DFT Study of the BH4− Hydrolysis on Au(111) Surface

The mechanism of the catalytic hydrolysis of BH₄⁻ on Au(111) as studied by DFT is reported. The results are compared to the analogous process on Ag(111) that was recently reported. It is found that the borohydride species are adsorbed stronger on the Au⁰-NP surface than on the Ag⁰-NP surface. The electron affinity of the Au is larger than that of Ag. The results indicate that only two steps of hydrolysis are happening on the Au(111) surface and the reaction mechanism differs significantly from that on the Ag(111) surface. These remarkable results were experimentally verified. Upon hydrolysis, only three hydrogens of BH₄⁻ are transferred to the Au surface, not all four, and H₂ generation is enhanced in the presence of surface H atoms. Thus, it is proposed that the BH₄⁻ hydrolysis and reduction mechanisms catalyzed by M⁰-NPs depend considerably on the nature of the metal.     

A physicochemical model for analyzing DNA sequences

In search of an ab initio model to characterize DNA sequences as genes and nongenes, we examined some physicochemical properties of each trinucleotide (codon), which could accomplish this task. We constructed three-dimensional vectors for each double-helical trinucleotide sequence considering hydrogen-bonding energy, stacking energy, and a third parameter, which we provisionally identified with DNA-protein interactions. As this three-dimensional vector moves along any genome, the net orientation of the resultant vector should differ significantly for gene and nongene regions to make a distinction feasible, if the underlying model has some merits. An analysis of 331 prokaryotic genomes comprising a total of 294 786 experimentally verified genes (nonoverlapping) and an equal number of nongenes presents a proof of concept of the model without the need for further parametrization. Also, initial analyses on Saccharomyces cerevisiae and Arabidopsis thaliana suggest that the methodology is extendable to eukaryotes. The physicochemical model (ChemGenome1.0) introduced has the potential to be developed into a gene-finding algorithm and, more pressingly, could be employed for an independent assessment of the annotation of DNA sequences.     

High density preheating effects on Q-ball decays and inflation in the minimal supersymmetric standard model

Nonperturbative preheating decay of postinflationary condensates often results in a high density, low momenta, nonthermal gas. In the case where the nonperturbative classical evolution also leads to Q balls, this effect shields them from instant dissociation, and may radically change the thermal history of the Universe. For example, in a large class of inflationary scenarios, motivated by the minimal supersymmetric standard model and its embedding in string theory, the reheat temperature changes by a multiplicative factor of 10(12).     

Mass spectrometry in structural and stereochemical problems—CCXXXV : A hidden hydrogen rearrangement in long chained anilides

The mass spectra of deuterium labeled hexananilides show an unexpected rearrangement of a hydrogen atom from C-4 with formation of a C₆H₇N⁺ ion. The decomposition of the McLafferty rearrangement ion in these compounds is shown to involve expulsion of the elements of ethynyl alcohol rather than ketene.     

Capillary electrophoresis—matrix-assisted laser-desorption ionization mass spectrometry of proteins

An “off-line” combination of capillary electrophoresis (CE) with matrix-assisted laser-desorption mass spectrometry (MALDI-MS) has been developed for the structural characterization of CE-separated peptides and proteins. Using a sheath flow interface, similar to that developed for “on-line” CE—fast atom bombardment MS and CE—electrospray MS, an efficient sample isolation procedure has been developed which is applicable to bioorganic compounds in aqueous buffer solutions. This isolation procedure, with subsequent transfer to the MALDI-MS sample target, has been successfully used for the direct analysis of CE-separated proteins of M _r up to 67 000, and a mixture of apolipoprotein AII monomer and homodimer, using sample amounts of less than 1 pmol.     

Spin-trapped Radicals: Determination by LC-TSP-MS and LC-ESI-MS

The 4-POBN[α-(4-pyridyl-l-oxide)-N-tert-butyl-nitrone] radical adducts of ethyl and pentyl radicals were determined by a combination of high performance liquid chromatography (HPLC) combined with electron paramagnetic resonance (EPR) with HPLC-electrospray (ESI)-mass spectrometry and HPLC-thermospray (TSP)-MS. The identifIcation of the peak corresponding to the spin-trapped radical was done by performing HPLC-EPR under the same chromatographic conditions as the HPLC-MS. The radical adducts could be determined by both techniques, even though for ESI only 12 μL/min of the total 1 mL/min HPLC flow rate could be directed into the ion source.     

An Apparent Interface Location as a Tool to Solve the Porous Interface Flow Problem

A new approach for solving the laminar flow problem above a porous medium is presented here, using an apparent interface for which both superficial velocity and intrinsic shear stress are continuous. The derivation of this approach is based on a detailed investigation of the Ochoa-Tapia and Whitaker (Int. J. Heat Mass Transfer 38:2635–2646, 1995a) jump condition and its sensitivity to the value of β (the jump condition coefficient) and to an error in the interface location. While the value of the jump condition coefficient is highly sensitive to the interface location, the new apparent interface approach does not require an a priori information about the location of the interface. This approach can be easily used knowing only one measurable parameter—the maximum velocity or the flow rate. Validation of the apparent interface approach against measurements from other works shows that it can be successfully used to predict the velocity profile for different geometrical models.