Repair of Protein Radicals by Antioxidants

In vivo, proteins are the main targets for radicals and other reactive species. Their reactions result in formation of amino acid radicals on the protein surface that often yield tryptophan and tyrosyl radicals or, in the presence of O₂, protein peroxyl radicals and hydroperoxides. All these species may propagate damage to biomolecules. Low molecular weight antioxidants, such as ascorbate, urate, and glutathione, are part of the defense system and function by repairing damaged proteins. We briefly review the existing knowledge about protein and amino acid radicals and their repair by antioxidants, including results of our investigations. The main question addressed is whether the antioxidants ascorbate, urate, and glutathione are able to repair amino acid radicals in model compounds and in proteins in vitro by pulse radiolysis. We show that ascorbate and urate repair tryptophan and tyrosyl radicals efficiently and inhibit proton-coupled electron transfer from tyrosine residues to tryptophan radicals in a number of proteins. In contrast, repair by glutathione is much slower. Ascorbate also rapidly reduces the peroxyl radicals of the N-acetylamide derivatives of glycine, alanine, and proline, whereas glutathione reduces peroxyl radicals in lysozyme. In vivo urate, ascorbate, and glutathione may prevent biological damage or, at least, reduce its rate, because they: (a) repair tryptophan and tyrosyl radicals in proteins and (b) reduce protein peroxyl radicals to the corresponding protein hydroperoxides. Most likely, in vivo, ascorbate and glutathione do not inhibit the reaction of C-centered amino acid radicals with O₂. Glutathione is less efficient that urate and ascorbate in repairing protein radicals; furthermore, the resulting glutathiyl radical is harmful. Ascorbate may be the more important repair agent in cells and tissues characterized by high ascorbate concentrations, such as the lens and brain; urate may be mainly responsible for repair in tissue compartments with higher urate concentrations, such as in plasma and saliva.     

Synthesis and Surface Active Properties of Novel Carbohydrate-based Cationic Surfactants

The synthesis of new cationic carbohydrate surfactants is presented in this paper. The obtained surfactants have structures that are typical for saponins, which contain fatty amide hydrophobic chains and hydrophilic heads with cationic carbohydrate units. Their surface active properties and biodegradability have been studied. For two types, the biodegradability was above 85% and comparable to standard carbohydrate surfactants.     

Secondary ketonization of primary alcohol over LaMn-based mixed oxides with perovskite-like structure

LaMnO₃-based mixed oxides with perovskite-like structure both bulk and supported on La–Al₂O₃, show high catalytic activity in dehydrogenation of n-butanol to an aldehyde, which then undergoes a secondary reaction to produce a symmetrical ketone. Partial substitution of Cu, V or Sr into LaMnO₃ structure does not destroy the perovskite-like structure and enables to control the acid–base surface properties. It allows linking up these qualitative and quantitative features with activity and selectivity of these materials. The degree of n-butanol conversion depends on the total concentration of basic and acidic sites. Selectivity to butyraldehyde can be related with the share of basic sites. Selectivity to dipropyl ketone is affected both by the acidity and concentration of acidic sites. LaMnO₃/La–Al₂O₃ seems to posses an optimum set of surface characteristics for the examined ketonization of a primary alcohol.     

Simulations of passivation phenomena based on discrete lattice gas automata

We present simulation results for a simple lattice gas cellular automata model of passivation. The lattice sites representing the corrosion product are produced at the corroding surface and diffuse executing a random walk. Asymmetric simple exclusion rules of the random walk account for an attractive potential between the corrosion product particles. The particles can aggregate and when sufficiently numerous form a compact phase on the corroding surface. The model predicts a transition from the active to passive state when increasing the reactivity of the surface. The transition is characterized by a sudden increase in the surface coverage of the corrosion product interpreted as a passive layer formation. The layer blocks contact of the metal surface with the environment and reduces the corrosion rate. The model reproduces the known paradox of passivity—the surface must be reactive enough for the layer to form. A further increase in the bare reactivity reduces largely the observed reaction rate. The simulations yield information on the morphological changes of the surface layer before and after the transition. In terms of the corrosion current, the active state is described by the current increase with the polarizing potential according to the Tafel law while in the passive state the current is independent of the anodic potential. Our simple model reproduces principal features of passivation.     

Study to analyze the influence of sprouting of the wheat grain on the grinding process

Several studies have been carried out on the grinding characteristic of three species of common wheat (Triticum aestivum, ssp. vulgare). The three-day germinated kernels were pulverized in a micro hammer mill equipped with a changeable screen. The moisture of samples was 12% (w.b.). The results showed that the sprouting of wheat had a significant influence on the grinding process. The average particle size of the pulverized material obtained from the sprouted kernels was almost always significantly lower than those from the sound kernels. The highest changes were observed in the increase of the fraction of particles below a size of 200 μm, caused by sprouting. The sprouting caused a decrease in the value of specific grinding energy in all cultivars. Based on the parameters of screen openings and cultivar, the values of specific grinding energy ranged from 35.5 to 141.6 kJ kg⁻¹ and from 41.4 to 164.3 kJ kg⁻¹ for the sprouted and sound kernels, respectively. In addition, the other values of grinding energy indices confirmed that sprouting significantly reduced the grinding energy requirements. The average value of the grinding ability index was 3.9 and 4.8 kJ m⁻² for the sprouted and sound wheat, respectively. Whereas, sprouting caused a decrease in the average value of the grinding index from 71.2 to 58.0 kJ kg⁻¹ mm^0.5.     

Direct determination of benzodiazepines in biological fluids by restricted-access solid-phase microextraction

A biocompatible solid-phase microextraction (SPME) fiber was prepared using an alkyl-diol-silica (ADS) restricted-access material as the SPME coating. The ADS-SPME fiber was able to simultaneously fractionate the protein component from a biological sample, while directly extracting several benzodiazepines, overcoming the present disadvantages of direct sampling in biological matrixes by SPME. The fiber was interfaced with an HPLC-UV system, and an isocratic mobile phase was used to desorb, separate, and quantify the extracted compounds. The calculated clonazepam, oxazepam, temazepam, nordazepam, and diazepam detection limits were 600, 750, 333, 100, and 46 ng/mL in urine, respectively. The method was confirmed to be linear over the range of 500-50000 ng/mL with an average linear coefficient (R2) value of 0.9918. The injection repeatability and intraassay precision of the method were evaluated over 10 injections, resulting in a RSD of approximately 6%. The ADS-SPME fiber was robust and simple to use, providing many direct extractions and subsequent determination of benzodiazepines in biological fluids.     

Symmetries, Group Actions, and Entanglement

We address several problems concerning the geometry of the space of Hermitian operators on a finite-dimensional Hilbert space, in particular the geometry of the space of density states and canonical group actions on it. For quantum composite systems we discuss and give examples of entanglement measures.     

Analysis of emptiness (lacunarity) as a measure of the degree of space filling and of the internal structure of a set

The study presents a comparative evaluation of emptiness (lacunarity) in model structures with different types of inhomogeneity of dispersed particle distributions. The research on emptiness (lacunarity) as a measure of the degree of space filling and, at the same time, of the internal characterization of a set has been based on the optimal covering and gliding-box methods.     

Estimating the entropy rate of spike trains via Lempel-Ziv complexity

Normalized Lempel-Ziv complexity, which measures the generation rate of new patterns along a digital sequence, is closely related to such important source properties as entropy and compression ratio, but, in contrast to these, it is a property of individual sequences. In this article, we propose to exploit this concept to estimate (or, at least, to bound from below) the entropy of neural discharges (spike trains). The main advantages of this method include fast convergence of the estimator (as supported by numerical simulation) and the fact that there is no need to know the probability law of the process generating the signal. Furthermore, we present numerical and experimental comparisons of the new method against the standard method based on word frequencies, providing evidence that this new approach is an alternative entropy estimator for binned spike trains.     

Solid-phase microextraction field sampler

To facilitate the use of solid-phase microextraction (SPME) for field sampling, a new field sampler was designed and tested. The sampler was versatile and user-friendly. The SPME fiber can be positioned precisely inside the needle for time-weighted average sampling or exposed completely outside the needle for grab sampling. The needle is protected within a shield at all times, hereby eliminating the risk of operator injury and fiber damage. A replaceable Teflon cap is used to seal the needle to preserve sample integrity. Factors that affect the preservation of sample integrity (sorbent efficiency, temperature, sealing materials) were studied. The use of a highly efficient sorbent for the fiber is recommended as the first choice for the preservation of sample integrity. Teflon was a good material for sealing the fiber needle, had little memory effect, and could be used repeatedly. To address adsorption of high boiling point compounds on fiber needles, several kinds of deactivated needles were evaluated. RSC-2 fiber needles were the more effective. A preliminary field sampling investigation demonstrated the validity of the new SPME device for field applications.