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A new method for detoxification of hydrophilic chloroorganic pollutants in effluent water was developed, using a combination of ultrasound waves, electrochemistry and Fenton''s reagent. The advantages of the method are exemplified using two target compounds: the common herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and its derivative 2,4-dichlorophenol (2,4-DCP). The high degradation power of this process is due to the large production of oxidizing hydroxyl radicals and high mass transfer due to sonication. Application of this sono-electrochemical Fenton process (SEF) treatment (at 20 kHz) with quite a small current density, accomplished almost 50% oxidation of 2,4-D solution (300 ppm, 1.2 mM) in just 60 s. Similar treatments ran for 600 s resulted in practically full degradation of the herbicide; sizable oxidation of 2,4-DCP also occurs. The main intermediate compounds produced in the SEF process were identified. Their kinetic profile was measured and a chemical reaction scheme was suggested. The efficiency of the SEF process is tentatively much higher than the reference degradation methods and the time required for full degradation is considerably shorter. The SEF process maintains high performance up to concentrations which are higher than reference methods. The optimum concentration of Fe2+ ions required for this process was found to be of about 2 mM, which is lower than that in reference techniques. These findings indicate that SEF process may be an effective method for detoxification of environmental water. [Copyright &y& Elsevier]

Ultrasound-based water treatment is often applied for degradation of stable organic pollutants, such as polycyclic aromatic hydrocarbons and halogenated compounds. Monitoring the degradation process, during the application of ultrasound radiation, is of considerable economical interest. In this work, the possibility of performing on-line spectral analysis during sonication was examined and it was found that direct absorption or fluorescence readings are misleading. Optical monitoring is strongly affected by the absorption and scattering of light by cavitation micro-bubbles and ultrasound induced particulates. A model was developed to account for these effects and to allow for on-line fluorescence analysis. The model takes into account the absorption and scattering coefficients of the micro-bubbles and particulates, as well as their time dependent concentration. The model parameters are found from independent measurements where the pollutants are added to already sonicated pure water. Then, the model is tested for predicting the actual fluorescence behavior during the sonication process. It has been shown that the model allows for recovery of the true degradation data, as obtained by off-line HPLC measurements. [Copyright &y& Elsevier]

The time-resolved ion-induced voltages obtained from multiphoton ionization (MPI) in gases were applied, for the first time, together with time-resolved laser-induced fluorescence (TR-LIF) for fast detection of organic compounds in ambient air. The target compounds were polycyclic aromatic hydrocarbons (PAHs) and nitroaromatics. The concepts of the proposed method are presented and examined. It is shown that the MPI signals allow for estimation of the molecular weight, while the fluorescence data supply additional quantitative and qualitative information. A 3D data presentation is suggested for obtaining selectivity. The proposed dimensions are the MPI-based mass estimation, the maximum LIF wavelength and the measured fluorescence lifetime. Since all required data are acquired simultaneously and since the setup can be continuously operated, this analytical concept is suggested for on-line applications. The common air components are not ionized at the selected wavelengths and only the organic pollutants are detected under these conditions. Moreover, it is shown that the resonant MPI mode provides a certain level of selectivity. Therefore, this setup may become the basis of an air sniffer. [Copyright &y& Elsevier]

Examines laser-induced fluorescence (LIF) on perylene in acetonitrile solutions, for different light-scattering and absorbing microparticle matrixes. Description of research methods utilized; Information of experiments conducted; Details on white-colored microparticle suspensions.

The development of rapid methods for the detection of virus particles based on their intrinsic fluorescence (the native auto-fluorescence that originates from the non-labeled analyte) is challenging. Pure viruses may be detected in filtered solutions, based on the strong fluorescence of the amino acid tryptophan (Trp) in their proteins. Nevertheless, Trp also exists in high quantities in the hosts and host cultivation media. In this work, we developed a new method for the detection of the naked φX-174 virus. We show that a separation of φX-174 from its Escherichia coli host (grown on the standard cultivation medium nutrient agar) by simple extraction and filtration is not sufficient for its detection based on the intrinsic fluorescence since ~ 70% of the Trp fluorescence is derived from impurities. We formulate a new cultivation medium with a very low Trp concentration. We apply synchronous fluorescence measurements to show that no Trp fluorescence is detected in the extract solution upon incubation of this medium substrate with ammonium acetate extraction buffer. Finally, we apply synchronous fluorescence to detect φX-174 based on the spectral fingerprint of its native Trp content. Such a method is more rapid than usual traditional separation and detection methods which can take several hours and does not require any addition of labeling agents such as fluorescent dyes or antibodies for the detection. As other virus species contain Trp as one of the amino acids presents in their proteins, this method has the potential to apply to the detection of other viral species., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

Human health is consistently threatened by different species of pathogenic bacteria. To fight the spread of diseases, it is important to develop rapid methods for bacterial identification. Over the years, different kinds of biosensors were developed for this cause. Another environmental risk is poly-aromatic hydrocarbons (PAHs) that may be emitted from industrial facilities and pollute environmental water and soil. One of the methods for their purification is conducted by the addition of bacteria that can degrade the PAHs, while the bacteria can be filtrated at the end of the process. Although many studies reported monitoring of the PAHs degradation by fluorescence, not much attention was dedicated to studying the influence of the PAHs on the intrinsic fluorescence of the degrading bacteria. In this work, we apply synchronous fluorescence (SF) measurements to study the ability of the 5 PAHs: 9-Antracene carboxylic acid (9ACA), Pyrene, Perylene, Pentacene, and Chrysene to interact with bacteria and change its fluorescence spectra. We show that upon incubation of each PAH with the bacterium E. coli, only the 2 PAHs 9ACA and Perylene cause an intensity decrease in the emission at λ = 300-375 nm, which derives from the emission of tyrosine and tryptophan (TT). Also, we show that upon incubation of 9ACA and Perylene with 5 different pathogenic bacteria, the intensity increase or decrease in the TT emission is unique to each bacterial species. Based on this observation, we suggest that the PAHs 9ACA and Perylene can be utilized as biosensors for bacterial identification., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

Our previously reported computational study of the decomposition pathways of triacetone triperoxide (TATP), 1, predicted that unlike most energetic materials, which involve self-combustion of fuel and oxidants, 1 decomposes via a thermoneutral, non-redox pathway that involves entropy burst. These predictions are now corroborated by time-resolved monitoring of deflagration or detonation of 1 using a fast video camera following initiation by a short pulse focused laser beam. While a fireball always accompanies the explosion of 1 under air, the formation of a fireball is totally prevented under a nitrogen atmosphere. These observations indicate that combustion of the gaseous primary products occurs as a secondary event only in the presence of exogenous oxygen. The composition of the product mixture was found to depend on the experimental conditions. With long pulse focused laser beam (150 μs at 1064 nm) at either 210 or 110 mJ, the small amounts of charcoal needed for initiation suggest that the energy required to initiate 1 by pulse laser is 4-10 mJ, much smaller than the energy required for initiation by either mechanical stress or electric discharge. This time-resolved study highlights the very unusual properties of the peroxide based explosives.

β-site APP-cleaving enzyme (BACE1) cleaves the wild type (WT) β-site very slowly (k(cat)/K(m): 46.6 m(-1) s(-1)). Therefore we searched for additional β-secretases and identified three cathepsins that split the WT β-site much faster. Human cathepsin S cleaves the WT β-site (k(cat)/K(m): 54 700 m(-1) s(-1)) 1170-fold faster than BACE1 and cathepsins B and L are 440- and 74-fold faster than BACE1, respectively. These cathepsins split two bonds flanking the WT β-site (K-MD-A), where the K-M bond (85%) is cleaved more efficiently than the D-A bond (15%). Cleavage at the major K-M bond yields Aβ (amyloid β-peptide) extended by N-terminal Met that should be removed to generate Aβ initiated by Asp1. The activity of cytosol and microsomal aminopeptidases on relevant peptides revealed rapid removal of N-terminal Met but not N-terminal Asp. Brain aminopeptidases showed similar specificity. Thus, aminopeptidases would convert Aβ extended by Met into regular Aβ (Asp1) found in amyloid plaques. Earlier studies indicate that Aβ is likely produced in the endosome and lysosome system where cathepsins S, B and L are localized and cysteine cathepsin inhibitors reduce the level of Aβ in cells and animals. Taken together, cathepsins S, B and L deserve further evaluation as therapeutic targets to develop disease modifying drugs to treat Alzheimer's disease.

This highlight article describes three Alzheimer's disease (AD) studies presented at the 5th General Meeting of the International Proteolysis Society that address enzymatic mechanisms for producing neurotoxic beta-amyloid (Abeta) peptides. One group described the poor kinetics of BACE 1 for cleaving the wild-type (WT) beta-secretase site of APP found in most AD patients. They showed that cathepsin D displays BACE 1-like specificity and cathepsin D is 280-fold more abundant in human brain than BACE 1. Nevertheless, as BACE 1 and cathepsin D show poor activity towards the WT beta-secretase site, they suggested continuing the search for additional beta-secretase(s). The second group reported cathepsin B as an alternative beta-secretase possessing excellent kinetic efficiency and specificity for the WT beta-secretase site. Significantly, inhibitors of cathepsin B improved memory, with reduced amyloid plaques and decreased Abeta(40/42) in brains of AD animal models expressing amyloid precursor protein containing the WT beta-secretase site. The third group addressed isoaspartate and pyroglutamate (pGlu) posttranslational modifications of Abeta. Results showed that cathepsin B, but not BACE 1, efficiently cleaves the WT beta-secretase isoaspartate site. Furthermore, cyclization of N-terminal Glu by glutaminyl cyclase generates highly amyloidogenic pGluAbeta(3-40/42). These presentations suggest cathepsin B and glutaminyl cyclase as potential new AD therapeutic targets.

Many studies suggest that BACE 1 is the genuine beta-secretase; however, this is not undisputed. The wild-type (WT) beta-site of the amyloid precursor protein (APP) present in the worldwide population is cleaved very slowly (kcat/Km: approx. 50 m(-1) s(-1)), while proteases acting on relevant substrates are much more efficient (kcat/Km: 10(4)-10(6) m(-1) s(-1)). Knock-out of BACE 1 in mouse markedly reduces A beta formation. Nevertheless, studies in other systems show that knock-out experiments in rodents and corresponding genetic defects in human may reveal different phenotypes. Considering these issues, we searched for other beta-secretase candidate(s), identified cathepsin D, and evaluated properties of cathepsin D related to BACE 1 that were not examined previously. The kinetic constants (kcat, Km, kcat/Km) for cleaving peptides with beta-sites of the WT or the mutated Swedish families (SW) APP by human BACE 1 and cathepsin D were determined and found to be similar. Western blots reveal that in human brain cathepsin D is approximately 280-fold more abundant than BACE 1. Furthermore, pepstatin A strongly inhibits the cleavage of SW and WT peptides by both brain extracts and cathepsin D, but not by BACE 1. These findings indicate that beta-secretase activity observed in brain extracts is mainly due to cathepsin D. Nevertheless, as both BACE 1 and cathepsin D show poor activity towards the WT beta-site sequence, it is necessary to continue the search for additional beta-secretase candidate(s).

Competitive inhibitors can activate proteases (papain, trypsin, and cathepsin S) to catalyze the synthesis of peptide bonds and accelerate the hydrolysis of poor substrates (from 1 to 99%). Reaction mixtures contained intermediate molecules that were formed by the coupling of the inhibitor with the poor substrate. This and other findings suggest the following chain of events. Part of the binding energy of formation of the enzyme-inhibitor complex was used to activate the inhibitor, i.e., to form acyl-enzyme species with a high-energy bond (e.g., a thioester bond in the case of papain) required for coupling the inhibitor with the substrate to form the intermediate molecule. The latter was subjected to successive reactions which led to a stepwise degradation of the substrate, as well as to the regeneration of the inhibitor. One mole of the inhibitor could catalyze rapid hydrolysis of at least 53 mol of substrate. The intermediate molecules were the species undergoing rapid hydrolysis. Therefore, 1 mol of inhibitor was involved in the synthesis of 53 mol of intermediate molecules; i.e., the inhibitor functioned as a cofactor that catalyzed the synthesis of peptides. Thus, the binding energy of formation of the enzyme-inhibitor complex can be utilized to catalyze the synthesis of peptide bonds in the absence of an exogenous energy source (e.g., ATP).