Synthesis of Fluorescent Dansyl Derivatives of Methoxyamine and Diphenylhydrazine as Free Radical Precursors

Bianca Patrascu,Anca Paun,Codruta Popescu,Augustin M Madalan,Mihaela Matache,Petre Ionita,Sorin Mocanu,Anca Coman

doi:10.3390/ijms21103559

Bianca Patrascu, Anca Paun + Show 6 more

Open Access

https://doi.org/10.3390/ijms21103559

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Abstract

Starting from dansyl-chloride, in reaction with 1,1-diphenylhydrazine and methoxyamine, two new fluorescent derivatives 1 and 2 were obtained and characterized by NMR, IR, UV-Vis, HR-MS, and fluorescence spectroscopy. The single-crystal X-ray structure was obtained for compound 2. Both compounds generate free radicals by oxidation, as demonstrated by ESR spectroscopy. Compound 1 generates the corresponding hydrazyl-persistent free radical, evidenced directly by ESR spectroscopy, while compound 2 generates in the first instance the methoxyaminyl short-lived free radical, which decomposes rapidly with the formation of the methoxy radical, evidenced by the ESR spin-trapping technique. By oxidation of compounds 1 and 2, their fluorescence is quenched.

Highlights

Compound 1 generates the corresponding hydrazyl-persistent free radical, evidenced directly by ESR spectroscopy, while compound 2 generates in the first instance the methoxyaminyl short-lived free radical, which decomposes rapidly with the formation of the methoxy radical, evidenced by the ESR spin-trapping technique
Hydrazyl free radicals are a class of organic compounds that possess astonishing properties
Due to its stability and to the fact that, either in solid state or in solution, it is a 100% free radical, it is used as a standard in electron spin resonance spectroscopy (ESR or EPR) [2]

Summary

Introduction

Hydrazyl free radicals are a class of organic compounds that possess astonishing properties. Hydrazyl radicals participate in redox reactions (electron transfer) or in acid–base ones (proton transfer). Such reactions are paired with color changes, making it very easy to follow even by the naked eye. 2,2,-Diphenyl-1-picrylhydrazyl free radical, well known as DPPH (Figure 1), is a solid soluble in organic solvents, developing a purple color. These free radicals hold important properties, they seem to almost be forgotten nowadays among the nitroxides and verdazyls classes of stable free radicals (see Figure 1), which are much often encountered in the literature [4,5]. FiguFriegu2.reM2.eMtheotxhyoaxmyaimneinaenadndhyhdydrarazzinineeddeerriivvativess,,pprreeccuurrssoorsrsofopf epresrisstiesntetnfrtefereraedriacdalisc,aclosn, tcaoinitnagining a pFyigreuanrpeyo2rr.eMnNeeBotDrhNoflxBuyDoarmfolupinohreoaprenh.dorhe.ydrazine derivatives, precursors of persistent free radicals, containing a pyrene or NBD fluorophore

Results and Discussion

Photo-Physical Properties

Synthesis

Conclusions