Extremely Large 3D Cages in Metal-Organic Frameworks for Nucleic Acid Extraction

Three-dimensional(3D) cages in the mesopore regime (2-50nm) assembled from molecular building blocks are highly desirablein biological applications; however, their synthesis in crystallineform is quite challenging, as well as their structure characterization.Here, we report the synthesis of extremely large 3D cages in MOF crystals,with internal cage sizes of 6.9, and 8.5 nm in MOF-929; 9.3 and 11.4nm in MOF-939, in cubic unit cells, a = 17.4 and22.8 nm, respectively. These cages are constructed from relativelyshort organic linkers with the lengths of 0.85 and 1.3 nm, where theinfluence from molecular motion is minimized, thus favoring theircrystallization. A 0.45 nm linker length elongation leads to a maximum2.9 nm increase in cage size, giving a supreme efficiency in cageexpansion. The spatial arrangements of these 3D cages were visualizedby both X-ray diffraction and transmission electron microscopy. Theefforts to obtain these cages in crystals pushed forward the sizeboundary for the construction of 3D cages from molecules and alsoexploited the limit of the area in space possibly supported per chemicalbond, where the expansion efficiencies of the cages were found toplay a critical role. These extremely large 3D cages in MOFs wereuseful in the complete extraction of long nucleic acid, such as totalRNA and plasmid from aqueous solution.

Automated summary

In this study, a method for synthesizing highly desirable three-dimensional cage structures in the mesopore regime was reported. These cages, with extremely large sizes, were constructed in MOF crystals and visualized by X-ray diffraction and transmission electron microscopy.