Isotopic exchange of CO adsorbed on Pt(111)

The isotopic exchange of CO adsorbed on Pt(111) was studied using polarization modulation IR reflection absorption spectroscopy (PM-IRRAS) and temperature programmed desorption. It was found that the rate constants for the exchange reaction are much higher than would be expected from previous investigations of CO adsorbed on Pt nanoparticles. The adsorption of CO on Pt(111) under elevated pressures of CO and H(2) was also studied using PM-IRRAS. It was seen that CO pressures above 1 mbar lead to a shift in the absorption peak arising from CO adsorbed on a bridge site from 1850 to 1875 cm(-1). Exposing the CO-covered Pt(111) surface to 1000 mbar H(2) did not lead to any significant desorption of CO at room temperature, whereas at 363 K H(2) exposure did lead to a significant desorption of CO, due to the increased chemical potential of H(2). In a mixture of CO and H(2) with partial pressures of 0.01 mbar and 1000 mbar, respectively, no significant effect of H(2) on the PM-IRRAS spectrum was seen at temperatures below 423 K.     

Two-dimensional nuclear Overhauser enhancement NMR experiments on pelargonidin-3-glucopyranoside, an anthocyanin of low molecular mass.

Pelargonidin-3-glucoside has been isolated from the acidified methanolic extract of strawberries (Fragaria anannassa variety Corona) by successive application of an ion-exchange resin, droplet-counter chromatography and gel filtration. The pigment in acidified methanolic solution was studied by means of the two-dimensional nuclear Overhauser enhancement NMR technique, and the sugar unit was found to be attached to the 3-position on the aglycone. At +20 degrees C the pigment was found to be in the extreme narrowing limit where the NOESY cross-peaks are negative. However, at -20 degrees C this low-mass anthocyanin could be studied in the slow motion regime where the NOESY cross-peaks are positive. With a mixing time of 0.3 s, the glucose H1"-H4" proton pair was measured in the initial cross-relaxation rate and their cross-peak volume corresponded to the H1"-H4" distance found in a 4C1 chair conformation.     

Atmospheric chemistry of 4:2 fluorotelomer alcohol (n-C4F9CH2CH2OH): products and mechanism of Cl atom initiated oxidation in the presence of NOx

Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of 4:2 fluorotelomer alcohol (C(4)F(9)CH(2)CH(2)OH, 4:2 FTOH) in the presence of NO(x) in 700 Torr of N(2)/O(2) diluent at 296 K. Chemical activation effects play an important role in the atmospheric chemistry of the peroxy, and possibly the alkoxy, radicals derived from 4:2 FTOH. Cl atoms react with C(4)F(9)CH(2)CH(2)OH to give C(4)F(9)CH(2)C(*)HOH radicals which add O(2) to give chemically activated alpha-hydroxyperoxy radicals, [C(4)F(9)CH(2)C(OO(*))HOH]*. In 700 Torr of N(2)/O(2) at 296 K, approximately 50% of the [C(4)F(9)CH(2)C(OO(*))HOH]* radicals decompose "promptly" to give HO(2) radicals and C(4)F(9)CH(2)CHO, the remaining [C(4)F(9)CH(2)C(OO(*))HOH]* radicals undergo collisional deactivation to give thermalized peroxy radicals, C(4)F(9)CH(2)C(OO(*))HOH. Decomposition to HO(2) and C(4)F(9)CH(2)CHO is the dominant atmospheric fate of the thermalized peroxy radicals. In the presence of excess NO, the thermalized peroxy radicals react to give C(4)F(9)CH(2)C(O(*))HOH radicals which then decompose at a rate >2.5 x 10(6) s(-1) to give HC(O)OH and the alkyl radical C(4)F(9)CH(2)(*). The primary products of 4:2 FTOH oxidation in the presence of excess NO(x) are C(4)F(9)CH(2)CHO, C(4)F(9)CHO, and HCOOH. Secondary products include C(4)F(9)CH(2)C(O)O(2)NO(2), C(4)F(9)C(O)O(2)NO(2), and COF(2). In contrast to experiments conducted in the absence of NO(x), there was no evidence (<2% yield) for the formation of the perfluorinated acid C(4)F(9)C(O)OH. The results are discussed with regard to the atmospheric chemistry of fluorotelomer alcohols.     

A novel method for the filterless preconcentration of iron

A novel method of analysis of iron by filterless preconcentration is presented. This is the first example of efficient preconcentration of a refractory transition metal where coprecipitation and columns were omitted. The method applies a manifold of flow injection analysis (FIA) to iron species that are preconcentrated on the inner walls of a tubular reactor. It was found that the adsorption of iron species to the walls was particularly pronounced in reactors of nylon material and enrichment factors of 30-35 could be attained, as dependent on the length of the reactor and on the time of preconcentration. In the preconcentration step of the FIA accessory, the optimum efficacy was obtained when the acidity of the samples was adjusted by HCl to pH = 2.5 whereas the ammonia preconcentration buffer should be kept alkaline at pH = 9.8. After being preconcentrated on the tubular reactor, the iron species were eluted by hydrochloric acid and analysed by flame atomic absorption spectrometry (FAAS). An unprecedented low limit of detection (LOD, 3sigma) of 1.8 microg L(-1) was thus obtained for the analysis of iron by FAAS, and the calibration line was linear up to 100 microg L(-1). A high sampling frequency of 40 per hour was obtained and the protocol allowed analysis of small amounts of iron in drinking water, in digested samples and in saline water. The major influence of interferences originated from ligands that are known to complex strongly to iron species. The method thus developed was uncomplicated in operation and it exhibited an excellent long-term stability and a high selectivity. Further, it was environmentally safe owing to production of non-toxic waste disposals. Equally high enrichment factors (EF) were obtained for Fe(ii) and Fe(iii), which is explained by the very low solubility product of both species.