Search Results (4)

Fermentation has been considered as an effective means to improve the feed nutrient digestibility of corn stalks, and it is beneficial to animal growth performance and health. The beneficial functions of fermented corn stalks are related to the variety of metabolites produced through fermentation, but the nature of these components is still unclear. In this study, gas chromatography–mass spectrometry, combined with principal component analysis and partial least squares discriminant analysis, was used to explore the differential metabolites of corn stalks before and after Aspergillus niger fermentation. A total of 32 potential characteristic compounds were obtained, mainly including sugar and glycoside derivatives, organic acids and their derivatives, alcohol compounds, benzene and its substituted derivatives, amino acids, phenolic compounds, and flavonoids. Compared with the metabolites in corn straw before fermentation, the relative content of D-threitol, mannitol-1-phosphate, coniferin, citrazinic, oxoglutaric acid, chenodeoxycholic acid, naproxen, 5-aminovaleric acid, vanillin, catechin, and UDP-glucuronic acid was significantly increased, and the relative content of N-acetylgalactosamine, heneicosanoic acid, chlorogenic acid, and adenosine was significantly decreased. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that 20 metabolic pathways corresponded to the differential characteristic metabolites. The results of this study will provide theoretical support for the quality evaluation of fermented corn stalks and high-value product development in the future. Full article

The molecular model is one of the most appealing to explain the peculiar optical properties of Carbon nanodots (CNDs) and was proven to be successful for the bottom up synthesis, where a few molecules were recognized. Among the others, citrazinic acid is relevant for the synthesis of citric acid-based CNDs. Here we report a combined experimental and computational approach to discuss the formation of different protonated and deprotonated species of citrazinic acid and their contribution to vibrational and magnetic spectra. By computing the free energy formation in water solution, we selected the most favoured species and we retrieved their presence in the experimental surface enhanced Raman spectra. As well, the chemical shifts are discussed in terms of tautomers and rotamers of most favoured species. The expected formation of protonated and de-protonated citrazinic acid ions under extreme pH conditions was proven by evaluating specific interactions with H₂SO₄ and NaOH molecules. The reported results confirm that the presence of citrazinic acid and its ionic forms should be considered in the interpretation of the spectroscopic features of CNDs. Full article

The origin of carbon-dots (C-dots) fluorescence and its correlation with the dots structure still lack a comprehensive model. In particular, the core-shell model does not always fit with the experimental results, which, in some cases, suggest a molecular origin of the fluorescence. To gain a better insight, we have studied the response of molecular-like fluorophores contained in the C-dots at extreme pH conditions. Citric acid and urea have been employed to synthesize blue and green-emitting C-dots. They show a different emission as a function of the pH of the dispersing media. The photoluminescence has been attributed to molecular-like fluorophores: citrazinic acid and 4-hydroxy-1H-pyrrolo[3,4-c]-pyridine-1,3,6-(2H,5H)-trione. 3D and time-resolved photoluminescence, ultraviolet–visible (UV–vis) spectroscopy, and dynamic light scattering have been used to determine the aggregation state, quantum yield and emission properties of the C-dots. The dependence of the C-dots blue and green components on the chemical environment indicates that the origin of fluorescence is due to molecular-like fluorophores. Full article

A series of pyridines, pyrimidinones, oxazinones and their derivatives were synthesized as antimicrobial agents using citrazinic acid (2,6-dihydroxyisonicotinic acid) as a starting material. α,β-Unsaturated ketones 3a–c were condensed with cyanothio-acetamide in the presence of ammonium acetate to give 2-cyanopyridinethiones 4a–c, which were reacted with ethyl chloroacetate to yield the corresponding cyano esters 5a–c. The esters 5a–c were cyclized by action of sodium methoxide to aminoesters 6a–c, which were aminolyzed with ammonia to corresponding aminoamide derivatives 7a-c. Also, the esters 6a–c were hydrolyzed with NaOH to the corresponding sodium salt 8a–c, which were treated with acetic anhydride to afford 2-methyloxazinones 9a–c. The latter compounds were treated with ammonium acetate to afford 2-methylpyrimidinones 10a–c, followed by methylation with methyl iodide to yield 2,3-dimethyl-pyrimidinones 11a–c. The antimicrobial screening showed that many of these compounds have good antibacterial and antifungal activities comparable to streptomycin and fusidic acid used as reference drugs. Full article