Preparation Of Chiral Carbon Dot Catalysts And Their Performance In Direct Asymmetric Aldol Condensation

Direct asymmetric aldol condensation reaction is the most basic reaction that can increase the carbon chain in biosynthesis.Its products are widely used in biomedicine and other fields.At present,the reaction catalyst has the disadvantages of long and complicated preparation period and no economic benefit.As a heterogeneous chiral catalyst,the chiral carbon dots synthesized by one step method have the characteristics of simple preparation,environmental protection and cheap.Aiming at the problems of heterogeneous chiral catalysis,a one-step synthesis method was used instead of the traditional covalent bond method,and a chiral carbon-point heterogeneous chiral catalyst with a simple one-step structure of chiral functional groups was designed.The structure of the catalyst was characterized by field emission transmission electron microscopy(STEM),infrared spectroscopy(FT-IR),circular dichroism(CD)and other techniques.The catalytic properties of chiral carbon dots in direct asymmetric aldol condensation reactions were studied.The main research contents are as follow:(1)Preparation and performance study of a chiral carbon point catalyst prepared by one-step method using D-proline as chiral source and citric acid as raw material.STEM characterization showed that the chiral carbon dots had a crystal plane structure similar to graphene and had a particle size of about 5.5 nm.FT-IR analysis found that the chiral carbon dots contained the same amino and carboxyl functional groups compared to the raw material,the reversed-phase stretching vibration peak of the N-H bond disappeared,and the N-H and O-H bonds dehydrated to form new C-N bonds.CD characterization indicates that the addition of D-proline makes the carbon quantum dots have optical activity while being synthesized.Fluorescence spectrum analysis showed that the chiral carbon dots have fluorescent properties.The effect of hydrothermal time on the structure and properties of chiral carbon dots was investigated.It was found that the longer the hydrothermal time of the prepared catalyst,the weaker the chiral signal of CD,and the smaller the enantiomeric ratio of the synthesized product.The catalytic activity of the chiral carbon dots reached the best at 4h of hydrothermal time,with a yield of 98%and an ee value of 73%.Chiral carbon dots synthesized with D-proline as a chiral source have excellent catalytic performance in direct asymmetric aldol condensation reactions.The excellent catalytic performance can be attributed to the co-promotion of D-proline with the carbon core and C-N.The valence bonds are connected,and the chiral sites are scattered on the surface of the chiral carbon dots.(2)Preparation and performance study of a chiral carbon point catalyst prepared by one-step method using D/L-alanine as chiral source and citric acid as carbon source.By means of CD,fluorescence spectrum and other characterization methods,it was shown that carbon quantum dots with chirality and fluorescence were synthesized.The effects of hydrothermal temperature on the chirality,fluorescence and quantum yield of the synthesized carbon dots were studied.The D-and L-type raw materials Indi-cate that the chiral carbon dots prepared with different chiral configurations have good catalytic activity for the direct asymmetric aldol reaction(The corresponding product configurations are S and R).The yield is 86-95%,and the ee value is 67-80%.There is favorable evidence for the application of chiral carbon dots in chiral catalysis.