Novel Green Procedure for the Synthesis of 2-Arylbenzothiazoles Under Microwave Irradiation in Peg 200 Or Peg 400

An improved green procedure for the synthesis of 2-aryl- and 2-hetarylbenzothiazoles by condensation of equivalent amounts of 2,2′-diaminodiphenyldisulfides or 2-aminothiophenols and various aromatic aldehydes in PEG 200/400 under microwave irradiation has been developed. This method allows the synthesis of 2-arylbenzothiazoles in high yields and with high purity regardless of the state of the starting compounds (liquid or solid) or the nature of the substituents in the aromatic ring.     

Stress–strain relations in finite viscoelastoplasticity of rigid-rod networks: applications to the Mullins effect

Received December 12, 2000 / Published online: June 1, 2001     

Mechanochemical and Size Reduction Machines for Biorefining

In recent years, we have witnessed an increasing interest in the application of mechanochemical methods for processing materials in biomass refining techniques. Grinding and mechanical pretreatment are very popular methods utilized to enhance the reactivity of polymers and plant raw materials; however, the choice of devices and their modes of action is often performed through trial and error. An inadequate choice of equipment often results in inefficient grinding, low reactivity of the product, excess energy expenditure, and significant wear of the equipment. In the present review, modern equipment employing various types of mechanical impacts, which show the highest promise for mechanochemical pretreatment of plant raw materials, is examined and compared—disc mills, attritors and bead mills, ball mills, planetary mills, vibration and vibrocentrifugal mills, roller and centrifugal roller mills, extruders, hammer mills, knife mills, pin mills, disintegrators, and jet mills. The properly chosen type of mechanochemical activation (and equipment) allows an energetically and economically sound enhancement of the reactivity of solid-phase polymers by increasing the effective surface area accessible to reagents, reducing the amount of crystalline regions and the diffusion coefficient, disordering the supramolecular structure of the material, and mechanochemically reacting with the target substances.     

Floating boundary particle swarm optimization algorithm

A new modification to the particle swarm optimization (PSO) algorithm is proposed aiming to make the algorithm less sensitive to selection of the initial search domain. To achieve this goal, we release the boundaries of the search domain and enable each boundary to drift independently, guided by the number of collisions with particles involved in the optimization process. The gradual modification of the active search domain range enables us to prevent particles from revisiting less promising regions of the search domain and also to explore the areas located outside the initial search domain. With time, the search domain shrinks around a region holding a global extremum. This helps improve the quality of the final solution obtained. It also makes the algorithm less sensitive to initial choice of the search domain ranges. The effectiveness of the proposed Floating Boundary PSO (FBPSO) is demonstrated using a set of standard test functions. To control the performance of the algorithm, new parameters are introduced. Their optimal values are determined through numerical examples.     

Radical Stability Directs Electron Capture and Transfer Dissociation of β‐Amino Acids in Peptides

We report on the characteristics of the radical‐ion‐driven dissociation of a diverse array of β‐amino acids incorporated into α‐peptides, as probed by tandem electron‐capture and electron‐transfer dissociation (ECD/ETD) mass spectrometry. The reported results demonstrate a stronger ECD/ETD dependence on the nature of the amino acid side chain for β‐amino acids than for their α‐form counterparts. In particular, only aromatic (e.g., β‐Phe), and to a substantially lower extent, carbonyl‐containing (e.g., β‐Glu and β‐Gln) amino acid side chains, lead to N? C_β bond cleavage in the corresponding β‐amino acids. We conclude that radical stabilization must be provided by the side chain to enable the radical‐driven fragmentation from the nearby backbone carbonyl carbon to proceed. In contrast with the cleavage of backbones derived from α‐amino acids, ECD of peptides composed mainly of β‐amino acids reveals a shift in cleavage priority from the N? C_β to the C_α? C bond. The incorporation of CH₂ groups into the peptide backbone may thus drastically influence the backbone charge solvation preference. The characteristics of radical‐driven β‐amino acid dissociation described herein are of particular importance to methods development, applications in peptide sequencing, and peptide and protein modification (e.g., deamidation and isomerization) analysis in life science research.     

Approximation of the Fraunhofer diffraction peak, produced by particles of arbitrary shape

A simple analytical formula is developed to describe light diffraction by chaotically oriented particles of arbitrary shape. The formula expresses the angular pattern through three well-defined microphysical characteristics of an ensemble: the average cross-sectional area, the average area squared, and the average length of the contour bordering the particle projection.     

The similarity problem for J-nonnegative Sturm-Liouville operators

Sufficient conditions for the similarity of the operator with an indefinite weight r(x)=(sgnx)|r(x)| are obtained. These conditions are formulated in terms of Titchmarsh-Weyl m-coefficients. Sufficient conditions for the regularity of the critical points 0 and ∞ of J-nonnegative Sturm-Liouville operators are also obtained. This result is exploited to prove the regularity of 0 for various classes of Sturm-Liouville operators. This implies the similarity of the considered operators to self-adjoint ones. In particular, in the case r(x)=sgnx and , we prove that A is similar to a self-adjoint operator if and only if A is J-nonnegative. The latter condition on q is sharp, i.e., we construct such that A is J-nonnegative with the singular critical point 0. Hence A is not similar to a self-adjoint operator. For periodic and infinite-zone potentials, we show that J-positivity is sufficient for the similarity of A to a self-adjoint operator. In the case q≡0, we prove the regularity of the critical point 0 for a wide class of weights r. This yields new results for “forward-backward” diffusion equations.     

Metabolic activation of chemicals: in-silico simulation

The role of metabolism in prioritising chemicals according to their potential adverse health effects is extremely important given the fact that innocuous parents can be transformed into toxic metabolites. Our recent efforts in simulating metabolic activation of chemicals are reviewed in this work. The application of metabolic simulators to predict biodegradation (microbial degradation pathways), bioaccumulation (fish liver metabolism), skin sensitisation (skin metabolism), mutagenicity (rat liver S-9 metabolism) are discussed. The ability of OASIS approach to predict metabolism (toxicokinetics) and toxicity (toxicodynamics) of chemicals resulting from their metabolic activation in a single modelling platform is an important advantage of the method. It allows prioritisation of chemicals due to predicted toxicity of their metabolites.