Electron induced dissociation: A mass spectrometry technique for the structural analysis of trinuclear oxo-centred carboxylate-bridged iron complexes

We report electron induced dissociation (EID) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry of the singly-charged cations [Fe₃O(CH₃COO)₆]⁺³ and [Fe₃O (HCOO)₆+H₂O]⁺. Trinuclear oxo-centered carboxylate-bridged iron complexes of this type are of interest due to their electronic and magnetic properties, and because of their role as synthetic precursors of single molecule magnets. EID of these complexes is particularly efficient and provides detailed information about the triangular core, and the nature and number of ligands. EID behavior is in marked contrast to the collision induced dissociation (CID) of these species. Whereas EID allows virtually complete structural characterization, the structural information provided by CID is very limited. The results suggest that EID is particularly suitable for the structural analysis of singly-charged polynuclear metal complexes.     

Rapid biochemical profiling of endothelial dysfunction in diabetes,hypertension and cancer metastasis by hierarchical cluster analysis of Raman spectra

Raman spectroscopy is a label free, versatile, simple and fast method that is increasingly used to detect pathological changes in the cells and tissues that could be useful in medical diagnostics. In this work, we tested the hypothesis that Raman spectroscopy may serve to detect endothelial dysfunction in murine models of lifestyle diseases associated with endothelial dysfunction. For that purpose, we analysed spectra from ex vivo vessels taken from mice with diabetes, hypertension and cancer metastasis. We extracted 50–70 random, single spectra, recorded in 0.2 s, from endothelium of mice with diseases and respective control animals and subjected them to hierarchical cluster analysis. Independently on the sample preparation protocol, very good discrimination was obtained for three‐tested murine models, i.e. diabetes, hypertension and cancer metastasis. Obtained sensitivity and specificity parameters were between 93% and 96% (with the exception of sensitivity in the diabetes model equalled to 88%). Our results show that single, random spectra of endothelium, recorded in less than a second, contains enough information on biochemical content of the endothelium to detect endothelial dysfunction. Furthermore, we demonstrated that biochemical profile of the endothelial dysfunction in diabetes, hypertension or cancer metastasis differs with a very high specificity and sensitivity. This conclusion can be a good starting point for the development of in vivo fast diagnostic methodology of endothelium in the future. Copyright © 2016 John Wiley & Sons, Ltd.     

Advection of methane in the hydrate zone: model,analysis and examples

A two‐phase two‐component model is formulated for the advective–diffusive transport of methane in liquid phase through sediment with the accompanying formation and dissolution of methane hydrate. This free‐boundary problem has a unique generalized solution in L¹; the proof combines analysis of the stationary semilinear elliptic Dirichlet problem with the nonlinear semigroup theory in Banach space for an m‐accretive multi‐valued operator. Additional estimates of maximum principle type are obtained, and these permit appropriate maximal extensions of the phase‐change relations. An example with pure advection indicates the limitations of these estimates and of the model developed here. We also consider and analyze the coupled pressure equation that determines the advective flux in the transport model. Copyright © 2015 John Wiley & Sons, Ltd.     

Water-based route to colloidal Mn-doped ZnSe and core/shell ZnSe/ZnS quantum dots

Relatively monodisperse and highly luminescent Mn(2+)-doped zinc blende ZnSe nanocrystals were synthesized in aqueous solution at 100 °C using the nucleation-doping strategy. The effects of the experimental conditions and of the ligand on the synthesis of nanocrystals were investigated systematically. It was found that there were significant effects of molar ratio of precursors and heating time on the optical properties of ZnSe:Mn nanocrystals. Using 3-mercaptopropionic acid as capping ligand afforded 3.1 nm wide ZnSe:Mn quantum dots (QDs) with very low surface defect density and which exhibited the Mn(2+)-related orange luminescence. The post-preparative introduction of a ZnS shell at the surface of the Mn(2+)-doped ZnSe QDs improved their photoluminescence properties, resulting in stronger emission. A 2.5-fold increase in photoluminescence quantum yield (from 3.5 to 9%) and of Mn(2+) ion emission lifetime (from 0.62 to 1.39 ms) have been observed after surface passivation. The size and the structure of these QDs were also corroborated by using transmission electron microscopy, energy dispersive spectroscopy, and X-ray powder diffraction.     

Principal component analysis of thermal decomposition of magnesium salts used as drugs

Thermal decomposition of magnesium salts of organic acids used in medicine (Mg acetate, Mg valproate, Mg lactate, Mg citrate, Mg hydrogen aspartate, Zn hydrogen aspartate) was analyzed by thermoanalytical, calorimetrical, and computational methods. Thermoanalytical studies were performed with aid of a derivatograph. 50-, 100-, and 200-mg samples were heated in a static air atmosphere at a heating rate of 3, 5, 10, and 15 °C min⁻¹ up to the final temperature of 700–900 °C. By differential thermal analysis (DTA), thermogravimetry (TG), and derivative thermogravimetry (DTG) methods, it has been established that thermal decomposition of the salts under study occurs via two stages. The first stage (dehydratation) was distinctly marked on the thermoanalytical curves. Calorimetrical studies were carried out by using of a heat-flux Mettler Toledo differential scanning calorimetry (DSC) system. Ten milligram samples of compounds under study were heated in the temperature range from 20 to 400 °C at a heating rate of 10 and 20 °C min⁻¹ under an air stream. The studies showed that the values of transitions heats and enthalpies of dehydration for investigated salts varied with the increasing of heating rate. For chemometric evaluation of thermoanalytical results, the principal component analysis (PCA) was applied. This method revealed that points on PC1 versus PC2 diagrams corresponding to the compounds of similar chemical constitution are localized in the similar ranges of the first two PC’s values. This proves that thermal decomposition reflects similarity in the structure of magnesium salts of organic acids.     

In vivo 13C NMR spectroscopy and metabolic modeling in the brain: a practical perspective

In vivo 13C NMR spectroscopy has the unique capability to measure metabolic fluxes noninvasively in the brain. Quantitative measurements of metabolic fluxes require analysis of the 13C labeling time courses obtained experimentally with a metabolic model. The present work reviews the ingredients necessary for a dynamic metabolic modeling study, with particular emphasis on practical issues.     

Determination of adrenolytic drugs by SPME–LC–MS

Five adrenolytic drugs have been analyzed by liquid chromatography–mass spectrometry (LC–MS). Samples were prepared by solid-phase microextraction (SPME) using polypyrrole fibers coated on stainless steel support as an adsorbent for the drugs. Adsorption efficiencies were 95% and were close for all the drugs investigated. Relative standard deviations (RSD), calculated for samples prepared in standard solutions, were in the range 2.5–13%, however RSD values for the drugs in human plasma were 2.5–4.5%. Using LC–MS the limit of detection (LOD) and the limit of quantification (LOQ) were in the ranges 0.11–0.18 and 0.39–0.54 ng mL⁻¹, respectively, for the five drugs.     

Ψ-density topology

We study the notion of ψ-density point and ψ-density topologies for non-decreasing continuous functions ψ. Also basic properties of ψ-approximately continuous functions are considered.     

Environmental Effects in Computational Spectroscopy: Accuracy and Interpretation

Spectroscopic techniques are valuable tools for understanding the structure and dynamics of complex systems, such as biomolecules or nanomaterials. Most of the current research is devoted to the development of new experimental techniques for improving the intrinsic resolution of different spectra. However, the subtle interplay of several different effects acting at different length and time scales still makes the interpretation and analysis of such spectra a very difficult task. In this respect, computational spectroscopy is becoming a needful and versatile tool for the assignment and interpretation of experimental spectra. It is in fact possible nowadays to model with relatively high accuracy the physical–chemical properties of complex molecules in different environments, and to link spectroscopic evidence directly to the structural and dynamical properties of optically or magnetically active solvated probes. In this Review, significant steps toward the simulation of entire spectra in condensed phases are presented together with some basic aspects of computational spectroscopy, which highlight how intramolecular and intermolecular degrees of freedom influence several spectroscopic parameters.     

Constructive role of noise: Fast fluctuation asymptotics of transport in stochastic ratchets

The constructive role of random fluctuations is studied in the context of transport in stochastic ratchets. We discuss the interplay of independent white (thermal) and discrete (external) noises and their generation of transport in anisotropic potentials. The constructive cooperation of such fluctuations is most apparent in the asymptotic limit of fast discrete-valued noise, a limit which presents some interesting mathematical features. We describe the asymptotic analysis of the current in the limit of fast external noise, pointing out the strong qualitative dependence of the current on the interplay of the independent noise sources and its surprising sensitivity to the regularity of the underlying anisotropic ratchet potential. (c) 1998 American Institute of Physics.