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Site-selective synthesis of an amine-functionalized β-ketoenamine-linked covalent organic framework for improved detection and removal of Cu2+ ion from water
Abstract
The development of new dual-functional materials for detection and removal of heavy metal ions is of great significance in environmental protection. Herein, a new amine-functionalized β-ketoenamine-linked covalent organic framework (termed as NH2–Th-Tfp COF) containing rich O,N,O′-chelating sites and free amine groups has been synthesized through the site-selective synthesis strategy under solvothermal conditions. The as-synthesized NH2–Th-Tfp COF shows strong fluorescence in water dispersion and can be used as highly sensitive and selective fluorescent probe for Cu²⁺ detection. As a sensing platform, the limit of detection for NH2–Th-Tfp COF toward Cu²⁺ ion is estimated to be 0.19 μM. Besides, the NH2–Th-Tfp COF possesses high adsorption capacity of 153 mg/g toward Cu²⁺ ion in aqueous solution. More importantly, this NH2–Th-Tfp COF exhibits higher sensitivity and larger adsorption capacity toward Cu²⁺ ion in comparison with the non-amine functionalized Th-Tfp COF, which may be attributed to the large number of free amine groups in the pore walls of NH2–Th-Tfp COF. The coordination interactions between Cu²⁺ ion with the O, N, O′-chelating sites and free amine groups in the pore walls of NH2–Th-Tfp COF can greatly enhance its recognition and absorption performances toward Cu²⁺ ion, as verified by X-ray photoelectron spectroscopy. This work may pave the way for designing new fluorescent COF materials with dual functions for simultaneous detection and removal of specific metal ions.
... This approach is simple to execute and yields targeted COFs in a single reaction step. [35,44,45] It leverages the different reactivities of amine and hydrazide with aldehyde to produce amine-functionalized 2D COFs, exclusively giving rise to honeycomb-like COFs to date. ...
Tuning the topology of two‐dimensional (2D) covalent organic frameworks (COFs) is of paramount scientific interest but remains largely unexplored. Herein, we present a site‐selective synthetic strategy that enables the tuning of 2D COF topology by simply adjusting the molar ratio of an amine‐functionalized dihydrazide monomer (NH2−Ah) and 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tribenzaldehyde (Tz). This approach resulted in the formation of two distinct COFs: a clover‐like 2D COF with free amine groups (NH2−Ah−Tz) and a honeycomb‐like COF without amine groups (Ah−Tz). Both COFs exhibited good crystallinity and moderate porosity. Remarkably, the clover‐shaped NH2−Ah−Tz COF, with abundant free amine groups, displayed significantly enhanced adsorption capacities toward crystal violet (CV, 261 mg/g) and congo red (CR, 1560 mg/g) compared to the non‐functionalized honeycomb‐like Ah−Tz COF (123 mg/g for CV and 1340 mg/g for CR), underscoring the pivotal role of free amine functional groups in enhancing adsorption capacities for organic dyes. This work highlights that the site‐selective synthetic strategy paves a new avenue for manipulating 2D COF topology by adjusting the monomer feeding ratio, thereby modulating their adsorption performances toward organic dyes.
... Postsynthetic introduction of primary amine groups or the presence of unreacted amino or carbonyl groups in imine-linked COFs have been shown to result in functional properties that are otherwise difficult to attain in fully formed networks. [98][99][100][101] In this context, several synthetic strategies, including functional group interconversions, 102-105 transamination reactions, 106,107 and siteselective [108][109][110][111][112] and regioselective synthesis, 113 have been reported to introduce primary amine groups in 2D COFs. ...
Covalent Organic Frameworks (COFs) are a class of porous materials generated from organic molecules resulting in two-dimensional (2D) or three-dimensional (3D) networks. Multifunctional molecules with defined symmetry react to give...
... Hence, as illustrated in Fig. 8, a chemical interaction between the lead (II) ions and the synthesized nanocomposites is established by the formation of the complex , Huang et al. 2022. The obtained results of coordination between the amide group and the heavy metals are in agreement with the reported one (Dong et al. 2022). Moreover, SEM pictures of the Fe 3 O 4 @CS@CMC-SiNH 2 NCs before and after the adsorption of lead (II) ions are presented in the Supplementary Information (Figures S7 and S8). ...
The removal of heavy metals from industrial wastewater is nowadays one of the most interesting challenges in water remediation using adsorbent nanomaterials. The present study presents a novel adsorbent (Fe3O4@[email protected]2) nanocomposite (NC), by functionalization of the carboxymethyl cellulose (CMC) cross-linked to magnetic chitosan nanoparticles (Fe3O4@CS NPs) with aminopropyl triethoxysilane layer (APTES), and evaluate its performance toward lead (II) removal from wastewater. The synthesized NCs were characterized using several techniques. The optimization of the adsorption process was performed using the Response Surface Methodology with the Box-Behnken Design model. The optimal conditions for lead (II) ion removal were found to be; pH of 5.1, a dose of 0.10 g/L, and a temperature of 36 ℃ using Fe3O4@[email protected]2 NCs which proved to have superior adsorption performance with a maximum adsorption capacity of 555.56 mgPb(II)/gNC, and fast achievement of the adsorption equilibrium (30 min). Favorable monolayer chemisorption was estimated and proved to be a coordination bond between the [sbnd]NH amide and lead (II) ions using FTIR, as well as up to seven adsorption–desorption cycles were effective for lead (II) ion removal from aqueous solutions. In addition, the Fe3O4@[email protected]2 NCs showed 98.10%, and 97.21 % removal of lead (II) ions in the absence, and the presence of other contaminants of heavy metals such as cadmium (II) and mercury (II). Moreover, the Fe3O4@[email protected]2 NC exhibited high efficiency in the removal of lead (II) ions from wastewater, can be easily separated from water by magnetic separation, showed satisfactory reusability for five cycles of the adsorption–desorption process of lead (II) ion removal from tap water and wastewater. Consequently, Fe3O4@[email protected]2 NC is a prospective adsorbent nanomaterial for lead (II) ions removal from wastewater.
Covalent Organic Frameworks (COFs) have emerged as a promising class of crystalline porous materials with customizable structures, high surface areas, and tunable functionalities. Their unique properties make them attractive candidates for addressing environmental contamination caused by pharmaceuticals, pesticides, industrial chemicals, persistent organic pollutants (POPs), and endocrine disruptors (EDCs). This review article provides a comprehensive overview of recent advancements and applications of COFs in removing and remedying various environmental contaminants. We delve into the synthesis, properties, and performance of COFs and their potential limitations and future prospects.
Covalent organic frameworks (COFs) are a class of porous crystalline materials based on organic building blocks containing light elements, such as C, H, O, N, and B, interconnected by covalent bonds. Because of their regular crystal structure, high porosity, stable mechanical structure, satisfactory specific surface area, easy functionalization, and high tunability, they have important applications in several fields. Currently, most of the established methods based on COFs can only be used for individual detection or adsorption of the target. Impressively, fluorescent COFs as a special member of the COF family are able to achieve highly selective and sensitive detection of target pollutants by fluorescence enhancement or quenching. The construction of a dual-functional platform for detection and adsorption based on fluorescent COFs can enable the simultaneous realization of visual monitoring and adsorption of target pollutants. Therefore, this paper reviews the research progress of fluorescent COFs as fluorescence sensors and adsorbents. First, the fluorescent COFs were classified according to the different bonding modes between the building blocks, and then the applications of fluorescent COF-based detection and adsorption bifunctional materials for various environmental contaminants were highlighted. Finally, the challenges and future application prospects of fluorescent COFs are discussed.
Although significant progress on the development of functional covalent organic frameworks (COFs) as effective porous adsorbents for capturing radioactive iodine has been achieved, systematic study on regulating the iodine adsorption...
Covalent organic frameworks (COFs) are an emerging type of porous crystalline polymers formed by combining strong covalent bonds with organic building blocks. Due to their large surface area, high intrinsic pore space, good crystallization properties, high stability, and designability of the resultant units, COFs are widely studied and used in the fields of gas adsorption, drug transport, energy storage, photoelectric catalysis, electrochemistry, and sensors. In recent years, the rapid development of the Internet of Things and people’s yearning for a better life have put forward higher and more requirements for sensors, which are the core components of the Internet of Things. Therefore, this paper reviews the recent progress of COFs in synthesis methods and sensing applications, especially in the last five years. This paper first introduces structure, properties, and synthesis methods of COFs and discusses advantages and disadvantages of different synthesis methods. Then, the research progress of COFs in different sensing fields, such as metal ion sensors, gas sensors, biomedical sensors, humidity sensors, and pH sensors, is introduced systematically. Conclusions and prospects are also presented in order to provide a reference for researchers concerned with COFs and sensors.
The development of chiral covalent organic frameworks (COFs) by postsynthetic modification is challenging due to the common occurrences of racemization and crystallinity decrement under harsh modification conditions. Herein, we employ an effective site-selective synthetic strategy for the fabrication of an amine-functionalized hydrazone-linked COF, NH2-Th-Tz COF, by the Schiff-base condensation between aminoterephthalohydrazide (NH2-Th) and 4,4',4″-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (Tz). The resulting NH2-Th-Tz COF with free amine groups on the pore walls provides an appealing platform to install desired chiral moieties through postsynthetic modification. Three chiral moieties including tartaric acid, camphor-10-sulfonyl chloride, and diacetyl-tartaric anhydride were postsynthetically integrated into NH2-Th-Tz COF by reacting amine groups with acid, acyl chloride, and anhydride, giving rise to a series of chiral COFs with distinctive chiral pore surfaces. Moreover, the crystallinity, porosity, and chirality of chiral COFs were retained after modification. Remarkably, the chiral COFs exhibited an exceptional enantioselective adsorption capability toward tyrosine with a maximum enantiomeric excess (ee) value of up to 25.20%. Molecular docking simulations along with experimental results underscored the pivotal role of hydrogen bonds between chiral COFs and tyrosine in enantioselective adsorption. This work highlights the potential of site-selective synthesis as an effective tool for the preparation of highly crystalline and robust amine-decorated COFs, which offer an auspicious platform for the facile synthesis of tailor-made chiral COFs for enantioselective adsorption and beyond.
The versatile photophysicalproperties, high surface‐to‐volume ratio, superior photostability, higher biocompatibility, and availability of active sites make graphene quantum dots (GQDs) an ideal candidate for applications in sensing, bioimaging, photocatalysis, energy storage, and flexible electronics. GQDs‐based sensors involve luminescence sensors, electrochemical sensors, optical biosensors, electrochemical biosensors, and photoelectrochemical biosensors. Although plenty of sensing strategies have been developed using GQDs for biosensing and environmental applications, the use of GQDs‐based fluorescence techniques remains unexplored or underutilized in the field of food science and technology. To the best of our knowledge, comprehensive review of the GQDs‐based fluorescence sensing applications concerning food quality analysis has not yet been done. This review article focuses on the recent progress on the synthesis strategies, electronic properties, and fluorescence mechanisms of GQDs. The various GQDs‐based fluorescence detection strategies involving Förster resonance energy transfer‐ or inner filter effect‐driven fluorescence turn‐on and turn‐off response mechanisms toward trace‐level detection of toxic metal ions, toxic adulterants, and banned chemical substances in foodstuffs are summarized. The challenges associated with the pretreatment steps of complex food matrices and prospects and challenges associated with the GQDs‐based fluorescent probes are discussed. This review could serve as a precedent for further advancement in interdisciplinary research involving the development of versatile GQDs‐based fluorescent probes toward food science and technology applications.
Copper and zinc are routinely used in livestock antimicrobial footbaths in commercial farming. The footbath mix is a cost to farmers, and the disposal of spent footbath into slurry tanks leads to soil contamination, as well as the potential for antimicrobial metal resistance and co-selection. This study assesses the potential to mitigate a source of antimicrobial metal resistance in slurry tanks while recovering copper and zinc from spent cattle footbaths. This is the first study in literature to investigate the potential of recovering copper from cattle footbath solutions via any method. The sorbent, Ca2Al-EDTA Layered Double Hydroxides (LDH), were used to remove Cu2+ from a Cu2SO4·5H20 solution at different temperatures. The maximum Cu2+ uptake from the Cu2SO4·5H20 solution was 568 ± 88 mg g−1. Faster and higher equilibrium uptake was achieved by increasing the temperature of the solution. The sorbent was found to be effective in removing copper and zinc from a commercially available cattle footbath solution (filtered footbath solution Cu2+ uptake 283 ± 11.05 mg g−1, Zn2+ uptake 60 ± 0.05 mg g−1). Thus, this study demonstrates the opportunity for a completely novel and potentially economically beneficial method of mitigating antimicrobial resistance in agriculture and the environment, while also providing a new valuable copper and zinc waste stream for secondary metal production.
Full paper available until January 16 2019 at:
https://authors.elsevier.com/c/1Y7nsB8ccghHY
Removing sulfur dioxide (SO2) from exhaust flue gases of fossil fuel power plants is an important issue given the toxicity of SO2 and subsequent environmental problems. To address this issue, we successfully developed a new series of imide-linked covalent organic frameworks (COFs) that have high mesoporosity with large surface areas to support gas flowing through channels; furthermore, we incorporated 4-[(dimethylamino)methyl]aniline (DMMA) as the modulator to the imide-linked COF. We observed that the functionalized COFs serving as SO2 adsorbents exhibit outstanding molar SO2 sorption capacity, i.e., PI-COF-m10 record 6.30 mmol SO2 g−1 (40 wt%). To our knowledge, it is firstly reported COF as SO2 sorbent to date. We also observed that the adsorbed SO2 is completely desorbed in a short time period with remarkable reversibility. These results suggest that channel-wall functional engineering could be a facile and powerful strategy for developing mesoporous COFs for high-performance reproducible gas storage and separation.
Covalent organic frameworks (COFs) are a class of crystalline porous polymer that allows the atomically precise integration of organic units into extended structures with periodic skeletons and ordered nanopores. One important feature of COFs is that they are designable; that is, the geometry and dimensions of the building blocks can be controlled to direct the topological evolution of structural periodicity. The diversity of building blocks and covalent linkage topology schemes make COFs an emerging materials platform for structural control and functional design. Indeed, COF architectures offer confined molecular spaces for the interplay of photons, excitons, electrons, holes, ions and guest molecules, thereby exhibiting unique properties and functions. In this Review, we summarize the major progress in the field of COFs and recent achievements in developing new design principles and synthetic strategies. We highlight cutting-edge functional designs and identify fundamental issues that need to be addressed in conjunction with future research directions from chemistry, physics and materials perspectives.
The development of novel materials with dual functions of simultaneous detection and removal of heavy metal ions has been an important pursuit of environmental remediation. Herein, we demonstrate that two-dimensional covalent organic frameworks (COFs) with well-defined functional chelating sites can combine the inherent advantages of COF materials to prepare novel materials with the dual functions of selective detection and effective removal of Ni²⁺ from aqueous solutions. A new pyridine-based COF material (TAPA-PCBA) containing functional N,N,N-chelating sites has been designed and synthesized by the imine condensation reactions between tris(4-aminophenyl)amine and 2,6-pyridinedicarboxaldehyde under solvothermal conditions. The newly designed TAPA-PCBA possesses high crystallinity, moderate specific surface area and robust chemical and thermal stability. These excellent properties of TAPA-PCBA, together with its extended π-conjugated framework structure and the dense distribution of functional N,N,N chelating sites, enable TAPA-PCBA to selectively detect and effectively remove Ni²⁺ from aqueous solutions. This dual function can be attributed to the coordination interactions between Ni²⁺ and N,N,N-chelating sites embedded in the skeleton structure of TAPA-PCBA. These results reveal that COFs with reasonable design have great development prospects in heavy metal ion related environmental remediation.
Covalent organic frameworks (COFs) with excellent porosity and pre-designable structure have emerged as ideal and promising organic scaffolds for broad applications such as in gas storage, heterogeneous catalysis and fluorescence sensing. Herein, a hydrazone-based COF was synthesized by the condensation of 2,5-bis(2-methoxyethoxy) terephthalohydrazide (BMTH) with 1,3,5-triformylbenzene (TFB) under solvothermal conditions. The resulting COF material (TFB-BMTH) exhibits high crystallinity, excellent porosity with a BET surface area of 632 m² g⁻¹ and good thermal and chemical stability. The photoactive TFB-BMTH shows significant catalytic activity and recyclability in photocatalytic oxidative hydroxylation of arylboronic acid. The high photocatalytic performance of TFB-BMTH could be attributed to the effective light-harvesting platform with the efficient generation, migration and separation properties of photogenerated charge pairs in such a system. In addition, TFB-BMTH showed significant fluorescence quenching for the sensing of Cu²⁺. X-ray photoelectron spectroscopy and Fourier transform infrared techniques verified the interaction between Cu²⁺ and functional units in TFB-BMTH. This work demonstrates the development of multifunctional COFs and makes important contributions to functional exploration in heterogeneous organic transformation and sensing applications.
Two-dimensional covalent organic frameworks (COFs) with specific morphologies including nanofibers and nanoplates are highly desired in both nanoscience research and practical applications. Thus far, however, morphology engineering for COFs remains challenging because the mechanism underlying the morphology formation and evolution of COFs is not well understood. Herein, we propose a strategy of surfactant mediation coupled with acid adjustment to engineer the morphology of a β-ketoenamine-linked COF, TpPa, during solvothermal synthesis. The surfactants function as stabilizers that can encapsulate monomers and prepolymers to create micelles, enabling the formation of fiber-like and plate-like morphologies of TpPa rather than irregularly shaped aggregates. It is also found that acetic acid is important in regulating such morphologies, as the amino groups inside the prepolymers can be precisely protonated by acid adjustment, leading to an inhibited ripening process for the creation of specific morphologies. Benefitting from the synergistic enhancement of surfactant mediation and acid adjustment, TpPa nanofibers with a diameter down to ∼20 nm along with a length of up to a few microns and TpPa nanoplates with a thickness of ∼18 nm are created. Our work sheds light on the mechanism underlying the morphology formation and evolution of TpPa, providing some guidance for exquisite control over the growth of COFs, which is of great significance for their practical applications.
Here, tripolycyanamide (TPA) and 2,4,6-triformyl pyrogallol (TDBA) are used to prepare a highly crystalline covalent-organic frameworks based on imine linkages (COFTDBA-TPA) for heavy metal ions (HMIs) detection and removal. Each unit of COFTDBA-TPA had 6 adsorption sites for HMIs (-C=O, -NH2, -C=N), which could selectively capture HMIs. The typical lamellar structure made COFTDBA-TPA have a larger specific surface area, and the mesoporous structure provided numerous channels for the adsorption of HMIs. Therefore, the COFTDBA-TPA-based electrochemical sensor could realize the detection of Cd²⁺, Cu²⁺, Pb²⁺, Hg²⁺ and Zn²⁺ in drinking water simultaneously. The limits of detection for five HMIs were as low as 0.922 nM, 0.450 nM, 0.309 nM, 0.208 nM and 0.526 nM, respectively. The adsorption capacity of COFTDBA-TPA for each HMI were as high as 711.6 mg/g, 716.9 mg/g, 603.7 mg/g and 618.3 mg/g, respectively. Compared with other adsorbents, it had higher capacity and faster adsorption kinetics. After being recycled five times, the adsorption performance was maintained. This not only provides a reliable platform for the removal of HMIs in wastewater, but also provides new ideas for the use of COFs in the electrochemical field.
Mercury (Hg²⁺), a heavy metal ion, is considered one of the most toxic metals on earth and is widespread as an environmental pollutant. Various promising adsorbents have been developed with accessible chelating sites and high affinity for heavy metal ions. Herein, we utilized the advantages of covalent organic frameworks (COFs) and designed benzobisthiazole-bridged (BBT) fluorescent COFs (FCOFs) for Hg²⁺ sensing applications. The BBT-FCOF nanosheets has a π-π transition, effective electron transfer, and enhanced delocalization within the π orbitals of the BBT ring. It emits a white fluorescence enabling real-time detection of Hg²⁺ metal ions. The excellent sensing property of BBT-FCOF nanosheets was attributed to the high sensitivity towards Hg²⁺; this was confirmed by the x-ray photoelectron spectroscopy binding energy of sulfur and nitrogen atom in BBT-FCOF. The limit of detection of Hg²⁺ was 30 ppb, which is very low compared to other published methods. ICP-mass measurement also proved that BBT-FCOF nanosheets removed almost 99% of Hg and BBT-FCOF distribution coefficient (Kd) was calculated to be 5 × 10⁵ g⁻¹. The recyclability test proved that HCl effectively removed the adsorbed Hg²⁺ metal ions from BBT-FCOF nanosheets, making it a useful tool for real-time Hg²⁺ detection and removal from waste water.
Based on the electrostatic interaction, we constructed a ratiometric fluorescence nanomixture of graphene quantum dots-gold nanoclusters (GQDs-AuNCs) for the quantitative detection of Cu²⁺ and Cd²⁺. When Cu²⁺ or Cd²⁺ was added into the reaction system, the fluorescence of GSH-AuNCs at 565 nm can be quenched by Cu²⁺ and enhanced by Cd²⁺ while the intensity of N-GQDs at 403 nm stayed constant. Under the optimized conditions, the fluorescence intensity ratio (I565/I403) of the GQDs-AuNCs system was proportional to the concentration of Cu²⁺ and Cd²⁺ in the range of 8×10⁻⁸ mol/L-6×10⁻⁶ mol/L and 1×10⁻⁶ mol/L-4×10⁻⁵ mol/L, respectively, with detection limits of 4.12×10⁻⁹ mol/L and 9.43×10⁻⁷ mol/L, respectively. In the presence of Cu²⁺ and Cd²⁺, the paper-based vision sensor would produce visible fluorescent color changes, which can be used for rapid detection on site. The method has been successfully applied to the determination of Cu²⁺ and Cd²⁺ in scallops with satisfactory results.
It is well known that Hg(II) ion is one of the most toxic chemical species in the environment, thus developing new sensors for recyclable detection of Hg(II) with excellent sensitivity and selectivity is highly desirable. Herein, a new bipyridine-containing hydrazone-linked covalent organic framework (COF), termed Bpda-Bth COF, is synthesized using 2,2'-bipyridine-5,5'-dicarbaldehyde (Bpda) and benzene-1,3,5-tricarbohydrazide (Bth) as building blocks. Given that the obtained Bpda-Bth COF possesses good crystallinity, high chemical stability and rich functional N,N’-chelating sites from the bipyridine units, a novel COF-based quartz crystal microbalance (QCM) sensor, which can be prepared by the in-situ growth of Bpda-Bth COF on the amino-modified QCM chip, is developed for the determination of Hg(II) ion in aqueous solution. Remarkably, the resulting Bpda-Bth COF-based QCM sensor can monitor Hg(II) ion in real-time and online with excellent selectivity, relatively low detection limit (58 nM) and good recyclability (at least five cycles). Moreover, fluorescence spectroscopy, X-ray photoelectron spectroscopy and zeta potential measurements are further conducted, which indicate that the highly sensitive and selective detection of the COF-based QCM sensor toward Hg(II) is assignable to the specific coordination interaction between Hg(II) ion and the N,N’-chelating sites in the pore wall of the bipyridine-containing Bpda-Bth COF. To the best of our knowledge, this is the first report on the development of COF-based QCM sensor for detecting Hg(II) ion. Our work demonstrates that COFs with specific functional sites can be designed and used as ideal sensing materials to fabricate novel QCM sensors for the targeted detection of metal ions.
Since Fe(III) ion is of importance in biological systems, the development of new sensors for detecting Fe(III) with excellent selectivity and low detection limit is desirable. Herein, a new stable...
A suitable porous adsorbent with prominent adsorption performance and better selectivity for the target containments such as non-steroidal anti-inflammatory drugs (NSAIDs) is highly desired in wastewater treatment. Owing to the intrinsic attributes known as predictable structure, tunable pore size, high chemical stability as well as the reliable post-synthetic modification, covalent organic frameworks (COFs) are considered as brilliant adsorbent candidates which have drawn great attentions. Herein, two COFs with different functional groups (COF-NO2 and COF-NH2) were designed and prepared in order to enhance selective adsorption ability toward the Ketoprofen (KTP) molecule via functional group tuning. For KTP, due to amino group which could interact with not only carboxylic acid but also carbonyl group, COF-NH2 exhibited twice adsorption capacity as high as other two counterparts Ibuprofen (IBP) and Naproxen (NPX). However, there was no selectivity for those three NSAIDs when COFs containing nitro groups (COF-NO2) were used as adsorbents. We also found that the adsorption process followed the pseudo-second-order kinetic model well, which confirmed the capture of KTP onto COF-NH2 was dominated by chemical adsorption. The COF-NH2 will be a particularly promising porous adsorbent to selectively eliminate the KTP from effluents, and COFs with specific binding sites for various pollutants can be acquired via functional group tuning.
Designed porous materials, such as covalent organic frameworks (COFs), are promising materials for the removal of toxic metals from wastewater. To assess the contamination and removal of toxic metal ions, their ultrasensitive detection is extremely important. However, to date, there have been very few reports on the ultrasensitive (picomolar) detection of toxic metal ions using highly porous COFs. Therefore, in this study, we synthesized a highly porous and durable COF containing amine and sulfonyl groups using the hydrothermal method. We demonstrated the impressive performance of obtained COF for the selective and ultrasensitive detection of Hg2+. Owing to its excellent luminescence properties and highly p-conjugated system, this metal-free COF can be used as a signal transducer for the selective and sensitive detection of Hg2+ at the picomolar level (640 pM). We studied the influence of various factors (e.g., pH, concentration, and temperature) on the sensitive detection of Hg2+. Owing to excellent luminescence properties and ultrasensitive detection of Hg2+, COF works as highly adsorbent materials for Hg2+ with the effective removal capacity of 99.8% at neutral pH. The obtained COF was also applied as a probe for the simultaneous detection and removal of Hg2+ in a natural river water sample. The results indicate a new path toward metal-free chemical sensors for toxic pollutants.
Here, by virtue of the natural merits of covalent organic frameworks (COFs), we report the rational design of a novel reaction-based recyclable fluorescent COF for both sensing and removal applications. The design concept is demonstrated by constructing allyl together with hydroxy groups functionalized COF material, AH-COF, for the exclusive detection and effective removal of mercury (II): the densely and well-distributed allyl cooperated with hydroxy groups as the Hg²⁺ reaction receptor sites via forming unique mercury-containing product based on the specific mercury-promoted reaction, and the π-conjugation structure as the signal sensor. The satisfactory detection performance of AH-COF was obtained in aspects of excellent uniqueness, high sensitivity, facile visualization, and real-time response. More fascinatingly, AH-COF can be easily recycled in the presence of NaBH4. Moreover, the effective Hg²⁺ removal from water and the easy recycling of AH-COF provides the potential prospect for actual applications. Furthermore, the solid-state NMR investigations overwhelmingly certified the privileged reaction between Hg²⁺ and the allyl in cooperation with hydroxy groups of AH-COF. This study not only shows the use of fluorescent COFs for both exclusive detection and facile removal of Hg²⁺, but also emphasizes a novel design concept for rational structure construction of functionalized COFs for Hg²⁺ remediation.
Since the widespread presence of metal ions in the ecosystem, especially heavy metal ions could bring severe damage to living organisms, development of chemosensors for heavy metal ions is in high demand. In this contribution, we designed and synthesized a new corrole-based covalent organic framework (CorMeO-COF) with good crystallinity and high porosity. CorMeO-COF can detect Cu(II) with high sensitivity and selectivity based on the efficient fluorescence quenching caused by photoinduced electron transfer (PET) process. More interestingly, CorMeO-COF can selectively detect trivalent metal ions such as Ga(III), Al(III), Cr(III) or Fe(III) with fluorescence enhancement. In-depth mecha-nism study revealed that the binding of metal ions on the skeleton can inhibit the aggregation-caused quenching (ACQ) resulting in the improved photoluminescence (PL). Notably, this fluorescence-on/off feature of CorMeO-COF cannot be accessed by its counterpart (e.g. corrole monomer, model compound). These results point out a new direc-tion to use corrole-based COF materials as efficient chemosensors to detect trace amount of metal ions in the environmental and biological systems.
Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures. Unlike other polymers, a significant feature of COFs is that they are structurally predesignable, synthetically controllable, and functionally manageable. In principle, the topological design diagram offers geometric guidance for the structural tiling of extended porous polygons, and the polycondensation reactions provide synthetic ways to construct the predesigned primary and high-order structures. Progress over the past decade in the chemistry of these two aspects undoubtedly established the base of the COF field. By virtue of the availability of organic units and the diversity of topologies and linkages, COFs have emerged as a new field of organic materials that offer a powerful molecular platform for complex structural design and tailor-made functional development. Here we target a comprehensive review of the COF field, provide a historic overview of the chemistry of the COF field, survey the advances in the topology design and synthetic reactions, illustrate the structural features and diversities, scrutinize the development and potential of various functions through elucidating structure-function correlations based on interactions with photons, electrons, holes, spins, ions, and molecules, discuss the key fundamental and challenging issues that need to be addressed, and predict the future directions from chemistry, physics, and materials perspectives.
Mercury is one of the most toxic elements in the environment. Recently, a number of covalent organic frameworks (COFs) were developed for simultaneous detection and removal of mercury. They rely on post-synthetically modified sulfur-based ligands for irreversible mercury binding. In addition, their rigid structures resulted in low fluorescence yields. Herein, a novel highly luminescent COF named TFPPy-CHYD with a quantum yield of 13.6% was designed by integrating a pyrene-based building block with a flexible carbohydrazide linker. The nitrogen-based ligand allows reversible and highly selective binding of Hg2+. As a sensing platform, it has an ultra-low detection limit of 17 nM mercury. More importantly, TFPPy-CHYD exhibits excellent performance in removing mercury from both air and water, providing very high Hg0 and Hg2+ adsorption capacities of 232 and 758 mg/g, respectively. This work demonstrates enormous potential of luminescent COF for metal detection and remediation. By rational introducing metal ligands, a suite of new COF materials might be synthesized for the detection and removal of other metal ions.
Connecting molecular building blocks by covalent bonds to form extended crystalline structures has given sharp upsurge in the field of porous materials especially covalent organic frameworks (COFs), thereby translating the accuracy, precision, versatility of covalent chemistry from discrete molecules to two-dimensional and three-dimensional crystalline structures. COFs are crystalline porous frameworks prepared by a bottom-up approach from predesigned symmetric units with well-defined structural properties such as high surface area, distinct pores, cavity, channels, thermal and chemical stability, structural flexibility and functional design. Due to the tedious and few times impossible introduction of certain functionalities into COFs via de novo synthesis, pore surface engineering through judicious functionalization with range of functionalities under ambient or harsh condition using the principle of coordination chemistry, chemical conversion, building block exchange is of profound importance. In this review, we aim to summarize dynamic covalent chemistry, frameworks linkage in context of design features, different ways and perspective of pore surface engineering along with their versatile role in a plethora of applications such as biomedical, gas storage and separation, catalysis, sensing, energy storage and environmental remediation.
The research work carried out involves synthesis of quinine derivatized hydrogel film (Q-gel film) based on dextrin and Polyvinyl alcohol hybrid mixture. The maximum percentage swelling obtained for the synthesized gel-film was 295% for 1.88 mol/L acrylamide concentration, 0.266 mol/L glutaradehyde concentration, 5.48 × 10⁻² mol/L ammonium persulphate concentration, 30 ml water at 70 °C after 4 h reaction time. It was converted to its quinine derivative using lipase enzyme based condensation (Q-gel film). The Q-gel film could detect the lowest concentration of 0.0421 μM and 0.0521 μM of copper and lead ions, respectively which was well below the Environmental Protection Agency (EPA) standards. The removal efficiency was around 95.77% and 92.89% for toxic copper and lead ions, respectively in distilled water. It followed a pattern of Flory Huggins and Langmuir adsorption isotherms for the case of copper and lead ions, respectively. Second order kinetics was being followed for all concentrations of copper and lead nitrates. Stern Volmer linearity at lower concentrations signified complex formation with the film via interaction with its functional groups. Intraparticle diffusion model refers to two steps followed during adsorption which is being followed in addition to second order kinetics. After the repetitive five cycles of desorption-adsorption, maximum percentage adsorption obtained for copper and lead ions was 82.45% and 79.45%, respectively. The application of the Q-gel film on real water samples revealed that it could remove 96.45% and 92.115% of copper ions in case of tap and drinking water. The percentage removal obtained in case of lead ion was 93.79% and 90.12%, respectively for tap and drinking water. The synthesized sample is biodegradable and follows a nature friendly greener approach.
A novel covalent organic framework (COF) polymer has been designed and synthesized by Suzuki polymerization of two monomers based on triarylamine derivatives, and the polymer displays nanosphere morphology due to mini-emulsion reaction system. On the basis of the above polymer, we further fabricated a Schiff base covalent organic framework polymer fluorescent sensor for efficient detection and removal of mercury(II) ions. The material underwent a fluorescence and colour change upon the touching of mercury(II) ions. Thus, taking advantage of the material to detect the presence of mercury(II) ions is quite convenient. Furthermore, the material is capable of efficiently adsorbing mercury(II) ions from aqueous solution. The fluorescence sensing device was successfully fabricated by immobilizing the polymer probe on a macroporous sponge, which was more convenient to detect and remove mercury(II) ions relative to powdery polymer probe.
Amine-functionalized silicon nanoparticles (A-SiNPs) with intense green fluorescence and photostability are synthesized via a one-step, low-cost hydrothermal method under mild conditions using 3-aminopropyl triethoxysilane (APTES) as a silicon source and L-ascorbic acid (AA) as a reducing reagent. The amine-rich surface not only improves water dispersability and stability of the A-SiNPs but also offers a specific copper(II) ion (Cu2+) coordination capability. The as-prepared A-SiNPs can be directly employed for Cu2+ detection in “turn-off” mode, resulting from Cu2+ coordination-induced fluorescence quenching effect. Under optimal conditions, Cu2+ detection was accomplished with a linear range from 1 to 500 μM and a limit of detection (LOD) at 0.1 μM, which was much lower than the maximum level (~ 20 μM) of Cu2+ in drinking water permitted by the US Environmental Protection Agency (EPA). In addition, the A-SiNPs were successfully used to detect Cu2+ in spiked river water, demonstrating its good selectivity and potential application for analysis of surface water samples.
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Hg/Hg(II) have been recognized as highly poisonous to human as they cause severe health and environmental problems. Designing suitable adsorbent decorated with abundance of accessible chelating sites at the solid surface together with its high affinity for heavy metals is a big challenge to overcome the mercury contamination. Here we report, a new thioether functionalized covalent triazine nanosphere SCTN-1 and this has been employed as a highly efficient adsorbent for the removal of toxic mercury from contaminated water with an excellent adsorption performance of 1253 and 813 mg g-1 for Hg2+ and Hg(0) respectively, which largely outperformed several recently reported thiol and thioether functionalized adsorbents. Our kinetic studies suggested that SCTN-1 showed fastest adsorption rate for the removal of mercury from aqueous solutions among all adsorbents known till date. Based on its adsorption performance and high recycling efficiency this thio-functionalized nanoporous polymeric material has huge potential to be explored in environmental remediation.
There are several researches on preparation and application of hydrazone-linked COFs, and all of them generally necessitate rigid aromatic amines. Herein, we report a strategy for design and synthesis of COF with flexible alkyl-amine as building block and intramolecular hydrogen bonding as knot in the network. The proof-of-concept design was demonstrated by exploring 1,3,5-triformylphloroglucinol (Tp) and oxalyldihydrazide (ODH) as precursors to synthesize a novel COF material (TpODH), in which the different organic building units are combined through hydrazone bonds to form 2D porous frameworks. It should be pointed that irreversible enol-to-keto tautomerism and intramolecular N-H···O=C hydrogen bonding of TpODH would enhance the crystallinity and chemical stability, leading to large specific surface area of 835 m2/g. However, another COF synthesized with 1,3,5-triformylbenzene (TFB) and ODH exhibited less crystallinity and low special surface area (94 m2/g). Representatively, the resulting TpODH afforded Cu (II) and Hg (II) capacities of 324 and 1692 mg g-1, respectively, which exceeded most COFs previously reported. Moreover, the FT-IR and XPS spectra analyses were taken to demonstrate the adsorption mechanism. These results suggested that the materials could be applied to the removal of metallic ions in the future.
Metal-free fluorescent covalent organic frameworks (COFs) were synthesized initially with Q-Graphene (QG) scaffolds by the one-step covalent reactions of melamine-aldehyde and phenol-aldehyde poly-condensations using paraformaldehyde. It was discovered that onion-like hollow QG, which consists of multi-layer graphene and different carbon allotropes having a high proportion of folded edges and surface defects, could endow the scaffolded COFs with enhanced green fluorescence and environmental stability. Unexpectedly, they could exhibit the powerful absorption for Cu²⁺ ions resulting in the specific quenching of fluorescence. A fluorimetric strategy with QG-scaffolded COFs was thereby developed to probe Cu²⁺ ions separately in blood and wastewater with the linear concentration ranges of 0.0010–10.0 μM (limit of detection of 0.50 nM) and 0.0032–32.0 μM (limit of detection of 2.4 nM), respectively, promising the potential applications for the field-applicable monitoring of Cu²⁺ ions in the clinical and environmental analysis fields. In addition, the prepared COFs sorbents were employed to absorb Cu²⁺ ions in wastewater showing high removal efficiency. More importantly, such an one-pot fabrication route with hollow QG scaffolds may be tailorable extensively for the preparation of a variety of metal-free multifunctional COFs with enhanced fluorescence, water solubility, environmental stability, and metal removal capability.
One pressing concern today is to construct sensors that can withstand various disturbances for highly selective and sensitive detecting trace analytes in complicated samples. Molecularly imprinted polymers (MIPs) with tailor-made binding sites are preferred to be recognition elements in sensors for effective targets detection, and fluorescence measurement assists in highly sensitive detection and user-friendly control. Accordingly, molecular imprinting-based fluorescence sensors (MI-FL sensors) have attracted great research interest in many fields such as chemical and biological analysis. Herein, we comprehensively review the recent advances in MI-FL sensors construction and applications, giving insights on sensing principles and signal transduction mechanisms, focusing on general construction strategies for intrinsically fluorescent or nonfluorescent analytes and improvement strategies in sensing performance, particularly in sensitivity. Construction strategies are well overviewed, mainly including the traditional indirect methods of competitive binding against pre-bound fluorescent indicators, employment of fluorescent functional monomers and embedding of fluorescence substances, and novel rational designs of hierarchical architecture (core-shell/hollow and mesoporous structures), post-imprinting modification, and ratiometric fluorescence detection. Furthermore, MI-FL sensor based microdevices are discussed, involving micromotors, test strips and microfluidics, which are more portable for rapid point-of-care detection and in-field diagnosing. Finally, the current challenges and future perspectives of MI-FL sensors are proposed.
In the present study, a fluorescent ion-imprinted sensor (FIIS) for rapid and convenient detection of Cu²⁺ ions was fabricated. A fluorescent polymerizable ligand, i.e., 4-(2-aminomethyl)pyridine-N-allylnaphthalimide, was designed and synthesized. The FIIS was prepared by surface functionalization of PVDF membrane with a thin layer of copper (II) ion-imprinted polymer using the synthesized ligand as the fluorescent functional monomer. The intensity of fluorescence emission of FIIS decreased linearly with the increase of copper (II) ions concentration in the range of 0-70.0μM. The results of selectivity tests indicated that FIIS has high specific recognition ability for Cu²⁺ ions. The recoveries for the spiked samples were in the range of 96.4-104.4%, and the relative standard deviations (RSDs) were found to be 2.17-4.75%. The FIIS was successfully applied to the determination of copper (II) ions in real water samples. The Limits of detection (LODs) for Cu²⁺ ions in real water samples were in the range of 0.11-0.14 uM. The present study provided a feasible strategy for construction of fluorescent ion-imprinted sensor for convenient, sensitive and selective detection of metal ions.
A guest-induced reversible crystal-structure transformation is identified in a new 3D covalent organic framework (COF) by the comprehensive analyses of powder X-ray diffraction, organic vapor sorption isotherm, and 129Xe NMR spectroscopy. The utilization of revolving imine-bond in interpenetrating 3D networks is uncovered as the key to the dynamic behavior, whose potential applications have been illustrated by gas separation and heterogeneity catalysis, thus, paving the way to the design of stimuli-responsive and multifunctional COF materials.
A key challenge in environmental remediation is the design of adsorbents bearing an abundance of accessible chelating sites with high affinity, to achieve both rapid uptake and high capacity for the contaminants. Herein, we demonstrate how two-dimensional covalent organic frameworks (COFs) with well-defined mesopore structures display the right combination of properties to serve as a scaffold for decorating coordination sites to create ideal adsorbents. The proof-of-concept design is illustrated by modifying sulfur derivatives on a newly designed vinyl-functionalized mesoporous COF (COF-V) via thiol–ene “click” reaction. Representatively, the material (COF-S-SH) synthesized by treating COF-V with 1,2-ethanedithiol exhibits high efficiency in removing mercury from aqueous solutions and the air, affording Hg²⁺ and Hg⁰ capacities of 1350 and 863 mg g–1, respectively, surpassing all those of thiol and thioether functionalized materials reported thus far. More significantly, COF-S-SH demonstrates an ultrahigh distribution coefficient value (Kd) of 2.3 × 10⁹ mL g–1, which allows it to rapidly reduce the Hg²⁺ concentration from 5 ppm to less than 0.1 ppb, well below the acceptable limit in drinking water (2 ppb). We attribute the impressive performance to the synergistic effects arising from densely populated chelating groups with a strong binding ability within ordered mesopores that allow rapid diffusion of mercury species throughout the material. X-ray absorption fine structure (XAFS) spectroscopic studies revealed that each Hg is bound exclusively by two S via intramolecular cooperativity in COF-S-SH, further interpreting its excellent affinity. The results presented here thus reveal the exceptional potential of COFs for high-performance environmental remediation.
The predesignable porous structures found in covalent organic frameworks (COFs) render them attractive as a molecular platform for addressing environmental issues such as removal of toxic heavy metal ions from water. However, a rational structural design of COFs in this aspect has not been explored. Here we report the rational design of stable COFs for Hg(II) removal through elaborate structural design and control over skeletons, pore size, and pore walls. The resulting framework is stable under strong acid and base conditions, possesses high surface area, has large mesopores, and contains dense sulfide functional termini on the pore walls. These structural features work together in removing Hg(II) from water and achieve a benchmark system that combines capacity, efficiency, effectivity, applicability, selectivity, and reusability. These results suggest that COFs offer a powerful platform for tailor-made structural design to cope with various types of pollutions.
2-Hydroxyethylmethacrylate (HEMA) based ion-imprinted cryogel membranes (IIP) were synthesized using histidine containing functional monomer, N-methacryloyl-l-histidine (MAH) as complexing/chelating agent, Cu(II) ions as template, methylene bisacrylamide as cross-linker, TEMED and APS as redox pair in both magnetic and non-magnetic forms through free radical polymerization method for selective Cu(II) ion removal. A control non-imprinted cryogel (NIP) was also prepared for comparison. The matrices were characterized by swelling tests, scanning electron microscopy (SEM), BET, and FTIR. Effect of several parameters (pH, temperature, contact time, etc.) on adsorption capacities was examined in batch mode.
A natural isorhamnetin-based fluorescent sensor for highly sensitive and selective detection of copper ions had been studied. The fluorescent sensor isorhamnetin (Iso) after binding to Cu2+ ions in pH 7.40 buffer solution generated quenching in fluorescent emission intensity. The binding constant value was obtained 1.79 × 106. The sensor Iso can be applied to the quantification of Cu2+ ion with a linear range of 1.0 × 10−8-1.9 × 10−6 mol·L−1, the detection limit of 4.0 × 10−9 mol·L−1, and the reproducibility of the sensor is good. The sensor showed high selectivity toward Cu2+. As a result, the isorhamnetin fluorescent sensor was successfully applied for determination of Cu2+ in rivers, lakes, vegetables and fruits with good recovery.
A hydrogen bond assisted azine-linked covalent organic framework, COF-JLU3, was synthesized under solvothermal conditions. Combining excellent crystallinity, porosity, stability and luminescence, it can be the first COF as a fluorescent sensor for toxic metal ions, exhibiting high sensitivity and selectivity to Cu(2+).
Wastewater quality is usually assessed using physical, chemical and microbiological tests, which are not suitable for online monitoring, provide unreliable results, or use hazardous chemicals. Hence, there is an urgent need to find a rapid and effective method for the evaluation of water quality in natural and engineered systems and for providing an early warning of pollution events. Fluorescence spectroscopy has been shown to be a valuable technique to characterize and monitor wastewater in surface waters for tracking sources of pollution, and in treatment works for process control and optimization. This paper reviews the current progress in applying fluorescence to assess wastewater quality. Studies have shown that, in general, wastewater presents higher fluorescence intensity compared to natural waters for the components associated with peak T (living and dead cellular material and their exudates) and peak C (microbially reprocessed organic matter). Furthermore, peak T fluorescence is significantly reduced after the biological treatment process and peak C is almost completely removed after the chlorination and reverse osmosis stages. Thus, simple fluorometers with appropriate wavelength selectivity, particularly for peaks T and C could be used for online monitoring in wastewater treatment works. This review also shows that care should be taken in any attempt to identify wastewater pollution sources due to potential overlapping fluorophores. Correlations between fluorescence intensity and water quality parameters such as biochemical oxygen demand (BOD) and total organic carbon (TOC) have been developed and dilution of samples, typically up to x10, has been shown to be useful to limit inner filter effect. It has been concluded that the following research gaps need to be filled: lack of studies on the on-line application of fluorescence spectroscopy in wastewater treatment works and lack of data processing tools suitable for rapid correction and extraction of data contained in fluorescence excitation-emission matrices (EEMs) for real-time studies.
Heavy metal ions are highly toxic and widely spread as environmental pollutants. New strategies are being developed to simultaneously detect and remove these toxic ions. Herein, we take the intrinsic advantage of covalent organic frameworks (COFs) and develop the fluorescent COFs for sensing applications. As a proof-of-concept, a thioether-functionalized COF material, COF-LZU8, was "bottom-up" integrated with multi-functionality for the selective detection and facile removal of mercury(II): the π-conjugated framework as the signal transducer, the evenly-and-densely distributed thioether groups as the Hg2+ receptor, the regular pores to facilitate the real-time detection and mass transfer, together with the robust COF structure for the recycle use. The excellent sensing performance of COF-LZU8 was achieved in terms of high sensitivity, excellent selectivity, easy visibility, and real-time response. Meanwhile, the efficient removal of Hg2+ from water and the recycle use of COF-LZU8 offered the possibility for practical applications. In addition, XPS and solid-state NMR investigations verified the strong and selective interaction between Hg2+ and the thioether groups of COF-LZU8. This research not only demonstrates the utilization of fluorescent COFs for both sensing and removal of metal ions, but also highlights the facile construction of functionalized COFs for environmental applications.
Porous solids are important as membranes, adsorbents, catalysts, and in other chemical applications. But for these materials to find greater use at an industrial scale, it is necessary to optimize multiple functions in addition to pore structure and surface area, such as stability, sorption kinetics, processability, mechanical properties, and thermal properties. Several different classes of porous solids exist, and there is no one-size-fits-all solution; it can therefore be challenging to choose the right type of porous material for a given job. Computational prediction of structure and properties has growing potential to complement experiment to identify the best porous materials for specific applications.
Copyright © 2015, American Association for the Advancement of Science.
The legume-rhizobium symbiosis has been proposed as an important system for phytoremediation of heavy metal contaminated soils due to its beneficial activity of symbiotic nitrogen fixation. However, little is known about metal resistant mechanism of rhizobia and the role of metal resistance determinants in phytoremediation. In this study, copper resistance mechanisms were investigated for a multiple metal resistant plant growth promoting rhizobium, M. amorphae 186. Three categories of determinants involved in copper resistance were identified through transposon mutagenesis, including genes encoding a P-type ATPase (CopA), hypothetical proteins and other proteins (a GTP-binding protein and a ribosomal protein). Among these determinants, copA played the dominant role in copper homeostasis of M. amorphae 186. Mutagenesis of a hypothetical gene lipA in mutant MlipA exhibited pleiotropic phenotypes including sensitivity to copper, blocked symbiotic capacity and inhibited growth. In addition, the expression of cusB encoding part of an RND-type efflux system was induced by copper. To explore the possible role of copper resistance mechanism in phytoremediation of copper contaminated soil, the symbiotic nodulation and nitrogen fixation abilities were compared using a wild-type strain, a copA-defective mutant and a lipA-defective mutant. Results showed that a copA deletion did not affect the symbiotic capacity of rhizobia under uncontaminated condition, but the protective role of copA in symbiotic processes at high copper concentration is likely concentration-dependent. In contrast, inoculation of a lipA-defective strain led to significant decreases in the functional nodule numbers, total N content, plant biomass and leghemoglobin expression level of R. pseudoacacia even under conditions of uncontaminated soil. Moreover, plants inoculated with lipA-defective strain accumulated much less copper than both the wild type strain and the copA-defective strain, suggesting an important role of a healthy symbiotic relationship between legume and rhizobia in phytostabilisation.
Protein engineering by resurfacing is an efficient approach to provide new molecular toolkits for biotechnology and bio-analytical chemistry. H39GFP is a new variant of green fluorescent protein containing 39 histidine residues in the primary sequence, which was developed by protein resurfacing. Herein, taking H39GFP as the signal reporter, a label-free fluorometric sensor for Cu2+ sensing was developed based on the unique multivalent metal ion-binding property of H39GFP and fluorescence quenching effect of Cu2+ by electron transfer. The high affinity of H39GFP with Cu2+ (Kd, 16.2 nM) leads to rapid detection of Cu2+ in 5 min with low detection limit (50 nM). Using acetylthiocholine (ATCh) as the substrate, this H39GFP/Cu2+ complex-based sensor was further applied for the turn-on fluorescence detection of acetylcholinesterase (AChE) activity. The assay was based on the reaction between Cu2+ and thiocholine, the hydrolysis product of ATCh by AChE. The proposed sensor is highly sensitive (LOD, 0.015 mU mL-1) and is feasible for screening inhibitors of AChE. Furthermore, the practicability of this method was demonstrated by the detection of pesticide residue (carbaryl) in real food samples. Hence, the successful applications of H39GFP in detection of metal ion and enzyme activity presents the prospect of resurfaced proteins as versatile biosensing platforms.
A Schiff base, 2-amino-benzoic acid [1-(2-hydroxy-phenyl)-propylidene]-hydrazide (H2abph) and its mononuclear complex [Mn(Habph)2] and one-dimensional coordination polymers [Cu(abph)·DMSO]n and [Zn2(abph)2·2DMSO]n have been synthesised and characterised by various physico-chemical and spectroscopic techniques. The molecular structures of the compounds are also determined by single crystal X-ray crystallography. The reaction of ligand with Cu(II) and Zn(II) in methanol gives polymeric complex, while the similar reaction with Mn(II) results in the formation of a cyclised quinazoline derivative 2,2-dimethyl-3-(1-phenyl-propylideneamino)-2,3-dihydro-1H-quinazolin-4-one. However, the reaction of ligand with Mn(II) in ethanol gives a mononuclear Mn(II) complex. In Mn(II) complex, the ligand coordinates through azomethine-N, carbonyl-O and phenolate-O forming a 6-coordinate distorted octahedral geometry around metal ion. In Cu(II) and Zn(II) complexes, the ligand bonds through azomethine-N, carbonylate-O and phenolate-O. The Cu(II) complex forms a distorted square planar geometry, which polymerises via anthranilate-NH2 group of second unit. The Zn(II) complex exhibits a phenolate-O bridged dimer, which polymerises through anthranilate-NH2 group forming a 5-coordinate distorted square pyramid geometry around each metal ion. The synthesised compounds show an appreciable corrosion inhibition property for mild steel in 1 M HCl medium which varies in the order: H2abph < Mn(II) complex < Cu(II) complex < Zn(II) complex.
A variety of aromatic amines/hydrazides and aldehydes have been utilized for the construction of crystalline COFs at a faster rate and in high yield, irrespective of their reactivity and solubility using the Liquid-Assisted Grinding (LAG) method.
This article concerns a new and precise strategy for the determination of Cu(2+) based on a color reaction and outer filter effects (OFEs). Cu(2+) can react with sodium diethyldithiocarbamate trihydrate (DDTC) to form a DDTC-Cu(2+) complex with a significant absorption at 447 nm. Being positively correlated with Cu(2+), the absorption could be treated as the basis for the determination of Cu(2+). When cuvettes containing the complex were fixed in the light path of a fluorescence spectrophotometer, the excitation/emitted light were absorbed by the OFEs, similar to absorption mechanisms of inner filter effects. Under suitable conditions, OFEs from the complex could quantitatively reduce the fluorescence intensities of quinine sulfate and acridine yellow by absorbing the excitation or emission light. Compared with traditional absorption spectroscopy (with a detection limit at 0.9 µmol/L), indirect OEF techniques showed increased sensitivities by about 1 order of magnitude. The strategy could be extended to many different systems where components absorb the excitation wavelength and/or emission wavelength of fluorescers.
Beta-cyclodextrin-modified chitosan 1 was synthesized via the Schiff base reaction between 6-O-(4-formylphenyl)-beta-cyclodextrin and chitosan (CHIT), and then the supramolecular dyad assemblies 2 and 3 were respectively fabricated from the subunit 1 through the inclusion of adamantane-modified pyrene into the beta-cyclodextrin cavity and the wrapping of a CHIT chain on multiwalled carbon nanotubes (MWCNTs). The water-soluble dyad 3 further interacted with adamantane-modified pyrene, forming a stable triad assembly 4. They were extensively characterized by NMR, thermogravimetric analysis, UV-vis, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy (AFM). Furthermore, the DNA condensation abilities of 1-4 were validated by AFM and dynamic light scattering, which indicates that the DNA-condensing capability of CHIT can be pronouncedly improved by either the pyrene grafts or the MWCNT medium. The cooperation between cationic and aromatic groups as well as the dispersion of CHIT agglomerates by MWCNTs are the key factors to enhance DNA condensation of cationic polymers.
Metal ions are prevalent in biological systems and are critically involved in essential life processes. However, excess concentrations of metals can pose a serious danger to living organisms. Oligonucleotides represent a versatile sensing platform for the detection of various molecular entities including metal ions. This review summarizes the recent advances in the development of oligonucleotide-based luminescent detection methods for metal ions.
It is generally accepted that copper toxicity is a consequence of the generation of reactive oxygen species (ROS) by copper ions via Fenton or Haber-Weiss reactions. Copper ions display high affinity for thiol and amino groups occurring in proteins. Thus, specialized proteins containing clusters of these groups transport and store copper ions, hampering their potential toxicity. This mechanism, however, may be overwhelmed under copper overloading conditions, in which copper ions may bind to thiol groups occurring in proteins non-related to copper metabolism. In this study, we propose that indiscriminate copper binding may lead to damaging consequences to protein structure, modifying their biological functions. Therefore, we treated liver subcellular membrane fractions, including microsomes, with Cu2+ ions either alone or in the presence of ascorbate (Cu2+/ascorbate); we then assayed both copper-binding to membranes, and microsomal cytochrome P450 oxidative system and GSH-transferase activities. All assayed sub-cellular membrane fractions treated with Cu2+ alone displayed Cu2+-binding, which was significantly increased in the presence of Zn2+, Hg2+, Cd2+, Ag+1 and As3+. Treatment of microsomes with Cu2+ in the microM range decreased the microsomal thiol content; in the presence of ascorbate, Cu2+ added in the nM concentrations range induced a significant microsomal lipoperoxidation; noteworthy, increasing Cu2+ concentration to > or =50 microM led to non-detectable lipoperoxidation levels. On the other hand, microM Cu2+ led to the inhibition of the enzymatic activities tested to the same extent in either presence or absence of ascorbate. We discuss the possible significance of indiscriminate copper binding to thiol proteins as a possible mechanism underlying copper-induced toxicity.
Covalent organic frameworks (COFs) have been designed and successfully synthesized by condensation reactions of phenyl diboronic
acid {C6H4[B(OH)2]2} and hexahydroxytriphenylene [C18H6(OH)6]. Powder x-ray diffraction studies of the highly crystalline products (C3H2BO)6·(C9H12)1 (COF-1) and C9H4BO2 (COF-5) revealed expanded porous graphitic layers that are either staggered (COF-1, P63/mmc) or eclipsed (COF-5, P6/mmm). Their crystal structures are entirely held by strong bonds between B, C, and O atoms to form rigid porous architectures
with pore sizes ranging from 7 to 27 angstroms. COF-1 and COF-5 exhibit high thermal stability (to temperatures up to 500°
to 600°C), permanent porosity, and high surface areas (711 and 1590 square meters per gram, respectively).
Cited By (since 1996):713, Export Date: 18 October 2014