利用红外光谱评价文物微环境中有机酸对蚕丝纤维化学结构影响

研究文物微环境污染因素对文物材料影响是分析文物老化原因和妥善保存文物的重要基础。利用红外光谱(FTIR/ATR)剖析了文物微环境中甲酸、乙酸气体对蚕丝纤维结构影响。结果表明:低浓度甲酸气体能减弱纤维分子内氢键,使酰胺Ⅰ(1 617cm-1)谱峰减弱、酰胺Ⅱ谱峰(1 515cm-1)变窄、无规线团构象的酰胺Ⅲ谱峰(1 230cm-1)增强、纤维结晶度下降;当浓度高于8.1mg.m-3时,呈β-折叠构象的肽链段(GlyAla)n特征谱峰(1 000,975cm-1)增强、纤维结晶度提高。分析认为呈无规线团构象的短肽链发生β-折叠构象转变。乙酸气体对酰胺Ⅰ和酰胺Ⅱ谱峰影响不明显,但能引起无规线团构象增加和纤维结晶度降低,其作用弱于甲酸气体。本研究为进一步分析丝织品保存环境污染物的危害作用提供基础数据。

Infrared spectroscopy investigation on conformational change of silk fiber induced by gaseous organic acids existing in museum

Study on the impact of pollutants on cultural materials in storing or displaying micro-environment in museum is considered as very important for the preservation of cultural relics and its aging prevention. This paper applied the Fourier transform infrared (attenuated total reflection) technique to assess silk structural changes under volatile organic acids (formic acid/acetic acid), which usually come from decorative materials emission and commonly exist in the surface or around cultural materials. The focus of this work was on investigating the changes of peptide bond in the area of amide I-amide III, as well as the peptide chains (GlyAla), characteristic region. The structural and conformational changes in silk fiber treated with gaseous formic and acetic acid were assessed. The results indicate that both the gaseous acids can weaken the intermolecular hydrogen bond in fiber peptide, based on the spectral changes in the increased intensity of amide I (1 617 cm(-1)), the narrowing amide II peak (1 515 cm(-1)), the increased intensity of random coil conformation in amide III peak (1 230 cm(-1)), and the decreased fiber crystallinity as well. The obvious secondary structural conformation occurred when the concentration of gaseous formic acid reached 8.1 mg x m(-3) in simulated environment. The conformational transformation was supported by the observation of the rapidly reduced random coil conformation, the increased short peptide chains (GlyAla)n with beta-sheet conformation characteristic peak (1 000, 975 cm(-1)), and the enhanced fiber crystallinity degree as well. In contrast, gaseous acetic acid has less impact on the amide I and amide II bond based on the spectral changes, but it did promote random coil conformation and decreased fiber crystallinity. This work also provides a potential application of the infrared spectroscopy in non-destructive investigation of silk in-situ.