Linghui Meng,Jie Jiang,Xuesong Peng,Lin Zhu,Ruopeng Li,Yaqiang Li,Maozhong An
Developing a cyanide-free gold electrodeposition system is significant for replacing the cyanide electroplating gold plating system, which is highly harmful to the environment and toxic to human health. In our study, a cyanide-free system for electrodepositing gold (Au) coatings was proposed with AuCl as the main salt and 5,5-dimethyl hydantoin (DMH) as the Au (I) complexing agent. Through theoretical calculations and electrochemical test screening, 4,6-dimethyl-2-mercaptopyrimidine (DMP) is suitable for DMH-based gold electrodeposition and was selected as an electroplating additive. The role of DMP in gold electrodeposition was further studied. In particular, the adsorption–coordination mechanism was proposed to elucidate the role of DMP, based on calculations of the Bader charge density difference for DMP adsorbed on the gold surface and the interaction between DMP and Au+. Electrochemical tests such as cyclic voltammetry and chronoamperometry were utilized to study the impact of varying DMP concentrations on gold electrodeposition behavior. Chronoamperometric analysis indicates that Au electrodeposition obeys a 3D diffusion-controlled progressive nucleation process, independent of DMP concentration and applied potential, while the presence of DMP markedly suppresses grain growth. The addition of DMP significantly improved the surface morphology and brightness of the gold coating, resulting in a smooth and dense layer with a golden-yellow appearance. XRD results showed that the addition of DMP reduced the grain size of the Au coating from 22.1 to 15.7 nm, with the gold coating primarily growing along the Au (111) plane. The XPS test results show that the purity of the gold plating layer is high, and there is no inclusion of additives in the coating.
Li Ran,Yongjun Wu,Jing Jin,Lincheng Zhang,Cen Li,Shuoqiu Tong,Feng Wen,ZhongHui Mou
The globalization of food culture has driven the growth of the flavor market, with Bacillus subtilis- fermented soybean products widely used as traditional Asian condiments due to their distinctive soy sauce-like aroma. However, the molecular mechanism underlying aroma formation remains incompletely understood. Building on previous systematic multi-omics studies, this study identifies a key role for l -threonine catabolism in regulating pyrazine biosynthesis. Using homologous recombination, we performed targeted knockouts of the tdh and kbl genes to generate single mutants (BJ3-2Δ tdh and BJ3-2Δ kbl ) and a double mutant (BJ3-2Δ tdh - kbl ). Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS), along with sensory evaluation, revealed that the tdh knockout drastically reduced 2,5-dimethylpyrazine (2,5-DMP) levels by 96.79%. The double knockout achieved a 97.73% reduction and completely eliminated 3-ethyl-2,5-dimethylpyrazine (EDMP). Interestingly, the kbl knockout alone enhanced 2,5-DMP production by 65.34%, and the odor activity value of EDMP increased to 10.50. Exogenous supplementation experiments confirmed that 2,5-DMP is a critical contributor to nutty, sweet, and buttery aromas, while also intensifying smoky undertones. Overall, this study elucidates the regulatory function of l -threonine catabolism in pyrazine biosynthesis, linking microbial metabolism to food flavor and offering a metabolic engineering strategy for targeted aroma modulation in fermented foods. Practical Applications This research provides valuable insights into the mechanism underlying the formation of soy sauce-like aroma, laying the foundation for optimizing 2,5-dimethylpyrazine (2,5-DMP) concentrations to fine-tune aroma profiles. These findings may support the environmentally friendly production of high-quality soy sauce-like aroma foods, potentially reducing reliance on artificial additives.
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