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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >CH Mode Mixing Determines the Band Shape of the Carboxylate Symmetric Stretch in Apo-EDTA, Ca2+-EDTA, and Mg2+-EDTA
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CH Mode Mixing Determines the Band Shape of the Carboxylate Symmetric Stretch in Apo-EDTA, Ca2+-EDTA, and Mg2+-EDTA

机译：CH模式混合决定了apo-EDTA，CA2 + -EDTA和MG2 + -EDTA中羧酸羧酸盐对称拉伸的带形状

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摘要

The infrared spectra of EDTA complexed with Ca2+ and Mg2+ contain, to date, unidentified vibrational bands. This study assigns the peaks in the linear and two-dimensional infrared spectra of EDTA, with and without either Ca2+ or Mg2+ ions. Two-dimensional infrared spectroscopy and DFT calculations reveal that, in both the presence and absence of ions, the carboxylate symmetric stretch and the terminal CH bending vibrations mix. We introduce a method to calculate participation coefficients that quantify the contribution of the carboxylate symmetric stretch, CH wag, CH twist, and CH scissor in the 1400-1550 cm(-1) region. With the help of participation coefficients, we assign the 1400-1430 cm(-1) region to the carboxylate symmetric stretch, which can mix with CH modes. We assign the 1000-1380 cm(-1) region to CH twist modes, the 1380-1430 cm(-1) region to wag modes, and the 1420-1650 cm(-1) region to scissor modes. The difference in binding geometry between the carboxylate-Ca2+ and carboxylate-Mg2+ complex manifests as new diagonal and cross-peaks between the mixed modes in the two complexes. The small Mg2+ ion binds EDTA tighter than the Ca2+ ion, which causes a redshift of the COO symmetric stretches of the sagittal carboxylates. Energy characterizes the importance of electrostatics and deformation energy in the bound complexes.
机译：EDTA与Ca2+和Mg2+络合的红外光谱迄今为止包含未知的振动带。本研究确定了EDTA的线性和二维红外光谱中的峰，有无Ca2+或Mg2+离子。二维红外光谱和DFT计算表明，在存在和不存在离子的情况下，羧酸盐对称拉伸和末端CH弯曲振动混合。我们介绍了一种计算参与系数的方法，该方法量化了1400-1550 cm（-1）区域内羧酸盐对称拉伸、CH wag、CH扭曲和CH剪刀的贡献。借助参与系数，我们将1400-1430 cm（-1）区域分配给羧酸盐对称拉伸，它可以与CH模式混合。我们将1000-1380厘米（-1）区域分配给CH扭曲模式，将1380-1430厘米（-1）区域分配给wag模式，将1420-1650厘米（-1）区域分配给剪刀模式。羧酸盐-Ca2+和羧酸盐-Mg2+络合物之间结合几何结构的差异表现为两个络合物中混合模式之间的新对角线和交叉峰。小的Mg2+离子与EDTA的结合比Ca2+离子更紧密，这导致矢状羧酸盐的COO对称延伸红移。能量表征了束缚络合物中静电和形变能的重要性。

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