An Organic Capsule as a Matrix to Capture and Store Reactive Molecules at Room Temperature in Aqueous Solution: 7-cis-β-Ionone.

Abstract

Low-temperature m atrix isolation method is the most popular one to generate and store reactive molecules and characterize them by insitu IR spectroscopy. Recognizing the need for a simpler method to trap and store such molecules and characterize by NMR spectroscopy at room temperature in solution, we have performed experiments exploring the value of water-soluble octa acid (OA) capsule as a storage vessel. The molecule we have chosen to illustrate the feasibility is the highly hindered 7-cis-β-ionone, which has been established to exist in equilibrium with its cyclic form with the later favored at room temperature. In this study, we have shown that confined space can be an alternative to temperature to tilt an equilibrium toward higher energy isomer. During the course of the study, we were surprised to note that 7-trans-β-ionone aggregates in water and has distinct 1 H NMR spectra. Ability to assemble characterizable organic aggregates in water reveals the value of water as a reaction medium that is yet to be fully explored by photochemists. Finally, we have clarified the likely mechanism of secondary photoreaction of α-pyran to the final photoproduct that involves 1,5-hydrogen migration.