Design,Synthesis And Properties Studies Of Naphthalimide-amide Probes For Ions

To date, the design and development of synthetic probes and chemsensors for the detection of different analytes have received considerable attention, based on their short response time and low-cost instrumentation. Probes based on ion-induced changes in fluorescence appear to be particularly attractive due to the simplicity of the method and the low limit of detection of the fluorescence. Among others, naphthalimide-based dyes have exceptional photophysical properties due to their high photostability, quantum yield and large Stokes shift lead to their extensive use in the detection of metal cations, anions and proton.A wide array of pH probes has been constructed, in most of which the change in fluorescence property is induced by the protonation or deprotonation of a specific functional group, some of them respond to neutral pH ranging from 6 to 8 or weak acid pH ranging from 4 to 6, however, very few probes respond to pH values below 4 and are suitable for use under extremely acidic condition. Accordingly, the present study focused on the design of novel compounds with 1,8-naphthalimide as fluorophore, the electron-donating piperazinyl group and amide group which easily combined with hydrogen ions as receptor, eight naphthalimide-amide derivatives have been synthesized, and characterized by elemental analysis, UV-vis, FT-IR, NMR, a further study of photophysical properties, H+ recognition properties and the possible mechanism for the derivatives were studied, the interaction with DNA were researched finally, eight naphthalimide derivatives are as follows:1. N-allyl-4-(4'-N,N-diethylpropionamide-acetamido-piperazinyl)-1,8-naphthalimide(L1)2. N-allyl-4-(4'-N,N-dibutylpropionamide-acetamido-piperazinyl)-1,8-naphthalimide(L2)3. N-allyl-4-(4'-N,N-dioctylpropionamide-acetamido-piperazinyl)-1,8-naphthalimide(L3)4. N-allyl-4-(4'-N,N-dibutylpropionamide-ethanone-piperazinyl)-1,8-naphthalimide(L4)5. N-allyl-4-(4'-N,N-disobutylpropionamide-ethanone-piperazinyl)-1,8-naphthalimide(L5)6. N-(N,N-dibutylpropionamide)-acetamido-4-allyl-1-piperazinyl-1,8-naphthalimide(L6)7. N-(N,N-dioctylpropionamide-acetamido)-4-allyl-1-piperazinyl-1,8-naphthalimide(L7)8. N-(N,N-dibenzylpropionamide-acetamido)-4-allyl-1-piperazinyl-1,8-naphthalimide(L8)Experimental results of structural characterization indicate that the synthesized compounds are in accord with our original design, then, their photophysical characteristics were studied, these compounds are green-emitting fluorescent materials, and their fluorescence intensity and fluorescence quantum yield are related to in organic solvents of different polarity.Then, the influences to their properties caused by pH fluctuation and the mutual relationship have been studied, the UV absorption of these compounds have insignificant change when change from alkaline gradually to acid, but the maximum absorption wavelengths have marked blue shift, the molar absorption coefficient and Stokes shift also have different degrees of changes, these results illustrate that compounds could respond to the change of pH values. The following fluorescence spectroscopy study has further proved the view above, fluorescence intensities have enhanced dramatically when change from alkaline gradually to acid, the fluorescence intensities enhanced 32.3, 24.53, 16.36 times for probe L1, L2, L3 and that for L6, L7, L8 are 78.44, 66.06, 59.83 times respectively, and linear mathematical relationship exists between fluorescence intensity and a fixed range of pH values. The results of ion competition experiment also illustrate that other cations have negligible influence to recognize H+ mean that the compounds have good selectivity to hydrogen ion.The PET recognition mechanism has been put forward based on their structure that protonation of probes hinder the PET process make remarkable fluorescence enhancement, 1H NMR spectroscopy data of protonated probes proved the previous assumptions that they are PET-based probes.Naphthalimide derivatives also have significant application in biological area(interact with DNA), so including UV titration experiment, fluorescence titration experiment and viscosity determination have been done, the experimental results of DNA-binding about the compounds suggest that they bind to DNA in an intercalation mode. These findings indicate that these naphthalimide derivatives have many potential practical applications for the development of nucleic acid molecular probes and new therapeutic reagents for diseases on the molecular level.