Jackson R. de Sousa

Characterization of a 1,4-dithiane gold self-assembled monolayer: an electrochemical sensor for the cyt-c redox process

Electrochemical desorption and spectroscopic investigations of the gold electrode surface modified with 1,4-dithiane (1,4-dt) organothiol species were performed. The wave observed at � /0.87 V versus Ag j AgCl in the LSV (linear sweep voltammetry) reductive curve of the 1,4-dt compared to that for a similar 4-mercaptopyridine (pyS) system (� /0.56 V) is indicative of a most effectively chemisorbed monolayer. The evaluation of the capability of the 1,4-dt self-assembled monolayer (SAM) in assessing the direct electron transfer (ET) of cytochrome c (cyt c) metalloprotein was investigated by cyclic voltammetry. The electrochemical response of the cyt c (E1/2 :/0.0 V vs. Ag j AgCl, DEp :/50 mV) showed the characteristics of a reversible redox process. The cyt c voltammetric parameters acquired with the 24-h air exposure modified electrode, and after 100 cycles suggest a considerable improvement of the 1,4-dt electrode performance. The surface enhanced Raman spectroscopy (SERS) spectra revealed that 1,4-dt species is in a mixed gauche and trans orientation on the gold surface. The shift for higher wavenumbers observed for the C � /S stretching modes in the SERS spectra, comparatively to the normal Raman spectrum, is assigned to the 1,4-dt coordination to surface gold atoms via a p interaction with the sulfur p-orbitals. The data collected suggest that this p interaction plays an important role on the stability of the 1,4-dt adlayer, improving the assessment of the cyt c heterogeneous electron transfer reaction. # 2003 Elsevier Science B.V. All rights reserved.

Self-assembled monolayers formed by [M(CN)5(pyS)]4−(M = Fe, Ru) on gold: a comparative study on stability and efficiency to assess the cyt c heterogeneous electron transfer reaction

A comparative study involving SAMs formed by [(CN)5M(pyS)]4− inorganic complexes (M = Fe, Ru; pyS = 4-mercaptopyridine) on gold (MpySAu) has been performed. The characterization data for these complexes suggests that the ruthenium complex exhibit a greater π-back-bonding effect that more strongly stabilizes the MpyC–S bond, thus anticipating its application as a SAM that would better enhance the gold adlayer stability than the iron complex. The MpySAu electrodes were characterized by SERS and electrochemical (LSV) techniques. The ex situ SERS spectra data for both SAMs suggest a σ interaction between the gold and sulfur atom of the complexes, inducing a perpendicular arrangement in relation to the surface. The spectra performed for freshly prepared MpySAu adlayers did not show any significant changes that would reflect the degradation of the adlayer. The LSV desorption curves of the SAMs indicate a better enhancement in the C–S bond strength of the pyS ligand when coordinated to the [Ru(CN)5]3− moiety. Comparatively to the data obtained for the desorption process of the pyS monolayer, the reductive desorption potentials, Erd, present shifts of −170 and −110 mV for the Ru and Fe complexes, respectively. The voltammetric curves of cytochrome c (cyt c) performed with the MpySAu electrodes showed electrochemical parameters consistent with that reported for the native protein. These results taken together reinforce that the π back-bonding effect from the [M(CN)5]3− metal center [Ru (4d) > Fe (3d)] strongly affects the MpySAu adlayer stability, reflecting the adlayer performance on the assessment of the cyt c hET reaction.

A novel and simple synthetic route for a piperazine derivative

Um novo derivado da piperazina, 5-oxopiperazinio-3-sulfonato monohidratado, foi produzido a partir de uma rota sintetica simples como resultado da adicao do ion bisulfito, HSO3-, ao anel e do ataque nucleofilico de moleculas de agua a moleculas de pirazina. O material isolado foi caracterizado por RMN, espectrometria de massa, infravermelho e difracao de raios-X.

On the correlation between electronic intramolecular delocalization and Au-S bonding strength of ruthenium tetraammine SAMs

Trans-[Ru(L)(NH3)4(L’)](PF6)n type complexes, where L = 4-cyanopyridine (CNpy), NCS-, CN-, and L’ = CNpy, 1,4-dithiane (1,4-dt), 4-mercaptopyridine (pyS) and thionicotinamide (tna), were synthesized and characterized. SAMs on gold of the complexes containing sulfur were studied by reductive desorption and SERS spectroscopy. Depending on the nature of L’, the withdrawing capability of the CNpy ligand is strong enough to partially oxidize the ruthenium atom and, as a consequence, delocalize the s electronic density from the trans located ligand. The reductive desorption results showed that the stability of the SAMs is directly related to this effect.

A biphosphinic ruthenium complex with potent anti-bacterial and anti-cancer activity

Metal-based compounds have emerged as a novel strategy to improve our arsenal of medicines. Among these compounds, carbon monoxide donor agents have been developed mainly as metal complexes. These compounds have shown exciting biological activities, among them strong anti-inflammatory, antibiotic, and anticancer activity, although some of those properties might be associated with the metal moiety as well. Aiming to prepare a new ruthenium complex containing CO, we prepared a cis-[RuCl(CO)(dppb)(dppz)]PF6 complex (dppb = 1,4-bis(diphenylphosphino)butane and dppz = dipyrido[3,2-a:2′,3′-c]phenazine), which was fully characterized along with DFT studies. This compound exhibited great thermal stability in phosphate buffer solution, but showed fast and efficient release of CO upon light irradiation, including blue LED. Surprisingly, DNA binding was quite weak, despite the dppz ligand moiety, suggesting that steric effects prevented intercalation binding. Nonetheless, this compound exhibited promising antibiotic activity against S. aureus, S. epidermidis and C. albicans in a low micromolar range. However, there was no further improvement upon light irradiation suggesting that there is no role of CO. Additionally, cytotoxicity assay using cancer cells showed quite low IC50 (92 nM, HCT-116) along with moderate to low toxicity assayed in lymphocytes and Artemia. Altogether, these results supported that this compound has great potential as a biological agent, whereas neither CO release nor DNA binding seemed to have a direct role in its activity.