A combined Kirchhoff–Master equation approach to electronic transport in one-dimensional molecular conductors

We discuss classical one-dimensional conductivity problems using Kirchhoff’s law comprising resistor network nodes that can only be occupied by a limited number of charge carriers, leading to the formulation of combined Kirchhoff–Master equations (KMEs) of electronic transport. For illustrative purposes, the equations are solved for simple two site systems; and we present a numerical solution by means of a Monte Carlo method for arbitrary systems. As an example, the procedure is applied to describe DNA charge transfer through a nanojunction at ambient conditions in the regime of small external voltages.     

Thermoanalytical and structural characterization of fluoridated calcium phosphates prepared in anhydrous alcohols

A thermoanalytical, morphological, and structural study of fluoridated calcium phosphates that were prepared by different variants of a synthesis in anhydrous alcohols is reported. The obtained materials were neither fully amorphous nor single-phased crystalline, and their nature considerably depended on the synthesis conditions. In all cases, the retention of significant amounts of solvent in the solid product was observed. A complete removal of the solvent was only possible by heating to temperatures above ~573–673 K which resulted in variations in the elemental composition, phase changes, and an increase of the crystallinity. Consequently, this synthesis in anhydrous alcohols is not a viable route to obtain materials with a defined crystallinity and stoichiometry.     

Quantitative analysis of low‐abundance peptides in HeLa cell cytoplasm by targeted liquid chromatography/mass spectrometry and stable isotope dilution: emphasising the distinction between peptide detection and peptide identification

We present the application of a targeted liquid chromatography/mass spectrometry (LC/MS) approach developed on a linear ion trap for the evaluation of the abundance of cytoplasmic proteins from a HeLa cell extract. Using a standard data‐dependent approach, we identified some specific peptides from this extract which were also commercially available in their AQUA form (use for absolute quantitation). For some of the peptides, we observed a non‐linear response between the intensity and the added quantity which was then fitted using a quadratic fit. All AQUA peptides spiked into a mix of 3 µg of the HeLa cell digest extract were detected down to 16 fmol. We placed an emphasis on peptide detection which, in this study, is performed using a combination of properties such as three specific Q3‐like ion signatures (for a given Q1‐like selection) and co‐elution with the AQUA peptide counterparts. Detecting a peptide without necessarily identifying it using a search engine imposes less constraint in terms of tandem mass (MS/MS) spectra purity. An example is shown where a peptide is detected using those criteria but could not be identified by Mascot due to its lower abundance. To complement this observation, we used a cross‐correlation analysis approach in order to separate two populations of MS/MS fragments based on differences in their elution patterns. Such an approach opens the door to new strategies to analyse lower intensity peptide fragments. An in silico analysis of the human trypsinosome allows the evaluation of how unique are the sets of features that we are using for peptide detection. Copyright © 2010 John Wiley & Sons, Ltd.