Woo Sung Jeon

Selective Inclusion of a Hetero‐Guest Pair in a Molecular Host: Formation of Stable Charge‐Transfer Complexes in Cucurbit[8]uril

Two different molecules are selectively included in cucurbit[8]uril to form a stable 1:1:1 ternary complex, which has been characterized by X-ray crystallography. The inclusion of a hetero-guest pair (a pyridinium derivative (blue) and 2,6-dihydroxynaphthalene (magenta)) in the molecular host is driven and stabilized by a charge-transfer interaction between the electron-rich and electron-deficient guests.

Inclusion of methylviologen in cucurbit[7]uril

The inclusion behavior of methylviologen (N,N′-dimethyl-4,4′-bipyridinium, MV) dication in cucurbit[7]uril (CB[7]) has been studied by using various spectroscopic and electrochemical methods. The inclusion complex of MV dication in CB[7] is stable thermodynamically and kinetically. The electrochemical study reveals that unlike β-cyclodextrin, CB[7] prefers the charged species, MV dication (MV2+), and cation radical (MV+⋅) to the fully reduced neutral (MV0 species as guests. Dimerization of MV+⋅ is suppressed effectively by forming a stable complex with CB[7] in aqueous solution as confirmed by spectroelectrochemical experiments. Furthermore, the first redox process (MV2+/MV+⋅) of the MV2+–CB[7] complex occurs predominantly via the direct electron transfer pathway, whereas the second redox process (MV+⋅/MV0) occurs via both the direct and indirect pathway because of the low affinity of the fully reduced species MV0 to CB[7].

Control of the stoichiometry in host–guest complexation by redox chemistry of guests: Inclusion of methylviologen in cucurbit[8]uril

The binding stoichiometry of a host-guest complex can be effectively controlled by the redox chemistry of the guest: a 1:1 inclusion complex of methylviologen dication (MV2+) in cucurbit[8]uril (CB[8]) converts completely and reversibly to a 2:1 inclusion complex of cation radical (MV+.) in CB[8] upon the reduction of the guest.

Stable π-dimer of a tetrathiafulvalene cation radical encapsulated in the cavity of cucurbit[8]uril

The first stable pi-dimer of a tetrathiafulvalene (TTF) cation radical encapsulated in the cavity of cucurbit[8]uril has been isolated at room temperature and fully characterized; it shows absorption bands at 400, 540 and 760 nm, characteristic of the TTF cation radical dimer.

Synthetic Molecular Machine Based on Reversible End-to-Interior and End-to-End Loop Formation Triggered by Electrochemical Stimuli

We have designed and synthesized a novel [2]pseudorotaxane-based molecular machine in which the interconversion between end-to-interior and end-to-end loop structures is reversibly controlled by electrochemical stimuli. Cucurbit[8]uril (CB[8]) and the thread molecule 3(4+) with an electron-rich hydroxynaphthalene unit and two electron-deficient viologen units form the 1:1 complex 4(4+) with an end-to-interior loop structure, which is reversibly converted into an end-to-end structure upon reduction. Large changes in shape and size of the molecule accompany the reversible redox process. The key feature of the machine-like behavior is the reversible interconversion between an intramolecular charge-transfer complex and viologen cation radical dimer inside CB[8] triggered by electrochemical stimuli.

A Rationally Designed NH4+ Receptor Based on Cation–π Interaction and Hydrogen Bonding

A cage-type receptor binds an NH4+ ion by cation-π interactions and hydrogen bonding with high sensitivity and selectivity, comparable or even superior to those of the natural antibiotic nonactin over a wide pH range. The high performance, low cost, and easy synthesis may offer practical applications for this receptor as an ammonium ion sensor.

Novel dendron-stabilized gold nanoparticles with high stability and narrow size distribution

Dendron-stabilized gold nanoparticles synthesized with Frechet-type dendrons possessing a single thiol group at the focal point have small cores (average diameters of 2.4–3.1 nm) with narrow size distribution and remarkably high stability; in particular, the nanoparticles synthesized with the second generation dendron has an almost monodisperse core (2.4 ± 0.2 nm).

Electrochemically Controllable Reversible Formation of Cucurbit[8]uril-Stabilized Charge-Transfer Complex on Surface

The reversible formation of cucurbit[8]uril (CB[8])-stabilized charge-transfer (CT) complex on gold, which can be regulated by electrochemical stimuli, is reported. A viologen-based thread molecule with a thiol terminus was designed to synthesise a stable CB[8]-threaded [2]pseudorotaxane (5 2 + ). A mixed self-assembled monolayer (SAM) of 5 2 + and 3-mercaptopropionic acid (3-MPA) on gold was prepared and characterised by reflectance FT-IR spectroscopy. The formation and disruption of a CT complex on surface was investigated by cyclic voltammetry with the SAM on gold as a working electrode in a supporting electrolyte solution containing 2,6-dihydroxynaphthalene (DHNp). The cathodic peak was shifted to a more negative potential (ΔE∼40 mV) when compared with that measured without DHNp in the electrolyte, which confirmed the formation of a CT complex on gold upon immersion of the SAM of 5 2 + on gold in the supporting electrolyte containing DHNp. When the viologen unit was reduced, the CT complex was destroyed and the electron-rich guest molecule was released. Upon reoxidation of the reduced viologen unit, however, the CT complex was slowly reformed.

A new cucurbit[6]uril-based ion-selective electrode for acetylcholine with high selectivity over choline and related quaternary ammonium ions

Detection of acetylcholine (ACh+) with high sensitivity and selectivity in the presence of interfering ions including choline (Ch+) poses a significant analytical challenge. A cucurbit[6]uril derivative, (allyloxy)12CB[6], forms a stable 1:1 inclusion complex with ACh+ but does not interact significantly with Ch+ in solution. Based on this result, we prepared ion-selective electrodes (ISEs) for ACh+ using (allyloxy)12CB[6] as an ionophore. The (allyloxy)12CB[6]-based ISEs detect ACh+ with unprecedentedly high selectivity over Ch+ as well as other interfering ions such as dopamine, NH4 +, and .