Tetraammine ruthenate complexes: cationic SAMs for cytochrome c recognition

Abstract

O processo redox da metaloproteína cyt c foi observado através da utilização de eletrodos de ouro modificados com os complexos [Ru(CNPy)(NH 3) 4 (1,4-dt)] 2+ e [Ru(CNPy)(NH 3) 4 (pyS)] 2+ , onde CNPy = 4-cianopiridina, pyS = 4-mercaptopiridina e 1,4dt = ditiano. Os valores dos potenciais redox observados indicam a forma in natura da proteína. A forma dos voltamogramas, todavia, é dependente da conformação do complexo modificador sobre a superfície que, por sua vez, foi determinada por SERS. Os potenciais de dessorção redutiva, observados em-0,52 e-0,64 V vs Ag|AgCl|Clpara os complexos [Ru(CNPy)(NH 3) 4 (1,4-dt)] 2+ e [Ru(CNPy)(NH 3) 4 (pyS)] 2+ , respectivamente, são indicativos do tipo de ligação com a superfície e da capacidade π retiradora do ligante CNpy. The redox process of the cyt c metalloprotein was assessed by the cationic SAMs formed with [Ru(CNPy)(NH 3) 4 (1,4-dt)] 2+ and [Ru(CNPy)(NH 3) 4 (pyS)] 2+ complexes on gold, where CNPy = 4-cyanopyridine, pyS = 4-mercaptopyridine and 1,4-dt = dithiane. The observed cyt c redox potentials are indicative of the native protein form. The voltammograms, however, were observed to be affected by the conformation of the modifiers, determined by SERS spectroscopy. The [Ru(CNPy)(NH 3) 4 (pyS)] 2+ complex, which exhibits trans conformation on the surface, presented a well-defined voltammogram. On the other hand, the gauche conformation of the [Ru(CNPy)(NH 3) 4 (1,4-dt)] 2+ SAM seems to make the assessment of the cyt c hET reaction difficult. The reductive desorption potentials, at-0.52 and-0.64 V vs Ag|AgCl|Clfor the [Ru(CNPy)(NH 3) 4 (1,4-dt)] 2+ and [Ru(CNPy)(NH 3) 4 (pyS)] 2+ SAMs, respectively, are indicative of the bonding mode with the surface and the π withdrawing capability of the CNpy ligand.

Release of Cyanopyridine from a Ruthenium Complex Adsorbed on Gold: Surface-Enhanced Raman Scattering, Electrochemistry, and Density Functional Theory Analyses

“…The first SERS study of the SAM formed with [Ru(NH 3 ) 4 (CNpy)-(pyS)] 2+ on gold was performed in air and without applied potential. 16 In such work, the gold surface was modified by immersion in an aqueous solution containing the complex which had been previously synthesized in homogeneous medium. As already commented and as expected for sulfurcontaining molecules, 9,13−16,20,21,41−43 the complex adsorbs on gold through the sulfur atom of the pyS moiety.…”

“…In the field of molecular electronics, where the charge transfer is a crucial process and has to be controlled, the insertion of redox compounds in SAMs formed on metallic surfaces represents a great advantage as it can serve as model for studying the fundamentals of electron transfer since the distance to the underlying gold surface, for instance, is known. − The insertion of redox moieties in SAMs can be achieved by the formation of coordination compounds on surface which, in comparison to the organic counterpart, are likely to form more robust molecular assemblies due to the metal-to-ligand back-donation. This interaction enhances the electron density on the adsorption fragment, thereby strengthening the bonding with the surface. − Coordination compounds have been used as SAMs on gold to study electron transfer of metalloproteins, coordination reactions on surface, conduction as molecular wires, and so on. − …”

Synthesis, characterization, and SAMs electroactivity of ruthenium complexes with sulfur containing ligands

“…This conclusion is based on the cyt c electrochemical response observed for the SAMs formed with the [Ru(CN) 5 (1,4-dt)] 3À and [Ru(CNpy)(NH 3 ) 4 (1,4-dt)] 2+ [30] complexes. Although both compounds are gauche adsorbed on surface, as indicated by the SERS spectra, the cyclic voltammogram of the cyt c protein is better resolved for the [Ru(CN) 5 (1,4-dt)] 3À complex, which is negatively charged.…”

“…Since we have reported a series of Fe II and Ru II metal complexes with ligands containing sulfur as donor atoms [26,[30][31][32] that form SAMs able to assess the electrochemistry of cyt c metalloprotein, attempts were made aiming to modify gold polycrystalline surfaces with the synthesized complexes. The characterization of the gold modified surfaces was performed by SERS spectroscopy.…”

“…By using Monte Carlo and molecular dynamics simulation approach, Zhou et al [41] concluded that, for a satisfactorily molecular SAM-cyt c recognition, the desired protein orientation is perpendicular to the surface and that strongly charged surfaces will cause a larger conformational change and the loss of bioactivity. More recently, the E 1/2 values observed for the cyt c protein by using SAMs formed with the [Ru(CNpy)(NH 3 ) 4 (1,4-dt)] 2+ and [Ru(CNpy)(NH 3 ) 4 (pyS)] 2+ complexes, where pyS = 4-mercaptopyridine, are indicative of the native form [30]. The shape of the cyt c voltammograms, however, showed to be dependent on the complex conformation on surface.…”