Coordination-Dependent Spectroscopic Signatures of Divalent Metal Ion Binding to Carboxylate Head Groups: H2- and He-Tagged Vibrational Spectra of M2+·RCO2¯ (M = Mg and Ca, R = −CD3, −CD2CD3) Complexes,The Journal of Physical Chemistry Letters

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Coordination-Dependent Spectroscopic Signatures of Divalent Metal Ion Binding to Carboxylate Head Groups: H2- and He-Tagged Vibrational Spectra of M2+·RCO2¯ (M = Mg and Ca, R = −CD3, −CD2CD3) Complexes
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2017-01-11 00:00:00 , DOI: 10.1021/acs.jpclett.6b02964
Joseph W. DePalma ₁ , Patrick J. Kelleher ₁ , Laís C. Tavares ₂ , Mark A. Johnson ₁

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We explore the intramolecular distortions present in divalent metal ion–carboxylate ion pairs using vibrational spectroscopy of the cryogenically cooled, mass-selected species isolated in the gas phase. The spectral signatures of the C–O stretching modes are identified using the perdeutero isotopologues of the acetate and propionate anions to avoid congestion arising from the CH₂ fundamentals. Both Ca²⁺ and Mg²⁺ are observed to bind in a symmetrical, so-called “bidentate” arrangement to the −CO₂¯ group. The very strong deformations of the head groups displayed by the binary complexes dramatically relax when either neutral water molecules or counterions are attached to the Mg²⁺RCO₂¯ cation. These results emphasize the critical role that local coordination plays when using the RCO₂¯ bands to deduce the metal ion complexation motif in condensed media.

中文翻译：

二价金属离子与羧酸根首基结合的配位依赖性光谱学特征：M ₂⁺ ·RCO _2的H _2-和He标记振动光谱（M = Mg和Ca，R = -CD ₃，-CD ₂ CD ₃）配合物

我们使用在气相中分离的低温冷却，质量选择物种的振动光谱研究了二价金属离子-羧酸根离子对中存在的分子内畸变。使用乙酸根和丙酸根阴离子的全氘同位异构体来鉴定C–O拉伸模式的光谱特征，以避免由CH ₂基本原理引起的拥塞。观察到Ca ²⁺和Mg ²⁺均以-CO ₂基对称，所谓的“双齿”排列结合。当中性水分子或抗衡离子附着在Mg ²⁺ RCO _2上时，二元配合物显示的头基团非常强烈的变形会显着放松阳离子。这些结果强调了在使用RCO ₂谱带推导冷凝介质中的金属离子络合基序时，局部配位发挥的关键作用。

更新日期：2017-01-11

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