抗壞血酸對二價銅自氧化催化反應之保護作用   全文下載

The Protective Effect of Amino Acids on the Copper(II)—Catalyzed Autoxidation of Ascorbic Acid

抗壞血酸（AA：維生素C）可保護來自二價銅催化之自氧化反應。本研究探討在缺乏和存在二價銅離子時，於室溫及離子強度為0.1（KNO3），在暴露於空氣中的反應條件下，抗壞血酸自氧化情形。八個生物化學上重要氨基酸（丙胺酸、甘胺酸、天門冬胺酸、天門冬醯胺、麩胺酸、麩醯胺、苯丙胺酸和組氨酸）在這個系統上之作用被研究著。在溶液中未氧化的抗壞血酸之濃度，可以分光光度計方法測得氨基酸之CUPRAC（銅離子還原抗氧化能力）。當銅離子被固定時，抗壞血酸減少，氨基酸濃度增加；當氨基酸濃度被固定時，二價銅離子濃度增加，此為自動氧化速率常數。穩定之含銅氨基酸複合物會抑制抗壞血酸之自氧化；組氨酸對銅離子複合物有很高的穩定性，且具有很強之抑制作用。氨基酸可共處於食物及藥物中，可以用於增加維生素C 商品之穩定性。

Protection of ascorbic acid (AA: vitamin C) from Cu(II)-catalyzed autoxidation is an important aspect of antioxidant chemistry. The autoxidation of AA in the absence and presence of Cu(II) ions was investigated in aerated solution at room temperature and I = 0.1 ionic strength (KNO3). Effects of eight biochemically important amino acids (alanine, glycine, aspartic acid, asparagine, glutamic acid, glutamine, phenylalanine, and histidine) on this system were studied. The concentration of unoxidized AA remaining in solution was measured with the CUPRAC (cupric ion reducing antioxidant capacity) spectrophotometric method without interference from the amino acids tested. The autoxidation rate constants of AA decreased with increasing amino acid concentration for fixed Cu, and increased with Cu(II) for fixed amino acid concentrations. Catalytic autoxidation of AA was inhibited by stable Cuamino acid complexes; histidine, having the highest conditional stability constant for its Cu-complex, showed the strongest inhibitive effect. Since amino acids are food and drug compatible compounds, they can be used in commercial products to increase the stability of vitamin C.