Enantioselective Recognition And Enanti-oseparation Of Ofloxacin Enantiomers Via DNA-Cu(â…¡) Self-assembly

Owing to the distinct nanostructures and versatile functions, DNA-metal ionself-assembly has attracted great interest in drug delivery, molecular recognition, bio-sensor and bio-inspired catalysis. This work systematically studied the chiral recogni-tion and enantioseparation of ofloxacin enantiomers via Cu(II)-coordinated DNA, aswell as the conformational and morphological changes of Cu(II)-DNA complexes in-duced by ofloxacin enantiomers.First, we investigated the chiral recognition mechanism of ofloxacin enantiomersvia Cu(II)-DNA complexes based on the specific interactions of Cu2+with theself-complementary DNA sequences involving d[G4C4(GC)2G4C4], d[(GC)10] andd[(AT)10](abbreviated as G4C4, GC and AT). It is found that the Cu(II)-coordinatedGC-rich DNAs exhibit amplified enantioselectivity towards S-enantiomer of ofloxa-cin. Especially in the case of d[G4C4(GC)2G4C4] containing successive guanines, thehighest enantiomeric excess and separation factor of ofloxacin enantiomers in thepermeate after being adsorbed by the Cu(II)-DNA complex is obtained as49.1%inR-enantiomer at the Cu2+/base molar ratio of0.25, respectively. S-ofloxacin couldintercalate into the two adjacent guanine bases through the minor groove mediatedby Cu2+, which causes large steric hindrance between R-enantiomer and DNA phos-phate backbone, leading to a relatively weak binding.Next, we investigated the conformational and morphological changes of polynu-cleotide-Cu(II) complexes induced by ofloxacin enantiomers using Micrococcus lute-us DNA (ML DNA) and calf thymus DNA (CT DNA). The binding between ofloxa-cin enantiomers and Cu(II)-DNA complex is a induced-fit process. As Cu(II) coordi-nation, ofloxacin could induce the transition of Cu(II)-DNA complex from an ex-tended state to local compaction, the degree of which to a large extent depends on theCu2+/base molar ratio, the concentrations and the chirality of enantiomer.Finally, we studied the adsorption capacity of polynucleotides involving Micro-coccus luteus DNA (ML DNA) and calf thymus DNA (CT DNA), and their Cu(II)complexes for S-and R-ofloxacin as well as the enantioseparation of racemic ofloxa-cin by centrifugal ultrafiltration and HPLC detection. The results suggest the presence of positive cooperative effect during the adsorption of ofloxacin enantiomers ontopolynucleotides and their Cu(II) complexes. The maxmium adsorption capacities of S-and R-enantiomer for ML DNA are obtained at the Cu2+/base molar ratio of0.1, as0.34μmol/mg and0.28μmol/mg, respectively. And at the Cu2+/base molar ratio of0.1, the enantiomeric excess and the separation factor in the permeate for ML DNAreach the highest as65.6%and4.81(R-enantiomer excess), respectively. The regen-eration and the reuse of Cu(II)-DNA complexes can be performed by the reversibleEDTA/Cu2+and pH adjustment. And the optical purity of the specific enantiomer canbe further improved by a multi-stage adsorption.