Degree Of Deprotonation Research Articles

Control nucleation for strong and tough crystalline hydrogels with high water content

Hydrogels, provided that they integrate strength and toughness at desired high content of water, promise in load-bearing tissues such as articular cartilage, ligaments, tendons. Many developed strategies impart hydrogels with some mechanical properties akin to natural tissues, but compromise water content. Herein, a strategy deprotonation-complexation-reprotonation is proposed to prepare polyvinyl alcohol hydrogels with water content as high as ~80% and favorable mechanical properties, including tensile strength of 7.4 MPa, elongation of around 1350%, and fracture toughness of 12.4 kJ m−2. The key to water holding yet improved mechanical properties lies in controllable nucleation for refinement of crystalline morphology. With nearly constant water content, mechanical properties of as-prepared hydrogels are successfully tailored by tuning crystal nuclei density via deprotonation degree and their distribution uniformity via complexation temperature. This work provides a nucleation concept to design robust hydrogels with desired water content, holding implications for practical application in tissue engineering.

Single-Pore Nanofluidic Logic Memristor with Reconfigurable Synaptic Functions and Designable Combinations.

The biological neural network is a highly efficient in-memory computing system that integrates memory and logical computing functions within synapses. Moreover, reconfiguration by environmental chemical signals endows biological neural networks with dynamic multifunctions and enhanced efficiency. Nanofluidic memristors have emerged as promising candidates for mimicking synaptic functions, owing to their similarity to synapses in the underlying mechanisms of ion signaling in ion channels. However, realizing chemical signal-modulated logic functions in nanofluidic memristors, which is the basis for brain-like computing applications, remains unachieved. Here, we report a single-pore nanofluidic logic memristor with reconfigurable logic functions. Based on the different degrees of protonation and deprotonation of functional groups on the inner surface of the single pore, the modulation of the memristors and the reconfiguration of logic functions are realized. More noteworthy, this single-pore nanofluidic memristor can not only avoid the average effects in multipore but also act as a fundamental component in constructing complex neural networks through series and parallel circuits, which lays the groundwork for future artificial nanofluidic neural networks. The implementation of dynamic synaptic functions, modulation of logic gates by chemical signals, and diverse combinations in single-pore nanofluidic memristors opens up new possibilities for their applications in brain-inspired computing.

Surfactant-Mediated Crystalline Structure Evolution Enabling the Ultrafast Green Synthesis of Bismuth-MOF in Aqueous Condition.

Green synthesis of stable metal-organic frameworks (MOFs) with permanent and highly ordered porosity at room temperature without needing toxic and harmful solvents and long-term high-temperature reactions is crucial for sustainable production. Herein, a rapid and environmentally friendly synthesis strategy is reported to synthesize the complex topological bismuth-based-MOFs (Bi-MOFs),[Bi9(C9H3O6)9(H2O)9] (denoted CAU-17), in water under ambient conditions by surfactant-mediatedsonochemical approach, which could also be applicable to other MOFs. This strategy explores using cetyltrimethylammonium bromide (CTAB) amphiphilic molecules as structure-inducing agents to control the removal of non-coordinated water (dehydration) and enhance the degree of deprotonation of the ligands, thereby regulating the coordination and crystallization in aqueous solutions. In addition, another two new strategies for synthesizing CAU-17 by crystal reconstruction and one-step synthesis in binary solvents are provided, and the solvent-induced synthesis mechanism of CAU-17 is studied. The as-prepared CAU-17 presents a competitive iodine capture capability and effective delivery of the antiarrhythmic drug procainamide (PA) for enteropatia due to the broad pH tolerance and the unique phosphate-responsive destruction in the intestine. The findings will provide valuable ideas for the follow-up study of surfactant-assisted aqueous synthesis of MOFs and their potential applications.

Binding of uranyl cations to a Zr-based metal-organic framework by density functional theory

Zr-based metal–organic frameworks (Zr-MOFs) have been widely used as ion adsorbents for the removal or extraction of toxic and/or radionuclide species from aqueous solutions. However, the mechanisms by which uranyl cations (UO22+) interact with Zr-MOFs have not been established. In this work, the nature of the bonding of uranyl cations with a Zr-MOF was determined using density functional theory for nineteen structurally distinct candidate complexes. The results showed that in all cases the binding energy was of the order of 1.5 eV, but depended on the specific bonding site. The most stable structure involved coordination of the uranyl cation and two structurally distinct oxygens in the Zr-MOF metal node. It was also found that higher degree of deprotonation in Zr-MOF correlated with higher binding energy between the Zr-MOF and uranyl cations. These insights can aid in the design of Zr-MOFs with optimized features for efficient capture of uranyl cations.

Mangiferin is a new potential antimalarial and anticancer drug for targeting serine hydroxymethyltransferase

Mangiferin, a polyphenolic xanthone glycoside found in various botanical sources, including mango (Mangifera indica L.) leaves, can exhibit a variety of bioactivities. Although mangiferin has been reported to inhibit many targets, none of the studies have investigated the inhibition of serine hydroxymethyltransferase (SHMT), an attractive target for antimalarial and anticancer drugs. SHMT, one of the key enzymes in the deoxythymidylate synthesis cycle, catalyzes the reversible conversion of l-serine and (6S)-tetrahydrofolate (THF) into glycine and 5,10-methylene THF. Here, in vitro and in silico studies were used to probe how mangiferin isolated from mango leaves inhibits Plasmodium falciparum and human cytosolic SHMTs. The inhibition kinetics at pH 7.5 revealed that mangiferin is a competitive inhibitor against THF for enzymes from both organisms. Molecular docking and molecular dynamic (MD) simulations demonstrated the inhibitory effects of the deprotonated forms of mangiferin, specifically the C6–O- species and its resonance C9–O- species appearing at pH 7.5, combined with two docked poses, either a xanthone or glucose moiety, placed inside the THF-binding pocket. The MD analysis revealed that both C6–O- and its resonance-stabilized C9–O- species can favorably bind to SHMT in a similar fashion to THF, supporting the THF competitive inhibition of mangiferin. In addition, characterization of the proton dissociation equilibria of isolated mangiferin revealed that only three hydroxy groups of the xanthone moiety, C6–OH, C3–OH, and C7–OH, underwent varying degrees of deprotonation with pKa values of 6.38 ± 0.11, 8.21 ± 0.35, and 12.37 ± 0.30, respectively, while C1–OH remained protonated. Altogether, our findings demonstrate a new bioactivity of mangiferin and provide the basis for the future development of mangiferin as a potent antimalarial and anticancer drug.

Improving the Properties of Anion Exchange Blend Membranes via Optimizing the NPBI Content and Deprotonation Degree: A Theoretical Study

Blending poly[2,2′-(1,4-naphthalene)-5,5′-benzimidazole] (NPBI) with main chain-type N-spirocyclic quaternary ammonium ionenes (SI) could effectively improve the dimensional stability of anion exchange blend membranes (AEBMs), while the mechanism of the effect on OH– transport has not been elucidated. In this work, the effect of the NPBI content and deprotonation degree on OH– transport was revealed by molecular dynamics simulation. The simulation results showed that the free water content increased with increasing NPBI content at the same NPBI deprotonation degree, which facilitated the OH– transport. However, the decreased distance between adjacent N-spirocyclic quaternary ammonium cations (NSQAs) in the interchain and the increased correlation between OH– were detrimental to OH– transport. These resulted in AEBMs with 20 wt % NPBI content exhibiting the best OH– transport. When the NPBI content was 20 wt %, the distance between adjacent NSQAs in the interchain increased and OH– was more dispersed in the aqueous phase with decreasing NPBI deprotonation degrees, leading to the increased OH– transport. Because of the “trade-off” effect between the OH– transport and dimensional stability of AEBMs, we suggest that AEBMs with 20 wt % NPBI content and 50% NPBI deprotonation degree (SI/NP-50-20) can be selected to balance OH– transport and dimensional stability. This work will provide further guidance for the design of blend modification of AEBMs.

Binuclear, tetranuclear and hexadecanuclear thio-oxomolybdenum(V/IV) glycolates with selective adsorptions of gases.

By adjusting the pH values of the solutions, binuclear, tetranuclear and hexadecanuclear glycolato thio- and oxomolybdenum(V/IV) complexes [MoV2O2(μ2-O)(μ2-S)(Hglyc)2(Hpz)2]·H2O (1, H2glyc = glycolic acid, Hpz = pyrazole), (Hdpa)[MoV2O2(μ2-S)2(Hglyc)(glyc)(H2O)] (2, dpa = 2,2'-dipyridylamine), (Hdpa)4[MoV4O4(μ3-O)2(μ2-S)2(glyc)2(S2O3)2] (3) and Na2[MoIV4MoV12O12(μ2-O)6(μ2-OH)2(μ3-O)12(glyc)4(Hpz)4(pz)8]·28H2O (4) have been obtained successfully. Here the glycolates existed in varying aggregates with different degrees of protonation and deprotonation in 1-4. The stable formations of 1 and 2 are attributed to strong hydrogen bonds formed between the molecules. In particular, the asymmetric unit in 2 is a tetramer linked by hydrogen bonding [2.574(9) Å] between α-hydroxy and α-alkoxy groups for further construction of unsaturated penta-coordination environments. Moreover, deprotonated glycolates act as bridging ligands to form tetra- and hexadecanuclear compounds 3 and 4, respectively. The smallest unit in 4 exhibits mixed valences of 4+ and 5+ simultaneously, where its gas adsorption experiments manifest that 4 is obviously beneficial for O2 and CO2 compared with no adsorption of N2, CH4 and H2 at different pressures.

Oxalamide Based Fe(II)-MOFs as Potential Electrode Modifiers for Glucose Detection

In an attempt to expand the coordination chemistry of N,N′-bis(2,4-dicarboxyphenyl)-oxalamide (H6L) ligand, we isolated and structurally characterized two new Fe(II) Metal-Organic Frameworks (MOFs), namely [Fe2(H2L)(H2O)5] (3D-Fe-MOF) and [Fe(H4L)(H2O)2]∙2H2O, (2D-Fe-MOF) by carefully adjusting the reaction conditions to achieve the optimal degree of deprotonation of the bridging ligand. Both MOFs were found stable in water, as evidenced by powder X-ray diffraction data and their ability to sorb glucose (GLU) from either an aqueous solution or artificial sweat was investigated only to show negligible sorption. A graphite paste sensor (GPE) using the 3D-Fe-MOF as a modifier was fabricated. The 3D-Fe-MOF modified GPE was assessed for non-enzymatic GLU detection in aqueous solution at pH 6 via differential pulse voltammetry and the preliminary results were discussed.

Selenite and Selenate Sequestration during Coprecipitation with Barite: Insights from Mineralization Processes of Adsorption, Nucleation, and Growth.

Coprecipitation of selenium oxyanions with barite is a facile way to sequester Se in the environments. However, the chemical composition of Se-barite coprecipitates usually deviates from that predicted from thermodynamic calculations. This discrepancy was resolved by considering variations in nucleation and growth rates controlled by ion-mineral interactions, solubility, and interfacial energy. For homogeneous precipitation, ∼10% of sulfate, higher than thermodynamic predictions (<0.3%), was substituted by Se(IV) or Se(VI) oxyanion, which was attributed to adsorption-induced entrapment during crystal growth. For heterogeneous precipitation, thiol- and carboxylic-based organic films, utilized as model interfaces to mimic the natural organic-abundant environments, further enhanced the sequestration of Se(VI) oxyanions (up to 41-92%) with barite. Such enhancement was kinetically driven by increased nucleation rates of selenate-rich barite having a lower interfacial energy than pure barite. In contrast, only small amounts of Se(IV) oxyanions (∼1%) were detected in heterogeneous coprecipitates mainly due to a lower saturation index of BaSeO3 and deprotonation degree of Se(IV) oxyanion at pH 5.6. These roles of nanoscale mineralization mechanisms observed during composition selection of Se-barite could mark important steps toward the remediation of contaminants through coprecipitation.

Framework robustness in early d-block metal complexes with tripodal polyalcohol ligands

While performing our research on the tetranuclear “star-shaped” complexes formulated as [M3M'(LR)2(dpm)6], where M, M' are first-row d-block metals; H3LR is a tripodal alcohol, RC(CH2OH)3, with R = Et, Me or Ph; and Hdpm = dipivaloylmethane, we isolated a series of binuclear, alkoxide-bridged chelate complexes of titanium and chromium upon spontaneous deprotonation of the polyalcohol. In the titanium system, both [TiIII2Cl4(H2LEt)2]·4thf and [TiIV2Cl4(HLEt)2]·2thf were identified; they present analogous binuclear frameworks but distinct metal oxidation states and polyalcohol deprotonation degrees. Four similar CrIII2 compounds were also isolated, differing in the tripodal R groups and cocrystallized solvent or proligand molecules. The products were characterized by single-crystal X-ray diffraction analysis and spectroscopic, thermogravimetric and magnetic measurements. Cocrystallization influences the nature, strength and pattern of intermolecular interactions. Among the binuclear MIII products, all those containing solvating tetrahydrofuran, [M2Cl4(H2LR)2]·x thf (R = Et, Ph; x = 4 or 5 respectively), lose solvent upon gradual polyalcohol deprotonation, mild heating or vacuum drying. The versatile tripodal skeleton assembles the alkoxide-bridged M2 units (M = TiIII/IV or CrIII) in various experimental conditions, including air or inert atmosphere and non-protic or protic media, and confers remarkable robustness to the final binuclear aggregates.

The influence of solvent controlled morphology on capacitive properties of metal-organic frameworks based on polyaminocarboxybenzene ligands

In order to overcome the low capacitive performance of traditional metal organic frameworks (MOFs) applied to supercapacitors, a novel conjugated small molecule monomer(3,5-diaminobenzoic acid, DABA) with amino and carboxyl groups was used as a ligand, and Ni and Co ions as metal nodes to construct novel highly electroactive bimetallic MOF(DABA-MOF) materials through a simple one-step solvothermal method. The structure and capacitive performance of obtained DABA-MOF in three organic solvents with different polarities and degrees of deprotonation (methanol, ethanol, N,N-dimethylformamide) was investigated, and it was found that with the increase of solvent deprotonation degree, the morphology of DABA-MOF with the coexistence of amino and carboxyl groups gradually changes from a smooth rod-shaped solid structure to a rough hydrangea-like structure, and the corresponding capacitive performance of DABA-MOF is also gradually enhanced. In particular, DABA-MOF synthesized in DMF can reach a maximum specific capacitance of 621 C g−1 at 1 A g−1, and the capacitance remains as high as 81.05% even after 5000 cycles, which exhibit excellent capacitance properties. This study shows that it has potential advantages to select the mixed coordination active MOF with amino and carboxyl groups as the electrode material for supercapacitor, and the deprotonation degree of solvent has a great influence on the structure and morphology of MOF with mixed active coordination sites.

Structural variety, fluorescence and photocatalytic activity of dissymmetric thiosemicarbazone complexes

A new dissymmetric bis(thiosemicarbazone) ligand, H2L2, containing a 4-(1-naphthyl)-3-thiosemicarbazone branch has been easily prepared and characterized. The reactivity of this ligand and the hybrid isopropylthiosemicarbazone/naphtoylhydrazone, H2L1, with zinc(II), copper(II) and nickel(II) nitrates in the presence of different amounts of lithium hydroxide has been explored. The results show that although both ligands present two different acidic protons, the degree of deprotonation of the ligand cannot be selectively controlled, since in almost all the reactions carried out without base the ligand is at least singly deprotonated. Nevertheless, an interesting structural diversity is found, also influenced by the metal structural preferences, leading to the formation of monomeric (1–5, 8 and 9), dimeric (6) and polymeric (7) species. The different degree of deprotonation of the ligands, together with the presence or the absence of nitrate ions and solvent molecules, lead to the formation of different supramolecular architectures based on different hydrogen bond arrays. Fluorescence spectroscopy in the solid state for the ligands and the complexes was performed and the results show that whereas H2L1 is fluorescent, for H2L2 no fluorescence emission was detected. Complexation of H2L1 leads, in general, to a quench of the fluorescence emission, except for complex [ZnL1(EtOH)] 2, which is much more fluorescent than the free ligand. Conversely, complexation of H2L2 with zinc(II) causes fluorescence emission. Photocatalytic experiments with the nickel and copper complexes shows that the four complexes can effectively degrade methyl orange under UV–vis irradiation.

The inhibiting water uptake mechanism of main-chain type N-spirocyclic quaternary ammonium ionene blended with polybenzimidazole as anion exchange membrane

Molecular dynamics (MD) and density functional theory (DFT) were utilized to evaluate the effect of deprotonation degree and flexibility of polybenzimidazole (PBI) on the inhibiting water uptake mechanism of main-chain type N-spirocyclic quaternary ammonium ionene (SI) as anion exchange membranes (AEMs). Results show that the electrostatic interactions play a key role in inhibiting water uptake of the blend membranes, which is mainly originated from the N+ of SI and the N- of deprotonated PBI and partly from the inter-molecular weak hydrogen bonding C-H···N and C-H···π. The Eele between SI and PBI of SI/NP-50 and SI/NP-100 increases by 745.6% and 1291.8% compared with SI/NP-0 at λ=40, respectively, which exhibits the PBI deprotonation enhances the electrostatic interactions. And the Eele between SI and PBI increases as the flexibility of PBI decreases. Furthermore, the π-π stacking interactions contribute to the inhibiting water uptake of SI AEMs. The AEM of SI blended with low flexible poly[2,2′-(1,4-naphthalene)-5,5′-bibenzimidazoles] (NPBI) exhibits excellent dimensional stability due to strong electrostatic interactions. Our work deepens the understanding of the inhibiting water uptake mechanism of SI blended with PBI as AEMs from a microscopic viewpoint, and provides guidance for the selection of PBI structure.

Acid-Base Equilibrium and Dielectric Environment Regulate Charge in Supramolecular Nanofibers.

Peptide amphiphiles are a class of molecules that can self-assemble into a variety of supramolecular structures, including high-aspect-ratio nanofibers. It is challenging to model and predict the charges in these supramolecular nanofibers because the ionization state of the peptides are not fixed but liable to change due to the acid-base equilibrium that is coupled to the structural organization of the peptide amphiphile molecules. Here, we have developed a theoretical model to describe and predict the amount of charge found on self-assembled peptide amphiphiles as a function of pH and ion concentration. In particular, we computed the amount of charge of peptide amphiphiles nanofibers with the sequence C 16 − V 2 A 2 E 2. In our theoretical formulation, we consider charge regulation of the carboxylic acid groups, which involves the acid-base chemical equilibrium of the glutamic acid residues and the possibility of ion condensation. The charge regulation is coupled with the local dielectric environment by allowing for a varying dielectric constant that also includes a position-dependent electrostatic solvation energy for the charged species. We find that the charges on the glutamic acid residues of the peptide amphiphile nanofiber are much lower than the same functional group in aqueous solution. There is a strong coupling between the charging via the acid-base equilibrium and the local dielectric environment. Our model predicts a much lower degree of deprotonation for a position-dependent relative dielectric constant compared to a constant dielectric background. Furthermore, the shape and size of the electrostatic potential as well as the counterion distribution are quantitatively and qualitatively different. These results indicate that an accurate model of peptide amphiphile self-assembly must take into account charge regulation of acidic groups through acid–base equilibria and ion condensation, as well as coupling to the local dielectric environment.

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

Modulating the Structures and Magnetic Properties of Dy(III) Single-Molecule Magnets through Acid-Base Regulation.

Chemical modulation on the structures and physical properties of the coordination complexes is of great interest for the preparation of new functional materials. By changing the acidity or basicity of the reaction medium, the deprotonation degree of a multidentate ligand with multiple active protons, H4daps (H4daps = N',N'″-((1E,1'E)-pyridine-2,6-diylbis(ethan-1-yl-1-ylidene))bis(2-hydroxybenzohydrazide)), can be regulated on purpose. With this ligand of different deprotonation and charges, three new DyIII complexes ([Dy(H3daps)(CH3COO)2(EtOH)]·CH3COOH (1Dy), [Dy2(H2daps)2(EtOH)2(H2O)2(MeOH)2](CF3SO3)2·(H2O)2 (2Dy), and [Dy3(H1daps)2(H2daps)(μ3-OH)(EtOH)(H2O)] (3Dy)) of different nuclearities (mono-, di-, and trinuclear for 1Dy to 3Dy, respectively) have been synthesized and characterized structurally and magnetically. Analyses on the related bond lengths and resulting hydrogen bond modes in the complexes provide the details of the deprotonation position and the charge of the ligands, which can be in the form of H3daps-, H2daps2-, and H1daps3-. Interestingly, the more deprotonated ligand can act as a bridging ligand between the DyIII centers using the phenol and/or carbonyl oxygen atoms, which leads to the multinuclear structures. Magnetic studies on these complexes revealed that complex 1Dy is a field-induced single-molecule magnet (SMM), while complexes 2Dy and 3Dy show SMM behavior under a zero dc field.

FeIII in a high-spin state in bis(5-bromosalicylaldehyde 4-ethylthiosemicarbazonato-κ3O,N1,S)ferrate(III) nitrate monohydrate, the first example of such a cationic FeIII complex unit.

The synthesis and crystal structure (100 K) of the title compound, [Fe(C10H11BrN3OS)2]NO3·H2O, is reported. The asymmetric unit consists of an octahedral [FeIII(HL)2]+ cation, where HL- is H-5-Br-thsa-Et or 5-bromosalicylaldehyde 4-ethylthiosemicarbazonate(1-) {systematic name: 4-bromo-2-[(4-ethylthiosemicarbazidoidene)methyl]phenolate}, a nitrate anion and a noncoordinated water molecule. Each HL- ligand binds via the thione S, the imine N and the phenolate O atom, resulting in an FeIIIS2N2O2 chromophore. The ligands are orientated in two perpendicular planes, with the O and S atoms in cis and the N atoms in trans positions. This [Fe(HL)2](anion)·H2O compound contains the first known cationic FeIII entity containing two salicylaldehyde thiosemicarbazone derivatives. The FeIII ion is in the high-spin state at 100 K. In addition, a comparative IR spectroscopic study of the free ligand and the ferric complex is presented, demonstrating that such an analysis provides a quick identification of the degree of deprotonation and the coordination mode of the ligand in this class of metal compounds. The variable-temperature magnetic susceptibility measurements (5-320 K) are consistent with the presence of a high-spin FeIII ion with a zero-field splitting D= 0.439 (1) cm-1.

Anion Specific Effects at Negatively Charged Interfaces: Influence of Cl-, Br-, I-, and SCN- on the Interactions of Na+ with the Carboxylic Acid Moiety.

Unlike counterion interactions with charged interfaces, the influence of co-ions is only scarcely reported in the literature. In this work, the effect of SCN– and the halide co-ions in the interactions of Na+ with carboxylic acid Langmuir monolayers is investigated by using vibrational sum frequency spectroscopy. At 1 M concentrations in the subphase, the identity of the anion is shown to have a remarkable influence on the charging behavior and degree of deprotonation of the monolayer, with ions ordering in the sequence I– > SCN– > Cl– ≈ Br–. The same trend is observed at both pH 6 and pH 9 when the monolayer is intrinsically more charged. Spectroscopic evidence is found for both the presence of I– and SCN– in the interfacial region at levels close to their detection limits. The results contradict electrostatic theories on charged interfaces where co-ions are not expected to play any significant role. The higher propensity for the large polarizable anions to deprotonate the monolayer is explained in terms of their ability to modify the cations affinity toward the carboxylic acid groups present at the surface.

Anodic Transformation of a Core‐Shell Prussian Blue Analogue to a Bifunctional Electrocatalyst for Water Splitting

AbstractDeveloping low‐cost oxygen evolution reaction (OER) catalysts with high efficiency and understanding the underlying reaction mechanism are critical for electrochemical conversion technologies. Here, an anodized Prussian blue analogue (PBA) containing Ni and Co is reported as a promising OER electrocatalyst in alkaline media. Detailed post‐mortem characterizations indicate the transformation from PBA to Ni(OH)2 during the anodic process, with the amorphous shell of the PBA facilitating the transformation by promoting greater structural flexibility. Further study with operando Raman and X‐ray photoelectron spectroscopy reveal the increase of anodic potential improves the degree of deprotonation of the transformed core‐shell PBA, leading to an increase of Ni valence. Density functional theory calculations suggest that the increase of Ni valence results in a continuous increase in the adsorption strength of oxygen‐containing species, exhibiting a volcano relationship against the OER activity. Based on the experiments and calculated results, an OER mechanism for the transformed product is proposed. The fully activated catalyst also works as the cathode and the anode for a water‐splitting electrolysis cell with a high output current density of 13.7 mA cm−2 when a cell voltage of 1.6 V applied. No obvious performance attenuation is observed after 40 h of catalysis.

Thermodynamic Study on the Dissociation and Complexation of Coumarinic Acid with Neodymium(III) and Dioxouranium(VI) in Aqueous Media

In the frame of a systematic study on the sequestering ability of natural antioxidants towards metal cations, the complexation of coumarin-3-carboxilic acid (HCCA) with neodymium(III) and dioxouranium(VI) (uranyl, UO22+), and overall stability constants of the resulting complexes, were evaluated from the pH-potentiometric titration data at 37 °C and in an aqueous solution (i.e., 0.16 mol/L NaClO4). The graphic representation of the complex’s concentration curves is given by the distribution diagrams, which provide a depiction of all the species present in the solution in the selected pH ranges. The protonation constant of HCCA was also determined to evaluate the competition of the ligand for the metal cations and H+. The ligand-to-metal concentration ratio was varied between 1 and 10, and the hydrogen ion concentration was decreased stepwise until the incipient precipitation of a basic salt of the metal, which occurred at different values depending on the specific metal cation and the ligand to metal ratio. Speciation profiles obtained by potentiometric titrations and supported by UV-Vis data show that a complexation occurs at a ligand-to-Nd(III) and to –UO22+ ratio of 1:1 and 2:1, with different degrees of deprotonation: Nd(OH)(CCA)+, UO2(OH)(CCA), UO2(OH)2(CCA)−, and Nd(OH)(CCA)2, UO2(CCA)2 and (UO2)2(OH)2(CCA)2.