Citrate Anions Research Articles

Citrate ions-modified NiFe layered double hydroxide for durable alkaline seawater oxidation

Seawater electrolysis taking advantage of coastal/offshore areas is acknowledged as a potential way of large-scale producing H2 to substitute traditional technology. However, anodic catalysts with high overpotentials and limited lifespans (caused by chloride-induced competitive chemical reactions) hinder the system of seawater electrolysis for H2 production. Herein, we present a citrate anion (CA) modified NiFe layered double hydroxide nanosheet array on nickel foam (NiFe LDH@NiFe-CA/NF), which serves as an efficient and stable electrocatalyst towards long-term alkaline seawater oxidation. It requires only a low overpotential of 387 mV to achieve a current density of 1000 mA cm−2, outperforming NiFe LDH/NF (414 mV). Moreover, NiFe LDH@NiFe-CA/NF exhibits continuous oxygen evolution testing for 300h at 1000 mA cm−2 due to its anti-corrosion characterization. Additionally, the fabricated cell can stably operate at 300 mA cm−2 (60 °C, 6 M KOH + seawater) and only require 1.69 V, achieving low energy consumption of seawater splitting.

Effect of citrate anion incorporation on dielectric properties of anodic oxide grown on Ti-Si alloy

Effect of citrate anion incorporation on dielectric properties of anodic oxide grown on Ti-Si alloy

Control for selective sorption of heavy metals cations with anion exchanger AB-17-8 by modifying the surface with citrate groups

The citric acid modification produces an intermediate layer on the AB-17-8:C6H8O7 surface; the layer, on one hand, is firmly secured to the surface owing to the electrostatic coupling between the citrate anion and the positively charged trimethylammonium centers of the anion exchanger surface; on the other hand, it has carbonyl groups with a local negative electron density. The sorption of heavy metals cations occurs through coordination interactions via electrostatic mechanism with local centers of negative electron density, in particular, with the carbonylic oxygen atom.

Investigation of laccase activity in cholinium-based ionic liquids using experimental and molecular dynamics techniques

Laccases hold great potential for biotechnological applications, particularly in environmental pollutant remediation. Laccase activity is governed by the solvent environment, and ionic liquids (ILs) emerge as a versatile solvent for activation or stabilization of enzymes. Herein, effects of cholinium-based ILs formulated with carboxylic acids, inorganic acid, and amino acids as anionic species, on the catalytic activity of laccase from Trametes versicolor were investigated by experimental and computational approaches. Experimental results showed that laccase activity was enhanced by 21.39 % in 0.5 M cholinium dihydrogen citrate ([Cho][DHC]), in relation to the laccase activity in phosphate buffer medium. However, cholinium aminoate ILs negatively affected laccase activity, as evidenced by the partial deactivation of laccase in both cholinium glycinate and cholinium phenylalaninate, at concentrations of 0.1 M and 0.5 M, respectively. Molecular dynamics studies revealed that the enhancement of laccase activity in [Cho][DHC] might be attributed to the highly stabilized and compact structure of laccase, facilitating a better internal electron transfer during the laccase-substrate interactions. Enhanced catalytic performance of laccase in [Cho][DHC] was postulated to be driven by the high accumulation level of dihydrogen citrate anions around laccase's surface. [Cho][DHC] holds great promise as a cosolvent in laccase-catalyzed biochemical reactions.

On the selective transport of mixtures of organic and inorganic anions through anion-exchange membranes: A case study about the separation of nitrates and citric acid by electrodialysis

Electrodialysis is finding an increasing number of applications, recently also in the separation and purification of organic acids. This technology involves reducing the use of chemicals and the generation of wastes, as compared to conventionally used processes. Gaining insights about the competitive transport between organic and inorganic ions in ED systems is key to achieving efficient separation processes in the bioresource industry. In the present study, the competitive transport of organic (citrates) and inorganic anions (nitrates) through anion-exchange membranes is investigated, under varying pH conditions, ion concentrations, and applied currents, by means of chronopotentiometry and ED experiments. In the absence of nitrate ions and under acidic conditions (pH 2), the resistance of the membrane system is very high because citric acid is mainly present in its undissociated and uncharged form. In the case of sodium citrate (pH 8), the membrane resistance decreases, especially at high current densities, which promote dissociation reactions and the subsequent concentration increase in ionic species near the membrane. Such phenomenon is identified both in chronopotentiometric curves and in long-term ED experiments by a gradual drop in membrane voltage with time. Although being less concentrated than citrates, the selective removal of nitrates is the most effective choice for the separation of both types of species. The selectivity factor of nitrates over citrates reaches the highest values at low applied current densities (below the limiting current density), with stable permselectivity values higher than 20. Such conditions also lead to the least specific energy consumption per nitrates removed (<0.5 kW·hr·kgNO3--1). Therefore, ED can be used under such favorable operating conditions after a clarification step in order to remove inorganic ions from fermentation broths and increase the purity of organic acids. At higher current densities, the enhanced transport of citrate anions produces a significant drop in selectivity towards nitrates and increases the specific energy consumption.

The Antagonistic and Synergistic Role of Fe3+ Compounds in Chemo- and Electrochemotherapy in Human Colon Cancer In Vitro.

Colon cancer (CC) management includes surgery, radio- and chemotherapy based on treatment with 5-fluorouracil (5-FU) or its derivatives. However, its application is limited to low-grade carcinomas. Thus, much research has been conducted to introduce new techniques and drugs to the therapy. CC mostly affects older people suffering from cardiac diseases, where iron compounds are commonly used. Ferric citrate and iron (III)-EDTA complexes have proven to be effective in colon cancer in vitro. This study aimed to determine the potency and action of iron-containing compounds in colon cancer treatment by chemo- and electrochemotherapy in both nano- and microsecond protocols. The viability of the cells was assessed after standalone iron (III) citrate and iron (III)-EDTA incubation. Both compounds were also assessed with 5-FU to determine the combination index. Additionally, frataxin expression was taken as the quantitative response to the exposition of iron compounds. Each of the substances exhibited a cytotoxic effect on the LoVo cell line. Electroporation with standalone drugs revealed the potency of 5-FU and iron(III)-EDTA in CC treatment. The combination of 5-FU with iron(III)-EDTA acted synergistically, increasing the viability of the cells in the nanosecond electrochemotherapy protocol. Iron(III)-EDTA decreased the frataxin expression, thus inducing ferroptosis. Iron(III) citrate induced the progression of cancer; therefore, it should not be considered as a potential therapeutic option. The relatively low stability of iron(III) citrate leads to the delivery of citrate anions to cancer cells, which could increase the Krebs cycle rate and promote progression.

Tris(2-hydroxyethyl)ammonium-Based Protic "Ionic Liquids": Synthesis and Characterization.

The proton transfer associated with the synthesis of protic ionic liquids (PILs) is often incomplete, meaning that the parent compounds may coexist with the ionic species. However, PILs are proposed for many applications as pure compounds without analysis of their ionicity. This work focuses on tris(2-hydroxyethyl)ammonium-based PILs with lactate, hydrogen succinate, hydrogen malate, and dihydrogen citrate anions. The interest of these anions lies in their low toxicity and capacity to disrupt the hydrogen-bonding network inherent to biopolymers. To improve current synthesis methods of this kind of PILs, which frequently lead to impurities derived from decomposition of reactants, working in the absence of solvents and at moderate temperatures is proposed. Through NMR studies, the ionicity of these systems was found to be low, from 20% to 86%, so the widely used term "ionic liquid" is not rigorous and must be used with caution. The un-ionized acid and base species coexist with the corresponding ionic forms, and this has to be considered in the studies involving these chemicals. The thermal characterization of the PILs was carried out. The influence of the anion on the thermal stability was found to be low. Isothermal thermogravimetric analysis showed that mass loss of these PILs starts at temperatures close to 350 K.

Sustainable smart coatings of chitosan and LDH loaded with natural inhibitors for corrosion protection of Mg AZ31 alloy

In this study, sustainable smart coatings based on chitosan and layered double hydroxides (LDH), loaded with natural anions, were developed to enhance the corrosion resistance of AZ31 magnesium alloy. The LDH was synthesized using the co-precipitation method, loaded with natural inhibitors (vanillate, gallate and citrate anions) by an anion exchange process and characterized by various techniques, such as scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis. The kinetics of inhibitor release was investigated at different pH and the results show higher rates as the pH increases. The corrosion resistance offered by the sustainable smart coatings was determined by electrochemical impedance spectroscopy and hydrogen evolution tests, while the coating morphology, before and after the corrosion tests, was analyzed by SEM and optical microscopy, respectively. All of the results demonstrated that the smart coating containing gallate ions significantly improved the corrosion resistance of AZ31 magnesium alloy.

Citric Acid as Multidentate Flexible Ligand for Multinuclear Late‐3 d‐Metal Complexes and Single‐Molecule Magnets

AbstractCitric acid (citH4) is a ubiquitous product in nature with an interesting chemistry owing to its three carboxy and one hydroxy groups, which can be deprotonated in a stepwise manner into six kinds of citrate anions involving two protonation isomers. Deprotonated citrates easily coordinate to late‐3d‐metal ions (Mn, Fe, Co, Ni, Cu, and Zn), affording complexes including mono‐, di‐, tri‐, tetra‐, hexa‐, hepta‐, octa‐, nona‐, and 21‐nuclear complexes with a variety of structures. Magnetic interactions between metal centers are mainly generated via superexchange through hydroxylate or carboxylate bridging, whereas weaker magnetic dipole interactions appear in the absence of superexchange interactions. In citrate complexes, both ferromagnetic and antiferromagnetic interactions have been found. Citrate has a great potential to serve as a bridge between spin quantum magnetism and green chemistry. In this review, the structures and magnetism of discrete citrate complexes of late‐3d‐metals, as well as their single‐molecule magnet properties are discussed.

Extraction of caffeine from coffee husk employing choline-based ionic liquids: Optimization of the process and theoretical study on solute-salts interactions

The effectiveness of a series of five aqueous solutions of choline (Ch)-based ionic liquids (IL), where the corresponding counterions were propanoate [Prop], hexanoate [Hex], nicotinate [Nic], citrate [Cit], and tartrate [Tar], was compared to extracting caffeine (Caf) from a sample of coffee husk (CH), an abundant agro-industrial by-product. The [Ch][Hex] was the most efficient of the series, whereas no significant differences were found among the others. A response surface methodology (RSM) using a three-factor central composite design 23 was used to optimize the process, considering temperature (T), solid/liquid ratio (R) and [Ch][Hex] concentration (C) as the more influential variables. The estimated optimal conditions for the extraction were 95 °C, 0.021 g/mL, and 2.34 M, respectively, which yield 4347.50 ± 115 mgCaf/kgCH; in addition, the [Ch][Hex] solution was reusable, at least twice, without drastically reducing its efficiency. On the other hand, the non-covalent interactions between ILs and caffeine within the complexes IL-Caf were obtained at a DFT level of calculation, including temperature and the solvation effect of water, through AIM and NCI analyses. A net of hydrogen bonds can be observed among the components of the complexes, the strongest ones taking place between hydrogen atoms and hydroxyl or carboxylic groups of the anions, mainly in the citrate and tartrate anions. In contrast, weak hydrogen bonds and van der Waals interactions are predominant between hexanoate and caffeine. Thus, a hydrotropic effect seems to be the driving force in the extraction of the alkaloid with [Ch][Hex]. Thermochemistry of the complexation process was also calculated, and findings were in good agreement with experimental results for the ILs under study.

A simple indicator displacement assay ensemble for rapid and selective determination and naked-eye detection of Cu2+ and citrate through a novel diazo-based colorimetric chemosensor

ABSTRACT Citrate as a naturally occurring ion with important biological roles, especially in metabolic cycles, and as an important biomarker in the early diagnosis of many diseases, including prostate cancer, has received special attention. In the present study, a novel, sensitive, fast and simple colorimetric bisazo-based chemosensor was developed for sequential determination and naked-eye detection of Cu2+ and citrate. UV-Vis spectroscopic studies showed that Reactive Red 141 (RR141) exhibits high selectivity and sensitivity towards Cu2+ in the presence of many other cations in deionised water (10 mmol L−1 MES(2-(N-morpholino)ethanesulfonic acid)/NaOH buffer solution, pH 6.0) and complex real samples as well. The obvious colorimetric response while interaction with copper and citrate is due to complexation between RR141 and Cu2+, and then the citrate detection occurred through metal transfer from the RR141-Cu2+ towards the citrate anion releasing RR141 via an indicator displacement route. The mechanism of detection has been carefully investigated using the semi-empirical calculation method of MM2 molecular mechanics. The proposed detection method for citrate ion has a detection limit of 0.15 µmol L−1 and a satisfactory linear range of 1.92–45.96 µmol L−1, which is consistent with the desired average diagnostic concentration in prostate cancer (less than 2 mmol L−1). Our studies’ results indicate the high capability of the developed chemical sensor for quantitative and qualitative citrate detection in various complex media, including biological and clinical real samples.

Readily available, biocompatible sodium citrate catalyst for efficient glycerol carbonate production through transesterification of glycerol and ethylene carbonate

As a by-product in the biodiesel industry, surplus glycerol (Gly) has attracted considerable concern. The transesterification of Gly is one of the most promising reaction pathways to convert Gly to a value-added chemical such as glycerol carbonate (GC). Currently, development of catalysts for the transesterification with high activity is underway. Herein, a readily available biocompatible sodium citrate (Na3-citrate) catalyst was applied for efficient production of GC through transesterification of Gly and ethylene carbonate (EC). The effects of reaction parameters such as reaction time, EC to Gly molar ratio, reaction temperature, and catalyst loading on the reaction were investigated. Under optimal conditions, 0.01 wt% of Na3-citrate showed high catalytic activities with a Gly conversion of > 99 %, a GC yield of > 99 %, and a high turnover frequency of 16,925 gGC⋅g−1Cat⋅h−1. Furthermore, the reaction kinetic model for transesterification was established, and the activation energy of the Na3-citrate catalyzed transesterification was calculated as 51.3 kJ·mol−1. In addition, density functional theory calculations were used to unveil mechanism of the Na3-citrate catalyzed transesterification. It revealed that citrate anion of Na3-citrate could activate hydroxy of Gly via strong hydrogen bond interaction, thereby efficiently promoting transesterification by reducing energy barrier of rate-determining step.

Anticorrosion Protection of Low‐Carbon Steel by the Eco‐Friendly Composition Based on Gum Arabic

Inhibitory properties of an eco‐friendly composition based on gum arabic polysaccharide and citric acid salt–sodium citrate for corrosion prevention of low‐carbon steel in neutral environment was investigated. Corrosion resistance of low‐carbon steel in a 0.1% NaCl solution with and without composition after 3 and 24 h immersion was investigated by electrochemical and weight loss methods. The inhibitory composition with 0.5 g/L concentration was obtained by adding 0.25 g/L of gum arabic and 0.25 g/L of sodium citrate in 1L 0.1% NaCl solution. It was established that the inhibitory efficiency of the composition is enhanced with increasing concentration (0; 0.25; 0.50; 0.75; 1; 1.50; 2.0 g/L) and reaches a maximum at 2.0 g/L of each component. The protective effect of the composition is determined by the combination of two compounds of different natures, which have hydroxyl and carboxyl functional groups. The inhibitory ability of the composition is due to the dominant competitive adsorption between citrate anions with gum arabic and chloride ions on the steel surface. Adsorption of citrate and gum arabic on the steel surface corresponds to the Frumkin isotherm, and the Gibbs energy value was −12.25 kJ/mol, which indicates physical adsorption. The morphology and chemical content of the steel surface after immersion in a solution with an inhibitory composition were investigated by the scanning electron microscopy (SEM) and EDX analysis. The formation of a protective film based on gum arabic and citrate probably occurs by chelation, which effectively blocks the access of corrosively active Cl− ions. It was shown that the corrosion rate Km was 0.42·10−5 g/cm2·h and the inhibitory efficiency for protection of the steel was 80.4% after 24 h immersion in a 0.1% NaCl solution with composition.

Insights into the catalytic performance of LDHs-derived CoAlO oxides with different anions intercalation for propane total oxidation

Constructing effective and stable non-noble metal catalysts is of great significance and prospect for catalytic oxidation of stable light alkanes at low temperature. Herein, the CoAlO oxide catalysts derived from the CoAl layered double hydroxides (LDHs) intercalated with CO32–, CH3COO– (Ac), SO42-, NO3– and citrate (CA) anions were prepared, and their catalytic performances for propane oxidation were investigated. Among all CoAlO catalysts, the CoAlO-Ac-3 catalyst (CH3COO– anion intercalation) exhibited better catalytic activity for propane oxidation (T90 = 300 °C), with the highest reaction rate (2.79 × 10-7 mol g−1 s−1) and TOF value (0.13 × 10-3 s−1) at 240 °C. Characterization results revealed that the interlayer anions affected the valence distribution of metals and surface active oxygen species, and CH3COO– anion intercalation CoAlO-Ac catalyst showed the highest Co3+/Co2+ molar ratio and active oxygen species. Combining with Raman and in-situ DRIFTS results, the lattice distortion of catalyst caused by the interlayer anions promoted the migration of active oxygen species, thus accelerating the propane adsorption and activation. Meanwhile, CoAlO-Ac-3 catalyst exhibited excellent stability and water resistance for propane oxidation.

CITRIC ACID–SODIUM CITRATE–WATER SOLUTIONS ACID-BASE AND ELECTROCHEMICAL BEHAVIOR

The protolytic equilibria in the system citric acid (H3Cit)–sodium citrate (Na3Cit)–water at a total content of citrates forms (citric acid, dihydrocitrate (H2Cit-), hydrocitrate (HCit2-) and citrate (Cit3-) anions) 1.0 mol/l have been studied by pH- and conductometric methods in the temperature range 293 ÷ 313 K. The first concentration ranges at which pH – lg(νH3Cit/νNa3Cit) and κ – CNa+/Ccit functions are linear correspond to the H3Cit/H2Cit- buffer system; the second ones – to H3Cit/H2Cit- and H2Cit-/HCit2-; the third ones to – HCit2-/Cit3- buffer system. The investigated solutions ion-molecular composition and ionic strength (m, mol/l) have been calculated using the mathematical model taking into account the law of mass action, material balance for citrates and electrical neutrality principle. The ionic strength concentration dependences have a complex character due to the ion-molecular composition multicomponent nature for the studied solutions. The ionic strength values are directly proportional to the ratio [Na+]/CCit in the concentration intervals 0 ≤ [Na+]/CCit ≤ 1.0 and 2.0 ≤ [Na+]/CCit ≤ 3.0. In the concentration range 1.0 ≤ [Na+]/CCit ≤ 2.0, the values of m = 1.15 ± 0.27 mol/l) weakly depend on the [Na+]/CCit ratio and practically do not depend on temperature. Citric acid concentration and thermodynamic constants for the first, second, and third dissociation stages have been determined. The obtained data on the acid-base and electrochemical characteristics of the solutions HOC3H4(COOH)3 – HOC3H4(COONa)3 – H2O(СCit = 1.0 mol/l; СNa+ = 0 ÷ 1.0 mol/l) can be used in chemical analysis, microbiological and biochemical studies, and the acidity data of the solutions studied can simulate chemisorption of acidic (SO2) and/or basic (NH3) gases.

Citrate modulation of CoAl(OH)x Catalyst/Sb–TiO2 nanorods interface boosting photocarrier separation and injection for enhanced water oxidation

The design of an oxygen evolution catalyst (OEC) coupled photoanode ensuring effective charge separation, transfer, and injection is always desirable for enhanced water oxidation kinetics. Here, we have designed Sb-doped TiO2 nanorods (NRs) photoanode coupled with the ultrathin amorphous CoAl(OH)x OEC via citrate anion bridging. The CoAl(OH)x performs as a hole scavenger OEC, a hole storage layer, surface defect passivation layer, and also generates a band banding leading to the built-in potential at the semiconductor/catalyst interface favoring rapid hole separation. The citrate linking improves the CoAl(OH)x/Sb–TiO2 interfacial bonding and reduces the interfacial impedance to boost the photocarrier separation. Citrate bridging also serves as an efficient hole extraction layer and transportation pathway and promotes oxygen vacancy formation, which favors adsorbing OH− during the OER. As a result, the CoAl(OH)x/cit/Sb–TiO2 NRs photoanode exhibits a superior photocurrent density of 1.73 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (VRHE), close to the theoretical maxima of titanium dioxide, with a very low onset potential of 0.12 VRHE and an extremely high hole injection efficiency of 93.1%. This work demonstrates an effective design strategy to boost the performance of OER catalyst coupled photo harvesting semiconductor photoanodes to achieve efficient solar water splitting.

Development of an electrochemical surface‐enhanced Raman spectroscopic biosensor for the direct detection of glutathione

AbstractGlutathione is an important biological free radical scavenger, aiding in the prevention of oxidative stress in living organisms. A decrease in glutathione concentration in cells or bodily fluids is associated with serious health issues including certain cancers and Alzheimer's disease. Rapid detection and quantification of salivary glutathione could play a crucial role in healthcare monitoring as well as in therapeutic progress. This paper reports on the development of a direct electrochemical surface‐enhanced Raman spectroscopic (EC‐SERS) method for the monitoring of glutathione deposited via drop casting from a prepared aqueous stock solution and measured in 0.1‐M sodium fluoride and in artificial saliva. The detection platform for this study is constructed by modifying the working electrode of a carbon screen‐printed electrode with silver nanoparticles of approximately 30 nm in diameter, followed by potassium chloride treatment to remove interfering citrate anions prior to analysis. The coupling of SERS and an applied electrochemical potential resulted in a significantly enhanced spectrum for glutathione compared with those previously reported. Vibrational mode assignment confirmed that glutathione was indeed in close proximity to the surface of the working electrode and had varying anchor points as the potential was stepped anodically. Quantitative analysis of glutathione in artificial saliva showed that the 653 cm−1 marker peak intensity varies linearly (R2 = 0.990) over the concentration of 0.005–1.00 mM on the modified electrode surface. The signal limit of detection of glutathione using EC‐SERS in artificial saliva was determined to be 5 μM. This direct and rapid EC‐SERS detection platform is promising for point‐of‐care diagnostics.

The role of citrate in heterogeneous silver metal catalyst formation: A mechanistic consideration

The formation of silver particles as initial catalyst for the electroless copper deposition is an essential part of the formation of conductive structures in flexible electronics. In this work, we have investigated the basic mechanism using the citrate anion for the fixation of silver species and later metal catalyst formation directly on a textile substrates surface. During the particle formation process and the subsequent electroless copper deposition, silver changes its oxidation state several times. While the decomposition of bulk silver citrate leads to silver metal, the distribution on the substrate surface leads to silver oxide due to the oxidation under air. Finally, the reducing conditions in the copper deposition step, i.e. alkaline formaldehyde, convert any silver-ion to silver metal. In parallel, the thermal decomposition of silver citrate also forms CO2 and hexane-2,5-dione. The latter is the result of an auto oxidation reaction similar to Kolbe electrolysis, i.e. symmetrical radical recombination of two acetonyl radicals remaining from the decarboxylated citrate scaffold.

Multilayer Coatings Based On Citrate-Stabilized Gold Nanoparticles and Polydiallyldimethylammonium Chloride for the Electrophoretic Separation of Carboxylic Acids

The conditions for the formation of physically adsorbed three-layer coatings of quartz capillary walls in capillary electrophoresis (CE) with successively deposited oppositely charged layers of polydiallyldimethylammonium chloride (PDADMAC) modifiers and citrate-stabilized gold nanoparticles (GNPs) are proposed. It was shown that three-layer PDADMAC–GNP–PDADMAC coatings favorably differ from monolayer coatings with PDADMAC by greater stability in a wide range of pH (2–10). The formed coatings were characterized by scanning electron microscopy, and the presence of a uniform dense layer of nanoparticles on the capillary surface was confirmed. The applicability of the modified capillaries under CE conditions was demonstrated by the separation of a mixture of 16 carboxylic acids. An increase in the separation selectivity achieved with the use of three-layer coatings based on GNPs was explained by the reversible exchange of citrate anions on the GNP surface with negatively charged analytes in the course of electrophoretic analysis.

Promotion effect of intercalated citrate anion on the reconstruction of NiFe LDH for oxygen evolution reaction

The promotion effect of citrate anions (CA) on OER activity is considered. CA intercalation could accelerate the structure reconstruction to re-form the catalytically active Ni(Fe)OOH.