Detection of nitroaromatic and cyclic nitramine compounds by cyclodextrin assisted capillary electrophoresis quadrupole ion trap mass spectrometry

An Agilent 3DCE capillary electrophoresis system using sulfobutylether-beta-cyclodextrin (SB-beta-CD)-ammonium acetate separation buffer pH 6.9 was coupled to a Bruker Esquire 3000+ quadrupole ion trap mass detector via a commercially available electrospray ionization interface with acetonitrile sheath flow. The CE-MS system was applied in negative ionization mode for the resolution and detection of nitroaromatic and polar cyclic or caged nitramine energetic materials including TNT [2,4,6-trinitrotoluene, formula mass (FW) 227.13], TNB (1,3,5-trinitrobenzene, FW 213.12), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine, FW 222.26) HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, FW 296.16), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, FW 438.19). The CE-MS system conformed to the high-performance liquid chromatography with ultraviolet absorbance detection (HPLC-UV) and HPLC-MS reference methods for the identification of energetic contaminants and their degradation products in soil and marine sediment samples.     

Second‐Sphere Biomimetic Multipoint Hydrogen‐Bonding Patterns to Boost CO2 Reduction of Iron Porphyrins

Inspired by nature's orchestra of chemical subtleties to activate and reduce CO₂, we have developed a family of iron porphyrin derivatives in to which we have introduced urea groups functioning as multipoint hydrogen‐bonding pillars on the periphery of the porphyrinic ring. This structure closely resembles the hydrogen‐bond stabilization scheme of the carbon dioxide (CO₂) adduct in the carbon monoxide dehydrogenase (CODH). We found that such changes to the second coordination sphere significantly lowered the overpotential for CO₂ reduction in this family of molecular catalysts and importantly increased the CO₂ binding rate while maintaining high turnover frequency (TOF) and selectivity. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO₂ reduction.     

Sub-wavelength probing and modification of photonic crystal nano-cavities

In this work we present a sizeable and reversible spectral tuning of the resonances of a two-dimensional photonic crystal nano-cavity by exploiting the introduction of a sub-wavelength size glass tip. The comparison between experimental near-field data and results of numerical calculations shows that the spectral shift induced by the tip is proportional to the local electric field intensity of the cavity mode. This observation proves that the electromagnetic local density of states in a microcavity can be directly measured by mapping the tip-induced spectral shift with a scanning near-field optical microscope. Moreover, a non-linear control on the cavity resonance is obtained by exploiting the local heating induced by near-field laser excitation at different excitation powers. The temperature gradient due to the optical absorption results in an index of refraction gradient which modifies the dielectric surroundings of the cavity and shifts the optical modes.     

The normal approximation rate for the drift estimator of multidimensional diffusions

We consider the problem of the density and drift estimation by the observation of a trajectory of an \mathbbR^d{\mathbb{R}^{d}}-dimensional homogeneous diffusion process with a unique invariant density. We construct estimators of the kernel type based on discretely sampled observations and study their asymptotic distribution. An estimate of the rate of normal approximation is given.     

Structural features of glycol-split low-molecular-weight heparins and their heparin lyase generated fragments

Periodate oxidation followed by borohydride reduction converts the well-known antithrombotics heparin and low-molecular-weight heparins (LMWHs) into their “glycol-split” (gs) derivatives of the “reduced oxyheparin” (RO) type, some of which are currently being developed as potential anti-cancer and anti-inflammatory drugs. Whereas the structure of gs-heparins has been recently studied, details of the more complex and more bioavailable gs-LMWHs have not been yet reported. We obtained RO derivatives of the three most common LMWHs (tinzaparin, enoxaparin, and dalteparin) and studied their structures by two-dimensional nuclear magnetic resonance spectroscopy and ion-pair reversed-phase high-performance liquid chromatography coupled with electrospray ionization mass spectrometry. The liquid chromatography–mass spectrometry (LC-MS) analysis was extended to their heparinase-generated oligosaccharides. The combined NMR/LC-MS analysis of RO-LMWHs provided evidence for glycol-splitting-induced transformations mainly involving internal nonsulfated glucuronic and iduronic acid residues (including partial hydrolysis with formation of “remnants”) and for the hydrolysis of the gs uronic acid residues when formed at the non-reducing ends (mainly, in RO-dalteparin). Evidence for minor modifications, such as ring contraction of some dalteparin internal aminosugar residues, was also obtained. Unexpectedly, the N-sulfated 1,6-anhydromannosamine residues at the enoxaparin reducing end were found to be susceptible to the periodate oxidation. In addition, in tinzaparin and enoxaparin, the borohydride reduction converts the hemiacetalic aminosugars at the reducing end to alditols. Typical LC-MS signatures of RO-derivatives of individual LMWH both before and after digestion with heparinases included oligosaccharides generated from the original antithrombin-binding and “linkage” regions.

Spectroscopic Characterisation of a Bio-Inspired Ni-Based Proton Reduction Catalyst Bearing a Pentadentate N2S3 Ligand with Improved Photocatalytic Activity

Inspired by the sulfur-rich environment found in active hydrogenase enzymes, a Ni-based proton reduction catalyst with pentadentate N₂S₃ ligand was synthesised. When coupled with [Ru(bpy)₃]²⁺ (bpy=2,2′-bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N₂S₂ ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time-resolved X-ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The Ni^II catalyst undergoes a photoinduced metal-centred reduction to form a Ni^I intermediate with distorted square-bipyramidal geometry. Further kinetic analyses revealed differences in charge-separation dynamics between the pentadentate and tetradentate forms.     

SPME in environmental analysis: biotransformation pathways

Solid-phase microextraction (SPME) is an organic solvent-free sample preparation tool suitable for direct adsorption of analytes from the headspace or the aqueous phase of a matrix followed by desorption into a gas chromatograph (GC) or high-performance liquid chromatograph (HPLC) for subsequent analysis. The SPME technique is designed to accommodate the use of fibers coated with different polymers suitable for the extraction of chemicals with varied hydrophobic and polar properties. Also, the technique can minimize interference from other artefacts associated with complex samples, such as those encountered in biological matrices or reaction mixtures. The preceding characteristics of SPME make the technique suitable for real-time measurements of intermediate reaction products and, thus, able to provide insight into the fate of target chemicals and their degradation pathways. In the present article, the current state of knowledge on the use of SPME-GC and SPME-HPLC in the determination of frequently encountered environmental chemicals and their (bio)transformation pathways are critically reviewed. Future opportunities of SPME in real time in situ process monitoring such as the use of agricultural feed stocks to bio-based industrial products termed henceforth "process analytical chemistry" are also discussed.     

An iterative method for finding common solutions of equilibrium and fixed point problems

We introduce an iterative method for finding a common element of the set of solutions of an equilibrium problem and of the set of fixed points of a finite family of nonexpansive mappings in a Hilbert space. We prove the strong convergence of the proposed iterative algorithm to the unique solution of a variational inequality, which is the optimality condition for a minimization problem.     

Assessing the cost of capital for longevity risk

The cost of capital is a key element of the embedded value methodology for the valuation of a life business. Further, under some solvency approaches (in particular, the Swiss Solvency Test and the developing Solvency 2 project) assessing the cost of capital constitutes a step in determining the required capital allocation.Whilst the cost of capital is usually meant as a reward for the risks encumbering a given life portfolio, in actuarial practice the relevant parameter has been traditionally chosen, at least to some extent, inconsistently with such risks. The adoption of market-consistent valuations has then been advocated to reach a common standard.A market-consistent value usually acknowledges a reward to shareholders’ capital as long as the market does, namely if the risk is systematic or undiversifiable. When dealing with a life annuity portfolio (or a pension plan), an important example of systematic risk is provided by the longevity risk, i.e. the risk of systematic deviations from the forecasted mortality trend. Hence, a market-consistent approach should provide appropriate valuation tools.In this paper we refer to a portfolio of immediate life annuities and we focus on longevity risk. Our purpose is to design a framework for a valuation of the portfolio which is market-consistent, and therefore based on a risk-neutral argument, while involving some of the basic items of a traditional valuation, viz best estimate future flows and allocated capital. This way, we try to reconcile the traditional with a market-consistent (or risk-neutral) approach. This allows us, in particular, to translate the results obtained under the risk-neutral approach in terms of a properly redefined embedded value.