The structure and thermodynamics of binary microclusters: A Monte Carlo simulation

The Monte Carlo computer simulation technique of classical statistical mechanics is employed to determine the structure and thermodynamics of binary microclusters of Lennard-Jones atoms as a function of cluster size, composition and temperature. Further, amorphous microclusters are prepared by a Monte Carlo quench, and their structural properties are examined. The properties of interest include the internal energy, instantaneous “snapshot” pictures of the microcluster's atomic configuration, and the single-particle and pair distribution functions. The Lennard-Jones potential parameters are chosen to model Ar₁₃, Ar₇Kr₆, Ar₃₆Kr₁₉ and Ar₁₉Kr₃₆, as well as to crudely model the bimetallic clusters of Cu₁₉Ni₃₆, Cu₁₉Ru₃₆ and Cu₁₉Os₃₆. A large variety of interesting features associated with these systems are described.     

Plastics as nuclear track detectors for thermal neutron dosimetry

An attempt is made to determine the response of CR-39 and cellulose nitrate plastic track detectors subjected to thermal neutrons. The α-particles are produced from (n, α) reactions in lithium tetraborate convertor placed in contact with different plastics and are recorded in the detectors. The corrected track density gives a fluence sensitivity and dose sensitivity of the order of 10^?4 tracks per neutron and 10² tracks/cm² mrem respectively. A linear relationship is observed between track density and neutron fluence.     

A combinatorial approach toward the generation of ambiphilic peptide-based inhibitors of protein:geranylgeranyl transferase-1

A combinatorial synthesis of oligopeptide analogues and their evaluation as protein:geranylgeranyl transferase inhibitors is presented. The combinatorial strategy is based on the random mutation, in each new generation, of one of any of the four amino acid building blocks of which the most effective compounds of the previous generation are assembled. In this way, a progressive improvement of the average inhibitory activity was observed until the fifth generation. The most active inhibitors were found to inhibit PGGT-1 in the low micromolar range (IC(50): 3.8-8.1 microM).     

Ultrasound assisted microwave digestion

Simultaneous microwave and ultrasound irradiation is shown as a new technique for digestion of solid and liquid samples suitable for chemical and food analysis. Its application in analytical chemistry has been shown by decreases in digestion time: determination of copper in edible oils and total Kjeldahl nitrogen.     

A practical synthesis of gramicidin s and sugar amino Acid containing analogues

A practical gram-scale and high-yielding synthesis of the antimicrobial peptide gramicidin S is presented. An Fmoc-based solid-phase peptide synthesis protocol is employed for the generation of the linear decapeptide precursor, which is cyclized in solution to afford the target compound. The versatility of our method is demonstrated by the construction of eight gramicidin S analogues (15a-h) having nonproteinogenic sugar amino acid residues (4-7) incorporated in the turn regions.     

Alkylated sugar amino acids: a new entry toward highly functionalized dipeptide isosters

[reaction: see text] Novel highly functionalized dipeptide isosters are synthesized via a diastereoselective alkyl/arylation protocol of a glucose-derived (R)-tert-butanesulfinylimine. One of these novel sugar amino acid derivatives, a D-Ala-Ser/Thr isostere, was applied in a peptide synthesis protocol to afford a cyclic tetramer.     

The structure of a self-assembled calixarene aqua-channel system

The crystal structure of the complex 12.calix-[4]-arene dihydroxyphosphonic acid, 12.propane diammonium, 12.ethanol and 40.water molecules is based on dimeric units of the calix, assembled via trigonal units into a hexameric tube of 15 A radius and 16 A depth, further assemby via spanning propane diammonium cations and ethanol molecules forms a channel (40 A), selectively containing all the water molecules.     

Environmental application of rice straw in energy production and potential adsorption of uranium and heavy metals

The sustainable development of agricultural waste is nowadays a main strategy in producing neutral CO₂ energy and metal removal technologies. In Egypt, large amounts of rice straw are annually burnt in the open air causing severe air pollution that could be directed to co-firing and adsorption technologies. On bench scale, rice straw was positively contributed in a clean and smokeless co-firing process with methanol due to the oxidizing effect of the alcohol. The co-firing temperature control is vital to develop the adsorptive character of the residual ash and to avoid prolonged time needed to improve the physical properties of the rice straw if applied directly as a biosorbent. The consumed methanol in the process ranges from 0.15 to 0.3 liter per each kg of straw depending on its compaction. The grossed heat value from such process may drive steam generator for electricity. The residual ash was subsequently cross-linked in uranium and heavy metals adsorption tests from solutions. The porous texture of the residual ash and the amorphous nature of the silica along with potassium content provide a suitable condition for uranium immobilization especially if phosphorus or vanadium exist. The resulted chemical precipitate is analogues in composition to meta-ankoleite (KUO₂PO₄·3H₂O) or hydrated carnotite (K₂(UO₂)₂V₂O₈)·1-3H₂O respectively. The XRD data of the latter form show an enhancement in crystallinity of the amorphous precipitate with the heated samples.     

On the deformation of linear r-fields

We study the question: For which (r,n) can a linear r-field on the (n-1)-sphere in an n-dimensional real linear space be deformed through a continuous path of linear r-fields into an orthonormal r-field. We provide complete answers for the cases: (r,n)=(2,4),(3,4), and provide several partial results for the cases (r,n)=(2,2m), where m is an even integer satisfying m4. Characterizations of linear r-fields are pivotal in the investigation.