Carboxylic Proton Research Articles

Supramolecular assembly strategy of modified starch chains for achieving recyclable emulsion biocatalysis within a narrow pH range

Stimuli-responsive Pickering emulsions are promising in biocatalysis for their ease of product separation and emulsifier recovery. However, pH responsiveness, though simple and cost-effective, faces challenges in precise control and narrow transition ranges, limiting its use in enzymatic catalysis. Herein we introduced amorphous octenyl succinic anhydride-modified debranched starch chains (Am-OSA-St) to control emulsion properties within a pH range suitable for enzymatic catalysis. By adjusting the OSA group density and molecular weight, Am-OSA-St allowed emulsions to transition reversibly between pH 7.3 and 5.5 and enabled self-recycling through supramolecular self-assembly. Employing molecular dynamics simulations and physicochemical characterization, we elucidated the control mechanism of oil-water interfaces via the microstructure transformation of Am-OSA-St. The findings revealed that protonation of carboxylate groups disrupted the charge balance and polarity of starch chains, leading to strong electrostatic and van der Waals interactions that drove self-assembly. This entanglement caused starch chains in the aqueous phase to “drag” those at the oil-water interface, moving them into the aqueous phase and forming micelles. These micelles, with a hydrophobic interior and hydrophilic exterior, prevented re-adsorption. Testing with Candida antarctica Lipase B (CALB) and N-acetylneuraminic lyase showed that the pH-regulated emulsion system maintained excellent efficiency and cycling stability in mild conditions.

Ionized Carboxyl Protonation Strategy to Improve Water Resistance of Carboxymethyl Cellulose-Based Ultraviolet-Shielding Films

Ionized Carboxyl Protonation Strategy to Improve Water Resistance of Carboxymethyl Cellulose-Based Ultraviolet-Shielding Films

On-demand release of silver from composite hydrogel by cold atmospheric plasma jet for wound infection control

Silver is an antimicrobial commonly used within wound care chiefly in advanced dressings or in a topical cream form, such as silver sulfadiazine (SSD). Although silver is effective at controlling the growth of many common wound bacteria, it can be cytotoxic and can build up in tissue, stalling the healing process. Here, we demonstrate the development of an on-demand release system for delivery of silver from a composite hydrogel comprising sodium polyacrylate particles dispersed in a cryo-crosslinked polyvinyl alcohol carrier gel. Application of cold atmospheric plasma (CAP) jet to the silver loaded hydrogel resulted in controlled release of silver. This release is thought to occur due to the formation of nitrous acids in the hydrogel by the CAP, resulting in protonation of carboxylate groups in the hydrogel and subsequent gel de-swelling due to the reduction in interchain charge repulsion. The location of silver within the sodium polyacrylate particles was probed using scanning electron microscopy and EDX imaging. The released silver inhibited the growth of Enterococcus faecalis, Pseudomonas aeruginosa, and Staphylococcus aureus and significantly reduced the viable cell count of the P. aeruginosa biofilm.

Synthesis, Characterization and Evaluation of the Antimicrobial and Herbicidal Activities of Some Transition Metal Ions Complexes with the Tranexamic Acid.

New tranexamic acid (TXA) complexes of ferric(III), cobalt(II), nickel(II), copper(II) and zirconium(IV) were synthesized and characterized by elemental analysis (CHN), conductimetric (Λ), magnetic susceptibility investigations (μeff), Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR), ultraviolet visible (UV-vis.), optical band gap energy (Eg) and thermal studies (TG/DTG and DTA). TXA complexes were established in 1 : 2 (metal: ligand) stoichiometric ratio according to CHN data. Based on FT-IR and 1H-NMR data the disappeared of the carboxylic proton supported the deprotonating of TXA and linked to metal ions via the carboxylate group's oxygen atom as a bidentate ligand. UV-visible spectra and magnetic moment demonstrated that all chelates have geometric octahedral structures. Eg values indicated that our complexes are more electro conductive. DTA revealed presence of water molecules in inner and outer spheres of the complexes. DTA results showed that endothermic and exothermic peaks were identified in the degradation mechanisms. The ligand and metal complexes were investigated for their antimicrobial and herbicidal efficacy. The Co(II) and Ni(II) complexes showed antimicrobial activity against some tested species. The obtained results showed a promising herbicidal effect of TXA ligand and its metal complexes particularly copper and zirconium against the three tested plants.

Novel bioactive petrodispersing agents based on cationic polymeric surfactant: Design, synthesis, and surface indices

Novel bioactive cationic polymeric surfactants based on fatty acid derived from natural wastes were developed with different hydrophilic head groups, which were employed for collecting the thin petroleum film from water surface and dispersing it. The preparation procedures pass through three steps, in first step lauryl methacrylate (LMA) was copolymerized with methacrylic acid (MAA) with different feed from the two monomers to obtain five copolymers of poly(LMA-co-MAA) (P1-5) of different molar ratio. In second step, carboxylic groups in copolymers (P1-5) were esterified with N,N‘-dimethyl-ethanol amine and finally the modified copolymers (PE1-5) were quaternized with Butyl-2-chloroacetate and Hexyl-2-chloroacetate to afford the bioactive PSB1-5 and PSH1-5, respectively. The structure of synthetic compounds was confirmed by FT-IR and 1H NMR. Upon examination, the surface-active characteristics of the bioactive petrodispersing agents that were synthesized exhibited significant defoaming capacity, good wettability, and foaming qualities. The synthesized PSB1-5 and PSH1-5 were applied for petro-collecting and dispersing in solid state and diluted form on three water sources. In sea water and diluted form, the results showed that PSB1-5 showed better effects than PSH1-5. Also, the antimicrobial efficiency of the synthesized PSB(1-5) and PSH(1-5) were tested. The data obtained from FT-IR and 1H NMR spectra proved the esterification of carboxylic group in copolymers due to the appearing of peak at 1738 cm−1 for carbonyl group of formed esters and the disappearing for proton of carboxylic group in 1H NMR. Also, data obtained from antimicrobial studies showed that the highest inhibition zone diameter against C. albicans, L. monocytogenes, S. aureus, Salmonella sp. and E. coli were observed for PSH(1-5). Which PSH-2 gives the highest value of inhibition zone diameter of 3.2 mm against L. monocytogenes. The results exhibited that PSH(1-5) showed the stronger antimicrobial functions than PSB(1-5).

Elucidating the Structure of the Eu‐EDTA Complex in Solution at various Protonation States

Ethylenediaminetetraacetic acid (EDTA), which has two amine and four carboxylate protonation sites, forms stable complexes with lanthanide ions. This work analyzes the coordination structure, in atomic resolution, of the Eu3+ ion complexed with EDTA in all its protonation states in aqueous solution. Eu‐EDTA complexes were modeled using classical molecular dynamics (MD) simulations using force field parameters optimized with ab initio molecular dynamics (AIMD) simulations. Structures from the MD simulations were used to predict extended X‐ray absorption fine structure (EXAFS) spectra and compared with EXAFS measurements of the Eu3+ aqua ion and Eu‐EDTA complexes at pH 3 and 11. This work details how Eu‐EDTA complex coordination structures change with increasing protonation of the EDTA ligand in the complex, from the tightly bound unprotonated complex to the unbinding of the fully protonated EDTA ligand from the Eu3+ ion as both become solvated by water. Agreement between predicted and measured EXAFS spectra supports the findings from simulation.

Rational Design of 2D Supramolecular Networks Switchable by External Electric Fields.

The reversible formation of hydrogen bonds is a ubiquitous mechanism for controlling molecular assembly in biological systems. However, achieving predictable reversibility in artificial two-dimensional (2D) materials remains a significant challenge. Here, we use an external electric field (EEF) at the solid/liquid interface to trigger the switching of H-bond-linked 2D networks using a scanning tunneling microscope. Assisted by density functional theory and molecular dynamics simulations, we systematically vary the molecule-to-molecule interactions, i.e., the hydrogen-bonding strength, as well as the molecule-to-substrate interactions to analyze the EEF switching effect. By tuning the building block's hydrogen-bonding ability (carboxylic acids vs aldehydes) and substrate nature and charge (graphite, graphene/Cu, graphene/SiO2), we induce or freeze the switching properties and control the final polymorphic output in the 2D network. Our results indicate that the switching ability is not inherent to any particular building block but instead relies on a synergistic combination of the relative adsorbate/adsorbate and absorbate/substrate energetic contributions under surface polarization. Furthermore, we describe the dynamics of the switching mechanism based on the rotation of carboxylic groups and proton exchange, which generate the polarizable species that are influenced by the EEF. This work provides insights into the design and control of reversible molecular assembly in 2D materials, with potential applications in a wide range of fields, including sensors and electronics.

Exploring Ring Conformation in Uronate Monosaccharides: Insights from Ab Initio Calculations and Classical Molecular Dynamics Simulations.

The study focuses on the conformational properties of biologically relevant monosaccharides belonging to the group of uronates: α-l-iduronate, O2-sulfated-α-l-iduronate, and O2-sulfated-α-l-guluronate, either unfunctionalized or O1-methylated. We applied the previously proposed two-step methodology, combining classical MD simulations and subsequent ab initio (QM) calculations, performed on a rationally subsampled set of molecular configurations. We found that, regardless of the number of molecular configurations considered, the level of theory, and the weighting scheme applied, none of the QM approaches is capable of predicting the correct conformational equilibrium of sulfated iduronates as long as the tight counterion binding is not considered. Multicenter, ring-shape-specific binding of either Na+ or Ca2+ ions drastically shifts the conformational equilibrium of the pyranose ring in sulfated iduronates toward 1C4 but does not significantly affect the conformation of non-sulfated compounds. A similar shift is observed upon the protonation of carboxyl groups in all iduronates. In addition, we report a set of average J-coupling constant values related to vicinal protons bound to the pyranose ring of iduronates and corresponding to each of the three main groups of ring conformers, i.e., 4C1, B/S (boat/skew boat), and 1C4. In combination with the conformational energies or with the experimental data, these values allowed the relative proportions of the ring conformers to be estimated and the Karplus-type equations linking the 3JHH-coupling constants to the torsion angles within the pyranose ring to be refined.

A Janus hydrogel sealant with instant wet adhesion and anti-swelling behavior for gastric perforation repair

Achieving instant adhesion on wet tissues and preventing the concurrently occurred postoperative tissue adhesion remain tough challenges but urgently demanded. And the deteriorated cohesion and adhesion caused by undesired swelling of hydrogel could not be ignored. Herein, we developed a Janus hydrogel with instant wet adhesion and anti-swelling behavior, based on poly (acrylic acid) (PAA), gelatin (GT) and hyperbranched polymers modified with catechol (HBPC). The asymmetric structure is achieved through complexed one-side of the hydrogel with cationic polymers. The strong physical interaction between PAA and GT formed during immersing in water enhanced the mechanical strength of the gels. And the hydrogel exhibits good anti-swelling behavior, which circumvents the limitations of conventional hydrogel caused by swelling. Water drainage induced by hydrophobic component and the following removal of water residuals achieved by hydrophilic PAA synergistically enhanced the instant wet adhesion of the hydrogel. Besides, pH-responsive protonation of carboxyl groups in PAA equipped the adhesive with extreme acid-tolerance. The in vivo evaluation results demonstrated that the asymmetric adhesive hydrogel could promote the repair of gastric perforation while reducing the risk of postoperative tissue adhesion. The hydrogel with asymmetric wet adhesion might provide valuable insights into the establishment of bioadhesives for gastric sealing and repair.

SOLVOTHERMAL SYNTHESIS, STRUCTURE, AND PROPERTIES OF CADMIUM(II)-ORGANIC COORDINATION POLYMER CONTAINING CARBOXYL GROUPS

Under the conditions of solvothermal synthesis, a new metal-organic coordination polymer of the composition Cd[H2L] (I, H4L = 4,4'-([2,2'-bipyridine]-6,6'-diylbis(oxy))diphthalic acid). According to X-ray diffraction analysis, each Cd(II) cation binds four organic ligands: one via the coordination of the chelate bipyridyl fragment, two via the bidentate coordination of deprotonated COO groups, and one more via the monodentate coordination of the protonated carboxylate group. The obtained three-dimensional metal-organic framework does not contain free space capable of including guest molecules. Compound I was characterized by powder X-ray diffraction, IR spectroscopy, elemental (C, H, N) and thermogravimetric analyses, and luminescence spectra were recorded for it.

Quantum Design and Synthesis of a Gasoline Marker Based on a Phenol‐Functionalized Supramolecular Quaternary‐Salt Complex

AbstractWe present the development of supramolecular surfactants (SSs) based on MR⋅⋅⋅OA⋅⋅⋅(PhOH)i complexes among methylene red (MR), oleyl amine (OA) and stoichiometric amounts of phenol (PhOH), aimed at obtaining markers for the identification of gasolines by harnessing their supramolecular interactions‐mediated stability and homogeneous distribution within gasoline, as well as their very‐characteristic nuclear magnetic resonance (NMR), Fourier‐transform infrared (FTIR), and UV‐visible (UV‐vis) signals. Density functional theory (DFT), together with the conductor‐like screening model (COSMO), reveal that the supramolecular interactions are due to a non‐ionic to ionic reaction under which the carboxylic proton is transferred from MR to OA, and that PhOH confers solubility to SSs withing gasoline by hiding their ionic heads. The proton transference was confirmed by 1H NMR and 13C NMR, FTIR, and thermogravimetric analysis spectroscopies, whereas the solubility in gasoline through UV‐vis absorbance measurements that, together with viscosity measurements, also revealed that the maximum content of PhOH for adequate performance is 3, in agreement with DFT‐COSMO calculations, which predict that for 3 the SSs’ interaction energy per additional PhOH becomes weaker. All theoretical and experimental results support the viability of MR⋅⋅⋅OA⋅⋅⋅(PhOH)i complexes as gasoline markers due to their full compatibility with gasoline and their well‐defined spectroscopic‐fingerprints.

Dissecting Reaction Mechanisms and Catalytic Contributions in Flavoprotein Fumarate Reductases.

The interconversion between fumarate and succinate is fundamental to the energy metabolism of nearly all organisms. This redox reaction is catalyzed by a large family of enzymes, fumarate reductases and succinate dehydrogenases, using hydride and proton transfers from a flavin cofactor and a conserved Arg side-chain. These flavoenzymes also have substantial biomedical and biotechnological importance. Therefore, a detailed understanding of their catalytic mechanisms is valuable. Here, calibrated electronic structure calculations in a cluster model of the active site of the Fcc3 fumarate reductase were employed to investigate various reaction pathways and possible intermediates in the enzymatic environment and to dissect interactions that contribute to catalysis of fumarate reduction. Carbanion, covalent adduct, carbocation, and radical intermediates were examined. Significantly lower barriers were obtained for mechanisms via carbanion intermediates, with similar activation energies for hydride and proton transfers. Interestingly, the carbanion bound to the active site is best described as an enolate. Hydride transfer is stabilized by a preorganized charge dipole in the active site and by the restriction of the C1-C2 bond in a twisted conformation of the otherwise planar fumarate dianion. But, protonation of a fumarate carboxylate and quantum tunneling effects are not critical for catalysis of the hydride transfer. Calculations also suggest that the driving force for enzyme turnover is provided by regeneration of the catalytic Arg, either coupled with flavin reduction and decomposition of a proposed transient state or directly from the solvent. The detailed mechanistic description of enzymatic reduction of fumarate provided here clarifies previous contradictory views and provides new insights into catalysis by essential flavoenzyme reductases and dehydrogenases.

Exploring the Macroscopic Properties of Humic Substances Using Modeling and Molecular Simulations

Soil organic matter (SOM) is composed of a complex and heterogeneous mixture of organic compounds, which poses a challenge in understanding it on an atomistic level. Based on the progress of molecular dynamics simulations and our efforts to create molecular systems that resemble SOM, in this work, we expanded our knowledge of SOM through the use of humic substances (HSs). Specifically, we studied the standardized samples of HS of the International Humic Substances Society (IHSS). This society provided the elemental and organic composition used as input parameters for our Vienna Soil Organic Matter Modeler 2 (VSOMM2). We modeled and simulated different HS samples from various sources, including soil, peat, leonardite, and blackwater river. In order to compare between different HS, we reduced the organic composition information to two principal components, which are associated principally with the amount of carboxyl and aromatic groups in the HS, denominated as PCacid and PCarom, respectively. We performed a plethora of analyses to characterize the structure and dynamics of the systems, including the total potential energy, density, diffusion, preferential solvation, hydrogen bonds, and salt bridges. In general terms, at the water content value of 0.2, we observed that most properties depend on the carboxyl group protonation state. The Coulombic interactions from this ionic specie and the interaction with cations determine the overall behavior of the studied systems. Furthermore, the type of cations and the pH influence those properties. This study exemplifies the importance of molecular dynamics to explain macroscopic properties from the structure and dynamics of the molecules modeled, such as the interaction network, i.e., hydrogen bonds or salt bridges of molecules presented in the system and their mobility.

NMR and DFT studies of monounsaturated and ω-3 polyunsaturated free fatty acids in the liquid state reveal a novel atomistic structural model of DHA

Structures of low-energy conformers of caproleic acid (CA; 10:1 cis-9), oleic acid (OA; 18:1 cis-9), α-linolenic acid (ALA; 18:3 cis-9,12,15 ω-3), eicosapentaenoic acid (EPA; 20:5 cis-5,8,11,14,17 ω-3), and docosahexaenoic acid (DHA; 22:6 cis-4,7,10,13,16,19 ω-3) in the liquid state, based on detailed 1D NOE and density functional theory calculations of 1H NMR chemical shifts are presented. Transient 1D NOE experiments with variable mixing time showed significant through-space proximity of the CH2–COOH protons and the terminal CH3– groups. Variable temperature 1H NMR experiments revealed strong intermolecular centro-symmetric cyclic hydrogen bond interactions of the carboxylic groups of the monounsaturated oleic and caproleic acids (δ(COOH) ∼ 12.0–12.4 ppm), ALA and EPA (δ(COOH) ∼ 11.0 ppm). On the contrary, the carboxylic proton of DHA is strongly shielded with δ(COOH) ∼ 8.5 ppm. DFT calculations were interpreted in terms of aggregates of dimerized fatty acids with parallel and antiparallel interdigitated structures. The antiparallel arrangement was found to be in excellent agreement with experimental 1D NOE NMR data. For the dimeric DHA, a flip-flop process between a classical intermolecular centro-symmetric hydrogen bond through carboxylic groups and a novel intramolecular hydrogen bond between the carboxylic group and the terminal ω-3 double bond is demonstrated.

Interaction of Chondroitin and Hyaluronan Glycosaminoglycans with Surfaces of Carboxylated Carbon Nanotubes Studied Using Molecular Dynamics Simulations

Interaction of β-D-glucopyranuronic acid (GlcA), N-acetyl-β-D-glucosamine (GlcNAc), N-acetyl-β-D-galactosamine (GalNAc) and two natural decameric glycosaminoglycans, hyaluronic acid (HA) and Chondroitin (Ch) with carboxylated carbon nanotubes, were studied using molecular dynamics simulations in a condensed phase. The force field used for carbohydrates was the GLYCAM-06j version, while functionalized carbon nanotubes (fCNT) were described using version two of the general amber force field. We found a series of significant differences in carbohydrate-fCNT adsorption strength depending on the monosaccharide molecule and protonation state of surface carboxyl groups. GlcNAc and GalNAc reveal a strong adsorption on fCNT with deprotonated carboxyl groups, and a slightly weaker adsorption on the fCNT with protonated carboxyl groups. On the contrary, GlcA weakly adsorbs on fCNT. The change in protonation state of surface carboxyl groups leads to the reversal orientation of GlcNAc and GalNAc in reference to the fCNT surface, while GlcA is not sensitive to that factor. Adsorption of decameric oligomers on the surface of fCNT weakens with the increasing number of monosaccharide units. Chondroitin adsorbs weaker than hyaluronic acid and incorporation of four Ch molecules leads to partial detachment of them from the fCNT surface. The glycan-fCNT interactions are strong enough to alter the conformation of carbohydrate backbone; the corresponding conformational changes act toward a more intensive contact of glycan with the fCNT surface. Structural and energetic features of the adsorption process suggest the CH-π interaction-driven mechanism.

4 in 1: multifunctional europium-organic frameworks with luminescence sensing properties, white light emission, proton conductivity and reverse acetylene-carbon dioxide adsorption selectivity.

Lanthanide metal-organic frameworks (Ln-MOFs) combine the lanthanide luminescence characteristics and the advantages of porous materials, which can be used in various research fields by exploring their multifunctional properties. A three-dimensional water-stable and high-temperature resistant Eu-MOF [Eu(H2O)(HL)]·0.5MeCN·0.25H2O (H4L = 4-(3,5-dicarboxyphenoxy)isophthalic acid), demonstrating a high photoluminescence quantum yield, was synthesized and structurally characterized. In terms of luminescence, the Eu-MOF exhibits excellent selectivity and quenching sensing for Fe3+ (LOD = 4.32 μM) and ofloxacin, as well as color modulation with Tb3+ and La3+ to develop white LED components with high illumination efficiency (color rendering index, CRI = 90). On the other hand, narrow one-dimensional channels of the Eu-MOF decorated with COOH groups enable a rare reverse adsorption selectivity in a CO2/C2H2 gas mixture. In addition, the protonated carboxyl groups in the Eu-MOF provide an efficient conducting platform for proton transfer with a conductivity value of 8 × 10-4 S cm-1 at 50 °C and RH 100%.

A combined solid-state NMR and quantum chemical calculation study of hydrogen bonding in two forms of α-d-glucose

Hydrogen bonding plays an important role in the structure and function of a wide range of materials. Solid-state 1H nuclear magnetic resonance (NMR) spectroscopy provides a very sensitive tool to investigate the local structure of hydrogen atoms involved in hydrogen bonding. While there is extensive 1H solid-state NMR data on O–H - - O hydrogen bonding in solid carboxylic acids, there has been no systematic 1H solid-state NMR studies of hydroxyl groups in carbohydrates (and hydroxyl groups in general). With a view to studying the hydrogen bonding in more complex materials such as cellulose polymorphs, we carried out a detailed solid-state 1H NMR investigation of the model compounds α-d-glucose and α-d-glucose monohydrate. Through a combination of fast magic-angle spinning (MAS), combined rotation and multiple pulse spectroscopy (CRAMPS), and two-dimensional (2D) correlation experiments carried out at ultrahigh magnetic fields, it was possible to assign all of the aliphatic (CH), hydroxyl (OH), and water (H2O) 1H chemical shifts in both forms of α-d-glucose. Plane-wave DFT calculations were employed to improve the hydrogen atom positions for α-d-glucose monohydrate and to calculate 1H chemical shifts, providing additional support for the experimentally determined peak assignments. Finally, the relationship between the hydroxyl 1H chemical shifts and their hydrogen bonding geometry was investigated and compared to the well-established relationship for carboxylic acid protons.

Stimulation–Inhibition of Protein Release from Alginate Hydrogels Using Electrochemically Generated Local pH Changes

The electrochemically controlled release of proteins was studied in a Ca2+-cross-linked alginate hydrogel deposited on an electrode surface. The electrochemical oxidation of ascorbate or reduction of O2 was achieved upon applying electrical potentials +0.6 or -0.8 V (vs Ag/AgCl/KCl 3 M), respectively, resulting in decreasing or increasing pH locally near an electrode surface. The obtained local acidic solution resulted in the protonation of carboxylic groups in the alginate hydrogel and, as a result, the formation of a hydrophobic shrunken hydrogel film. Conversely, the produced alkaline local environment resulted in a hydrophilic swollen hydrogel film. The release of the proteins was effectively inhibited from the shrunk hydrogel and activated from the swollen hydrogel film. Overall, the electrochemically produced local pH changes allowed control over the biomolecule release process. While the release inhibition by applying +0.6 V was always effective and could be maintained as long as the positive potential was applied, the release activation was different depending on the protein molecular size, being more effective for smaller species, and molecule charge, being more effective for negatively charged species. The repetitive change from the inhibited to stimulated state of the biomolecule release process was obtained upon cyclic application of oxidative and reductive potentials (+0.6 V ↔ -0.8 V). The alginate hydrogel film shrinking-swelling as well as the protein release process were studied and visualized using a confocal fluorescent microscope. In order to be observed, an external surface of the alginate film and the loaded protein molecules were labeled with different fluorescent dyes, which then produced colored fluorescent images under a confocal microscope.

Novel Enrofloxacin Schiff Base Metal Complexes: Synthesis, Spectroscopic Characterization, Computational Simulation and Antimicrobial Investigation against Some Food and Phyto-Pathogens

Condensation of the reaction between enrofloxacin and ethylenediamine in the existence of glacial acetic acid produced a new N,N-ethylene (bis 1-cyclopropyl-7-(4-ethylpiperazin-1-yl)-6-fluoro-1,4-dihydroquinoline-3-carboxylic acid Schiff base (H2Erx-en). H2Erx-en was used as a tetra-dentate ligand to produce novel complexes by interacting with metal ions iron(III), yttrium(III), zirconium(IV), and lanthanum(III). The synthetic H2Erx-en and its chelates had been detected with elemental analysis, spectroscopic methods, mass spectrometry, thermal studies, conductometric and magnetic measurements experiments. The calculated molar conductance of the complexes in 1 × 10−3 M DMF solution shows that iron(III), yttrium(III) and lanthanum(III) are 1:1 electrolytes, however the zirconium(IV) complex is non-electrolyte. The infrared spectra of H2Erx-en chelates indicated that the carboxylic group is deprotonated and H2Erx-en is associated with metals as a tetra-dentate through nitrogen and oxygen atoms. The disappearance of the carboxylic proton in all complexes corroborated information concerning H2Erx-en deprotonation and complexation with metal ions, according to 1H NMR data. Thermal analysis revealed the abundance of H2O particles in the chelates’ entrance and outlet spheres, indicating the disintegration pattern of H2Erx-en and their chelates. The Coats–Redfern and Horowitz–Metzeger approaches were utilized to calculate the thermodynamic items (Ea, ΔS *, ΔH *, and ΔG *) at n = 1 and n ≠ 1. The resulting data reveal better organized chelate building activation. Density functional theory (DFT) was created to properly grasp the optimal architecture of the molecules. The chelates are softer than H2Erx-en, with estimates varying between 95.23 eV to 400.00 eV, compared to 31.47 eV for H2Erx-en. The disc diffusion technique was utilized to assess H2Erx-en and their chelates in an antimicrobial assay against various food and phytopathogens. The zirconium(IV) chelate has the most potent antibacterial action and is particularly efficient against Salmonella typhi.

Resin-Mediated pH Control of Metal-Loaded Ligand Exchangers for Selective Nitrogen Recovery from Wastewaters.

Highly selective separation materials that recover total ammonia nitrogen (i.e., ammonia plus ammonium, or TAN) from wastewaters as a pure product can supplement energy-intensive ammonia production and incentivize pollution mitigation. We recently demonstrated that commercial acrylate cation exchange polymer resins loaded with transition metal cations, or metal-loaded ligand exchangers, can recover TAN from wastewater with high selectivity (TAN/K+ equilibrium selectivity of 10.1) via metal-ammine bond formation. However, the TAN adsorption efficiency required further improvement (35%), and the optimal concentration and pH ranges were limited by both low ammonia fractions and an insufficiently strong resin carboxylate-metal bond that caused metal elution. To overcome these deficiencies, we used a zinc-acrylate ligand exchange resin and a tertiary amine acrylic weak base resin (pH buffer resin) together to achieve resin-mediated pH control for optimal adsorption conditions. The high buffer capacity around pH 9 facilitated gains in the adsorbed TAN per ligand resin mass that enhanced the TAN adsorption efficiency to greater than 90%, and constrained zinc elution (below 0.01% up to 1 M TAN) because of decreased ammonia competition for zinc-carboxylate bonds. During TAN recovery, resin-mediated pH buffering facilitated recovery of greater than 99% of adsorbed TAN with 0.2% zinc elution, holding the pH low enough to favor ammonium but high enough to prevent carboxylate protonation. For selective ion separation, solid phase buffers outperform aqueous buffers because the initial solution pH, the buffering capacity, and the ion purity can be independently controlled. Finally, because preserving the resin-zinc bond is crucial to sustained ligand exchange performance, the properties of an ideal ligand resin functional group were investigated to improve the properties beyond those of carboxylate. Ultimately, ligand exchange adsorbents combined with solid pH buffers can advance the selective recovery of nitrogen and potentially other solutes from wastewaters.