Improved DFT-based interpretation of ESI-MS of aqueous metal cations

The identification of Al nanoclusters by electrospray ionization mass spectrometry (ESI-MS)

Lacking consolidated qualitative and quantitative analysis methods of Al nanoclusters in aqueous, the distributions and concentrations of each Al species could not be revealed with single method before or after coagulation, which limited the development of environmental Al clusters control. As the ESI-MS applied in the inorganic cluster's identification tentatively, the deficient identification of Al species could be analyzed qualitatively and quantitatively with mass spectrum directly. Although many studies have applied the ESI-MS to analyze Al species in aqueous, the experimental conditions were not compared and not reached an agreement. Therefore, this work is the first study to review the methodology developments of ESI-MS in Al identification and to summarize the qualitative and quantitative analysis promoted by ESI-MS. The principle and rationality of quantitative ESI-MS method were inducted and discussed from the prospects of resolving mass spectrum assignment and transforming species in ionization. The qualitative ESI-MS results in previous studies were also analyzed by quantitative ESI-MS analysis in this work. The quantitative Al species results are accordant with the distribution results concluded via Al-Ferron and ²⁷Al NMR methods. The identification principles and instrumental parameters were summarized and unified, which would give hints to further methodological applications and modifications. This study puts forward the further possibilities and prospects of ESI-MS applied in the transformation and in-situ identification of Al₁₃ nanocluster in aqueous.

Electrospray ionization time-of-flight mass spectrum analysis method of polyaluminum chloride flocculants

Electrospray mass spectrometry has been reported as a novel technique for Al species identification, but to date, the working mechanism is not clear and no unanimous method exists for spectrum analysis of traditional Al salt flocculants, let alone for analysis of polyaluminum chloride (PAC) flocculants. Therefore, this paper introduces a novel theoretical calculation method to identify Al species from a mass spectrum, based on deducing changes in m/z (mass-to-charge ratio) and molecular formulas of oligomers in five typical PAC flocculants. The use of reference chemical species was specially proposed in the method to guarantee the uniqueness of the assigned species. The charge and mass reduction of the Al cluster was found to proceed by hydrolysis, gasification, and change of hydroxyl on the oxy bridge. The novel method was validated both qualitatively and quantitatively by comparing the results to those obtained with the (27)Al NMR spectrometry.

Pressure induced speciation changes in the aqueous Al³⁺ system

We have developed a simple model for incorporating the influence of external pressure and solution pH into a cluster based (i.e. comprising the central Al(3+) cation and nearest neighbor coordinating H2O and OH(-) ligands) 1st principles approach to investigate the hydrolysis equilibria of aqueous Al(3+) monomeric species in high pressure environments such as are found in the Earth's mantle. Our model is demonstrated to reproduce the well documented bulk chemistry of the aqueous Al(3+) system under ambient conditions, namely the system is dominated at low and high pH by the 6-coordinated aqua species and 4 coordinated hydroxide species, respectively, while all remaining species occupy a narrow intermediate pH range. Coupling this model to changes in solution pH is achieved by using [H3O(+)] as a parameter in the definition of the formation equilibrium constants used; the influence of external pressure is evaluated using Planck's equation. This approach predicts that changes in external pressure will induce drastic changes in the aqueous solubility of these species under high pressure conditions and moderate changes at as low as 5 GPa. Finally, some industrial and geochemical implications of this result are discussed.

Aluminium in biological environments: a computational approach

The increased availability of aluminium in biological environments, due to human intervention in the last century, raises concerns on the effects that this so far “excluded from biology” metal might have on living organisms. Consequently, the bioinorganic chemistry of aluminium has emerged as a very active field of research. This review will focus on our contributions to this field, based on computational studies that can yield an understanding of the aluminum biochemistry at a molecular level. Aluminium can interact and be stabilized in biological environments by complexing with both low molecular mass chelants and high molecular mass peptides. The speciation of the metal is, nonetheless, dictated by the hydrolytic species dominant in each case and which vary according to the pH condition of the medium. In blood, citrate and serum transferrin are identified as the main low molecular mass and high molecular mass molecules interacting with aluminium. The complexation of aluminium to citrate and the subsequent changes exerted on the deprotonation pathways of its tritable groups will be discussed along with the mechanisms for the intake and release of aluminium in serum transferrin at two pH conditions, physiological neutral and endosomatic acidic. Aluminium can substitute other metals, in particular magnesium, in protein buried sites and trigger conformational disorder and alteration of the protonation states of the protein's sidechains. A detailed account of the interaction of aluminium with proteic sidechains will be given. Finally, it will be described how alumnium can exert oxidative stress by stabilizing superoxide radicals either as mononuclear aluminium or clustered in boehmite. The possibility of promotion of Fenton reaction, and production of hydroxyl radicals will also be discussed.