Absolute proton affinity of some polyguanides

The problem of the absolute proton affinity (APA) of some polyguanides is addressed by the MP2(fc)/6-311+G//HF/6-31G theoretical model. It is shown that the linear chain polyguanides exhibit increased basicity as a function of the number of guanide subunits. However, the saturation effect yields an asymptotic APA value of 254 kcal/mol. Branched polyguanides on the other hand have higher APAs than their linear counterparts. The largest proton affinity is found in a doubly bifurcated heptaguanide, being as high as 285 kcal/mol, thus potentially representing one of the strongest organic bases. Finally, it is found that all polyguanides protonate at imino nitrogen atoms, since they are apparently susceptible the most to the proton attack. The origin of their very high intrinsic basicity is traced down to a dramatic increase in the resonance interaction of the corresponding conjugate bases. For instance, the increase in the resonance energy in the protonated guanidine is estimated to be in a range of 24-27 kcal/mol, which is higher than the aromatic stabilization in benzene. The proton affinity of some polycyclic guanides including Schwesinger proton sponge and porphine is briefly discussed.     

On Gradient Ricci Solitons

In the first part of the paper we derive integral curvature estimates for complete gradient shrinking Ricci solitons. Our results and the recent work in M. Fernandez-Lopez and E. Garcia-Rio, Rigidity of shrinking Ricci solitons in Math. Z. (2011) classify complete gradient shrinking Ricci solitons with harmonic Weyl tensor. In the second part of the paper we address the issue of existence of harmonic functions on gradient shrinking Kähler and gradient steady Ricci solitons. Consequences to the structure of shrinking and steady solitons at infinity are also discussed.     

Modulated structures in bent-core liquid crystals: two faces of one phase

The Landau-de Gennes type continuous model is used to describe the 2D modulated structures made of bent-core liquid crystals. It is shown that modulation is a direct consequence of the chiral symmetry breaking. Structures with synclinic and anticlinic layer tilt are found to coexist in the polarization modulated and layer undulated (PM-LU) liquid crystal phase. The synclinic PM-LU structure corresponds to the columnar B(1RevTilted) phase. Experimentally obtained electron density maps are included, which support theoretical findings.     

Kinetic determination of morphine by means of Bray-Liebhafsky oscillatory reaction system using analyte pulse perturbation technique

A novel kinetic method for micro-quantitative determinations of morphine (MH) is proposed and validated. The method is based on the potentiometric monitoring of the concentration perturbations of the oscillatory reaction system being in a stable non-equilibrium stationary state close to the bifurcation point between stable and oscillatory state. The response of the Bray-Liebhafsky (BL) oscillatory reaction as a matrix system, to the perturbations by different concentrations of morphine, is followed by a Pt-electrode. The proposed method relies on the linear relationship between maximal potential shift, ΔE_m, and the logarithm of the added morphine amounts in the range of 0.004-0.18 μmol. Under optimum conditions, the sensitivity of the proposed method (as the limit of detection) is 0.001 μmol and the method is featured by good precision (R.S.D. = 1.6%) as well as the excellent sample throughput (45 samples h⁻¹). In addition to standard solution analysis, this approach was successfully applied for quantitative determination of morphine in a typical pharmaceutical dosage form. Some aspects of the possible mechanism of morphine action on the BL oscillating chemical system are discussed in detail.     

Biotic patterns of heart rate variation in depressed and psychotic subjects

This article presents novel quantitative methods to study R to R interval (RRI) series that identify their characteristic pattern of organization, Bios, and their variation in psychiatric illness. In this study twenty-four hour series of RRI were extracted from Holter recordings of healthy subjects (N = 74) and small groups of patients with affective depression or psychosis. These data were analyzed with recurrence and statistical methods. In all subjects, RRI series showed complexes (clusters of recurrences), such as those observed with mathematically-generated biotic series but not in chaotic or random series. RRI series from healthy persons showed diversification (increase in variance with the duration of the series analyzed), novelty (less recurrence isometry than copies randomized by shuffling), causal order (more consecutive isometry than shuffled copies), and asymmetric statistical distribution. These imprints of creative processes are characteristic of mathematical Bios, and are absent in chaos. Bios can be distinguished from random walk series by the nonrandom pattern of the series of differences between heartbeats, as well as by measures of consecutive isometry and of partial autocorrelation. These defining characteristics of Bios are significant signs of health. In comparison with healthy controls, psychiatric patient groups showed more isometry and more consecutive isometry than healthy subjects. Psychiatric patients also showed no diversification. This study highlights the process that produces heart rate variation as being non-stationary and creative (bios, not equilibrium or chaos) and causal (not stochastically generated by the coexistence of multiple factors). These results thus are significant regarding psychiatric health.     

On the extension of the mean curvature flow

Consider a family of smooth immersions ${F(\cdot,t): M^n\to \mathbb{R}^{n+1}}$ of closed hypersurfaces in ${\mathbb{R}^{n+1}}$ moving by the mean curvature flow ${\frac{\partial F(p,t)}{\partial t} = -H(p,t)\cdot \nu(p,t)}$ , for ${t\in [0,T)}$ . Cooper (Mean curvature blow up in mean curvature flow, arxiv.org/abs/0902.4282) has recently proved that the mean curvature blows up at the singular time T. We show that if the second fundamental form stays bounded from below all the way to T, then the scaling invariant mean curvature integral bound is enough to extend the flow past time T, and this integral bound is optimal in some sense explained below.     

Curcumin: an anti-inflammatory molecule from a curry spice on the path to cancer treatment

Oxidative damage and inflammation have been pointed out in preclinical studies as the root cause of cancer and other chronic diseases such as diabetes, hypertension, Alzheimer's disease, etc. Epidemiological and clinical studies have suggested that cancer could be prevented or significantly reduced by treatment with anti-oxidant and anti-inflammatory drugs, therefore, curcumin, a principal component of turmeric (a curry spice) showing strong anti-oxidant and anti-inflammatory activities, might be a potential candidate for the prevention and/or treatment of cancer and other chronic diseases. However, curcumin, a highly pleiotropic molecule with an excellent safety profile targeting multiple diseases with strong evidence on the molecular level, could not achieve its optimum therapeutic outcome in past clinical trials, largely due to its low solubility and poor bioavailability. Curcumin can be developed as a therapeutic drug through improvement in formulation properties or delivery systems, enabling its enhanced absorption and cellular uptake. This review mainly focuses on the anti-inflammatory potential of curcumin and recent developments in dosage form and nanoparticulate delivery systems with the possibilities of therapeutic application of curcumin for the prevention and/or treatment of cancer.     

Adsorption of nicotine from aqueous solution onto hydrophobic zeolite type USY

The isothermal adsorption of nicotine from an aqueous solution onto zeolite type USY was investigated. The adsorption isotherms of nicotine onto the zeolite at different temperatures ranging from 298 to 322 K were determined. It was found that the adsorption isotherms can be described by the model of Freundlich adsorption isotherm. Based on the adsorption isotherms the changes of adsorption heat, free energy and entropy with adsorption degree were determined. The determined decrease of adsorption heat with adsorption degree can be explained by the presence of the adsorption centers of different energy and concentration on interface of zeolite-nicotine solution. It was found that the probability function of density distribution of the heat of adsorption (DDF) has exponential form. It was concluded that the possibility of fitting the adsorption isotherms of nicotine onto the zeolite by Freundlich adsorption isotherm was a direct consequence of that. The determined increase in entropy with the increase in adsorption degree can be explained with the change of phase state of adsorbed nicotine.     

Substrate-promoted formation of a catalytically competent binuclear center and regulation of reactivity in a glycerophosphodiesterase from Enterobacter aerogenes

The glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes is a promiscuous binuclear metallohydrolase that catalyzes the hydrolysis of mono-, di-, and triester substrates, including some organophosphate pesticides and products of the degradation of nerve agents. GpdQ has attracted recent attention as a promising enzymatic bioremediator. Here, we have investigated the catalytic mechanism of this versatile enzyme using a range of techniques. An improved crystal structure (1.9 A resolution) illustrates the presence of (i) an extended hydrogen bond network in the active site, and (ii) two possible nucleophiles, i.e., water/hydroxide ligands, coordinated to one or both metal ions. While it is at present not possible to unambiguously distinguish between these two possibilities, a reaction mechanism is proposed whereby the terminally bound H2O/OH(-) acts as the nucleophile, activated via hydrogen bonding by the bridging water molecule. Furthermore, the presence of substrate promotes the formation of a catalytically competent binuclear center by significantly enhancing the binding affinity of one of the metal ions in the active site. Asn80 appears to display coordination flexibility that may modulate enzyme activity. Kinetic data suggest that the rate-limiting step occurs after hydrolysis, i.e., the release of the phosphate moiety and the concomitant dissociation of one of the metal ions and/or associated conformational changes. Thus, it is proposed that GpdQ employs an intricate regulatory mechanism for catalysis, where coordination flexibility in one of the two metal binding sites is essential for optimal activity.     

Selective immobilization of Acinetobacter junii on the natural zeolitized tuff in municipal wastewater

The immobilization of desired bacteria onto material was usually performed in synthetic media. The aim of this study was to test the immobilization of phosphate (P)-accumulating bacteria Acinetobacter junii onto natural zeolitized tuff (NZ) in the raw or sterilized municipal wastewater containing the common bacteria Escherichia coli and Enterococcus faecalis and the performance of immobilized A. junii in the same type of wastewater. In the sterilized wastewater which contained the mixture of A. junii, E. coli and E. faecalis, the A. junii was selectively immobilized onto NZ in significantly higher numbers than E. coli and E. faecalis. The A. junii added in the form of bioparticles to the wastewater containing E. coli and E. faecalis, multiplied and removed P from wastewater. The P removal from wastewater was a function of biomass of P-accumulating bacteria and not the amount of NZ or bioparticles used. The performance of A. junii was significantly better in membrane filtered than in autoclaved wastewater. The experiments that were performed in raw non sterilized wastewater showed that A. junii can be successfully immobilized onto NZ in competition with natively present heterotrophic bacteria, retain its metabolic activity and successfully remove P from such water, which makes this technology feasible from biotechnological aspect.