Biomedical subjects

Roger H Bisby

Publications and source records attributed to Roger H Bisby.

4 recordsLinked to original sources

PubMed2006

Formation of singlet oxygen from solutions of vitamin E.

Vitamin E offers protection against oxidative stress and is an efficient quencher of singlet oxygen. A recent report suggests that photo-excitation of vitamin E results in the formation of a triplet state (Naqvi et al. Photochem Photobiol Sci 2, 381 (2003)). This leads to the possibility of the triplet state of vitamin E being able to sensitize singlet oxygen and if this is the case it would be counter productive in terms of the biological protective function of vitamin E. We report the production of singlet oxygen, detected by 1270 nm luminescence, from pulsed laser excitation (308 nm) of vitamin E and an analogue, 2,2,5,7,8-pentamethyl-6-hydroxy-chroman (PMHC), with quantum yields between ~0.1 and 0.2. The luminescence was identified as singlet oxygen from self-quenching by vitamin E with solvent-dependent rate constants similar to published values. Whilst the beneficial antioxidant aspects of vitamin E are well established, these results indicate that vitamin E when directly excited can sensitize singlet oxygen formation and may, therefore, be capable of inducing biochemical and biological damage. The results are discussed in relation to recent reports on the deleterious effects of vitamin E dietary supplementation and pro-oxidant effects of vitamin E.

Antioxidants↗

PubMed2005

Single- and multi-photon excited fluorescence from serotonin complexed with beta-cyclodextrin.

The fluorescence of serotonin on binding with beta-cyclodextrin has been studied using both steady state and time-resolved methods. Steady state fluorescence intensity of serotonin at 340 nm showed approximately 30% increase in intensity on binding with K(A) approximately 60 dm(3) mol(-1) and the fluorescence lifetimes showed a corresponding increase. In contrast, the characteristic green fluorescence ('hyperluminescence') of serotonin observed upon multiphoton near-infrared excitation with sub-picosecond pulses was resolved into two lifetime components assigned to free and bound serotonin. The results are of interest in relation to selective imaging and detection of serotonin using the unusual hyperluminescence emission and in respect to recent determinations of serotonin by capillary electrophoresis in the presence of cyclodextrin. The results also suggest that hyperluminescence occurs from multiphoton excitation of a single isolated serotonin molecule.

Electrophoresis, Capillary↗

PubMed2003

Investigation of multiphoton-induced fluorescence from solutions of 5-hydroxytryptophan.

It is reported (J. B. S. Shear, C. Xu and W. W. Webb, Photochem. Photobiol. 1997, 65, 931) that multiphoton near infrared excitation of 5-hydroxytryptophan results in a transient product with green fluorescence. Visible fluorescence from multiphoton excitation enables detection of 5-hydroxytryptophan with extremely high sensitivity and also has potential applications in imaging of biological systems and investigation of protein dynamics. The characteristic fluorescence at 500 nm has now also been observed in a two laser experiment whereby 308 nm photolysis of the solution is followed by an excitation step at 430 nm. Fluorescence was observed in aerated and deaerated solutions and in the presence of ascorbate. Enhancement of fluorescence was observed on addition of ethanol. Transient absorption experiments with 308 nm photolysis showed the formation of three transient species. In the presence of ascorbate the radical formed by photoionisation was quenched, revealing a long-lived species (tau > 1 ms) with a similar absorption spectrum, which is ascribed to the fluorescing species. Fluorescence induced by multiphoton excitation had a lifetime of 910 +/- 10 ps and was also unaffected by ascorbate. In the presence of organic solvents there was an increase in fluorescence lifetime, but a decrease in overall fluorescence intensity. The fluorescence intensity and fluorescence lifetime both decreased in acidic solution (pH < 3). The results indicate that the fluorescence does not originate from the 5-indoxyl radical as previously suggested but from one or more other transient products which require further characterisation.

5-Hydroxytryptophan↗

PubMed2002

One-electron oxidation of "photo-Fenton" reagents and inhibition of lipid peroxidation.

The "photo-Fenton" reagent, 2-mercaptopyridine N-oxide (MPO), which releases a hydroxyl radical on ultraviolet irradiation, has been found to act as an antioxidant. In the peroxidation of linoleate initiated by a water-soluble azo-initiator, MPO has about one-third the activity of the water-soluble vitamin E analogue Trolox C. In contrast, the oxygen-containing analogue, 2-hydroxypyridine N-oxide (HPO), does not have measurable antioxidant activity in this system. Both reagents react with hydroxyl radical with second order rate constants very close to the diffusion-controlled limit. With the less oxidising dithiocyanate radical anion, MPO reacts approximately 50 times more rapidly than HPO at pH>7. The more reducing properties of MPO result in its activity as an antioxidant and make it less suitable than HPO as a source of hydroxyl radicals for investigation of oxidative stress in biological systems.

Antioxidants↗