Isotope effect in proton-transfer and association-dissociation reactions for butylamine by ultrasonic relaxation methods

Ultrasonic absorption coefficients were measured for butylamine in heavy water (D2O) in the frequency range from 0.8 to 220 MHz and at concentrations from 0.0278 to 2.5170 mol dm(-3) at 25 degrees C; two kinds of relaxation processes were observed. One was found in relatively dilute solutions (up to 0.5 mol dm(-3)), which was attributed to the hydrolysis of butylamine. In order to compare the results, absorption measurements were also carried out in light water (H2O). The rate and thermodynamic parameters were determined from the concentration dependence of the relaxation frequency and the maximum absorption per wavelength. The isotope effects on the diffusion-controlled reaction were estimated and the stability of the intermediate of the hydrolysis was considered while comparing it with the results for propylamine in H2O and D2O. Another relaxation process was observed at concentrations greater than 1 mol dm(-3) in D2O. In order to examine the solution characteristics, proton NMR measurements for butylamine were also carried out in D2O. The chemical shifts for the gamma- and delta-proton in butylamine molecule indicate the existence of an aggregate. From profiles of the concentration dependence of the relaxation frequency and the maximum absorption per wavelength of sound absorption, the source of the relaxation was attributed to an association-dissociation reaction, perhaps, associated with a hydrophobic interaction. The aggregation number, the forward and reverse rate constants and the standard volume change of the reaction were determined. It was concluded from a comparison with the results in H2O that the hydrophobic interaction of butylamine in D2O is stronger than that in H2O. Also, the isotope effect on this reaction was interpreted in terms of the solvent structure.

Specific mass spectrometric fragmentations from the dissociation of intermediate ion-neutral complexes

It is reported that two kinds of specific mass spectrometric fragmentations are generated from dissociations of the intermediates of both the ion-neutral complex and the proton-bound complex. Collision-induced dissociation, isotopic labelling, and semi-empirical AM1 calculations were used to investigate the formation mechanism of the ion of m/z 139 from ionized tetrahydroimidazole-substituted methylene beta-diketones and the unimolecular fragmentations pathway of 3-phenyl-1-butyn-3-ol upon electron impact.

UNIMOLECULAR DISSOCIATION REACTIONS OF DOUBLY-CHARGED IONS [C12H12N2O](2+) AND [C12H12N2S](2+) IN GAS-PHASE

The unimolecular dissociation reactions of doubly charged ions were reported, which resulted from a tandem mass spectrometer and a reversed geometry double focusing mass spectrometer by electron impact, Mass analyzed ion kinetic energy spectrometry (MIKES) was used to obtain the kinetic energy releases in charge separation reactions of doubly charged ions, The intercharge distances between the two charges at transition states can be calculated from the kinetic energy releases, Transition structures of unimolecular dissociation reactions were infered from MIKES and MS/MS.

THERMODYNAMICS OF AMINO-ACID DISSOCIATION IN MIXED-SOLVENTS .3. GLYCINE IN AQUEOUS GLUCOSE SOLUTIONS FROM 5-DEGREES-C TO 45-DEGREES-C

The first thermodynamic dissociation constants of glycine in 5, 15 mass % glucose + water mixed solvents at five temperatures from 5 to 45-degrees-C have been determined from precise emf measurements of a cell without liquid junction using hydrogen and Ag-AgCl electrodes and a new method of polynomial approximation proposed on the basis of Pitzer's electrolytic solution theory in our previous paper. The results obtained from both methods agree within experimental error. The standard free energy of transfer for HCl from water to aqueous mixed solvent have been calculated and the results are discussed.

Formation and dissociation of protonated pyridine-methanol cluster ions at 355 and 266 nm

The multi-photon ionization process of the hydrogen-bond cluster of pyridine-methanol has been investigated using a conventional and reflectron time-of-flight mass spectrometer (RTOF-MS) at 355 and 266 nm laser wavelengths, respectively. The sequences of the protonated cluster ions (CH3OH)(n)H+ and (C5H5Nn)(CH3OH)(m)H+ (n = 1,2) were observed at both laser wavelengths, while the sequence of the cluster ions (CH3)OHn (H2O)H+ was observed only at 355 nm laser wavelength. The difference between the relative signal intensities of the protonated methanol cluster ions at different laser wavelengths is attributed to different photoionization mechanisms. Some nascent cluster ions in metastable states dissociated during free flight to the detector. The dissociation kinetics is also discussed. (C) 2000 Elsevier Science B.V.

Determination of dissociation constants of Strychnos alkaloids from Strychnos nux-vomica L. by capillary electrophoresis

An accurate capillary electrophoresis method was developed for the determination of dissociation constants of five Strychnos alkaloids from Strychnos nux-vomica L. The method relies on measuring the effective mobility of the solute as a function of the buffer pH. The mathematical relationship was strictly derived from the fundamental electrophoresis theory and the dissociation equilibrium of a weak base without any simplifications. Careful optimization of the running buffer permitted base-line resolution of the five structurally similar alkaloids.