Intramolecular hydrogen bonds and antioxidant activity of aminophenols

Abstract

We have used IR Fourier spectroscopy to study intramolecular interactions in solutions of aminophenols in nhexane. When the hydroxyl group in the molecule is ortho to the amino group, O-H⋅⋅⋅N and N-H⋅⋅⋅O intramolecular hydrogen bonds are formed in the aminophenols. Adding two tert-butyl groups to the benzene ring of ortho-aminophenols strengthens the O-H⋅⋅⋅N bond in the molecules, and prevents formation of an N-H⋅⋅⋅O bond. Additional acylation of the amino group in ortho-aminophenols leads to formation of an O-H⋅⋅⋅O=C intramolecular hydrogen bond. Formation of the above-indicated intramolecular hydrogen bonds in aminophenols affects the course of radiation-induced reactions occurring in n-hexane with participation of these compounds. The antioxidant properties of the aminophenols are enhanced when the hydroxyl groups in the molecules are found in the free state, and are diminished when strong O-H⋅⋅⋅N or O-H⋅⋅⋅O=C intramolecular hydrogen bonds are formed.

Spectroscopic properties of pharmacologically active phenols

“…In the IR spectra of antiviral active aminophenol compounds, there is no marked absorp tion in the range of vibrations of free OH groups. This means that OH groups are involved in the formation of intramolecular hydrogen bonds of the O-H⋅⋅⋅N type [11,[15][16][17][18].…”

“…In the interval 3100-2800 cm -1 , this band of O-H vibrations is over lapped with the absorption of C-H bonds of the aro matic ring and tert butyl groups. For N-H vibrations, a band with ν max = 3432 cm -1 (the range of vibrations of free NH groups) is observed [12,[15][16][17]. The absence of the band of vibrations of bound NH groups in the spectrum of the active compound indicates that the hydrogen atom of the hydroxyl group plays an active role in intramolecular interactions.…”

“…As a result of the formation of intramolecular hydrogen bonds with the participation of the hydrogen atom of the hydroxyl group, ν max of the absorption band is shifted toward the spectral range in which frequencies of C-H vibrations are commonly located. Such a considerable shift of the absorption band of O-H vibrations toward the low frequency range of the spectrum is caused by the for mation of intramolecular hydrogen bonds of the О-Н⋅⋅⋅О=С type in molecules of AP VI [12,[15][16][17].…”

“…The study of phenols by optical methods is impor tant due to high pharmacological activity of these compounds [11][12][13][14][15][16][17][18][19]. A detailed analysis of their IR Fourier transform spectra makes it possible to consid erably extend our notions of the ability of phenols to manifest antimicrobial and antiviral properties and to determine interrelations between the structure of these compounds, their optical properties, and their phar macological functions.…”

Characterization of aminophenol isomer adsorption on silver nanostructures

“…Only three SERS investigations exist in the literature with regard to adsorption of aminophenol (AP) isomers [9][10][11]. This is a surprise when considering the strong intermolecular hydrogenbonding in crystals and films of AP isomers that lend to many biochemical, polymer, catalytic, and nanochemistry applications [12][13][14][15][16][17].…”