| The development of asymmetric catalysts is a key objective in modern organic chemistry.Because of its good catalytic stereoselectivity and high catalytic efficiency,DNA hybrid catalysts have been rapidly developed since its discovery in 2005.The heterozygous catalyst consists of a chiral center chiral scaffold,a catalytic center metal ion,and a linking ligand.Through the transformation and modification of these three parts,we can realize the optimization of the performance of the catalyst and the exploration of the catalytic mechanism.In this dissertation,peptide nucleic acid duplex(PNA-PNA)and PNA-DNA hybridization chain were used as the chiral scaffold was applied to asymmetric reactions for the first.time.Simultaneously with the traditional DNA-DNA double-stranded chiral scaffold hybrid catalysts to explore the impact of the size of the ditch on catalytic performance.As a structural analog of DNA,PNA can form a duplex with DNA by Watson-Crick bond.In this paper,three types of chiral scaffolds were synthesized,which were complexed with dmbpy-CuⅡ to form hybrid catalysts.The catalytic performance of the novel hybrid catalysts was evaluated by Friedel-Crafts alkylation reaction.The results show that the three types of synthetic double-stranded hybrid catalysts can catalyze the reaction and may be obtained for enantiomeric excess(enantiomeric excess,ee),By comparing the experimental data,we found that with the deepening of the intervention of the PNA chain,the ee value of the reaction showed a decreasing trend.This may be caused by the absence of electrostatic repulsion between the neutral double strands of the PNA backbone,which in turn changes the size of the double-stranded ditches.The ionic strength experiment verifies this conclusion from the perspective of DNA channels Reproducibility experiments showed that the catalytic effect of the heterozygous catalyst after PNA intervention is more stable than that of the DNA hybrid catalyst and can be reused many times.To further discuss the reasons for differences in catalytic results,the thesis of a series of characterization methods spectroscopy.Circular dichroism experiment shows that there is a significant difference in the mode of action of dmbpy-CuⅡ and the three double-stranded chains.UV titration experiments showed that the Kb values of PNA-PNA double-strand and dmbpy-CuⅡ were larger,indicating that the structure of PNA double-stranded and dmbpy-CuⅡhas strong affinity,which proves that the lower ee value of PNA catalytic reaction is not due to free dmbpy-CuⅡ.Tm experimental results showed that the PNA double-stranded chain was the most stable,indicating that the PNA hybrid catalyst has practical application value.This paper applied PNA to the field of hybrid catalysis for the first time,broadened the scope of chiral scaffolds,and discussed the differences in the catalytic effects of the hybrid DNA-DNA,DNA-PNA and PNA-PNA hybrid scaffolds as chiral scaffolds.The reason for this has broadened the thinking for the study of heterogenic catalyst chiral scaffolds. |
