Spectrochemical characterization of L-Histidine in simulated body fluid

M. O. Iwunze; Adedunni Adeyemo

doi:10.1117/12.632665

24 October 2005 Spectrochemical characterization of L-Histidine in simulated body fluid

M. O. Iwunze, Adedunni Adeyemo

Proceedings Volume 6017, Nanophotonics for Communication: Materials and Devices II; 60170M (2005) https://doi.org/10.1117/12.632665
Event: Optics East 2005, 2005, Boston, MA, United States

Abstract

L-Histidine is a naturally occurring essential amino acid. In addition it is biologically important in the dismutation of superoxide radical (O₂^-.) by superoxide dismutase (SOD). In this work, fluorescence and absorptiometric techniques are used to characterize the photo-phenomena of this compound in a simulated body fluid (SBF). In this medium L-histidine fluoresces at 458 nm when excited at 390 nm. Its wavelength of maximum absorbance, λ_max, was observed at 272 nm and a molar absorptivity, ε, of 1.50 x 10³/M-cm. This absorptiometric data suggest that L-histidine undergoes an n→π* electronic transition reaction in an SBF medium. The observed bimolecular quenching rate constant, k_q, of 1.68 x 10⁸/M-s, by hydrogen peroxide as quencher, suggests a non-diffusional quenching but rather an activation-controlled mechanism with a rate constant, ka, of 1.68 x 10⁸/M-s and an electron transfer rate constant of 3.65 x 10⁸/s. A quantum yield, Φ_f, of 0.09 and a fluorescence lifetime of 12.2 ns, respectively, were determined. The observed radiative and non-radiative rate constants, k_r and k_nr, of 7.38 x 10⁶/s and 7.46 x 10⁷/s, respectively, suggest that the deactivation of the thermally excited L-histidine is mainly through a non-radiative route rather than by normal fluorescence, which can account for the low quenching constant, KSV, of 2.13/M that was obtained. The solvent reorganization energy, λ_s, and the reaction free energy change, ΔG, of 1.48 eV and -2.47 eV, respectively, suggest that the electron transfer reaction in the L-histidine-H₂O₂ reaction in SBF medium is through a solvent separated mechanism.

Citation Download Citation

M. O. Iwunze and Adedunni Adeyemo "Spectrochemical characterization of L-Histidine in simulated body fluid", Proc. SPIE 6017, Nanophotonics for Communication: Materials and Devices II, 60170M (24 October 2005); https://doi.org/10.1117/12.632665

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