将小分子碳氢化合物包封到穴状配体-卟啉过程的动力学研究。

Nakazawa Jun, Sakae Yoshitake, Aida Misako, Naruta Yoshinori

Graduate School of Sciences, and Institute for Materials Chemistry and Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, Japan.

J Org Chem. 2007 Dec 7;72(25):9448-55. doi: 10.1021/jo701299v. Epub 2007 Nov 3.

Exchange of guest molecules into capsule shaped host molecules is the most fundamental process in host-guest chemistry. Several examples of quantitative measurements of guest exchange rates have been reported. However, there have been no reports on the activation energies of these processes. A molecule known as cavitand-porphyrin (H2CP) has been reported to have a flexible host structure capable of facilitating moderate guest exchange rates suitable for kinetic measurements of the guest exchange process with 1H NMR. In this article, various kinetic and thermodynamic parameters related to the process of encapsulation of small hydrocarbons into H2CP in CDCl3 solution were determined by 2D exchange spectroscopy (EXSY): association and dissociation rate constants (k(ass) = 320 M-1 s-1, k(diss) = 1.4 s-1 for methane at 25 degrees C), the corresponding activation energies (E(a,ass) = 27 kJ.mol-1, E(a,diss) = 58 kJ.mol-1), and thermodynamic parameters for each process (DeltaG++(ass) = 59 kJ.mol-1, DeltaG++(diss) = 72 kJ.mol-1, DeltaH++(ass) = 25 kJ.mol-1, DeltaH++(diss) = 55 kJ.mol-1, DeltaS++(ass) = -113 J.K-1.mol-1, and DeltaH++(diss) = 58 J.K-1.mol-1 for methane). The thermodynamic parameters (DeltaG degrees = -13 kJ.mol-1, DeltaH degrees = -31 kJ.mol-1, DeltaS degrees = -60 J.K-1.mol-1 for methane) for this encapsulation equilibrium determined by EXSY were comparable to those for methane determined by 1D 1H NMR titration (DeltaG degrees = -11 kJ.mol-1, DeltaH degrees = -33 kJ.mol-1, DeltaS degrees = -75 J.K-1.mol-1 for methane). In addition, the structure of the methane encapsulation process was revealed by ab initio MO calculations. The activation energies for methane association/dissociation were estimated from MP2 calculations (E(a,ass) = 58.3 kJ.mol-1, E(a,diss) = 89.1 kJ.mol-1, and DeltaH degrees = -30.8 kJ.mol-1). These values are in accord with the experimentally determined values. The observed guest exchange rates and energies are compared with the corresponding values of various reported capsule-shaped hosts.

客体分子与胶囊状主体分子的交换是主客体化学中最基本的过程。已有多篇关于客体交换速率定量测量的报道。然而，尚未有关于这些过程活化能的报道。据报道，一种名为穴状卟啉（H2CP）的分子具有灵活的主体结构，能够促进适度的客体交换速率，适合用1H NMR对客体交换过程进行动力学测量。在本文中，通过二维交换光谱（EXSY）测定了CDCl3溶液中与小烃类封装到H2CP过程相关的各种动力学和热力学参数：缔合和解离速率常数（25℃时甲烷的k(ass)=320 M-1 s-1，k(diss)=1.4 s-1）、相应的活化能（E(a,ass)=27 kJ.mol-1，E(a,diss)=58 kJ.mol-1）以及每个过程的热力学参数（甲烷的ΔG++(ass)=59 kJ.mol-1，ΔG++(diss)=72 kJ.mol-1，ΔH++(ass)=25 kJ.mol-1，ΔH++(diss)=55 kJ.mol-1，ΔS++(ass)=-113 J.K-1.mol-1，ΔH++(diss)=58 J.K-1.mol-1）。通过EXSY测定的该封装平衡的热力学参数（甲烷的ΔG°=-13 kJ.mol-1，ΔH°=-31 kJ.mol-1，ΔS°=-60 J.K-1.mol-1）与通过一维1H NMR滴定测定的甲烷热力学参数（甲烷的ΔG°=-11 kJ.mol-1，ΔH°=-33 kJ.mol-1，ΔS°=-75 J.K-1.mol-1）相当。此外，通过从头算MO计算揭示了甲烷封装过程的结构。从MP2计算估计了甲烷缔合/解离的活化能（E(a,ass)=58.3 kJ.mol-1，E(a,diss)=89.1 kJ.mol-1，ΔH°=-30.8 kJ.mol-1）。这些值与实验测定值一致。将观察到的客体交换速率和能量与各种已报道的胶囊状主体的相应值进行了比较。