The Pushkin—Varshney—Kamoonpuri equation for the evaluation of association constants for the charge transfer complexes of sparingly soluble acceptors

The proposed Pushkin—Varshney—Kamoonpuri equation proposes a simple way in which the association constants of complexes of sparingly soluble acceptors may be evaluated. The method can be used where the concentration of the acceptor is not known.     

The oxidative coupling of phenols catalyzed by soluble copper—polymer complexes. The active role of the polymer chain during activation of the substrate—catalyst complexes

The kinetics of the oxidative coupling of 2,6-dimethylphenol and 2,6-diphenylphenol was studied using a catalyst consisting of copper(II) chloride and polystyrene partially substituted with dimethylaminomethyl ligand groups. The polymers were not covalently crosslinked and were completely soluble in the reaction mixture. At an amino-nitrogen to copper ratio of 1 the reaction rate depended on the degree of substitution, α, of the polystyrenes. This effect was explained in terms of activation parameters obtained from the temperature dependence of the rate constant for the electron transfer step. It appeared that the polymer chain plays an active role in the activation process merely by increasing the entropy of activation with α. The formation of diphenoquinone appeared to be dependent on the reaction temperature and was almost independent of α.     

Evaluation of Accuracy for the Measurement of Octanol–Water Partition Coefficient by MEEKC

Microemulsion electrokinetic chromatography (MEEKC) has been widely used as an indirect tool to measure octanol–water partition coefficients (logP _ow) of various kinds of compounds. In this paper, we present for the first time a mathematical model of the precision of logP _ow (ΔlogP _ow) as a function of the deviation of migration time (Δt _m) in MEEKC, and more importantly evaluated the accuracy of the MEEKC. Our model shows that for a given microemulsion system, there is an interval of migration times, where a high precision in the determination of logP _ow can be obtained. However, when the migration time approaches either the migration time of the electroosmotic flow or that of the microemulsion phase, the precision of logP _ow deteriorates rapidly. The model was experimentally verified by the microemulsion system with migration times of 6.50 and 32.00?min for the electroosmotic flow and microemulsion phase, respectively, and we found the useful logP _ow interval to be 0.50–5.50. The paper also demonstrates that the calibration constants between migration times t _m and predicted logP _ow values could be transferred with high accuracy from one MEEKC system to another as long as both systems are set up to use the same operational parameters.     

Charge transfer spectra of organometallic complexes—IX. Evaluation of solvent effects on the electron donor—acceptor interactions between trimethyltinisothiocyanate and iodine

Charge transfer energies of trimethyltinisothiocyanate—iodine complexes in solution are found to depend on the nature of the solvent. The relationship of these solvent shifts with various solvent properties, and is discussed. Stabilization energies of the excited states in the different solvents are determined using the Onsager theory of dielectrics.     

Molecular complexes of cyclophanes—XIII. Charge-transfer complexes of cyclophanes with fluoranil

The charge-transfer (CT) complexes of some methylated [2.2]para-, multibridged cyclo- and [2.2]indenophanes as π-donors with fluoranil (TFQ) as π-acceptor have been studied spectrophotometrically. The role of the molecular structure of the donors on their Lewis basicities and stability of their CT complexes with TFQ are discussed. Eight pure crystalline complexes were prepared. Their i.r. spectra indicate an increase of the electron density in the TFQ part of the CT complex.     

Vibrational spectra of carboxylato complexes—II. Some oxo-tetranuclear complexes

The i.r. and Raman spectra of the compounds Be₄O(OOCCH₃)₆, Be₄O(OOCCD₃)₆, Be₄O(OOCH)₆ and Zn₄O(OOCCH₃)₆ have been analysed and assigned in detail. In particular, the vibrational modes of the O(MO₃)₄ subunits, and their interactions with the carboxylate ligand vibrations, have been identified. The compound Zn₄O(OOCC₂H₅)₆ has the same oxo-centred structure as the others.     

Note on the effect of activity coefficients on the NMR association constants for the 2,4-dinitrotoluene—diphenylamine system. The Qureshi—Varshney—Kamoonpuri equation. Possible role of hydrogen bonding.

The NMR studies of the charge transfer complex between 2,4-dinitrotoluene and diphenylamine in CCl₄ are reinvestigated. The proposed Qureshi-Varshney-Kamoonpuri equation shows that activity coefficients have a profound effect on the NMR association constants. The possibility of hydrogen bonding in the system has also been considered.     

n—π electron-donor—acceptor complexes—IV. The interaction of aliphatic amines with 1,3-dicyanobenzene in n-hexane. The importance of preferred orientation in the stability of the complexes

The stability constants (K) for the electron-donor—acceptor (EDA) complexes formed between aliphatic amines as n-donors and 1,3-dicyanobenzene (1,3-DCB) have been determined in n-hexane as solvent. By means of free energy substitutent parameters and regression analysis, the electronic and steric effects of the N-amine substituents were quantitatively separated. Thus, values of log K were correlated with Taft's polar substituents, σ*, and Hancock's corrected steric substituent constants, E^C_s. Large steric effects are inferred which lead us to propose a preferential site of interaction. This preferential orientation may also explain the greater stability of the 1,3-DCB—amine complexes with respect to the corresponding 1,4-DCB—amine complexes. The proposal is supported by the excess of atomic charge predicted by the Mulliken population analysis, obtained by MNDO calculations for the acceptors and by considering that for weak n—π complexes, the electrostatic energy may be of major importance in the energy of interaction.     

Evaluation of Electrochemically Reduced Gold Nanoparticle—Graphene Nanocomposites for the Determination of Dopamine

Two gold nanoparticle-graphene nanocomposites were electrochemically obtained by the one-step constant potential coreduction of graphene oxide and gold ions or the electrodeposition of gold nanoparticles on graphene oxide followed by electrochemical reduction of graphene oxide. The surface morphology, electron transfer rate, and electrocatalytic activity toward the oxidation of dopamine on these nanocomposites were systematically studied. The results showed that both preparations synthesized gold nanoparticle-graphene nanocomposites. The nanocomposite obtained by the one-step synthesis showed higher electron transfer kinetics and electrocatalytic activity toward dopamine than the material obtained by the two-step synthesis. Consequently, the one-step nanocomposite was used to modify a glassy carbon electrode to form a dopamine sensor. Differential pulse voltammetry was used to detect dopamine with a detection limit of 0.1 micromolar and a linear dynamic range from 0.2 to 20 micromolar. The sensor displayed good stability, high reproducibility, and was used for the determination of dopamine in human urine.     

Evaluation of the abilities of ��-cyclodextrin to form complexes by surface plasmon resonance with a Biacore? system

Although phase-solubility studies have often been used to evaluate the interaction of cyclodextrins (CDs) with various drugs, hundreds of milligrams of both CD and drug are required to prepare a phase diagram. A method that would require considerably less material for evaluating complex formation between a CD and guest compound is therefore needed. We previously reported the detection of the interactions between ??-CD and various drugs using a Biacore^® system. In this study, we succeeded in immobilizing 6-monodeoxy-6-monoamino-??-CD on the gold surface of a sensor chip and in detecting the interactions between the immobilized ??-CD and various drugs. The interaction processes were kinetically analyzed using Biacore^®. The surface plasmon resonance sensorgrams indicated that the association and dissociation rates of the interactions between ??-CD and drugs were faster than those between ??-CD and drugs. Although the association constants calculated from the sensorgrams were smaller than those calculated from phase-solubility studies, good correlation was shown between these data.     

Amperometric Biosensor for Evaluation of Competitive Cholinesterase Inhibition by the Reactivator HI‐6

Abstract

Amperometric biosensors containing enzymes butyrylcholinesterase or acetylcholinesterase were prepared. The biosensors were employed for studying of cholinesterase reactivator: HI‐6. Competitions between HI‐6 and acetylthiocholine as enzyme substrate were used for determination of IC₅₀ value. Biosensors with butyrylcholinesterase from human serum determined IC₅₀ as (1.00±0.02)×10^?6 M; the biosensor with acetylcholinesterase from human erythrocytes performance provided IC₅₀ (3.31±0.13)×10^?6 M, the one with human recombinant acetylcholinesterase (2.00±0.06)×10^?6 M and finally biosensor with acetylcholinesterase from electric eel (6.17±0.17)×10^?6 M when 5 mM acetylthiocholine as substrate was used. We are encouraged to consider presented biosensors as a very useful for evaluation of newly prepared cholinesterase reactivators.     

Interaction parameter for hydrogen-containing mixtures in the Peng—Robinson equation of state

A new correlation for the Peng—Robinson interaction parameter δ_ij of hydrogen-containing mixtures is proposed here. Values of δ_ij obtained from literature vapour—liquid equilibrium data are represented by a cubic polynomial in terms of the temperature. The correlation predicts better values than other correlations proposed in the literature for the same systems, and is applicable to wider ranges of temperature. Applications of the proposed equations to VLE are presented.     

Infrared intensities of charge transfer complexes—I. Iodine cyanide complexes

Infrared intensities of some ICN complexes were measured in solution, and the observed intensity changes on complex formation were explained on the basis of the electronic reorientation during molecular vibration. Formation constants were obtained as well from i.r. measurements for the purpose of the determination of equilibrium concentrations in the complex solutions.     

Analytical properties of the amidoxime group—xii. Spectrophotometric study of several metal-amidoxime complexes

The spectrophotometric behaviour of a number of amidoxime-metal complexes is studied, mainly those formed by Cu(II). The influence of several variables (pH, time etc …) on complex formation is determined, together with the performance of Beer's law and the precision according to Ringbom. For the Cu(II) complexes of several polyamidoximes the conditional stability constants are calculated and refined by means of the MINISPEF program. These constants, after correction using the appropriate side-reaction coefficients, are used to draw the corresponding distribution diagrams.     

Comparative semiempirical and ab initio study of the harmonic vibrational frequencies of aniline—I. The ground state

The harmonic vibrational frequencies of the ground state S₀ of aniline obtained from various ab initio methods [6-31G, 6-31G(*) and 6-31G* basis sets] and semiempirical methods (MINDO/3, MNDO, AM1 and PM3) have been compared to the experimental vibrational spectra. Detailed theoretical analyses of the atomic Cartesian displacements of all normal modes are presented. The semiempirical PM3 method reproduces the experimental frequencies of aniline with comparable accuracy to the ab initio methods. Ale PM3 method will be useful in predicting the vibrational spectra of larger aromatic amines.     

Evaluation of Argentation TLC—Densitometry for the Determination of trans Fatty Acids in Butterfat

JPC – Journal of Planar Chromatography – Modern TLC - A stand-alone argentation TLC (Ag-TLC) procedure has been established for rapid estimation of the authenticity and densitometric...     

Molecular interpretation of Trouton’s and Hildebrand’s rules for the entropy of vaporization of a liquid

The entropy of vaporization at a liquid’s boiling point is well approximated by Trouton’s rule and even more accurately by Hildebrand’s rule. A cell method is used here to calculate the entropy of vaporization for a range of liquids by subtracting the entropy of the gas from that of the liquid. The liquid’s entropy is calculated from the force magnitudes measured in a molecular dynamics simulation based on the harmonic approximation. The change in rotational entropy is not accounted for except in the case of liquid water. The predicted entropies of vaporization agree well with experiment and Trouton’s and Hildebrand’s rules for most liquids and for water except other liquids with hydrogen bonds. This supports the idea that molecular rotation is close to ideal at a liquid’s boiling point if hydrogen bonds are absent; if they are present, then the rotational entropy gain must be included. The method provides a molecular interpretation of those rules by providing an equation in terms of a molecule’s free volume in a liquid which depends on the force magnitudes. Free volumes at each liquid’s boiling point are calculated to be ～1 Å³ for liquids lacking hydrogen bonds, lower at ～0.3 Å³ for those with hydrogen bonds, and they decrease weakly with increasing molecular size.     

Vibrational spectra of carboxylato complexes—IV. Mixed-metal and mixed-valence oxo-trinuclear complexes

Infrared spectra of mixed-metal complexes [Cr_3-nFe_nO(OOCR)₆L]⁺ (n = 1,2; R = H, CH₃; L = H₂O, γ-picoline, pyridine), and of mixed-valence complexes [Fe^III₂Fe^IIO(OOCCH₃)₆py₃], [Ru^III₂Ru^IIO(OOCCH₃)₆L₃] (L = H₂O, P(C₆H₅)₃) are reported and compared with analogous symmetrical (Cr^III)₃, (Fe^III)₃ and (Ru^III)₃ species. The effects of lowered symmetry are seen in the mixed-metal but not in the mixed-valence complexes.