The hydrolysis reactions of AlCl3 in 0.1 M aqueous solutions at pH 3.27-4.20 were monitored by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) as a function of time. The cationic and anionic ESI mass spectra of aluminum(III) solutions gave strong evidence of the presence of a variety of monomeric and polymeric complexes. Competition between the OH- and Cl- ligands within the same aluminum core was observed. The influence of the sample cone voltage on the product distribution was also explored. The optimum sample cone voltage for the cationic spectra was 70 V. For the anionic spectra no optimum sample cone voltage was found and the appearance of the anionic spectra was strongly dependent on the sample cone voltage within the whole range explored.

Earlier characterization of some hydrolysis products of AlCl 3 ·6H 2 O was confirmed by electrospray ionization tandem mass spectrometry with increasing collision energy of projectile ions. At lower collision energies, the aqua ligands were stripped off. At higher energies, two hydroxo groups formed a bridging oxo group with loss of one water molecule. Aluminum complexes could also capture aqua ligands in the collision chamber so long as the parent ion did not fragment, and the fragment ion spectra broadened toward higher m/z values. The chloro ligands were eliminated as hydrochloric acid. The aluminum cores remained highly intact.

Formation of ternary complexes between Gd-DTPA, Gd-DTPA-BMA, and Gd-DOTA, used as contrast enhancement agents in MRI and the endogenously available carbonate and phosphate ions, has been demonstrated. The extent of ternary complex formation and its effect on the proton relaxation, measured at 9 MHz, rates is negligible at around pH < 8. The complex Gd-EDTA forms more stable ternary complexes with carbonate and phosphate and it also strongly coordinates the terdentate citrate ligand. The formation of ternary complexes Gd-EDTA(X) (X = CO3(2-), Cit3-) results in a significant decrease in the proton relaxation rates under physiological conditions.

No abstract

ElectroSpray Ionization-Mass Spectrometry (ESI-MS) and computational methods (DFT, MP2, and COSMO) were used to investigate the hydrolysis products of aluminium chloride as a function of sulfate concentration at pH 3.7. With the aid of computational chemistry, structural information was deduced from the chemical compositions observed with ESI-MS. Many novel types of hydrolysis products were noted, revealing that our present understanding of aluminium speciation is too simple. The role of counterions was found to be critical: the speciation of aluminium changed markedly as a function of sulfate concentration. Ab initio calculations were used to reveal the energetically most favoured structures of aluminium sulfate anions and cations selected from the ESI-MS results. Several interesting observations were made. Most importantly, the bonding behaviour of the sulfate group changed as the number of aqua ligands increased. The accompanying structural rearrangement of the clusters revealed the highly active role of sulfate as a ligand. The gas phase calculations were expanded to the aquatic environment using a conductor-like screening model. As expected, the bonding behaviour of the sulfate group in the minimum energy structures was distinctly different in the aquatic environment compared to the gas phase. Together, these methods open a new window for research in the solution chemistry of aluminium species.

No abstract

No abstract

The hydrolysis reactions of FeCl3 in 0.1 mM aqueous solutions were monitored by electrospray ionisation time-of-flight mass spectrometry (ESI-ToF-MS). In contrast to the other ionisation techniques, electrospray ionisation provides information on the composition of the elemental cores even in water and salt cluster ions. Therefore, the technique facilitates detection of the bonding of the chloride ions in the oxo-hydroxo-iron cores. A variety of mononuclear and polynuclear iron-oxohydroxo-chloride complexes were characterised from the cationic and anionic mass spectra of iron(III) solutions. Oxidation and reduction reactions of iron, as well as competition between OH- and Cl- ions within one iron core, were also observed.