Specificity of substrate recognition by Pseudomonas fluorescens N3 dioxygenase. The role of the oxidation potential and molecular geometry

Pseudomonas fluorescens N3 is able to grow on naphthalene as the sole carbon and energy source. The mutant TTC1, blocked at the dihydrodiol dehydrogenase level, which can transform the hydrocarbon into the corresponding dihydrodiol, has been used to produce bioconversion products. To rationalize the different grades of conversion obtained with different substrates, a study was performed using non-naphthalene derivatives, including benzenes, conjugated benzenes, and polycyclic aromatic hydrocarbons. The corresponding diols obtained by bioconversion have been isolated and characterized. A theoretical model that considers both energy and geometry factors has been proposed to rationalize the experimental data. Good agreement has been found between the calculated values and the experimental results.     

Examination of a Structural Model of Peptidomimicry by Cyclic Acyldepsipeptide Antibiotics in Their Interaction with the ClpP Peptidase

The cyclic acyldepsipeptide (ADEP) antibiotics act by binding the ClpP peptidase and dysregulating its activity. Their exocyclic N‐acylphenylalanine is thought to structurally mimic the ClpP‐binding, (I/L)GF tripeptide loop of the peptidase's accessory ATPases. We found that ADEP analogues with exocyclic N‐acyl tripeptides or dipeptides resembling the (I/L)GF motif were weak ClpP activators and had no bioactivity. In contrast, ADEP analogues possessing difluorophenylalanine N‐capped with methyl‐branched acyl groups—like the side chains of residues in the (I/L)GF motifs—were superior to the parent ADEP with respect to both ClpP activation and bioactivity. We contend that the ADEP's N‐acylphenylalanine moiety is not simply a stand‐in for the ATPases' (I/L)GF motif; it likely has physicochemical properties that are better suited for ClpP binding. Further, our finding that the methyl‐branching on the acyl group of the ADEPs improves activity opens new avenues for optimization.     

Variables Applicable to Benchmarking of Tap-Hole Life-Cycle Management Practices in Coke-Bed-Based Ferroalloy Production

Benchmarking is a tool available to furnace operators to evaluate their tap-hole life-cycle management practices against those of their peers. It allows furnace operators to challenge their own practices in order to increase furnace utilization. To facilitate the benchmarking process, it is necessary to define the variables to be considered and how they relate to one another. This article develops, from the literature and industry interviews, a holistic conceptualization of the variables that form part of tap-hole lifecycle management and performance. Specifically, the article focuses on the variables related to coke-bed-based processes (FeCr, SiMn, and HCFeMn) applying SAF technology of circular design.     

Sequential linear programming and particle swarm optimization for the optimization of energy districts

This article deals with the optimization of energy resource management of industrial districts, with the aim of minimizing customer energy expenses. A model of the district is employed, whose optimization gives rise to a nonlinear constrained optimization problem. Here the focus is on its numerical solution. Two different methods are considered: a sequential linear programming method and a particle swarm optimization method. Efficient implementations of both approaches are devised and the results of the tests performed on several energetic districts are reported, including a real case study.     

Reversible crosslinks in cotton modified with N-hydroxymethylacetylthioacetamide

The reaction of cotton fabric with N-hydroxymethylacetylthioacetamide (HOCH₂-NHCOCH₂SCOCH₃) yields acetylthioacetamidomethylcellulose, which can be saponified under mild conditions to the corresponding thiol derivative, mercaptoacetamidomethylcellulose. Some reactions of the thiol group are discussed, including oxidation to disulfide, repeated reduction-oxidation cycles, and blocking with alkyl halides. Chemical methods were used in establishing the occurrence and extent of the predicted reactions and their dependence on specific variables in the system. Changes in the crease recovery and tensile strength of the cotton derivative obtained in the reactions were found to be qualitatively consistent with the expected structures. The results of this work show that crosslinks can be obtained reversibly in cotton by this sequence of reactions. Intervening side reactions produce a gradual decrease in the yield of the desired products, however, as the number of cycles increases. Mercaptoacetamidomethylcellulose provides a limited but useful model for the investigation of reversible crosslinks in cellulose.     

Use of a multicomponent reaction for chemoselective derivatization of multiple classes of metabolites

We demonstrate that the Ugi reaction enables chemoselective derivatization of biological amines, carboxylic acids, aldehydes, or ketones with a chromophore under one set of reaction conditions, even in the presence of water. Derivatization of neurotransmitters, hormones, disease biomarkers and other metabolites bodes well for systems biology and diagnostic medicine.     

Electroreduction of volatile organic halides on activated silver cathodes

The electroreduction of polychloromethanes and polychloroethanes has been studied by means of cyclic voltammetry (CV) and preparative electrolysis experiments in acetonitrile (ACN), dimethylformamide (DMF) and their admixtures with water. Silver has been used as cathode material, on account of our extended experience on its well established electrocatalytic activity toward reductive dehalogenation reactions of organic compounds. Polychloro-methanes and -ethanes are common chlorinated solvents pertaining to the large family of volatile organic halides (VOH), whose high toxicity, or even carcinogenicity, demands careful treatment of contaminated soils, drinking waters and gaseous emissions. The results confirm the electrocatalytic role of silver and suggest a general route for the development of appropriate degradation processes.     

A Simple Fragment of Cyclic Acyldepsipeptides Is Necessary and Sufficient for ClpP Activation and Antibacterial Activity

The development of new antibacterial agents, particularly those with unique biological targets, is essential to keep pace with the inevitable emergence of drug resistance in pathogenic bacteria. We identified the minimal structural component of the cyclic acyldepsipeptide (ADEP) antibiotics that exhibits antibacterial activity. We found that N‐acyldifluorophenylalanine fragments function via the same mechanism of action as ADEPs, as evidenced by the requirement of ClpP for the fragments' antibacterial activity, the ability of fragments to activate Bacillus subtilis ClpP in vitro, and the capacity of an N‐acyldifluorophenylalanine affinity matrix to capture ClpP from B. subtilis cell lysates. N‐acyldifluorophenylalanine fragments are much simpler in structure than the full ADEPs and are also highly amenable to structural diversification. Thus, the stage has been set for the development of non‐peptide activators of ClpP that can be used as antibacterial agents.     

Reaction centre accessibility. II. Role of reaction centre congestion in the calculation of reaction centre accessibility

Accessibility to reaction centres is as important as electronic reactivity in determining the success of a reaction. The possibility of its calculation becomes a necessary requisite in the prediction of reaction products. Using a recently proposed approach to the calculation of reaction centre congestion based on a two dimensional representation of molecules, a new system has been realised that can quickly evaluate the desired accessibility. The system is based on the simulation of the steric interaction between reactants in different orientations. The calculation of an interaction energy for each orientation and their combination permits the approximate estimation of the reaction probability for the steric factors concerned. Even though all the operations were performed using a two-dimensional representation the results are encouraging. It is obvious that at this level it is impossible to predict face accessibility preference.     

Role of particle size in visible light photocatalysis of Congo Red using TiO<Subscript>2</Subscript>·[ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>]<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanocomposites

TiO₂·[ZnFe₂O₄] _x (x = 0·0-0·5) nanocomposites (NCs) with an average particle size of 72·4 nm were synthesized by the method of co-precipitation/hydrolysis (CPH). For the comparison of particle-size dependent effects, a set of polycrystalline samples with similar compositions was also prepared by solid state reaction (SSR) route. Average particle size for SSR prepared samples was about 3·0 μm. All the samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer, Raman spectroscopy and Fourier transform infra-red (FTIR) spectroscopy. Their visible light photocatalytic activity was tested for the degradation of Congo Red dye. Maximum photodegradation was observed for the NC with x = 0·1 synthesized by CPH (particle size, 71 nm). Similar composition prepared by SSR method (particle size, 6·19 μm) showed lower photoactivity in comparison even with that observed for pure TiO₂ (particle size, 4·03 μm). It was, therefore, concluded that enhanced photodegradation is directly related to the reduced particle size of the composites, which implies that photosensitization is the process primarily involved. Although, doping of TiO₂ with ZnFe₂O₄ does extend the cut-off wavelength towards visible parts of the spectrum, its contribution in the enhancement is not as significant as that due to the photosensitization.