Aggregation-Inducede Mission And Application In Biological Fluorescence Probe Of 1,8-Naphthalimide - Pamam Dendron

In this paper, a new 4-(2-pyridylvinyl)-naphthalimide-PAMAM (PN-PAMAM) dendron was synthesized by Heck coupling reaction and condensation reaction with PAMAM as the core, and 4-(2-pyridylvinyl)-naphthalimide as branches. The structure was characterized by melting point,1H NMR,13C NMR and HRMS-MALDI-TOF. The aggregation-induced emission (AIE) properties of PN-PAMAM were studied in different water content in the mixed solvent, and the mechanism was studied. The interaction of PN-PAMAM with BSA was examined by fluorescence and circular dichroism spectral method. The binding constant was calculated and the changes of the a-helix content of BSA. The interaction and mechanism of PN-PAMAM with ct-DNA and protons were also demonstrated.1.The 4-(2-pyridylvinyl)-1,8-naphthalimide modified PAMAM dendron (PAMAM) was synthesized with PAMAM as the core, naphthalimide as the inner unit and pyridine as branches. The structure was characterized by melting point,1H NMR, 13C NMR and HRMS-MALDI-TOF. The mechanisms of condensation reaction and Heck reaction were discussed.2. The AIE properties of PN-PAMAM was studied in this paper. PN-PAMAM emitted bright yellow fluorescence in solid state, which the maximum emission peak located at 533nm. The fluorescence intensity of PN-PAMAM was significantly enhanced when the water fraction exceeded 10%. When the water fraction was increased from 0% to 60%, the fluorescence intensity of PN-PAMAM dendron was correspondingly enhanced. This increase in fluorescence intensity was considered to be a result of the AIEE effect. After reaching a maximum intensity at 60%, the fluorescence intensity of PN-PAMAM decreased with the increase in water content. Then the mechanism of PN-PAMAM was studied through measuring the fluorescence spectra in glycerol/DMF mixture.3. Complexation of PN-PAMAM with BSA was investigated by spectrometric titrations in aqueous phosphate buffer (pH=7.4). The PN-PAMAM emission was increased visibly by the addition of BSA, and the binding constant was calculated (Ksv= 1.03*l05 L/mol) by Stern-Volmer equation. The effect of PN-PAMAM dendron on the fluorescence intensity and circular dichroism spectral of BSA was also studied. The fluorescence intensity of BSA decreases regularly with the increasing concentration of PN-PAMAM dendron, and the binding constant was calculated (Ksv=1.66×105L/mol) by Stern-Volmer equation. It suggested that the above quenching may be initiated by static quenching for the formation of BSA/dendron complexes. With the increase of PN-PAMAM dendron concentrations, the CD spectra intensities at 208 and 222 nm decreased remarkably. The CD spectra indicated that dendron can induce decreases in the helix structure content of BSA and also the changes in the secondary structure of BSA.4. The fluorescence spectra of probe PN-PAMAM combining with ctDNA in PH 7. 4 PBS buffer were measured. The PN-PAMAM emission was increased visibly by the addition of ct-DNA, and the binding constant and number of binding sites n were calculated (Kb=0.124 mL/μg, n=0.32). It suggesting that the above quenching initiated by static quenching. And the circular dichroism was also studied on the interactions of PN-PAMAM dendron with ct-DNA. The CD spectra indicated that dendron binding with ct-DNA was by the insetment mode. The influence of protons on the fluorescent response of PN-PAMAM was investigated in the 2.94-12.21 pH values range. PN-PAMAM exhibit high sensitivity to the presence of protons. The highest fluorescence intensities obtained at acidic pH are due to the fact that the resulting tertiary nitrogen atoms of the core are protonated. This prevents the PET process causing an enhancement in the fluorescence intensity. The calculated pKa value is 8.1...