Using accurate mass electrospray ionization-time-of-flight mass spectrometry with in-source collision-induced dissociation to sequence peptide mixtures

Although data-dependent LC-MS-MS with database searching has become au courant for identifying proteins, the technique is constrained by duty-cycle inefficiency and the inability of most tandem mass analyzers to accurately measure peptide product ion masses. In this work, a novel approach is presented for simultaneous peptide fragmentation and accurate mass measurement using in-source collision-induced dissociation (CID) on electrospray ionization (ESI)-time-of-flight (TOF) MS. By employing internal mass reference compounds, mass measurement accuracy within +/-5 ppm for tryptic peptide precursors and +/-10 ppm for most sequence-specific product ions was consistently achieved. Analysis of a complex solution containing several digested protein standards did not adversely affect instrument performance.     

Thermal sigmatropic rearrangements of isopyrazoles and pyrazolenines to pyrazoles

Thermal rearrangement of 4-allyl-, 4-dimethylallyl-, and 4-propargyl-isopyrazoles proceed by [3,3]-sigmatropic processes to pyrazoles. The migration terminus is the C(3) Me group, if present, and the rearrangement is preceded by imine-enamine tautomerism. When enamine formation is not possible the rearrangment is diverted to nitrogen. Thermal rearrangements of 4-alkyl- and 4-benzyl-isopyrazoles also occur although at higher temperatures and evidence is presented suggesting [1,5]-sigmatropic processes are involved. Some pyrazolenine to pyrazole rearrangements involving migration of ester and phenyl groups are also reported.     

Identification, isolation, and characterization of cysteinate and thiolactate complexes of bismuth

Although bismuth compounds have been used in medicine for over 200 years, chemical characterization of complexes involving biological molecules is minimal and mechanisms of bioactivity are ill-defined. The thiophilic nature of bismuth implicates sulfur centers as likely sites for interaction, and we have exploited this feature to identify, isolate, and characterize complexes of bismuth with thiolate-carboxylate bifunctional ligands including the amino acid l-cysteine. The solid-state structures of potassium dichloro(thiopropionato)bismuth (K[1d]), dimethylaminoethanethiolato(thiopropionato)bismuth (4), and dinitrato(cysteinato)bismuthphenanthroline [5(phen)] are compared with data from electrospray ionization mass spectrometry (ESI-MS). ESI-MS is applied to reactions of BiCl(3) or Bi(NO(3))(3) with mercaptosuccinic, malic, and succinic acids to illustrate the general observation of 1:1 and 1:2 complexes.     

Nature of interaction energy anisotropy in the Li(<Superscript>2</Superscript>S)–HF (˜X<Superscript>1</Superscript>Σ<Superscript>+</Superscript>) van der Waals complex. A theoretical study

The potential-energy surface for the Li(²S)–HF (? X¹Σ⁺ interaction, where HF is kept rigid, is calculated using the supermolecular unrestricted fourth-order Møller–Plesset perturbation theory. The basis set superposition error corrected potential indicates two minima. The global minimum occurs for the bent Li...FH structure at R=1.95 Å and θ=70° with a relatively deep well of D_e=1,706 cm^?1 and the secondary minimum is found for the linear Li...HF configuration at R=4.11 Å with a well depth ofD_e=288 cm^?1. A barrier of 177 cm^?1 (with respect to the secondary linear minimum) separates these two minima. In this study 27 bound states of the bent Li...FH minimum and eight bound states of the linear Li...HF minimum up to the Li+HF dissociation threshold are calculated. The energy partitioning using the intermolecular perturbation theory scheme shows that the origins of the stability of the structures studied are entirely different. The global minimum is stabilised using the attractive Coulombic interaction and unrestricted Hartree–Fock deformation energy. The latter term originates from the mutual electric polarisation effects. The secondary linear minimum is mostly determined by the anisotropy of the repulsive Heitler–London exchange-penetration and attractive dispersion energies.     

Spectrophotometric determination of niobium in tantalum metal

A new method for the determination of traces of niobium in tantalum metal has been developed. The niobium is separated from tantalum by solvent extraction with hexone from hydrofluoric acid-hydrochloric acid solution, and from molybdenum and tungsten by solvent extraction with oxine-chloroform solution from ammoniacal citrate solution. The niobium is then determined by the spectrophotometric thiocyanate method.     

On-chip cell lysis by local hydroxide generation

We present a novel method for on-chip cell lysis based on local hydroxide electro-generation. Hydroxide ions porate the cell membrane, leading to cell lysis. After lysis occurs, hydrogen ions, also generated on chip, react with excess hydroxide, creating a neutral pH lysate and eliminating the need for a wash step. Three different cell types are shown to be effectively lysed by this method: red blood cells, HeLa (human tumor line) and Chinese Hamster Ovary (CHO) cell lines. The release of cytoplasmic molecules from HeLa and CHO cells is demonstrated by monitoring the escape of a membrane impermeant dye from the cytoplasm. In the vicinity of the cathode, the hydroxide concentration is predicted by finite element simulations and shown to fit the lysis rates at different distances from the generating cathode. For flow-through experiments, a second device integrating a mechanical filter with hydroxide generation is fabricated and tested. The purpose of the filter is to trap whole cells and only allow lysate to pass through. The flow rate dependence of hydroxide concentration at the lysis filter is modeled and lysis efficiency is experimentally determined to be proportional to the hydroxide concentration for flow rates from 15 to 30 microl min(-1).