Dynamic Determinants of Quorum Quenching Mechanism Shared among N-terminal Serine Hydrolases

Due to the alarming global crisis of the growing microbial antibiotic resistance, investigation of alternative strategies to combat this issue has gained considerable momentum in the recent decade. A quorum quenching (QQ) process disrupts bacterial communication through so-called quorum sensing that enables bacteria to sense the cell density in the surrounding environment. Due to its indirect mode of action, QQ is believed to exert limited pressure on essential bacterial functions and consequently avoid inducing resistance. Although many enzymes are known to display the QQ activity towards various molecules used for bacterial signaling, the in-depth mechanism of their action is not well understood hampering their possible optimization for such exploitation. In this study, we compare the potential of three members of N-terminal serine hydrolases to degrade N-acyl homoserine lactones--signaling compounds employed by Gram-negative bacteria. Using molecular dynamics simulation of free enzymes and their complexes with two signaling molecules of different lengths, followed by quantum mechanics/molecular mechanics molecular dynamics simulation of their initial catalytic steps, we explored molecular details behind their QQ activities. We observed that all three enzymes were able to degrade bacterial signaling molecules following an analogous reaction mechanism. For the two investigated penicillin G acylases from Escherichia coli (ecPGA) and Achromobacter spp. (aPGA), we confirmed their putative activities experimentally hereby extending the set of known quorum quenching enzymes by these representatives of biotechnologically well-optimized enzymes. Interestingly, we detected enzyme- and substrate-depended differences among the three enzymes caused primarily by the distinct structure and dynamics of acyl-binding cavities. As a consequence, the first reaction step catalyzed by ecPGA with a longer substrate exhibited an elevated energy barrier due to a too shallow acyl-binding site incapable of accomodating this molecule in a required configuration. Conversely, unfavorable energetics on both reaction steps were observed for aPGA in complex with both substrates, conditioned primarily by the increased dynamics of the residues gating the entrance to the acyl-binding cavity. Finally, the energy barriers of the second reaction step catalyzed by Pseudomonas aeruginosa acyl-homoserine lactone acylase with both substrates were higher than in the other two enzymes due to distinct positioning of Arg297β. These discovered dynamic determinants constitute valuable guidance for further research towards designing robust QQ agents capable of selectively controlling the virulence of resistant bacteria species.

Mathematical Study of a Two-Stage Anaerobic Model When the Hydrolysis Is the Limiting Step

A two-step model of the anaerobic digestion process is mathematically and numerically studied. The focus of the paper is put on the hydrolysis and methanogenesis phases when applied to the digestion of waste with a high content of solid matter: existence and stability properties of the equilibrium points are investigated. The hydrolysis step is considered a limiting step in this process using the Contois growth function for the bacteria responsible for the first degradation step. The methanogenesis step being inhibited by the product of the first reaction (which is also the substrate for the second one), and the Haldane growth rate is used for the second reaction step. The operating diagrams with respect to the dilution rate and the input substrate concentrations are established and discussed.

A review on the halodefluorination of aliphatic fluorides

Halodefluorination of alkylfluorides using Group 13 metal halides has been known for quite some time (first reported by Newman in 1938) and is often utilised in its crude stoichiometric form to substitute fluorine with heavier halogens. However, recently halodefluorination has undergone many developments. The reaction can be effected with a range of metal halide sources (including s-block, f-block and p-block metals), and has been developed into a catalytic process. Further, methods for monoselective halodefluorination in polyfluorocarbons have been developed allowing exchange of only a single fluorine with a heavier halogen. The reaction has also found use in cascade processes where the final product may not even contain halide, yet the conversion of fluorine to more reactive halogens is a pivotal reaction step in the cascade. This review provides a summary of the developments in the reaction since its inception until now.

Synthesis and Characterization of an Amphoteric Asphalt Emulsifier

A novel amphoteric asphalt emulsifier of octadecylbis(propanamide)-(3’-sodium phosphate-2’-hydroxypropyl)ammonium chloride was synthesised from the raw materials octadecylamine, acrylamide, epichlorohydrin and sodium dihydrogen phosphate. The tertiary amine octadecyl-bis(propanamide) was synthesised from octadecylamine and acrylamide (step 1). Sodium 3-chloro-2-hydroxypropyl phosphate (intermediate) was obtained from epichlorohydrin and sodium dihydrogen phosphate (step 2). The asphalt emulsifier was obtained from octadecyl-bis(propanamide)-tertiary amine and the intermediate by quaternisation reaction (step 3). The yield of the final product reached 94.90%. The structure was identified by FTIR, 1H-NMR and elemental analysis. The critical micelle concentration of the product is 1.46 × 10–5 mol L–1. The surface tension at CMC is 37.78 mN ν–1. The saturated adsorption amount of asphalt emulsifier is 2.72 × 10–3 mmol ν–2. The occupied area per asphalt emulsifier molecule at CMC is 0.611 nm2 mol–1. The surfactant is a fast-setting asphalt emulsifier.

Supported TiO2 in Ceramic Materials for the Photocatalytic Degradation of Contaminants of Emerging Concern in Liquid Effluents: A Review

The application of TiO2 as a slurry catalyst for the degradation of contaminants of emerging concern (CEC) in liquid effluents has some drawbacks due to the difficulties in the catalyst reutilization. Thus, sophisticated and expensive separation methods are required after the reaction step. Alternatively, several types of materials have been used to support powder catalysts, so that fixed or fluidized bed reactors may be used. In this context, the objective of this work is to systematize and analyze the results of research inherent to the application of ceramic materials as support of TiO2 in the photocatalytic CEC removal from liquid effluents. Firstly, an overview is given about the treatment processes able to degrade CEC. In particular, the photocatalysts supported in ceramic materials are analyzed, namely the immobilization techniques applied to support TiO2 in these materials. Finally, a critical review of the literature dedicated to photocatalysis with supported TiO2 is presented, where the performance of the catalyst is considered as well as the main drivers and barriers for implementing this process. A focal point in the future is to investigate the possibility of depurating effluents and promote water reuse in safe conditions, and the supported TiO2 in ceramic materials may play a role in this scope.

Investigation of Substitution Reactions Between Zinc(II) Complexes with Different Geometries and N-bonding Nucleophiles

Aims: Investigation of interactions between zinc(II) complexes with different geometrical structures and relevant nitrogen donor nucleophiles at physiological pH. Background: The lack of clear distinction between the therapeutic and toxic doses of platinum drugs is a major challenge for the design of novel non-platinum DNA and protein targeting metal-based anticancer agents. The non-platinum antitumor complexes could be alternatives to platinum-based drugs due to their better characteristics and different mechanism of action. Objective This study could provide more information for the design of future zinc-based anticancer drugs, as well as providing a better understanding of the mechanism of interactions between Zn(II) complexes and nitrogen-donor nucleophiles (important from a medical point of view) and clarifies the changes in geometrical structures of zinc(II) that are referred to structure-reactivity correlation Methods Mole-ratio method and UV-Vis spectroscopic kinetic method were applied in this study. Objective : This study could provide more information for the design of future zinc-based anticancer drugs, as well as providing a better understanding of the mechanism of interactions between Zn(II) complexes and nitrogen-donor nucleophiles (important from a medical point of view) and clarifies the changes in geometrical structures of zinc(II) that are referred to structure-reactivity correlation Methods Mole-ratio method and UV-Vis spectroscopic kinetic method were applied in this study. Result: The results indicated additional coordination of chlorides in the first coordination sphere with changes in coordination geometry and formation of the octahedral complex anion [ZnCl4(en)]2- while an excess of chloride didn’t affect the square-pyramidal structure of [ZnCl2(terpy)]. The substitutions of studied complexes and relevant nucleophiles proceed in two consecutive reaction steps that depend on the nucleophile concentration. Octahedral complex anion [ZnCl4(en)]2- forms rapidly, and all substitution processes of this complex species should be considered. We assume that the first reaction step is accompanied by the dissociation of chloride ligands. Nucleophile 1,2,4-triazole have shown the highest affinity toward [ZnCl2(en)], and rates of both steps are almost the same value, which indicates parallel reactions. Conclusion: The different order of reactivity of relevant N-donor ligands toward [ZnCl2(en)] and [ZnCl2(terpy)] complexes for the first reaction step occurred due to the influence of different geometrical structures of complexes. In contrast, low reaction rates for the second reactions of [ZnCl2(en)] complex with imidazole and pyrazine were a consequence of interconversion between octahedral and tetrahedral structure during substitution processes.

Spray Flame Synthesis (SFS) of Lithium Lanthanum Zirconate (LLZO) Solid Electrolyte

A spray-flame reaction step followed by a short 1-h sintering step under O2 atmosphere was used to synthesize nanocrystalline cubic Al-doped Li7La3Zr2O12 (LLZO). The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline La2Zr2O7 (LZO) pyrochlore phase while Li was present on the nanoparticles’ surface as amorphous carbonate. However, a short annealing step was sufficient to obtain phase pure cubic LLZO. To investigate whether the initial mixing of all cations is mandatory for synthesizing nanoparticulate cubic LLZO, we also synthesized Li free LZO and subsequently added different solid Li precursors before the annealing step. The resulting materials were all tetragonal LLZO (I41/acd) instead of the intended cubic phase, suggesting that an intimate intermixing of the Li precursor during the spray-flame synthesis is mandatory to form a nanoscale product. Based on these results, we propose a model to describe the spray-flame based synthesis process, considering the precipitation of LZO and the subsequent condensation of lithium carbonate on the particles’ surface.

Synthesis of biologically active heterocycles by domino reactions with SN2/Thorpe-Ziegler reaction step.

The review includes methods for the synthesis of five- and six-membered heterocycles and their annulated analogs. These methods are based on anionic domino reactions, which have a common step - SN2/Thorpe-Ziegler reaction. Data on the biological activity of these heterocycles are summarized.

Passion fruit seed oil: extraction and subsequent transesterification reaction

This work aims to remove the oil from passion fruit seeds using ethanol as solvent and then to carry out the transesterification of the product from the extraction step (oil + ethanol). The effects of operational variables in the ultrasound-assisted extraction (UAE) were evaluated and traditional extraction was performed for comparison. The extraction product was directed to the reaction step using an enzymatic catalyst. UAE provided oil yield from 12.32 to 21.76%, and the maximum value (73.7% of the traditional extraction yield) was obtained at 60 °C and 50 min using a solvent-to-seed ratio of 4. Oil removal was favored by increases in the investigated variables. g-tocopherol, δ-tocopherol and a high concentration of polyunsaturated fatty acids were identified in the oils. The oil obtained by UAE presented higher phytosterol contents. From the reaction step, samples were obtained with higher concentrations of ethyl esters, in addition to emulsifiers (diglycerides and monoglycerides).