Application of DOSY:Analysis of guest encapsulation

Tetrakis(4-hydroxyphenyl)-cavitand (1) and tetra(4-pyridyl)-cavitand (2) self-assembly into a heterodimeric capsule (1･2) via hydrogen bonds in chloroform solution. This heterodimeric capsule possesses internal nanospace and encapsulates a guest molecule. For example, addition of 1 equiv of p-diacetoxybenzene to a capsule 1･2 forms 1:1 guest-encapsulating 1･2, namely, p-diacetoxybenzene@(1･2). This guest encapsulation to the internal nanospace was confirmed via ¹H chemical-shift changes and NOESY.

Analysis of DOSY spectrum

Figure 1 shows a DOSY spectrum of 1:1 mixture solution of p-diacetoxybenzene@(1･2) and p-diacetoxybenzene, manifesting two components having substantially different diffusion coefficients; free p-diacetoxybenzene shows a large coefficient (upper in the spectrum) while p-diacetoxybenzene@(1･2) a small coefficient (lower in the spectrum). The almost identical coefficients of encapsulated p-diacetoxybenzene and heterodimeric capsule 1･2 firmly prove their encapsulation. Also, two distinct components of p-diacetoxybenzene inside and outside of the capsule suggest that their exchange should be slow on the NMR time scale and that p-diacetoxybenzene@(1･2) be stable.

*The present study is collaboration with Prof. K. Kobayashi of Shizuoka University.

Reference

Orientational Isomerism Controlled by the Difference in Electronic Environments of a Self-Assembling Heterodimeric Capsule Kenji Kobayashi, Ryosuke Kitagawa, Yoshifumi Yamada, Masamichi Yamanaka, Takako Suematsu, Yoshihisa Sei, and Kentaro Yamaguchi J.Org.Chem. 2007, 72, 3242-3246.