RESUMEN
The syntheses and crystal structures of the monopotassium salts of difluorinated and tri/perfluorinated trimesic acid (1,3,5-benzenetricarboxylic acid ≡ H3BTC) are presented, namely, K(H2 dF-BTC) ( Fdd2, Z = 16) and K(H2 pF-BTC) ( Cc, Z = 4). For the first time, together with already known K(H2 mF-BTC), all fluorination degrees of trimesic acid are accessible and can be used for a systematic study of the influence of fluorination on the stability of the resulting coordination polymers and metal-organic frameworks (MOFs). The monopotassium salts show a decreasing (chemical) stability in water upon heating, as well as a decreasing thermal stability, as evidenced by differential scanning calorimetry/thermogravimetric analysis (DSC/TGA). A similar decreasing thermal stability is found for two series of isostructural coordination polymers (UHM-33 topology: ∞2[Cu2(L)2(DMA)2]·2DMA with L2- = H mF-BTC2- and H dF-BTC2-) and MOFs (∞3[Ba(L)(H2O)2]·1/2H2O with L2- = HBTC2-, H mF-BTC2- and H dF-BTC2-). Remarkably, while the decomposition temperatures decrease with increasing fluorination of the linker, the releasing temperatures for embedded solvent molecules (DMA and H2O, respectively) increase. To identify possible candidates for the synthesis of isostructural coordination polymers and MOFs with BTC3- ligands with different degrees of fluorination, a database-adapted approach was developed, which utilizes the increased torsion angle between the carboxylate groups and the phenyl rings in these materials as a structure-determining parameter.
RESUMEN
Hollow mesoporous silica capsules (HMSC) are potential drug transport vehicles due to their biocompatibility, high loading capacity and sufficient stability in biological milieu. Herein, we report the synthesis of ellipsoid-shaped HMSC (aspect ratio â¼2) performed using hematite particles as solid templates that were coated with a conformal silica shell through cross-condensation reactions. For obtaining hollow silica capsules, the iron oxide core was removed by acidic leaching. Gas sorption studies on HMSC revealed mesoscopic pores (main pore width â¼38 Å) and a high surface area of 308.8 m2 g-1. Cell uptake of dye-labeled HMSC was confirmed by incubating them with human cervical cancer (HeLa) cells and analyzing the internalization through confocal microscopy. The amphiphilic nature of HMSC for drug delivery applications was tested by loading antibiotic (ciprofloxacin) and anticancer (curcumin) compounds as model drugs for hydrophilic and hydrophobic therapeutics, respectively. The versatility of HMSC in transporting hydrophilic as well as hydrophobic drugs and a pH dependent drug release over several days under physiological conditions was demonstrated in both cases by UV-vis spectroscopy. Ciprofloxacin-loaded HMSC were additionally evaluated towards Gram negative (E. coli) bacteria and demonstrated their efficacy even at low concentrations (10 µg ml-1) in inhibiting complete bacterial growth over 18 hours.