Chirality Modified Metal-Organic Framework For Enantioselective Adsorption And Sensing

Metal-organic frameworks(MOFs),as a unique class of coordination polymers,exist as well-organized crystalline structures and exhibit varied coordination geometries.The diversity of metals and organic bridging ligands offers numerous structural and functional variations of MOFs,and directs the materials to various promising applications,such as catalysis,gas storage,chromatographic separation,chemical sensing,membranes,and drug delivery.Considering the importance of chirality,today,research work on chirality has been expanded to numerous fields.One of the most actively emerging fields is the design and synthesis of chiral MOFs and exploring their applications in various fruitful research fields,including asymmetric catalysis,molecular recognition,non-linear optics,and enantioselective separation.Several structural features of chiral MOFs,such as their large internal surface area,high adsorption capacity,efficient porosity,chemically and thermally stable skeleton,and above all chiral atmosphere,play a vital role in performing the above-mentioned applications.However,the successful design and application of chiral MOFs are challenging tasks for researchers.It has been proven that surface modification is an efficient approach to tune the properties of MOFs.Surface modification,instead of modification inside of parent MOFs,will not alter the pore sizes and intrinsic properties of the parent MOFs.Depending on the functions of materials used for surface modification,multi-functions can be integrated into the composites.For example,composite of UiO-66-NH2@PANI have been used for cadmium ion detection and the MOF-PVP composite membranes exhibited enhanced low-humidity proton conductivity.PDMS modification on surface of MOF-5 dramatically enhanced its stability against moisture.However,papers about chiral surface modification on achiral MOFs are rarely reported so far.In this paper,we utilized MOFs as precursors,and functionalization the surface of MOFs by chirality modification,which can be applied to the chiral recognition and separation of enantiomers.1.Chiral recognition and separation is of general research interests in natural product separation and the pharmacy industry.In this work,we develop a novel strategy to modify achiral porous metal-organic framework(MOF)surfaces via a superficial chiral etching process(SCEP),in which reacting a presynthesized achiral MOF with a chiral ligand produces an achiral@chiral MOF core-shell hybrid composition.SCEP creates chiral species on an achiral porous MOF surface but does not change the porosity and pore structure,enabling core-shell composition enantioselective sorption.The resulting[Cu3(Btc)2]@[Cu2((+)-Cam)2Dabco]core-shell composition displays preferred sorption kinetics toward(S)limonene against(R)-limonene,with a similar discrimination effect with pure chiral[Cu2((+)Cam)2Dabco].Superficial chiral etching of the porous achiral MOF represents an economic and efficient strategy for enantioselective separation.2.We reported integration of conductivity,chirality and porosity into MIL-101 @chiral-PANI composite for synchronous chiral recognition,adsorption and sensing towards enantiomers.Adsorption behaviors of carvone enantiomers over chiral PANI and MIL-101 @chiral-PANI are satisfied with pseudo-first order fitting.In comparison with chiral PANI,MIL-101 @c-PANI exhibits a better enantioselectivity and much higher(>5 fold)adsorption amount over L-carvone than D-carvone.And MIL-101 @c-PANI is able to recognize the chirality of carvone via electrochemical sensing,taking advantage of the electric conductivity of chiral PANI.Our result demonstrated the feasibility of applying achiral MOF for enantioselective sensing and adsorption via installing chiral and conductive gates.And this chiral polymer modification strategy represents a universal way to entitle achiral MOFs with chiral functions.