Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria.
J Chem Theory Comput. 2020 Jul 14;16(7):4443-4453. doi: 10.1021/acs.jctc.0c00204. Epub 2020 Jun 9.
For more than half a century computer simulations were developed and employed to study ensemble properties of a wide variety of atomic and molecular systems with tremendous success. Nowadays, a selection of force-fields is available that describe the interactions in such systems. A key feature of force-fields is an adequate description of the electrostatic potential (ESP). Several force-fields model the ESP via point charges positioned at the atom centers. A major shortcoming of this approach, its inability to model anisotropies in the ESP, can be mitigated using additional charge sites. It has been shown that nitrogen is the most problematic element abundant in many polymers as well as large molecules of biological origin. To tackle this issue, small organic molecules containing a single nitrogen atom were studied. In performing rigorous scans of the surroundings of these nitrogen atoms, positions where a single extra charge can enhance the ESP description the most were identified. Significant improvements are found for ammonia, amines, and amides. Interestingly, the optimal location for the extra charge does not correlate with the chemically intuitive position of the nitrogen lone pair. In fact, the placement of an extra charge in the lone-pair location does not lead to significant improvements in most cases.
半个多世纪以来，计算机模拟技术得到了极大的发展和应用，成功地研究了各种原子和分子体系的集合性质。如今，已经有一系列的力场可以用来描述这些体系中的相互作用。力场的一个关键特征是对静电势（ESP）的充分描述。有几种力场通过位于原子中心的点电荷来模拟 ESP。这种方法的一个主要缺点是无法模拟 ESP 的各向异性，可以通过增加额外的电荷点来减轻这种缺点。已经表明，氮是许多聚合物以及生物来源的大分子中含量丰富的最具问题的元素。为了解决这个问题，研究了含有单个氮原子的小分子有机化合物。在对这些氮原子周围环境进行严格扫描时，确定了可以最大程度提高 ESP 描述的单个额外电荷的位置。在氨、胺和酰胺方面发现了显著的改进。有趣的是，额外电荷的最佳位置与氮孤对的化学直觉位置没有相关性。实际上，在孤对位置放置额外电荷在大多数情况下并不能带来显著的改进。
