Síntese, caracterização e ensaios cinéticos de novos complexos com os ligantes TPEN e Htmdp

Abstract

A presença de íons metálicos como constituintes naturais das enzimas responsáveis por uma ampla variedade de funções especificas associadas ao processo da vida, tem induzido químicos de coordenação a sintetizar e caracterizar complexos metálicos candidatos a modelos biomiméticos para os sistemas naturais. Com base nas informações disponíveis na literatura a respeito do ambiente de coordenação dos íons metálicos, da reatividade e mecanismos de reações das hidrolases e oxidases, planejamos a síntese de novos compostos bioinspirados. Neste trabalho foram sintetizados e caracterizados quatro novos complexos empregando-se os ligantes N,N,N',N'-Tetrakis(2-piridilmetil)etilenodiamena (TPEN) e 1,5-Bis[bis(2-piridilmetil)amino]-3-pentanol (htmdp). São eles: [Gd(TPEN)(NO3)2]NO3.MeOH (1), [Zn2(Htmdp)(µ-CH3COO)](ClO4)2 (2), [Cu2(Htmdp)(µ-OH)](ClO4)2.H2O (3) e [Gd2(Htmdp)(NO3)5]MeOH (4). Os complexos foram caracterizados por análise elementar de CHN, espectroscopia de infravermelho e espectrometria de massas. Os complexos 1, 3 e 4 também foram caracterizados por titulação potenciométrica. Ainda, os complexos 1, 2 e 3 foram caracterizados por difratometria de raios X. A partir da caracterização dos complexos 1 e 4 foi constatada que os ligantes utilizados neste trabalho não são bons coordenantes frente ao íon Gd(III). Os complexos 2 e 3 foram testados frente à hidrólise do substrato bis(2,4-dinitrofenil)fosfato como modelos para metoloenzimas hidrolíticas. O complexo 3 também se apresentou efetivo na reação de oxidação do substrato 3,5-di-terc-butilcatecol.<br>

Abstract : The presence of metal ions as natural constituents of the enzymes responsible for a wide variety of specific functions associated with the process of life has prompted coordination chemists to synthesize and characterize metal complexes candidates biomimetic models for natural systems. The complex models have a fundamental role in the elucidation of the mechanisms through which the catalytic process occurs in the native enzymes. Based on the information available in the literature concerning the environment for coordination of metal ions, reactivity and reaction mechanisms of hydrolases and oxidases, we planned the synthesis of new bioinspired compound. In this work were synthesized and characterized four new complexes of Gd (III), Zn (II) and Cu (II) employing ligands N,N,N#,N#-tetrakis(2-pyridylmethyl)etilenodiamine (TPEN) and 1,5-bis[bis(2-pyridylmethyl)amino]-3-pentanol (htmdp). Those are: [Gd(TPEN)(NO3)2]NO3.MeOH (1), [Zn2(Htmdp)(ì-CH3COO)](ClO4)2 (2), [Cu2(Htmdp)(ì-OH)](ClO4)2.H2O (3) e [Gd2(Htmdp)(NO3)5]MeOH (4). The complexes were characterized by elemental analysis, infrared spectroscopy and mass spectrometry. Complexes 1, 3 and 4 were also characterized by potentiometric titration. Further, the complexes 1, 2 and 3 were characterized by X ray diffraction. From the characterization of the complexes 1 and 4 was observed that the ligands used in this work are not good coordinating to ion Gd (III) because in solution was observed the dismantling the complex. Complexes 2 and 3 were tested toward the substrate bis(2,4-dinitrophenyl)phosphate as models for hydrolytic metolloenzymes. Based on structural, spectroscopic, electrochemical and potentiometric data, it was possible to propose a catalytic cycle for the catalytic cleavage of 2,4-bdnpp in the presence of the complex 3 which is compatible with a mechanism already described in the literature. Complex 3 also revealed itself quite effective on the oxidation of the 3,5-di-tert-butylcatechol. Thus, complex 3 can be regarded one synthetic model for studying catalytic prosmiscuity once it showed both hydrolase and oxireductase activities.