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Mechanistic study on substitution reaction of a citrato(p-cymene)Ru(ii) complex with sulfur-containing amino acids.

ABSTRACT: The reactions of a dichloro(p-cymene)ruthenium(ii) dimer, [RuCl₂(p-cymene)]₂, with citric acid and sulfur-containing amino acids gave only [Ru(L)(p-cymene)]-type complexes (L = citrate (Cit), l-penicillaminate (l-Pen), S-methyl-l-cysteinate (S-Me-l-Cys) and l-methioninate (l-Met)) in aqueous solutions at various pHs and molar ratios of the reactants, where Cit and the amino acids act as a tridentate ligand. These sulfur-containing amino acid complexes with bound nitrogen, oxygen and sulfur atoms and η⁶-p-cymene take S absolute configuration around Ru(ii) selectively, having the α-proton oriented in the opposite direction from the Ru(ii) center. The concentration dependences of the observed pseudo-first-order rate constants were provided for the substitution reactions of the citrato complex, [Ru(Cit)(p-cymene)], with a large excess of the sulfur-containing amino acids at various temperatures at pH 7.3, where solvolysis path was observed for S-Me-l-Cys and l-Met as an intercept but not for l-Pen. The activation parameters for the substitution reactions by the direct attack of the amino acids were changed significantly, indicating that the reaction mechanism varies sensitively with the amino acids from an associative mechanism to an interchange one. The pH dependences of the rate constants of the substitution reactions suggest that the carboxylate group is an attacking group for S-Me-l-Cys and l-Met under neutral conditions and the thiol group of l-Pen acts as an entering group constantly at any pH showing a considerably smaller activation energy compared with S-Me-l-Cys and l-Met. Differences in stabilities of the amino acid complexes were obtained from the equilibrium constants for the substitution reactions between the amino acids. These results indicate that the activation energies for the substitution reactions of the citrato complex with the amino acids are moderately correlated with the stabilities of the formed amino acid complexes.

SUBMITTER: Aizawa SI

PROVIDER: S-EPMC9069928 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Mechanistic study on substitution reaction of a citrato(p-cymene)Ru(ii) complex with sulfur-containing amino acids.

Aizawa Sen-Ichi SI Takizawa Kohei K Aitani Momoko M

RSC advances 20190813 43

The reactions of a dichloro(p-cymene)ruthenium(ii) dimer, [RuCl2(p-cymene)]2, with citric acid and sulfur-containing amino acids gave only [Ru(L)(p-cymene)]-type complexes (L = citrate (Cit), l-penicillaminate (l-Pen), S-methyl-l-cysteinate (S-Me-l-Cys) and l-methioninate (l-Met)) in aqueous solutions at various pHs and molar ratios of the reactants, where Cit and the amino acids act as a tridentate ligand. These sulfur-containing amino ac ...[more]

PMID: 35528666

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Project description:The sulfur-containing amino acids methionine and cysteine play an important role in food industry. These amino acids are used to confer a sulfur smell or meat-related aroma to food products. Besides their use as food additives, methionine and cysteine participate in flavor formation in dairy fermentations. For instance, the characteristic aroma of Cheddar cheeses is derived from methionine. Therefore, bacterial strains with the ability to overproduce and secrete these amino acids are relevant for the food industry. In addition, the quantification of these compounds in food matrices is a laborious task that involves sample preparation and specific analytical methods such as high-performance liquid chromatography. The ability of bacteria to naturally sense metabolites has successfully been exploited to develop biosensors. The presence of a specific metabolite is sensed by the biosensors, and it is subsequently translated into the expression of one or more reporter genes. In this study we aim to develop biosensors to detect methionine and cysteine, which are produced and secreted by wild-type Lactococcus lactis strains. We employed two strategies to create L. lactis biosensors, the first one is based on the methionine auxotrophy of this bacterium and the second strategy is based on a cysteine-responsive promoter. The characterization of the biosensors showed their specific response to the presence of these amino acids. Subsequently, we applied the methionine biosensor to quantify the presence of methionine in bacterial supernatants of wild-type L. lactis that naturally secretes methionine to benchmark the performance of our biosensors. The methionine biosensor responded linearly to the amounts of methionine present in the bacterial supernatants, i.e., the increases in the biosensor cell densities were proportional to the amounts of methionine present in the supernatants. The biosensors developed in this study tackle the limitations of amino acid quantification and the selection of strains with secretion of amino acids. These biosensors may eventually be used for screening of engineered strains to increase methionine and cysteine production, and may facilitate the detection of these amino acids in complex food matrices.

Dataset Information

Mechanistic study on substitution reaction of a citrato(p-cymene)Ru(ii) complex with sulfur-containing amino acids.

Publications

Mechanistic study on substitution reaction of a citrato(<i>p</i>-cymene)Ru(ii) complex with sulfur-containing amino acids.

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