在水溶液中的离子-π相互作用的热力学
Paloma Arranz-Mascarós1, Carla Bazzicalupi, Antonio Bianchi
1Department of Inorganic and Organic Chemistry, University of Jaen, 23071, Jaen, Spain.
Journal of the American Chemical Society
|December 25, 2012
概括
阳离子-π相互作用为水中的带电分子提供了显著的稳定性,由而不是热驱动. 这些相互作用对于理解分子结合和复杂形成至关重要.
科学领域:
- 超分子化学 超分子化学
- 物理化学 物理化学
- 晶体学 晶体学是指结晶学.
背景情况:
- 阳离子识别在生物和化学系统中至关重要.
- 了解像离子-π这样的非共价相互作用是设计分子受体的关键.
- 酸氨基胺衍生物作为充电物种的潜在受体.
研究的目的:
- 为了研究离子与酸氨基胺体受体结合背后的热力学驱动力.
- 量化-π相互作用对结合稳定性的贡献.
- 通过结晶学分析阐明这些相互作用的结构基础.
主要方法:
- 电位计定位用于确定约束常数和热力学参数.
- 异热定位热量计 (ITC) 用于精确测量结合热力学.
- 用X射线晶体学来确定受体-阴离子复合体的固态结构.
主要成果:
- 阳离子-π 相互作用对结合的自由能量贡献大约 -10 kJ/mol.
- 结合在很大程度上是无热的,具有显著的有利的热贡献 (TΔS°).
- 晶体结构显示出一个短的CN···中心距离 (2.786(3) Å),表明强烈的阴离子-π相互作用.
结论:
- 阳离子-π 相互作用是水溶液中高电荷阳离子的显著稳定力.
- 观察到的热有利性表明,在结合时,水结构的破坏减少了.
- 这项研究提供了结构和热力学证据,证明通过离子-π相互作用有效地识别离子.
相关概念视频
Ionic Association
The ionic association is the association of oppositely charged ions in an electrolyte solution to form ion pairs. Bjerrum defined ion pairs as two oppositely charged ions whose electrostatic attraction exceeds the thermal energy of the system, typically expressed as 2kT. Electrostatic attraction depends on ionic charge, separation distance, and the dielectric constant of the medium. Thermal energy, represented by kT, reflects the tendency of ions to move independently due to molecular motion.
Aqueous Solutions and Heats of Hydration
Water and other polar molecules are attracted to ions. The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
Intermolecular Forces
Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Ions as Acids and Bases
Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
Polyprotic Acids
Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:


