Unraveling complexation and separation of novel asymmetric uranyl-5-methoxy-2-(4-methoxy-6'-(quinazolin-2-yl)-[2,2'-bipyridin]-6-yl ) quinazoline to chiral fungicides R/S-metalaxyls and R/S-benalaxyls

Chiral fungicides R/S-metalaxyls(R/S-MTLs) and R/S-benalaxyls(R/S-BNLs) have different biotoxicity. It is very important to unravel molecular recognition and enantiomeric separation of R/S-MTLs or R/S-BNLs. In this paper, we designed a novel asymmetric ligand: 5-methoxy-2-(4-methoxy-6"-(quinazolin-2-yl)-[2,2"-bipyridin]-6-yl)quinazoline(MMQBQ), further constructed a new asymmetric receptor Uranyl-MMQBQ by coordination of MMQBQ with uranyl. The complexation and separation of receptor Uranyl-MMQBQ with guests R/S-MTLs or R/S-BNLs were systematically studied using density functional theory (DFT) method. The respects of ESP, MBO, RFC, LOL, EDDM, EST-NOCV, QTAIM, FMOs, IGMH, and Gibbs free energy changes were calculated and analyzed. The results indicated that the MMQBQ could form a stable receptor Uranyl-MMQBQ with uranyl, which could selectively recognize and separate chiral R/S-MTLs or R/S-BNLs by receptor's U coordinating to carbonyl oxygens of guests. For R/S-MTLs, separation factors(SFS/R) of Uranyl-MMQBQ were more than 16 in water, chlorobenzene, toluene, carbon tetrachloride and cyclohexane, enantioselectivity coefficients(ESCs) ranged of 99.92%-94.24% in the above four solvents. While for R/S-BNLs, ESCs of Uranyl-MMQBQ were over 99% and SFS/R values were a range of 533.97-2839.36 in the above organic solvents. The findings provide valuable information for design of novel uranyl ligand and its complexes, meanwhile supply useful guidance for experiments on separation of other chiral fungicides in environmental protection.