红外光谱法研究古代彩绘蛋白胶料光老化的二级结构变化

Study on Secondary Structural Changes of Proteinaceous Binding Media in Ancient Polychromy Artwork after Light Aging by FTIR Spectroscopy

动物胶和蛋清是古代重要彩绘文物蛋白胶结材料,对其光老化蛋白质结构变化的研究与探索彩绘文物病变机理和选择科学保护材料、修复方法密切相关。以维也纳艺术历史博物馆的动物胶(骨胶、兔皮胶、鲟鱼胶)和蛋清为研究对象,利用红外光谱技术,结合酰胺Ⅰ带去卷积和高斯拟合法研究光老化过程中蛋白质二级结构的改变。结果表明,四种胶光老化后仍然具备蛋白质红外光谱的典型吸收特征。但红外吸收峰出现了不同程度的位移,其中蛋清糖苷键明显蓝移。酰胺Ⅰ带去卷积和高斯拟合结果显示,蛋白胶的二级结构占比发生了改变。其中,骨胶α-螺旋结构占比降低22.24%,逐渐解螺旋,无规则卷曲结构占比明显增高(9.76%);兔皮胶和鲟鱼胶α-螺旋结构占比分别降低5.31%,4.15%,前者无规则卷曲增幅最低(6.96%),后者反而减少,推测两者的光老化稳定性高。蛋清α-螺旋占比降低程度最高(44.45%),无规则卷曲占比增幅极大(27.49%),光老化稳定性最差。证实利用红外光谱技术,结合酰胺Ⅰ带去卷积和高斯拟合法研究文物蛋白胶料二级结构变化的方法是可行的,但其转化机理还需后期进一步探讨。

Animal glue and egg white are important proteinaceous binding media of ancient polychromy artworks, and the research of their structural changes caused by light aging is highly related to the exploration of pathological changes mechanism as well as the selection of scientific materials and proper conservative methods.Regarding the animal glues（bone,rabbit skin,sturgeon） and egg white in Kunsthistorisches Museum Vienna as the study objects,this paper aimed at studying the protein secondary structure changes after light aging by Fourier transform infrared spectroscopy（FTIR）with the help of deconvolved Amide I and Gaussian fitting method.Results illustrated that the four binders still possessed the typical FTIR spectra characteristics after light aging in spite of some peaks shift,among which glycosidic bond in egg white showed an obvious blue shift.Moreover,deconvolved Amide I and Gaussian fitting results indicated that the contents ofα-helix,parallelβ-sheets,anti-parallelβ-sheets,β-turns and r and om coils of each binder varied after the light aging.To be specific,α-helix＇s content of the bone decreased22.24% but r and om coils increased 9.76%,which deduced the uncoiling of theα-helix caused by light.Theα-helix＇s contents of the rabbit skin and sturgeon reduced 5.31% and 4.15% respectively, and r and om coils content of the former showed the minimum growth（6.96%）while that of the latter decreased.Thus,these two were supposed to be of high stability versus light.Egg white showed the poorest light stability due to the highest reduction ofα-helix（44.45%） and obvious rise of r and om coils（27.49%）.In addition,the anti-parallelβ-sheets＇ contents of all the binders increased while theβ-turns kept stable.Parallelβ-sheets showed a decline trend among all the binders except the sturgeon glue.This research confirmed the feasibility of studying the proteinaceous binders＇ secondary structure changes by deconvolved Amide I,Gaussian fitting method and FTIR spectroscopy,which was proved to be a promising method in studying the aging phenomenon of the proteinaceous binders in artworks.However,the transformation mechanism needs further explorations.