Reaction of B-Carotene with Nitrite Anion in a Homogenous Acid System. An Electron Paragmagetic Resonance and Ultraviolet-Visible Study

” S.N. MENDIARA, R.P. BAQUERO, M.R. KATUNAR, A.Y. MANSILLA, AND L.J. PERISINOTTI

APPLIED MAGNETIC RESONANCE

SPRINGER WIEN

Año: 2009 vol. 35 p. 549 - 567

0937-9347

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US;} span.abstractheading {mso-style-name:abstractheading;} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Abstract  Ultraviolet and visible spectroscopy was applied to characterize and to measure the concentration of β-carotene dissolved in a dioxane and water mixture. The reaction of β-carotene in the presence of nitrite anion and acid medium was studied at different temperatures. The reaction systems were homogeneous and were kept anaerobic. Pseudo-first-order rate constants in respect of β-carotene were measured in the range from 293 to 313 K and pH 5.8 ± 0.2. The energy of activation was calculated to be E a = 67.2 ± 3.4 kJ/mol. We interpolate a value that may have biological interest, kβ-carotene(310 K) = (9.70±0.78) · 10−3 s−1, in the presence of 9.3 · 10−3 M nitrite anion. Electron paramagnetic resonance spectroscopy was applied to characterize and quantify a persistent intermediate radical generated in the reaction system described. The recorded spectra showed triplet-type signals with a peak-to-peak value of 12.7 G. Nearly the same triplet radical-type intermediates were detected when studying the following reaction systems in pure dioxane: nitrogen dioxide (NO2)/β-carotene, nitric oxide (NO)/β-carotene and NO/NO2/β-carotene. Therefore, we proposed that the nitrogen oxides have also been intermediates in the reaction system of β-carotene, nitrite anion and acid medium, in the dioxane and water mixture. A mechanism was proposed and checked by employing the chemical kinetics simulation. The explanations developed would lead to a better understanding of the behavior of carotenoids in the presence of nitrite anion and nitrogen oxides.