Citrate Anions Research Articles

Synergetic effect of vancomycin loaded silver nanoparticles for enhanced antibacterial activity.

In recent years, there is significant growth in the bacterial resistance to various classic antibiotics. This has opened and enhanced the field of metal nanoparticles and antibiotic-metal nanoparticle complex. This research was designed to load a glycopeptide antibiotic named vancomycin on citrate-capped silver nanoparticles to enhance its antibacterial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. Colloidal solution of silver nanoparticles (AgNPs) was prepared by chemical reduction method using silver nitrate (AgNO3) as a precursor in the presence of ionic surfactant trisodium-citrate which acts as a both capping and reducing agent. Synthesized nanoparticles were functionalized with vancomycin to form nano-drug complex (Van@AgNPs). Various analytical techniques such as UV-vis absorption spectra, FTIR, DLS, TEM and XRD were carried out to study the loading and interaction of drug with silver nanoparticles. The observed shift in SPR peak of UV-vis and various reflections of XRD spectra is attributed towards the loading of vancomycin on silver nanoparticle surface. FTIR studies shows the hydrogen bonding between vancomycin and silver nanoparticles through NH (amine) group of vancomycin and oxygen of anionic citrate. The increase in average particle size and particle size distribution of vancomycin-loaded nanoparticles in comparison to bare NPs also hints the drug loading. Agar well diffusion method was used to study the synergetic antibacterial activity of vancomycin-loaded silver nanoparticles against both test strains. The well diffusion test showed the notable enhancement in antibacterial activity against both class of bacteria. This enhancement has been observed to be synergetic rather than the additive.

Interaction of americium with citric acid: Structural and spectral study of (NH4)2{Co(NH3)6}2[Am3(Citr)4(OH)(H2O)2]·nH2O

Americium citrate, (NH4)2{Co(NH3)6}2[Am3(Citr)4(OH)(H2O)2]·nH2O, was synthesized and characterized using X-ray crystallography, IR and optical spectroscopy. Americium atoms are coordinated by citrate anions acting as tetradentate ligands. All carboxylic and hydroxylic groups of citric acid are deprotonated. By this means, complex anions [Am3(Citr)4(OH)(H2O)2]8− are formed. Large cavities present in the structure contain solvate water molecules.

Cyano-Bridged Cu-Ni Coordination Polymer Nanoflakes and Their Thermal Conversion to Mixed Cu-Ni Oxides

Herein, we demonstrate the bottom-up synthesis of 2D cyano-bridged Cu-Ni coordination polymer (CP) nanoflakes through a controlled crystallization process and their conversion to Cu-Ni mixed oxides via a thermal treatment in air. The chelating effect of citrate anions effectively prevents the rapid coordination reaction between Cu2+ and K2[Ni(CN)4], resulting in the deceleration of the crystallization process of CPs. Specifically, with addition of trisodium citrate dehydrate, the number of nuclei formed at the early stage of the reaction is decreased. Less nuclei undergo a crystal growth by interacting with [Ni(CN)4]2−, leading to the formation of larger Cu-Ni CP nanoflakes. Following heat treatment in air, the -CN- groups present within the CP nanoflakes are removed and nanoporous Cu-Ni mixed oxide nanoflakes are generated. When tested as an electrode material for supercapacitors using a three-electrode system, the optimum Cu-Ni mixed oxide sample shows a maximum specific capacitance of 158 F g−1 at a current density of 1 A g−1. It is expected that the proposed method will be useful for the preparation of other types of 2D and 3D CPs as precursors for the creation of various nanoporous metal oxides.

Negative‐Imaging of Citrate Layers on Gold Nanoparticles by Ligand‐Templated Metal Deposition: Revealing Surface Heterogeneity

AbstractSurface heterogeneity of a metal nanoparticle is typically regarded as boundary defects and various crystalline facets. While organic capping ligands of a single type are assumed to be homogeneously distributed on the nanoparticle surface, heterogeneous surface coverage of citrate molecules on individual facets of gold nanoparticles (AuNPs) is revealed. Pt metallic clusters with 2 nm in diameter, epitaxially grown on the surface of AuNPs by chemical reaction and imaged by high‐resolution transmission electron microscopy, are utilized as negative‐imaging probes for densely packed adlayers where the underneath gold surface may not be accessible for Pt deposition. At pH > 5.0, citrate anions form only a loosely packed layer. At pH 4.5, citrates and citric acids form both loosely packed and densely packed layers that appear phase separated, and the densely packed domain as small as 5 nm × 5 nm is likely composed of fully protonated citric acids. IR spectra indicate that citric acid binds to a surface Au adatom through the oxygen atom of the central hydroxyl group, and similarly, citrate anions bind to Au adatoms through the carboxylate oxygen atom. This study also reveals the role of Au adatom in the adsorption of citrate species on the metallic surface of AuNPs.

Density, Structure, and Stability of Citrate3– and H2citrate– on Bare and Coated Gold Nanoparticles

We simulate the packing of citrate3– and H2citrate– onto gold nanoparticles (AuNPs) to understand how citrate anions cap and stabilize AuNPs. We determine the molecular configurations of citrate on 4, 6, and 8 nm AuNP surfaces as a function of charge state and packing density and find that both the distribution of configurations and maximum packing density are independent of AuNP size. A combination of molecular dynamics simulations and in situ Fourier transform infrared spectroscopy (FTIR) is employed to compare the molecular configurations, stability, and density of citrate on 4 nm citrate-coated (cit-AuNPs) and within polycation-wrapped 4 nm cit-AuNPs. FTIR experiments indicate the presence of H2citrate– within polycation-wrapped cit-AuNPs with coordination between the H2citrate– layer and polycation layer in agreement with simulations. Intermolecular hydrogen bonding between terminal carboxylic acid groups of H2citrate– stabilizes the anionic layer at the interface between cit-AuNPs and adsorbing char...

Novel fluorescent probes for relay detection copper/citrate ion and application in cell imaging.

Two novel fluorescent probes, 2‑(2'‑hydroxyphenyl)‑4‑(2'‑hydroxymethyl‑8‑quinolinamino)methyloxazole (L1), and 2‑(2'‑hydroxyphenyl)‑4‑(2'‑methyl‑8‑quinolinamino)methyloxazole (L2), exhibited colorimetric and "turn off" fluorometric response to Cu2+ ion in DMSO/H2O solution (v/v = 1/1, 0.01 M, Tris-HCl buffer, pH 7.20) and the corresponding detection limit were found to be 2.14 × 10-8 and 2.70 × 10-8 M, which were much lower than drinking water permission concentrations by the United States Environmental Protection Agency (U.S. EPA) and World Health Organization (WHO). The L1-Cu2+ and L2-Cu2+ complexes ensemble detected citrate anions (CA) sequentially through fluorescence recovery response due to the extrusion of Cu2+ ion from the complexes. The binding processes were investigated by UV-vis, fluorescence, IR and DFT calculation. Furthermore, the vivo sensitivity experiments of Cu2+ ion and CA was demonstrated through fluorescence imaging in living cells.

Crystal structure of hydroxyquinol 1,2-dioxygenase PnpC from Pseudomonas putida DLL-E4 and its role of N-terminal domain for catalysis.

Hydroxyquinol 1,2-dioxygenase is a key enzyme in the hydroxyquinol pathway of p-nitrophenol (PNP) degradation, and catalyzes the ring cleavage of benzenetriol to maleylacetate. Here, we report the first structure of a hydroxyquinol 1,2-dioxygenase from the Gram-negative bacterium Pseudomonas putida DLL-E4 (PnpC) at the resolution of 2.1 Å. The tertiary structure of PnpC resembles that of the homologous intradiol dioxygenases. The catalytic Fe(III) is pentacoordinated by the conserved Tyr160, Tyr194, His218 and His220, the citrate anion and one water molecule. Among the residues expected to interact with the substrate, structural comparison with the (chloro)catechol dioxygenases suggested that Asp80, Thr81 and Val248 are responsible for the substrate specificity. Moreover, truncation of the N-terminal α-helix of PnpC suggested the N-terminal domain is required for its soluble expression and enzyme catalysis. Our results might provide insights in the substrate recognition and rational design of this enzyme class to be used in bioremediation.

Controlled synthesis of Cu2O microcrystals in membrane dispersion reactor and comparative activity in heterogeneous Fenton application

A surfactant-free approach is proposed to fabricate various-shaped Cu2O particles with good uniformity by ceramic membrane dispersion. Glucose reduced cupric salt and precipitated Cu2O (dimension ca. 1 μm and crystal size 18.5 nm) whose homogeneity was distinctly improved by distributing glucose solution through the ceramic mesoporous membrane. Particle shape including cube, sphere-like, octahedron and eight-pod was controlled kinetically by changing the concentration of sodium carbonate and sodium citrate with constant copper concentration. Morphologic transformation mechanism was studied with diffraction intensity ratio of (111)/(100) crystal planes. Micro-cubes formed at low pH and octahedral ones formed at high pH since crystal facet (111) is more stable than (100) with increased alkalinity. At the same pH, eight-pod grains were formed instead of cubes by adding citrate anions. Cu2O powders in octahedral shape was of the highest catalytic activity to degrade the organic pollutants in a heterogeneous Fenton reaction. CODs in an industrial pulp wastewater was eliminated from initial value 133 mg/L as low as to 26 mg/L. Reduction rate of CODs in water by the octahedral Cu2O was 80% while the commercial Cu2O was only 30%.

Transverse Relaxivity of Nanoparticle Contrast Agents for MRI: Different Magnetic Cores and Coatings

Four types of magnetic nanoparticles were synthesized, namely, the La0.65Sr0.35MnO3and La0.80Na0.20MnO3 perovskite manganites and the Mn0.61Zn0.42Fe1.97O3 and Co0.44Zn0.70Fe1.86O4 spinel ferrites. Subsequent coating with silica provided typical core–shell particles with the mean shell thickness of 14–19 nm and the mean size of cores of 49–52 nm in the case of manganites and 26–33 nm in the case of ferrites. Moreover, two other surface modifications were employed for Mn–Zn ferrite nanoparticles, specifically coating with titania, leading to larger clusters with more complex morphology, and the stabilization by citrate anions. The products were characterized by powder X-ray diffraction and transmission electron microscopy, and their magnetic properties were probed by SQUID magnetometry. The main attention was devoted to the relaxometry on aqueous suspensions of particles in a magnetic field of 0.5 T. For distinct types of the prepared core–shell nanoparticles, the temperature dependence of transverse relaxivity was measured and the role of different relaxation regimes was analyzed.

Synthesis and characterization of citrate intercalated layered double hydroxide as a green adsorbent for Ni2+ and Pb2+ removal.

Recently, a considerable attention has been paid on the preparation of layered double hydroxide (LDH) as a green adsorbent. This research presents a study on nickel and lead removal by Ca/Fe layered double hydroxides intercalate with citrate anions (Ca-Fe/LDH-Cit) which was successfully prepared through the co-precipitation and hydrothermal method. The as-synthesized Ca-Fe/LDH-Cit was characterized by various techniques including FT-IR, XRD, TGA, FE-SEM, and TEM techniques. The maximum uptake capacities of Ca-Fe/LDH-Cit were 2.26mg/g for Ni(II) and 61.73mg/g for Pb(II) inferred from the Langmuir model at the contact time of 30min and pH of 7. Based on the results, the adsorption and kinetic isotherms were in good agreement with the Langmuir model and the pseudo-second-order equation, respectively. The results suggested that the composite adsorbent has the good ability to remove the Ni2+ and Pb2+ ions from aqueous solutions. The results reveal that the composite adsorbent can be considered as a high-capacity absorbent for Ni(II) and Pb(II) removal and also as a potential candidate for practical applications.

Ferric pyrophosphate citrate: interactions with transferrin

There are several options available for intravenous application of iron supplements, but they all have a similar structure:—an iron core surrounded by a carbohydrate coating. These nanoparticles require processing by the reticuloendothelial system to release iron, which is subsequently picked up by the iron-binding protein transferrin and distributed throughout the body, with most of the iron supplied to the bone marrow. This process risks exposing cells and tissues to free iron, which is potentially toxic due to its high redox activity. A new parenteral iron formation, ferric pyrophosphate citrate (FPC), has a novel structure that differs from conventional intravenous iron formulations, consisting of an iron atom complexed to one pyrophosphate and two citrate anions. In this study, we show that FPC can directly transfer iron to apo-transferrin. Kinetic analyses reveal that FPC donates iron to apo-transferrin with fast binding kinetics. In addition, the crystal structure of transferrin bound to FPC shows that FPC can donate iron to both iron-binding sites found within the transferrin structure. Examination of the iron-binding sites demonstrates that the iron atoms in both sites are fully encapsulated, forming bonds with amino acid side chains in the protein as well as pyrophosphate and carbonate anions. Taken together, these data demonstrate that, unlike intravenous iron formulations, FPC can directly and rapidly donate iron to transferrin in a manner that does not expose cells and tissues to the damaging effects of free, redox-active iron.

Salt-Induced Thermoresponsivity of a Cationic Phosphazene Polymer in Aqueous Solutions

Poly(ethylaminophosphazene) (PEAP) in salt-free aqueous solution does not reveal thermoresponsive properties but acquires thermoresponsivity upon addition of various poly(protic acid)s. Energetics of the salt-induced phase separation transition of the PEAP solutions upon heating was investigated by high-sensitivity differential scanning calorimetry at pH 3.5. At low concentrations of poly(carboxylic acid)s (10–100 mM), the transition temperature and enthalpy vary from 90 to 25 °C and from 1.5 to 35 J g–1, respectively, depending on the pKa1 and the apparent hydrophobicity of the acids. Dependences of the transition parameters (Tt, Δth, and Δtcp) on the citrate buffer concentration were obtained. The binding curve of citrate anions to PEAP was derived. High concentrations of sulfate anions (0.1–0.8 M) induced a marginal phase transition at high temperatures. A mechanism of the PEAP thermoresponsivity is proposed. The Okado–Tanaka model for cooperative hydration of macromolecules is used to quantitatively d...

Novel fluorescent probes for sequential detection of Cu2+ and citrate anion and application in living cell imaging

Three novel fluorescent probes (L1, L2 and L3) derived from 2-hydroxyphenyl-4-chloromethyloxazole 8-ydroxyquinaldine were designed and synthesized. The probes showed highly selectively and sensitivity towards Cu2+ ion through “turn off” response in DMF/H2O solution (v/v = 1/1, 0.01 M, Tris-HCl buffer, pH 7.30). The detection limits of probes were up to 8.24 × 10−8 M for Cu2+ ion, which were much lower than drinking water permission concentrations by the United States Environmental Protection Agency. Sequentially, the L1-Cu2+, L2-Cu2+ and L3-Cu2+ complexes detected citrate anion (CA) through “turn on” response. The probes, were also found to be reversible and recyclable toward Cu2+ ion and CA controlled “On–Off–On” fluorescent switch and acted as molecular logic gates. Furthermore, the in vivo sensitivity experiments of Cu2+ ion and CA were demonstrated through fluorescence imaging in living cells.

The effect of chelating anions on the retention of Co(II) by γ-alumina from aqueous solutions under the unadjusted pH condition of supported catalyst preparation

This study analyzes the effect of the addition of acetate, citrate, and nitrilotriacetate anions on the retention of Co(II) cations by the γ-alumina surface in view of the preparation of alumina supported cobalt catalysts. The emphasis was placed on the way the Co(II) species attach to the solid surface when adsorbed from aqueous solutions under the unadjusted pH condition. The individual adsorption isotherms onto γ-Al2O3 support for cobalt and a given ligand were determined by following the solution depletion method in single-solute and bi-solute systems. These adsorption data were supplemented by the results of potentiometric titrations. In the case of bi-solute systems, the adsorption procedures allowed either co-impregnation of γ-alumina with equimolar solutions of cobalt and ligand salts or pre-impregnation of γ-alumina with the ligand anions and the subsequent adsorption of cobalt. Changes in the pH of the equilibrium solid-liquid suspension were also monitored along the adsorption isotherms. The adsorption of Co(II) onto γ-Al2O3 in the presence of acetate and nitrilotriacetate led to the formation of the type A (i.e., solid-metal-ligand) ternary complexes. The use of citrate anions together with Co(II) cations was shown to improve the impregnation process through the formation of ternary complexes of type B (i.e., solid-ligand-metal). The comparison with a system containing tricarballylate anions allowed concluding that the presence of the hydroxyl group in the citrate anion enhanced its affinity for the alumina surface by contributing to the inner-sphere character of its surface-bound complexes.

Dilithium (citrate) crystals and their relatives.

New compounds of the type LiMHC6H5O7 (M = Li, Na, K, Rb) have been prepared from the metal carbonates and citric acid in solution. The crystal structures have been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. The compounds crystallize in the triclinic space group P-1 and are nearly isostructural. The structures are lamellar, with the layers in the ab plane. The boundaries of the layers consist of hydrophobic methylene groups and very strong intermolecular O-H...O hydrogen bonds. The O...O distances range from 2.666 Å for M = Li to 2.465 Å for M = Rb. The Li-O bonds exhibit significant covalent character, while the heavier M-O bonds are ionic. The Li atoms are four-, five-, or six-coordinate, while the coordination numbers of the larger cations are higher, i.e. eight for Na and nine for K and Rb. The citrate anion occurs in the trans,trans conformation, one of the two low-energy conformations of an isolated citrate anion. The crystal structure of LiRbHC6H5O7·H2O was also solved and refined. It consists of the same layers as in the anhydrous M = Rb compound, with interlayer water molecules and a different hydrogen-bonding pattern.

Broadband dielectric spectroscopy of protic ethylammonium-based ionic liquids synthetized with different anions

In this work, we present the synthesis of the of 2‑Hydroxy ethylammonium Lactate (HELa) and of 2‑Hydroxy ethylammonium Citrate (HECi) protic ionic liquids and their electric characterization by broadband dielectric spectroscopy. The complex permittivity ε∗ and electrical conductivity σ∗ of HELa and HECi as a function of frequency and of temperature are obtained. The experimental results are discussed considering the type of anion in each ionic liquid. In the high frequency range (f > 1KHz), at room temperature (T ~25 °C), the HELa protic ionic liquid has been shown an electric conductivity higher than that formed by citrate anion.

Coacervation of the Recombinant Mytilus galloprovincialis Foot Protein-3b.

The underwater adhesion of marine mussels is a fascinating example of how proteinaceous adhesives, although water-soluble to begin with, can be used in seawater. Marine mussels adhere to the substrate via adhesive plaques, where the adhesive proteins are located especially at the substratum's interface. One major compound of the adhesives in Mytilidae is the mussel foot protein 3b (mfp-3b). Here, recombinant mfp-3b (rmfp-3b) was produced in Escherichia coli. rmfp-3b showed upper critical solution temperature (UCST) mediated complex coacervation at pH 3.0 in the presence of citrate yielding a liquid-liquid phase separation. Further, the rmfp-3b coacervation could also be induced in seawater conditions such as the respective pH and ionic strength, but without UCST behavior. In particular, sulfate and citrate anions could significantly induce complex coacervation. This study provides insights into the molecular behavior of one of the key proteins of mussels involved in underwater adhesion and may inspire new applications of bioadhesives using recombinant mussel foot proteins.

Study of liquid-liquid equilibria in aqueous two-phase systems formed by poly (ethylene glycol) (PEG) and sodium thiosulfate pentahydrate (Na2S2O3.5H2O) at different temperatures

This study aimed at providing experimental liquid-liquid equilibrium (LLE) data for aqueous two-phase systems (ATPSs) formed by poly (ethylene glycols) (PEG) of different molecular weights (1500 or 4000 or 6000) g.mol−1 and sodium thiosulfate pentahydrate at different temperatures (293.15–313.15) K and under atmospheric pressure. Correlations of experimental data of binodal curves were carried out using the Merchuk methodology. The effects of temperature, polymer molecular weight and of the nature of the anion of salts on binodal curves were discussed. In comparison with other anions previously investigated, the salting-out ability of the thiosulfate anion was between those of citrate and tartrate anions. Finally, the Othmer-Tobias and Bancroft equations and the NRTL activity coefficient model were used for correlating tie line compositions.

Adsorption Dynamics and Structure of Polycations on Citrate-Coated Gold Nanoparticles

Despite the widespread application of engineered multilayered polyelectrolyte-coated gold nanoparticles (AuNPs), their interparticle interaction is not fully understood in part because of a lack of molecular scale observation of the layer-by-layer assembly of the polyelectrolyte coating. While top-down coarse-grained models of polyelectrolyte-coated AuNPs have focused on polyelectrolytes of short length, from 10 to a 100 monomers represented as one charged bead per monomer, here we use molecular dynamics and bottom-up coarse-grained approaches to access more typical polymer lengths on the order of 200 monomers. Specifically, we simulate the adsorption dynamics and structure of one or two such long polycations on negatively charged 4 nm citrate-coated AuNPs within implicit or explicit solvents. The first polycation coats approximately half of the AuNP surface regardless of solvent model and leaves a significant part of the anionic citrate layer exposed to absorption by a second polycation. We find that the...

(Invited) Impacts of Anions on Oxygen Reduction Reaction Kinetics on Platinum and Palladium Surfaces

Fundamental understandings on the impacts induced by anions and cations on oxygen reduction reaction (ORR) are of great interest in designing more efficient catalysts and identifying reasons for discrepancies in activities measured in different protocols. In this study, the specific adsorption of F-, Cl-, ClO4 -, CO3 2-, SO4 2-, Nafion ionomer, and citrate anions on Pt/C, Pd/C and transition metal, N co-doped carbon-based (Me-N-C) catalysts, and their effects on the ORR kinetics were systematically investigated. It was found that ClO4 - had a negligible impact on the ORR activity of Pt/C possibly due to its weak adsorption. Nafion ionomers, on the other hand showed a significant poisoning effect on the bulk Pt electrode. Its impact on Pt/C, however is negligible even with a very high I/C ratio (1.33) in acidic solutions. The three catalysts showed different behaviors in alkaline solutions. The non-covalent interaction between hydrated cations and surface OH groups was found on Pt/C and had an obvious impact on the ORR kinetics. This non-covalent interaction, however was not observed on Pd/C, which showed the same ORR activity in all three electrolytes (LiOH, NaOH and KOH). The ORR activity of Me-N-C increased following the order of KOH < NaOH < LiOH. This trend is totally opposite to that of Pt/C. Self-dissociation of citrate anion was found to occur on both Pt/C and Pd/C in the H adsorption/desorption and double layer regions. For the first time, surface enhanced infrared absorption spectroscopy (SEIRAS) with the attenuated total reflection (ATR) technique was used to investigate the self-dissociation of citrate on Pt and Pd thin film electrodes. The break of carboxylic groups and carbon backbone were proposed as possible dissociation pathways for citrate. The adsorbed species have a negligible effect on ORR activity on Pt/C as they are removed by oxidation before 0.75 V. In contrast, their oxidation on Pd/C surfaces is not completed until 0.91 V, which causes a lower ORR activity observed in rotating disk electrode measurements.