Design And Synthesis Of Fluorescent Probe For Detection Of Cysteine And Theoretical Calculation Of Several Near-infrared Fluorophores

Organic small molecule fluorescent probes have become important tools for living imaging and small molecule detection in biological samples due to their high sensitivity,excellent selectivity,and fast response.Selecting ready-made fluorophores or constructing new ones,and combining specific recognition groups to build organic small molecule fluorescent probes are currently the main research directions.In this paper,the research work is mainly divided into the following two aspects.(1)A water-soluble near-infrared(NIR)fluorescent probe MTR-C was designed and synthesized,with a cyanine-like structure and a recognition unit of the acrylate group.Through an aromatic ring nucleophilic substitution reaction based on sulfhydryl moiety,an off-on fluorescence response toward cysteine(Cys)was realized.The probe exhibited excellent spectral performance with an emission wavelength of 720 nm and a detection limit of 0.20 ?mol/L.The spectral properties,selectivity and anti-interference performance of the probe were systematically investigated.Density functional theory(DFT)calculations were conducted to clarify the luminescence mechanism of the probe.Furthermore,the probe was successfully applied to the detection of free Cys in human serum and the NIR imaging of endogenous Cys in living cells.(2)We designed and synthesized four hydroxyxanthracene-hemicyanine-based NIR fluorophores(CyR,MOR,MTR,EQR),and studied their spectral properties.Four fluorescent probes can emit NIR light after being excited,and the quantum yields are 0.16,0.08,0.15,and 0.28,respectively.It still shows good emission spectrum in phosphate buffered solution(PBS,pH 7.4)containing 1% DMSO,which makes it possible for further applications in living systems.The photophysical properties of fluorophores were studied using DFT and time-dependent DFT(TDDFT)methods,combined with analytical methods such as front-line orbit,electrostatic potential,and electron-hole.The results show that EQR has the strongest conjugation effect,and the planar rigidity of CyR,MTR,and MOR are weakened in turn;the contributions of dimethyl,S,and O atoms in the fluorophore to the energy gap of HOMO and LUMO are weakened in turn;the quinoline ring in the molecule has the strongest electron-drawing ability,benzothiazole is greater than benzoxazole,and the benzoindol of bismethyl has the weakest electronic ability;the electronic transition of the maximum absorption spectrum mainly belongs to the local excitation(LE)transition;the centroid distance between the electron and hole in the emission spectrum has increased,and the charge transfer(CT)transition trend has increased,but it still belongs to the LE transition.