Are Clusters Important in Understanding the Mechanisms in Atmospheric Pressure Ionization? Part 1: Reagent Ion Generation and Chemical Control of Ion Populations

It is well documented since the early days of the development of atmospheric pressure ionization methods, which operate in the gas phase, that cluster ions are ubiquitous. This holds true for atmospheric pressure chemical ionization, as well as for more recent techniques, such as atmospheric pressure photoionization, direct analysis in real time, and many more. In fact, it is well established that cluster ions are the primary carriers of the net charge generated. Nevertheless, cluster ion chemistry has only been sporadically included in the numerous proposed ionization mechanisms leading to charged target analytes, which are often protonated molecules. This paper series, consisting of two parts, attempts to highlight the role of cluster ion chemistry with regard to the generation of analyte ions. In addition, the impact of the changing reaction matrix and the non-thermal collisions of ions en route from the atmospheric pressure ion source to the high vacuum analyzer region are discussed. This work addresses such issues as extent of protonation versus deuteration, the extent of analyte fragmentation, as well as highly variable ionization efficiencies, among others. In Part 1, the nature of the reagent ion generation is examined, as well as the extent of thermodynamic versus kinetic control of the resulting ion population entering the analyzer region.

Neuritogenic activity-guided isolation of a free base form manzamine A from a marine sponge, Acanthostrongylophora aff. ingens (Thiele, 1899)

Two manzamine-class alkaloids, manzamine A (1) and 8-hydroxymanzamine (2) were isolated from a Japanese marine sponge Acanthostrongylophora aff. ingens, together with three known alkaloids manzamine E (3), manzamine F (4), and manzamine X (5). The spectral features of 1 and 2 were different from the reported data. Detailed structure analysis using 2D NMR revealed the structure of 1 and 2 as a free base form of hydrochloric salt. These manzamine-class alkaloids showed neuritogenic activity against Neuro 2a cells.     

Platinum-Iron(II) Oxide Sites Directly Responsible for Preferential Carbon Monoxide Oxidation at Ambient Temperature: An Operando X-ray Absorption Spectroscopy Study**

Operando X-ray absorption spectroscopy identified that the concentration of Fe²⁺ species in the working state-of-the-art Pt−FeO_x catalysts quantitatively correlates to their preferential carbon monoxide oxidation steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe²⁺ sites. The active Fe²⁺ species are presumably Fe⁺²O⁻² clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe³⁺) and metallic iron (Fe⁰) partially alloyed with platinum. The concentration of active sites and, therefore, the catalyst activity strongly depends on the pretreatment conditions. Fe²⁺ is the resting state of the active sites in the preferential carbon monoxide oxidation cycle.     

Adaptive Wavelet Schwarz Methods for the Navier-Stokes Equation

In this article, we are concerned with domain decomposition methods for the stationary incompressible Navier-Stokes equation. We construct an adaptive additive Schwarz method based on discretization by means of a divergence-free wavelet frame. We prove that the method is convergent and asymptotically optimal with respect to the degrees of freedom involved.     

On a Finite Difference Scheme for an Inverse Integro-Differential Problem Using Semigroup Theory: A Functional Analytic Approach

In this article, the problem of reconstructing an unknown memory kernel from an integral overdetermination in an abstract linear (of convolution type) evolution equation of parabolic type is considered. After illustrating some results of the existence and uniqueness of a solution for the differential problem, we study its approximation by Rothe's method. We prove a result of stability and another concerning the order of approximation of the solution in dependence of its regularity. The main tool is a maximal regularity result for solutions to abstract parabolic finite difference schemes. Two model problems to which the results are applicable are illustrated.     

Use of the bromine isotope ratio in HPLC-ICP-MS and HPLC-ESI-MS analysis of a new drug in development

A combination of inductively coupled plasma mass spectrometry (ICP-MS) and electrospray ionization mass spectrometry (ESI-MS) was deployed for the metabolite profiling and metabolite identification of a new antituberculosis compound (R207910, also known as TMC207) that is currently in drug development. R207910 contains one bromine atom, allowing the detection by ICP-MS. Fluctuations in the Br sensitivity caused by the HPLC gradient were counteracted by the use of species-unspecific isotope dilution. In order to evaluate the method developed, the results obtained were compared with those acquired via radioactivity detection. HPLC-ESI-MS was used for the structural identification of R207910 and its metabolites. The ⁷⁹Br/⁸¹Br isotope ratio is also valuable in the search for metabolites in the complex background of endogenous compounds obtained using HPLC-ESI-MS analyses. Data-dependent scanning using isotope recognition with an ion trap mass spectrometer or processing of Q-Tof data provides HPLC-ICP-MS-like “bromatograms”. The combination of accurate mass measurements and the fragmentation behavior in the MS² spectra obtained using the Q-Tof Ultima mass spectrometer or MSⁿ spectra acquired using the LTQ-Orbitrap allowed structural characterization of the main metabolites of R207910 in methanolic dog and rat faeces extracts taken 0–24 h post-dose. Figure Analyses of a rat faeces extract taken 0–24 h post-dose: a HPLC-ICP-MS using isotope dilution, b corresponding Br mass flow chromatogram, c radio-HPLC, d Q-Tof ESI-MS TIC, e Q-Tof ESI-MS bromatogram after Br stripping, f LTQ-Orbitrap ESI-MS² TIC obtained with isotopic-data-dependent scanning