Comparison of Planar and 3‐D Interdigitated Electrodes as Electrochemical Impedance Biosensors

It has been reported that the introduction of a dielectric barrier between adjacent digits of an interdigitated electrode array can improve the sensitivity of the array as an electrochemical impedance biosensor. Here we present an in‐depth analysis of the impedance in planar interdigitated electrodes and 3‐D interdigitated electrodes (with dielectric barriers). The analysis indicates that the planar geometry not only provides lower impedance but also a higher change impedance as a result of molecular immobilization on the electrode array surface.     

Boxicity of Leaf Powers

The boxicity of a graph G, denoted as boxi(G), is defined as the minimum integer t such that G is an intersection graph of axis-parallel t-dimensional boxes. A graph G is a k-leaf power if there exists a tree T such that the leaves of the tree correspond to the vertices of G and two vertices in G are adjacent if and only if their corresponding leaves in T are at a distance of at most k. Leaf powers are used in the construction of phylogenetic trees in evolutionary biology and have been studied in many recent papers. We show that for a k-leaf power G, boxi(G)??? k?1. We also show the tightness of this bound by constructing a k-leaf power with boxicity equal to k?1. This result implies that there exist strongly chordal graphs with arbitrarily high boxicity which is somewhat counterintuitive.     

Determination of aliphatic amines by gas chromatography–mass spectrometry after in-syringe derivatization with pentafluorobenzoyl chloride

A simple and highly sensitive gas chromatographic method has been developed for the determination of low molecular weight short-chain aliphatic amines (SCAAs) after their simultaneous extraction and in-syringe derivatization with pentafluorobenzoyl chloride (PFBOC). Derivatization of the low molecular weight aliphatic amines in bicarbonate buffer of pH 10.5 with PFBOC was followed by immersed solvent microextraction. Derivatization conditions, including reagent concentration, reaction pH, ionic concentration of buffer, reaction time, stirring rate, reaction temperature and extraction solvent, have been investigated for method optimization. Linearity was studied within range of 0.15 pg ml⁻¹–50 ng ml⁻¹. The correlation coefficients were between 0.9934 and 0.9999. Detection limit of derivatized amines proved to be in the range of 0.117–1.527 pg ml⁻¹, and the intraday and interday relative standard deviation (RSD) values were less than 8% with respect to peak area. The method was applied for analysis of lake, river and industrial waste water. The recoveries of extraction from lake, river and industrial waste water samples, which have been spiked with different levels of aliphatic amines, were in the range of 68–99%, 63–102% and 62–105%, respectively.     

Synthesis and antibacterial activity of some 5-hydroxy-5-trifluoromethyl-4,5-dihydropyrazol-1-thiocarboxamides, 3-trifluoromethylpyrazol-1-thiocarboxamides and 4-aryl-2-(5(3)-trifluoromethyl-1-pyrazolyl)thiazoles

5-Hydroxy-5-trifluoromethyl-4,5-dihydropyrazol-1-thiocarboxamides 3 and 3-trifluoromethylpyrazol-1-thiocarboxamides 4, regioselectively obtained by the condensation of trifluoromethyl-β-diketones with thiosemicarbazide under neutral and acidic conditions, on further reaction with phenacyl bromides 5 afforded 4-aryl-(5-trifluoromethyl-pyrazol-1-yl)thiazoles 6 and 4-aryl-(3-trifluoromethyl-pyrazol-1-yl)thiazoles 7, respectively. Five 4,5-dihydropyrazoles (3a–e) and two pyrazolylthiazoles (6a and 6c) were tested against one Gram-positive and one Gram-negative bacteria to assess their in vitro antibacterial activity. Compounds 3a, 3b and 3e showed moderate antibacterial activity against Gram-positive bacterium, Bacillus pumilus.     

Determination of organic acid impurities in lactic acid obtained by fermentation of sugarcane juice

Lactic acid produced by fermentation process mostly contains a number of aliphatic carboxylic acids as impurities. In this work, carboxylic acid impurities in lactic acid samples from a number of sources were determined at ppm levels. A simple HPLC method was developed that utilized a new generation polar embedded reverse phase, 20mM phosphate buffer at pH 2.20 (±0.05) and UV detection at 210 nm. The method enabled quantitative analysis of the above acids in lactic acid matrix. The experimental conditions for column temperature, mobile phase pH and flow rate were optimized. A detailed validation of the method was performed for linearity, precision, accuracy, selectivity, limit of detection (LOD), limit of quantitation (LOQ), ruggedness and repeatability and reproducibility (R&R).     

Do commercially available metal salts mediate calixarene formation via hydrogen-bonded dimers?

In this article we report the first example of a Lewis acid promoted, one-pot, Br?nsted acid free, high-yielding synthesis of the calixarene macrocycle from the "monomer" p-tert-butylphenol. We report that when a commercially available metal salt (Lewis acid) is incorporated within the calixarene-forming reaction, a certain amount of control over the size of the calixarenes produced can be gained. Although a detailed mechanistic rationale on how the macrocycle is assembled is unclear, what is evident from this work is that the metal cation, the counteranion, and the oxidation state of the salt employed are all important contributors to the outcome of the reaction process. Indeed, evidence to date suggests that a subtle "symbiotic" relationship exists between the metal cation, its oxidation state, and the anion that allows the efficient transformation of the "monomeric" p-tert-butylphenol into linear oligomers and, ultimately, into macrocyclic calixarenes. Athough the metal salt mediated process described herein is efficient and high-yielding, what is also fundamentally important is that a comprehensive mechanistic understanding of how the calixarenes are assembled be accrued. Searching for possible indicators or clues, we propose that oligomeric methylene-linked phenolic entities are initially formed and that these, we tentatively suggest, generate metal and/or anion hydrogen-bonded supramolecular intermediates. It is possible that the preorganization of the linear polyphenolic oligomers allows the formation of hydrogen-bonded structures which, critically, result in the formation of supramolecular assemblies that are subsequently "stitched" together, generating the p-tert-butylcalix[n]arenes (n = 4-9) in excellent yields. Substantiating the possibility that hydrogen-bonded entities are generated (and that these subsequently afford metal-templated assemblies), we make reference to a seldom cited 1962 Nature publication that reported the propensity of polyphenolic linear oligomers to form "well-defined intramolecularly hydrogen-bonded conformations".     

Chemical constituents of the new endophytic fungus Mycosphaerella sp. nov. and their anti-parasitic activity

Chemical investigation of a new endophytic fungus, Mycosphaerella sp. nov. strain F2140, associated with the foliage of the plant Psychotria horizontalis (Rubiaceae) in Panama, resulted in the isolation of cercosporin (1) and a new cercosporin analog (3) as the major components. The structures of minor compounds in the extract were elucidated by detailed spectroscopic analysis as 2-(2-butyl)-6-ethyl-3-hydroxy-6-methylcyclohex-2-ene-1,5-dione (4), 3-(2-butyl)-6-ethyl-5-hydroxy-2-methoxy-6-methyl-cyclohex-2-enone (5), and an isomer of 5 (6). To study the influence of the hydroxy groups on the anti-parasitic activity of cercosporin, compound 1 was acetylated to obtain derivative 2. The isolated compounds 1- 6 were tested in vitro to determine their anti-parasitic activity against the causal agents of malaria (Plasmodium falciparum), leishmaniasis (Leishmania donovani), and Chagas disease (Trypanosoma cruzi). Cytotoxicity and potential anticancer activity of these compounds were evaluated using mammalian Vero cells and MCF7 cancer cell lines, respectively. Compounds 1 and 2 displayed high potency against L. donovani (IC50 0.46 and 0.64 microM), T. cruzi (IC50 1.08 and 0.78 microM), P. falciparum (IC50 1.03 and 2.99 microM), and MCF7 cancer cell lines (IC50 4.68 and 3.56 microM). Compounds 3-6 were not active in these assays at a concentration of 10 microg/mL.     

Reduced-order models for control of fluids using the eigensystem realization algorithm

As sensors and flow control actuators become smaller, cheaper, and more pervasive, the use of feedback control to manipulate the details of fluid flows becomes increasingly attractive. One of the challenges is to develop mathematical models that describe the fluid physics relevant to the task at hand, while neglecting irrelevant details of the flow in order to remain computationally tractable. A number of techniques are presently used to develop such reduced-order models, such as proper orthogonal decomposition (POD), and approximate snapshot-based balanced truncation, also known as balanced POD. Each method has its strengths and weaknesses: for instance, POD models can behave unpredictably and perform poorly, but they can be computed directly from experimental data; approximate balanced truncation often produces vastly superior models to POD, but requires data from adjoint simulations, and thus cannot be applied to experimental data. In this article, we show that using the Eigensystem Realization Algorithm (ERA) (Juang and Pappa, J Guid Control Dyn 8(5):620?C627, 1985) one can theoretically obtain exactly the same reduced-order models as by balanced POD. Moreover, the models can be obtained directly from experimental data, without the use of adjoint information. The algorithm can also substantially improve computational efficiency when forming reduced-order models from simulation data. If adjoint information is available, then balanced POD has some advantages over ERA: for instance, it produces modes that are useful for multiple purposes, and the method has been generalized to unstable systems. We also present a modified ERA procedure that produces modes without adjoint information, but for this procedure, the resulting models are not balanced, and do not perform as well in examples. We present a detailed comparison of the methods, and illustrate them on an example of the flow past an inclined flat plate at a low Reynolds number.     

A mathematical fractional model with nonsingular kernel for thrombin receptor activation in calcium signalling

In calcium signalling, activation of receptor is a very significant aspect. To understand the mechanism of calcium signalling, receptors are the important components. The mobilization of intracellular calcium from intracellular stores depends upon binding of agonist to cell surface receptor. Thrombin is chosen as model ligand. In order to understand thrombin receptor activation, we analyze fractional model incorporating derivative of arbitrary order and nonsingular kernel which can precisely describe the effect of memory and can explain the model in better and more efficient manner as compared with fractional operators with singular kernels. The problem has been solved by perturbation iterative method. Using fixed‐point theorem, it is proved that solution of the system will exist and also it will be unique.