Post-synthetic Modification Research Articles

Eu3+-functionalized metal organic framework applied as “red-green indicator” for tetracycline

The misuse of antibiotics, such as tetracycline (TC), can seriously harm human health so it is of great practical importance to sensitively and rapidly detect TC. In this paper, an Eu3+-functionalized Zr-MOF (Eu3+@UiO-66-(OH)2) was successfully prepared by a post-synthetic modification strategy as a ratiometric fluorescent sensor for ultrasensitive and specific detection of TC in aqueous medium. The proposed Eu3+@UiO-66-(OH)2 sensor possessed remarkable fluorescence enhancement properties besides high specific surface area and excellent stability. In the quantitative analysis of TC, the sensor exhibited fast response (<60 s), wide linear range (0–160 μM), high sensitivity (detection limit as low as 1.33 nM) and high selectivity for TC. Furthermore, it has been successfully utilized in determination of TC in real samples, demonstrating its application potential in complex environmental water system.

Precise Post-Synthetic Modification of Heterometal-Organic Capsules for Selectively Encapsulating Tetrahedral Anions.

Post-synthetic modification plays a crucial role in precisely adjusting the structure and functions of advanced materials. Herein, we report the self-assembly of a tubular heterometallic Pd3Cu6L16 capsule that incorporates Pd(II) and CuL1 metalloligands. This capsule undergoes further modification with two tridentate anionic ligands (L2) to afford a bicapped Pd3Cu6L16L22 capsule with an Edshammer polyhedral structure. By employing transition metal ions, acid, and oxidation agents, the bicapped capsule can be converted into an uncapped one. This uncapped form can then revert back to the bicapped structure on the addition of Br- ions and a base. Interestingly, introducing Ag+ ions leads to the removal of one L2 ligand from the bicapped capsule, yielding a mono-capped Pd3Cu6L16L2 structure. Furthermore, the size of the anions critically influences the precise control over the post-synthetic modifications of the capsules. It was demonstrated that these capsules selectively encapsulate tetrahedral anions, offering a novel approach for the design of intelligent molecular delivery systems.

Covalent Post-Synthetic Modification of Metal-Organic Cages: Concepts and Recent Progress.

Metal-organic cages (MOCs) are supramolecular coordination complexes that have internal cavities for hosting guest molecules and exhibiting various properties. However, the functions of MOCs are limited by the choice of the building blocks. Post-synthetic modification (PSM) is a technique that can introduce new functional groups and replace existing ones on the MOCs without changing their geometry. Among many PSM methods, covalent PSM is a promising approach to modify MOCs with tailored structures and functions. Covalent PSM can be applied to either the internal cavity or the external surface of the MOCs, depending on the functionality expected to be customized. However, there are still some challenges and limitations in the field of covalent PSM of MOCs, such as the balance between the stability of MOCs and the harshness of organic reactions involved in covalent PSMs. This concept article introduces the organic reaction types involved in covalent PSM of MOCs, their new applications after modification, and summarizes and provides an outlook of this research field.

Silver Nanoparticle-Functionalized Postsynthetically Modified Thiol MOF UiO-66-NH-SH for Efficient CO2 Fixation.

Thiols are essential functional groups imparting unique properties, such as reactivity and selectivity, to many vital enzymes and biomolecules. The integration of electronically soft thiol groups within metal-organic frameworks (MOFs) yields elevated reactivity and a pronounced affinity for soft metal ions. However, the scarcity of thiol-based ligands and synthetic challenges hinder the advancement of thiol-based MOFs. To bypass the difficulties of synthesizing thiol MOFs by a direct reaction between thiol-based ligands and corresponding metal salts, postsynthetic modification (PSM) of MOFs is an efficient strategy to introduce thiol functionality. Herein, we have introduced Ag nanoparticles in postsynthetically modified thiol MOFs UiO-66-NH-SH (1) (synthesized by reaction between UiO-66-NH2 and thioglycolic acid) and UiO-66-NH-SH (2) (synthesized by reaction between UiO-66-NH2 and 3-mercaptopropionic acid) to synthesize a series of heterogeneous catalysts for CO2 fixation. Catalysts Cat 1-2 and Cat 3 - 4 were synthesized from UiO-66-NH-SH (1) and UiO-66-NH-SH (2), respectively, by using varying concentrations of silver (AgNO3). Catalyst Ag@UiO-66-NH-SH (1) (Ag = 3.45%; namely Cat 2) shows the highest efficiency for the catalytic conversion of propargylic alcohol and terminal epoxide to the corresponding cyclic carbonates. Finally, a rationalized reaction mechanism is proposed by correlating our results with the current literature. This work presents a viable strategy to utilize the thiol functionality of MOFs (avoiding the complexities associated with synthesizing thiol MOFs directly from thiol ligands) as a platform for introducing catalytically active metal centers and applying them as a heterogeneous catalyst for CO2 fixation reactions.

Postsynthetic Modification of Thermo-Treated Metal-Organic Framework for Combined Photothermal/Photodynamic Antibacterial Therapy.

Metal-organic frameworks (MOFs) are emerging porous materials that can serve as carriers of photosensitizers and photothermal agents. Meanwhile, a large number of active sites in MOFs endow them with the characteristics of modification by postsynthetic modification. Herein, a dual-modal PDT/PTT therapeutic agent HMIL-121-acriflavine-tetrakis (4-amoniophenyl) porphyrin (HMIL-ACF-Por), prepared by the postsynthetic modification of the MOF (HMIL-121), was reported for antibacterial applications. The prepared HMIL-ACF-Por enables the generation of abundant reactive oxygen species, including the superoxide anion radical (O2-) and singlet oxygen (1O2), and thermal energy under 808 nm NIR laser irradiation. HMIL-ACF-Por showed good antibacterial ability against Escherichia coli and Staphylococcus aureus in vitro. Meanwhile, HMIL-ACF-Por can effectively inhibit the inflammatory response caused by bacterial infection and accelerate S. aureus-infected wound healing under laser irradiation owing to the synergistic effect of photodynamic therapy (PDT) and photothermal therapy (PTT). These results demonstrate that HMIL-ACF-Por is a promising PDT/PTT therapeutic agent. This work also contributes to offering an effective solution for treating bacterial infections and promotes the application of MOF-based materials in biomedicine.

DNA three-way junction structures with amino acid side chains prepared via post-synthetic amide condensation

DNA three-way junction (3WJ) structures with three amino acid side chains in the core have been synthesized via post-synthetic DNA modification. Amide condensation reactions of oligonucleotides containing 2′-aminouridine with activated esters yielded DNA strands modified with His, Cys and Asp side chains to form modified 3WJs. Even a 3WJ with three negatively charged Asp side chains formed stably at room temperature. Furthermore, DNA hybridization alone placed two (His and Asp) and three (His, Cys, and Asp) side chains within the 3WJs, indicating that the DNA 3WJs are a useful platform for spatial arrangement of amino acid side chains.

Accelerating the Phosphatase-like Activity of Uio-66-NH2 by Catalytically Inactive Metal Ions and Its Application for Improved Fluorescence Detection of Cardiac Troponin I.

Compared with natural enzymes, nanozymes usually exhibit much lower catalytic activities, which limit the sensitivities of nanozyme-based immunoassays. Herein, several metal ions without enzyme-like activities were engineered onto Uio-66-NH2 nanozyme through postsynthetic modification. The obtained Mn+@Uio-66-NH2 (Mn+ = Zn2+, Cd2+, Co2+, Ca2+and Ni2+) exhibited improved phosphatase-like catalytic activities. In particular, a 12-fold increase in the catalytic efficiency (kcat/Km) of Uio-66-NH2 was observed after the modification with Zn2+. Mechanism investigations indicate that both the amino groups and oxygen-containing functional groups in Uio-66-NH2 are the binding sites of Zn2+, and the modified Zn2+ ions on Uio-66-NH2 serve as the additional catalytic sites for improving the catalytic performance. Furthermore, the highly active Zn2+@Uio-66-NH2 was used as a nanozyme label to develop a fluorescence immunoassay method for the detection of cardiac troponin I (cTnI). Compared with pristine Uio-66-NH2, Zn2+@Uio-66-NH2 can widen the linear range by 1 order of magnitude (from 10 pg/mL-1 μg/mL to 1 pg/mL-1 μg/mL) and also lower the detection limit by 5 times (from 4.7 pg/mL to 0.9 pg/mL).

Solid-State Phosphine Ligand Engineering via Postsynthetic Modification of Amine-Functionalized Metal–Organic Frameworks

Solid-State Phosphine Ligand Engineering via Postsynthetic Modification of Amine-Functionalized Metal–Organic Frameworks

Mechanically Triggered Polymer Deconstruction through Mechanoacid Generation and Catalytic Enol Ether Hydrolysis.

Polymers that amplify a transient external stimulus into changes in their morphology, physical state, or properties continue to be desirable targets for a range of applications. Here, we report a polymer comprising an acid-sensitive, hydrolytically unstable enol ether backbone onto which is embedded gem-dichlorocyclopropane (gDCC) mechanophores through a single postsynthetic modification. The gDCC mechanophore releases HCl in response to large forces of tension along the polymer backbone, and the acid subsequently catalyzes polymer deconstruction at the enol ether sites. Pulsed sonication of a 61 kDa PDHF with 77% gDCC on the backbone in THF with 100 mM H2O for 10 min triggers the subsequent degradation of the polymer to a final molecular weight of less than 3 kDa after 24 h of standing, whereas controls lacking either the gDCC or the enol ether reach final molecular weights of 38 and 27 kDa, respectively. The process of sonication, along with the presence of water and the existence of gDCC on the backbone, significantly accelerates the rate of polymer chain deconstruction. Both acid generation and the resulting triggered polymer deconstruction are translated to bulk, cross-linked polymer networks. Networks formed via thiol-ene cross-linking and subjected to unconstrained quasi-static uniaxial compression dissolve on time scales that are at least 3 times faster than controls where the mechanophore is not covalently coupled to the network. We anticipate that this concept can be extended to other acid-sensitive polymer networks for the stress-responsive deconstruction of gels and solvent-free elastomers.

Reversible Postsynthetic Modification in a Metal-Organic Framework.

Postsynthetic modification (PSM) of metal-organic frameworks (MOFs) provides access to functional materials and advanced porous solid engineering. Herein, we report the reversible PSM of a multivariate isoreticular MOF by applying dynamic furan-maleimide Diels-Alder (DA) chemistry. The key step involves incorporating a furan group into the MOF via "click" PSM, which can then undergo repeated cycles of modification and de-modification with maleimides. The structural integrity, crystallinity, and porosity of the furan-appended MOF remained intact even after three consecutive PSM/de-modification cycles using three different functionalized maleimides.

Reversible Postsynthetic Modification in a Metal–Organic Framework

AbstractPostsynthetic modification (PSM) of metal–organic frameworks (MOFs) provides access to functional materials and advanced porous solid engineering. Herein, we report the reversible PSM of a multivariate isoreticular MOF by applying dynamic furan‐maleimide Diels–Alder (DA) chemistry. The key step involves incorporating a furan group into the MOF via “click” PSM, which can then undergo repeated cycles of modification and de‐modification with maleimides. The structural integrity, crystallinity, and porosity of the furan‐appended MOF remained intact even after three consecutive PSM/de‐modification cycles using three different functionalized maleimides.

Enhancement of adsorption performance for I2 and Cr(VI) by the metal-organic framework UiO-66-NH2 via post-synthetic modification

Excessive emissions of radioactive I2 and toxic Cr(VI) have been a significant threat to the environment and human health. Thus, the adsorption of I2 and Cr(VI) has attracted great attention. Here a new functionalized UiO-66-NH2 MOF with pyrazole and amide groups were fabricated through postsynthetic modification (PSM) (denoted as UiO-66-AMmpz) and used to study the adsorption of gaseous I2 and aqueous phase Cr(VI). UiO-66-AMmpz exhibited good adsorption capacities of 1.21 g·g−1 for I2 at 75 °C and 291.2 mg·g−1 for Cr(VI) at pH 2, which significantly surpasses the pristine UiO-66-NH2. By analyzing the IR, XPS, EPR, Raman spectra of UiO-66-AMmpz before and after I2 adsorption, it was deduced that the good adsorption performance was attributed to the strong interactions between the adsorbed I2 and abundant N and O sites in the surface and pores of UiO-66-AMmpz, which mainly came from post-introduced the pyrazole and amide groups. In addition, the Cr(VI) adsorption process followed the pseudo-second-order kinetics and its adsorption data also fit well the Langmuir model. Simultaneously, the thermodynamic parameters suggested that the Cr(VI) adsorption process is spontaneous and endothermic process. Moreover, XPS and IR analysis revealed that the adsorbed Cr(VI) was partially reduced to Cr(III) and then fixed on UiO-66-AMmpz. This work can aid us to appreciate the surface interaction between I2 and Cr(VI) and the framework of MOFs and provide a promising MOF material to adsorb gaseous I2 and remove Cr(VI) from water.

A novel amine-functionalized polyoxometalate-based metal-organic framework: A reusable heterogeneous nanocomposite for selective oxidation of alcohols

Keggin-type H5PMo10V2O40 (PMoV2) immobilized onto amine-functionalized UiO-66-NH2 via acid-base interaction to create a highly efficient catalyst, called PMoV2@UiO-66-NH2, using post-synthetic modification. This POM-based MOF nanocomposite was used to synthesize carbonyl compounds from alcohols using H2O2 as an oxidant in a green oxidation process. The PMoV2 was successfully immobilized on the amine-functionalized MOF surface through electrostatic interaction, as confirmed by standard characterization methods including FT-IR, EDX, TGA, FE-SEM, MAP images, XRD, and ICP-OES. PMoV2@UiO-66-NH2 exhibited remarkable catalytic activity, with complete conversion of benzyl alcohol and high selectivity towards benzaldehyde. The superior catalytic performance of PMoV2@UiO-66-NH2 can be attributed to its large surface area, uniform dispersion of PMoV2, and the presence of V5+/V4+ redox pairs. The catalyst exhibited attractive yields, required minimal packing, and retained its catalytic activity for up to six cycles.

Greener Approach Towards Synthesis of Palladium-Decorated Graphene Derivatives for Hydrogen Adsorption.

A simple, green, and relatively fast procedure was used to prepare palladium decorated graphene-based materials. A parent graphene-like material with a high specific surface area of up to 384 m2 /g and a total pore volume of 0.42 cm3 /g was prepared via a fast, solvent-free ball milling of graphite powder only. Post-synthetic modification of this graphene-like material was performed via a simplified method using palladium chloride and a small amount of a non-harsh reducing agent - formic acid. Palladium decoration (2.1 wt%) allowed obtaining a few times higher hydrogen adsorption (0.42 wt% at 30 °C and 40 bar) compared to that on bare graphene-based materials. Palladium-decorated graphene materials are promising for hydrogen storage and their usage in this application represents an alternative for conventional fossil fuels. The proposed synthesis and post-modification strategies are in line with green synthesis strategies.

Post-synthetic modification of MIL-53(Fe) with Tb3+ and guanosine monophosphate: Construction of a fluorescent dual-target sensor

The development of fluorescence-based multi-target sensing sensors has great potential for applications in food safety monitoring and biomedical analysis. Nevertheless, the intricate design remains a hurdle in the construction of these sensors. Luminescent metal-organic frameworks (LMOFs) are suitable materials for the construction of multi-target fluorescent sensors due to their ability to introduce multiple luminescent centers and specific reaction sites through post-synthetic modification (PSM). In this study, a dual-target fluorescent sensor was fabricated via PSM of MIL-53(Fe) with Tb3+ and guanosine monophosphate (GMP). The Tb-GMP@MIL-53(Fe) sensor, with multiple luminescent centers and specific recognition sites, successfully achieved the detection of hydrogen peroxide (H2O2) and acid phosphatase (ACP) with a limit of detection (LOD) of 0.18 μM and 0.73 U/L, respectively. More significantly, this study demonstrates the potential of post-synthetic modified LMOFs in developing dual/multiple-target fluorescent sensors, expanding the scope of sensor designs for various analytes.

Postsynthetic Modification of Calixarene-Based Porous Coordination Cages

Postsynthetic Modification of Calixarene-Based Porous Coordination Cages

Boosting catalytic performance for CO2 cycloaddition under mild condition via amine grafting on MIL-101-SO3H catalyst

The efforts to achieve sustainable chemical conversion and efficient CO2 utilization are critical to addressing climate change and environmental sustainability, and therefore the development of effective CO2 conversion catalysts is crucial. In this study, novel acid-base bifunctional catalysts, MIL-101-SO3H@Atz and MIL-101-SO3H@DAtz, were successfully synthesized using MIL-101-SO3H as an acid support material through post-synthetic modification with 3-amino-1,2,4-triazole (Atz) and 3,5-diamino-1,2,4-triazole (DAtz) for CO2 conversion reaction. The incorporation of the amine species into MIL-101-SO3H created unique synergistic effects with dual acid-base catalytic sites, facilitating the efficient conversion of CO2 and epoxides into cyclic carbonates. Among the catalysts, MIL-101- SO3H@DAtz demonstrated superior catalytic performance with achieving 100% epichlorohydrin (ECH) conversion with over 99% selectivity to cyclic carbonate with high selectivity of > 99% under the ambient condition of 1 bar CO2 without any co-catalyst or solvent. The elucidated CO2 cycloaddition reaction mechanism highlights the synergistic effects of acid-base functionalities and CO2-philic Lewis bases as well as hydrogen bonding donor groups, providing valuable insights into the factors contributing to superior catalytic performance. The simulated flue gas (15% CO2/85% N2, v/v) was also conducted using MIL-101-SO3H@DAtz catalyst. Additionally, the MIL-101-SO3H@DAtz catalyst exhibited remarkably robust structural stability and recyclability, maintaining its activity over multiple cycles.

Sequence-Defined Tertiary Amine-Based Oligomer Employing a Scalable, Support-Free, and Protection/Deprotection-Free Iterative Strategy.

Sequence-defined oligomers (SDOs) with their unique monomeric sequence and customizable nature are attracting the attention of researchers globally. The structural and functional diversity attainable in SDOs makes this platform promising, albeit with challenges in the synthesis. Herein, we report the design and synthesis of a novel class of SDO by incorporating tertiary amines into the backbone from commercially available inexpensive materials. Tertiary amines were selected due to their various material and biomedical applications. Even though the synthesis and purification of amine compounds are challenging, their various significant applications, such as pharmaceuticals, catalysts, surfactants, corrosion inhibitors, dye intermediates, polymer additives, rubber accelerators, gas treating agents, agriculture, and analytical chemistry, make them fascinating. The synthetic strategy that is designed here is extremely efficient and economical for the scalable synthesis of the SDO and is support-free, protection-deprotection chemistry-free, and catalyst/template-free. Most importantly, no extra design and synthesis of the monomer is required here. The key reactions employed for the SDO synthesis are (i) transformation of the hydroxy group to a halide and (ii) substitution of the halide by the secondary amine units. Including the purifying processes, the multigram synthesis of 4-mer was completed in 12-14 h. The synthetic strategy was established by synthesizing two different sequences of SDOs. The SDOs are characterized by 1H NMR and LC-MS. The tandem MS (MS/MS) experiment was conducted in order to validate the sequences over the SDO chain. Furthermore, the SDO platform was advanced in two ways: (i) by increasing the chain length via attaching a linker, which provides a rapid method for increasing the tertiary amine over the SDO chain, and (ii) postsynthetic modification of SDO with other functional groups, including guanidine for biological importance and a well-known fluorophore dansyl group for material significance.

Leveraging ordered voids in microporous perovskites for intercalation and post-synthetic modification.

We report the use of porous organic layers in two-dimensional hybrid organic-inorganic perovskites (HOIPs) to facilitate permanent small molecule intercalation and new post-synthetic modifications. While HOIPs are well-studied for a variety of optoelectronic applications, the ability to manipulate their structure after synthesis is another handle for control of physical properties and could even enable use in future applications. If designed properly, a porous interlayer could facilitate these post-synthetic transformations. We show that for a series of copper-halide perovskites, a crystalline arrangement of designer ammonium groups allows for permanently porous interlayer space to be accessed at room temperature. Intercalation of the electroactive molecules ferrocene and tetracyanoethylene into this void space can be performed with tunable loadings, and these intercalated perovskites are stable for months. The porosity also enables reactivity at the copper-halide layer, allowing for facile halide replacement. Through this, we access previously unobserved reactivity with halogens to perform halide substitution, and even replace halides with pseudohalides. In the latter case, the porous structure allows for stabilization of new phases, specifically a novel copper-thiocyanate perovskite phase, only accessible through post-synthetic modification. We envision that this broad design strategy can be expanded to other industrially relevant HOIPs to create a new class of highly adjustable perovskites.

Improving the sulfite-detection performance of a fluorescent probe via post-synthetic modification with a metal-organic framework.

In this work, a post-synthetic modification strategy was attempted to improve the performance of the probe for sulfite detection. The assembled platform UiO-66-NH-DQA, which was acquired by anchoring the sulfite-response fluorescent probe DQA onto the surface of UiO-66-NH2via amide covalent bonds, exhibited enhanced fluorescence intensity and practical intracellular imaging capability. In spite of the structural similarity, as verified by characterization tests, the conversion rate of post-synthetic modification was calculated as 35%, equaling an approximate assembly ratio of 1 : 2 between UiO-66-NH2 and DQA. Most significantly, conversion into UiO-66-NH-DQA led to a 5.6-fold enhancement in the reporting signal with a red shift of 20 nm. For sulfite detection, the linear range was 0-150 μM, with a limit of detection value of 0.025 μM. UiO-66-NH-DQA retained advantages including high stability (within pH 5.0-9.0), rapid response (within 15 min) and high selectivity. Based on low cytotoxicity and relatively rapid cellular uptake, UiO-66-NH-DQA achieved the imaging of both the exogenous and endogenous sulfite levels in living cells. In particular, its rapid cell-permeating capability was guaranteed during the modification. The post-synthetic modification strategy reported herein has potential for improving the practical properties of fluorescent monitoring materials.