ABSTRACT
Gas-phase Na+ affinities of modified or unmodified nucleobases were determined theoretically at the density functional theory level, with the B3P86 functional and the 6-31 + G* basis set, and experimentally using electrospray ionization ion trap mass spectrometry (ESI-ITMS) and the kinetic method. For the calculations, the sodium cation affinities (SCA) were obtained from energies of the most stable complexes of the free nucleobases. Experimentally and theoretically relative scales of cation affinities were determined using eight modified and unmodified nucleobases and a very good agreement was obtained.
Subject(s)
Nucleic Acids/chemistry , Nucleic Acids/metabolism , Sodium/chemistry , Spectrometry, Mass, Electrospray Ionization , Cations/chemistry , Entropy , Kinetics , Models, Molecular , Molecular Structure , ThermodynamicsABSTRACT
The proton affinities of four characteristic amino acids, glycine, proline, cysteine and phenylalanine, have been calculated using three different types of wave function, HF, DFT and MP2. These wave functions were combined with several basis sets using the valence double- or triple-xi with polarisation functions, and included or not a diffuse d function on heavy atoms. Calculations were carried out using Gaussian 98 on a LINUX system (2 GHz, 2 GB of RAM). The calculated results have been compared with the experimental values obtained using Cooks' kinetic method, in particular on an electrospray ionisation ion trap mass spectrometer. An excellent agreement was found between the experimental values and the theoretical results obtained using the B3P86/6-31+G*//B3LYP/6-31G* level.
Subject(s)
Amino Acids/chemistry , Protons , Spectrometry, Mass, Electrospray Ionization/methods , Cysteine/chemistry , Glycine/chemistry , Models, Molecular , Molecular Conformation , Phenylalanine/chemistry , Proline/chemistry , Reproducibility of ResultsABSTRACT
The optimization of a continuous flow system for electrochemical hydride generation coupled to microwave-induced plasma atomic emission spectrometry (MIP-AES) for the determination of Se is presented. A small electrolytic cell with a porous glassy carbon working electrode was used for hydride generation. When using an Ar MIP operated in a TE101 cavity a detection limit of 0.6 ng mL(-1) (3sigma) could be achieved. The calibration curve was linear up to 1 microgram mL(-1). A standard deviation of less than 2% (10 replicate analyses) could be achieved. It was shown that interferences of transition metals are of the same order of magnitude as with a larger electrolysis cell described earlier, and light elements hardly caused any signal depression as tested. It was possible to distinguish between Se(IV) and Se(VI) species and seleno-DL-methionine, because under optimized conditions of an electrolysis current of 10 mA, a microwave power of 210 W, an Ar flow rate of 15 L h(-1) and a sample flow rate of 2.5 mL min(-1) only Se(IV) was transformed to H2Se and transferred into the plasma. Finally, the possibility of an electrochemical pre-enrichment was shown to enable it to further decrease the detection limit.
ABSTRACT
A low-cost digital acquisition unit for a CARY-210 spectrophotometer has been designed and constructed. The data-flow is controlled by a 6809 microprocessor driving four parallel interface adapters. Two RS232-C serial links are provided for communication with a terminal and a mass storage unit. The acquired data are processed by a personal computer. Included are several software modules, based on powerful signal-processing algorithms, which are highly useful in kinetic studies.
