Antibacterial and cytotoxic activities of the sesquiterpene lactones cnicin and onopordopicrin

The antimicrobial and cytotoxic activities of chloroform extracts from the weeds Centaurea tweediei and C. diffusa, and the main sesquiterpene lactones isolated from these species, onopordopicrin and cnicin, respectively, were assayed. Results show that the chloroform extracts from both Centaurea species possess antibacterial activities against a panel of Gram-positive and Gram-negative bacteria. Remarkable antibacterial activity against methicillin-resistant Staphylococcus aureus was also measured. Both the extracts and the purified sesquiterpene lactones show high cytotoxicity against human-derived macrophages. Despite this cytotoxicity, C. diffusa chloroform extract and cnicin are attractive candidates for evaluation as antibiotics in topical preparations against skin-associated pathogens.     

Modeling the cohesive energy and melting point of nanoparticles by their average coordination number

We present a relation between the average coordination number and the cohesive energy for nanoparticles that shows that the ratio of nanoparticles cohesive energy to the bulk value is equal to the ratio of the nanoparticles average coordination number to that of the bulk. We consider the effect of lattice and surface packing factors on the average coordination numbers of the atoms in the nanoparticle. The melting temperature of nanoparticles has been calculated from the obtained relation for cohesive energy, and predictions for the cohesive energy and melting temperature of the nanoparticles have been compared with other theoretical models and available experimental data and the results of molecular dynamics simulations.     

Modeling size dependence of melting temperature of metallic nanoparticles

A model has been developed to account for the dependence of melting temperature of nanoparticles on their size, shape and lattice type. This model is consistent with reported experimental data and shows better consistency than the liquid drop and bond energy model. A general equation is proposed which correlates with the bond energy model formula and has high potential for application in research and development. The model also leads to an equation showing the limiting size for nanoparticles.     

Synthesis of N-Vinylpyrazoles

A method is proposed for the alkylation of pyrazoles with dichloroethane in water in the presence of the phase-transfer catalyst benzyltriethylammonium chloride (TEBAC). It was shown that dehydrochlorination of the corresponding N-(β-chloroethyl)pyrazoles in water under conditions of phase-transfer catalysis proceeds smoothly with the formation of N-vinylpyrazoles in 80–90% yield.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 533–536, April, 2005.     

Melting entropy of nanocrystals: an approach from statistical physics

Considering size effect on the equations obtained from statistical mechanical theories for the entropy of crystal and liquid phases, a new model has been developed for the melting entropy of nanocrystals, including the effects of the quasi-harmonic, anharmonic and electronic components of the overall melting entropy. Then with the use of our suggested new proportionality between the melting point and the entropy temperature (θ(0)), the melting entropy of nanocrystals has been obtained in terms of their melting point. Moreover, for the first time, the size-dependency of the electronic component of the overall melting entropy, arising from the change in the electronic ground-state of the nanocrystal upon melting, has been taken into account to calculate the melting entropy of nanocrystals. Through neglecting the effect of the electronic component, the present model can corroborate the previous model for size-dependent melting entropy of crystals represented by Jiang and Shi. The present model has been validated by the available computer simulation results for Ag and V nanoparticles. Moreover, a fairly constant function has been introduced which couples the melting temperature, the entropy temperature and the atomic density of elements to each other.     

Subset selection for parameter estimation in an HIV model

This paper discusses methodologies for subset selection for nonlinear least squares parameter estimation. In particular, we will present approaches for partitioning the parameter space into well-conditioned and ill-conditioned subsets. The algorithms are applied to a simplified mathematical model of the physiologic response of the human immunodeficiency virus (HIV) in humans. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)