Oglufanide disodium

Chirality is an essential property of nature. Chiral recognition is of great significance to life sciences, pharmaceutical industry, food analysis, and so on. Chiral carbon dots (CCDs), as green nanomaterials, have great prospects in chiral sensing. However, CCDs with enantioselectivity for tryptophan (Trp) enantiomers are scarce. Moreover, most chiral sensing platforms depend on the difference of fluorescence intensity at the same emission wavelength to identify enantiomers, it is still a challenge to distinguish enantiomers by the positions of fluorescent emission peaks.

Novel CCDs with specific chiral recognition ability for Trp enantiomers are synthesized using l-lysine and l-cysteine as precursors. The CCDs have two fluorescent emission peaks at 390 nm and 450 nm. Interestingly, the fluorescence intensity of CCDs at 390 nm enhances obviously on the addition of L-Trp, while it enhances slightly at 450 nm in the presence of D-Trp. This chiral sensing system not only can identify Trp enantiomers according to fluorescence intensity, but also achieves the distinguishment depending on emission wavelength. The enantioselectivity (I_L/I_D) reaches 4.5 when the concentration of Trp enantiomer is 1 mM. This chiral sensing platform not only can be used for quantitative analysis of D-Trp and L-Trp, but also can be used for determining the enantiomeric excess of racemates. The chiral recognition mechanism is investigated by molecular simulation. It is found that L-Trp has higher binding energy with CCDs.

This work presents a novel kind of CCDs with special chiral recognition performance for Trp enantiomers, and opens the door to identify chiral isomers according to wavelength difference, which has profound significance for the development of chiral sensing platforms, and may provide inspirations for the design of novel CCDs with excellent chiral recognition performance.

The enantioselective performance of porous chiral metal-organic frameworks (CMOFs) is closely related to the pore size and uniformity of easily accessible active sites. The chiral recognition efficiency of microporous CMOFs is hindered by the restricted diffusion of the guest. Hierarchical porous chiral CMOFs with multiple pore size regimes ranging from micropores to macropores have emerged as potential candidates in chiral separation applications. 3DOM Zn-MOF-74 crystalline porous material with ordered macro-micropore structure was prepared with a general bottom-up strategy by carrying out the controllable confined growth of Zn-MOF-74 precursor in a removable three-dimensional ordered macroporous (3DOM) polystyrene (PS) template. Then l-tryptophan ( l -Trp) was introduced into MOFs by the strategy of postsynthetic modifications, and finally, a chiral hierarchical porous functional material 3DOM Zn-MOF-74-l-Trp was successfully fabricated. Based on the two luminescent centers from the achiral ligand H₄DOBC and chiral ligand l-Trp, the proportional fluorescence sensor 3DOM Zn-MOF-74-l-Trp was hopeful to be applied in the field of enantioselective fluorescence sensing. The enantioselectivity factor values of microporous M-Zn-MOF-74-l-Trp for 1,1'-bi-2-naphthol (Binol) and mandelic acid (MA) were 1.08 and 1.12, respectively. In comparison, the construction of hierarchical porous structure greatly enhanced the chiral recognition performance, which may be due to the improved mass-transfer efficiency of chiral guest molecules and highly swelled accessibility to the chiral recognition sites in this CMOF composite, making the enantioselectivity factor values correspondingly increased to 1.29 and 2.26, respectively.