Malysheva Lyuba, Onipko Alexander, Valiokas Ramunas, Liedberg Bo
Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine, Division of Physics, Luleå University of Technology, S-971 87 Luleå, Sweden.
J Phys Chem B. 2005 Jul 14;109(27):13221-7. doi: 10.1021/jp0503765.
First-principle modeling is used to obtain a comprehensive understanding of infrared reflection absorption (RA) spectra of helical oligo(ethylene glycol) (OEG) containing self-assembled monolayers (SAMs). Highly ordered SAMs of methyl-terminated 1-thiaoligo(ethylene glycols) [HS(CH2CH2O)(n)CH3, n = 5, 6] on gold recently became accessible for systematic infrared analyses [Vanderah et al., Langmuir, 2003, 19, 3752]. We utilized the quoted experimental data to validate the first-principle modeling of infrared RA spectra of HS(CH2CH2O)(5,6)CH3 obtained by (i) DFT methods with gradient corrections (using different basis sets, including 6-311++G) and (ii) HF method followed by a Møller-Plesset (MP2) correlation energy correction. In focus are fundamental modes in the fingerprint and CH-stretching regions. The frequencies and relative intensities in the calculated spectra for a single molecule are unambiguously identified with the bands observed in the experimental RA spectra of the corresponding SAMs. In addition to confirming our earlier assignment of the dominating peak in the CH-stretching region to CH2 asymmetric stretching vibrations, all other spectral features observed in that region have received an interpretation consistent (but not in all cases coinciding) with previous investigations. The obtained results provide an improved understanding of the orientation and conformation of the molecular building blocks within OEG-containing assemblies, which, in our opinion, is crucial for being able to predict the folding and phase characteristics and interaction of OEG-SAMs with water and proteins.
第一性原理建模用于全面理解含螺旋状低聚乙二醇（OEG）的自组装单分子层（SAMs）的红外反射吸收（RA）光谱。最近，金表面甲基封端的1-硫代低聚乙二醇[HS(CH2CH2O)(n)CH3, n = 5, 6]的高度有序自组装单分子层可用于系统的红外分析[范德阿等人，《朗缪尔》，2003年，19卷，3752页]。我们利用所引用的实验数据来验证通过以下方法获得的HS(CH2CH2O)(5,6)CH3红外RA光谱的第一性原理建模：（i）采用梯度校正的密度泛函理论（DFT）方法（使用不同的基组，包括6-311++G），以及（ii）哈特里-福克（HF）方法，随后进行莫勒-普莱塞特（MP2）相关能校正。重点关注指纹区和CH伸缩振动区的基模。计算得到的单个分子光谱中的频率和相对强度与相应自组装单分子层的实验RA光谱中观察到的谱带明确对应。除了证实我们先前将CH伸缩振动区的主导峰归属于CH2不对称伸缩振动外，在该区域观察到的所有其他光谱特征都得到了与先前研究一致（但并非在所有情况下都吻合）的解释。所获得的结果有助于更好地理解含OEG组装体中分子结构单元的取向和构象，我们认为这对于预测OEG-自组装单分子层的折叠、相特征以及与水和蛋白质的相互作用至关重要。
