Selenoproteins: the key factor in selenium essentiality. State of the art analytical techniques for selenoprotein studies

Selenium is an essential element for human health. The benefits of selenium are many including protection against cancer, heart diseases and other cardiovascular and muscle disorders. Selenium is also helpful in controlling gastrointestinal disorders, enhancing immunity of the human body and reducing age-related diseases. The health-promoting properties of Se are due to vital functions of selenoproteins in which selenium is present as selenocysteine, the 21st amino acid. To date, dozens of selenoprotein families have been described though many have roles that have not been fully elucidated. Selenoproteins research has attracted tremendous interest from different scientific areas. Analytical chemists have not remained indifferent to the attractive features of these unique proteins. Different analytical techniques, such as multidimensional chromatography–inductively coupled plasma mass spectrometry (ICPMS), electrospray (tandem) mass spectrometry (ESI-MS/MS), matrix-assisted laser desorption ionization time-of flight (MALDI-TOF) and sodium dodecyl sulphate polyacrylamide gel electrophoresis–laser ablation inductively coupled plasma mass spectrometry (SDS-PAGE-LA-ICPMS), have been applied to the determination of selenoproteins and selenium-containing proteins. This review describes the best-characterized selenoproteins to date in addition to the major contributions of analytical chemistry to the field of selenoproteins. The article also highlights the challenges of combining elemental and molecular mass spectrometry for the determination of selenoproteins and selenium-containing proteins.     

Fundamental Gaps in Numerical Semigroups with Respect to Their Multiplicity

For a numerical semigroup, we introduce the concept of a fundamental gap with respect to the multiplicity of the semigroup. The semigroup is fully determined by its multiplicity and these gaps.We study the case when a set of non-negative integers is the set of fundamental gaps with respect to the multiplicity of a numerical semigroup, Numerical semigroups with maximum and minimum number of this kind of gaps are described.     

The Rigged Hilbert Space of the Free Hamiltonian

We explicitly construct the Rigged Hilbert Space (RHS) of the free Hamiltonian H ₀. The construction of the RHS of H ₀ provides yet another opportunity to see that when continuous spectrum is present, the solutions of the Schrödinger equation lie in a RHS rather than just in a Hilbert space.     

Use of C-18 reverse-phase cartridges for estimation of metal complexation by a residue from olive oil industry

 Formation of complexes between Cu and organic polymers present in olive mill wastewater (OMW) is shown to be a cause of metal solubilization by the residue, using C-18 reverse-phase cartridges (RPC) for separating the complexed metal. Nearly 100% of the metal released from a polluted river sediment by OMW solutions is retained by the cartridges. The proportion of Cu retained by the cartridges is somewhat lower (50–80%), if the OMW solution initially contains Cu. About 70–80% of Cu released by OMW from a soil column previously loaded with high doses of metal is also retained by the cartridges. Incomplete Cu retentions are not thought to be due to a lack of efficiency of RPC in immobilizing Cu complexes, but to the formation of an equilibrium between free and complexed forms of the metal. Received: 3 June 1996/Revised: 29 September 1996/Accepted: 10 October 1996     

A method for Lyapunov spectrum estimation using cloned dynamics and its application to the discontinuously-excited FitzHugh–Nagumo model

This work presents a new method to calculate the Lyapunov spectrum of dynamical systems based on the time evolution of initially small disturbed copies (“clones”) of the motion equations. In this approach, it is not necessary to construct the tangent space associated with the time evolution of linearized versions of motion equations, being the Lyapunov exponents directly estimated in terms of the rate of convergence or divergence of these disturbed clones with respect to the fiducial trajectory, there being periodic correction via the Gram–Schmidt Reorthonormalization procedure. The proposed method offers the possibility of partial estimation of the Lyapunov spectrum and can also be applied to nonsmooth dynamics, since the linearization procedure is no longer required. The idea is tested for representative continuous- and discrete-time dynamical systems and validated by means of comparison with the classical method to perform this calculation. To illustrate its applicability in the nonsmooth context, the largest Lyapunov exponent of the FitzHugh–Nagumo neuronal model under discontinuous periodic excitation is calculated taking the amplitude of stimulation as control parameter. This analysis reveals some complex behaviours for this simple neuronal model, which motivates relevant discussions about the possible role of chaos in the cognitive process.     

The Oversemigroups of a Numerical Semigroup

Abstract. We study the set of numerical semigroups containing a given numerical semigroup. As an application we prove characterizations of irreducible numerical semigroups that unify some of the existing characterizations for symmetric and pseudo-symmetric numerical semigroups. Finally we describe an algorithm for computing a minimal decomposition of a numerical semigroup in terms of irreducible numerical semigroups.     

Electrocatalytic amperometric determination of amitrole using a cobalt-phthalocyanine-modified carbon paste electrode

Cobalt-phthalocyanine-modified carbon paste electrodes are shown to be excellent indicators for electrocatalytic amperometric measurements of triazolic herbicides such as amitrole, at low oxidation potentials (+0.40 V). The detection and determination of amitrole in flow injection analysis with a modified carbon paste electrode with Co-phthalocyanine is described. The concentrations of amitrole in 0.1 M NaOH solutions were determined using the electrocatalytic oxidation signal corresponding to the Co(II)/Co(III) redox process. A detection limit of 0.04 microg mL(-1) (4 ng amitrole) was obtained for a sample loop of 100 microL at a fixed potential of +0.55 V (vs. Ag/AgCl) in 0.1 M NaOH and a flow rate of 4.0 mL min(-1). Furthermore, the modified carbon paste electrodes offers reproducible responses in such a system, and the relative standard deviation was 3.3% using the same surface, 5.1% using different surface, and 6.9% using different pastes. The performance of the cobalt-phthalocyanine-modified carbon paste electrodes is illustrated here for the determination of amitrole in commercial formulations. The response of the electrodes is stable, with more than 80% of the initial retained activity after 50 min of continuous use.     

Fatty alcohols or fatty acids as niosomal hybrid carrier: effect on vesicle size, encapsulation efficiency and in vitro dye release

Niosomal hybrid mixtures are prepared with bilayer stabilizer cholesterol from non-ionic surfactants span 20 (HLB value 8.6), span 60 (HLB 4.7) and span 85 (HLB 1.8) in presence of dicetyl phosphate (DCP) where fatty acids or fatty alcohols (C14, C16 and C18) are used as carrier. Hybrid mixtures upon hydration with aqueous phosphate buffer (pH 7.4) spontaneously produce vesicular phase which can encapsulate 5(6)-carboxyfluorescein (CF). Effect of fatty alcohols and fatty acids on the vesicle size has been studied by dynamic light scattering (DLS), freeze-fracture scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Release rates of CF from vesicular suspensions are found to be dependent on carriers as well as surfactants used. Fatty acid coated hybrids form large multilamellar vesicles (LMV) (size range 10-15 microm) where as fatty alcohol coated hybrid systems form small multilamellar vesicles (SMV) with an average diameter of 400 nm, in all cases vesicles are polydisperse (PI approximately 0.9) in nature.     

Stability study of As(III), As(V), MMA and DMA by anion exchange chromatography and HG-AFS in wastewater samples

The stability of arsenic species (arsenate [As(V)], monomethylarsonate [MMA], dimethylarsinate [DMA] and arsenite [As(III)]) in two types of urban wastewater samples (raw and treated) was evaluated. Water samples containing a mixture of the different arsenic species were stored in the absence of light at three different temperatures: +4 degrees C, +20 degrees C and +40 degrees C. At regular time intervals, arsenic species were determined by high performance liquid chromatography (HPLC)-hydride generation (HG)-atomic fluorescence spectrometry (AFS). The experimental conditions for the separation of arsenic species by HPLC and their determination by AFS were directly optimised from wastewater samples. As(III), As(V), MMA and DMA were separated on an anion exchange column using phosphate buffer (pH 6.0) as the mobile phase. Under these conditions the four arsenic species were separated in less than 10 min. The detection limits were 0.6, 0.9, 0.9 and 1.8 micro g L(-1) for As(III), DMA, MMA and As(V), respectively. As(V), MMA and DMA were found stable in the two types of urban wastewater samples over the 4-month period at the three different temperatures tested, while the concentration of As(III) in raw wastewater sample decreased after 2 weeks of storage. A greater stability of As(III) was found in the treated urban wastewater sample. As(III) remained unaltered in this matrix at pH 7.27 over the period studied, while at lower pH (1.6) losses of As(III) were detected after 1 month of storage. The results show that the decrease in As(III) concentration with time was accompanied by an increase in As(V) concentration.     

Regarding the validity of the time-dependent Kohn-Sham approach for electron-nuclear dynamics via trajectory surface hopping

The implementation of fewest-switches surface-hopping (FSSH) within time-dependent Kohn-Sham (TDKS) theory [Phys. Rev. Lett. 95, 163001 (2005)] has allowed us to study successfully excited state dynamics involving many electronic states in a variety of molecular and nanoscale systems, including chromophore-semiconductor interfaces, semiconductor and metallic quantum dots, carbon nanotubes and graphene nanoribbons, etc. At the same time, a concern has been raised that the KS orbital basis used in the calculation provides only approximate potential energy surfaces [J. Chem. Phys. 125, 014110 (2006)]. While this approximation does exist in our method, we show here that FSSH-TDKS is a viable option for computationally efficient calculations in large systems with straightforward excited state dynamics. We demonstrate that the potential energy surfaces and nonadiabatic transition probabilities obtained within the TDKS and linear response (LR) time-dependent density functional theories (TDDFT) agree semiquantitatively for three different systems, including an organic chromophore ligating a transition metal, a quantum dot, and a small molecule. Further, in the latter case the FSSH-TDKS procedure generates results that are in line with FSSH implemented within LR-TDDFT. The FSSH-TDKS approach is successful for several reasons. First, single-particle KS excitations often give a good representation of LR excitations. In this regard, DFT compares favorably with the Hartree-Fock theory, for which LR excitations are typically combinations of multiple single-particle excitations. Second, the majority of the FSSH-TDKS applications have been performed with large systems involving simple excitations types. Excitation of a single electron in such systems creates a relatively small perturbation to the total electron density summed over all electrons, and it has a small effect on the nuclear dynamics compared, for instance, with thermal nuclear fluctuations. In such cases an additional, classical-path approximation can be made. Third, typical observables measured in time-resolved experiments involve averaging over many initial conditions. Such averaging tends to cancel out random errors that may be encountered in individual simulated trajectories. Finally, if the flow of energy between electronic and nuclear subsystems is insignificant, the ad hoc FSSH procedure is not required, and a straightforward mean-field, Ehrenfest approach is sufficient. Then, the KS representation provides rigorously a convenient and efficient basis for numerically solving the TDDFT equations of motion.