The adsorption of mono-, di-, and trifluoroacetate anions at gold electrodes is studied in perchloric acid solutions by cyclic voltammetry and in situ infrared and Raman spectroscopies. Surface enhanced infrared reflection absorption spectroscopy experiments under attenuated total reflection conditions (ATR-SEIRAS) and surface enhanced Raman scattering (SERS) experiments were carried out with gold thin-film electrodes sputtered on silicon and on a polycrystalline gold substrate, respectively. Theoretical harmonic vibrational frequencies of trifluoroacetate species adsorbed with different geometries on Au clusters with (111), (100), and (110) orientations, as well as IR and Raman intensities, have been obtained from B3LYP/LANL2DZ, 6−31+G(d) calculations. This theoretical study was extended to di- and monofluoroacetate anions adsorbed on Au(111) clusters. The theoretical and experimental results confirm the bidentate bonding of fluoroacetate anions with the OCO plane perpendicular to the metal surface irrespective of the surface crystallographic orientation. No significant effect of either the surface crystallographic orientation or the total charge of the metal cluster−adsorbate on the vibrational frequencies of adsorbed fluoroacetate species can be deduced from the DFT calculations. The ATR-SEIRA spectra show the existence of nonhydrogen-bonded water molecules coexisting with adsorbed fluoroacetate anions, in an extent that depends on both the fluoroacetate coverage and the number of fluorine atoms in the fluoroacetate anion. Step-scan ATR-SEIRAS measurements carried out with the gold thin-film electrodes have allowed for the monitoring of the time-dependent behavior of trifluoroacetate adsorption in potential step experiments, showing a Langmuir-type adsorption kinetics.

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BackgroundThe role of rotavirus as main etiologic agent of diarrhea has been well documented worldwide, including in Venezuela. However, information about the prevalence of gastrointestinal viruses such as calicivirus, adenovirus and astrovirus is limited and the contribution of other agents as Aichi virus and klassevirus is largely unknown. To explore the etiological spectrum of diarrhea associated with agents other than rotaviruses, 227 stool samples from children under 5 years old with acute gastroenteritis, collected in Valencia (Venezuela) from 2001 to 2005, and previously tested as rotavirus-negative, were analyzed for caliciviruses, adenoviruses, astroviruses, Aichi viruses, klasseviruses, picobirnaviruses and enteroviruses by specific RT-PCRs.ResultsAt least one viral agent was detected in 134 (59%) of the samples analyzed, mainly from children under 24 months of age and most of them belonging to the lowest socioeconomic status. Overall, enterovirus was identified as the most common viral agent (37.9%), followed by calicivirus (23.3%), adenovirus (11.5%), astrovirus (3.5%), klassevirus (1.3%) and Aichi virus (0.4%), while no picobirnavirus was detected. Klasseviruses were found during 2004 and 2005 and Aichi viruses only in 2005, indicating their circulation in Venezuela; meanwhile, the rest of the viruses were detected during the whole study period. Coinfections with two or more viruses were found in 39 (29.1%) of the infected children, most under 24 months of age. Adenovirus was involved as the coinfecting agent in at least 46.9% of the cases, but no differences concerning socio-demographic variables were observed between the coinfected and the single infected children.ConclusionsThe results show that various enteric viruses, including enteroviruses, caliciviruses and adenoviruses, accounted for a significant proportion of infantile diarrhea cases in Venezuela before rotavirus vaccine implementation. In addition, emerging viruses as Aichi virus and klassevirus were found, indicating the need to continue monitoring their spreading into the communities. Efforts are needed to develop more accurate methods to identify the major causes of diarrhea and to provide tools for more effective preventive measures.

Prevalence and molecular epidemiology studies for hepatitis B (HBV) and C (HCV) virus are scarce in Warao Amerindians from Venezuela, where an epidemic of human immunodeficiency virus type 1 (HIV-1) has recently been documented. To carry out a molecular epidemiology analysis of hepatitis B (HBV) and C (HCV) virus in Warao individuals from the Delta Amacuro State of Venezuela. A total of 548 sera were tested for serological and molecular markers for HBV and HCV. The prevalence of active infection (presence of HBV surface antigen, HBsAg), exposure to HBV (presence of Antibody to HBV core antigen, anti-HBc) and anti-HCV, was 1.8%, 13% and 0% respectively. HBV exposure was significantly lower in men below 18 years old and also lower than rates previously reported in other Amerindian communities from Venezuela. Thirty one percent (31%, 25/80) of individuals without evidence of HBV infection exhibited anti-HBs titer ≥ 10U.I / ml, being significantly more frequent in individuals younger than 20 years. A higher HBV exposure was observed among HIV-1 positive individuals (33% vs 11%, p <0.005). A high prevalence of occult HBV infection was also observed (5.6%, 11/195). Phylogenetic analysis of S gene and complete HBV genomes showed that F3 is the only circulating subgenotype, different from the F2 subgenotype found in 1991 in this population. These results suggest a recent introduction of subgenotype F3, with a low divergence among the isolates. These results highlight the importance of molecular epidemiology studies for viral control, and support the effectiveness of vaccination in reducing transmission of HBV.

The adsorption of anions from glyoxylic acid solutions at gold electrodes has been studied by cyclic voltammetry and in situ infrared (external reflection and ATR-SEIRAS) and Raman (SERS) spectroscopies using both Au(111) single crystals and sputtered gold thin-film electrodes. In addition, theoretical harmonic IR frequencies and intensities of glyoxylate (HCOCOO -) and hydrated glyoxylate (gem-diol, HC(OH) 2 COO -) species adsorbed with different geometries on Au(111) clusters have been obtained from B3LYP/LANL2DZ, 6-31+G(d) calculations. Although only hydrated glyoxylate anions have been detected in the glyoxylic acid-containing solutions, the ATR-SEIRA spectra in conjunction with density functional theory (DFT) calculations have demonstrated the existence of both adsorbed glyoxylate and hydrated-glyoxylate anions on the gold surfaces. The ratio between the coverages of these two adsorbates depends on the glyoxylic acid concentration in solution, the relative glyoxylate coverage increasing when the glyoxylic acid concentration increases. The theoretical and experimental results have confirmed bidentate bonding of the anions with their OCO plane perpendicular to the metal surface. Furthermore, the in situ infrared data have shown the formation of adsorbed (bi)oxalate and formate as intermediates in the oxidation of glyoxylate and hydrated glyoxylate to carbon dioxide. The presence of adsorbed formate has been confirmed by the SERS spectra, whereas external reflection infrared experiments have shown the formation of carbon dioxide.

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