Identification of phosphorylation sites of equine β‐casein isoforms

Equine β‐casein is phosphorylated at variable degrees and isoforms carrying 3 to 7 phosphate groups (3P–7P) have been found in milk, but the phosphorylated amino acid residues of each isoform are not yet identified. In the present work, the different phosphorylation variants were first isolated by ion‐exchange chromatography and then hydrolysed by trypsin to generate caseinophosphopeptides (CPPs), each containing all the potential phosphorylation sites. The equine CPPs were prepared by metal oxide affinity chromatography, a method based on the affinity of phosphate groups towards titanium dioxide immobilized onto a micro‐column. This method turned out to be an efficient tool to separate the CPPs Arg¹–Lys³⁴ and Glu⁴–Lys³⁴ from non‐phosphorylated peptides. Purification was achieved by reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and each CPP was hydrolyzed by endoproteinase Glu‐C. Finally, the digests were analyzed by RP‐HPLC/electrospray ionization mass spectrometry (RP‐HPLC/ESI‐MS) and identified by nano‐electrospray ionization tandem mass spectrometry (nESI‐MS/MS) to locate the phosphorylated sites of the β‐casein isoforms 4P–7P with accuracy. Thus, the isoform 4P was found to be phosphorylated on residues Ser⁹, Ser²³, Ser²⁴, and Ser²⁵. Addition of phosphate groups on Ser¹⁸, Thr¹², and Ser¹⁰ led to the formation of the isoforms 5P–7P, respectively. The results indicated that the in vivo phosphorylation of the equine β‐casein follows a sequential way and is not randomly performed. Copyright © 2010 John Wiley & Sons, Ltd.     

An SQP method for mathematical programs with vanishing constraints with strong convergence properties

We propose an SQP algorithm for mathematical programs with vanishing constraints which solves at each iteration a quadratic program with linear vanishing constraints. The algorithm is based on the newly developed concept of \({\mathcal {Q}}\)-stationarity (Benko and Gfrerer in Optimization 66(1):61–92, 2017). We demonstrate how \({\mathcal {Q}}_M\)-stationary solutions of the quadratic program can be obtained. We show that all limit points of the sequence of iterates generated by the basic SQP method are at least M-stationary and by some extension of the method we also guarantee the stronger property of \({\mathcal {Q}}_M\)-stationarity of the limit points.     

Effect of synthesis conditions on the microstructure of TEOS derived silica hydrogels synthesized by the alcohol-free sol–gel route

Silica matrices synthesized from a pre-hydrolysis step in ethanol followed by alcohol removal at low pressure distillation, and condensation in water, are suitable for encapsulation of biomolecules and microorganisms and building bioactive materials with optimized optical properties. Here we analyze the microstructure of these hydrogels from the dependence of I(q) data acquired from SAXS experiments over a wide range of silica concentration and pH employed in the condensation step. From the resulting data it is shown that there is a clear correlation between the microscopic parameters—cluster fractal dimension (D), elementary particle radius (a) and cluster gyration radius (R)—with the attenuation of visible light when the condensation step proceeds at pH < 6. At higher pHs, there is a steep dependence of the cluster density (~R ^D−3) with the condensation pH, and non-monotonous changes of attenuance are less than 20%, revealing the complexity of the system. These results, which were obtained for a wide pH and silica concentration range, reinforce the idea that the behavior of gels determined in a restricted interval of synthesis variables cannot be extrapolated, and comparison of gelation times is not enough for predicting their properties.     

Specific O₂⁻ generation in corona discharge for ion mobility spectrometry

This study deals with O₂⁻ generation in corona discharge (CD) in point to plane geometry for single flow ion mobility spectrometry (IMS) with gas outlet located behind the ionization source. We have designed CD of special geometry in order to achieve the high O₂⁻ yield. Using this ion source we have achieved in zero air conditions that up to 74% all negative ions were O₂⁻ or O₂⁻(H₂O). It has been demonstrated that the non-electronegative nitrogen positively influences the efficiency of O₂⁻ generation in O₂/N₂ mixtures. The reduced ion mobility of 2.27 cm² V⁻¹ s⁻¹ has been measured for O₂⁻/O₂⁻(H₂O) ions in zero air. Additional ions detected in zero air (less than 200 ppb CO₂) using the mass spectrometric and IMS technique were, NO₂⁻, N₂O₂⁻ (2.37 cm² V⁻¹ s⁻¹), NO₃⁻, N₂O₃⁻ and N₂O₃⁻(H₂O). The CO₃⁻ and CO₄⁻ ions have been detected after the introduction of 5 ppm CO₂ into zero air.     

On-line two-dimensional liquid chromatography-tandem mass spectrometric determination of estrogens in sediments

The development of an on-line system for the simultaneous determination of α-estradiol, β-estradiol, estrone and 17α-ethynylestradiol in river sediments is described. The analytes were extracted from sediments by microwave-assisted extraction. A crude extract was directly analysed by a heart-cutting two dimensional high-performance liquid chromatography-ion trap-tandem mass spectrometry with an atmospheric pressure photoionization source operating in the positive mode. The method shows excellent performance in terms of accuracy, precision, and sensitivity. The accuracy of each estrogen was in the range of 98.8-107.1%. Intra-batch and inter-batch precisions were in the range of 6.2-7.0% and 8.3-9.5%, respectively. The limits of detection ranged from 90 to 250 pg g(-1). A significant reduction in the total analysis time and a reduction in sample manipulation are the main advantages of the proposed method. Finally, the method was applied on real sediment samples.     

An adaptive multi-start graph partitioning algorithm for structuring cellular networks

In mobile network design, the problem of assigning network elements to controllers when defining network structure can be modeled as a graph partitioning problem. In this paper, a comprehensive analysis of a sophisticated graph partitioning algorithm for grouping base stations into packet control units in a mobile network is presented. The proposed algorithm combines multi-level and adaptive multi-start schemes to obtain high quality solutions efficiently. Performance assessment is carried out on a set of problem instances built from measurements in a live network. Overall results confirm that the proposed algorithm finds solutions better than those obtained by the classical multi-level approaches and much faster than classical multi-start approaches. The analysis of the optimization surface shows that the best local minima values follow a Gumbel distribution, which justifies the stagnation of naive multi-start approaches after a few attempts. Likewise, the analysis shows that the best local minima share strong similarities, which is the reason for the superiority of adaptive multi-start approaches. Finally, a sensitivity analysis shows the best internal parameter settings in the algorithm.     

Gold and silver determination in Waters by SPHERON® Thiol 1000 preconcentration and ETAAS

A reliable procedure for the electrothermal atomic absorption spectrometry (ETAAS) determination of gold and silver in waters at trace level is described. The method is based on prior separation and preconcentration of the metals using a chelating sorbent SPHERON® Thiol 1000 after acidification of water samples (pH < 3) with nitric acid. Optimization of analytical variables during enrichment and ETAAS determination of the metals are discussed. The accuracy of the method is verified by analysis of certified reference materials. The limits of determinations based on 10 σ definition were 0.005 ng cm^?3 for Au and 0.02 ng cm^?3 for Ag. Precision of studied elements determination expressed by relative standard deviation varied in the range from 2.9 % to 16.4 %.     

Classical Invariants for Global Actions and Groupoid Atlases

A global action is the algebraic analogue of a topological manifold. This construction was introduced in first place by A. Bak as a combinatorial approach to K-Theory and the concept was later generalized by Bak, Brown, Minian and Porter to the notion of groupoid atlas. In this paper we define and investigate homotopy invariants of global actions and groupoid atlases, such as the strong fundamental groupoid, the weak and strong nerves, classifying spaces and homology groups. We relate all these new invariants to classical constructions in topological spaces, simplicial complexes and simplicial sets. This way we obtain new combinatorial formulations of classical and non classical results in terms of groupoid atlases.      

On fuzzy multi-valued functions part 3: Fixed-point theorem

In this paper a Fixed-Point Theorem and an application is presented.     

On fuzzy multi-valued functions part 2: Some topological properties

In this paper new topological concepts connected with fuzzy multi-valued functions theory-as presented in the first part of this work-are introduced and their properties are investigated. As will be shown in future papers these concepts and properties are indispensable in connection with the analysis of fuzzy economic systems.