Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy.
J Chem Phys. 2012 Aug 21;137(7):075102. doi: 10.1063/1.4746390.
We present density functional theory (DFT) and quantum Monte Carlo (QMC) calculations of the glutamic acid and glutamate ion in vacuo and in various dielectric continuum media within the polarizable continuum model (PCM). In DFT, we employ the integral equation formalism variant of PCM while, in QMC, we use a PCM scheme we have developed to include both surface and volume polarization. We investigate the gas-phase protonation thermochemistry of the glutamic acid using a large set of structural conformations, and find that QMC is in excellent agreement with the best available theoretical and experimental results. For the solvated glutamic acid and glutamate ion, we perform DFT calculations for dielectric constants, ε, between 4 and 78. We find that the glutamate ion in the zwitterionic form is more stable than the non-zwitterionic form over the whole range of dielectric constants, while the glutamic acid is more stable in its non-zwitterionic form at ε = 4. The dielectric constant at which the two glutamic acid species have the same energy depends on the cavity size and lies between 5 and 12.5. We validate these results with QMC for the two limiting values of the dielectric constant, and find qualitative agreement with DFT even though the solvent polarization is less pronounced at the QMC level.
我们提出了在真空中以及在极化连续体模型（PCM）中的各种介电连续体介质中谷氨酸和谷氨酸离子的密度泛函理论（DFT）和量子蒙特卡罗（QMC）计算。在 DFT 中，我们采用 PCM 的积分方程形式变体，而在 QMC 中，我们使用我们开发的 PCM 方案来包括表面和体积极化。我们使用大量结构构象研究了谷氨酸的气相质子化热化学，并发现 QMC 与最可用的理论和实验结果非常吻合。对于溶剂化的谷氨酸和谷氨酸离子，我们在介电常数ε为 4 到 78 之间进行了 DFT 计算。我们发现，在整个介电常数范围内，两性离子形式的谷氨酸离子比非两性离子形式更稳定，而在ε=4 时，谷氨酸则更稳定。两种谷氨酸物种具有相同能量的介电常数取决于腔的大小，并且在 5 到 12.5 之间。我们使用 QMC 对两种介电常数的极限值验证了这些结果，并且即使在 QMC 水平下溶剂化的极化程度较低，也发现了与 DFT 的定性一致。
