Pb(II)-binding capability of aminohydroxamic acids: primary hydroxamic acid derivatives of alpha-amino acids as possible sequestering agents for Pb(II).
Complexes of aminohydroxamic acids, D,L-alpha-alaninehydroxamic acid (alpha-Alaha), sarcosinehydroxamic acid (Sarha), D,L-N-methyl-alpha-alaninehydroxamic acid (N-Me-alpha-Alaha), beta-alaninehydroxamic (beta-Alaha), L-aspartic acid-beta-hydroxamic acid (Asp-beta-ha), L-glutamic acid-gamma-hydroxamic acid (Glu-gamma-ha) and L-histidinehydroxamic acid (Hisha) with lead(II) in aqueous solution were studied by pH-potentiometric, 1H NMR and electrospray ionization mass spectrometric (ESI MS) methods. The results were compared to those of a simple monohydroxamic acid, acetohydroxamic acid and the effects of the amino group, hydroxamate-N, as well as, additional side chain donors on the co-ordination mode and on the stability of the complexes formed were evaluated. It was found that the amino nitrogen atom situating in beta- or in gamma-position (beta-Alaha, Asp-beta-ha, Glu-gamma-ha) does not co-ordinate to Pb(II), only hydroxamate type chelates are formed before the hydrolytic processes. However, the amino-N in alpha-position (alpha-Alaha, Sarha, Hisha) seems to form a stable 5-membered (N,N)-type chelate together with the deprotonated hydroxamate-N above pH 6. On the other hand, the hydroxamate (O,O)-type chelate also exists. Since steric reasons do not allow the coordination of these two chelates of a molecule to the same Pb(II) ion, polynuclear complexes with mixed co-ordination modes are formed with the alpha-derivatives above pH 6. Simple hydroxamate type complexes are formed with N-Me-alpha-Alaha, where the hydroxamate-N is not able to co-ordinate. The co-ordination of the side chain imidazole of Hisha is not measurable, while a weak interaction of the side chain carboxylates of Asp-beta-ha and especially of Glu-gamma-ha can be suggested.
Bátka
Dávid
D
Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem ter 1, H-4010 Debrecen, Hungary.
Farkas
Etelka
E
D000596:Amino Acids / Q000737:chemistry*; D001224:Aspartic Acid / Q000737:chemistry; D018698:Glutamic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006877:Hydroxamic Acids / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D019216:Metals, Heavy / Q000737:chemistry; D011199:Potentiometry; D011522:Protons
D000596:Amino Acids; D006877:Hydroxamic Acids; D008024:Ligands; D019216:Metals, Heavy; D011522:Protons; D007854:Lead; D001224:Aspartic Acid; D018698:Glutamic Acid