Adsorption of mercury on gold and silver surfaces

In order to study the adsorption mechanism of Hg on Au and Ag substrates, thin film Au(111) and Ag(111) substrates were exposed to gaseous metallic mercury, while the mercury concentration, substrate temperature, and exposure length were varied. The resulting changes in the surface morphology of the substrates were studied with scanning tunneling microscopy (STM). The amount of adsorbed Hg required to cause saturation, i.e. a decrease in the adsorption rate was found to be dependent on the mercury concentration and substrate temperature. The observations lead to the conclusion that the adsorption includes place exchange processes and concerted adsorption of more than one Hg atom in one process. The results show that the collection efficiency of single-crystalline surfaces is a function of both mercury concentration and temperature. Therefore, results from measurements performed at different conditions using single-crystalline surfaces may not be comparable. Received: 3 February 1999 / Revised: 7 June 1999 / Accepted: 9 June 1999     

Artificial ribonucleases

Mimicking the action of enzymes by simpler and more robust man-made catalysts has long inspired bioorganic chemists. During the past decade, mimics for RNA-cleaving enzymes, ribonucleases, or, more precisely, mimics of ribozymes that cleave RNA in sequence-selective rather than base-selective manner, have received special attention. These artificial ribonucleases are typically oligonucleotides (or their structural analogs) that bear a catalytically active conjugate group and catalyze sequence-selective hydrolysis of RNA phosphodiester bonds.     

A computational and experimental study of the structures and Raman and 77Se NMR spectra of SeX3+ and SeX2 (X = Cl, Br, I): FT-Raman spectrum of (SeI3)[AsF6

The ability of MP2, B3PW91 and PBE0 methods to produce reliable predictions in structural and spectroscopic properties of small selenium-halogen molecules and cations has been demonstrated by using 6-311G(d) and cc-pVTZ basis sets. Optimized structures and vibrational frequencies agree closely with the experimental information, where available. Raman intensities are also well reproduced at all levels of theory. Calculated GIAO isotropic shielding tensors yield a reasonable linear correlation with the experimental chemical shift data at each level of theory. The largest deviations between calculated and experimental chemical shifts are found for selenium-iodine species. The agreement between observed and calculated chemical shifts for selenium-iodine species can be improved by inclusion of relativistic effects using the ZORA method. The best results are achieved by adding spin-orbit correction terms from ZORA calculations to nonrelativistic GIAO isotropic shielding tensors. The calculated isotropic shielding tensors can be utilized in the spectroscopic assignment of the 77Se chemical shifts of novel selenium-halogen molecules and cations. The experimental FT-Raman spectra of (SeI3)[AsF6] in the solid state and in SO2(l) solution are also reported.     

Direct monitoring of glycohemoglobin A1c in the blood samples of diabetic patients by capillary electrophoresis. Comparison with an immunoassay method

The capillary electrophoresis (CE) study was focused on quantifying glycohemoglobin A1c, HbA1c, in whole blood samples of patients suffering diabetes mellitus. The results showed that dynamic polyionic coating of the capillary made the method very reproducible. The precision evaluation, method comparison and bias estimation in CE were performed during 20 days with patient blood samples and with four control samples. The influence of the storage time and temperature on the glycohemoglobin levels were also tested. High resolution in CE could be used to show evidences of the ageing of the samples stored at -70 degrees C. The results showed that the ageing peak was not originated from HbA1c, because it did not affect the HbA1c level which was in balance with the results of fresh samples measured with immunoassay. The HbA1c % values of blood samples of 105 patients measured with the CE technique varied between 3.6 and 11.8 and they were approximately 2-3% lower than measured with immunoassay. The correlation (R2) of CE results with immunoassay and HPLC results were 0.962 and 0.781, respectively.     

Trace metal analysis of coal fly ash collected plain and on a quartz fibre filter

A simple, uniform procedure has been developed for microwave-based digestion of fly ash samples collected from the hoppers of an electrostatic precipitator (ESP), or collected from flue gases on a heat-resistant quartz fibre filter and for subsequent atomic absorption spectrometric analysis of trace metals (Be, Cd, Co, Cr, Cu, Mn, Ni, Pb, V and Zn). HNO(3), HCl, HF and mixtures have been tested as digestion acids. The combination of HNO(3) and HF has been found to be efficient for the digestion of fly ash samples with and without quartz fibre filter material. In spite of the complicated matrix, results with satisfactory accuracy and precision (relative standard deviation below 10% for most of the elements) have been obtained. In the case of analysis of fly ash together with a quartz fibre filter, the calibration curve has to be determined by standard addition to a blank solution containing a dissolved blank quartz fibre filter.