Free radical chemistry of phenolic compounds

This project aims to develop our understanding of the free radical chemistry of some selected phenolic compounds that are commonly found in foods and plant products with medicinal properties. There is also a growing use phenols, particularly polyphenols, as dietary supplements. Although much is known about the safety and toxicity of these compounds, there is growing evidence that an appreciable fraction of their biological activities originates from metabolites rather than the parent molecules. It is impractical to attempt to identify all of the metabolic products from even a relatively simple molecule, because phenols tend to react via complex free radical reaction pathways. It is, however, feasible to develop an understanding of these free radical reactions. This information will be essential for future identification of the main products that are likely to be formed. Various oxidation and free radical scavenging reactions of phenols will be investigated by electron paramagnetic resonance (EPR) and related spectroscopic techniques. EPR is able to provide detailed information on molecules with unpaired electrons (free radicals) as a result of the interaction of the electron magnetic moment with the magnetic moments of nuclei with non-zero spins (e.g. 1 H, 13C, 14N, 31P). For radicals with limited stability, various approaches will be used in order to obtain their spectra. These will include, generation within the spectrometer by UV irradiation or electrolysis, or by using a flow system that allows solutions to pass through the spectrometer a short and known time after mixing of reagents that generate the radicals. In addition, spin trapping methods, in which unstable free radicals form (more) stable radical adducts, with diamagnetic molecules (spin traps), will be used to provide information on very short-lived radicals. Occasionally, when there are several magnetic nuclei in a free radical, the resulting EPR spectra are too complex for an unambiguous assignment of these hyperfine splittings; in these cases the related techniques of ENDOR and TRIPLE resonance spectroscopies will be used to simplify the spectral assignments. In addition, theoretical calculations of the relative energies of possible structures of various radicals will be performed to confirm the spectroscopic assignments.

This project aims to develop our understanding of the free radical chemistry of some selected phenolic compounds that are commonly found in foods and plant products with medicinal properties. There is also a growing use phenols, particularly polyphenols, as dietary supplements. Although much is known about the safety and toxicity of these compounds, there is growing evidence that an appreciable fraction of their biological activities originates from metabolites rather than the parent molecules. It is impractical to attempt to identify all of the metabolic products from even a relatively simple molecule, because phenols tend to react via complex free radical reaction pathways. It is, however, feasible to develop an understanding of these free radical reactions. This information will be essential for future identification of the main products that are likely to be formed. Various oxidation and free radical scavenging reactions of phenols will be investigated by electron paramagnetic resonance (EPR) and related spectroscopic techniques. EPR is able to provide detailed information on molecules with unpaired electrons (free radicals) as a result of the interaction of the electron magnetic moment with the magnetic moments of nuclei with non-zero spins (e.g. 1 H, 13C, 14N, 31P). For radicals with limited stability, various approaches will be used in order to obtain their spectra. These will include, generation within the spectrometer by UV irradiation or electrolysis, or by using a flow system that allows solutions to pass through the spectrometer a short and known time after mixing of reagents that generate the radicals. In addition, spin trapping methods, in which unstable free radicals form (more) stable radical adducts, with diamagnetic molecules (spin traps), will be used to provide information on very short-lived radicals. Occasionally, when there are several magnetic nuclei in a free radical, the resulting EPR spectra are too complex for an unambiguous assignment of these hyperfine splittings; in these cases the related techniques of ENDOR and TRIPLE resonance spectroscopies will be used to simplify the spectral assignments. In addition, theoretical calculations of the relative energies of possible structures of various radicals will be performed to confirm the spectroscopic assignments.