System of mobile agents to model social networks

We propose a model of mobile agents to construct social networks, based on a system of moving particles by keeping track of the collisions during their permanence in the system. We reproduce not only the degree distribution, clustering coefficient, and shortest path length of a large database of empirical friendship networks recently collected, but also some features related with their community structure. The model is completely characterized by the collision rate, and above a critical collision rate we find the emergence of a giant cluster in the universality class of two-dimensional percolation. Moreover, we propose possible schemes to reproduce other networks of particular social contacts, namely, sexual contacts.     

A database-centric virtual chemistry system

We describe an Oracle database application for general use within virtual chemistry. The application functions as a central hub and repository for chemical data with interfaces to external calculators. It deals with the general problems of merging data from disparate sources and with scheduling of computational tasks for parallel or sequential execution in a mixed environment. The central database is used for the storage of input, intermediary, and final data as well as for job control. A calculation job is split into distinct tasks, or units of work, which are put in a queue. Tasks are dequeued and handled by specialized calculators. These calculators are in-house or commercial programs for which adaptor modules for connection to the database must be written. Tasks are handled in a transactional fashion, so that uncompleted or failed tasks are left in the queue. This makes the system stable to many types of disturbances. Sorting, filtering, and merging operations are handled by the database itself. Usage is very general, but some specific examples are (1) as a back end for a chemical property calculator Web page, (2) in an automated quantitative structure-activity relationship system, and (3) in virtual screens.     

Kinetic effects of hydrogen bonds on proton-coupled electron transfer from phenols

The kinetics and mechanism of proton-coupled electron transfer (PCET) from a series of phenols to a laser flash generated [Ru(bpy)(3)](3+) oxidant in aqueous solution was investigated. The reaction followed a concerted electron-proton transfer mechanism (CEP), both for the substituted phenols with an intramolecular hydrogen bond to a carboxylate group and for those where the proton was directly transferred to water. Without internal hydrogen bonds the concerted mechanism gave a characteristic pH-dependent rate for the phenol form that followed a Marcus free energy dependence, first reported for an intramolecular PCET in Sj?din, M. et al. J. Am. Chem. Soc. 2000, 122, 3932-3962 and now demonstrated also for a bimolecular oxidation of unsubstituted phenol. With internal hydrogen bonds instead, the rate was no longer pH-dependent, because the proton was transferred to the carboxylate base. The results suggest that while a concerted reaction has a relatively high reorganization energy (lambda), this may be significantly reduced by the hydrogen bonds, allowing for a lower barrier reaction path. It is further suggested that this is a general mechanism by which proton-coupled electron transfer in radical enzymes and model complexes may be promoted by hydrogen bonding. This is different from, and possibly in addition to, the generally suggested effect of hydrogen bonds on PCET in enhancing the proton vibrational wave function overlap between the reactant and donor states. In addition we demonstrate how the mechanism for phenol oxidation changes from a stepwise electron transfer-proton transfer with a stronger oxidant to a CEP with a weaker oxidant, for the same series of phenols. The hydrogen bonded CEP reaction may thus allow for a low energy barrier path that can operate efficiently at low driving forces, which is ideal for PCET reactions in biological systems.     

Amino-functionalization of large-pore mesoscopically ordered silica by a one-step hyperbranching polymerization of a surface-grown polyethyleneimine

A simple method for surface functionalization of large-pore mesoporous silica by hyperbranching polymerization resulting in a high loading of amine groups is presented.     

Efficient and selective sulfoxidation by hydrogen peroxide, using a recyclable flavin--[BMIm]PF6 catalytic system

A new flavin catalyst 2 immobilized in an ionic liquid ([BMIm]PF6) was used for the highly selective oxidation of sulfides to sulfoxides by hydrogen peroxide. The sulfoxides were obtained in good to high yields and high selectivity without any detectable overoxidation to sulfone. The catalyst in the ionic liquid was recycled up to seven times without loss of activity or selectivity.     

Developmental trajectory of the endocannabinoid system in human dorsolateral prefrontal cortex

ABSTRACT: BACKGROUND: Endocannabinoids provide control over cortical neurotransmission. We investigated the developmental expression of key genes in the endocannabinoid system across human postnatal life and determined whether they correspond to the development of markers for inhibitory interneurons, which shape cortical development. We used microarray with qPCR validation and in situ hybridisation to quantify mRNA for the central endocannabinoid receptor CB1R, endocannabinoid synthetic enzymes (DAGLalpha for 2-arachidonylglycerol [2- AG] and NAPE-PLD for anandamide), and inactivating enzymes (MGL and ABHD6 for 2- AG and FAAH for anandamide) in human dorsolateral prefrontal cortex (39 days - 49 years). RESULTS: CB1R mRNA decreases until adulthood, particularly in layer II, after peaking between neonates and toddlers. DAGLalpha mRNA expression is lowest in early life and adulthood, peaking between school age and young adulthood. MGL expression declines after peaking in infancy, while ABHD6 increases from neonatal age. NAPE-PLD and FAAH expression increase steadily after infancy, peaking in adulthood. CONCLUSIONS: Stronger endocannabinoid regulation of presynaptic neurotransmission in both supragranular and infragranular cortical layers as indexed through higher CB1R mRNA may occur within the first few years of human life. After adolescence, higher mRNA levels of the anandamide synthetic and inactivating enzymes NAPE-PLD and FAAH suggest that a late developmental switch may occur where anandamide is more strongly regulated after adolescence than earlier in life. Thus, expression of key genes in the endocannabinoid system changes with maturation of cortical function.     

ChemInform Abstract: Comparison of the Bulk and Surface Properties of Ceria and Zirconia by ab initio Investigations.

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