The Use of PAMAM Dendrimers as a Platform for Laccase Immobilization: Kinetic Characterization of the Enzyme

The kinetic behavior of the enzyme laccase in solution and immobilized onto carbon platforms using poly(amido amine) (PAMAM) dendrimers has been investigated. The results with the immobilized enzymes have demonstrated that almost ten times more enzyme on the carbon support is required for satisfactory kinetic rates to be achieved. Furthermore, the study as a function of the substrate concentration revealed that the kinetic behavior of the enzyme in solution fits the Michaelis?CMenten model. However, when the enzyme is immobilized onto the carbon surface, the catalyzed reaction follows a particular kinetic behavior with apparent positive cooperativity. The highest activity with laccase (in solution or immobilized) is achieved around pH?4.5, and the substrate conversion rate clearly diminishes with rising pH. The optimum temperature lies around 60?°C. The enzyme displays good catalytic activity in a wide range of pH and temperature values. The stability tests evidenced that there is no appreciable reduction in the enzymatic activity after immobilization within the first 30?days. Taking into account both the kinetic and stability tests, one can infer that the use of PAMAM dendrimers seems to be a very attractive approach for the immobilization of enzymes, as well as a feasible and useful methodology for the anchoring of enzymes with potential application in many biotechnological areas.     

Shannon and Fisher entropies for a hydrogen atom under soft spherical confinement

We calculate Shannon and Fisher entropies in the position and momentum space, and some complexity measures for a variationally described hydrogen atom confined in soft and hard spherical boxes of varying dimension $r_c$ and selected values of strength $U_0$. We include calculations for a free particle trapped in impenetrable boxes. It is found that the Shannon entropy $S_r$ becomes negative for small cavity radii and large values of $U_0$, due to the highly localized nature of the particle. For soft confinement and small cavity dimensions, the entropies change very rapidly over short radial intervals.     

The confined helium atom: An information–theoretic approach

In this article, we study the helium atom confined in a spherical impenetrable cavity by using informational measures. We use the Ritz variational method to obtain the energies and wave functions of the confined helium atom as a function of the cavity radius $r_0$. As trial wave functions we use one uncorrelated function and five explicitly correlated basis sets in Hylleraas coordinates with different degrees of electronic correlation. We computed the Shannon entropy, Fisher information, Kullback–Leibler entropy, Tsallis entropy, disequilibrium and Fisher–Shannon complexity, as a function of $r_0$. We found that these entropic measures are sensitive to electronic correlation and can be used to measure it. As expected these entropic measures are less sensitive to electron correlation in the strong confinement regime ( a.u.).     

Analytical challenges in doping control: Comprehensive two-dimensional gas chromatography with time of flight mass spectrometry,a promising option

Doping control screening based on the enhanced resolution of comprehensive two-dimensional (2D) gas chromatography hyphenated to time of flight mass spectrometer was investigated. The identification of anabolic agents (clenbuterol, norandrosterone, epimetendiol, two methyltestosterone metabolites and 3′-hydroxystanozolol) contained in a spiked urine sample (2 ng/ml) was demonstrated. Special emphasis was given to 3′-hydroxystanozolol, mainly considering the difficulty in its detection. In contrast to conventional GC–MS approaches that must use single-ion monitoring, the GC × GC–TOFMS method enabled the identification of that metabolite through the deconvolution of the full mass spectrum and also resolved the co-eluted peaks of 3′-hydroxystanozolol and an endogenous component.     

Quantum gravity at the LHC

We study the production of massless gravitons at the LHC and compare our results to those obtained in extra-dimensional models. The signature in both cases is missing energy plus jets. In case of non-observation, the LHC could be used to put the tightest limit to date on the value of the Planck mass.     

Synthesis and rational design of anti‐inflammatory compounds: N‐phenyl‐cyclohexenyl sulfonamide derivatives

The synthesis of (±)‐ethyl 6‐[N‐(2‐chloro‐4‐fluorophenyl)sulfamoyl]cyclohex‐1‐ene‐1‐carboxylate ( 5n ) has been reproduced from a method previously described and served as the background for the preparation of a nitro derivative, potentially useful as an anti‐inflammatory agent. Furthermore, a structure‐based QSAR analysis of a series of N‐arylsulfamoyl congeners derived a highly predictive model for the activities of novel small‐molecule inhibitors of NO and cytokine production, whose preparation may be successfully achieved according to a similar procedure as above. Copyright © 2009 John Wiley & Sons, Ltd.     

Analytical treatment of synchronization of spin-torque oscillators by microwave magnetic fields

An analytical approach is presented for the study of synchronization effects in spin-transfer-driven nanomagnets subjected to radio-frequency magnetic fields. The conditions are derived and discussed under which the current-induced magnetization precession is synchronized by the radio-frequency field. Exact analytical results are obtained for the case when the problem exhibits uniaxial symmetry around the axis perpendicular to the device plane. It is demonstrated that the magnetization dynamics under nonzero current and nonzero rf field is identical in structure to that under zero current. On this basis, analytical predictions are obtained for: the existence of phase-locking between current-induced magnetization precession and rf field oscillations; the frequency pulling effect in proximity of phase locking; the occurrence of hysteresis effects in phase-locking as a function of the spin-polarized current. The proposed approach is valid for arbitrary rf field amplitude and current intensity.     

Memory effects in the two-level model for glasses

We study an ensemble of two-level systems interacting with a thermal bath. This is a well-known model for glasses. The origin of memory effects in this model is a quasistationary but nonequilibrium state of a single two-level system, which is realized due to a finite-rate cooling and slow thermally activated relaxation. We show that single-particle memory effects, such as negativity of the specific heat under reheating, vanish for a sufficiently disordered ensemble. In contrast, a disordered ensemble displays a collective memory effect [similar to the Kovacs effect], where nonequilibrium features of the ensemble are monitored via a macroscopic observable. An experimental realization of the effect can be used to further assess the consistency of the model.