Ab initio molecular dynamics simulations of the liquid/vapor interface of sulfuric acid solutions

Ab initio molecular dynamics simulations of the liquid-vapor interface are presented for thin slabs of 72 water molecules containing a single molecule of sulfuric acid. Trajectories in the 306-330 K range are calculated for two functionals with double- and triple-ζ quality basis sets. Comparisons are made between BLYP and HCTH/120 results for the slab simulations and for bulk simulations of one H(2)SO(4) in a periodic box with 63 waters. Good agreement is found with the available experimental data and the results of other relevant AIMD studies with respect to ionization of the acid, size of the coordination shells, partitioning of the ions with the hydronium exhibiting a surface preference and the anions in the interior, and the orientational distributions for the hydronium ions and for the surface/subsurface water molecules. The major differences in the performance of the two functionals are attributable to the greater basicity of the anion oxygen atoms with the HCTH functional and the more structured aqueous solution with BLYP. The enhanced basicity results in larger aqueous coordination shells for the anion oxygens. The structuring of the BLYP aqueous solution is observed in the corrugation of the water density profile, the higher first peak in g(OO)(r), and a smaller water self-diffusion constant. This structuring with the BLYP functional yields anion hydrogen bonds that endure longer and where the dissociated ions more rapidly and directly segregate in the slab. The simulations indicate that aqueous surfaces containing ionizable diprotic acids can be modeled with rather modest sized systems and be informative.     

Study of active naphtodianthrone St John's Wort compounds by electrospray ionization Fourier transform ion cyclotron resonance and multi‐stage mass spectrometry in sustained off‐resonance irradiation collision‐induced dissociation and infrared multiphoton dissociation modes

Five well‐known active naphtodianthrone constituents of Hypericum perforatum (St John's Wort) extracts have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and ESI‐FTICRMSⁿ. The studied compounds were hypericin, pseudohypericin, protohypericin, protopseudohypericin (biosynthetic precursors of the two former compounds, respectively) and isopseudohypericin (alkaline degradation product of pseudohypericin). Dissociation mass spectrometry measurements performed on the [M–H]^? ion presented a variable efficiency as a function of the used activation mode. Sustained off‐resonance irradiation collision‐induced dissociation (SORI–CID) only led to a restricted number of fragment ions. In contrast, IRMPD ensured the detection of numerous product ions. Ions detected in ESI‐FTICRMS and ESI‐FTICRMSⁿ experiments were measured with a very high mass accuracy (typically mass error is lower than 0.5 mDa at m/z close to 500) that allowed unambiguous formulae to be assigned to each signal observed in a mass spectrum. In spite of similar structures, specific fragmentation patterns were observed for the different compounds investigated. This study may be useful in the future to characterize in natural extracts these compounds (or derivatives of these compounds) by liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments by considering the MS/MS transitions highlighted in this paper. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of imidazolium and pyridinium-based ionic liquids and application of 1-alkyl-3-methylimidazolium salts as pre-catalysts for the benzoin condensation using solvent-free and microwave activation

An efficient one-pot procedure for the synthesis of ionic liquids based on nitrogen-containing heterocycles, imidazolium or pyridinium under ‘green chemistry’ conditions has been described. Imidazolium salts and DBU have been found to catalyze efficiently the benzoin condensation giving good yields within very short reaction time using solvent-free microwave activation conditions.     

Homotopy Algorithm for Optimal Control Problems with a Second-order State Constraint

This paper deals with optimal control problems with a regular second-order state constraint and a scalar control, satisfying the strengthened Legendre-Clebsch condition. We study the stability of structure of stationary points. It is shown that under a uniform strict complementarity assumption, boundary arcs are stable under sufficiently smooth perturbations of the data. On the contrary, nonreducible touch points are not stable under perturbations. We show that under some reasonable conditions, either a boundary arc or a second touch point may appear. Those results allow us to design an homotopy algorithm which automatically detects the structure of the trajectory and initializes the shooting parameters associated with boundary arcs and touch points.     

Allylic C-H activations using Cu(II) 2-quinoxalinol salen and tert-butyl hydroperoxide

Using a Cu(II) 2-quinoxalinol salen complex as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant, allylic activations of olefin substrates can be converted to the corresponding enones or 1,4-enediones. Excellent yields can be achieved (up to 99%) within a very short reaction time and with great tolerance for additional functional groups. Possible mechanistic pathways have been characterized using Raman spectroscopy, cyclic voltammetry, and theoretical calculations.     

New trends in sustainable nanocatalysis: Emerging use of earth abundant metals

Noble metals are well-known to afford highly active, selective and durable catalysts, and have thus been at the core of the development of greener processes. In recent years, however, growing concerns about their scarcity, cost and toxicity has triggered research efforts towards the development of earth-abundant catalysts. In this Current Opinion, recent examples of the use in catalysis of pure earth-abundant metals, earth-abundant metals with minute quantities of noble metals, or earth-abundant metals activated by light are presented. This highlight article showcases the current trends in sustainable organic transformations, catalyzed by nanomaterials.     

Development of an integrated optical system for warpage and hermeticity test of microdisplay

We have developed an integrated optical system to measure the warpage of a microdisplay product at post-packaging die-attach temperature and to test its hermeticity after manufacturing. This system is constructed based on the principle of Twyman/Green (T/G) interferometry and Newton interferometry. T/G interferometry is used to characterize warpage of the microdisplay's base-plate, while Newton interferometry is used to characterize the gap variance between face-plate and base-plate of the microdisplay. With these measurements, deformation and shape of the microdisplay can be comprehensively determined during its manufacturing process, which is critical for its quality test and reliability evaluation. Delicate mechanical system was designed to facilitate the optics integration and alignment. To evaluate the performance of the optical system itself, warpage of a sample was re-measured with Tailor–Hobson profilometer whose resolution is 10 nm, the results from these two testing systems agree well with each other. Some application examples of the integrated testing system were presented to verify its work efficiency.