Design Of The Biomimetic Antioxidation System And Its Stability

Plants grow in the aerobic environment. There are many kinds of oxygen-containing organic compounds（such as aldehydes, ketones, carboxylic acids, esters） in plants’ body, and there are a variety of reactions catalyzed by bio-enzymes. Most of bio-enzymes are proteins, which are made up of amino acid chains, but the amino-groups are susceptible to oxidation. In addition, a plant can’t grow well without sunlight. Sunlight can not only provide energy for the growth and metabolism of plants, but also can be used as excitation signals in a variety of physiological processes, which makes it one of the most important environmental factors. However, in the metabolic process, O₂ is easy to be transformed into H₂O₂, hydroxyl radicals, superoxide or other oxidizing species under a light condition, resulting in the inactivation of bio-enzymes. So the presence of antioxidant system is the assurance of the enzyme-catalyzed reactions under the biological conditions.An evergreen plant can keep evergreen throughout the year in the existence of the microelements（or micronutrients） and organic acids. Therefore, microelements, organic acids were chosen as the components to constitute biomimetic antioxidant system, and their roles in antioxidation were investigated. The main conclusions are as follows:In the leaves of three evergreen plants, the contents of iron and zinc are higher in old leaves than those in newborn ones, while the content of manganese is higher in newborn leaves than those in old ones. Acetic acid, salicylic acid, malic acid, tartaric acid, citric acid, oxalic acid and fumaric acid were found in all leaves of Chinese ilex（a kind of hollies）. In the range of ultraviolet-visible light wavelength, Fe³⁺-salicylic acid complex has greater absorbance than Fe³⁺-tartaric acid complex, and its maximum absorption appears in the range of wavelength of 520-530 nm. With the saturation method（molar ratio）, the complexation ratio of Fe³⁺ to salicylic acid is determined to be 2:1. The complexing ability of tartaric acid with Fe³⁺/Fe²⁺ is stronger than that of salicylic acid with Fe³⁺/Fe²⁺.A biomimetic antioxidant system was preliminarily designed, in which tartaric acid formed a complex with Fe³⁺/Fe²⁺ in the proportion of 20:1. It exists stable in the KH₂PO₄ / K₂HPO₄ buffer solution in the range of p H 5⁷. A certain amount of boric acid is helpful to its stability. The Fe³⁺/Fe²⁺–tartaric acid system could efficiently catalyze the decomposition of oxidizing substances H₂O₂ formed under sunlight condition, and thus showed certain stability under sunlight. Fe³⁺/ Fe²⁺–tartaric acid system showed a low electrode potential, suggesting that it has strong reducing ability. Therefore it was easy to consume reactive oxygen species, and exhibited redox stability.