Facile Post-modification Research Articles

Rational Design of Regenerable Amino-Functionalized Fluorescent Covalent Organic Framework for the Exclusive Detection of Mercury(II).

Goal-oriented development of novel covalent organic frameworks (COFs) to construct a sensing platform for highly toxic mercury (II, Hg2+) is of tremendous significance. Recently, numerous COFs with sulfur-based ligands were developed for Hg2+ monitoring; however, strong binding of Hg2+ by sulfur makes their regeneration very tough. Herein, we designed and developed an amino-functionalized fluorescent COF (COF-NH2) through facile postmodification for Hg2+ detection in which the π-conjugation skeleton is the signal reader and the nitrogen-based side is the highly selective Hg2+ receptor. More importantly, this nitrogen-based receptor permits the reversible binding of Hg2+. As a sensing platform, the outstanding performance of COF-NH2 for Hg2+ detection was reached with respect to high sensitivity with an ultralow detection of 15.3 nM, real-time response with rapid signal change of 10 s, and facile visualization with significant fluorescence color change. Expectedly, COF-NH2 obtained facile recycling which still shows excellent response performance toward Hg2+ after six cycles based on the reversible interaction between amino groups and Hg2+. Our work not only shows an attractive foreground of fluorescent COF for Hg2+ detection but also emphasizes the easy construction of novel COF materials via the rational introduction of metal ligands for the recognition of other metal ions.

Au-allenylidene promoted decarboxylative annulation to access unsaturated γ-lactams/lactones.

A novel Au-allenylidene promoted decarboxylative annulation by intramolecular α-nucleophilic addition has been disclosed. The unsaturated cyclic ethynylethylene carbamates/carbonates can be converted to unique nucleophiles attached with alkylidene ketenes by sequential decarboxylation and oxidation processes. Such alkylidene ketenes can be rapidly trapped by intramolecular α-attacking annulation to generate potential biological active unsaturated γ-lactams/lactones with broad scope, facile post-modification, high regioselectivity and efficiency.

Exploiting NIR Light-Mediated Surface-Initiated PhotoRAFT Polymerization for Orthogonal Control Polymer Brushes and Facile Postmodification of Complex Architecture through Opaque Barriers

Exploiting NIR Light-Mediated Surface-Initiated PhotoRAFT Polymerization for Orthogonal Control Polymer Brushes and Facile Postmodification of Complex Architecture through Opaque Barriers

Post-Modification of Pyrrolopyrrole Aza-BODIPY toward High Near-Infrared Fluorescence Brightness

Pyrrolopyrrole aza-BODIPYs (PPABs), dimeric aza-BODIPY analogues, exhibit intense absorption and fluorescence in the visible and near-infrared (NIR) regions. Here, we developed a facile postmodification by palladium-catalyzed coupling reactions to synthesize a series of donor-acceptor-donor (D-A-D) PPABs. Despite the possible fluorescence quenching dictated by the energy-gap low, D-A-D PPABs exhibit high-fluorescence brightness in the NIR region, implying their potential use as a bright NIR emitter.

Facile post modification synthesis of copper-doped mesoporous bioactive glass with high antibacterial performance to fight bone infection

Successful treatment of infected bone defects caused by multi-drug resistant bacteria (MDR) has become a major clinical challenge, stressing the urgent need for effective antibacterial bone graft substitutes. Mesoporous bioactive glass nanoparticles (MBGNs), a rapidly emerging class of nanoscale biomaterials, offer specific advantages for the development of biomaterials to treat bone infection due to endowed antibacterial features. Herein, we propose a facile post-modification sol-gel strategy to synthesize effective antibacterial MBGNs doped with copper ions (Cu-PMMBGNs). In this strategy, amine functional groups as chelating agents were introduced to premade mesoporous silica nanoparticles (MSNs) which further facilitate the incorporation of high content of calcium (∼17 mol%) and copper ions (∼8 mol%) without compromising nanoparticle shape, mesoporosity, and homogeneity. The resulting nanoparticles were degradable and showed rapidly induce abundant deposition of apatite crystals on their surface upon soaking in simulated body fluids (SBF) after 3 days. Cu-PMMBGNs exhibited a dose-dependent inhibitory effect on Methicillin-resistant Staphylococcus aureus (MRSA) bacteria, which are common pathogens causing severe bone infections. Most importantly, the nanoparticles containing 5 mol% copper ions at concentrations of 500 and 1000 μg.mL−1 showed highly effective antibacterial performance as reflected by a 99.9 % reduction of bacterial viability. Nanoparticles at a concentration of 500 μg.mL−1 showed no significant cytotoxicity toward preosteoblast cells (∼85–89 % cell viability) compared to the control group. In addition, the nanoscale properties of synthesized Cu-PMMBGNs (∼100 nm in size) facilitated their internalization into preosteoblast cells, which highlights their potential as intracellular carriers in combating intracellular bacteria. Therefore, these copper-doped nanoparticles hold strong promise for use as an antibacterial component in antibacterial bone substitutes such as hydrogels, nanocomposites, and coatings.

Enhanced Chiral Recognition Abilities of Cyclodextrin Covalent Organic Frameworks via Chiral/Achiral Functional Modification.

β-Cyclodextrin covalent organic frameworks (β-CD COFs) show great potential in enantioseparation due to their uniformly distributed chiral recognition sites and good chemical stability. The hydroxyl and amino groups of β-CD COFs enable facile post-modification to introduce the desired functionality into the frameworks. In this study, we perform post-modification of β-CD COFBPDA with 1,4-butane sultone and [(3R,4R)-4-acetyloxy-2,5-dioxooxolan-3-yl] acetate to construct two kinds of novel functional β-CD COFs. The capillary columns prepared with these two functional β-CD COFs separated chiral dihydropyridines and fluoroquinolones with excellent selectivity and repeatability in capillary electrochromatography, while β-CD COFBPDA-modified capillary columns did not present the chiral recognition ability for these drugs. The mechanism of chiral recognition and the enhanced enantioselectivity of functional β-CD COFs were further demonstrated by molecular docking simulation. The divergent chiral separation performances of β-CD COFs suggest that the introduction of functional groups enables the modification of β-CD COF properties and tuning of its chiral recognition abilities for the diversity of enantioseparation.

Rapid detection of heterocyclic aromatic amines in cakes by digital imaging colorimetry based on magnetic solid phase extraction with sulfonated hyper-cross-linked polymers

To improve the hydrophobicity and poor separability of hyper-cross-linked polymers (HCPs) in extraction, a porous magnetic adsorbent (Fe3O4@SHCP) was constructed by facile post-modification to introduce sulfonic acid groups and magnetic nanoparticles for the magnetic solid-phase extraction of heterocyclic aromatic amines (HAAs). Owing to the double extraction mechanism adopted by Fe3O4@SHCP, it has a high extraction efficiency for HAAs. Coupled with high-performance liquid chromatography (HPLC), 5 HAAs in baked cakes were detected at one time. Under optimal extraction conditions, the enrichment factor of HAAs was up to 952–986, with LODs at 0.05–0.3 ng·g−1. Based on the HPLC method, novel digital imaging colorimetry (DIC) was developed to accurately and rapidly monitor HAAs in cakes. Additionally, the established DIC method has been used to successfully evaluate the effect of baking temperature and duration on HAAs in baked cakes.

A facile post-modification strategy for carboxylic acid-functionalized UV-responsive pressure-sensitive adhesives

UV-responsive pressure-sensitive adhesives (PSAs) were achieved through the ring-opening reactions of N-carbonyl aziridine radicals.

Nano-3D-Printed Photochromic Micro-Objects.

Molecular photoswitches that can reversibly change color upon irradiation are promising materials for applications in molecular actuation and photoresponsive materials. However, the fabrication of photochromic devices is limited to conventional approaches such as mold casting and spin-coating, which cannot fabricate complex structures. Reported here is the first photoresist for direct laser writing of photochromic 3D micro-objects via two-photon polymerization. The integration of photochromism into thiol-ene photo-clickable resins enables rapid two-photon laser processing of highly complex microstructures and facile postmodification using a series of donor-acceptor Stenhouse adduct (DASA) photoswitches with different excitation wavelengths. The versatility of thiol-ene photo-click reactions allows fine-tuning of the network structure and physical properties as well as the type and concentration of DASA. When exposed to visible light, these microstructures exhibit excellent photoresponsiveness and undergo reversible color-changing via photoisomerization. It is demonstrated that the fluorescence variations of DASAs can be used as a reporter of photoswitching and thermal recovery, allowing the reading of DASA-containing sub-micrometric structures in 3D. This work delivers a new approach for custom microfabrication of 3D photochromic objects with molecularly engineered color and responsiveness.

A glycine-functionalized graphene quantum dots synthesized by a facile post-modification strategy for a sensitive and selective fluorescence sensor of mercury ions.

In this work, we have developed a facile method for the synthesis of glycine-functionalized graphene quantum dots (Gly-GQDs) through post-modification of graphene quantum dots with Gly under alkaline conditions. The as-synthesized Gly-GQDs exhibit an excellent blue emission at 444nm, independent of excitation, as well as a high quantum yield (QY) of 35.7%. The Gly-GQDs have a narrow size distribution with an average size of 5.9nm. Moreover, the as-prepared Gly-GQDs showed a better selective and sensitive recognition capability towards mercury ion (Hg2+) in aqueous solutions with a low detection limit of 8.3nM, compared with GQDs and other nitrogen-doped GQDs synthesized through the one-step solvent thermal method. Gly-GQDs are successfully applied for the determination of Hg2+ in real water samples. This work shows a new promising approach for the design and synthesis of desirable GQDs with a given function.

Postmodified Dual Functional UiO Sensor for Selective Detection of Ozone and Tandemly Derived Sensing of Al3.

Development of highly sensitive and selective fluorescent sensors toward hazardous analytes represents great progress in fabricating sensing devices for practical applications. In this work, a highly selective sensor with dual functions has been fabricated via facile postmodification of the UiO-MOF. Butene modified salicylaldehyde is covalently linked to the UiO-66 scaffold via an efficient Schiff-base reaction, resulting in a highly fluorescent ozone sensor of UiO-66-butene. Ozonolysis of the terminal olefin followed by β-elimination could significantly quench the bright blue fluorescence of UiO-66-butene, and linear turn-off detection of ozone in the range of 0-100 μM is well established. The detection is highly sensitive and selective, and a detection limit of 73 nM was calculated. Remarkably, the ozonolysis afforded product could further act as a selective sensor for Al3+ via turn-on fluorescence with a detection limit of 142 nM, representing a second potential sensing function. The chemically selective sequential ozonolysis/β-elimination and remarkable dual functions offer the exclusive detection of ozone over other oxidative species as well as Al3+ over other cations following a tandem process, representing the first example of a direct MOF sensor for dual sensing of ozone and Al3+. This work demonstrates the potential of employing combinatorial principles for fabricating highly selective sensors, and postmodification of MOFs represents a promising facile strategy for developing various functional sensors.

Isomerization of α-pinene with a hierarchical mordenite molecular sieve prepared by the microwave assisted alkaline treatment

Abstract To develop effective catalysts for α-pinene isomerization reaction is important to get high valuable products. A hierarchical mordenite molecular sieve is prepared using alkaline treatment assisted by the microwave radiation. After the alkaline treatment, the relative crystalline decreases by ~20% and mesopores are introduced in the mordenite molecular sieve. Compared to conventional heating method, microwave assisted alkaline treatment exhibits a selective etching of zeolitic silicon atoms. Aluminum atoms adjacent to silicon atoms are extracted to form Al–OH hydroxyl groups. These extracted aluminum atoms are reconnected to zeolitic silicon atoms. Mordenite after microwave assisted alkaline treatment has a good dispersion of mesopores, higher retention of BrOnsted acid sites in 12-membered rings, and lower concentration of Lewis acid sites. The isomerization reaction of α-pinene suggests that alkaline treatment increases the accessibility of acid sites for α-pinene molecules. The hierarchical porosity increases the conversion of α-pinene from 46.1 to 94.7%. The yields for camphene and limonene increase by 17.0 and 5.4%, respectively. Disproportionation of limonene is inhibited when using microwave assisted alkaline treated mordenite due to a low concentration of Lewis acid sites. These results are important to propose a facile post modification method to realize a selective extraction of zeolitic framework atoms.

Benzoxazine monomers containing triphenylimidazole: Polymerization of monomers and properties of polybenzoxazines

In this study, two novel benzoxazine monomers containing triphenylimidazole (TBZ) and triphenylimidazolium (MTBZ) moieties are synthesized and fully characterized. The thermal ring-opening polymerization process of the two monomers is monitored by the 1H NMR and GPC analyses, which demonstrates that such a polymerization proceeds through a rearrangement of ketal-type linkage in the main chain into Mannich-type polymer along with the fast increasing in molecular weight. The structures of the triphenylimidazole-containing polybenzoxazines, poly-TBZ and poly-MTBZ, are verified by 1H NMR and FT-IR spectroscopies, and the thermal and mechanical properties of such polybenzoxazines are investigated by TGA and DMA analyses. Owing to the good solubility of poly-TBZ and poly-MTBZ in common organic solvents, poly-TBZ can be easily converted into poly-MTBZ through a facile post-modification approach. More importantly, the poly-TBZ shows the acid-dependent spectral properties due to formation of amine salts, whereas poly-MTBZ can be used as a chemodosimeter for the detection of Ag+, which exhibits high selectivity, good linearity and naked-eye distinguishable color change. This strategy can be utilized to prepare triphenylimidazole-containing polybenzoxazines with good solubility and tunable spectral properties, thereby extending their functionalities and applications.

Dual ATP and pH responsive ZIF-90 nanosystem with favorable biocompatibility and facile post-modification improves therapeutic outcomes of triple negative breast cancer in vivo

Zeolitic imidazole frameworks (ZIFs) are becoming a notable nanosystem in biomedicine field, due to their unique properties of favorable biocompatibility, pH-responsive degradable structure and high drug loading. Compared with the increasing attention on ZIF-8 in cancer diagnosis and treatment, there is limited research about the bio-application of ZIF-90, especially its in vivo therapeutic efficacy and related toxicity. Here, we synthesize nano ZIF-90 through a fast self-assembling process, and the synthesized nano ZIF-90 is about 75 nm with a negative zeta potential, providing better mitochondria targetability, cell biocompatibility and in vivo survival rate comparing to nano ZIF-8. To further explore the applicability of ZIF-90 in cancer treatment, a facile post-modification is used to conjugate Y1 receptor ligand [Asn6, Pro34]-NPY (AP) on the surface of doxorubicin (DOX)-encapsulated nano ZIF-90. AP-ZIF-90 significantly reduces premature DOX release at physiological pH level, and triggers more effective and faster DOX release inside the tumor cells with dual responsive to high adenosine triphosphate (ATP) and low pH condition. Combining targeted delivery and dual responsive release of DOX significantly improves the therapeutic efficacy of AP-ZIF-90@DOX in MDA-MB-231 tumor bearing mouse, and results in 80% survival rate over 40 days of treatment. At the given dosage, nano ZIF-90 is with excellent biocompatibility in vivo, inducing minimal side effect on the liver and renal functions. Therefore, nano ZIF-90 combines with Y1 receptor ligand with favorable biocompatibility and dual responsiveness can be used as a promising nanosystem for targeted triple negative breast cancer treatment in vivo.

Penetration and exchange kinetics of primary alkyl amines applied to reactive poly(pentafluorophenyl acrylate) thin films

We investigated the mechanism of primary amine-induced post-polymerization modification of active ester polymer thin films composed of pentafluorophenyl acrylate (PFPA) polymers. The most important physical parameters in the post-polymerization modification are the molecular weight of the PFPA polymers and the aliphatic chain length of the primary amines. The effects of these two parameters on the penetration depth, as well as the exchange kinetics were systematically studied by neutron reflectivity and quartz crystal microbalance with dissipation, accompanied by the measurement of surface morphological changes by an atomic-force microscopy and optical microscopy. The spin-cast PFPA polymer thin films showed distinctive differences in the exchange kinetics, as well as the penetration depth of amines as a function of the PFPA polymer molecular weight. The aliphatic chain length of primary alkyl amines markedly influenced the penetration kinetics into low-molecular weight poly(PFPA) films, whereas there was no significant penetration effect on the high-molecular weight films. The high-molecular weight of the poly(PFPA) films led to the deceleration of the dissolution of amine-functionalized polymer chains in a good solvent. The results of this study may provide a good physical background for developing reactive poly(PFPA) thin film platforms based on simple and quantitative post-modification with amine-containing molecules. The poly(pentafluorophenyl acrylate) thin film provides a reactive surface platform through facile post-modification with primary alkyl amines. We report the effect of the most important parameters in this reaction, molecular weight of the reactive polymers and the aliphatic chain length of primary amines, on the degree of exchange of the thin films. The studies with neutron reflectivity and quartz crystal microbalance offer physical backgrounds for developing versatile functional thin films based on this chemistry, in terms of penetration and exchange kinetics as a function of molecular weight of reactive ester polymers and primary amines.

Synthesis and biomedical applications of functional poly(α-hydroxy acids) via ring-opening polymerization of O-carboxyanhydrides.

Poly(α-hydroxy acids) (PAHAs) are a class of biodegradable and biocompatible polymers that are widely used in numerous applications. One drawback of these conventional polymers, however, is their lack of side-chain functionalities, which makes it difficult to conjugate active moieties to PAHA or to fine-tune the physical and chemical properties of PAHA-derived materials through side-chain modifications. Thus, extensive efforts have been devoted to the development of methodology that allows facile preparation of PAHAs with controlled molecular weights and a variety of functionalities for widespread utilities. However, it is highly challenging to introduce functional groups into conventional PAHAs derived from ring-opening polymerization (ROP) of lactides and glycolides to yield functional PAHAs with favorable properties, such as tunable hydrophilicity/hydrophobicity, facile postpolymerization modification, and well-defined physicochemical properties. Amino acids are excellent resources for functional polymers because of their low cost, availability, and structural as well as stereochemical diversity. Nevertheless, the synthesis of functional PAHAs using amino acids as building blocks has been rarely reported because of the difficulty of preparing large-scale monomers and poor yields during the synthesis. The synthesis of functionalized PAHAs from O-carboxyanhydrides (OCAs), a class of five-membered cyclic anhydrides derived from amino acids, has proven to be one of the most promising strategies and has thus attracted tremendous interest recently. In this Account, we highlight the recent progress in our group on the synthesis of functional PAHAs via ROP of OCAs and their self-assembly and biomedical applications. New synthetic methodologies that allow the facile preparation of PAHAs with controlled molecular weights and various functionalities through ROP of OCAs are reviewed and evaluated. The in vivo stability, side-chain functionalities, and/or trigger responsiveness of several functional PAHAs are evaluated. Their biomedical applications in drug and gene delivery are also discussed. The ready availability of starting materials from renewable resources and the facile postmodification strategies such as azide-alkyne cycloaddition and the thiol-yne "click" reaction have enabled the production of a multitude of PAHAs with controlled molecular weights, narrow polydispersity, high terminal group fidelities, and structural diversities that are amenable for self-assembly and bioapplications. We anticipate that this new generation of PAHAs and their self-assembled nanosystems as biomaterials will open up exciting new opportunities and have widespread utilities for biological applications.

Post-synthetic modification of MIL-101(Cr) with pyridine for high-performance liquid chromatographic separation of tocopherols

Effective separation of tocopherols is challenging and significant due to their structural similarity and important biological role. Here we report the post-synthetic modification of metal–organic framework (MOF) MIL-101(Cr) with pyridine for high-performance liquid chromatographic (HPLC) separation of tocopherols. Baseline separation of four tocopherols was achieved on a pyridine-grafted MIL-101(Cr) packed column within 10min using hexane/isopropanol (96:4, v/v) as the mobile phase at a flow rate of 0.5mLmin−1. The pyridine-grafted MIL-101(Cr) packed column gave high column efficiency (85,000platesm−1 for δ-tocopherol) and good precision (0.2–0.3% for retention time, 1.8–3.4% for peak area, 2.6–2.7% for peak height), and also offered much better performance than unmodified MIL-101(Cr) and commercial amino-bonded silica packed column for HPLC separation of tocopherols. The results not only show the promising application of pyridine-grafted MIL-101(Cr) as a novel stationary phase for HPLC separation of tocopherols, but also reveal a facile post-modification of MOFs to expand the application of MOFs in separation sciences.

UV-induced functionalization of poly(divinylbenzene) nanoparticlesvia efficient [2 + 2]-photocycloadditions

A facile postmodification strategy for the surface functionalization of nanoparticles is presented based on [2 + 2] photoconjugation with particles made from miniemulsion polymerization of divinylbenzene.