Bergami Mateus, Charry Jorge, Reyes Andres, Coutinho Kaline, Varella Márcio T do N
Instituto de Física, Universidade de São Paulo, Rua do Matão 1371, CEP 05508-090 São Paulo, SP, Brazil.
Department of Physics and Materials Science, University of Luxembourg, L-1511 Luxembourg City, Luxembourg.
J Phys Chem B. 2024 Oct 17;128(41):10178-10188. doi: 10.1021/acs.jpcb.4c03627. Epub 2024 Oct 9.
We performed a computational study of positron attachment to hydrated amino acids, namely glycine, alanine, and proline in the zwitterionic form. We combined the sequential quantum mechanics/molecular mechanics (s-QM/MM) method with various levels of any particle molecular orbital (APMO) calculations. Consistent with previous studies, our calculations indicate the formation of energetically stable states for the isolated and microsolvated amino acids, in which the positron localizes around the carboxylate group. However, for the larger clusters, composed of 7 to 40 water molecules, hydrogen bonding between the solute and solvent molecules disfavors positron attachment to the amino acids, giving rise to surface states in which the positron is located around the water-vacuum interface. The analysis of positron binding energies, positronic orbitals, radial probability distributions, and annihilation rates consistently pointed out the change from positron-solute to positron-solvent states. Even with the inclusion of an electrostatic embedding around the aggregates, the positrons did not localize around the solute. Positron attachment to molecules in the gas phase is a well-established fact. The existence of hydrated positronic molecules could also be expected from the analogy with transient anion states, which are believed to participate in radiation damage. Our results indicate that positron attachment to hydrated biomolecules, even to zwitterions with negatively charged carboxylated groups, would not take place. For the larger clusters, in which positron-water interactions are favored, the calculations indicate an unexpectedly large contribution of the core orbitals to the annihilation rates, between 15 and 20%. Finally, we explored correlations between positron binding energies (PBEs) and dipole moments, as well as annihilation rates and PBEs, consistent with previous studies for smaller clusters.
我们对正电子与两性离子形式的水合氨基酸（即甘氨酸、丙氨酸和脯氨酸）的附着进行了计算研究。我们将顺序量子力学/分子力学（s-QM/MM）方法与不同水平的任意粒子分子轨道（APMO）计算相结合。与先前的研究一致，我们的计算表明，孤立的和微溶剂化的氨基酸会形成能量稳定状态，其中正电子定位于羧酸根基团周围。然而，对于由7至40个水分子组成的较大团簇，溶质和溶剂分子之间的氢键不利于正电子附着于氨基酸，从而产生正电子位于水 - 真空界面周围的表面态。对正电子结合能、正电子轨道、径向概率分布和湮灭率的分析一致指出了从正电子 - 溶质态到正电子 - 溶剂态的变化。即使在聚集体周围包含静电嵌入，正电子也不会定位于溶质周围。正电子附着于气相中的分子是一个既定事实。从与被认为参与辐射损伤的瞬态阴离子态的类比中，也可以预期水合正电子分子的存在。我们的结果表明，正电子不会附着于水合生物分子，甚至不会附着于带有带负电荷羧基化基团的两性离子。对于正电子 - 水相互作用占优的较大团簇，计算表明核心轨道对湮灭率有意外大的贡献，在15%至20%之间。最后，我们探索了正电子结合能（PBEs）与偶极矩之间的相关性，以及湮灭率与PBEs之间的相关性，这与先前对较小团簇的研究一致。
