Polymeric Carbon Nitride with Chirality Inherited from Supramolecular Assemblies.

The facile synthesis of chiral materials is of paramount importance for various applications. Supramolecular preorganization of monomers for thermal polymerization has been proven as an effective tool to synthesize carbon and carbon nitride-based (CN) materials with ordered morphology and controlled properties. However, the transfer of an intrinsic chemical property, such as chirality from supramolecular assemblies to the final material after thermal condensation, was not shown. Here, we report the large-scale synthesis of chiral CN materials capable of enantioselective recognition. To achieve this, we designed supramolecular assemblies with a chiral center that remains intact at elevated temperatures. The optimized chiral CN demonstrates an enantiomeric preference of ca. 14 %; CN electrodes were also prepared and show stereoselective interactions with enantiomeric probes in electrochemical measurements. By adding chirality to the properties transferrable from monomers to the final product of a thermal polymerization, this study confirms the potential of using supramolecular precursors to produce carbon and CN materials and electrodes with designed chemical properties.

Chiral Porous Carbon Surfaces for Enantiospecific Synthesis.

Chiral surfaces, developed in the last decade, serve as media for enantioselective chemical reactions. Until today, they have been based mostly on developments in silica templating, and are made mainly from imprints of silicate materials developed a long time ago. Here, a chiral porous activated carbon surface was developed based on a chiral ionic liquid, and the surface chemistry and pore structure were studied to lay a new course of action in the field. The enantioselectivities of surfaces are examined by using variety of methods such as circular dichroism, linear sweep voltammetry and catalysis. These techniques revealed a 28.1% preference for the D enantiomer of the amino acid proline, and linear sweep voltammetry confirmed chirality recognition by another probe. An aldol surface chiral catalytic reaction was devised and allowed to determine the root of the enantiomeric excess. These results affirm the path toward a new type of chiral surface.

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

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.

Amino acid-based ionic liquids as precursors for the synthesis of chiral nanoporous carbons.

The synthesis of chiral nanoporous carbons based on chiral ionic liquids (CILs) of amino acids as precursors is described. Such unique precursors for the carbonization of CILs yield chiral carbonaceous materials with high surface area (≈620 m2 g-1). The enantioselectivities of the porous carbons are examined by advanced techniques such as selective adsorption of enantiomers using cyclic voltammetry, isothermal titration calorimetry, and mass spectrometry. These techniques demonstrate the chiral nature and high enantioselectivity of the chiral carbon materials. Overall, we believe that the novel approach presented here can contribute significantly to the development of new chiral carbon materials that will find important applications in chiral chemistry, such as in chiral catalysis and separation and in chiral sensors. From a scientific point of view, the approach and results reported here can significantly deepen our understanding of chirality at the nanoscale and of the structure and nature of chiral nonporous materials and surfaces.