Microbiologic oxidation of isosafrole into piperonal

The biotransformation of isosafrole by Cladosporium sphaerospermum yielded piperonal, which is a compound of great commercial importance in the flavor and fragrance industries. The experiments were performed in 500-mL conical flasks containing 100 mL of Czapek-modified medium in an orbital shaker with controlled agitation and temperature. Spores of C. sphaerospermum were used as inocula, and after 96 h of incubation the substrate was added to the culture. Samples of 2 mL were withdrawn at 24-h intervals and analyzed by gas chromatography, (GC) and/or GC/MS spectroscopy.     

On the microbial reduction of ethyl α-methylacetoacetate

In the present work several microorganisms were screened in the reduction of methyl and ethyl acetoacetates. Good to excellent ees were obtained with up to quantitative substrate conversions. These microorganisms were also tested in the reduction of ethyl α-methylacetoacetate with good des and excellent ees. It was noticed that Kluyveromyces marxianus and Trichoderma harzianum were found to lead to products of opposite configuration with the use of methyl or ethyl acetoacetates, which is a very unusual finding.     

Theoretical study of three-body nonadditive interactions for the H2S-(H2O)2 system

An ab initio SCF MO study of the hydrogen-bonded system formed by an H₂S molecule interacting with two water molecules is presented. The nonadditive contributions to the interaction energies are obtained using the 4-31G basis sets which tend to overestimate the dipole moments of the H₂S and H₂O molecules. Thus possibly too large interactions, including upper-limit values for the nonadditive three-body contributions, were obtained. The nonadditive corrections were found to be comparable in magnitude to the cases of other first-row hydride trimers. On this basis one can infer that they probably do not affect the proton and deuterium exchange in hydrated H₂S (as occurs in the G-S heavy water enrichment process) and that they do not play an important role in the formation of clathrates involving hydrogen sulphide.     

Number theoretic example of scale-free topology inducing self-organized criticality

In this Letter we present a general mechanism by which simple dynamics running on networks become self-organized critical for scale-free topologies. We illustrate this mechanism with a simple arithmetic model of division between integers, the division model. This is the simplest self-organized critical model advanced so far, and in this sense it may help to elucidate the mechanism of self-organization to criticality. Its simplicity allows analytical tractability, characterizing several scaling relations. Furthermore, its mathematical nature brings about interesting connections between statistical physics and number theoretical concepts. We show how this model can be understood as a self-organized stochastic process embedded on a network, where the onset of criticality is induced by the topology.     

Phase diagram of the two-dimensional Ising model with random competing interactions

An Ising model with ferromagnetic nearest-neighbor interactions J₁ (J₁>0) and random next-nearest-neighbor interactions [+J₂ with probability p and −J₂ with probability (1−p); J₂>0] is studied within the framework of an effective-field theory based on the differential-operator technique. The order parameters are calculated, considering finite clusters with n=1,2, and 4 spins, using the standard approximation of neglecting correlations. A phase diagram is obtained in the plane temperature versus p, for the particular case J₁=J₂, showing both superantiferromagnetic (low p) and ferromagnetic (higher values of p) orderings at low temperatures.     

Ferromagnetic phases due to competing short- and long-range interactions in the spin-5/2 and spin-2 Blume–Capel model

We broaden the study of the statistical physics of the spin-S Blume–Capel model with ferromagnetic mean-field interactions J in competition with short-range antiferromagnetic interactions K in a linear chain in the thermodynamic limit. This work is dedicated to the case when S takes the half-integer spin $S=5/2$ and when S assumes the integer value $S=2$. In both cases the phase diagrams exhibit new ferromagnetic phases (for certain values of K) enclosed by branches emerging from the first-order frontiers of the pure ferromagnetic model. For finite temperatures the complex topologies were obtained by numerical minimization of the free energy and some results were confirmed by Monte Carlo simulations.