Toward Efficient Synthesis of Porous All-Carbon-Based Nanocomposites for Enantiospecific Separation.

Milena Perovic,Martin Oschatz,Yitzhak Mastai,Markus Antonietti,Wuyong Zhang,Sapir Shekef Aloni

doi:10.1021/acsami.1c02673

Abstract

Chiral separation and asymmetric synthesis and catalysis are crucial processes for obtaining enantiopure compounds, which are especially important in the pharmaceutical industry. The efficiency of the separation processes is readily increased by using porous materials as the active material can interact with a larger surface area. Silica, metal–organic frameworks, or chiral polymers are versatile porous materials that are established in chiral applications, but their instability under certain conditions in some cases requires the use of more stable porous materials such as carbons. In addition to their stability, porous carbon materials can be tailored for their ability to adsorb and catalytically activate different chemical compounds from the liquid and the gas phase. The difficulties imposed by the functionalization of carbons with chiral species were tackled in the past by carbonizing chiral ionic liquids (CILs) together with a template to create pores, which results in the entire body of a material that is built up from the precursor. To increase the atomic efficiency of ionic liquids for better economic utilization of CILs, the approach presented here is based on the formation of a composite between CIL-derived chiral carbon and a pristine carbon material obtained from carbohydrate precursors. Two novel enantioselective carbon composite materials are applied for the chiral recognition of molecules in the gas phase, as well as in solution. The enantiomeric ratio of the l-composite for phenylalanine from the solution was (L/D) = 8.4, and for 2-butanol from the gas phase, it was (S/R) = 1.3. The d-composite showed an opposite behavior, where the enantiomeric ratio for phenylalanine was (D/L) = 2.7, and for 2-butanol from the gas phase, it was (R/S) = 1.3.

Highlights

Some of the principal concepts in the pharmaceutical and agricultural industry rely on the fact that biological activity is directly correlated with the chirality of a chemical compound
Carbon composite materials with chiral surfaces were synthesized by coating porous carbon with a chiral ionic liquid and its subsequent carbonization
Ordered mesoporous carbon (CMK-3, in further text denoted as C) was obtained by impregnation of a silica hard template (SBA-15) with sucrose followed by its carbonization and template removal.[45,46]

Summary

■ INTRODUCTION

Some of the principal concepts in the pharmaceutical and agricultural industry rely on the fact that biological activity is directly correlated with the chirality of a chemical compound. Structure, allotropes of carbon with higher atomic order, such as carbon nanotubes (CNTs), graphene, or fullerene, have been more intensely studied for chirality-related applications.[29−31] The likely reason is the uncomplicated uniform functionalization of their well-defined surface by covalent chemical coupling of functional groups These types of carbon materials are not intrinsically porous. After low-temperature carbonization of the CIL coatings from two different enantiomers, two carbon composites with opposite chiral information are obtained Their chiral recognition is investigated in the gas phase by the adsorption of chiral vapor and in solution by isothermal titration calorimetry with enantiopure titrants. Water and chiral gas physisorption measurements were performed using (S)-(+)-2-butanol or (R)-(−)-2butanol at 25 °C (sample weight, ∼50 mg) on a Quantachrome. Data analysis was performed using Origin software provided by MicroCal

■ RESULTS AND DISCUSSION

Summary

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES