Dually fluorescent silica nanoparticles

The cationic dyes 9-aminoacridine (9AA) and safranine (Sf) were entrapped into silica spheres of about 0.2 μm diameter prepared by modified Stöber method. The fluorescent materials are investigated by steady-state and time-resolved emission, in addition of confocal fluorescence microscopy. Silica particles containing 9-aminoacridine (SP9AA) and safranine (SPSf) or both dyes (SPSf9AA) are emissive particles. When both dyes are present in the same particle but loaded in sequential stages 9AA emission is quenched as a consequence of energy transfer from 9AA (donor) to Sf (acceptor). This result suggests that particle growing processes where the acceptor is incorporated first into the core do not prevent donor/acceptor pairs to be close due to an overlay of the concentration gradients of both dyes in a radial core-shell like distribution.     

Synthesis of triazolyl anthracene as a selective fluorescent chemosensor for the Cu(II) ion

The Cu(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC) has been used to synthesize an anthracene-based fluorescent compound that undergoes strong fluorescence quenching in the presence of Cu(II). Fluorescence studies indicate that the compound forms a 1:1 complex and can be used to quantitatively determine micromolar concentrations of Cu(II) in aqueous solution.     

Coupling of Fischer carbene complexes with conjugated enediynes featuring radical traps: Novel structure and reactivity features of chromium complexed arene diradical species

The reaction of Fischer carbene complexes with conjugated enediynes that feature a pendant alkene group has been examined. The reaction proceeds through carbene–alkyne coupling to generate an enyne–ketene intermediate. This intermediate then undergoes Moore cyclization to generate a chromium complexed arene diradical, which then undergoes cyclization with the pendant alkene group. The radical cyclization prefers the 6-endo mode unless radical-stabilizing groups are present to favor the 5-exo mode. The intermediate diradical species were evaluated computationally in both the singlet and triplet configurations. Arene triplet diradicals feature minimal spin density at oxygen and delocalization to chromium. The 6-endo cyclization product was kinetically and thermodynamically favored.     

Combination of COFRADIC and high temperature-extended column length conventional liquid chromatography: a very efficient way to tackle complex protein samples, such as serum

The previously reported COmbined FRActional DIagonal Chromatography (COFRA-DIC) methodology, in which a subset of peptides representative for their parent proteins are sorted, is particularly powerful for whole proteome analysis. This peptide-centric technology is built around diagonal chromatography, where peptide separations are crucial. This paper presents high efficiency peptide separations, in which four 250 x 2.1 mm, 5 microm Zorbax 300SB-C18 columns (total length 1 m) were coupled at operating temperatures of 60'C using a dedicated LC oven and conventional LC equipment. The high efficiency separations were combined with the COFRADIC procedure. This extremely powerful combination resulted, for the analysis of serum, in an increase in the uniquely identified peptide sequences by a factor of 2.6, compared to the COFRADIC procedure on a 25 cm column. This is a reflection of the increased peak capacity obtained on the 1 m column, which was calculated to be a factor 2.7 higher than on the 25 cm column. Besides more efficient sorting, less ion suppression was noticed.     

Assessing a novel microfluidic interface for shotgun proteome analyses

Microfluidic interfaces coupled to ESI mass spectrometers hold great potential for proteomics as they have been shown to augment the overall sensitivity of measurements and require only a minimum of operator manipulations as compared to conventional nano-LC interfaces. Here, we evaluated a new type of HPLC-Chips holding larger enrichment columns (thus an increased sample loading capacity) for gel-free proteome studies. A tryptic digest of a human T-cell proteome was fractionated by strong cation exchange chromatography and selected fractions were analyzed by MS/MS on an IT mass spectrometer using both the new HPLC-Chip as well as a conventional nano-LC-MS/MS interface. Our results indicate that the HPLC-Chip is capable of handling very complex peptide mixtures and, in fact, leads to the identification of more peptides and proteins as compared to when a conventional interface was used. The HPLC-Chip preferentially produced doubly charged tryptic peptides. We further show that MS/MS spectra of doubly charged tryptic peptide ions are more readily identified by MASCOT as compared to those from triply charged precursors and thus argue that besides the improved chromatographic conditions provided by the HPLC-Chip, its peptide charging profile might be a secondary factor leading to an increased proteome coverage.     

Identification of the oxidation products of cysteamine and cystamine by CE-MS interfaced by a noncommercial electrospray ionization source

Sodium cysteamine phosphate is a prodrug derivative of cysteamine that can be used in cystinosis treatment. Although titrimetric assays are very well established and precise, iodimetric determination of sodium cysteamine phosphate requires considerably more carefulness and time from the analyst than usual. The possibility to assess sodium cysteamine phosphate by CE was evaluated by means of the quantification of its oxidation product, cystamine, which is a more suitable substance to be used as primary standard than sodium cysteamine phosphate. Apparently, this approach should be straightforward, but systematic differences between the results obtained with CE and titrimetric assays were noticed. MS and CE-MS were employed to aid in the investigation of the possible causes of imprecision of the sodium cysteamine phosphate titration and CE determination. For this purpose, a simple and inexpensive ESI source was constructed. It was observed that cystamine is not the final product of the cysteamine and/or sodium cysteamine phosphate iodine-oxidation and other species besides cystamine may be formed depending on the reaction conditions, which explains the difficulties observed in the sodium cysteamine phosphate quantification.     

Unified origin for baryonic visible matter and antibaryonic dark matter

We present a novel mechanism for generating both the baryon and dark matter densities of the Universe. A new Dirac fermion X carrying a conserved baryon number charge couples to the standard model quarks as well as a GeV-scale hidden sector. CP-violating decays of X, produced nonthermally in low-temperature reheating, sequester antibaryon number in the hidden sector, thereby leaving a baryon excess in the visible sector. The antibaryonic hidden states are stable dark matter. A spectacular signature of this mechanism is the baryon-destroying inelastic scattering of dark matter that can annihilate baryons at appreciable rates relevant for nucleon decay searches.     

Quantum Monte Carlo simulation of the high-pressure molecular-atomic crossover in fluid hydrogen

A first-order liquid-liquid phase transition in high-pressure hydrogen between molecular and atomic fluid phases has been predicted in computer simulations using ab initio molecular dynamics approaches. However, experiments indicate that molecular dissociation may occur through a continuous crossover rather than a first-order transition. Here we study the nature of molecular dissociation in fluid hydrogen using an alternative simulation technique in which electronic correlation is computed within quantum Monte Carlo methods, the so-called coupled electron-ion Monte Carlo method. We find no evidence for a first-order liquid-liquid phase transition.