Study Of Zinc(Ⅱ)、Cadmium(Ⅱ) Fluorescent Probes Based On2-aminobenzamide Skeleton

Fluoresent probe molecules, which can convert molecular identification information into theperceived optical signal, is widely attentioned by scientitsts because of its high sensitivity, thecontrollable switch, high spatial resolution, situ detection and achieving long-distancetransmission detection. Metal fluorescence probe is a kind of probe specific for metal ions.Compared with the previous detection technology, it has the advantages of high selectivity andstrong anti-interference ability.Some benzamide derivatives, as there are electron-donating formamido group on it, canemit strong fluorescence after chemical modification. Also, benzene ring is one of the commoninterval groups in the design of fluorescent probes, and it can acts as a bridge connectingbetween the complexation moity and fluorescence signal donor. Fluorescent probes for Zinc,Cadmium and other ions can be obtained respectively by modifying the benzamide with differentfluorephores and the complexating metal ions moiety, DPEA.Four novel Zn²⁺fluorescent sensors have been designed with N,N-bis（2-pyridylmethyl）ethylenediamine as chelator and2-aminobenzamide as fluorophore. These sensors were preparedin two or three steps from readily available starting materials. Of the four designed sensors,ZnABA was found to be the most efficient Zn²⁺-specific fluorescent probe and has goodsolubility in biological buffer, a large Stokes shift （186nm）, a high off–on fluorescence response（16-fold enhancement）, and distinct selectivity towards Zn²⁺over other metal ions. Our resultshave demonstrated an excellent linear relationship between the fluorescence intensity of ZnABAand the Zn²⁺concentration from0to10μM, which indicates that ZnABA has the potential to beused for the quantitative determination of Zn²⁺in an aqueous environment.Three fluorescent sensors CdABA’, CdABA and ZnABA’, which are structural isomers ofZnABA, have been designed with BPEA as the chelator and the2-aminobenzamide scaffold asthe fluorophore. These sensors can be divided into two groups: CdABA, CdABA’ for Cd²⁺andZnABA, ZnABA’ for Zn²⁺. Although there is little difference in their chemical structures, thetwo groups of sensors exhibit totally different fluorescence properties for preference of Zn²⁺or Cd2+. In the group of Zn2+sensors, ZnABA/ZnABA’ distinguish Zn2+from Cd2+with FZn2+/FCd2+=1.87-2.00. Upon interchanging the BPEA and carbamoyl groups on the aromatic ring of the fluorophore, the structures of ZnABA/ZnABA’ are converted into CdABA/CdABA’. Interest-ingly, the metal ions selectivity of CdABA/CdABA’ was switched to discriminate Cd2+from Zn2+with FCd2+/Fzn2+=2.27-2.36, indicating that a small structural modification could lead to a remarkable change of the metal ion selectivity.1H NMR titration and ESI mass experiments demonstrated that these fluorescent probers exhibited different coordination modes for Zn2+and Cd2+. With CdAB A’ as an example, generally, upon addition of Cd2+, the fluorescence response possesses PET pathway to display no obvious shift of maximum λem in the absence or presence of Cd2+. However, an ICT pathway could be employed after adding Zn2+into the CdABA’ solution, resulting in a distinct red-shift of maximal λem.