Matrix Isolation of Free Radicals from Carbohydrates

Summary

Photolytically produced H·-atoms in 6 mol dm⁻³ H₂SO₄/H₂O glasses trapped at 77 K react upon annealing to 130 K with dissolved carbohydrates to form carbon-located free radicals by abstraction of carbon-bound protons. Analysis of electron spin resonance (e.s.r.) spectra at various annealing stages from α- and β-d-glucose together with 6,6-d₂-d-glucose, 6-deoxy-d-glucose, 2-deoxy-d-glucose, glucose-1-phosphate, d-xylose, d-allose and d-mannose indicates radical formation at all possible carbon sites with a strong preference for C1 and a somewhat enhanced contribution of C4 over the statistical expectation. The corresponding component spectra are analysed either by spectra isolation or simulation and their parameters are given. Intramolecular radical transformation at temperatures of 140–160 K is explained by acid-catalysed H₂O-elimination. The findings are discussed in relation to the radiation-chemistry of aqueous glucose solutions. We thus show that the system of photolysed Fe²⁺ in acidic glasses at low temperatures containing 10 mmol dm⁻³ carbohydrate is suitable for studying H (D·)-reactions by means of e.s.r. spectroscopy. Unlike previously used glasses containing carbohydrates, contributions of oxidation and reduction by direct effects or mixtures of direct and indirect effects and phase-effects due to incomplete glass formation are avoided.

• electron spin
• resonance
• aqueous glasses
• H-reactions
• carbohydrates