Multi-center bonds as resonance hybrids: A real space perspective.

The concept of distinct bonds within molecules has proven to be successful in rationalizing chemical reactivity. However, bonds are not a well-defined physical concept, but rather vague entities, described by different and often contradicting models. With probability density analysis, which can-in principle-be applied to any wave function, bonds are recovered as spin-coupled positions within most likely electron arrangements in coordinate space. While the wave functions of many systems are dominated by a single electron arrangement that is built from two-center two-electron bonds, some systems require several different arrangements to be well described. In this work, a range of these multi-center bonded molecules are classified and investigated with probability density analysis. The results are compared with valence bond theory calculations and data from collision-induced dissociation experiments.

Structures of isolated Co2(alcohol)1 cluster anions.

Cobalt-alcohol cluster anions of the form Co(2)(alcohol)(1)(-) (alcohol = methanol, ethanol, propanol) are produced in a supersonic beam by using pulsed laser vaporization. The clusters are studied with IR spectroscopy in order to obtain vibrational spectra in the OH stretching region. The mechanisms of photodetachment and photodissociation are discussed. By comparing with DFT calculations the vibrational spectra are explained and structures are obtained in which the OH group of the alcohols is directed on the Co-Co bond. The reliability of DFT calculations with respect to clusters containing a Co(2)(-) dimer is further confirmed by comparison with high level CASPT2 calculations.

Tissue distribution and subcellular localization of the ClC-5 chloride channel in rat intestinal cells.

ClC-5 is the Cl- channel that is mutated in Dent's disease, an X-chromosome-linked disease characterized by low molecular weight proteinuria, hypercalciuria, and kidney stones. It is predominantly expressed in endocytically active renal proximal cells. We investigated whether this Cl- channel could also be expressed in intestinal tissues that have endocytotic machinery. ClC-5 mRNA was detected in the rat duodenum, jejunum, ileum, and colon. Western blot analyses revealed the presence of the 83-kDa ClC-5 protein in these tissues. Indirect immunofluorescence studies showed that ClC-5 was mainly concentrated in the cytoplasm above the nuclei of enterocytes and colon cells. ClC-5 partially colocalized with the transcytosed polymeric immunoglobulin receptor but was not detectable together with the brush-border-anchored sucrase isomaltase. A subfractionation of vesicles obtained by differential centrifugation showed that ClC-5 is associated with the vacuolar 70-kDa H+-ATPase and the small GTPases rab4 and rab5a, two markers of early endosomes. Thus these results indicate that ClC-5 is present in the small intestine and colon of rats and suggest that it plays a role in the endocytotic pathways of intestinal cells.

Monte Carlo methods in electronic structures for large systems.

Quantum Monte Carlo methods have recently made it possible to calculate the electronic structure of relatively large molecular systems with very high accuracy. These large systems range from positron complexes [NH(2),Ps] with approximately 10 electrons to C(20) isomers with 120 electrons, to silicon crystal structures of 250 atoms and 1000 valence electrons. The techniques for such calculations and a sampling of applications are reviewed.

ClC-5, the chloride channel mutated in Dent's disease, colocalizes with the proton pump in endocytotically active kidney cells.

Loss-of-function mutations of the ClC-5 chloride channel lead to Dent's disease, a syndrome characterized by low molecular weight proteinuria, hypercalciuria, and kidney stones. We show that ClC-5 is expressed in renal proximal tubule cells, which normally endocytose proteins passing the glomerular filter. Expression is highest below the brush border in a region densely packed with endocytotic vesicles, where ClC-5 colocalizes with the H+-ATPase and with internalized proteins early after uptake. In intercalated cells of the collecting duct it again localizes to apical intracellular vesicles and colocalizes with the proton pump in alpha-intercalated cells. In transfected cells, ClC-5 colocalizes with endocytosed alpha2-macroglobulin. Cotransfection with a GTPase-deficient rab5 mutant leads to enlarged early endosomes that stain for ClC-5. We suggest that ClC-5 may be essential for proximal tubular endocytosis by providing an electrical shunt necessary for the efficient acidification of vesicles in the endocytotic pathway, explaining the proteinuria observed in Dent's disease.

Recovery of nucleic acids from immobilized biotin-streptavidin complexes using ammonium hydroxide and applications in MALDI-TOF mass spectrometry.

The effects of ammonium hydroxide treatment of complexes consisting of biotinylated nucleic acids and immobilized streptavidin were investigated. It was found that incubation of such complexes with ammonium hydroxide at room temperature leads to denaturation of double-stranded DNA molecules, liberating only the complementary nonbiotinylated strand, whereas incubation at elevated temperatures leads to an efficient dissociation of biotin-streptavidin complexes. The introduced procedure is especially suitable as a purification and conditioning format prior to matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometric analysis of DNA from complex enzymatic reactions. This is demonstrated by analysis of polymerase chain reaction (PCR) and sequencing products.

Cerebellar atrophy with basilar artery occlusion.

Small and large vessel occlusive disease leading to chronic cerebral ischemia and brain atrophy is a concept originating in the last century. The modern notion of acute brain infarct, however, appears to have eclipsed the idea of chronic hypoperfusion as an important factor in ischemic cerebral damage. We present a patient history featuring recurrent episodes of acute posterior circulation infratentorial ischemia in addition to a progressive cerebellar syndrome over a course of several years. Laboratory work-up including cerebral angiography, repeated CT and MR scanning revealed basilar artery occlusion, a pontine infarct and a subsequently developing cerebellar atrophy without signs of cerebellar infarction. Findings indicating causes of cerebellar atrophy other than ischemia could not be elicited. We offer the hypothesis that basilar artery occlusion, inducing subsequent chronic ischemia, is the most likely cause of the cerebellar atrophy observed in our case.

Detection of hepatitis B virus DNA in serum samples via nested PCR and MALDI-TOF mass spectrometry.

In a blind study, nested polymerase chain reaction (PCR) was performed with control DNA and DNA preparations from serum samples of six patients. The detection limit was determined to be 100 molecules of template in 1 ml of serum. Hepatitis B virus (HBV) related products of nested PCR were purified by ultrafiltration and immobilisation on streptavidin coated magnetic beads. The immobilized PCR products were denatured from the beads and analyzed via matrix assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry. The results of MALDI-TOF MS analysis were in agreement with the results obtained by polyacrylamide gel electrophoresis (PAGE) and with the data obtained by serological analysis. The detection strategy introduced here has a high potential for automation and represents a fast and reliable method of detection for HBV DNA in serum without the need for time consuming gel electrophoresis and labeling or hybridization procedures.

Effect of bis(benzyl)polyamine derivatives on polyamine transport and survival of Brugia pahangi.

A potent filaricidal effect of bis(benzyl)polyamine derivatives is reported; the addition of 1 microM MDL 27695 to Brugia pahangi maintained in vitro killed the worms within 1 week. Using the labelled derivative, MDL 27391 uptake was demonstrated and evidence was provided for an uptake system that is independent of and clearly distinguishable from those for polyamines. The Km value for the uptake of MDL 27391 was determined to be 2 microM, and that for putrescine, spermidine, and spermine was 4.9, 1.7, and 4.8 microM, respectively. The uptake of MDL 27391 was not affected by polyamines. In contrast, bis(benzyl)polyamines were shown to be strong inhibitors of both the putrescine and the spermidine/spermine uptake system. As shown for MDL 27391, bis(benzyl)polyamines are not metabolized after uptake by Brugia worms; therefore, it is expected that the filaricidal effect of the drug depends on its interaction with potential polyamine-binding sites.