Citric acid

About: Citric acid is a research topic. Over the lifetime, 17745 publications have been published within this topic receiving 277125 citations. The topic is also known as: citrate & H3cit.

Solar photocatalytic reduction of Cr(VI) over Fe(III) in the presence of organic sacrificial agents

Abstract: Toxic hexavalent chromium reduction to less toxic trivalent chromium was evaluated using a solar driven photocatalytic system, Fe(III)/UV, in the presence of organic sacrificial agents. The photocatalytic reduction experiments were conducted in a lab-scale tubular photoreactor with compound parabolic collectors under simulated solar radiation. The effect of parameters such as iron (1–12 mg L −1 ) and citric acid (0.058–3.840 mM) concentrations, pH value (3.0–8.0), temperature (15–40 °C), UVA irradiation source and initial Cr(VI) concentration (1, 10, 20, 40 mg L −1 ) on the process efficiency was analyzed, and also the addition of other organic ligands like oxalic acid, maleic acid and EDTA. The presence of citric acid proved to enhance the Cr(VI) reduction by Fe(III)/UV due to the formation of Fe(III)-Citrate complexes, providing a quicker pathway for ferric iron regeneration in the presence of UV–vis light. The organic ligands proved to act also as sacrificial agents of reactive oxygen species formed, avoiding the Cr(III) re-oxidation. The catalytic activity of the organic ligands in the Cr(VI) reduction by Fe(III)/UV followed this order: citric acid > oxalic acid > EDTA > maleic acid. The best Cr(VI) reduction (99% in 15 min) was achieved with citric acid in a Cr(VI):Citric acid molar ratio of 1:3 at pH 5 and 25 °C. Finally, the photocatalytic reduction of Cr(VI) present in a real effluent was achieved after 30 min, demonstrating the potential of the Fe(III)/UVA-vis/citric acid system for the treatment of Cr(VI) containing wastewaters.

Functional Analysis of a MATE Gene OsFRDL2 Revealed its Involvement in Al-Induced Secretion of Citrate, but a Lower Contribution to Al Tolerance in Rice

Abstract: The multidrug and toxic compound extrusion (MATE) transporters represent a large transporter family in plants, but the role of most genes in this family has not been examined. We functionally characterized a MATE family member, OsFRDL2, in rice (Oryza sativa). OsFRDL2 showed an efflux transport activity for citrate when it was expressed in both Xenopus oocytes and cultured tobacco cells. OsFRDL2 was mainly expressed in the roots and its expression was not induced by iron (Fe) deficiency, but it was rapidly up-regulated by aluminum (Al). Furthermore, the expression of OsFRDL2 was regulated by ART1, a C2H2-type zinc-finger transcription factor for Al tolerance. OsFRDL2 protein was localized at unidentified vesicles in the cytosol, but not co-localized with either mitochondria or peroxisomes when expressed in both onion epidermal cells and cultured tobacco cells. Knockout of OsFRDL2 decreased Al-induced secretion of citrate from the roots, but did not affect the internal citrate concentration. The Al-induced inhibition of root elongation was similar between the OsFRDL2 knockout line and its wild-type rice. Knockout of OsFRDL2 did not affect the translocation of Fe from the roots to the shoots. A double mutant between osfrdl2 and osfrdl4 or osfrdl1 did not further decrease the Al-induced citrate secretion and Fe translocation compared with the single mutant. Collectively, our results indicate that although OsFRDL2 is involved in the Al-induced secretion of citrate, its contribution to high Al tolerance is relatively small in rice.

Characterization of citrate utilization in Corynebacterium glutamicum by transcriptome and proteome analysis

Abstract: Corynebacterium glutamicum grows aerobically on a variety of carbohydrates and organic acids as single or combined sources of carbon and energy. To characterize the citrate utilization in C. glutamicum on a genomewide scale, a comparative analysis was carried out by combining transcriptome and proteome analysis. In cells grown on citrate, transcriptome analysis revealed highest expression changes for two different citrate-uptake systems encoded by citM and tctCBA, whereas genes encoding uptake systems for the glucose- (ptsG), sucrose- (ptsS) and fructose- (ptsF) specific PTS components and permeases for gluconate (gntP) and glutamate (gluC) displayed decreased mRNA levels in citrate-grown cells. This pattern was also observed when cells grown in Luria-Bertani (LB) medium plus citrate were compared with cells grown in LB medium, indicating some kind of catabolite repression. Genes encoding enzymes of the tricarboxylic acid cycle (aconitase, succinyl-CoA synthetase, succinate dehydrogenase and fumarase), malic enzyme, PEP carboxykinase, gluconeogenic glyceraldehyde-3-phosphate dehydrogenase and ATP synthase displayed increased expression in cells grown on citrate. Accordingly, proteome analysis revealed elevated protein levels of these enzymes and showed a good correlation with the mRNA levels. In conclusion, this study revealed the citrate stimulon in C. glutamicum and the regulated central metabolic genes when grown on citrate.

Systems and methods for hydrogen generation from solid hydrides

Abstract: A system is disclosed for hydrogen generation based on the hydrolysis of solid chemical hydrides with the capability of controlled startup and stop characteristics wherein regulation of acid concentration, acid feed rate, or a combination of both control the rate of hydrogen generation. The system comprises a first chamber for storing a solid chemical hydride and a second chamber for storing an acidic reagent. The solid chemical hydride is a solid metal borohydride having the general formula MBH4, where M is selected from the group consisting of alkali metal cations, alkaline earth metal cations, aluminum cation, zinc cation, and ammonium cation. The acidic reagent may comprise inorganic acids such as the mineral acids hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as acetic acid, formic acid, maleic acid, citric acid, and tartaric acid, or mixtures thereof.