丝织品是由丝蛋白质组成, 高温、 高湿及污染物等因素会使其结构发生变化。 为了科学地评估博物馆中污染气体对丝织品结构的影响, 采取人工模拟实验制备二氧化氮、 二氧化硫、 乙酸和氨气常见博物馆污染气体环境, 利用傅里叶红外光谱(FTIR)从丝蛋白质肽链结构、 二级结构等方面探讨4种污染气体对丝织品蛋白质结构的影响。 实验结果表明, 二氧化氮老化30 h后样品的红外光谱在1 382 cm-1波数附近出现甲基对称变角振动吸收峰, 而其他气体老化50 d的丝织品仍未产生甲基对称变角振动, 说明二氧化氮对丝织品破坏最严重。 所有污染气体老化后, 样品的红外光谱在975和999 cm-1丝蛋白-Gly-Ala-和-Gly-Gly-肽链(一级)结构特征吸收峰处均有不同程度减弱, 但碱性气体氨气较酸性气体减弱更明显。 傅里叶红外光谱技术结合酰胺Ⅲ带(1 330～1 200 cm-1)去卷积和高斯拟合法研究表明, 50 d氨老化后仅引起丝蛋白质非结晶区的轻微变化, α-螺旋、 无规卷曲、 β-折叠含量变化幅度较小, 丝蛋白二级结构变化较小。 相比而言, 酸性气体对丝蛋白二级结构影响更加显著, 出现β-折叠相对含量大幅降低、 无规卷曲相对含量明显增加, 其结晶区遭受严重破坏。 在4种气体中, 二氧化氮对丝织品二级结构影响最显著, 老化30 h后β-折叠相对含量由原始值30.36%降低至18.12%, 约降低40%。 相应的二氧化氮对丝织品强度破坏最严重, 在β-折叠含量降低的同时, 材料的力学强度出现了显著降低。 利用波数在1 700和1 640 cm-1红外光谱吸收峰的比值(A1 700/1 640)和波数在1 620和1 514 cm-1红外光谱吸收峰的比值(A1 620/1 514)判断样品的老化方式, 实验结果表明二氧化氮、 二氧化硫、 氨气老化样品的方式主要为氧化老化, 而乙酸老化的样品则发生氧化老化和水解老化两种老化方式。 随着老化时间的延长, 4种气体中二氧化氮老化样品的A1 620/1 514比值增加最多、 氧化最严重。 推断与二氧化氮的强氧化性有关, 也与二氧化氮使丝织品产生显著的甲基对称变角振动有关。 建议博物馆应严格监测和控制二氧化氮气体浓度。 该研究为制定合理的丝织品文物存放环境提供科学依据, 对丝织品文物的保护具有重要意义。

As silk is made up of proteins, their structures are easy to be changed by high temperature, high humidity, pollutants and other factors. In order to scientifically evaluate the influence of pollutant gases on silk fabrics structures, artificial simulated experiments were conducted to prepare common pollutant gas environments in museums, including nitrogen dioxide, sulfur dioxide, acetic acid and ammonia. The effects of the four kinds of pollutant gases on protein peptides, secondary structures and other aspects were investigated using Fourier transform infrared spectroscopy (FTIR). The experimental results showed that for silk fabrics aging with nitrogen dioxide for 30 h, there arose the peak of the methyl symmetric deformation vibration, near 1 382 cm-1, which did not appear on the samples aging with other gases for 50 days. It was shown that nitrogen dioxide had the most serious damage to silk fabrics. After aging with all pollutant gases, the absorption peaks of -Gly-Ala- and -Gly-Gly-peptide chains (primary structure) at 975 and 999 cm-1 were all reduced in varying degrees, but the effect of the alkaline gas ammonia on the peptide chains was more obvious than that of other acidic gases. The deconvolution of the amide Ⅲ band (1 330～1 200 cm-1) and Gaussian fitting results showed that the samples aging with ammonia for 50 days had only slight changes in the amorphous region with slight content changes of α-helix, random coil and β-sheet, and the secondary structures of silk protein did not change much. In comparison with ammonia, acid gases had a significant influence on the secondary structures of silk protein. The relative content of β-sheet was greatly reduced with that of random coils increasing significantly, and the crystalline region was damaged seriously. Among the four gases, nitrogen dioxide has the most significant effect on secondary structures of silk fabrics. The relative content of β-sheets decreased from 30.36% to 18.12% after 30 hours’ aging, which reduced about 40%. The nitrogen dioxide had the most serious damage to the strength of silk fabrics. With the declining of the β-sheet, the mechanical strength of the material decreased. The ratios of infrared absorption peaks at different wavenumbers A1 700/1 640 and A1 620/1 514 were used to judge the aging modes. Oxidation reaction occurred mainly to the samples aging with nitrogen dioxide, sulfur dioxide, and ammonia. Both oxidation and hydrolysis reaction happened to the samples aging with acetic acid. With the increase of aging time, the ratio of A1 620/1 514 of the samples aged with nitrogen dioxide increased most among the four gases and the oxidation was the most severe. It was inferred that it was related to the strong oxidizing property of nitrogen dioxide, also associated with the significant methyl symmetry vibration occurring of the silk fabric aging with nitrogen dioxide. It is suggested that the concentration of nitrogen dioxide gas should be strictly monitored and controlled in museums. This study provides a scientific basis for formulating a reasonable storage environment for silk cultural relics, and is of great significance to the protection of silk cultural relics.