Spectroelectrochemical Behaviour of 4-Aminobenzenethiol on Nanostructured Platinum and Silver Electrodes

The adsorption of 4-aminobenzenethiol (4-ABT) on Ag and Pt nanoparticles is studied by spectroelectrochemical means (cyclic voltammetry, Surface-Enhanced Raman Spectroscopy (SERS) and Surface-Enhanced Infrared Reflection Absorption Spectroscopy (SEIRAS). Similar SERS spectra are obtained when 4-ABT is adsorbed on platinum and silver nanostructured substrates. In addition, unless a low power density of the laser is used, these spectra show, both under open circuit conditions and when applying electrode potentials above -0.50 V, bands not observed in the normal Raman spectrum of 4-ABT. These bands disappear when the electrode potential is shifted to more negative values. Conversely, the SEIRA spectra of 4-ABT adsorbed on Ag do not show any significant change with the electrode potential, which indicates that there are not new species electrochemically formed in the range of potentials considered, which include some anodic and cathodic processes as shown in the corresponding cyclic voltammograms. In this regard, SERS measurements put in evidence the time dependence of the spectra obtained at potentials above -0.50 V just after switching on the laser suggesting the formation of new species, probably dimercaptoazobenzene (4-4’-DMAB), formed by a photochemical process of the adsorbed 4-ABT.Financial support from Ministerio de Ciencia e Innovación (projects CTQ2010-16271, CTQ2009-13142, and Fondos Feder), Generalitat Valenciana (Prometeo/2009/045 and ACOMP/2011/200), and University of Alicante is greatly acknowledged

Spectroelectrochemical Study of the Photoinduced Catalytic Formation of 4,4′-Dimercaptoazobenzene from 4-Aminobenzenethiol Adsorbed on Nanostructured Copper

Surface-enhanced raman scattering (SERS) spectra of self-assembled monolayers of 4-aminobenzenethiol (4-ABT) on copper (Cu) and silver (Ag) surfaces decorated with Cu and Ag nanostructures, respectively, have been obtained with lasers at 532, 632.8, 785, and 1064 nm. Density functional theory (DFT) has been used to obtain calculated vibrational frequencies of the 4-ABT and 4,4′-dimercaptoazobenzene (4,4′-DMAB) molecules adsorbed on model Cu surfaces. The features of the SERS spectra depend on the electrode potential and the type and power density of the laser. SERS spectra showed the formation of the 4,4′-DMAB on the nanostructured Cu surface independently of the laser employed. For the sake of comparison SERS spectra of a self-assembled monolayer of the 4-ABT on Ag surfaces decorated with Ag nanostructures have been also obtained with the same four lasers. When using the 532 and 632.8 nm lasers, the 4,4′-DMAB is formed on Cu surface at electrode potentials as low as −1.0 V (AgCl/Ag) showing a different behavior with respect to Ag (and others metals such as Au and Pt). On the other hand, the surface-enhanced infrared reflection absorption (SEIRA) spectra showed that in the absence of the laser excitation the 4,4′-DMAB is not produced from the adsorbed 4-ABT on nanostructured Cu in the whole range of potentials studied. These results point out the prevalence of the role of electron–hole pairs through surface plasmon activity to explain the obtained SERS spectra.Financial support from Ministerio de Economía y Competitividad (Projects CTQ2013-48280-C3-3-R and CTQ2013-44083-P), Fondos Feder, and the University of Alicante are greatly acknowledged

Reduced mRNA abundance of the main enzymes involved in methionine metabolism in human liver cirrhosis and hepatocellular carcinoma

BACKGROUND/AIMS: It has been known for at least 50 years that alterations in methionine metabolism occur in human liver cirrhosis. However, the molecular basis of this alteration is not completely understood. In order to gain more insight into the mechanisms behind this condition, mRNA levels of methionine adenosyltransferase (MAT1A), glycine methyltransferase (GNMT), methionine synthase (MS), betaine homocysteine methyltransferase (BHMT) and cystathionine beta-synthase (CBS) were examined in 26 cirrhotic livers, five hepatocellular carcinoma (HCC) tissues and ten control livers. METHODS: The expression of the above-mentioned genes was determined by quantitative RT-PCR analysis. Methylation of MAT1A promoter was assessed by methylation-sensitive restriction enzyme digestion of genomic DNA. RESULTS: When compared to normal livers MAT1A, GNMT, BHMT, CBS and MS mRNA contents were significantly reduced in liver cirrhosis. Interestingly, MAT1A promoter was hypermethylated in the cirrhotic liver. HCC tissues also showed decreased mRNA levels of these enzymes. CONCLUSIONS: These findings establish that the abundance of the mRNA of the main genes involved in methionine metabolism is markedly reduced in human cirrhosis and HCC. Hypermethylation of MAT1A promoter could participate in its reduced expression in cirrhosis. These observations help to explain the hypermethioninemia, hyperhomocysteinemia and reduced hepatic glutathione content observed in cirrhosis