Elastomer-Clay Nanocomposites: Effect of Elastomer Polarity

Dynamic mechanical properties of non-polar and polar elastomer-based nanocomposites with Montmorillonite clay are studied in order to ascertain differences caused by elastomer's polarity. Natural as non-polar and polychloroprene as polar rubber are used to experimentally verify predictions based on different nature of elastomer-clay interactions in the two cases. The properties foretold and elucidated in terms of van der Waals interactions in the non-polar case and dipole-dipole interactions in the polar case agree well with experiment, concurrently sustaining general depiction of these unusual nanocomposites.     

Evaluation of the binding of oxovanadium(IV) to human serum albumin

The understanding of the biotransformations of insulin mimetic vanadium complexes in human blood and its transport to target cells is an essential issue in the development of more effective drugs. We present the study of the interaction of oxovanadium(iv) with human serum albumin (HSA) by electron paramagnetic resonance (EPR), circular dichroism (CD) and visible absorption spectroscopy. Metal competition studies were done using Cu(II) and Zn(II) as metal probes. The results show that V(IV)O occupies two types of binding sites in albumin, which compete not only with each other, but also with hydrolysis of the metal ion. In one of the sites the resulting V(IV)O-HSA complex has a weak visible CD signal and its X-band EPR spectrum may be easily measured. This was assigned to amino acid side chains of the ATCUN site. The other binding site shows stronger signals in the CD in the visible range, but has a hardly measurable EPR signal; it is assigned to the multi metal binding site (MBS) of HSA. Studies with fatted and defatted albumin show the complexity of the system since conformational changes, induced by the binding of fatty acids, decrease the ability of V(IV)O to bind albumin. The possibility and importance of ternary complex formation between V(IV)O, HSA and several drug candidates - maltol (mal), picolinic acid (pic), 2-hydroxypyridine-N-oxide (hpno) and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhp) was also evaluated. In the presence of maltol the CD and EPR spectra significantly change, indicating the formation of ternary VO-HSA-maltol complexes. Modeling studies with amino acids and peptides were used to propose binding modes. Based on quantitative RT EPR measurements and CD data, it was concluded that in the systems with mal, pic, hpno, and dhp (V(IV)OL(2))(n)(HSA) species form, where the maximum value for n is at least 6 (mal, pic). The degree of formation of the ternary species, corresponding to the reaction V(IV)OL(2) + HSA -->/<-- V(IV)OL(2)(HSA) is hpno > pic ≥ mal > dhp. (V(IV)OL)(n)(HSA) type complexes are detected exclusively with pic. Based on the spectroscopic studies we propose that in the (V(IV)OL(2))(n)(HSA) species the protein bounds to vanadium through the histidine side chains.     

Liquid chromatography-tandem mass spectrometric method for determination of the anti-inflammatory compound vicenin-2 in the leaves of L. ericoides Mart

This paper reports a rapid and sensitive method for determination of the anti-inflammatory compound vicenin-2 in L. ericoides Mart. using liquid chromatography-tandem mass spectrometry. Separation of the compound of interest was performed on a VP-ODS(18) (150 x 2 mm, Shimadzu, Japan) column and a pre-column packed with GPV-ODS C(18) (5 x 2 mm, Sigma-Aldrich, USA) with acetonitrile-water (15:85) mobile phase containing 2% acetic acid using isocratic flow at 0.5 mL/min for 2 min. Multiple-reaction monitoring of vicenin-2 was performed using electrospray positive ionization. The linear calibration curves were generated using a concentration range of 5-2500 ng/mL with correlation coefficients >0.99. The values of limit of detection and limit of quantitation were found to be 1 and 5 ng/mL, respectively. The method developed based on LC-ESIMS/MS is advantageous because it permits the rapid and selective detection of vicenin-2. Furthermore, the method can be easily applied to the routine analysis of vicenin-2 in plant extracts using a minimal amount of sample.     

Kinetics of induced absorption phenomena in YAlO 3 :Ce scintillator

The set of samples of YAlO 3 :Ce further codoped by ZrO 2 at several concentrations from 0 v ppm up to 1000 v ppm (grown in CRYTUR Ltd., Turnov, Czech Republic) was irradiated 30 v min at homogeneous gamma-radiation field, produced when irradiating W target by 21 v MeV electrons beam from microtrone accelerator. Dose rates were ranging from 12 to 33 v rad/min. Induced absorption spectra have three absorption bands. Temporal characteristics of the build-up and recovery of the induced absorption are evaluated using simple kinetics models. The obtained results are discussed.     

A weighted least square scheme for compressible flows

The article describes the development of a high order finite volume method for the solution of transonic flow problems. The method is based on a reconstruction procedure similar to the weighted essentially non-oscillatory scheme (WENO). The analysis of accuracy and stability of the method is carried out for the case of smooth data and for simple discontinuity. The computational results demonstrate the performance of the WLSQR method for the solution of several flow problems in 2D and 3D using both structured and unstructured meshes.     

Constructions for chiral polytopes

An abstract polytope of rank n is said to be chiral if its automorphismgroup has two orbits on flags, with adjacent flags lying indifferent orbits. In this paper, we describe a method for constructingfinite chiral n-polytopes, by seeking particular normal subgroupsof the orientation-preserving subgroup of an n-generator Coxetergroup (having the property that the subgroup is not normalizedby any reflection and is therefore not normal in the full Coxetergroup). This technique is used to identify the smallest examplesof chiral 3- and 4-polytopes, in both the self-dual and non-self-dualcases, and then to give the first known examples of finite chiral5-polytopes, again in both the self-dual and non-self-dual cases.     

Semisymmetric graphs from polytopes

Every finite, self-dual, regular (or chiral) 4-polytope of type {3,q,3} has a trivalent 3-transitive (or 2-transitive) medial layer graph. Here, by dropping self-duality, we obtain a construction for semisymmetric trivalent graphs (which are edge- but not vertex-transitive). In particular, the Gray graph arises as the medial layer graph of a certain universal locally toroidal regular 4-polytope.     

Increasing thermoelectric efficiency: a dynamical systems approach

Inspired by the kinetic theory of ergodic gases and chaotic billiards, we propose a simple microscopic mechanism for the increase of thermoelectric efficiency. We consider the cross transport of particles and energy in open classical ergodic billiards. We show that, in the linear response regime, where we find exact expressions for all transport coefficients, the thermoelectric efficiency of ideal ergodic gases can approach the Carnot efficiency for sufficiently complex charge carrier molecules. Our results are clearly demonstrated with a simple numerical simulation of a Lorentz gas of particles with internal rotational degrees of freedom.