Dielectric relaxation of sulfolane in benzene solution from microwave absorption data

The electric constant (ɛ′) and dielectric loss (ɛ″) for dilute solutions of sulfolane in benzene solution has been measured at 9.885 GHz at different temperatures (25, 30, 35, and 40°C) by using standard microwave techniques. Following the single frequency concentration variational method, the dielectric relaxation time (τ) and dipole moment (μ) have been calculated. It is found that dielectric relaxation process can be treated as the rate process, just like the viscous flow. Based on the above studies, monomer structure of sulfolane in benzene has been inferred. The presence of solute-solvent associations in benzene solution has been proposed. Energy parameters (ΔH _ɛ, ΔF _ɛ, ΔS _ɛ) for dielectric relaxation process of sulfolane in benzene at 25, 30, 35, and 40°C have been calculated and compared with the corresponding energy parameters (ΔH _η, ΔF _η, ΔS _η) for the viscous flow.     

Critical micelle concentration and self-aggregation of hexadecyltrimethylammonium bromide in aqueous glycine and glycylglycine solutions at different temperatures

Conductivities, densities and ultrasonic speeds measurements of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions of glycine (Gly) and glycylglycine (Gly-Gly) have been made at various temperatures. The critical micelle concentration (CMC), the degree of ionization (??) of the micelles, standard free energy, enthalpy, and entropy of the micellization process (??G _m ^° , ??H _m ^° , and ??S _m ^° ) for the present systems were estimated at different temperatures. The CMC values of HTAB in aqueous Gly and Gly-Gly were also evaluated by density and ultrasonic speed measurements. Apparent molar volumes, (V _?), apparent molar volumes at infinite dilution, (V _? ^° ), apparent molar compressibilities, (K _?), of HTAB in the pre- and post-micellar regions, and volume change on micellization (??V _? ^m ) were also estimated. Large positive values of T??S _m ^° and small negative values of ??H _m ^° suggest that micellization process is driven primarily by entropy increase. The increase in ??V _? ^m and K _? with rise in temperature is indicative of less compact micellar structure of HTAB in presence of amino acid additives. These data suggest that amino acids are solubilised probably in the palisade layer of the micelle.     

Thermodynamic, IR spectral and X-ray diffraction studies of the ����-cyclodextrin-para-aminobenzoic acid�� inclusion complex

The inclusion complex with stoichiometric composition 1:1 was formed as a result of intermolecular interactions between para-aminobenzoic acid and ??-cyclodextrin. The stability constant of ????-cyclodextrin-para-aminobenzoic acid?? inclusion complex at 289, 292 and 313 K was calculated by the Ketelar equation. The influence of temperature on the stability of ????-cyclodextrin-para-aminobenzoic acid?? inclusion complex was also examined, and thermodynamic parameters involved in the complex formation (??G, ??H, ??S) were calculated. Supramolecular complex formation between para-aminobenzoic acid and ??-cyclodextrin was confirmed by X-ray diffraction and IR spectroscopy studies.     

Preparation of LiZnPO4·H2O via a novel modified method and its non-isothermal kinetics and thermodynamics of thermal decomposition

The single phase ??-LiZnPO₄·H₂O was directly synthesized via solid-state reaction at room temperature using LiH₂PO₄·H₂O, ZnSO₄·7H₂O, and Na₂CO₃ as raw materials. XRD analysis showed that ??-LiZnPO₄·H₂O was a compound with orthorhombic structure. The thermal process of ??-LiZnPO₄·H₂O experienced two steps, which involved the dehydration of one crystal water molecule at first, and then the crystallization of LiZnPO₄. The DTA curve had the one endothermic peak and one exothermic peak, respectively, corresponding to dehydration of ??-LiZnPO₄·H₂O and crystallization of LiZnPO₄. Based on the iterative iso-conversional procedure, the average values of the activation energies associated with the thermal dehydration of ??-LiZnPO₄·H₂O, was determined to be 86.59?kJ?mol^?1. Dehydration of the crystal water molecule of ??-LiZnPO₄·H₂O is single-step reaction mechanism. A method of multiple rate iso-temperature was used to define the most probable mechanism g(??) of the dehydration step. The dehydration step is contracting cylinder model (g(??)?=?1?(1???)^1/2) and is controlled by phase boundary reaction mechanism. The pre-exponential factor A was obtained on the basis of E _a and g(??). Besides, the thermodynamic parameters (??S ^??, ??H ^??, and ??G ^??) of the dehydration reaction of ??-LiZnPO₄·H₂O were determined.     

Thermal behaviors of N-pyrrolidine-N′-(2-chlorobenzoyl)thiourea and its Ni(II), Cu(II), and Co(III) complexes

The N-pyrrolidine-N??-(2-chlorobenzoyl)thiourea, HL, and their Ni(II), Cu(II), and Co(III) complexes (NiL₂, CuL₂, and CoL₃) have been synthesized and characterized. The thermal decomposition reactions of all the compounds have been investigated by DTA/TG combined systems. The mass spectroscopy technique has been used to identify the products during pyrolytic decomposition. The pyrolytic final products have been analyzed by X-ray powder diffraction method. After comparison of thermogravimetric and mass results of HL, NiL₂, CuL₂, and CoL₃, the decomposition mechanism of these compounds have been suggested. The thermal stability of the Ni(II) and Cu(II) complexes according to the thermogravimetric curves follows the sequence: NiL₂?<?CuL₂. The values of the activation energy, E _a, have been obtained using model-free (Kissenger?CAkahira?CSunose, KAS, Flyn?CWall?COzawa, FWO, and Isoconversional) methods for all decomposition stages. The E _a versus the extent of conversion, ??, plots show that the values of E _a varies as ??. Thirteen kinetic model equations have been tested for selecting correct reaction models. The optimized value of E _a and Arrhenius factor, A, have been obtained using the best model equation. The thermodynamic functions (??H*, ??S*, and ??G*) have been calculated using these values.     

Exploring antibiotic resistant mechanism by microcalorimetry

In an effort to probe the reaction of antibiotic hydrolysis catalyzed by B3 metallo-??-lactamase (M??L), the thermodynamic parameters of penicillin G hydrolysis catalyzed by M??L L1 from Stenotrophomonas maltophilia were determined by microcalorimetric method. The values of activation free energy ??G _?? ^?? are 88.26, 89.44, 90.49, and 91.57?kJ?mol^?1 at 293.15, 298.15, 303.15, and 308.15?K, respectively, activation enthalpy ??H _?? ^?? is 24.02?kJ?mol^?1, activation entropy ??S _?? ^?? is ?219.2511?J?mol^?1?K^?1, apparent activation energy E is 26.5183?kJ?mol^?1, and the reaction order is 1.0. The thermodynamic parameters reveal that the penicillin G hydrolysis catalyzed by M??L L1 is an exothermic and spontaneous reaction.     

Viscosities of Binary Liquid Mixtures of 2-Methylpropane Nitrile and Some Aromatic Hydrocarbons at 303.15 K and 308.15 K

Viscosities, ??, of five binary mixtures of 2-methylpropane nitrile with aromatic hydrocarbons, viz. benzene, methylbenzene, 1,4-dimethylbenzene, chlorobenzene and 1,2-dichlorobenzene, have been measured at temperatures 303.15 and 308.15?K. Deviations in viscosities, ????, from the linear mixing rule have been determined for all of the binary mixtures studied at both experimental temperatures. The ???? values are negative for all the five systems at both experimental temperatures. Parameters of the Redlich?CKister and Myers and Scott equations have been fitted to the ???? values and standard deviations, ??(????), have also been evaluated. The correlating performances of several viscosity models have been evaluated. The Hind?CMcLaughlin?CUbbelohde viscosity model gives fairly constant interaction parameters with composition. Results are discussed in terms of unlike molecular interactions between the components of the binary mixtures.     

Thermodynamic properties of resveratrol in dimethyl sulfoxide

In this article, the enthalpies of dissolution of resveratrol in dimethyl sulfoxide (DMSO) were measured using a RD496-2000 Calvet microcalorimeter at 298.15?K under atmospheric pressure. The differential enthalpy (??_dif H _m) and molar enthalpy (??_sol H _m) of dissolution of resveratrol in DMSO were determined, and the relationship between heat and the amount of solute was also established. Based on the thermodynamic and kinetic knowledge, the corresponding kinetic equation, half-life, ??_sol H _m, ??_sol S _m, ??_sol G _m, the relative partial molar enthalpy (??_sol H _m(partial)) and the relative apparent molar enthalpy (??_sol H _m(app)) of the dissolution process were obtained. The results showed that this study not only provided a simple method for the determination of the half-life for a drug, but also offered a theoretical reference for the clinical application of resveratrol.     

Dielectric relaxation studies of binary mixtures of N-methylacetamide and N-methylformamide in benzene solutions using microwave absorption data

Using standard microwave X-band technique and by following Gopala Krishna's single frequency (9.90?GHz) concentration variational method, the dielectric relaxation times (τ) and the dipole moments (μ) of dilute solution of N-methylacetamide (NMA), N-methylformamide (NMF) and NMA?+?NMF binary mixtures in benzene solutions have been calculated at different temperatures. The energy parameters for the dielectric relaxation process for NMA?+?NMF binary mixture containing 30?mol% NMF have been calculated at 25, 30, 35 and 40°C and compared with the corresponding viscosity parameters. A good agreement between the free energy of activation from these two sets of values shows that the dielectric relaxation process like the viscous flow process can be treated as the rate process. From relaxation time behavior of NMA and NMF binary mixture in benzene solution, solute–solute types of the molecular association has been proposed.     

Selective self-assembly synthesis of MnV2O6·4H2O with controlled morphologies and study on its thermal decomposition

The MnV₂O₆·4H₂O with rod-like morphologies was synthesized by solid-state reaction at low heat using MnSO₄·H₂O and NH₄VO₃ as raw materials. XRD analysis showed that MnV₂O₆·4H₂O was a compound with monoclinic structure. Magnetic characterization indicated that MnV₂O₆·4H₂O and its calcined products behaved weak magnetic properties. The thermal process of MnV₂O₆·4H₂O experienced three steps, which involves the dehydration of the two waters of crystallization at first, and then dehydration of other two waters of crystallization, and at last melting of MnV₂O₆. In the DSC curve, the three endothermic peaks were corresponding to the two steps thermal decomposition of MnV₂O₆·4H₂O and melting of MnV₂O₆, respectively. Based on the Kissinger equation, the average values of the activation energies associated with the thermal decomposition of MnV₂O₆·4H₂O were determined to be 55.27 and 98.30?kJ?mol^?1 for the first and second dehydration steps, respectively. Besides, the thermodynamic function of transition state complexes (??H ^??, ??G ^?? , and ??S ^?? ) of the decomposition reaction of MnV₂O₆·4H₂O were determined.     

Thermodynamic behavior and stability constants of lanthanides–Schiff base complexes in mixed aqueous solvents

The stability constant of complexes of Ln³⁺ ions and butanamide-3-[(2-hydroxyphenyl methylene)amino]ethylimino N-phenyl were determined potentiometrically in 75% (v/v) dioxane?Cwater, 0.1?M (KNO₃) at different temperatures applying the Irving and Rossotti techniques. The nonlinear variation of the thermodynamic parameters (??G, ??H, and ??S) as a function of ionic potential of lanthanide elements was discussed. This behavior was explained in terms of difference in the dehydration of lighter Ln³⁺ from that of heavier ones. In different organic solvents (75% solvent?Cwater media), the stability constant values follow the order: dioxane?>?methanol?>?DMF, depending upon both the dielectric constant and the hydrogen bonding structure of the medium. The thermodynamic parameters at all complexes have been analyzed in terms of their electrostatic (el) and non-electrostatic (non) parts.     

Effect of plastic deformation on the character of micro-brownian motions in glassy poly(methyl methacrylate)

Glassy PMMA samples are plastically deformed at room temperature in the uniaxial compression regime to residual strains of e _res = 25%. Dielectric spectra of the initial and deformed samples are recorded via the method of broadband dielectric spectroscopy in the frequency range f = (5 × 10^?4) ? 10⁷ Hz. The results are compared with the dynamic mechanical spectra of samples deformed under the same conditions. Dielectric and mechanical spectra are noticeably distorted by deformation. As a result, dielectric permittivity ??? increases, shear modulus G?? decreases, and the intensity of dielectric ?? losses slightly increases, while dielectric and mechanical ?? losses increase appreciably. In addition, the ??anomaly?? of total dielectric ???_tot and total mechanical ??G _tot dispersions (???_tot = ?₀ ? ?_?? ?? ???_?? + ???_?? and ??G _tot = G ₀ ? G _?? ?? ??G _?? + ??G _??) occurs, that is, the polymer is transformed from the state with ???_?? ? ???_?? and ??G _?? < ??G _?? into the state with ???_?? > ???_?? and ??G _?? > ??G _??. The described phenomenon is related to a strong gain in ?? dielectric and mechanical losses in the deformed material. It is found that ?? losses increase owing to an anelastic deformation component arising during glass loading. This component is responsible for an increase in the internal energy of the glass during its anelastic deformation. Possible causes of the observed effects are discussed.     

Thermodynamic characteristics of thermal dissociation of inclusion compounds based on graphite fluorides

Thermal dissociation processes for acetonitrile inclusion compounds based on the polymer fluorographite host matrix C₂F _x Br_0.01·yCH₃CN, where x = 0.49?C0.92, y = 0.174?C0.285, are investigated. Thermodynamic parameters (??H°_av, ??S°_av, ??G°₂₉₈) for deintercalation of the compounds of the first filling step into the compounds of the second step and gaseous guest within temperature range 294?C352 K were determined. The effect of the host matrix fluorination degree on the thermodynamic characteristics of the studied processes is demonstrated.     

Densities, Viscosities, Speeds of Sound, FT-IR and 1H-NMR Studies of Binary Mixtures of n-Butyl Acetate with Ethanol, Propan-1-ol, Butan-1-ol and Pentan-1-ol at?298.15, 303.15, 308.15 and 313.15?K

Densities, viscosities and speeds of sound of binary mixtures of ethanol, propan-1-ol, butan-1-ol and pentane-1-ol with n-butyl acetate have been measured over the entire range of composition at temperatures of 298.15, 303.15, 308.15 and 313.15 K and atmospheric pressure. From the experimental densities, viscosities and speeds of sound, the excess molar volumes V ^E, deviations in viscosity ????, and deviations in isentropic compressibility ???? _S have been calculated. The excess molar volumes and deviations in isentropic compressibility are positive for all the binary systems studied over the whole composition, while deviations in viscosities are negative for all of the binary mixtures. The excess molar volumes, deviations in viscosity, and deviations in isentropic compressibility have been fitted to a Redlich?CKister type polynomial equation. FTIR and ¹H-NMR studies of these mixtures are also reported.     

Spectroscopic Study of the Interactions of Buflomedil to Serum Albumin and β-Cyclodextrin

The effects of buflomedil (BFM), a novel cerebrovascular medicine, on serum albumin and the feasibility of ??-cyclodextrin (??-CD) acting as a controlled releaser for BFM were investigated by molecular spectroscopy methods, including fluorescence emission, UV?Cvisible absorption, Fourier transform infrared (FT-IR), synchronous and three-dimensional fluorescence spectroscopies. The interaction of BFM with bovine serum albumin (BSA) was analyzed by fluorescence quenching and it was found that BFM had reacted with BSA in the ground state and had affected the secondary structure of BSA. The observed binding constant K _b, the number of binding sites n, the distance r between donor (BSA) and acceptor (BFM), the enthalpy change (??H ^?? ), Gibbs energy change (??G ^?? ) and entropy change (??S ^?? ) at different temperatures were calculated. The inclusion reaction between ??-CD and BFM was explored by the Lineweaver?CBurk equation. The inclusion constants and the thermodynamic parameters were determined. The mechanism of the inclusion reaction was discussed and the controlled release characteristics of ??-CD to BFM were considered at the molecule level.     

Investigation of the Interaction Between N-benzyl Piperidones and Bovine Serum Albumin by Spectroscopic Approaches

Fluorescence and ultraviolet spectroscopies were applied to investigate the interaction between five N-benzyl piperidones (NBP) and bovine serum albumin (BSA) under imitated physiological conditions. The experimental results show that these NBPs have a static fluorescence quenching effect on the endogenous fluorescence of BSA at the temperatures 302 and 310?K. According to the fluorescence quenching theory, the Stern?CVolmer quenching constant (K _SV), the binding constant (K _a), and the number of binding sites (n) were obtained. Also, the effect of substituents on the binding capacity between NBP and BSA is in the order: C₆H₅?<?4-CH₃OC₆H₄?<?4-CH₃C₆H₄?<?2,4-Cl₂C₆H₃?<?4-ClC₆H₄. The corresponding thermodynamic parameters (??G, ??H, and ??S) were obtained at two different temperatures and indicate that hydrogen bonding and van der Waals forces play main roles in stabilizing the BSA?CNBP complex. The binding distance between the tryptophan residue in BSA and NBP was found to be much <7?nm based on the F?rster theory of non-radiation energy transfer. The effect of NBP on the conformation of BSA was analyzed as well by synchronous fluorescence spectroscopy.     

A Thermodynamic Study of Complexation of Iron Ions with Clarithromycin and Roxithromycin in Methanol Using a Conductometric Method

The formation constants K _ML of Clarithromycin (CLA) and Roxithromycin (ROX) with Fe(III) and Fe(II) ions in methanol have been determined at various temperatures using a conductometric technique. The interaction yields complexes with metal-to-ligand compositions of 1:1. The conductivity data were analyzed using a computer program based on 1:1 stoichiometry from which the stability constants and the limiting molar conductance were obtained. The stability of these complexes was found to increase with temperature. Compared with Fe(II), Fe(III) forms more stable complexes with ROX and CLA. The values of the thermodynamic parameters enthalpies (??H ^°), entropies (??S ^°), and the derived Gibbs energies (??G ^°) were deduced from the dependence of the formation constants on temperature. The positive values of ??H ^° and ??S ^° indicate that the complexation processes is enthalpically unfavorable but entropically favored. The negative values of ??G ^° show the ability of the studied ligand to form stable complexes and that the complexation process is favorable.     

Thermochemical investigation of natural antlerite

Thermal and thermochemical investigations of natural hydroxyl-bearing copper sulfate Cu₃SO₄(OH)₄??antlerite have been carried out. The stages of its thermal decomposition have been studied employing the Fourier-transform IR spectroscopy. The enthalpy of formation of antlerite from the elements ??_f H _m ^o (298.15?K)?=?(?1750?±?10)?kJ?mol^?1 has been determined by the method of oxide melt solution calorimetry. Using value of S _m ^o (298.15?K), equal to (263.46?±?0.47)?J?K^?1?mol^?1, obtained earlier by the method of adiabatic calorimetry, the Gibbs energy value of ??_f G _m ^o (298.15?K)?=?(?1467?±?10)?kJ?mol^?1 has been calculated.     

Study of complexation process between 4′-nitrobenzo-15-crown-5 and yttrium(III) cation in binary mixed non-aqueous solvents using conductometric method

The complexation reaction of macrocyclic ligand (4??-nitrobenzo-15C5) with Y³⁺ cation was studied in acetonitrile-methanol (AN-MeOH), acetonitrile-ethanol (AN-EtOH), acetonitrile-dimethylformamide (AN-DMF) and ethylacetate-methanol (EtOAc-MeOH) binary mixtures at different temperatures using conductometry method. The conductivity data show that in all solvent systems, the stoichiometry of the complex formed between 4??-nitrobenzo-15C5 and Y³⁺ cation is 1: 1 (ML). The stability order of (4??-nitrobenzo-15C5). Y³⁺ complex in pure non-aqueous solvents at 25°C was found to be: EtOAc > EtOH > AN ?? DMF > MeOH, and in the case of most compositions of the binary mixed solvents at 25°C it was: AN??MeOH ?? AN-EtOH > AN-DMF > EtOAc-MeOH. But the results indicate that the sequence of the stability of the complex in the binary mixed solutions changes with temperature. A non-linear behavior was observed for changes of logK _f of (4??-nitrobenzo-15C5 · Y³⁺) complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent interactions and also the hetero-selective solvation of the species involved in the complexation reaction. The values of thermodynamic parameters (??H _c ^? and ??S _c ^? ) for formation of the complex were obtained from temperature dependent of the stability constant using the van??t Hoff plots. The results represent that in most cases, the complex is both enthalpy and entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.     

Stabilization of water structure in ammonium hydrogenphosphate solutions

Radio-frequency permittivity and dielectric loss of (NH₄)₂ HPO₄ solutions at 288–308 K in the water permittivity dispersion region (7.5–25 GHz) are studied. Low-frequency electrical conductivities of these solutions are measured, and ionic losses at high frequencies are calculated. The analysis is carried out in terms of the Cole-Cole relaxation model. Static dielectric constants ?_s and the activation times τ and thermodynamic parameters of activation (ΔH _? ⁺⁺ , ΔG _? ⁺⁺ , and TΔS _? ⁺⁺ ) for the dielectric relaxation of the solutions are calculated. The values of ?_s decrease in response to increasing salt concentration at all temperatures. The increasing τ and ΔH _? ⁺⁺ values indicate the stabilization of water structure in solutions where the anion and cation are hydrophilically hydrated.