Ni speciation in tea infusions by monolithic chromatography—ICP-MS and Q-TOF-MS

For humans, Ni is not considered to be an essential trace element. Its compounds, at levels present in foodstuffs and drinks, are generally considered to be safe for consumption, but for individuals who already suffer from contact allergy to Ni and may be subject to develop systemic reactions from its dietary ingestion, dietary exposure to Ni must be kept under control. Being the second most popular beverage, tea is a potential source of dietary Ni. Present knowledge on its speciation in tea infusions is poor. Therefore, complete speciation analysis, consisting of separation by liquid chromatography using a weak CIM DEAE-1 monolithic column, “on-line” detection by inductively coupled plasma mass spectrometry (ICP-MS) and “off-line” identification of ligands by hybrid quadrupole time-of-flight mass spectrometry (Q-TOF MS), was implemented for the first time to study Ni speciation in tea infusions. Total concentrations of Ni in dry leaves of white, green, oolong and black tea (Camellia sinensis) and flowers of herbal chamomile (Matricaria chamomilla) and hibiscus (Hibiscus sabdariffa) tea were determined after microwave digestion by ICP-MS. They lay between 1.21 and 14.4 mg?kg^?1. Good agreement between the determined and the certified values of the Ni content in the standard reference material SRM 1573a tomato leaves confirmed the accuracy of the total Ni determination. During the infusion process, up to 85 % of Ni was extracted from tea leaves or flowers. Separation of Ni species was completed in 10 min by applying aqueous linear gradient elution with 0.6 mol?L^?1 NH₄NO₃. Ni was found to be present in the chromatographic fraction in which quinic acid was identified by Q-TOF in all the tea infusions analysed, which had pH values between 5.6 and 6.0. The only exception was the infusion of hibiscus tea with a pH of 2.7, where results of speciation analysis showed that Ni is present in its divalent ionic form.     

Spin Echo Attenuation of Restricted Diffusion as a Discord of Spin Phase Structure

By using the particle probability density we analyze the spin echo attenuation of particles, diffusing in a bounded region. It provides a means to expand a nonuniform spin phase distribution into a series of waves that characterize the geometry and boundary conditions of confinement. Random motion disrupts the initial phase structure created by applied gradients and consequently discords its structure waves. By assuming the spin phase fluctuation and/or the randomness of spin phase distribution in the subensemble as a Gaussian stochastic process, we derive a new analytical expression for the echo attenuation related to the particle velocity correlation. For a diffusion in porous structure we get the expression featuring the same “diffusive diffraction” patterns as those being found and explained by P. T. Callaghan and A. Coy (“Principles of Nuclear Magnetic Resonance Microscopy,” Oxford Univ. Press, Oxford (1991);J. Chem. Phys.101, 4599–4609 (1994)) with the use of propagator theory. With the new approach we cast a new light on the phenomena and derive analitically how the diffusive diffractions appear when the sequence of finite or even modulated gradients are applied. The method takes into account the non-Markovian character of restricted diffusion, and therefore the echo dependence on the diffusion lengths and on the strength of applied gradient differs from the results of authors assuming the Markovian diffusion either by dealing with the diffusion propagators or by the computer simulation of Fick's diffusion.     

Sheaf coalgebras and duality

In this paper we construct an adjoint pair of functors between the category of sheaves on a smooth manifold M and the category of coalgebras over the ring of smooth functions with compact support on M. We show that the sheaf coalgebra associated to a sheaf E on M determines the sheaf E uniquely up to an isomorphism, and that the adjoint functors restrict to an equivalence between sheaves on M and sheaf coalgebras over .     

Protein-protein binding-sites prediction by protein surface structure conservation

A new algorithm to predict protein-protein binding sites using conservation of both protein surface structure and physical-chemical properties in structurally similar proteins is developed. Binding-site residues in proteins are known to be more conserved than the rest of the surface, and finding local surface similarities by comparing a protein to its structural neighbors can potentially reveal the location of binding sites on this protein. This approach, which has previously been used to predict binding sites for small ligands, is now extended to predict protein-protein binding sites. Examples of binding-site predictions for a set of proteins, which have previously been studied for sequence conservation in protein-protein interfaces, are given. The predicted binding sites and the actual binding sites are in good agreement. Our algorithm for finding conserved surface structures in a set of similar proteins is a useful tool for the prediction of protein-protein binding sites.     

Car-Parrinello molecular dynamics study of anharmonic systems: a Mannich base in solution

A Car-Parrinello molecular dynamics study was performed for 4,5-dimethyl-2-(N,N-dimethylaminomethyl)phenol, a Mannich base, to investigate the vibrational properties in solution of its intramolecular hydrogen bond. The dynamic behavior of this hydrogen-bonded system was investigated using an explicit solvent model. Addition of a nonpolar solvent permitted inclusion of delicate environmental effects on the strongly anharmonic system which was studied from first principles. Molecular dynamics and a posteriori quantization of the O-H motion were applied to reproduce the vibrational features of the O-H stretching mode. Consistent application of Car-Parrinello dynamics based on the density functional theory with subsequent solution of the vibrational Schr?dinger equation for the O-H stretching motion offers an effective method for strongly anharmonic systems, and this is supported by the comparison of the results with experimental spectra. As a further element of the intramolecular hydrogen bond study, the effects of deuteration were taken into account and a successful application of the O-H stretching mode quantization technique to the liquid phase is demonstrated. This provides a valuable computational methodology for investigations incorporating nuclear quantum effects in the liquid phase and enzyme active centers and can be used to investigate numerous systems that are not readily susceptible to experimental analysis.     

Examples of Analysis of Stochastic Processes Based on Time Series Data

Time series data from stochastic processes described by the Langevin equation are analyzed. Analysis is based on estimation of the deterministic and random terms of the Langevin equation from data. The terms are presented as fields and inspected visually. Forming a model of the process, the terms are also used to reconstruct the deterministic and stochastic process trajectories. The deterministic term is approximated by an analytical ansatz. The equations obtained by the approximation are used to generate deterministic process trajectories and to study their linear stability. Influence of measurement noise on the estimates is also discussed.     

A New Pathway of DNA G‐Quadruplex Formation

A new folding intermediate of Oxytricha nova telomeric Oxy‐1.5 G‐quadruplex was characterized in aqueous solution using NMR spectroscopy, native gel electrophoresis, thermal differential spectra (TDS), CD spectroscopy, and differential scanning calorimetry (DSC). NMR experiments have revealed that this intermediate (i‐Oxy‐1.5) exists in two symmetric bimolecular forms in which all guanine bases are involved in GG N1‐carbonyl symmetric base pairs. Kinetic analysis of K⁺‐induced structural transitions shows that folding of Oxy‐1.5 G‐quadruplex from i‐Oxy‐1.5 is much faster and proceeds through less intermediates than folding from single strands. Therefore, a new folding pathway of Oxy‐1.5 G‐quadruplex is proposed. This study provides evidence that G‐rich DNA sequences can self‐assemble into specific pre‐organized DNA structures that are predisposed to fold into G‐quadruplex when interacting with cations such as potassium ions.     

RuII,OsII, and IrIII Complexes with Chelating Pyridyl–Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis

Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir^III–Cp*‐ and Os^II–Cym complexes (Cp*=pentamethylcyclopentadienyl, Cym=p‐cymene=4‐isopropyl‐toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4‐substituted phenylacetylene building blocks have been used to introduce electronic fine‐tuning in the ligands. The ligands thus can be generally described as 4‐(4‐R‐phenyl)‐3‐methyl‐1‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐5‐ylidene (with R being H (L¹), Me (L²), OMe (L³), CN (L⁴), CF₃ (L⁵), Br (L⁶) or NO₂ (L⁷)). The corresponding complexes (Ir‐ 1 to Ir‐ 7 and Os‐ 1 to Os‐ 7 ) were characterized by standard spectroscopic methods, and the expected three‐legged, piano‐stool type coordination was unambiguously confirmed by X‐ray diffraction analysis of selected compounds. Together with Ru^II analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented.