title: Ion-exchange and potentiometric characterization of Al-cystine and Al-cysteine complexes.
abstract: The interaction between aluminium and cysteine and cystine was evaluated by means of ion-exchange experiments and potentiometry. Ion-exchange experiments included other ligands with affinity for aluminium and two kinds of resins, either a Na+ -form or an Al3+ -form exchanger. The ability of the ligands to keep aluminium in solution in the presence of the Na+ exchanger or to withdraw it from the Al3+ -form resin was evaluated. Aluminium quantification was carried out by either graphite-furnace or flame atomic absorption spectrometry. Aluminium extraction isotherms were linearised using the Scatchard plot, and stability constants were obtained from the curves' slopes. The experiments showed that the ability of the ligands to withdraw aluminium from the Al3+ -form resin increased following the order cysteine < oxalate < citrate = cystine < nitrilotriacetic acid < ethylenediaminetetraacetic acid. Potentiometric titrations, carried out in aqueous solution with constant ionic strength and temperature, showed that the predominant species in solution have a metal-ligand proportion of 1:1 for both amino acids. The main species are Al(OH)3L, with log K of 6.2 for cysteine, and AlL and Al(OH)L, with log K of 10.3 and 1.7, respectively, for cystine. Stability constants obtained from the Scatchard plots showed a linear correlation with the stability constants obtained by potentiometry for cystine and cysteine in this work and those collected from the literature for the other ligands. These results show that cysteine and cystine extract and maintain aluminium in solution, which may explain elevated concentrations of aluminium in parenteral nutrition solutions containing these amino acids.
authors.affiliation: Departamento de Química, Universidade Federal de Santa Maria, 97111-970, Santa Maria, RS, Brazil. ndenise@quimica.ufsm.br
authors.forename: Denise
authors.initials: D
authors.lastname: Bohrer
authors.forename: Vania Gabbi
authors.initials: VG
authors.lastname: Polli
authors.forename: Paulo
authors.initials: P
authors.lastname: Cícero do Nascimento
authors.forename: Jean Karlo A
authors.initials: JK
authors.lastname: Mendonça
authors.forename: Leandro Machado
authors.initials: LM
authors.lastname: de Carvalho
authors.forename: Solange Garcia
authors.initials: SG
authors.lastname: Pomblum
mesh_terms: D000535:Aluminum / Q000737:chemistry* / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry* / Q000378:metabolism; D003553:Cystine / Q000737:chemistry* / Q000378:metabolism; D007474:Ion Exchange; D007475:Ion Exchange Resins; D008024:Ligands; D011199:Potentiometry
chemical_list: D007475:Ion Exchange Resins; D008024:Ligands; D003553:Cystine; D000535:Aluminum; D003545:Cysteine