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Gold thick films have been characterized by means of cyclic voltammetry in nitric acid and are compared with a pure gold electrode. Surface reconstruction and roughening is found for all electrodes, whereby the pure gold reference sample rapidly exhibits stationary behavior. In contrast, the screen-printed electrodes show a permanent linear increase of the gold surface area as measured by the charge densities for gold oxidation, which is connected with the dissolution of glass-ceramic compounds. Oxides of bismuth and copper and their aluminates are regularly used to adjust the morphology of thick films and to enhance the adhesion of screen-printed layers. Electrochemical reactions of both elements (Bi, Cu) are detected. An in-house produced gold paste free of these oxides was used for comparison and shows a linear increase in oxidation charge density as well. Cu and Bi compounds take part in the electrochemical reaction and accelerate the surface increase. The dissolution of glass-ceramic components from the surface and at the interface between thick film and substrate is revealed in FESEM images of the electrodes and at cross-sections. A model is set up for the electrochemically induced localized degradation of the thick films, which are attacked at the boundary layer to the electrolyte and the glass-ceramic interface between the LTCC substrate and gold layers.

© 2023 Elsevier B.V.Microbial production of aromatic compounds is an attractive and sustainable biotechnological approach. With this motivation, here metabolic engineering of Corynebacterium glutamicum for L-tyrosine (L-Tyr) overproduction was attempted by pushing the carbon flux more towards L-Tyr. Translational start codon exchanges of prephenate dehydratase (pheA), anthranilate synthase (trpE), and phenylalanine aminotransferase (pat) genes revealed that reduced expression of pheA was the major contributor to increased L-Tyr titer while codon exchange in trpE was effective to a lower extent. Overexpression of aroE and qsuC, encoding shikimate dehydrogenase and 3-dehydroquinate dehydratase, respectively, and of dapC (cg1253), which is predicted to encode prephenate aminotransferase, were futile to increase L-Tyr titer. Similarly, deletion of the qsuABD gene cluster had also not enhanced titer. As for increasing precursor supply, deletion of ptsG of glucose uptake and overexpression of inositol permease (iolT2) and glucokinase (glcK) were not effective, but with utilization of xylose, enabled by overexpression of xylose isomerase (xylA) and xylulokinase (xylB), titer improved. Highest L-Tyr titer using the construct was 3.1 g/L on glucose and 3.6 g/L on a 1:3 (w/v) mixture of glucose and xylose. This result displays the potential of the constructed strain to produce L-Tyr from lignocellulosic renewable carbon sources.