Postsynthetic Functionalization Research Articles

Stable sandwich-type electrochemical lead ions sensor based on bismuth-metal organic framework and Mxene

For electrochemical Pb2+ detection, high sensitivity and stability are essential owing to the mutagenicity, carcinogenicity, and teratogenicity of aqueous Pb2+ ions. Herein, a three-dimensional bismuth-containing metal-organic framework (Bi-MOF) was synthesized using a hydrothermal method, followed by post-synthetic functionalization with thiol (-SH) groups. A sandwich-type Bi-MOF-SH/Mx/Bi-MOF-SH/GCE multilayer sensitive electrochemical sensor was then constructed on the surface of the glassy carbon electrode for Pb2+ detection. Differential pulse anodic stripping voltammetry (DPASV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to evaluate the performance of the sensor. The developed multilayer sensor demonstrated an exceptionally high current response, good sensitivity (0.03–20.0 μg/L), and an ultra-low level of detection of 0.012 μg/L (S/N=3) towards Pb2+ ions. The as-prepared electrode showed high stability, repeatability, and selectivity among possible interfering ions (Na+, Ca2+, Cu2+, Zn2+, K+, Mg2+, Al3+, and Cd2+), suggesting potential for use in real-world applications.

Tailored Postsynthetic Nitration of a Hypercrosslinked Polymer for Single-Step Ethylene Purification from a Ternary C2 Gas Mixture.

Purifying C2H4 from a ternary C2H2/C2H4/C2H6 mixture poses a substantial industrial challenge due to their close physical and chemical properties. In this study, we introduce an innovative design approach to regulate and optimize the nitration degree of a hypercrosslinked polymer to achieve targeted separation performance. We synthesized a porous organic polymer (HCP) using the solvent knitting method and carried out its postsynthetic nitration, resulting in HCP-NO2-1 and HCP-NO2-2 with different nitration degrees. Notably, the adsorption capacity shifted from C2H6 > C2H4 ≈ C2H2 for HCP to C2H2 > C2H6 > C2H4 for HCP-NO2-1 and to C2H2 > C2H4 ≈ C2H6 for HCP-NO2-2, demonstrating the controllable nature of the separation process via the polar nitro group insertion. Remarkably, HCP-NO2-1 exhibited a desirable, selective separation of C2H4 from the C2H6/C2H4/C2H2 mixture thanks to an exquisite combination of the acidic proton-polar nitro group and nonpolar C-H∙∙∙π interactions. Separation capability was further corroborated by computational simulations and breakthrough tests. This work marks a significant advancement as the first successful postsynthetic functionalization strategy for C2H4 purification from a ternary gas mixture among porous organic polymers.

Catalyst Editing via Post-Synthetic Functionalization by Phosphonium Generation and Anion Exchange for Nickel-Catalyzed Ethylene/Acrylate Copolymerization.

Rapid, efficient development of homogeneous catalysts featuring desired performance is critical to numerous catalytic transformations but remains a key challenge. Typically, this task relies heavily on ligand design that is often based on trial and error. Herein, we demonstrate a "catalyst editing" strategy in Ni-catalyzed ethylene/acrylate copolymerization. Specifically, alkylation of a pendant phosphine followed by anion exchange provides a high yield strategy for a large number of cationic Ni phosphonium catalysts with varying electronic and steric profiles. These catalysts are highly active in ethylene/acrylate copolymerization, and their behaviors are correlated with the electrophile and the anion used in late-stage functionalization.

Chitosan as Support Material for Metal-Organic Framework based Catalysts.

Turning waste into valuable products is one of the main challenges of the chemical industry. In this work, chitosan (CS), an abundant, low-cost, and non-toxic biopolymer derived from chitin, was reshaped into beads of ~3 mm. Their suitability as a support material for active phase catalyst materials was tested for a zirconium-based Metal-Organic Framework (MOF) with incorporated Pt, namely UiO-67-Pt. Its incorporation was investigated via two procedures: a one-pot synthesis (OPS) and a post-synthetic functionalization (PSF) synthesis method. Scanning electron microscopy (SEM) images show good UiO-67-Pt dispersion throughout the CS beads for the one-pot synthesized material (UiO-67-Pt-OPS@CS). However, this uniform dispersion was not observed for the post-synthetically functionalized material (UiO-67-Pt-PSF@CS). The success of the implementation of UiO-67-Pt was evaluated with ultraviolet-visible and infrared spectroscopy for both composite materials. Thermogravimetric analysis (TGA) reveals higher thermal stabilities for UiO-67-Pt-OPS@CS composite beads in comparison to pure CS beads, but not for UiO-67-Pt-PSF@CS. The study provides valuable insights into the potential of chitosan as a green, bead-shaped support material for MOFs, offering flexibility in their incorporation through different synthesis routes. It further contributes to the broader goal of the sustainable and eco-friendly design of a new generation of catalysts made from waste materials, which will be the topic of future studies.

Photocatalytic Hydrogen Peroxide Production through Functionalized Semiconductive Metal-Organic Frameworks.

Hydrogen peroxide (H2O2) holds significance as a vital chemical with the potential to serve as an energy carrier. Compared with the conventional anthraquinone process, photocatalytic H2O2 production has emerged as an appealing alternative because of its energy efficiency and environmental sustainability. However, the existing photocatalysts suffer from low catalytic efficiency, limited tunability of optical properties, and reliance on sacrificial agents due to high energy loss caused by inefficient charge separation. Therefore, developing catalysts with tunable optical properties and efficient charge separation is desirable. In this work, we introduce postsynthetic functionalization into an electrically conductive metal-organic framework, namely, DPT-MOF. Leveraging DPT (3,6-di(4-pyridyl)-1,2,4,5-tetrazine) as a pillar ligand, we exploited click-type chemistry to manipulate band position and charge separation efficiency, allowing for photocatalytic nonsacrificial H2O2 production. Notably, the fluorine-functionalized MOF exhibited the highest H2O2 production rate of 1676 μmol g-1 h-1 under visible light in O2-saturated water among our other samples. This high production rate is attributed to the tuned electronic structure and prolonged charge lifetime facilitated by the fluorine groups. This work highlights the effectiveness of postsynthetic methodology in tuning optical properties, opening a promising avenue for advancing the field of semiconductive MOF-based photocatalysis.

Post-synthetic functionalization of UiO-66-NH2 by polyacrylamide and polyvinylimidazolium salt brushes via ATRP and adsorption behavior

Aquacultural water pollution caused by methylene blue is an urgent environmental problem, posing a serious threat to aquaculture and human health. Adsorption is a potential and promising method to remove methylene blue from aquaculture water. In this study, UiO-66-NH2@PAM and UiO-66-NH2@PVIO post-synthetic functionalized by polyacrylamide and polyvinylimidazolium salt brushes onto UiO-66-NH2 by virtue of ATRP method were successfully synthesized, and adsorption performance for methylene blue were systematically studied. Adsorption kinetic curves with trend of first increase, and decrease, and then increase was explained by capillary effect. Experimental data were fitted best by pseudo second-order kinetic and Langmuir isotherm model. UiO-66-NH2@PVIO had comparatively higher adsorption capacities than UiO-66-NH2@PAM, because UiO-66-NH2@PVIO had stronger adsorption affinity and binding energy for methylene blue than UiO-66-NH2@PAM. Adsorption driving forces were electrostatic interaction, π-π conjugation effects, hydrogen-bonding interactions, induced dipoles, van der Waals forces, sieving effect so that adsorption processes were ascribed to physical adsorption. UiO-66-NH2@PAM and UiO-66-NH2@PVIO had very good reusability and stability, and could be utilized in practical application. The results can offer better help for the synthesis of MOF materials by the technology of post-synthetic functionalization, and provide technical guidance for actual application in dye removal from aquacultural water.

Revolutionizing the structural design and determination of covalent-organic frameworks: principles, methods, and techniques.

Covalent organic frameworks (COFs) represent an important class of crystalline porous materials with designable structures and functions. The interconnected organic monomers, featuring pre-designed symmetries and connectivities, dictate the structures of COFs, endowing them with high thermal and chemical stability, large surface area, and tunable micropores. Furthermore, by utilizing pre-functionalization or post-synthetic functionalization strategies, COFs can acquire multifunctionalities, leading to their versatile applications in gas separation/storage, catalysis, and optoelectronic devices. Our review provides a comprehensive account of the latest advancements in the principles, methods, and techniques for structural design and determination of COFs. These cutting-edge approaches enable the rational design and precise elucidation of COF structures, addressing fundamental physicochemical challenges associated with host-guest interactions, topological transformations, network interpenetration, and defect-mediated catalysis.

Vapor-phase postsynthetic amination of hypercrosslinked polymers for efficient iodine capture

Hypercrosslinked polymers (HCPs) with large surface areas, high intrinsic porosities and low production costs may be available platforms for iodine capture. However, the lack of iodine-philicity binding sites limits their adsorption capacity. Here we use vapor-phase postsynthetic amination strategy to introduce electron-donating amino groups into the prefabricated HCPs for enhancing their iodine capture performance. Through simple vapor-phase exposure, the halogen-containing HCPs can be grafted by amines through nucleophilic substitution toward chloro groups. Combining with the abundant amino groups and high porosities, the amino-functionalized porous polymers show substantially increased iodine adsorption capacity, about 221% as that of original one, accompanied by excellent recyclability. Mechanism investigations reveal the key roles of the electron-donor amino groups and π-conjugated benzene rings along with structure characteristics of porous polymer frameworks in iodine capture. Moreover, this vapor-phase amination strategy shows good generality and can be extended to various amines, e.g., ethylenediamine, 1,3-diaminopropane and diethylenetriamine. Our work proves that this simple vapor-phase postsynthetic functionalization strategy may be applied in other porous polymers with wide application prospects in adsorption, separation and storage.

Ligand Postsynthetic Functionalization with Fluorinated Boranes and Implications in Hydrogenation Catalysis.

The incorporation of boron functionalities into transition-metal catalysts has become a promising strategy to improve catalytic performance, although their synthesis typically entails the preparation of sophisticated bifunctional ligands. We report here the facile and direct postsynthetic functionalization of rhodium(I) compound [(η5-C9H7)Rh(PPh3)2] (1) by treatment with perfluorinated boranes. Borane addition to 1 results in an unusual C(sp2)-H hydride migration from the indenyl ligand to the metal with the concomitant formation of a C-B bond. In the case of Piers' borane [HB(C6F5)2], this is followed by a subsequent hydride migration that leads to an unprecedented 1,2-hydrogen shift reminiscent of Milstein's cooperative dearomatization pathways. Computational investigations provide a mechanistic picture for the successive hydride-migration steps, which enriches the non-innocent chemistry of widespread indenyl ligands. Moreover, we demonstrate that the addition of Piers' borane is highly beneficial for catalysis, increasing catalyst efficiency up to 3 orders of magnitude.

Dual-Function Platform Based on Postsynthetic Functionalization of a Water-Stable Hydrogen-Bonded Organic Framework: Ratiometric Sensing of Nicotine and Cotinine and Dynamic Anticounterfeiting for Information Encryption.

Nicotine and its major metabolite cotinine are widely used as markers of tobacco smoke abstinence as well as indicators of active smoking levels and the assessment of passive inhalation of tobacco smoke in nonsmokers. Therefore, using an easy-to-prepare sensing platform that can provide a rapid, highly sensitive response for the simultaneous detection of salivary nicotine levels and urinary cotinine levels is especially crucial for helping heavy cigarette smokers quit smoking and protecting public health. Hydrogen-bonded organic frameworks, as a novel class of porous crystalline materials, show immense potential for functional modification and optical sensing. Herein, a new HOF was prepared by a simple solvent evaporation method, and a dual-emitting material Eu(bpy)@HOF-215(1) was obtained by the postsynthetic modification of HOF by lanthanide luminescent complexes, which maintains favorable structural stability and introduces the characteristic emitting of Eu, allowing use as a ratiometric fluorescent sensor for salivary nicotine and urinary cotinine, with a limit of detection of nicotine of 0.045 μM in saliva and a limit of detection of cotinine of 0.591 μM in urine. Furthermore, luminescent inks based on HOF-215 have been fabricated based on the photoresponse variations of 1 to NIC and COT, which enables the multilevel encryption and decryption of information, in a dynamic and recyclable process. This work not only synthesizes a novel blue HOF but also provides a representative successful case of a dual-function platform for simultaneous application to ratiometric sensing and dynamic anticounterfeiting.

Hybrid Poly(β-amino ester) Triblock Copolymers Utilizing a RAFT Polymerization Grafting-From Methodology.

The biocompatibility, biodegradability, and responsiveness of poly(β-amino esters) (PBAEs) has led to their widespread use as biomaterials for drug and gene delivery. Nonetheless, the step-growth polymerization mechanism that yields PBAEs limits the scope for their structural optimization toward specific applications because of limited monomer choice and end-group modifications. Moreover, to date the post-synthetic functionalization of PBAEs has relied on grafting-to approaches, challenged by the need for efficient polymer-polymer coupling and potentially difficult post-conjugation purification. Here a novel grafting-from approach to grow reversible addition-fragmentation chain transfer (RAFT) polymers from a PBAE scaffold is described. This is achieved through PBAE conversion into a macromolecular chain transfer agent through a multistep capping procedure, followed by RAFT polymerization with a range of monomers to produce PBAE-RAFT hybrid triblock copolymers. Following successful synthesis, the potential biological applications of these ABA triblock copolymers are illustrated through assembly into polymeric micelles and encapsulation of a model hydrophobic drug, followed by successful nanoparticle (NP) uptake in breast cancer cells. The findings demonstrate this novel synthetic methodology can expand the scope of PBAEs as biomaterials.

Multi-hierarchical nanoparticles with tunable core by emulsion polymerization processes

Nanoparticles (NPs) with functional cores are gaining research interest due to their advanced architecture. However, exposed reactive groups on NP surfaces can lead to material side reactions and biomedical tissue damage. NPs with multi-hierarchical morphologies can be synthesized by various methods; however, controlling the size and position of the functional groups using conventional and scalable methods is still a challenge. This study explores emulsion-based polymerization methods for producing multi-hierarchical NPs with varying sizes and compositions. We compared micro-, macro-, and semi-batch emulsion polymerization using 2-hydroxyethyl methacrylate (HEMA) and pentafluorophenyl methacrylate (PFMA) as co-monomers. The components present in PFMA can be substituted and are used for post-synthetic functionalization. The results suggest that the architecture of the synthesized NPs is multi-hierarchical, with the substitutable pentafluorophenyl units surrounded by HEMA monomers. Additionally, we evaluated the NPs' ability to enhance dermal drug penetration using nile red as a hydrophobic drug model. Significant variations in skin permeation enhancement properties were observed among the NPs, underscoring the impact of the synthesis method on nanocarriers' drug delivery performance.

2'-Modified Thymidines with Bioorthogonal Cyclopropene or Sydnone as Building Blocks for Copper-Free Postsynthetic Functionalization of Chemically Synthesized Oligonucleotides.

The development of facile methods for conjugating relevant probes, ligands, or delivery agents onto oligonucleotides (ONs) is highly desirable both for fundamental studies in chemical biology and for improving the pharmacology of ONs in medicinal chemistry. Numerous efforts have been focused on the introduction of bioorthogonal groups onto phosphoramidite building blocks, allowing the controlled chemical synthesis of reactive ONs for postsynthetic modifications. Among these building blocks, alkyne, cyclooctynes, trans-cyclooctene, and norbornene have been proved to be compatible with automated solid-phase chemistry. Herein, we present the development of novel 2'-functionalized nucleoside phosphoramidite monomers comprising bioorthogonal methylcyclopropene or sydnone moieties and their introduction for the first time to ON solid-phase synthesis. Traceless ON postsynthetic modifications with reactive complementary probes were successfully achieved through either inverse electron-demand Diels-Alder (iEDDA) reactions or strain-promoted sydnone-alkyne cycloaddition (SPSAC). These results expand the set of bioorthogonal phosphoramidite building blocks to generate ONs for postsynthetic labeling.

Electron rich substituted β-carboline derivatives: Synthesis and photophysical properties

We report the synthesis and characterisation of known and novel analogues of β-carboline, a naturally occurring alkaloid. Striving to induce changes in the optical properties of carboline, we first focus on substitutions at position 1 before exploring other positions. The β-carbolines were synthesized using, on the one hand, post-synthetic functionalization of biosourced products and, on the other hand, total synthesis of the desired compounds. Our strategy mainly relies on the well-known Pictet-Spengler reaction, followed by aromatization using different techniques. Post functionalization were performed by Knoevenagel condensation or pallado-catalyzed cross-coupling. The measured UV–visible and fluorescence spectra show unexpected results with large shifts obtained when changing a few substituents only. For instance, the replacement of the aryl by a styryl substituent induces a bathochromic shift as large as 70 nm. This allowed controlling the position of the emission on a broad range (from 370 to 650 nm). Additionally, protonation of the compounds leads to profound changes in the spectroscopic properties. We indeed observe for some compounds a bathochromic shift in the emission as large as 200 nm upon protonation. The main experimental results are rationalized using theoretical calculations.

Precision Covalent Organic Frameworks for Surface Nucleation Control.

Unwanted accumulation of ice and lime scale crystals on surfaces is a long-standing challenge with major economic and sustainability implications. Passive inhibition of icing and scaling by liquid-repellent surfaces are often inadequate, susceptible to surface failure under harsh conditions, and unsuitable for long-term/real-life usages. Such surfaces often require a multiplicity of additional features such as optical transparency, robust impact resistance, and ability to prevent contamination from low surface energy liquids. Unfortunately, most promising advances have relied on using perfluoro compounds, which are bio-persistent and/or highly toxic. Here it isshown that organic, reticular mesoporous structures, covalent organic frameworks (COFs), may offer a solution. By exploiting simple and scalable synthesis of defect-free COFs and rational post-synthetic functionalization, nanocoatings with precision nanoporosity (morphology) are prepared that can inhibit nucleation at the molecular level without compromising the related contamination prevention and robustness. The results offer a simple strategy to exploit the nanoconfinement effect, which remarkably delays the nucleation of ice and scale formation on surfaces. Ice nucleation is suppressed down to -28°C, scale formation is avoided for >2weeks in supersaturated conditions, and jets of organic solvents impacting at Weber numbers >105 are resisted with surfaces that also offer optical transparency (>92%).

Self-Aggregated Nanoscale Metal-Organic Framework for Targeted Pulmonary Decorporation of Uranium.

The limited availability of effective agents for removing actinides from the lungs significantly restricts the effectiveness of medical treatments for nuclear emergencies. Inhalation is the primary route of internal contamination in 44.3% of actinide-related accidents, leading to the accumulation of radionuclides in the lungs and resulting in infections and potential tumor formation (tumorigenesis). This study focuses on the synthesis of a nanometal-organic framework (nMOF) material called ZIF-71-COOH, which is achieved by post-synthetic carboxyl functionalization of ZIF-71. The material demonstrates high and selective adsorption of uranyl, while also exhibiting increased particle size (≈2100nm) when it aggregates in the blood, enabling passive targeting of the lungs through mechanical filtration. This unique property facilitates the rapid enrichment and selective recognition of uranyl, making nano ZIF-71-COOH highly effective in removing uranylfrom the lungs. The findings of this study highlight the potential of self-aggregated nMOFs as a promising drug delivery system for targeted uranium decorporation in the lungs.

Bispalladium(II) Complexes of di-p-Pyrirubyrin Derivatives as Promising Near-Infrared Photoacoustic Dyes.

Incorporation of α,β'-pyridine moiety into expanded porphyrins opens a highly interesting area of research due to created the molecules' attractive optical and coordination properties. The insertion of palladium(II) into di-p-pyrirubyrin, results in mutually convertible bimetallic complexes. Post-synthetic functionalization of one of them yielded bispalladium(II) dioxo-di-p-pyrirubyrin and, after demetallation, dioxo-di-p-pyrirubyrin, introducing for the first time, the α,β'-pyridin-2-one unit into the macrocyclic frame. Bispalladium(II) di-p-pyrirubyrin 6, bispalladium(II) dioxo-di-p-pyrirubyrin 9, and dioxo-di-p-pyrirubyrin 10 absorb and emit light around 1000 nm and are characterized by high photostability. Thus, they are promising candidates for near-infrared photoacoustic dyes, ideally targeting (9) the wavelength of Yb-based fiber lasers.

Scalable Room-Temperature Synthesis of a Hydrogen-Sieving Zeolitic Membrane on a Polymeric Support

Synthesis of H2-sieving membranes for high-temperature applications is highly desired for improving the energy efficiency of H2 production from steam reforming and developing a low-cost solution for precombustion carbon capture. Zeolite-based membranes are ideal for this because they possess excellent hydrothermal stability. However, current methods to synthesize H2-sieving zeolite membranes rely on hydrothermal synthesis on expensive ceramic supports followed by postsynthetic functionalization to shrink the effective pore size. The scalable synthesis approach on a low-cost polymeric support implementable at room temperature is highly desired to advance applications based on H2-sieving membranes. Herein, we report the room-temperature fabrication of H2-sieving zeolitic membranes by simply assembling sodalite precursor, i.e., RUB-15 nanosheets, on a porous polybenzimidazole support. The presence of adsorbed surfactants on the nanosheets led to an entropically driven ordering of the nanosheets witnessed by a sharp (200) d-spacing peak by X-ray diffraction. The intersheet gap was successfully eliminated by the ion exchange of cationic surfactants by a diluted acetic acid solution. The resulting zeolitic films show attractive H2/CO2 and H2/CH4 separation performances at elevated temperatures. The fabrication of H2-sieving zeolitic membranes without resorting to hydrothermal synthesis or high-temperature activation is expected to push the efforts to scale up zeolite membranes for application in gas separation and membrane reactors.

Highly Efficient Capture of Heavy Metal Ions on Amine-Functionalized Porous Polymer Gels

Porous polymer gels (PPGs) are characterized by inherent porosity, a predictable structure, and tunable functionality, which makes them promising for the heavy metal ion trap in environmental remediation. However, their real-world application is obstructed by the balance between performance and economy in material preparation. Development of an efficient and cost-effective approach to produce PPGs with task-specific functionality remains a significant challenge. Here, a two-step strategy to fabricate amine-enriched PPGs, NUT-21-TETA (NUT means Nanjing Tech University, TETA indicates triethylenetetramine), is reported for the first time. The NUT-21-TETA was synthesized through a simple nucleophilic substitution using two readily available and low-cost monomers, mesitylene and α, α'-dichloro-p-xylene, followed by the successful post-synthetic amine functionalization. The obtained NUT-21-TETA demonstrates an extremely high Pb2+ capacity from aqueous solution. The maximum Pb2+ capacity, qm, assessed by the Langmuir model was as high as 1211 mg/g, which is much higher than most benchmark adsorbents including ZIF-8 (1120 mg/g), FGO (842 mg/g), 732-CR resin (397 mg/g), Zeolite 13X (541 mg/g), and AC (58 mg/g). The NUT-21-TETA can be regenerated easily and recycled five times without a noticeable decrease of adsorption capacity. The excellent Pb2+ uptake and perfect reusability, in combination with a low synthesis cost, gives the NUT-21-TETA a strong potential for heavy metal ion removal.

Enantioselective Au-Catalyzed Synthesis of Thia[5]- and Thia[6]helicenes and Their Transformation into Bowl-shaped Pleiadenes.

A series of helically shaped benzo[b]chryseno[4,3-d]thiophenes, naphtho[1,2-b]phenanthro[4,3-d]thiophenes, and chryseno[3,4-b]naphtho[1,2-d]thiophenes is synthesized via a highly enantioselective Au-catalyzed intramolecular alkyne hydroarylation reaction. The inversion barriers of the structures obtained are determined both theoretically and experimentally, and their chiroptical properties are reported. Preliminary studies on the post-synthetic functionalization of these thiahelicenes and their transformation into azahelicenes are also presented. In addition, a straightforward one-step protocol is developed, which wraps the initially obtained chryseno[3,4-b]naphtho[1,2-d]thiophenes into bowl-shaped pleiadene derivatives without erosion of the enantiopurity. The number of structurally related products that are obtained with high enantioselectivity enables the establishment of comprehensive correlations between the structure and conformational stability or (chir)optical properties.