Zou Ye, Ma Gang
Key Laboratory of Medicinal Chemistry and Molecular Diagnosis of Ministry of Education, College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China.
Int J Mol Sci. 2014 Jun 4;15(6):10018-33. doi: 10.3390/ijms150610018.
Second derivative and Fourier self-deconvolution (FSD) are two commonly used techniques to resolve the overlapped component peaks from the often featureless amide I band in Fourier transform infrared (FTIR) curve-fitting approach for protein secondary structural analysis. Yet, the reliability of these two techniques is greatly affected by the omnipresent water vapor in the atmosphere. Several criteria are currently in use as quality controls to ensure the protein absorption spectrum is negligibly affected by water vapor interference. In this study, through a second derivative study of liquid water, we first argue that the previously established criteria cannot guarantee a reliable evaluation of water vapor interference due to a phenomenon that we refer to as sample's absorbance-dependent water vapor interference. Then, through a comparative study of protein and liquid water, we show that a protein absorption spectrum can still be significantly affected by water vapor interference even though it satisfies the established criteria. At last, we propose to use the comparison between the second derivative spectra of protein and liquid water as a new criterion to better evaluate water vapor interference for more reliable second derivative and FSD treatments on the protein amide I band.
二阶导数和傅里叶自去卷积（FSD）是在蛋白质二级结构分析的傅里叶变换红外（FTIR）曲线拟合方法中，用于从通常无特征的酰胺I带中解析重叠成分峰的两种常用技术。然而，这两种技术的可靠性受到大气中普遍存在的水蒸气的极大影响。目前有几种标准用作质量控制，以确保蛋白质吸收光谱受水蒸气干扰的影响可忽略不计。在本研究中，通过对液态水的二阶导数研究，我们首先指出，由于一种我们称为样品吸光度依赖性水蒸气干扰的现象，先前建立的标准不能保证对水蒸气干扰进行可靠评估。然后，通过对蛋白质和液态水的比较研究，我们表明，即使蛋白质吸收光谱满足既定标准，它仍然会受到水蒸气干扰的显著影响。最后，我们建议将蛋白质和液态水的二阶导数光谱之间的比较作为一种新的标准，以更好地评估水蒸气干扰，从而对蛋白质酰胺I带进行更可靠的二阶导数和FSD处理。
