 430–460 nm has been observed under the action of the laser pulse on dibenzylidene cyclohexanone solutions in acetonitrile. The intermediate species has a lifetime of 40, 20, and 7 μs for dibenzylidene cyclohexanone and its dimethylthio and dimethoxy derivatives, respectively.

Theoretical investigation of the action mechanisms of N,N-di-alkylated diarylamine antioxidants

In this work, a density functional theory-based method was used to study the antioxidant properties and some reaction mechanism involved in the free radical-scavenging reactions of eight N,N-dialkylaminated diarylamines. The analyzed properties are the bond dissociation enthalpies of NH bond, electron transfer enthalpies, ionization potentials, proton affinities and proton dissociation enthalpies. The reaction mechanisms are hydrogen atom transfer, single electron transfer–proton transfer and sequential proton loss electron transfer. Computations were performed in two different solvents: water, and chlorobenzene. The aim of the work was to establish the effect of the progressive addition of nitrogen atoms into the diarylamines aryl rings on the thermodynamic parameters above mentioned, to individuate the preferred action mechanism of these compounds and the influence of media of different polarities. Results we have obtained indicate that the hydrogen atom transfer or more precisely the proton-coupled electron transfer from antioxidant to a particular free radical that was chosen as target, is the most probable action mechanism, that structural change made including nitrogen atoms into aryl rings does not give benefits nor from thermodynamic neither from kinetic point of view and that polarity of solvent has no significant influence.

Cholic acid dimers as invertible amphiphilic pockets: synthesis, molecular modeling, and inclusion studies

Two dimers of cholic acid were synthesized through simple covalent linkers. The dimers form invertible molecular pockets in media of different polarity; hydrophobic pockets are formed in water and hydrophilic pockets are formed in organic media. Fluorescence studies show that pockets formed by these dimers can serve as invertible hosts for the hydrophobic guest pyrene and the hydrophilic guest coumarin 343. The molecular pocket also enhances dissolution of the weakly soluble cresol red sodium salt in organic media. Molecular modeling was performed to better understand the host–guest complexation process of the invertible amphiphilic pockets. The calculated free energy changes indicate that the two dimers form the most stable complexes with coumarin 343 at a host to guest ratio of 2:2, whereas the host to guest ratio differs in the formation of complexes with pyrene for the two dimers. The dimer with the shorter, less flexible linker seems to form host–guest complexes that are more stable in both water and organic solvents.

Interaction of ferrocene with styrene and methyl methacrylates in the media of different polarity

The interaction of ferrocene with styrene and methyl methacrylate in media of different polarity (hexane, tetrachloromethane, and ethanol) has been studied by means of UV spectroscopy using the isomolar series method. For both monomers, intermediate complexes are formed, the medium polarity significantly affecting the complexes formation. Ferrocene acts differently in the interaction with styrene (being the electron acceptor) and methyl methacrylate (being the electron donor). It has been discovered that only in the case of ethanol a charge-transfer complex between ferrocene and styrene is formed. Possible structures of the intermediate complexes have been suggested.

The effect of the medium polarity on the mechanism of the reaction of hydroxybenzenes with hydrazyl radical in aprotic solvents

Mechanisms of the reaction of di- and trihydroxybenzenes with 2,2′-diphenyl-1-picrylhydrazyl (stable radical) in aprotic media of different polarity have been elucidated by experimental and quantum-chemical methods. Kinetic, stoichiometric, and activation parameters of the reaction have been determined. In benzene (nonpolar solvent), the studied reaction occurs via the hydrogen atom transfer mechanism; in the polar solvent with weak ionizing ability (i.e. DMSO), the reaction predominantly occurs via the faster mechanism of coupled electron and proton transfer.

Effect of substituents on spectral, luminescent and time-resolved characteristics of 2,5-diarylidene derivatives of cyclopentanone

Spectral, luminescent and time-resolved characteristics of 2,5-dibenzylidenecyclopentanone and its symmetrical derivatives (bis(N,N-diethylamino-), dimethoxy-, tetramethoxy-, dimethylthio-, and bis-18- crown-6 derivative) have been studied in media of different polarity (cyclohexane, toluene, acetonitrile, DMSO, and methanol) at room temperature. The absorption maximum of dibenzylidenecyclopentanone shifts bathochromically by 15 nm with an increase in polarity of the medium (cyclohexane–methanol). The introduction of electron-donating substituents in the aromatic rings of dibenzylidenecyclopentanone also results in a bathochromic shift of the absorption maximum by 100–130 nm in the media of different polarity and shifts the fluorescence maximum by 130 nm relative to the maximum of the dimethoxy derivative. Upon laser irradiation of oxygen-free solutions of dibenzylidenecyclopentanone and its tetramethoxy- and bis-18-crown-6 derivatives in acetonitrile, the triplet state with a half-life time of 0.3–1 μs is generated. For dimethoxy-, dimethylthio-, tetramethoxy-, and bis-18-crown-6 derivatives of dibenzylidenecyclopentanone, the isomers with a lifetime of ~50 ms are formed.

Polyelectrolyte Gel Swelling and Conductivity vs Counterion Type, Cross-Linking Density, and Solvent Polarity

A joint theoretical and experimental study is devoted to the swelling and electrical conductivity of highly charged polyelectrolyte (PE) gels in media of different polarity. Deprotected poly(tert-butyl carbamate l-alanine) gels provided with fluorine, bromine, chlorine, sulfate, and trifluoroacetic counteranions demonstrated different conductivity in aqueous medium as well as solvent uptake in water/methanol mixtures. Counterion specificity in PE gel properties was theoretically explained in the framework of the model which treats ion association within the network as a two-stage process. Manning-type condensation, being the first condensation stage not affected by counterion type, provides understanding of a gel maximal swelling at intermediate degrees of gel ionization f and a slight gel contraction at f tending to unity, which were earlier observed in experimental investigations. The second ion association stage is an ion pairing influenced by the kind of counterion. Since a considerable fraction of io...

Kinetic features of chain initiation reactions during the oxidation of unsaturated compounds in media of different polarity

The kinetics of chain initiation during the auto-oxidation of some unsaturated compounds (methyl linoleate, allyl acetate, allyl propyl ether, styrene, α-methyl styrene, butyl acrylate, butyl methacrylate, ethyl cinnamate, trans-1,2-diphenylethylene, trans,trans-1,4-diphenylbutadiene-1,3) in solvents of different polarity was studied at temperatures 343–383 K. The data array comprised of chain initiation rate constants of bi- and trimolecular reactions was obtained. It was shown that in some cases, the polarity of the medium is the key factor defining the initiation mechanism.

Influence of solvation on the kinetics of methyl methacrylate oxidation inhibited by aromatic amines

The kinetics of methyl methacrylate oxidation inhibited by aromatic amines in media of different polarities was studied. The complexing parameters in systems “oxidation substrate—aromatic amine—solvent” using IR and NMR spectroscopy were found. The correlations between inhibited oxidation rate constant and the polarity of the medium were obtained using Kirkwood–Onsager equation.

Effect of phenolic compounds on photodegradation of anthracene and benzo[a]anthracene in media of different polarity

Abstract The photodegradation of anthracene (Ant) and benz[a]anthracene (BaA) were studied in air-equilibrated hexane, methanol and pure water solutions in the absence and presence of phenolic compounds (4-methylcatechol, guaiacol and syringol). In the absence of phenolic compound, the pseudo first-order degradation rate constants of Ant and BaA increased with the polarity of solvent, demonstrating the influence of solvent effects on the photoreactivity. The differences can be attributed to factors such as the proton donating potential of the solvent, and the formation potentials of PAH radical cation and hydroxyl radical in solvent. In the presence of phenolic compound, Ant and BaA photodegradation rates were accelerated in hexane and methanol while inhibited in water solutions. Photodegradation kinetics of the phenolic compounds were also measured; and visible colored products were observed in all three solvents. The observed accelerations of Ant and BaA photodecay in the presence of the phenolic compounds can be explained by energy transfer from the phenolic compound to PAH, phenolic hydrogen abstraction by excited PAH and more reactive radical formation from the phenolic compound. However, the inhibition effects of Ant and BaA photodecay in water were more influenced by the quenching of photo-produced reactive oxygen species (ROS) by the phenolic compound and/or its photoproducts. The results indicate that the photodegradation of PAHs will be highly dependent on the aerosol water content. i.e., the chemical composition of the environmental aerosols.

Synthesis and optical properties of the isomeric pyrimidine and carbazole derivatives: Effects of polar substituents and linking topology

A series of nonlinear oligoarylenes with a pyrimidine unit as central core and carbazole containing aryl branches in positions 2, 4 and 4, 6 of the pyrimidine ring were successfully synthesized by sequential Suzuki coupling of the corresponding 2,4- or 4,6-dichloropyrimidines. Optical properties of the compounds were thoroughly investigated in the media of different polarity. Owing to pronounced electron-accepting properties of pyrimidine core, the compounds with donating carbazole groups showed expressed intramolecular charge transfer (ICT) character of the excited states, which was proved by solvatochromic dynamics and supported by DFT calculations. ICT resulted in the dramatic enhancement of excited state lifetime (up to 5 times) with increased solvent polarity. The competition of constantly decreasing radiative and nonradiative relaxation rates resulted in non-monotonous variation of fluorescence quantum yield from 24% to 74%. The tailoring of fluorescence quantum yield of the pyrimidine derivatives via altering linking topology and polarity of the substituents is discussed.

UV–Vis spectrophotometric studies of self-oxidation/dissociation of quaternary ammonium permanganates (QAP) – impact of solvent polarity

Self-oxidation/dissociation of some quaternary ammonium permanganates (QAPs), such as cetyltrimethylammonium permanganate (CTAP) and tetrabutylammonium permanganate (TBAP), have been studied spectrophotometrically in six different organic solvent media of different polarities wherein the compounds show good solubility and stability. The optical densities of the substrates at zero time (ODo) and first-order rate constants of dissociation (k1) have been determined from their successive scanning for 40min. At comparable experimental conditions, absorption capabilities of the substrates are compared from the ODo values in various organic media; the stability of the solutions is compared from the successive scan spectra in those media. The ODo values and the k1 values have been plotted against some solvent parameters to understand their effects on the absorbance and reactivity of the QAPs. These data are also subjected to multiple regression analysis to explain the influence of various solvent parameters on the ion-pairing properties of the substrates, thus elucidating their effects on the process of self-oxidation/dissociation of the substrates.

Thermodynamically controlled chemoselectivity in lipase-catalyzed aza-Michael additions

Chemoselective synthesis of N-protected β-amino esters involving lipase-catalyzed aza-Michael additions and α,β-unsaturated precursors is mainly hampered by the two electrophilic sites present on these compounds. In order to control the chemoselectivity a solvent engineering strategy based on the thermodynamic behaviour of products in media of different polarity was designed. This strategy allowed to obtain aza-Michael adducts from benzylamine and different acrylates with high selectivity. In almost all reactions carried out in n-hexane, a non-polar solvent, aminolysis was avoided while the corresponding Michael adducts were exclusively synthesized in 53–78% yields. On the contrary, in reactions carried out in a polar solvent such as 2-methyl-2-butanol the aminolysis products were favoured. Thermodynamic analyses of these processes using the COSMO-RS method helped to understand some of the key factors affecting chemoselectivity and confirmed that a reliable estimation of the thermodynamic interactions of solutes and solvents allows an adequate selection of a reaction media that may lead to chemoselectivity.

Erratum to: Nonradiative Transitions in Media of Different Polarities and Their Modeling for 12′-Apo-β-Caroten-12′-Al and 8′-Apo-β-Caroten-8′-Al

Erratum to: Nonradiative Transitions in Media of Different Polarities and Their Modeling for 12′-Apo-β-Caroten-12′-Al and 8′-Apo-β-Caroten-8′-Al

Nonradiative Transitions in Media of Different Polarities and Their Modeling for 12′-Apo-β-Caroten-12′-Al and 8′-Apo-β-Caroten-8′-Al

The theory of nonradiative transitions, based on the model of orientational broadening of electronic levels, is used to interpret known data on the effect of the polarity of the medium and temperature on the lifetime of the S 1(A − ) state for 12′-apo-β-caroten-12′-al and 8′-apo-β-caroten-8′-al. The effect of promoting vibrations on the rate constant for nonradiative transitions is considered. The results make it possible to hypothesize that the internal electric field created by the environment strongly perturbs the pigment molecules. Consequently, in the excited S 1(A − ) state, both pigments exist as different conformers I and II. Their structures differ by a 180° rotation of the cyclohexene ring relative to the polyene chain. Conformer II predominates in polar media, and is found in an intramolecular charge-transfer state S 1(A − /ICT). In addition, as a result of fluctuations in the internal electric field, it can also be found in a charge-separated state S 1(A − /CS).

Substituents and environment influences on aromaticity of peri- and para-substituted naphthalenes.

The influence of substituents and environment on the aromaticity of the naphthalene ring is shown for a series of peri- and para-substituted naphthalenes. Crystal structure geometries are compared with the single molecule structures in vacuum (optimized at the B3LYP/6-311++G** level) and with structures determined in media of different polarity. The harmonic oscillator model of aromaticity (HOMA) index of the naphthalene rings has been used to characterize the aromaticity of the investigated molecules. It has been shown that the ellipticity of the C2-C3 (C6-C7) bonds can be applied as a measure of participation of the quinoid resonance structure and through-resonance effect between the para-substituents.