Temperature dependence of structure and dynamics of the hydrated Ca2+ ion according to ab initio quantum mechanical charge field and classical molecular dynamics

Simulations using ab initio quantum mechanical charge field molecular dynamics (QMCF MD) and classical molecular dynamics using two‐body and three‐body potentials were performed to investigate the hydration of the Ca²⁺ ion at different temperatures. Results from the simulations demonstrate significant effects of temperature on solution dynamics and the corresponding composition and structure of hydrated Ca²⁺. Substantial increase in ligand exchange events was observed in going from 273.15 K to 368.15 K, resulting in a redistribution of coordination numbers to lower values. The effect of temperature is also visible in a red‐shift of the ion‐oxygen stretching frequencies, reflecting weakened ligand binding. Even the moderate increase from ambient to body temperature leads to significant changes in the properties of Ca²⁺ in aqueous environment. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Optimization of simulated moving bed chromatography with fractionation and feedback: Part II. Fractionation of both outlets

A new improvement based on outlet fractionation and feedback has been developed for simulated moving bed (SMB) chromatography. In this contribution, this fractionation and feedback SMB (FF-SMB) concept is extended to the general scenario which integrates a simultaneous fractionation of both outlet streams. A model-based optimization approach, previously adopted to investigate single fractionation, is extended to consider this flexible fractionation policy. Quantitative optimization studies based on a specific separation problem reveal that the double fractionation is the most efficient operating scheme in terms of maximum feed throughput, while the two existing single fractionation modes discussed in our previous study are also significantly superior to the conventional SMB operation. The advantages of the double fractionation extension are further demonstrated in terms of several more detailed performance criteria. In order to evaluate the applicability of the fractionation and feedback modification, the effect of product purity, adsorption selectivity, column efficiency and column number on the relative potential of FF-SMB over SMB is examined.     

Structural characterization of a completely alkyl-substituted Al-Sb Lewis acid-base adduct

The Lewis acid-base adduct t-Bu₃Al-SbMe₃ (1), which was synthesized by reaction of equimolar amounts of t-Bu₃Al and trimethylstibine SbMe₃, was characterized by multinuclear NMR (¹H, ¹³C) spectroscopy, elemental analyses as well as by single crystal X-ray diffraction.     

Quinol-containing ligands enable high superoxide dismutase activity by modulating coordination number,charge, oxidation states and stability of manganese complexes throughout redox cycling

Reactivity assays previously suggested that two quinol-containing MRI contrast agent sensors for H₂O₂, [Mn(H2qp1)(MeCN)]²⁺ and [Mn(H4qp2)Br₂], could also catalytically degrade superoxide. Subsequently, [Zn(H2qp1)(OTf)]⁺ was found to use the redox activity of the H2qp1 ligand to catalyze the conversion of O₂˙⁻ to O₂ and H₂O₂, raising the possibility that the organic ligand, rather than the metal, could serve as the redox partner for O₂˙⁻ in the manganese chemistry. Here, we use stopped-flow kinetics and cryospray-ionization mass spectrometry (CSI-MS) analysis of the direct reactions between the manganese-containing contrast agents and O₂˙⁻ to confirm the activity and elucidate the catalytic mechanism. The obtained data are consistent with the operation of multiple parallel catalytic cycles, with both the quinol groups and manganese cycling through different oxidation states during the reactions with superoxide. The choice of ligand impacts the overall charges of the intermediates and allows us to visualize complementary sets of intermediates within the catalytic cycles using CSI-MS. With the diquinolic H4qp2, we detect Mn(iii)-superoxo intermediates with both reduced and oxidized forms of the ligand, a Mn(iii)-hydroperoxo compound, and what is formally a Mn(iv)-oxo species with the monoquinolate/mono-para-quinone form of H4qp2. With the monoquinolic H2qp1, we observe a Mn(ii)-superoxo ↔ Mn(iii)-peroxo intermediate with the oxidized para-quinone form of the ligand. The observation of these species suggests inner-sphere mechanisms for O₂˙⁻ oxidation and reduction that include both the ligand and manganese as redox partners. The higher positive charges of the complexes with the reduced and oxidized forms of H2qp1 compared to those with related forms of H4qp2 result in higher catalytic activity (k_cat ∼ 10⁸ M⁻¹ s⁻¹ at pH 7.4) that rivals those of the most active superoxide dismutase (SOD) mimics. The manganese complex with H2qp1 is markedly more stable in water than other highly active non-porphyrin-based and even some Mn(ii) porphyrin-based SOD mimics.

Manganese complexes with polydentate quinol-containing ligands are found to catalyze the degradation of superoxide through inner-sphere mechanisms. The redox activity of the ligand stabilizes higher-valent manganese species.     

Application of displacement chromatography for the proteome analysis of a human plasma protein fraction

It was the aim of this study to compare the performance of displacement chromatography with gradient elution chromatography both applied as the cation-exchange separation step for a proteome analysis in a bottom-up approach using multidimensional chromatography for the separation of tryptic peptides prior to their mass spectrometric analysis. The tryptic digest of the human Cohn fraction IV-4 served as a sample. For both chromatography modes commonly used operating parameters were chosen thus ensuring optimal separation results of equal sample amounts for each mode. All resulting fractions were analyzed with an HPLC-chip–LC–MS system. The eluate of the HPLC-chip column was ionized by electrospray ionization (ESI) and analyzed with an ion-trap mass spectrometer. For guaranteeing high confidence concerning the identity of the peptides, the mass spectrometric data were processed by different bioinformatic tools applying stringent criteria. By the displacement approach the total amount of identified proteins (78) was significantly higher than in the gradient mode (58). The results showed that displacement chromatography is a well suited alternative in comparison to gradient elution separation for analysis of proteomes via the bottom-up approach applying multidimensional chromatography, especially in those cases when larger quantities of proteins are available.     

Shift operators contained in contractions, pseudocontinuable Schur functions and orthogonal systems on the unit circle

The main aim of this paper is to establish the connection between well-known criteria for the pseudocontinuability of a non-inner Schur function ?? in the unit disk (see Theorems 3.9, 4.2). In a canonical way we associate a probability measure ?? on the unit circle with ??. One of the two criteria will be reformulated in the face of ??, whereas the other one is drafted in view of a completely nonunitary contraction T having ?? as corresponding characteristic function. Our main result clarifies an immediate connection between the above-mentioned two criteria. In this way, we rewrite these criteria in terms of orthogonal systems with respect to the measure ?? (see Theorem 7.2).     

Time-reversal multiple signal classification in case of noise: a phase-coherent approach

The problem of locating point-like targets beyond the classical resolution limit is revisited. Although time-reversal MUltiple SIgnal Classification (MUSIC) is known for its super-resolution ability in localization of point scatterers, in the presence of noise this super-resolution property will easily break down. In this paper a phase-coherent version of time-reversal MUSIC is proposed, which can overcome this fundamental limit. The algorithm has been tested employing synthetic multiple scattering data based on the Foldy-Lax model, as well as experimental ultrasound data acquired in a water tank. Using a limited frequency band, it was demonstrated that the phase-coherent MUSIC algorithm has the potential of giving significantly better resolved scatterer locations than standard time-reversal MUSIC.     

Relativity and the lead-acid battery

The energies of the solid reactants in the lead-acid battery are calculated ab?initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13?V, compared with the experimental value of 2.11?V. All calculations agree in that 1.7-1.8?V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.     

Simultaneous measurements of multiple flow velocity components using frequency modulated lasers and a single molecular absorption cell

Since unsteady, complex flow phenomena play an important role, optical measurements techniques are required for flow investigations, which provide simultaneous measurements of multiple velocity components. Doppler global velocimetry has this potential. It is a flow measurement technique, where the Doppler shift of scattered light is measured by a molecular absorption cell for frequency-to-intensity conversion. However, novel Doppler global velocimeters with laser frequency modulation were only used for single component measurements yet. In order to enhance such a system for the simultaneous measurement of multiple components, a concept based on frequency division multiplexing is introduced for the first time. Besides multiple lasers, only a single molecular absorption cell and a single detector unit is required. Two-component measurements of velocity profiles from nozzle flows are presented as a proof of principle. The designed measurement system provides high measurement rates of up to 20 kHz, which is three orders of magnitude higher than for typical Doppler global velocimetry setups.