Thermodynamic Data for the Complex Formation of Alkylamines and Their Hydrochlorides with α-Cyclodextrin in Aqueous Solution

The formation of complexes between α-cyclodextrin and n-alkylamines and their hydrochlorides has been studied in aqueous solution using calorimetric titrations. All alkylamines form stronger complexes than the corresponding hydrochlorides. The values of the reaction enthalpies are smaller for the alkylamine hydrochlorides compared with the alkylamines. By increasing the number of methylene groups, these differences become smaller. In addition, the reaction enthalpies for protonation of the alkylamines and their complexes with α-cyclodextrin have been measured. The heat of protonation of these complexes is always smaller compared with the alkylamines. Due to the protonation and the formation of a strong solvation shell around the ammonium group the interactions with α-cyclodextrins are weakened. From a thermodynamic cycle using all measured reactions, it can be concluded that the aggregation of the alkylamines with long alkyl chains (heptyl-, octyl-, and nonylamine) has an influence on the values of the reaction enthalpies and entropies for the protonated form only.This revised version was published online in July 2005 with a corrected issue number.     

Thermodynamic and 13C NMR Studies of the Inclusion Complexes of α- and β-Cyclodextrins with Cyano- and Nitrophenols in Aqueous Solution

Equilibrium constants for the formation of 1 : 1 inclusioncomplexes of -cyclodextrin (-CD) with neutral and anionic phenol derivatives (3- and 4-cyanophenols and 3- and 4-nitrophenols) have been evaluated at 5, 12, 25, and 35 °C by means of spectrophotometry. Similarly, the equilibrium constants have been determined for the inclusion complexes of-cyclodextrin (-CD) with the phenols. Enthalpy and entropy changes for the formationof the inclusion complexes have been estimated from the temperature dependences of theequilibrium constants. With -CD, the enthalpy andentropy changes for the anionic species have been found to be more negative than those for the neutral ones, except for 4-cyanophenol, suggesting that the inclusion complexes of the anionic species are more rigid than those of the neutral species. From analyses of chemical shift differences in ¹³C NMR spectra of 3- and 4-cyanophenolsand 3- and 4-nitrophenols in aqueous solutions with and without CDs, a nitro ora cyano group has been found to be first bound to the - and -CD cavities.     

Simultaneous Calculation of Equilibrium Constants and Standard Formation Enthalpies from Calorimetric Data for Systems with Multiple Equilibria in Solution

The computer program HypΔH is a general-purpose Windows^® application designed to derive equilibrium constants and/or formation enthalpies of complexes from solution calorimetric data. Least-squares minimization is used with the analytically determined derivatives. The efficacy of the program is demonstrated by application to the calculation of formation constants and enthalpies for the formation of AgPy⁺ and AgPy ₂ ⁺ , and also of CH₃HgGly⁺, CH₃HgGlyH and (CH₃Hg)₂Gly²⁺. The results are compared with published data.     

Stability and Coordination Mode of Complexes of Polyphosphates and Polymetaphosphates with Copper(II) Ions in Aqueous Solution—Potentiometric,Spectral and Theoretical Studies

Complexes of copper(II) with a number of polyphosphate and polymetaphosphate anions have been studied in aqueous solutions by potentiometric, spectroscopic and theoretical methods. Stability constants of the complexes have been determined as well as their coordination modes. Results of the equilibrium studies provided evidence for the formation of ML, MHL and ML(OH) _x type complexes with the ligands studied. The length of the polyphosphate chain was found to affect the oxygen atom charge that is reflected in the stability constants of the ML type complexes. Moreover, the stability of the complex is also influenced by the spatial arrangement of the phosphate groups in phosphates and metaphosphates. The spectral parameters observed for certain complexes have permitted us to deduce the inner coordination sphere of the studied complexes.     

Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XI. Effects of the Preferential Solvation of Benzo-15-Crown-5 and Acid-Base Properties of the Mixtures on the Thermodynamic Functions for Complex Formation of Benzo-15-Crown-5 with Na+ in Propan-1-ol–Water Mixtures at 298.15 K

The thermodynamic functions of complex formation of benzo-15-crown-5 ether (B15C5) and sodium cation (Na⁺) in the mixtures of propan-1-ol (PrOH) with water at 298.15 K have been calculated from experimental measurements. The equilibrium constants of B15C5/Na⁺ complex formation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method. The complexes are enthalpy stabilized but entropy destabilized in the PrOH–H₂O mixtures. The effects of preferential solvation of B15C5 by molecules of the organic solvent, solvation of the sodium cation, as well as the acid-base properties of propan-1-ol–water mixtures on the complex formation processes are discussed.     

Inclusion Complexes of Cyclodextrins with Galangin: a Thermodynamic and Reactivity Study

The formation of the complexes of galangin (GAL) with native β-cyclodextrin (βCD), and with its substituted counterparts such as dimethyl-βCD (DMβCD) and hydroxypropyl-βCD (HPβCD), was studied by fluorescence spectra in aqueous medium. The binding association constants (K _a) of the complexes were determined at different temperatures. The formation constants obtained have the following trend upon complex formation at the three temperatures studied: HPβCD > DMβCD > βCD. The thermodynamic data for the inclusion of GAL in DMβCD and HPβCD indicated that is mainly enthalpy driven whereas for βCD it is an entropy-driven process.     

Stability Constants and Fluorescence of Terbium(Ⅲ) Complexes with Polyaminopolycarboxylates in Aqueous Solution

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A Proton NMR Study of the Stoichiometry and Stability of 18-Crown-6 Complexes with K+, Rb+ and Tl+ Ions in Binary Dimethyl Sulfoxide-Nitrobenzene Mixtures

Proton NMR spectroscopy was used to study the complexation reaction of 18-crown-6 (18C6) with K⁺, Rb⁺ and Tl⁺ ions in a number of binary dimethyl sulfoxide-nitrobenzene mixtures. In all cases, the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average ¹H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of dimethyl sulfoxide in the mixed solvent. It was found that, in all solvent mixtures used, Rb⁺ ion forms the most stable complex with 18-crown-6 in the series.     

Inclusion of α-phenyl-N-p-methylphenyl Nitrone in β- Cyclodextrin: Formation of 1G : 1H and 1G : 2H Complexes and the Remarkably Fast 1,3-Dipolar Cycloaddition of the 1G : 2H Complex with Olefins in the Solid State

The nitrone is found to be included in the -cyclodextrin cavity in two different stoichiometries viz., 1G : 1H and 1G : 2H – the existence of which is proved by physical methods. The 1G : 2H complex of the nitrone serves as a good potent dipolarophile in the 1,3-dipolar cycloaddition reactions with olefins resulting in rate acceleration and regioselection.     

Spontaneous Vesicle Formation in Mixed Aqueous Solution of Poly-tailed Cationic and Anionic Surfactants

Spontaneous vesicles from the mixed queous solution of poly-talied cationic surfactant PTA and anionic surfactant AOT are firstly obtained.Vesicle formation and characterizations are demonstrated by negative-staining TEM and dynamic light scattering.A monodisperse vesicle system is obtained with a polydispersity of 0.082.Ultrasonication can promote the vesicle formation,Mechanism of vesicle formation is discussed from the viewpoint of molecular interaction.     

Effect of the Composition of Ethanol–DMSO Solvents on the Stability of Silver(I) Complexes with 18-Crown-6

The effect of composition of ethanol–dimethyl sulfoxide (EtOH–DMSO) solvents (χ_DMSO = 0.0–1.0 mole fractions) on the stability of silver(I) complexes with 18-crown-6 ether (18C6) has been studied potentiometrically at 298.15 K. The increasing of DMSO concentrations in mixed solvents are shown to considerably reduce the stability of 18C6 complexes with silver(I) ion ([Ag18C6]⁺). A change in the solvation state of the central ion is suggested to be the key factor in shifting complexing equilibrium.     

Study on the Interaction of Pentachlorophenol with Urease in Aqueous Solution by Multiple Spectroscopic Techniques

The interactions between pentachlorophenol (PCP) and jack bean urease were studied using UV/vis absorption, CD, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectroscopic techniques. The fluorescence data showed that the fluorescence quenching of urease by PCP the results of the formation of a PCP–urease complex involving a hydrophobic interaction. The distance r between the donor (urease) and acceptor (PCP) was obtained from the fluorescence resonance energy transfer. The effect of PCP on the conformation of urease was analyzed using UV/vis absorption, synchronous fluorescence and three-dimensional fluorescence spectroscopic techniques. The result showed that PCP can enter into the hydrophobic pocket at the interface of urease and that the micro environments around the tyrosine and tryptophan residues were changed.     

Estimation of the Effectiveness of the Phosphate Group in Binary Phosphoserine/Biogenic Amine Systems in Aqueous Solution

Adduct formation in the binary systems of O-phospho-L-serine with biogenic amines (putrescine, spermidine or spermine) has been investigated. The overall stability constants of the adducts and the equilibrium constants of their formation have been determined using computer analysis of potentiometric data. Ion-ion interactions have been established to occur in the identified molecular complexes. The potential reaction centers are phosphate, carboxylate and amine groups from phosphorylated serine as well as the –NH₃⁺ and –NH₂⁺– groups from polyamine. The pH range of adduct formation is found to coincide with that in which the polyamine is protonated (positive reaction center) and the phosphoserine is partly or totally deprotonated (negative reaction center). The stability of the molecular complexes formed in the studied systems depends on the acid-base character of the substrates and on the structure of the reacting molecules. Sites of interactions in the bioligands have been deduced on the basis of the results of the equilibrium study and analysis of the changes in the positions of signals in the ¹³C and ³¹P NMR spectra.     

The Enthalpies of Solution of L-cysteine, L-serine and L-asparagine in Aqueous Solutions of Some Alcohols at 298.15 K

Heats of solution, Δ_sol H _m , of L-cysteine, L-serine and L-asparagine amino acids have been measured at different concentrations of aqueous ethanol, propanol and 2-propanol at 298.15 K using solvation calorimetry. These data are compared with the results reported earlier for L-alanine in ethanol. The enthalpic coefficients, h _xy , of the solute-organic cosolvent pair interaction in water have been obtained from the McMillan-Mayer approach and the data have been interpreted in terms of various interactions and changes in solvent structure.     

Thermodynamic Model for the Solubility of TcO2⋅xH2O in Aqueous Oxalate Systems

The room temperature solubility of amorphous, hydrous technetium(IV) oxide (TcO₂⋅xH₂O) was studied across a broad range of pH values extending from 1.5 to 12 and in oxalate concentrations from dilute (10⁻⁶ mol⋅kg⁻¹) to complete saturation with respect to sodium bioxalate at lower pH values, and to saturation with respect to sodium oxalate at higher pH values. The solubility was measured to very long equilibration times (i.e., as long a 1000 days or longer). The thermodynamic modeling results show that the dominant species in solution must have at least one more hydroxyl moiety present in the complex than proposed by previous investigators (e.g., TcO(OH)Ox⁻ rather than TcO(Ox)(aq)). Inclusion of the single previously unidentified species TcO(OH)Ox⁻ in our aqueous thermodynamic model explains a wider range of observed solubility data for TcO₂⋅xH₂O(am) in the presence of oxalate and over a broad range of pH values. Inclusion of this species is also supported by the recently proposed thermodynamic data for the TcO(OH)⁺ hydrolysis species that indicates that this species is stable at pH values as low as one.     

Standard Enthalpies of Formation of β-Aminobutyric Acid and Products of Its Dissociation in Aqueous Solution

Russian Journal of Physical Chemistry A - Heats of dissolution of β-aminobutyric acid in water and aqueous solutions of potassium hydroxide at 298.15 K are measured via direct calorimetry....     

The Partial Molar Heat Capacities and Expansions of Inosine, 2′-Deoxyinosine and 2′-Deoxyguanosine in Aqueous Solution at 298.15 K

Solution densities over the temperature range 288.15 to 313.15 K have been measured for aqueous solutions of the nucleosides inosine, 2′-deoxyinosine, and 2′-deoxyguanosine, from which the partial molar volumes of the solutes at infinite dilution, V ₂^o, were obtained. The partial molar expansions for the nucleosides at infinite dilution and 298.15 K, E ₂^o {E ₂^o=(∂ V ₂^o/∂ T) _p }, were derived from the V ₂^o results. The V ₂^o values at 298.15 K for the two sugars D-ribose and 2-deoxyribose also have been determined. The partial molar heat capacities at infinite dilution for all the solutes, C _p,2^o, have been determined at 298.15 K. These V ₂^o,E ₂^o, and C _p,2^o results are critically compared with all of the results available from the literature, and the use of group additivity to evaluate these solution thermodynamic properties for the sparingly soluble nucleoside guanosine is explored.     

1:1 and 1:2 Inclusion Complexes of Di-tert-butyl l-tartrate with α-Cyclodextrin: A Diffusion Study

The diffusion properties at two overall compositions of a ternary aqueous system containing α-cyclodextrin and a double-functional guest molecule, namely di-tert-butyl l-tartrate, have been studied by means of the Gouy interferometry. The experimental data are interpreted in terms of two independent chemical equilibria involving inclusion compounds. The elements of the diffusion coefficient matrix have been expressed as functions of the two equilibrium constants as well as of the diffusivities of the actual species occurring in solution. The reliability of the diffusion coefficients obtained through the Fujita–Gosting–Revzin procedure is also discussed in terms of its dependence on the composition of solutions used in the Gouy experiments.     

Isomorphous Substitution of Metallic Elements for Zeolite Y in the Aqueous Solution

The substitutions of Ti, Fe and Zr into zeolite Y in the aqueous solutions of (NH4)2TiF6, (NH4)3ZrF7 and (NH4)3FeF6 were systematically Investigated. It was found that Ai atoms in the framework can be replaced by some metallic elements and the extent of substitution depends on the M/A1 ratio of the solution. The maximum allowable M/A1 ratio of the aqueous solution Is related with the radius of the M atom and the stability constant of the MFnm- complex. The substituted zeolite samples with crystallinity greater than 80% were characterized by means of XRD, IR, DTA, TPR and NH3-TPD measurements. The incorporation of Ti, Fe and Zr into the zeolite leads to an increase in the unit cell parameter, a lowering of thermal stability and a red shift of the asymmetric stretching frequency. The extent of these changes is apparently related with the ionic radius of the metallic element and the degree of substitution. The results of various characterization methods show that the het-eroatoms are readily Introduced int