Thermochemistry of aqueous hydroxyl radical from advances in photoacoustic calorimetry and ab initio continuum solvation theory.
Thermochemistry of aqueous hydroxyl radical from advances in photoacoustic calorimetry and ab initio continuum solvation theory.
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水性羟基自由基的热化学来自光声量热法和从头开始连续溶剂化理论的进展。
DOI：
10.1021/ja039827u
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发表时间：
2004
影响因子：
15
通讯作者：
April D. Getty
中科院分区：
文献类型：
--
作者：
T. Autrey;A. K. Brown;D. Camaioni;M. Dupuis;Nancy S. Foster;April D. Getty
在10至45 ℃的温度范围内测量来自H2 O2的稀（约30 mM）溶液的光声信号，以获得H2 O2（aq）→ 2 OH（aq）的反应焓和体积变化，我们最终从其确定OH（aq）的Δ fG度、Δ fH度和偏摩尔体积v度。我们发现Δ H = 46.8 +/- 1.4 kcal/mol，比气相键能小4 kcal/mol，Δ Vr = 6.5 +/- 0.4 mL/mol。水中OH的v度为14.4 +/- 0.4 mL/ml：小于水的v度。利用从头算连续介质理论，通过一种新的方法计算出水合自由能为-3.9 +/-0.3千卡/摩尔（对于数密度浓度单位的标准状态），该方法被设计为在溶质腔的定义中捕获溶质与水溶剂分子的强度和特定相互作用。空腔的形状是由“滚动”的三维电子密度等值线的水的从头算水-OH最小相互作用表面上定义的。选择等值线的值以再现水中OH的体积。对于OH（aq），我们得到：Δ fH度= -0.2 +/-1.4和Δ fG度= 5.8 +/-0.4kcal/mol，这与文献值一致。结果提供了信心，在脉冲PAC技术测量水热化学的自由基和开放的方式来获得热化学的OH与水基质的反应，同时推进领域的连续溶剂化理论对从头定义的溶质腔可以形成的大多数自由基。
Photoacoustic signals from dilute ( approximately 30 mM) solutions of H2O2 were measured over the temperature range from 10 to 45 degrees C to obtain the reaction enthalpy and volume change for H2O2(aq) --> 2 OH(aq) from which we ultimately determined DeltafG degrees , DeltafH degrees and partial molal volume, v degrees , of OH (aq). We find DeltarH = 46.8 +/- 1.4 kcal/mol, which is 4 kcal/mol smaller than the gas-phase bond energy, and DeltaVr = 6.5 +/- 0.4 mL/mol. The v degrees for OH in water is 14.4 +/- 0.4 mL/ml: smaller than the v degrees of water. Using ab intio continuum theory, the hydration free energy is calculated to be -3.9 +/- 0.3 kcal/mol (for standard states in number density concentration units) by a novel approach devised to capture in the definition of the solute cavity the strength and specific interactions of the solute with a water solvent molecule. The shape of the cavity is defined by "rolling" a three-dimensional electron density isocontour of water on the ab initio water-OH minimum interaction surface. The value of the contour is selected to reproduce the volume of OH in water. We obtain for OH(aq): DeltafH degrees = -0.2 +/- 1.4 and DeltafG degrees = 5.8 +/- 0.4 kcal/mol that are in agreement with literature values. The results provide confidence in the pulsed PAC technique for measuring aqueous thermochemistry of radicals and open the way to obtaining thermochemistry for most radicals that can be formed by reaction of OH with aqueous substrates while advancing the field of continuum solvation theory toward ab initio-defined solute cavities.