Taft Model Research Articles

Spectroscopic and DFT evaluation of the positional effect of amino group on the properties of aminobenzenesulphonic acid: solvents interactions

Positional effect of NH2 group on the properties of aminobenzenesulphonic acid (AMBSA) has been investigated. Potential energy scan (PES) calculation revealed the energy difference between the two global minima predicted for each of the derivatives to be decreasing with the increasing distance between the –NH2 substituent and the –SO3H moiety. On the other hand, the zero-point energy affirmed the ortho and para substituted AMBSAs as being more stable than the meta counterpart by 1.7 kcal/mol. The derivatives showed comparable chemical reactivity, whereas the simulation of their solubility in the selected solvents affirmed the 4-aminobenzenesulphonic acid to be generally more soluble than the other derivatives. Application of Kamlet–Taft model on the absorption data of the aminobenzenesulphonic acids revealed the influence of solvent polarity together with hydrogen bonding ability on their solubility. On the part of vibrational property, the vibrational modes associated with –SO3H moiety were found to be sensitive to the position of amino substituent.

Solvent Effects on Gelation Behavior of the Organogelator Based on L-Phenylalanine Dihydrazide Derivatives

A series of organogelators based on L-phenylalanine has been synthesized and their gelation properties in various organic solvents were investigated. The results showed that these organogelators were capable of forming stable thermal and reversible organogels in various organic solvents at low concentrations, and the critical gel concentration (CGC) of certain solvents was less than 1.0 wt%. Afterward, the corresponding enthalpies (ΔHg) were extracted by using the van ’t Hoff equation, as the gel–sol temperature (TGS) was the function of the gelator concentration. The study of gelling behaviors suggested that L-phenylalanine dihydrazide derivatives were excellent gelators in solvents, especially BOC–Phe–OdHz (compound 4). The effects of the solvent on the self-assembly of gelators were analyzed by the Kamlet–Taft model, and the gelation ability of compound 4 in a certain organic solvent was described by Hansen solubility parameters and a Teas plot. Morphological investigation proved that the L-phenylalanine dihydrazide derivatives could assemble themselves into an ordered structure such as a fiber or sheet. Fourier-transform infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonance (1H NMR) studies indicated that hydrogen bonding, π–π stacking, and van der Waals forces played important roles in the formation of a gel.

Photophysical properties of novel fluorescent 1-(3-Hydroxy-benzofuran-2-yl)-benzo[f]chromen-3-one derivative: models for correlation solvent polarity scales

Photophysical and spectral properties of a new benzofuran-derivative-based fluorescent probe 1-(3-Hydroxy-benzofuran-2-yl)-benzo[f]chromen-3-one (1-HBBC) were considered in various parameters of solvents, making use of UV–Vis absorption and fluorescence emission spectroscopy. The absorption and fluorescence emission peak maxima were observed between 260–349 and 400–485 nm, respectively, prompting Stokes’ shift between 13 993 and 18 495 cm−1. Diverse solvent parameters have been utilized to understand the solvatochromism of 1-HBBC. This information is applied to understand the effects of the solvent, on the shifting in the spectra of 1-HBBC and access the execution of empirical solvatochromic models: the well-known Kamlet–Taft model and two recent Catalan models. Linear solvation energy relationships proposed by the Kamlet–Taft treatment for the 1-HBBC molecule indicate that it is appealing as a molecule for the hydrogen bond and solvent polarity properties it has exhibited. The models offer good statistical execution for all solvents studied in this work. A general decency of fit is found for benzofuran values for the models’ contractions, whereas these solvents are incorporated directly into the solvatochromic analysis. These reductions are comparable for the Kamlet–Taft and Catalan 4P models but important for the Catalan 3P model. The results shown herein can be used for outlining new luminescent tests for nonpolar and polar microenvironment.

Dissolution of antibiotics mycelium in ionic liquids: Performance and mechanism

Abstract Antibiotics mycelium, byproduct of pharmaceutical industry, contains high percentage of proteins, polysaccharides and lipids, while, the low solubility in traditional solvents limits its utilization. The dissolution process of penicillin mycelium was investigated using ionic liquids (ILs) as solvent. Quantitative correlation of solubility and ILs structure and dissolution mechanism were determined. About 91.45% of penicillin mycelium was dissolved in 1-butyl-3-methylimidazolium acetate ([Bmim]Ac) under the condition of 120.0 °C and [Bmim]Ac/mycelium (m/m) ratio of 3.90:1. Synergistic effect of ILs and DMSO was confirmed with the DMSO/[Bmim]Ac (v/m) ratio in the range of 0.0–1.0. At 25.0 °C, the dissolution of penicillin mycelium increased from 69.74% to 94.50%, with the ratio of DMSO to [Bmim]Ac (v/m) as 1:1. The room temperature dissolution of mycelium provides a novel and energy-saving process for its high-valued utilization. The NMR and FT-IR spectra showed that hydrogen bonds are the dominant driving force for the dissolution in ILs. Quantitative study on the effects of anions and cations of ILs on dissolution using Kamlet–Taft model showed that there was a linearly positive correlation between solubility of penicillin mycelium and β parameter of the ILs. The solubility of mycelium increased with increasing hydrogen bond accepting ability of anions and donating ability of cations.

Solvent effect on protonation of tpps in water-DMF mixtures

The protonation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin was investigated in aqueous solutions of N,N-dimethyformamide at 25 °C and 0.1 mol.dm-3 sodium perchlorate. The solvent effect on value of protonation constant was examined by using the linear solvation energy relationship concept. The value of logK1,logK2 and logKt was correlated with the macroscopic (dielectric constant) and microscopic Kamlet-Taft parameters (a, b and p*) of binary mixtures. The solvent effects were analyzed in the terms of Kamlet, Abboud and Taft model (KAT). Multiple linear regression were used to find the contribution of the microscopic parameters containing a (hydrogen-bond acidity), p* (dipolarity/polarizability) and b (hydrogen-bond basicity). It was found that a and b were the most predominant descriptors. Also, relationship with reciprocal of dielectric constant was obtained based on Born’s model, showing the significance of specific solute-solvent interactions. Therefore the hydrogen bonding interactions between solute and solvent components are mainly responsible for the change in protonation constants of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin in water- N,N-dimethyformamid binary mixtures. KEY WORDS: Protonation, TPPS, Solvent effects, Aqueous mixture, DMF Bull. Chem. Soc. Ethiop. 2016, 30(3), 457-464DOI: http://dx.doi.org/10.4314/bcse.v30i3.14

Solvatochromism and azo–hydrazo tautomerism of novel arylazo pyridone dyes: Experimental and quantum chemical study

The state of the tautomeric equilibria of eleven arylazo pyridone dyes was evaluated from UV–Vis absorption spectra with the aid of the quantum mechanical modeling. NMR analysis and theoretical calculations, by using PCM/ωB97X-D/6-311G(d,p) method, confirmed that prepared compounds exist mainly in Hydrazo form. Internal hydrogen bonding in Hydrazo tautomer, analyzed by AIM topological analysis and total electron density at the bond critical point (BCP), confirmed a presence of strong hydrogen bond which contributes to higher stability of Hydrazo form. Linear solvation energy relationships (LSERs) rationalized solvent influence on solvatochromism of all compounds in Hydrazo form and KT by using Kamlet–Taft model. Linear free energy relationships (LFERs) were applied to the substituent-induced NMR chemical shifts (SCS) using SSP (single substituent parameter) and DSP (dual substituent parameter) model. Density plots over the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO) energy surface provide information on the charge transfer during excitation. The molecular electrostatic potential (MEP) surface map was plotted over the optimized geometry of the molecules in order to visualize electron density distribution and explain origin of solvent/solute interactions.

Ionic Liquids: Additives for Manipulating the Nucleophilicity

Kinetic investigations of the SN2 reaction at the sulfur atom of p-toluenesulfonyl chloride with sodium azide in dried methanol in the presence of varying amounts of room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium acetate ([C4C1im][CH3COO]), 1-butyl-3-methylimidazolium chloride ([C4C1im]Cl) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C4C1im][PF6]), were carried out in order to explore and understand the impact of these additives on the rate of such reactions. The observed results indicate that the rate constant of the reaction increase appreciably with increases in the concentration of RTILs in RTIL–methanol binary solvent systems. The results were analyzed in light of a Kamlet–Taft model system, which established that the observed impact of RTILs can be attributed to the cumulative effects of increase in the β value (hydrogen bonding acceptor ability) which is expected to enhance the reactivity of p-toluenesulfonyl chloride as well as the nucleophilicity of the azide ion and decrease in the π* value (solvent dipolarity/polarizability) which is expected to enhance the reactivity of the azide ion. Of the three ionic liquids used in the presented studies, [C4C1im][CH3COO] was observed to be more effective in accelerating the rate constant; this we attribute to its comparatively stronger ability to increase the β value and decrease the π* value in the mixed solvent system.

Intramolecular charge transfer in coumarin based donor-acceptor systems: Formation of a new product through planar intermediate

Abstract Fluorescence behavior and intramolecular charge transfer (ICT) property of N,N′-dimethylamino substituted anil derivative of coumarinyl amine was studied by steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculation. Quantitative analysis of the effect of solvent hydrogen bonding on several spectral parameters was done using multiple regression analysis based on Kamlet–Taft model. The present system shows an additional long wavelength fluorescence band almost instantaneously in presence of methanol in sharp contrast to the model unsubstituted analogue. This new fluorescence band is believed to be due to the formation of a new isomer (cis-type) through a planar intermediate. While there is a substantial barrier (∼50 kJ mol−1) in the ground state, the isomerization process in the excited state in polar-protic environment proceeds very fast and believed to be catalyzed by hydrogen bond formation at the imine nitrogen atom in combination with stabilization of the resulting species through ICT.

Photophysics of a Coumarin in Different Solvents: Use of Different Solvatochromic Models

This study reported the photophysics of 7-(diethylamino)coumarin-3-carboxylic acid N-succinimidyl ester (7-DCCAE) in different neat solvents of varying polarity using steady-state absorption, fluorescence emission and picosecond time-resolved spectroscopy. In nonpolar solvents, the dye molecule predominantly exists in nonpolar structure and exhibits very low value of nonradiative decay rate constant (k(nr)), demonstrating the emission takes place from S(1) -LE to S(0) ground state. The fluorescence quantum yields, lifetime values of 7-DCCAE in different solvents are rationalized on the basis of intramolecular charge transfer (ICT) followed by twisted intramolecular charge transfer state formation (TICT) as well as specific solute-solvent interactions. Several solvatochromic models (such as Lippert, Dimroth, Kamlet-Taft, Catalán 3P and Catalán 4P models) were used to analyze the solvatochromic shift of 7-DCCAE in different solvents. The different empirical models show that the observed results are better correlate for nonchlorinated solvents and provide statistically significant best-fit result. A comparison was done between comparatively new solvatochromic model (Catalán 3P and Catalán 4P model) with Kamlet-Taft model. The ground state structure of the said molecule was optimized by using Density Functional Theory (DFT).

Complexation of Dioxovanadium (V) with CDTA in the Water + Methanol Solvent System

The solvent effect has been studied in this research for the interaction of the $$ {\text{VO}}_{2}^{ + } $$ cation with trans-1,2-diaminocyclohexane-N, N, N′, N′- tetraacetic acid monohydrate at T = 298 K, I = 0.10 mol·dm−3 sodium perchlorate, and in the range of 0–45 % water + methanol mixtures. UV absorbance data as a function of pH and dissociation constants, obtained from potentiometric titrations, were used for the determination of stability constants. The Kamlet–Abboud–Taft (KAT) model has been investigated for a plausible interpretation and calculation of the linear solvation energy relationship coefficient contribution to the formation of three species VO2H2L, VO2HL− and VO2L2−, which were identified in this work.

Lewis Molecular Acidity of Ionic Liquids from Empirical Energy–Density Models

Two complementary models of Lewis molecular acidity are introduced and tested in a wide series of 45 room temperature ionic liquids (RTIL). They are defined in the context of the conceptual density functional theory. The first one, which we tentatively call the excess electronic chemical potential, assesses the electron accepting power of the RTIL by relating the H-bond donor acidity with the charge transfer associated to the acidic H-atom migration at the cation of the RTIL considered as a HB-donor species. This global index accounts for the molecular acidity of the cation moiety of the ionic liquid that takes into account the perturbation of the anionic partner. The second index is defined in terms of the local charge capacity modeled through the maximum electronic charge that the cation, in its valence state, may accept from an unspecified environment. Each model is compared with the experimental HB-donor acidity parameter of the Kamlet Taft model. The best comparison is obtained for a combination of both the excess electronic chemical potential and the local charge capacity. As expected, the correlations with the Kamlet Taft α parameter do not lead to a universal model of HB-donor acidity. Reduced correlations for limited series of structurally related RTIL are obtained instead. Finally, we illustrate the reliability and usefulness of the proposed model of RTIL molecular acidity to explain the cation-dependent solvent effects on the reactivity trends for cycloaddition, Kemp elimination, and Menschutkin reactions, for which experimental rate coefficients are available from literature.

Solvent effects on the absorption and fluorescence spectra of Cu(II)-phthalocyanine and DFT calculations

The absorption and fluorescence spectra of Cu(II)-phthalocyanine were recorded in different solvents of varying types. The data fitted well to Lippert–Mataga equation thus confirming the dependence of orientation polarizability on the absorbance and emission values. The spectroscopic data also fitted well to the Kamlet–Abboud–Taft model. Density functional calculations were used to assign the absorption in the visible region to a π–π* transition between the HOMO-1 and LUMO of the complex. The visible region transition occurs between orbitals largely based on the phthalocyanine ligand, with no significant Cu character. The fluorescence emission of the molecule was effectively quenched in the presence of tetrachlorobenzoquinone (TCQ). The fluorescence quenching data shows that both static and dynamic quenching are operative in the present system. This may be due to the aggregation of the phthalocyanine complex in solution which arises from π–π stacking of its wide planar aromatic structure. The fluorescence quantum yields suggest that in the excited state the molecule interacts more with an aprotic solvent, while the ground state is preferentially stabilized in the presence of a protic solvent.

Gelation mechanism and microstructure of organogels formed with l-Valine dihydrazide derivatives

A new organogelator, N-Carbobenzoxy- l-Valine-Hexadecane Hydrazide (designated as Cbz-Val-HdHz) was synthesized, which can self-assemble in various organic solvents and turned them into thermally reversible physical supramolecular organogels at extremely low concentrations (<2 wt%). The effect of solvent polarity on the gelation properties was studied by using the Kamlet–Taft model. The gel–sol temperatures ( T GS) were determined as a function of gelator concentration and the corresponding enthalpies (Δ H g) were extracted. Scanning electron microscopy (SEM) measurements revealed that the gelator self-assembled into different supramolecular network structures in different gels. FT-IR spectroscopy studies revealed that intermolecular hydrogen bonding between N–H and C O of amide group and hydrophobic interaction of the alkyl groups were the driving forces for the formation of the gels. Based on the data of XRD and molecular modeling, the possible packing modes for the formation of organogelator aggregates were proposed.

Kinetics of proton transfer between metasubstituted benzoic acids and the carbinol base of crystal violet in toluene: Specific solvent effect–free metasubstituent effect on the reactivity of benzoic acids

AbstractApolar aprotic solvents are particularly advantageous for investigating the intrinsic metasubstituent effect free from complications of specific solvent effects. A kinetic study for toluene‐phase proton transfers between meta‐Me, F, Cl, Br, I, OMe, OPh, COPh, CF3, CN, NO2, H benzoic acids and Crystal Violet carbinol base has shown the forward rate constant (log k1) the most appropriate reactivity parameter in toluene. log k1 (toluene) as compared to other reported reactivity parameters in benzene or toluene have been found more sensitive to the metasubstituent effect. The regression results of the correlation of log k1 (toluene) of the acids according to the four dual substituent parameter models are statistically significant, and the best result has been obtained using Taft's model. The overall analysis reveals that metasubstituent's effect is exerted by a 65:35 pattern of its field and second‐order resonance effects. The results further demonstrate that a metasubstituent's resonance effect is virtually a relayed universal field/inductive effect. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 303–311, 2011

Modelling of carrier mediated transport of chromium(III) in the supported liquid membrane system with D2EHPA

The facilitated transport of Cr(III) in the SLM system with D2EHPA, was investigated with respect to the composition of feed phase (type of Cr(III) salt, initial Cr(III) concentration, initial ionic strength) and organic phase (carrier concentration and type of diluent) and also volume phase ratio. The effect of diluents on the initial flux and rate constant was expressed by means of their solvatochromic parameters and Leggett modification of Kamlet and Taft model of solute–solvent interactions.

Novel photochromic spirocyclic compounds of thienopyrroline series: 2. Spirooxazines

Photochromic properties of novel spirooxazines of the thienopyrroline series have been studied in comparison with those of an indoline analogue. Solvatochromism of the merocyanine photoisomers has been investigated using the Kamlet–Taft model. It has been found that inversion of the trends in the solvatochromic behavior of the spirooxazines takes place when passing from non-protogenic to protic solvents. Thienopyrroline spirooxazines possess relatively poor fatigue resistance. The origin of the processes causing their photodegradation has been studied.

Hammett MSP and Taft DSP analysis of substituent effects on Mulliken charges of 1‐(arylmethylene)‐1H‐cyclopropanaphthalene

AbstractDensity functional theory (DFT) method is used to investigate the effects of a variety of substituents (N(CH3)2, OCH3, CH3,Br, H, F, CN, and NO2) on Mulliken charge (QM) for C‐α and C‐β of 1‐(Arylmethylene)‐1H‐cyclopropanaphthalene using Hammett's mono substituent parameter (MSP) and Taft's dual substituent parameter (DSP) models. The Hammett's model approach gave statistically more significant results than the Taft's model for both carbons atoms. For the C‐α atom a reverse substituent effect was observed and attributed to localized π‐polarization. On the other hand, the MSP and DSP for the C‐β atom showed normal substituent effect. The λ value at the C‐α, explain that the resonance effects more contribution than inductive effects. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Cycloadditions in mixed aqueous solvents: the role of the water concentration

AbstractWe examined the kinetics of a series of cycloaddition reactions in mixtures of water with methanol, acetonitrile and poly(ethylene glycol) (MW 1000). The reactions include the Diels–Alder (DA) reaction between cyclopentadiene and N‐n‐butylmaleimide or acridizinium bromide, the retro‐Diels‐Alder (RDA) reaction of 1,4,4a,9a‐tetrahydro‐4a‐methyl‐(1α,4α,4aα,9aα)‐1,4‐methaneanthracene‐9,10‐dione and the 1,3‐dipolar cycloaddition of benzonitrile oxide with N‐n‐butylmaleimide. Plots of logk vs the molar concentration or volume fraction of water are approximately linear, but with a characteristic break around 40 M water. This break, absent for the RDA reaction, is ascribed to hydrophobic effects. Comparison with aqueous mixtures of the more hydrophobic 1‐propanol shows that these mixtures induce qualitatively similar effects on the rate, but that preferential solvation effects cause the mixtures of 1‐propanol to exhibit a more complex behavior of logk on composition. The results are analyzed using the Abraham–Kamlett–Taft model. The solvent effects in aqueous mixtures are not satisfactorily described by this model. For some cycloadditions, small maxima in rate are observed in highly aqueous mixtures of alcohols. The origin of these maxima and the aforementioned breaks is most likely the same. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Estimation of properties of dialkylorganophosphorus acidic extractants in two-phase liquid systems

The distribution, dimerization and dissociation constants of dialkylorganophosphorus acidic extractants XYP(O)OH affecting their behaviour in the two-phase liquid systems involving ‘dry’ solvents have been correlated with the properties of solutes and solvents in accordance with the Kamlet and Taft and Leggett models. It has been demonstrated that dialkyl derivatives of phosphoric, phosphonic and phosphinic acids could be regarded as members of the same family of acidic extractants. As a result, the distribution, dimerization and dissociation constants as well as the products of these constants can be estimated from the appropriate statistically valid correlations involving the molar intrinsic volumes and Kabatchnik constants of considered acids and solvatochromic parameters π*, α and β of ‘dry’ solvents. Both compared models are adequate for the analysis and estimation of equilibrium constants of dialkylorganosphosphorus acids; however, the Leggett model has been found as more convenient than the Kamlet and Taft model.

ChemInform Abstract: Application of the Kamlet and Taft Model in Solvent Extraction Chemistry of Metals

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.