Simultaneous determination of traces of iron, cobalt, nickel, copper, mercury and lead in water by energy-dispersive x-ray fluorescence spectrometry after preconcentration as their piperazino-1,4-bis(dithiocarbamate) complexes

A bidentate chelating agent has been proposed to preconcentrate seven metal ions dissolved in an aqueous sample for their simultaneous determination using energy-dispersive x-ray fluorescence spectrometry. The metal ions are precipitated as their polymeric piperazino-1,4-bis(dithiocarbamate) chelates, which are then collected by vacuum filtration on a Millipore membrane filter for direct examination by x-ray fluorescence analysis. Iron, cobalt, nickel, copper and zinc are determined by means of their K x-rays and mercury and lead by means of their L x-rays. A detection limit in the μg1⁻¹ range can be achieved for all metals tested in 250-ml water samples with a counting time of 600 s. Effective precipitation of all metals occurs at pH 6–7. The recoveries of eight analyses of the metals in a multielement standard using the proposed method ranged from 97 to 105% and the precision ranged from 2.3 to 3.1%. High concentrations of calcium and magnesium do not interfere with the method. The method is simple, sensitive and accurate, and has been used for the simultaneous determination of the seven metals under study in environmental samples and synthetic mixtures.     

A comparison of the HAM/3 semiempirical method with the MINDO/3 and CNDO/2 semiempirical methods and the GAUSSIAN 70 ab initio method; a comparison of ionization potential calculations and experimental photoelectron spectra of some imines and diimines

Molecular orbital calculations have been performed on eight molecules (containing 16–80 electrons) using the GAUSSIAN 70, MINDO/3, CNDO/2 and HAM/3 programs. The molecules contain nitrogen—nitrogen (diimines) or carbon—nitrogen (imines) double bonds. A comparison of the results of each method with experimental photoelectron data and an analysis of the cost effectiveness indicates that the HAM/3 method will prove a useful tool for photoelectron spectroscopists.     

Structure and Chemistry of Malonylmethyl- and Succinyl-Radicals. The search for homolytic 1,2-rearrangements

Malonylmethyl radical I [· CH₂CH(COOEt)₂] and its thioester analogue II [· CH₂CH(COOEt) (COSEt)] were generated by standard photolytic and thermolytic methods from perester and bromo precursors. The structures of I and II were examined by ESR spectroscopy and found to exist in preferred conformations. However, no indication for their rearrangement by 1,2-shift of either an ethoxycarboxyl or (ethylthio)carbonyl group to the corresponding succinyl radicals III and IV , respectively, was found at temperatures below ? 40°C. At higher temperatures of up to 140°C, the search for malonylmethyl → succinyl rearrangement was examined by thorough-product analysis of the perester decomposition. There is evidence for the rearrangement of the radical I to III by photolysis and of the radical II to IV by thermolysis at 130°C in chlorobenzene to only a small extent.     

NMR spectroscopic study of noble gas binding into the engineered cavity of HPr(I14A) from Staphylococcus carnosus

Xenon binding into preexisting cavities in proteins is a well-known phenomenon. Here we investigate the interaction of helium, neon, and argon with hydrophobic cavities in proteins by NMR spectroscopy. 1H and 15N chemical shifts of the I14A mutant of the histidine-containing phosphocarrier protein (HPr(I14A)) from Staphylococcus carnosus are analyzed by chemical shift mapping. Total noble gas induced chemical shifts, Delta, are calculated and compared with the corresponding values obtained using xenon as a probe atom. This comparison reveals that the same cavity is detected with both argon and xenon. Measurements using the smaller noble gases helium and neon as probe atoms do not result in comparable effects. The dependence of amide proton and nitrogen chemical shifts on the argon concentration is investigated in the range from 10 mM up to 158 mM. The average dissociation constant for argon binding into the engineered cavity is determined to be about 90 mM.     

Lipase-catalyzed reactions in ionic liquids

[reaction:see text] Candida antarctica lipase was shown to catalyze alcoholysis, ammoniolysis, and perhydrolysis reactions using the ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate or hexafluorophosphate as reaction media. Reaction rates were generally comparable with, or better than, those observed in organic media.     

An intermolecular methyl transfer during field desorption mass spectrometry. Identification of the [M + 14] peak in choline chloride

Choline chloride, bromide and iodide all contain a peak at m/e 118 [M + 14] in their field desorption mass spectra. Comparison with choline(methyl-d₉) chloride demonstrates that this peak arises from an intermolecular transfer of a methyl group. Partial exchange of hydroxyl hydrogen on choline chloride does not displace the m/e 118 peak, suggesting that this hydrogen is lost during methyl transfer. The structure of the [M + 14] species should then correspond to choline methyl ether.     

Dynamics in condensed molecular systems studied by incoherent light

Applications of incoherent light techniques to time-resolved studies in condensed matter are reviewed. Vibrational dephasing of-carotene and a heptamethine dye was studied by interferometric coherent anti-Stokes Raman scattering in solution revealing dephasing times between 300 fs and 1.1 ps. This technique gives results that are analogos to spectral methods, but vibrational frequencies can be determined more precisely. Electronic dephasing was studied for a variety of dyes. Forced light scattering is used to measure the initial evolution of the lineshape functiong(t) up to about 50 fs. In the lowest order approximation,g(t) = ² t ² /2,, the dephasing is characterized by a modulation strength = 25 to 150 THz depending on the dye, the solvent and its temperature, and the pump laser wavelength. Interestingly, the modulation decreases for heptamethine in the long-wavelength tail of the absorption band. Brillouin scattering gives rise to finite dephasing times of neat solvents in forced light scattering.     

Carrier-resolved technology for homogeneous and multiplexed DNA assays in a 'one-pot reaction'

For clinical diagnosis, a small number of targets (2-10 biomarkers) are often all that is required for disease assessment and accurate early disease diagnosis. In the current paper we have developed novel, carrier-resolved, single-label-based multiplexed assays for the simultaneous detection and quantification of a limited number of DNA targets associated with breast cancer. In contrast to current encoding strategies, every hybridization signal for the corresponding DNA target in our protocol is uniquely immobilized onto one carrier vehicle with a unique and intrinsic physico-chemical signature. Moreover, a simple chemiluminescence setup is employed to read the carrier code instead of expensive and complicated flow-cytometer or imaging-systems commonly used for multiplexed assays. Herein we demonstrate a new protocol using three homogeneous carriers, i.e. thermo-sensitive poly(N-isopropylacrylamide) (PNIP), polystyrene beads, and magnetic beads respectively. This new methodology allowed for the simultaneous determination of three oligonucleotide sequences (60 bases in length) associated with the breast cancer gene (BRCA1) and showed high selectivity and attomolar-femtomolar sensitivity. The mixture of three different capture probe conjugates first hybridizes with three corresponding target sequences, sandwiches with three biotinylated DNAs, and then reacts with peroxidase-streptavidin polymer in a single vessel without any washing, leading to the development of a 'one-pot reaction system'. Only one washing step in our protocol is required prior to detection leading to our whole procedure being simple and efficient. The results show that the hybridization response to sample mixtures containing increasing levels of each target is proportional to the amount of corresponding DNA targets, indicating minimal cross-interferences. The work presented here validates the design and concept of a system for the detection of a limited number of DNA targets and provides the foundation for the development of highly sensitive techniques with increased multi-analyte capabilities.