Coordinated Hydroxyl Groups Research Articles

Characteristics and mechanism of Ni2+ and Cd2+ adsorption by recovered perlite from agar extraction residue

Ni2+ and Cd2+ in wastewater accumulated through the ecological chain and could jeopardize human health. Adsorption of Ni2+ and Cd2+ from wastewater using recovered perlite was an important way to solve the problem of resource utilization of solid waste from agar production. Our previous study confirmed that recovered perlite from agar extraction residue had better pore size and specific surface area than commercial perlite. However, the adsorption efficiency and adsorption mechanism of recovered perlite were the main factors limiting its adsorption application. The adsorption process of Ni2+ and Cd2+ by recovered perlite in aqueous solution was described by the pseudo-second-order kinetic equation, and the relevant adsorption mechanism was mainly chemisorption. Compared with commercial perlite, the adsorption removal rate of Ni2+ and Cd2+ by enzymatic recovered perlite could reach 92.9% and 89.2%, respectively, and were improved by 12.63% and 13.03%. Langmuir isothermal adsorption model could better describe isothermal adsorption process of recovered perlite on heavy metal Ni2+ and Cd2+, and the relevant adsorption mechanism was mainly monolayer adsorption. The XPS results indicated that the decrease of Si-O Si2+ hydroxyl coordination bond and the increase of C-Si bond might make the binding effect of recovered perlite with heavy metals stronger. The competitive adsorption of Ni2+ and Cd2+ by recovered perlite was still dominated by chemisorption and monolayer adsorption. This study was expected to provide theoretical basis and technical support for the removal of Ni2+ and Cd2+ from wastewater using recovered perlite from seaweed residue.

The Angiotensin Metabolite His-Leu Is a Strong Copper Chelator Forming Highly Redox Active Species.

His-Leu is a hydrolytic byproduct of angiotensin metabolism, whose concentration in the bloodstream could be at least micromolar. This encouraged us to investigate its Cu(II) binding properties and the concomitant redox reactivity. The Cu(II) binding constants were derived from isothermal titration calorimetry and potentiometry, while identities and structures of complexes were obtained from ultraviolet-visible, circular dichroism, and room-temperature electronic paramagnetic resonance spectroscopies. Four types of Cu(II)/His-Leu complexes were detected. The histamine-like complexes prevail at low pH. At neutral and mildly alkaline pH and low Cu(II):His-Leu ratios, they are superseded by diglycine-like complexes involving the deprotonated peptide nitrogen. At His-Leu:Cu(II) ratios of ≥2, bis-complexes are formed instead. Above pH 10.5, a diglycine-like complex containing the equatorially coordinated hydroxyl group predominates at all ratios tested. Cu(II)/His-Leu complexes are also strongly redox active, as demonstrated by voltammetric studies and the ascorbate oxidation assay. Finally, numeric competition simulations with human serum albumin, glycyl-histydyl-lysine, and histidine revealed that His-Leu might be a part of the low-molecular weight Cu(II) pool in blood if its abundance is >10 μM. These results yield further questions, such as the biological relevance of ternary complexes containing His-Leu.

Polyphenol‐Copper Derived Self‐Cascade Nanozyme Hydrogel in Boosting Oxygenation and Robust Revascularization for Tissue Regeneration

AbstractThe regeneration of hypoxia‐impaired chronic tissue defects has long been challenging, mainly due to the inefficiency of oxygenation and the limited biological activity of existing oxygen delivery systems in regulating dynamic tissue regeneration process. Herein, a novel polyphenol‐copper coordination strategy to fabricate bioactive superoxide dismutase‐catalase self‐cascade nanozymes (SalB‐CuNCs) is reported, which can serve as an in situ oxygenator and induce angiogenesis simultaneously. The copper‐phenolic hydroxyl coordination structure in SalB‐CuNCs plays a critical role in promoting the enzyme‐like cascade reaction via catechol‐mediated Cu valence state transition and substrate capture mechanism. Furthermore, after incorporating SalB‐CuNCs into a Schiff base hydrogel (COC@SalB‐Cu), the resulting system exhibits outstanding antioxidant and robust oxygenation effect in mitigating the hypoxic microenvironment. Benefiting from the intrinsic angiogenic activity of SalB and copper, COC@SalB‐Cu hydrogel can induce a more complete tube formation by up‐regulating the expression level of vascular endothelial growth factor (VEGF), platelet‐endothelial cell adhesion molecule‐1 (CD31), and endothelial nitric oxide synthase (eNOS). In vivo experiments further demonstrate that the COC@SalB‐Cu hydrogel can significantly restore the oxygen and blood supply, leading to fast tissue regeneration. The present strategy holds enormous promise for the treatment of hypoxia‐related chronic tissue defects and vascular injury in the field of regenerative medicine.

Anti-moisture, anti-bacterial cellulosic triboelectric materials enabled by hydroxyl coordination effect

Owing to their low cost, customizability, and environmental stability, cellulosic triboelectric materials have emerged among polymer materials. However, the rich hydrogen bonding network inherent in cellulose limits its polarity and electron-donating ability, and charge dissipation caused by the hygroscopicity of the hydroxyl-rich groups limits its application as a triboelectric material. In this study, a more convenient, economical, and environmentally friendly "stent surgery" strategy was adopted. The wetting and swelling of fiber molecules allowed Cu (II) coordination with hydroxyl groups in nanocellulose. The coordination effect of cellulose hydroxyl groups weakens the intermolecular hydrogen bonding network, leading to an increase in the molecular dipole moment and the formation of new polar regions to regulate its space charge distribution, which significantly improved the electron-supplying capacity of the nanocellulose materials, and the maximum output power density increased by a factor of 2.78 (from 45 to 125 μW cm−2). Notably, the CNF-Cu (II) triboelectric material demonstrated excellent antimicrobial (>99%) and UV transmittance (<8%) as well as resistance to humidity interference, exhibiting only 5.9% voltage output loss at high humidity (90% RH). The design of this study provides new approaches for cellulose polarity modulation and energy harvesting adapted to harsh environments.

Fabrication, characterization, and application of pea protein isolate-polyphenol-iron complexes with antioxidant and antibacterial activity

Plant proteins are becoming increasingly popular as functional ingredients in foods because of their health, sustainability, and environmental benefits. The functional performance of plant proteins can often be improved by combining them with other food ingredients. For instance, they can be combined with polyphenols and metal ions to form surface active protein-polyphenol-iron complexes with biological activity. In this study, ternary complexes of pea protein isolate (PPI), epigallocatechin-3-gallate (EGCG) and iron (Fe3+) was prepared using a simple molecular self-assembly method. The formation mechanism, characteristics, and functional properties of these complexes were then characterized. Our results showed that PPI, EGCG, and Fe3+ could spontaneously combine to form nano-sheet networks held together by hydrogen bonds, phenolic hydroxyl coordination bonds, and electrostatic interactions. The addition of Fe3+ increased the fraction of disordered secondary structures, reduced the thermal denaturation temperature, reduced the surface hydrophobicity, increased the particle size, and altered the surface potential of the proteins in a dose dependent manner. Optimizing the EGCG-to-Fe3+ ratio in the complexes (1:2 w/w) led to the formation of protein composites with improved surface, antioxidant, and antibacterial activities. This study provided valuable insights into the interaction mechanisms of proteins, polyphenols, and metal ions in ternary complexes. These complexes may be used as multifunctional ingredients in plant-based foods because of their beneficial antioxidant, antimicrobial, nutritional, and emulsification properties.

Influencing mechanisms of tartaric acid on adsorption and degradation of tetracycline on goethite: insight from solid and liquid aspects.

The interactions between organic pollutants and iron minerals play an important role in their environmental fate. In this study, the effects of low-molecular-weight organic acids (LMWOAs) on the adsorption and degradation of tetracycline (TC) on goethite were investigated. Tartaric acid (TA) was taken as the representative of LMWOAs to study the influencing mechanism through batch experiments and microscale characterization. In addition, the properties of TC-TA clusters under different pHs were determined by density functional theory (DFT) calculations. The results showed that all five LMWOAs inhibited TC adsorption and degradation. The preferential adsorption of TA on goethite changed TC adsorption from inner spherical to outer spherical complexation and mainly inhibited TC adsorption and degradation of the singly coordinated hydroxyl group. TC degradation rate decreased from 0.0287 to 0h-1 in the first stage. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results showed that TA could influence the interactions of amide groups, C = O on the A-ring, and dimethylamino group of TC with goethite, and the formation of ≡Fe(II) was inhibited. In addition to competing for the effective sites, the effects of complexation between TA and TC in solution should be considered. According to DFT calculations, hydrogen bonds could be formed between the carboxyl group of TA and the H atom of TC at different pH. These findings can provide evidence for estimating the contribution of adsorption and degradation to TC removal by iron oxides with the coexistence of LMWOAs in a soil-water environment.

Conjugated Olefin Enabled Rollover Cyclometallation of Distant C-H Bonds: Regioselective Annulation of o-Alkenyl Phenols with Alkynes.

Although challenging, the distant C-H functionalization with precision is quite rewarding and has long been intriguing. Tailoring an appropriate template accomplishes the job but the prerequisite sets the limitation. We herein unveil our discovery of annulation of alkynes on to two distant (from directing group) C-H bonds through rollover cyclometallation assisted by conjugated C=C bond. The annulation follows a concomitant cyclization rewarding a rare triple C-H functionalization. The annulation is totally regioselective with an array of unsymmetrical alkynes, taking the leverage of an extended conjugation or a tertiary hydroxyl co-ordination. The mechanism is supported by control experiments, KIE & labelling studies and Mass spectrometry.

Hydrogen-bond-acceptor ligands enable distal C(sp3)-H arylation of free alcohols.

The functionalization of C-H bonds in organic molecules is one of the most direct approaches for chemical synthesis. Recent advances in catalysis have allowed native chemical groups such as carboxylic acids, ketones and amines to control and direct C(sp3)-H activation1-4. However, alcohols, among the most common functionalities in organic chemistry5, have remained intractable because of their low affinity for late transition-metal catalysts6,7. Here we describe ligands that enable alcohol-directed arylation of δ-C(sp3)-H bonds. We use charge balance and a secondary-coordination-sphere hydrogen-bonding interaction-evidenced by structure-activity relationship studies, computational modelling and crystallographic data-to stabilize L-type hydroxyl coordination to palladium, thereby facilitating the assembly of the key C-H cleavage transition state. In contrast to previous studies in C-H activation, in which secondary interactions were used to control selectivity in the context of established reactivity8-13, this report demonstrates the feasibility of using secondary interactions to enable challenging, previously unknown reactivity by enhancing substrate-catalyst affinity.

Ethanol-regulated iron corrosion for fabricating RuOx/FeOOH electrocatalyst toward enhanced hydrogen evolution

RuOx is a promising electrocatalyst for the hydrogen evolution reaction (HER), but it suffers from competition between *OH and *H adsorption and the over-binding effect of H on the RuOx surface. FeOOH features strong oxophilicity, making it expectedly form RuOx/FeOOH composite to efficiently catalyze HER. Considering the strong oxidability of Ru3+, it is desirable to design a moderate environment to form a RuOx/FeOOH composite with a homogeneous structure and accessible Ru sites. Herein, an ethanol-regulated corrosion strategy was developed to in-situ grow RuOx/FeOOH electrocatalyst on iron foam. To avoid the violent redox reaction, the coordination of hydroxyl groups in ethanol with Ru3+ reduces the oxidability and postpones the diffusion of Ru3+ ions. The prepared catalyst exhibited a low over-potential of 67 mV at 50 mA cm−2 and excellent water-splitting properties requiring 1.56 V at 100 mA cm−2 due to the optimized structure and the strong electron interaction between RuOx and FeOOH. According to the modulation mechanism of hydroxyl groups, ethylene glycol, n-propanol, isopropanol, and methanol are substitutable for ethanol to boost the HER activity of RuOx/FeOOH. This work proposes a coordination-regulation approach for preparing Ru-based composite catalysts with enhanced HER performance by adjusting iron corrosion behaviors.

Hydrolysis of ester phosphates mediated by a copper complex.

Phosphate ester hydrolysis is an important reaction that plays a major role in both enzymatic and non-enzymatic processes, including DNA and pesticide breaking. Although it is a widely studied reaction, the precise mechanistic details, especially for copper complexes, remain under discussion. To contribute to the debate, we present the catalyzed hydrolysis of phosphomono-, di- and tri-esters mediated by the [Cu(II)(1,10-phenanthroline)] complex. The reaction coordinates for several substrates were explored through the metadynamics formalism. Thus, we found that for mono- and di-substituted ester phosphates a concerted mechanism is observed, where a coordinated hydroxyl group attacks the phosphorus atom at the same side as the leaving group, along with a proton transfer. In contrast, tri-substituted phosphate remains coordinated with the metal, and the nucleophile acts independently following an addition-elimination process. That is, the metallic complex achieves a specific nucleophile-phosphate interaction that produces a concerted transition state in the phosphoester hydrolysis process.

Reductive dehalogenation in groundwater by Si-Fe(II) co-precipitates enhanced by internal electric field and low vacancy concentrations

Fe(II) and silicate can form Si-Fe(II) co-precipitates in anoxic groundwater and sediments, but their phase composition and reactivity towards subsurface pollutants are largely unknown. Three types of Si-Fe(II) co-precipitations with the same chemical composition, namely Si-Fe(II)-I, Si-Fe(II)-II, and Si-Fe(II)-III, have been synthesized by different hydroxylation sequences in this work. It was found that Si-Fe(II)-III reduce carbon tetrachloride (CT) much faster (k1=0.04419 min−1) than Si-Fe(II)-I (0 min−1) and Si-Fe(II)-II (7.860 × 10−4 min−1). XRD results show that the main component of Si-Fe(II)-III is ferrous silicate (FeSiO3), which is quite different from that of Si-Fe(II)-I and Si-Fe(II)-II. The unique arrangement of hydroxyl coordination, the less distorted octahedral structure, the polyhedral morphology and the absence of Si-A center vacancies in Si-Fe(II)-III are responsible for its high reductive dehalogenation reactivity. The highest redox activity of Si-Fe(II)-III was shown by electrochemical characterization. The [FeII-O-Si]+ in Si-Fe(II)-III may stabilize the dichlorocarbene anion (˸CCl2−), which favors the transformation of CT to methane (9.2%). The Si-Fe(II) co-precipitates consist of countless internal electric fields, and the transformation of hydroxyl and CT both consumed electrons. The coexistence of hydroxyl and CT increases the electron density in the electron-rich region due to their electronegativity, enhancing their electron-accepting capabilities. This study deepens our understanding of the phase composition and electronic structure of Si-Fe(II) co-precipitates, which fills the gap in the reductive dehalogenation of halides by Si-Fe(II) co-precipitates.

Insights into the mechanisms of aqueous Cd(II) reduction and adsorption by nanoscale zerovalent iron under different atmosphere conditions

Nanoscale zero-valent iron (NZVI) can effectively remove and recover Cd(II) from aqueous solutions. However, the oxygen effects on Cd(II) removal by NZVI have been overlooked and not well studied. In this research, the Cd MNN auger lines obtained by X-ray photoelectron spectroscopy (XPS) revealed that Cd(II) adsorbed on the NZVI surface could be reduced to Cd(0) by the Fe(0) core under anaerobic conditions. With coexisting oxygen, the Cd(II) removal efficiency declined significantly, and Cd(II) reduction was inhibited by the thickened surface γ-FeOOH layer. Furthermore, the post-oxygen intrusion corroded the generated Cd(0) and led to the dramatic leaching of Cd(II) ions. According to the density functional theory (DFT) simulation, the adsorbed Cd(II) was preferably coordinated via a monodentate model on the surface of Fe3O4 and γ-FeOOH, which are the dominant surface species of NZVI under anaerobic and aerobic conditions, respectively. Thus, γ-FeOOH with doubly coordinated hydroxyl groups provided fewer adsorption sites than Fe3O4 for Cd(II) ions. Overall, the atmospheric conditions of subsurface remediation and wastewater treatment should be considered when applying NZVI for Cd(II) removal. Favorable atmospheric conditions would improve the efficiency and cost-effectiveness of NZVI-based technologies for the practical remediation of Cd(II) pollution.

Polyphenol-Coordinated Supramolecular Hydrogel as a Promising “One-Stop-Shop” Strategy for Acute Infected Wound Treatment

The management and treatment of acute infected wounds, which are characterized by bacterial infections and excessive amount of reactive oxygen species, remains a major challenge in clinic. Herein, a facile and universal approach for constructing polyphenol-coordinated supramolecular hydrogel is developed for acute infected wound treatment. The hydrogels are mainly crosslinked via two types of noncovalent bond associations, i.e., the intermolecular hydrogen bonding between polyphenols and poly-vinylpyrrolidone/basic fibroblast growth factor (bFGF) components, and the metal-phenolic hydroxyl coordination interactions. Taking tannic acid (TA) as a model polyphenol for biomedical application, TA-based hydrogel (TPFe or TPFe/bFGF hydrogel) is demonstrated to possess multifunctional features, including: 1) potent adhesive capacity for adhesion to the wounds or cementing two separated tissues together; 2) hemostatic property against rats’ tail cut, liver incision, and heart hole bleeding within a few minutes; 3) antioxidant ability for DPPH and ABTS radical scavenging activities; 4) antibacterial activity especially for Staphylococcus aureus; 5) accelerated endothelial cells migration/proliferation and angiogenesis, which are attributed to bFGF delivery from the hydrogel. In vitro/vivo experimental results show that TPFe hydrogel has excellent biocompatibility, and faster healing rates are observed in animal tests whether with a full-thickness skin defect model or a bacterial-infected wound model. Hence, our work reveals that such supramolecular hydrogel with multiple functions may be well adaptive to the different stages of wound repair process, and thus highlights its great prospect as a promising “One-Stop-Shop” strategy for acute infected wound treatment.

Coordination site manipulation of the annular growth mechanism to assemble chiral lanthanide clusters with different shapes and magnetic properties

We are the first to achieve the directional construction of chiral lanthanide clusters by regulating the hydroxyl coordination sites at different positions on the ligands by manipulating the annular growth mechanism.

Tailored Oxidation State of Cu Centres in Metal–Organic Framework Via Tuning Phenolic Hydroxyl Coordination for Enhanced Co2 Photoreduction

Tailored Oxidation State of Cu Centres in Metal–Organic Framework Via Tuning Phenolic Hydroxyl Coordination for Enhanced Co2 Photoreduction

A comparative study for phosphate adsorption on amorphous FeOOH and goethite (α-FeOOH): An investigation of relationship between the surface chemistry and structure

Eutrophication is generally caused by excess nitrogen and phosphorus being released into surface waters by runoff. Developing adsorbents for adsorbing phosphate within soil buffer zones and/or water treatment columns may be effective methods to mitigate this problem. In this study, an amorphous FeOOH (AF) and a well-crystallized α-FeOOH (CF) was formulated to compare phosphate adsorption behavior. The physicochemical properties between these species showed significant differences in morphology, crystallization, zeta potential, and specific surface area. The AF exhibited higher phosphate uptake than CF. X-ray photoelectron spectroscopy (XPS) verified that the hydroxyl groups within AF were 13.28% higher than that in CF. The triply coordinated hydroxyl groups (μ3-OH) associated with AF and CF appeared at different positions as shown in the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses, confirming that AF contains more adsorption reactive sites (μ3-OH). Mechanisms for monodentate formations and a stable six-member ring structure were proposed. The X-ray absorption near the edge structure (XANES) and XPS results suggested that the iron valence in AF was dominated by Fe (III). XANES also demonstrated that the amorphous structure found in the AF was caused by the disordered tetrahedron and octahedron alignments, leading to a higher phosphate adsorption.

Novel Platinum(II) Complex-based Luminescent Probe for Detection of Hypochlorite in Cancer Cells.

Hypochlorite (ClO⁻) is of great importance either for the metabolism of living organisms or as disinfectant in daily life. However, improper concentration levels of ClO⁻ lead to serious health problems including erythrocyte damage, cardiovascular problems, neuron degeneration, lung/kidney injury and cancer. Therefore, a sensitive and selective detection method is required for the visualization and measurement of ClO⁻. In this work, a novel platinum(II) complex-based luminescent probe Pt-CHO was synthesized and utilized to detect ClO⁻. This "turn-off" probe exhibits high sensitivity, excellent selectivity, good pH stability, low limit of detection and instantaneous response ability. Moreover, the luminescent response is caused by the oxidation of aldehyde into carboxyl groups combined with the coordination of hydroxyl groups at the Pt center, which is rarely reported. The cell imaging of HeLa cells proved the considerable potential of the probe for ClO⁻ imaging in living cells.

Novel synthesis of mussel inspired and Fe3+ induced pH-sensitive hydrogels: Adhesion, injectable, shapeable, temperature properties, release behavior and rheological characterization

A novel EGCG-loaded DCKGM-CCKGM-Fe3+hydrogel was prepared by Dopamine–carboxymethyl konjac glucomannan (DCKGM) and an l-Cysteine–carboxymethyl konjac glucomannan (CCKGM) with Fe3+ as a cross-linking agent. Due to the dynamic property of Fe3+-phenolic hydroxyl coordination bond and intermolecular hydrogen bonding, the resultant hydrogel featured injectable, adhesive, temperature and pH-sensitive properties. The mechanisms were characterized using Rheological analysis, Fourier transform infrared spectroscopy, X-ray diffraction patterns, and scanning electron microscopy. Furthermore, the weak alkaline condition (pH 7.4) can trigger the release of EGCG, there was a cumulative release of 54.71 % of the loaded EGCG within 12 h in PBS at pH 1.2. When the pH of PBS was increased to 7.4, the cumulative release of EGCG increased to 68.54 %. Consequently, the EGCG-loaded DCKGM-CCKGM-Fe3+hydrogel (Fe3+Hydrogel) is a good candidate for the carrier for drug delivery. This paper provided a novel way for the preparation of hydrogel.

Versatile fabrication of ordered cellular structures double network composite hydrogel and application for cadmium removal

In this paper, a new type of double network composite (DNC) hydrogel adsorbent with good mechanical properties was synthesized using calcium alginate, graphene oxide and acrylic acid. The physical and chemical characteristics of DNC hydrogels were characterized by FTIR, TGA, XPS, SEM. The adsorption properties and adsorption mechanism of Cd2+ on hydrogels also were studied. The adsorption properties were investigated mainly by the effects of pH and ion concentration, adsorption kinetics and adsorption model studies, at the last, the thermodynamic studies also were carried out. The experimental results show that the pH has a good adsorption effect between 5 and 6. In the selective adsorption experiment, the order of adsorption of different metals is as follows: qe(Pb2+) > qe(Cu2+) > qe(Cd2+) > qe(Mn2+). According to the Langmuir isotherm adsorption model, the maximum theoretical adsorption capacity of Cd2+ on hydrogel at 20 °C, 30 °C, 40 °C is 71.93 mg·g−1, 88.05 mg·g−1, 115.65 mg·g−1, respectively and the adsorption equilibrium can be achieved within 120 min. The XPS was used to study the adsorption mechanism of Cd2+ on gel, and adsorption process mainly depends on ion exchange with Ca2+ and coordination of hydroxyl groups.

Fast Capture of Fluoride by Anion-Exchange Zirconium-Graphene Hybrid Adsorbent.

Fluoride contamination is a severe problem affecting the safety of drinking water around the world. High-rate adsorbent materials are particularly desirable for potable water defluoridation. Current research on fluoride adsorbent materials is primarily focused on metal-based adsorbents with high capacities. However, they generally suffer from slow adsorption kinetics due to the adsorption mechanism of a sluggish exchange between coordinated hydroxyl groups and fluoride ions. Designing metal-based adsorbents to mimic the rapid ion-exchange behavior of anion-exchange resins is a promising approach to integrate fast adsorption and high capacity for fluoride removal. Herein, a ZrO(OH)1.33Cl0.66-reduced graphene oxide (rGO) hybrid adsorbent containing exchangeable chloride ions was synthesized with the assistance of cation-π interactions. Unlike most adsorbents requiring a high surface area, this composite has a negligible surface area (1.45 m2 g-1), but can deliver a fast fluoride capture performance (reaching equilibrium in 5 min) with high adsorption rate constants of 1.05 min-1 and 0.171 mg g-1 min-1, around 10 times faster than the best result reported in the literature. Besides, ZrO(OH)1.33Cl0.66-rGO can also demonstrate a high fluoride uptake (44.14 mg g-1) and high removal efficiency (94.4%) in 35 mg L-1 fluoride solution, both among the highest performances for fluoride adsorption.