对形状限制对超分子有效度的影响的量化
Harry Adams1, Elena Chekmeneva, Christopher A Hunter
1Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom.
Journal of the American Chemical Society
|January 31, 2013
概括
这项研究量化了分子灵活性对超分子复合体稳定性的影响. 在甲-胺复合体中结旋转自由显著降低了结合亲和力,突出了限制运动的能量成本.
科学领域:
- 超分子化学 超分子化学
- 物理有机化学 有机化学
- 化学热力学化学热力学
背景情况:
- 色氨酸-氨酸复合体为研究非共价相互作用提供了一个模型系统.
- 内部分子键在稳定超分子组件方面发挥着至关重要的作用.
- 化学双突变循环是剖析结合能量贡献的强大工具.
研究的目的:
- 量化甲-二复合体中的分子内键的自由能量贡献.
- 为了确定分子内相互作用的有效度 (EM).
- 研究分子灵活性和溶剂极性对复杂稳定性的影响.
主要方法:
- 在烯和1,1,2,2-四乙烯 (TCE) 中测量了一系列96个甲-联结体复合物的关联常数.
- 构建64个化学双突变循环,以评估自由能量贡献.
- 通过比较分子内和分子间的结合常数来确定有效的度 (EM).
主要成果:
- 发现分子内H键的有效度 (EM) 独立于H键受体类型 (胺基与) 和溶剂 (托与TCE).
- 扭转自由度增加的体表现出EM值,比刚性对应物低一个数量级.
- 在超分子复合体中限制转子的能量成本被确定为大约5kJ/mol.
结论:
- 分子灵活性对超分子复合体的稳定性产生重大影响,限制运动会产生相当大的能量损失.
- 该方法为评估复杂分子系统中的非共价相互作用提供了强大的框架.
- 了解形状限制的能量成本对于设计新型超分子材料和催化剂至关重要.
相关概念视频
01:27Determination of Molar Masses of Polymers II
Polymer samples typically consist of macromolecular chains with a distribution of lengths, resulting in a range of molar masses rather than a single discrete value. Conventional descriptors such as the number-average molar mass and weight-average molar mass quantify this distribution but do not fully capture polymer behavior in solution..The viscosity-average molar mass provides a more realistic description of polymer behavior in solution because it accounts for the enhanced contribution of...
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
03:12Freezing Point Depression and Boiling Point Elevation
Boiling Point Elevation
The boiling point of a liquid is the temperature at which its vapor pressure is equal to ambient atmospheric pressure. Since the vapor pressure of a solution is lowered due to the presence of nonvolatile solutes, it stands to reason that the solution’s boiling point will subsequently be increased. Vapor pressure increases with temperature, and so a solution will require a higher temperature than will pure solvent to achieve any given vapor pressure, including one...
The boiling point of a liquid is the temperature at which its vapor pressure is equal to ambient atmospheric pressure. Since the vapor pressure of a solution is lowered due to the presence of nonvolatile solutes, it stands to reason that the solution’s boiling point will subsequently be increased. Vapor pressure increases with temperature, and so a solution will require a higher temperature than will pure solvent to achieve any given vapor pressure, including one...
02:48Expressing Solution Concentration
A solute is a component of a solution that is typically present at a much lower concentration than the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
Concentrations may be quantitatively assessed using a wide variety of measurement units, each convenient for particular applications. Molarity (M) is a useful concentration unit for many applications in chemistry.
Concentrations may be quantitatively assessed using a wide variety of measurement units, each convenient for particular applications. Molarity (M) is a useful concentration unit for many applications in chemistry.
01:15¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
01:24Determination of Molar Masses of Polymers I
Polymerization produces macromolecules with a range of chain lengths due to the random nature of molecular growth processes. As chains form and terminate at different stages, a single polymer sample contains molecules of varying sizes rather than a uniform structure. This variability is described using average molar masses and distribution-related parameters, which together provide a comprehensive understanding of polymer characteristics.The distribution of molar masses plays a critical role in...