It
is important to achieve a moderate sustained release rate for drug
delivery, so it is critical to regulate the host–guest interactions
for the rational design of a carrier. In this work, a nano-sized biocompatible
metal–organic framework (MOF), Mg(H2TBAPy)(H2O)3·C4H8O2 (TDL-Mg), was constructed by employing π-conjugated
1,3,6,8-tetrakis(p-benzoic acid)pyrene (H
4
TBAPy) as a ligand and used
for 5-fluorouracil (5-FU) loading (28.2 wt %) and sustained slow release. TDL-Mg exhibits a 3D supramolecular architecture featuring
a 1D rectangle channel with a size of 6.2 × 8.1 Å2 and a Brunauer–Emmett–Teller surface area of 627 m2·g–1. Channel microenvironment analysis
shows that the rigid H
2
TBAPy
2–
ligand adopts special
torsion to stabilize the channels and offer rich π-binding sites;
the partially deprotonated carboxyls not only participate in the formation
of strong hydrogen bonds but also create a mild pH buffer environment
for biological applications. Suitable host–guest interactions
are generated by the synergistic effect of polydirectional hydrogen
bonds, multiple π-interactions, and confined channels, which
allow 5-FU@TDL-Mg to release 76% of load in 72 h, a medically
reasonable rate. Microcalorimetry was used to directly quantify these
host–guest interactions with a moderate enthalpy of 22.3 kJ·mol–1, which provides a distinctive thermodynamic interpretation
for understanding the relationship between the MOF design and the
drug release rate. Additionally, the nano-sized 5-FU@TDL-Mg can be taken up by mouse breast cancer cells (4T1 cells) for imaging
based on the dramatic fluorescence change during the release of 5-FU,
exhibiting potential applications in biological systems.
A flexible multidentate ligand, 1H-benzimidazole-2-carboxylic acid, was synthesized to construct a series of lanthanide coordination polymers [Ln(HBIC) 3 ] n (Ln = Eu (1), Tb (2), Gd (3), Pr (4), Nd (5); H 2 BIC = 1H-benzimidazole-2-carboxylic acid) under hydrothermal conditions. All the compounds were fully characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, thermal analysis and various spectroscopic techniques. Structural analyses reveal that they are isostructural and feature a 2D wave-like layer structure with distorted grids, in which the adjacent Ln 3+ centers are bridged by the HBIC 2 ligands with two kinds of new coordination modes and the adjacent HBIC 2 ligands are tightly bound by two types of distinct intra-layer hydrogen bonds. The adjacent 2D layers are further interconnected by strong inter-layer hydrogen bond ring motifs R 2 2 (10)to generate a 3D supramolecular architecture. Optical studies indicate that the compounds 1, 2, 4 and 5 exhibit characteristic luminescence emission bands of the corresponding lanthanide ions in the visible or near-infrared regions at room temperature. In particular, compound 2 displays bright green luminescence in the solid state with a satisfactory 5 D 4 lifetime of 1.2 ms and a high overall quantum yield of 31%, due to an ideal energy gap between the lowest triplet state energy level of H 2 BIC ligand and the 5 D 4 state energy level of Tb 3+ . The energy transfer mechanisms in compounds 1 and 2 were also described and discussed.
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