Kai Xing

Controlled Zn2+-Triggered Drug Release by Preferred Coordination of Open Active Sites within Functionalization Indium Metal Organic Frameworks

Drug delivery in target regions could make extraordinary progress in chemoselective therapies. A novel preferred coordination (PC) strategy referring to proactive interacting with open active sites to replace previous occupation by ion-exchange for controlling release of drug molecules is well-constructed. Two topological types of MOF-In1 (Schläfli symbol: (4,8)-connected of (410·615·83)(45·6)2) and MOF-In2 (Schläfli symbol: (4,4)-connected of (66)) show the specific way. Increasing node connectivity as well as the trapping of guest OH- anions, 5-fluorouracil (5-FU) is preferentially captured into the MOF-In1, which exhibits an outstanding loading capacity around 34.32 wt %. 19F NMR spectroscopy was further employed to investigate host-guest interaction and reveal the binding constant (Ka = 3.84 × 102 M-1). Meanwhile, the controlled release of 5-FU in a simulated human body with liquid phosphate-buffered saline solution by biofriendly Zn2+-triggered is realized. With an elevated Zn2+ concentration, the drug release will be enhanced. This efficient strategy for MOFs as multifunctional drug carrier opens a new avenue for biological and medical applications.

Novel Hydrogen-Bonding Cross-Linking Aggregation-Induced Emission: Water as a Fluorescent “Ribbon” Detected in a Wide Range

The development of efficient sensors for detection of the water content in a wide detection range is highly desirable for balance in many industrial processes and products. Presented herein are six novel different substituted Schiff base Zn(II) complexes, which exhibit the remarkable capability to detect traces of water in a wide linear range (most can reach 0-94%, v/v), low detection limit of 0.2% (v/v), and rapid response time of 8 s in various organic solvents by virtue of an unusual water-activated hydrogen-bonding cross-linking AIE (WHCAIE) mechanism. As a proof-of-concept, the WHCAIE mechanism is explained well by single X-ray diffraction, absorption spectra, fluorescence spectra, dynamic light scattering, 1H NMR spectra, and theoretical calculations. In addition, the molecules demonstrated their application for the detection of humidity (42-80%). These Schiff base Zn(II) complexes become one of the most powerful water sensors known due to their extraordinary sensitivity, fast response, and wide detection range for water.

Unusually Flexible Indium(III) Metal–Organic Polyhedra Materials for Detecting Trace Amounts of Water in Organic Solvents and High Proton Conductivity

Humidity-induced single-crystal transformation was observed in the indium metal-organic polyhedra [In2(TCPB)2]·2H2O (In1), where H3TCPB is 1,3,5-tri(4-carboxyphenoxy)benzene. When the humidity is above 58% relative humidity (RH) at room temperature, the neutral compound In1 could be successfully converted into the positively charged compound In1-H along with the color change from yellow to deep red, which also undergoes a reversible transformation into In1 driven by thermal dehydration. Notably, the color of In1 takes only 5 min to change under 58% RH at room temperature, which is much quicker than common desiccant bluestone. As the water content is increased from 0.0% to 0.2% in acetonitrile solvent, compound In1 exhibits rapid detection of trace amounts of water through turn-off luminescence sensing mechanism with a low detection limit of 2.95 × 10-4%. Because of the formation of extensive hydrogen-bonding network between the metal-organic polyhedra (MOPs) and surrounding guest OH- ions, compound In1-H, along with isostructural Ga1-H, displays excellent proton conductivity up to 2.84 × 10-4 and 2.26 × 10-4 S cm-1 at 298 K and 98% RH, respectively. Furthermore, the activation energies are found to be 0.28 eV for In1-H and 0.34 eV for Ga1-H. This method of incorporation of OH- ions to obtain high proton conductivity MOPs with low activation energy demonstrates the advantage of OH- ion conduction in the solid-state materials.

A highly sensitive turn-on ratiometric luminescent probe based on postsynthetic modification of Tb3+@Cu-MOF for H2S detection

The fabrication of luminescent materials with lanthanide cations encapsulated within MOF pores is currently of interest because luminescent materials are used in numerous applications. In this study, a distinctive strategy via postsynthetic modification (PSM) of a novel metal–organic framework [Cu(HCPOC)2]n (Cu1) (H2CPOC = 5-(4′-carboxyphenoxy)nicotinic acid) and terbium ions (Tb3+) for sensing hydrogen sulfide (H2S) is reported. The obtained composite Tb3+@Cu1 emits a weak typical Tb3+ ion emission and strong ligand-centred emission. Interestingly, H2S, as a strong electron donor, can strongly enhance the luminescence of Tb3+ through its superior affinity for Cu2+ ions. The composite Tb3+@Cu1 was designed as a luminescent turn-on ratiometric probe for H2S detection, showing high sensitivity and selectivity. The detection limit of Tb3+@Cu1 (1.20 μM) is far below that of Cu1 (13.25 μM). Moreover, a similar ligand, 5-(4′-carboxyphenyl)nicotinic acid (H2CPC), was used to synthesize a fascinating structure, [Cu5(CPC)2(HCPC)2(OH−)4]n (Cu2), which was quite similar to that of the famous semiconductor MoS2, with the advantageous support of an organic linker between layers, and it showed a band gap of 2.45 eV.

Highly Stable and Regenerative Metal–Organic Framework Designed by Multiwalled Divider Installation Strategy for Detection of Co(II) Ions and Organic Aromatics in Water

MOF-based sensors capable of effectively and stably detecting toxic species in water have attracted huge attention in terms of improving environmental monitoring levels and water quality. Combining the flexibility of structure and modifying of pore surface, a multiwalled divider installation (MWDI) strategy is proposed and used for property enhancement. We herein report three metal-organic frameworks (MOFs) 1-3 based on a C3 symmetry organic phosphonic ligand with topology increased from 3,6-connected to 3,8-connected. Among them, MOFs 1 and 2 with remaining binding sites and large pores display lower luminescence response to Co2+ than does the applying standard. Guided by the MWDI strategy, 3 with high rigid framework and triple molecular installer divided rhombic pore was achieved under top-down topological analysis as anticipated, which endows high sensitivity and rapid response to Co2+, contributed by the synergy from free activated sites and appropriate pore and molecular dividing effect. Particularly, the high stability of 3 in boiling solvent and acid/base solutions has been evidenced and explained by structural robustness and kinetic inertness. Moreover, 3 shows excellent detection ability toward trinitrophenol (TNP) over other aromatic analytes in water, attributing to the predomination of energy transfers. Of note is that the used framework can be in situ regenerated into a fresh one. That provides a promising strategy to prepare effective and economic luminescent sensors in a predictable way for property modification.

Self-assembly of two supramolecular indium(III) metal–organic frameworks for reversible iodine capture and large band gap change semiconductor behavior

Under self-assembly, a novel polydentate benzimidazole ligand 2-(quinoline-2-yl)-benzimidazole (2-QLBM) and two In(III) compounds, [In(2-Hqlca)2Cl3·3H2O] (1) and {[In(2-QLBM)(2-qlca)Cl2]2·CH3CN·2H2O} (2) (2-Hqlca = 2-quinolinecarboxylic acid) have been synthesized and characterized. Both the In(III) compounds are driven by noncovalent interactions to assemble into supramolecular metal–organic frameworks (MOFs). Considering 2-QLBM and 2-Hqlc ligands with different geometrical structures, compound 1 possesses a (66)-dia network with a channel diameter of about 1.856 A, and compound 2 displays a (3,4)-connected topology network with the Schlafli symbol of (63)(65·8), whose channel diameter is about 3.683 A. Owing to large voids in the framework, 2 can serve as a host for reversible encapsulation of iodine corresponding to the 1.52 molecules of iodine per formula unit with a fast response and high sensitivity. Upon irradiation with UV light, the two compounds display tunable fluorescence emission from blue to yellow by varying the temperature. Moreover, the absorption spectra demonstrate that the band gaps of compounds 1 and 2 are 3.71 and 3.58 eV, respectively. When adsorbing iodine into the framework, the host structure of 2 is relatively perturbed by the presence of guests and exerts a remarkable influence on the band size and gap state.

Effect of noncovalent interactions on Ag(I)/Cu(II) supramolecular architecture for dual-functional luminescence and semiconductive properties

Four novel luminescent materials, namely, [Ag3(3,2′,3′-dpob)(bpy)]n (1·Ag), [Ag(3,3′,4′-H2dpob)(bpy)]n (2·Ag), [Ag3(3,2′,3′-Hdpob)(3,2′,3′-H2dpob)(bib)3·2H2O]n (3·Ag), and [Cu(3,2′,3′-Hdpob)(bib)·2H2O]n (4·Cu) [3,2′,3′-H3dpob = 3-(2′,3′-dicarboxylphenoxy)benzonic acid; 3,3′,4′-H3dpob = 3-(3′,4′-dicarboxylphenoxy)benzonic acid; bpy = 4,4′-bipyridine; bib = 1,4-bis(1-imidazoly)benzene] have been hydrothermally synthesized by mixed ligands and characterized using single crystal X-ray diffraction, infrared (IR), elemental analysis and thermogravimetric analysis (TGA). The crystal structures of four compounds indicate that the hydrogen bonding (O–H⋯O, C–H⋯O and C–H⋯π) and π⋯π stacking interactions play critical roles in the formation of the extended supramolecular array. 1·Ag displays a rare 3D compact structure with a 1D right-handed helical chain [–Ag1–CO2–Ag3–CO2–Ag1–]. 2·Ag and 3·Ag exhibit a 3D supramolecular architecture linked by intermolecular hydrogen bonds based on a 1D double-chain and 1D triple-chain, respectively. 4·Cu shows a 1D + 1D → 2D sheet, which is propagated to form an extended 3D structure with pcu (primitive cubic) topology via π⋯π stacking. The four compounds display remarkable narrow band emission with smaller full width at half-maximum (FWHM) (77 K, 97.91, 92.27, 72.98 and 77.96 nm; 298 K, 169.41, 241.98, 293.66 and 148.50 nm) in the solid state. The combination of such narrow FWHM and the red-shift from 298 K to 77 K endow them with a prominent thermochromic effect. It is worth noting that 2·Ag and 3·Ag display good aggregation-induced emission (AIE) properties. Both of them show very weak luminescence in dimethyl sulfoxide (DMSO, good solvent) while their intensities increased enormously with the addition of water (H2O, poor solvent) due to aggregation. In addition, adsorption spectra reveal their semiconductive nature (2.35 eV for 1·Ag and 2.91 eV for 3·Ag) and the role of Ag⋯Ag interactions in controlling the performance of semiconductive properties is highlighted.

Dual-emissive nanocomposites based on Eu(III) functionalized Cu(I)-coordination polymer for ratiometric fluorescent sensing and integrating Boolean logic operations

The most serious and yet unsolved problems of molecular logic operations consist of how to link molecular events in complex systems into a usable device with specific functions. Herein, a fluorescence system based on a Eu(III)-functionalized Cu(I)-coordination polymer was constructed to recognize and connect multiple components (AA/H2O2, H2S and Fe(II)) for developing dual-emissive (B485 and R616) ratiometric fluorescent sensing and integrating Boolean logic operations. More importantly, we first proposed the H2O2–Eu(III)@Cu-COOH system, which can realize the selective and quantitative detection of AA by fluorescence titration experiments of H2O2 even in the presence of various competitive analytes (e.g. H2S and Fe(II)). To demonstrate the strategy, by self-assembling, oxidizing, and connecting with each other, Eu(III)@Cu-COOH and the analytes achieved elementary logic operations (OR, NOR, AND, XOR, IMP and INH) and integrative logic operation (XOR(INH)–OR) to perform non-arithmetic functions and to analyze two or three analytes in a bio-mimicking environment. Considering its strong molecular recognition, the novel prototypes developed here may have potential applications in the fields of biological computers and intelligent multi-analytes detection systems.

Dual-Stimulus-Triggered Programmable Drug Release and Luminescent Ratiometric pH Sensing from Chemically Stable Biocompatible Zinc Metal–Organic Framework

Metal-organic frameworks (MOFs), as drug delivery carriers, with high loading capacity and controllable release behavior can provide a more efficacious therapy in cancer treatments. In our work, a novel biocompatible zinc MOF Zn-cpon-1 with the (3,6)-connected rtl 3D topological network was designed and synthesized via employing ClO4- anion as template. The optically and chemically stable Zn-cpon-1 could be verified as a pH-responsive dual-emission platform and excellent drug delivery carrier with higher 5-fluorouracil (5-FU) (44.75 wt %) loading behavior than 6-mercaptopurine (6-MP) (4.79 wt %) ascribed to the influence of size and shape matching. The multiple interactions between Zn-cpon-1 and 5-FU drug molecules have been discussed and evidenced, which could be quantitatively estimated via the rate constant related to the topological structure. Specially, the gust release behavior of 5-FU@Zn-cpon-1 microcrystal was described and programmed via the Weibull distribution model and could be dual-triggered by the temperature and pH stimulus. This study illustrates that the Zn-cpon-1 without any postmodification performs a favorable potential of being used as biomedical drug delivery alternative carriers in effective drug payload, flexible release administration, and superior dual-stimuli responsiveness.

Dual-Emitting Eu(III)–Cu(II) Heterometallic–Organic Framework: Simultaneous, Selective, and Sensitive Detection of Hydrogen Sulfide and Ascorbic Acid in a Wide Range

As important biomolecules, the deficiency or maladjustment of hydrogen sulfide (H2S) or ascorbic acid (AA) is associated with the symptoms of the same disease (e.g., cardiovascular disease or cancer). There is an urgent need to develop a fluorescent probe capable of distinguishing between H2S and AA simultaneously. Here, we report the syntheses, structure, and property of the first dual-detection fluorescent probe which can differentiate H2S or/and AA in aqueous media. Accordingly, a novel [EuCu(pydc)2(ox)0.5(H2O)3·1.5H2O]2 n (1, H2pydc = 2,3-pyridinedicarboxylic acid and ox = oxalic acid) for selective and sensitive detection of H2S and AA in a wide range has been constructed (H2S: [130 nM, +∞); AA: [55 nM, +∞)), exhibiting excellent catalytic activity comparable to horseradish peroxidase. In addition, the highly efficient detection in human serum sample also proves the potential application in medical diagnosis. Meanwhile, a combinatorial logic gate (AND(INH)-OR) based on activated 1 has also been constructed. Furthermore, this approach for simultaneous H2S and AA detection suggests that the current work will expand the potential application of metal-organic frameworks for dual or multiple detections in biomedical fields.