title: N-Salicylideneamino acidato complexes of oxovanadium(IV). The cysteine and penicillamine complexes.
abstract: Oxovanadium(IV) complexes with ligands derived from the reaction of salicylaldehyde with L-cysteine and with D- and D,L-penicillamine are prepared. The compounds are characterised by elemental analysis, spectroscopy (UV-VIS, CD, EPR), TG, DSC and magnetic susceptibility measurements (9-295 K). We discuss several aspects related to the structure of these complexes in the solid state and in solution; in particular, the possibility of forming thiazolidine complexes, and their comparison with the characterised complexes is studied by molecular mechanics and density functional theory calculations. The solution structures depend on pH and solvent, and while with L-Cys the spectroscopic results show trends similar to those of the L-Ala and L-Ser systems up to ca. pH 8-9, where thiolate coordination starts being detected, the penicillamine system is quite distinct, namely thiolate coordination occurs for pH > 6.5. In the presence of salicylaldehyde and V(IV)O the desulfydration of cysteine proceeds rapidly, but no similar reaction occurs with penicillamine, although its decomposition is also activated. The DFT calculations do not indicate any energetic basis for this distinct reactivity, which possibly results from different complexes present in the Cys and Pen systems. In the cysteine system, the N-salicylidenedehydroalanine-V(IV)O complex V is believed to form in an intermediate stage of the desulfydration. Further, addition of several nucleophiles to the cysteine reaction mixtures produce amino acid derivatives by a Michael-type base-catalysed addition, a result compatible with the formation of V. The products of these reactions were analysed by TLC and HPLC, and in some cases isolated.
authors.affiliation: Centro Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors.forename: João Costa
authors.initials: JC
authors.lastname: Pessoa
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Calhorda
authors.forename: Isabel
authors.initials: I
authors.lastname: Cavaco
authors.forename: Paulo J
authors.initials: PJ
authors.lastname: Costa
authors.forename: Isabel
authors.initials: I
authors.lastname: Correia
authors.forename: Dina
authors.initials: D
authors.lastname: Costa
authors.forename: Luís F
authors.initials: LF
authors.lastname: Vilas-Boas
authors.forename: Vitor
authors.initials: V
authors.lastname: Félix
authors.forename: Robert D
authors.initials: RD
authors.lastname: Gillard
authors.forename: Rui T
authors.initials: RT
authors.lastname: Henriques
authors.forename: Robert
authors.initials: R
authors.lastname: Wiggins
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D002942:Circular Dichroism; D003545:Cysteine / Q000737:chemistry*; D008024:Ligands; D010396:Penicillamine / Q000737:chemistry; D014638:Vanadates / Q000737:chemistry*
chemical_list: D000447:Aldehydes; D008024:Ligands; C013243:salicylaldehyde; C075743:oxovanadium IV; D014638:Vanadates; D010396:Penicillamine; D003545:Cysteine