The decomposition of N-chloro amino acids of essential branched-chain amino acids: Kinetics and mechanism

A new concern raised from algal bloom: Organic chloramines in chlorination

Algal blooms have become a significant challenge in water treatment all over the world. In chlorination of drinking water, algal organic matter (AOM) leads to the formation of organic chloramines. The objectives of this review are to comprehensively summarize and discuss the up-to-date researches on AOM-derived organic chloramines and their chemical activities and toxicity, thereby drawing attention to the potentially chemical and hygienic risks of organic chloramines. The predominant algal species in water sources varied with location and season. AOM from cyanobacteria, green algae, and diatoms are composed of diverse composition. AOM-derived amino acids take a low portion of the precursors of organic chloramines. Both experimental kinetic data and quantum chemical calculation demonstrate the preferential formation of organic chloramines in the chlorination of model compounds (amino acids and peptides). Organic chloramines are persistent in water and can transform into dichloro- and trichloro-organic chloramines, unknown low-molecular-weight organic chloramines, and nitrogenous disinfection byproducts with the excess of free chlorine. The active chlorine (Cl+) in organic chloramines can lead to the formation of chlorinated phenolic compounds. Organic chloramines influence the generation and species of radicals and subsequent products in UV disinfection. Theoretical predictions and toxicological tests suggest that organic chloramines may cause oxidative or toxic pressure to bacteria or cells. Overall, organic chloramines, as one group of high-molecular-weight disinfection byproducts, have relatively long lifetimes, moderate chemical activities, and high hygienic risks to the public. Future perspectives of organic chloramines are suggested in terms of quantitative detection methods, the precursors from various predominant algal species, chemical activities of organic chloramines, and toxicity/impact.

Oxidation of branched chain amino acids by HOCl: Kinetics and mechanism

The kinetics of the chlorination of leucine, isoleucine, and valine (BCAAs) was studied in excess HOCl by stopped-flow and spectrophotometric methods (25 ◦C, I = 1.0 M NaClO4). The intermediates and products were identified and monitored by 1H NMR spectroscopy. It was established that these reactions are fully analogous and proceed according to distinct mechanisms under alkaline and neutral conditions. At high pH, the formation and subsequent rate determining decomposition of N-monochloroamino acid control the process. The decomposition occurs via competing pH-independent and OH--assisted reaction paths and the sequence of chlorination, dichlorination and decarboxylation steps leads to the formation of N-chloroimines and their carbanionic forms, which are in fast acid - base equilibria. The dechlorination of the carbanions yields nitriles as the main products. The hydration of the N-chloro imines produces chloramine and aldehydes which are involved in further oxidation reactions with HOCl. The formation of chloroform and chloroacetaldehyde was confirmed in each system. At pH 7.0, the N-chloro derivatives of BCAAs form immediately and are converted into the corresponding N,N-dichloro species within a few seconds after mixing the reactants. In this reaction, the reactive form of the oxidant is Cl2O. The first-order decomposition of the dichloroamino acids occurs on stopped-flow timescale (k = 0.5 - 0.7 s-1) and yields N-chloroimines which slowly decompose with a characteristic first-order rate constant on the order of a few times 10-5 s-1. The main products are the corresponding nitriles that account for about 80% and 60% of the original amounts of amino acids under neutral and alkaline (cOH- = 5.00 × 10-2 M) conditions, respectively. Aldehydes, carboxylic acids, chloroform and NCl3 were also identified as by-products. The results unequivocally confirm that harmful chlorinated species may form from amino acids long after the chlorination step in water treatment technologies that deteriorates the quality of the finished water. ENVIRONMENTAL IMPLICATION: In source waters, amino acids account for about 75% of the total dissolved nitrogen. Therefore, it is an essential issue how the reactions of these compounds with hypochlorite ion can be controlled to avoid the formation of toxic compounds. The compounds formed from BCAAs are considered to be harmful both under alkaline and neutral conditions (chloroacetaldehyde, chloroform, nitriles). However, some of the intermediates have extended lifetime in these systems and they may also react with other components of raw water during water treatment processes.

Recovery of valuable metals from spent lithium-ion batteries via zinc powder reduction roasting and cysteine leaching

With the annual increase in lithium-ion batteries (LIBs) disposal, valuable resources are being generated with worrying waste, so it is strategically important to recover the critical metals from them. Individual high temperature or leaching processes do not apparently achieve very satisfactory results. In the present work, the reduction with zinc powder was able to convert the lithium in LiNixCoyMnzO2 (NCM) to soluble LiOH, while the reduction and ammonia complexation environment generated by the decomposition of cysteine (Cys) achieved an efficient leaching of transition metals without additional additives. The leaching efficiency of Li can reach more than 92 %, while that of Ni/Co/Mn reaches more than 97 % through the regulation of the parameters of each process. In particular, an in-situ redox mechanism is proposed to explain the efficient leaching of transition metals, which further enriches the theory of spent LIBs recycling and provides a promising idea for various hydrometallurgical extraction systems.

Investigation of Chloramines, Disinfection Byproducts, and Nitrification in Chloraminated Drinking Water Distribution Systems

Four chloraminated drinking water distribution systems (CDWDSs) required to maintain numeric versus "detectable" residuals were spatially and temporally sampled for water quality and associated trihalomethane (THM) and haloacetic acid (HAA) formation. Monochloramine decreased from entry point (EP) to maximum residence time (MRT) samples while THMs and HAAs initially increased and then stabilized or slightly decreased. Subsequently, EP and MRT samples were used in laboratory-held studies to further evaluate disinfectant residual stability, chloramine speciation, and nitrification occurrence. MRT water exhibited a faster monochloramine concentration decline compared to EP water, indicating a decreasing disinfectant residual stability from increasing water age through distribution. Using a simple technique based on published inorganic chloramine chemistry, samples were also investigated for nondisinfectant positive interference (NDPI) on total chlorine measurements. NDPI concentrations represented up to 100% of the total chlorine concentration when total chlorine concentrations decreased to 0.05 mg-Cl2/L, indicating little to no effective disinfectant residual remained.

The Chlorination of N-Methyl Amino Acids with Hypochlorous Acid: Kinetics and Mechanisms

The formation and decomposition kinetics of N-chloro-N-methyl amino acids were studied to predict the fate and impact of these compounds in water treatment technologies and biological systems. These compounds form in fast second-order reactions between N-methyl amino acids and hypochlorous acid. The comparison of the activation parameters for the reactions of N-methyl substituted and nonsubstituted branched-chain amino acids reveals the transition-state features less organized structure and stronger bonds between the reactants in the reactions with the N-methyl derivatives. This is due to a combined positive inductive effect of the N-methyl group and the alkyl side chain as well as to the steric effects of the substituents. N-Methyl-N-chloro amino acids decompose much faster than the nonsubstituted compounds. The reaction rates do not depend on the pH, and the same final product is formed in the entire pH range. N-Chlorosarcosine is an exception, as it decomposes via competing paths, k_d^obs = k_d + k_d^OH[OH^-], yielding different final products. This feature is most likely due to the lack of an alkyl substituent on the α-carbon atom. Under physiological pH, aldehydes and methylamine form in these reactions, which are not particularly toxic.

Effect of feed composition on the nutritional value of meat of African catfish

The article outlines the results of the research into the influence of feed composition on the amino acid value of African catfish meat. It has been shown that quality characteristics of fish meat depend on protein and fat content. It has been proved that high-protein feed ensures increase in the content of all amino acids in African catfish meat. Nevertheless, protein and fat content in the muscles of the studied fish is more than 2 times higher than the same indicator in the fish on low-protein and low-fat diet. Meat of the African catfish is rich in two amino acids – leucine and lysine. Two amino acids, tryptophan and methionine, are limitative at a high protein diet. At a lower protein diet, isoleucine amino acid is also added. The amino acid composition of African catfish meat is highest at high-protein feeds. The amino acid index of African catfish muscles at high-protein feeds is 0.48, significantly exceeding the index of fish bred on feeds with a reduced protein content. The conducted studies have shown that the use of high-protein feeds in catfish breeding stimulates protein metabolism, enriching the amino acid composition of muscle tissue and increasing the nutritional value of fish as a food product. The research has been funded by the Russian Foundation for Fundamental Research, project No. 18-016-00127.