Dissociation of 5-fluoro- and 3,5-dinitrosalicylic acids in water-methanol mixtures at 25 degrees

The association constants and molar conductivities, extrapolated to zero concentration, have been determined for 3,5-dinitrosalicylic and 5-fluorosalicylic acids in water-methanol mixtures at 25 degrees .     

High-performance liquid chromatographic separation of bile acids and bile alcohols diastereoisomeric at C-25

The high-performance liquid chromatographic separation of the 25R and 25S diastereoisomers of the bile alcohols 5 beta-cholestane-3 alpha,7 alpha,26-triol and 5 beta-cholestane-3 alpha,7 alpha, 12 alpha, 26-tetrol and the bile acids, 3 alpha,7 alpha-dihydroxy-5 beta-cholestane-26-oic acid and 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestane-26-oic acid is described. A Radial-Pak microBondapak C18 reversed-phase cartridge was used for the separations and elutions were carried out with acetonitrile-water-methanol-acetic acid mixtures. All eight diastereoisomeric compounds showed baseline separation when up to 200 micrograms of the isomeric mixtures were injected into the column and the method can be used for isolation of pure diastereoisomers of these bile acids and bile alcohols.     

Ionization of moderately strong acids in aqueous solution. Part III. Methane-, ethane-, and propanesulfonic acids at 25°C

Laser Raman spectroscopy has been used to obtain degrees of ionization (α) for three alkanesulfonic acids in aqueous solution at 25°C. PMR shift measurements using an internal standard give confirmatory values of α. Ionization constants estimated are 83±2 (Me), 48±2 (Et), and 34±6 (Pr) mole-kg^?1.     

The activity of calcium chloride in aqueous solutions of some amino acids at 25°C

The activity coefficients of calcium chloride in aqueous solutions of the amino acids glycine, β-alanine, γ-amino butyric acid, ε-aminocaproic acid, and glycylglycine have been determined with cells utilizing a calcium ion-exchange electrode. Application of the cross-differential relationship allows a measure of the variation of the salting-in parameter across the series of amino acids. The variation of this parameter is discussed using a semiempirical approach developed earlier.     

Thermodynamics of ionization processes for hydroxy-substitute benzoic acids in water—dimethylsulfoxide mixtures at 25°C

The ionization and solution enthalpies of the hydroxybenzoic acids were measured calorimetrically at 25°C in water—dimethylsulfoxide mixtures ranging from pure water to 0.8 DMSO mole fraction.In the same solution, the ΔG° values for the ionization processes have been determined by potentiometric measurements.The different enthalpy solvation values for the three hydroxy isomers were explained taking into account the prevalence of the resonance or the inductive effect as a function of the solvent composition.The intramolecular hydrogen bond of the undissociated molecules seems to be responsible for the greater degree of ionization of o-hydroxybenzoic acid with respect to the m and p-hydroxy isomers.     

Thermodynamics of ionization processes for chloro-substituted benzoic acids in water—dimethysulfoxide mixtures at 25°C

The ionization enthalpies of o-, m-, and p-chloro-benzoic acid were measured calorimetrically at 25°C in water—DMSO mixtures ranging from pure water up to 0.8 DMSO mole fraction. In the same mole fraction range, molar free energies and entropies were calculated for the ionization process.The different results obtained for the three acids were explained by taking into account the different effects displayed on the solvation and ionization phenomena by the chlorine atom in the various positions on the aromativ ring.Using the transfer enthalpy of benzoic acid in the same mixtures as a reference point, a solvation sequence is proposed both for the ions and undissociated molecules.     

Application of organolithium and related reagents in synthesis. Part 25: Novel specific synthesis of the 4-arylisochroman-3-acetic acids via conversion of benzoic acids

The transformation of the benzanilides 1 into 4-arylisochroman-3-acetic acids 8 applying the following sequence of reactions is described. At first, the 3-arylphthalides 3 were obtained via metallation [n-BuLi] of benzanilides 1 and subsequent treatment of the generated bis-lithiated anilides 2 with aromatic aldehydes. Next, the 3-arylphthalides 3 were reduced [LiBH₄] to phthalanes 5 and then, via reductive metallation [Li/C₁₀H₈] and reaction of the generated bis-lithiated species 6 with dimethylformamide, 3-hydroxy-4-arylisochromans 7 were produced. In the final step the isochromans 7 were treated with 1-methoxy-1-trimethylsilyloxyethene in the presence of titanium tetrachloride and furnished 4-arylisochromans-3-acetic acid methyl esters 8 as trans stereoisomers (Ψ-e/e).     

Analysis of 25 underivatized amino acids in human plasma using ion-pairing reversed-phase liquid chromatography/time-of-flight mass spectrometry

Amino acids in biological fluids have previously been shown to be detectable using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) with perfluorinated acids as ion-pairing agents. To date, these studies have used precursor mass, retention time and tandem mass spectrometry (MS/MS) to identify and quantify amino acids. While this is a potentially powerful technique, we sought to adapt the method to time-of-flight (TOF)MS. A new application of a recently described liquid chromatographic separation method was coupled with TOFMS to employ accurate mass for qualitative identification; resulting in additional qualitative data not available with standard single quadrupole data. In the current study, we evaluated 25 physiological amino acids and one dipeptide that are routinely quantified in human plasma. Accuracy and precision of the method was evaluated by spiking human plasma with a mix of the 25 amino acids; in addition, the inclusion of a cation-exchange cleanup step was evaluated. The calibration curves were linear over a range from 1.56 to 400 microM. The dynamic range was found to be within physiological levels for all amino acids analyzed. Accuracy and precision for most of the amino acids was between 80-120% spike recovery and <10% relative standard deviation (RSD). The LC/MS technique described in this study relies on mass accuracy and is suitable for the quantitation of free amino acids in plasma.     

The interaction of diaminodihydroxodicyano-platinum with nitric,sulfuric, and perchloric acids at 25 and 50°C

Russian Chemical Bulletin -     

Enthalpies of transfer of amino acids and sodium chloride from water to aqueous fructose at 25°C

Enthalpies of transfer H ₂ of three amino acids glycine, L-alanine, and L-phenylalanine, and of NaCl, from water to aqueous fructose at low fructose mole fraction were determined at 25°C. Comparison with H ₂ for glycine in the presence and absence of KCl shows that the effect of additional ion-dipole interactions is apparent only in more concentrated fructose solutions. Limiting slopes indicate that glycine resembles NaCl more than it does the other two amino acids. The effect on H ₂ of the polarity of the zwitterion is offset and dominated by the growing non-polar side chain. Values of H ₂ for glycine, L-phenylalanine, and NaCl from water to aqueous urea are compared with the results of the present study. A rough colligative effect similiar to that observed for NaCl in a variety of polar mixed aqueous solvents may also be possible for glycine, since the change of the enthalpies of transfer with mole fraction for glycine are the same for transfer to both aqueous urea and fructose.     

Evaluation of copper(II)-binding ability of humic acids in peat using sulphopropyl-Sephadex C-25 cation exchanger

A method for the determination of copper(II) complexes with humic acids was developed by batch operation with the cation exchanger sulphopropyl-Sephadex C-25 (C-25). The copper-binding ability (conditional stability constants and copper-complexing capacities) of humic acids which were extracted from peat in Hokkaido was evaluated. A solution containing copper(II) ions and humic acids was shaken with the C-25 exchanger. The copper-humic acid complexes remained in the supernatant and the uncomplexed free copper ion was retained on the C-25. The copper-humic acid complexes were determined by flame atomic absorption spectrometry. The copper-binding ability of nitrilotriacetic acid (NTA) as a model ligand was similarly determined with a Scatchard plot. The conditional stability constant obtained at pH 4.5 was in good agreement with the reported value. The copper-binding abilities of the humic acids from peat were estimated using a Scatchard plot adopting a two-site model. The functional groups in the humic acids which contribute to the complexation with copper were investigated by conductimetric and pH titration, and the relationship between the copper-binding sites and functional groups in the humic acids was investigated.     

Thermodynamic dissociation constants of salicylic and monochloroacetic acids in mixed solvent systems from conductance measurements at 25°C

The molar conductances of dilute solutions of salicylic and monochloroacetic acids in binary mixtures of methanol, ethanol, 1-propanol, N,N-dimethylformamide, acetone, acetonitrile, tetrahydrofuran and dioxane with water have been measured at 25°C. The Lee-Wheaton conductance equation was fitted to the data in order to derive thermodynamic dissociation constants and limiting molar conductances. The results were compared with those in the literature pertaining to analogous media, mostly derived potentiometrically. The findings are interpreted in terms of a solvent effect on the ionization of these acids in mixed solvent systems.This paper is dedicated to the late Professor Raymond M. Fuoss on his 3^rd anniversary.     

Energetic mixing of anti‐SNAP25 on lipid monolayers: degree of saturation of C18 fatty acids

In our study, various mixtures of C18 fatty acids with different degrees of saturation in their hydrocarbon chain, namely stearic acid (SA), oleic acid (L1), linoleic acid (L2), and linolenic acid (L3), and a polyclonal antibody, anti‐synaptosome‐associated protein of 25 kDa (SNAP25) (AS25), have been investigated using the Langmuir–Blodgett (LB) technique accompanied by atomic force microscopy (AFM) imaging. The cis‐double bonds in unsaturated lipids (L1, L2, and L3) have kinks in their molecular conformation and thus could not pack as tightly and uniformly as SA. The bends and kinks in the molecular structure may interfere with the packing of the lipid monolayer which will promote fluidity as shown in the analyzed compressibility modulus (C_s^?1 ) data. The negative values of Gibbs free energy of mixing (ΔG _mix ) of C18 fatty acids/AS25 confirm the spontaneity interaction of AS25 molecules on the monolayers. The amount of AS25 incorporated into the monolayer strongly affected the thermodynamic properties of the lipid monolayers. AFM surface roughness analyses also indicate that AS25 molecules are strongly bounded on the surface membrane as predicted by the obtained energetic data. In comparison to all C18 fatty acids studied, the strongest intermolecular interaction is observed in L1 at the investigated ranges. In particular, at mole ratio of 26:1, the most negative ΔG _mix is observed at L1. Thus, we can draw the conclusion that AS25 is best mixed with L1. This L1/AS25 ratio mimicking a half bilayer membrane serves as a very useful reference in preparing fatty‐acid nanoimmunoliposomes as the targeted drug‐delivery vehicles for cancer therapy. Copyright © 2016 John Wiley & Sons, Ltd.