Redox-induced partner radical formation and its dynamic balance with radical dimer in cucurbit[8]uril

Abstract

N-(4-Hydroxy-phenoxyethyl)-N'-ethyl-4,4'-bipyridium (1) can form a stable 1 : 1 inclusion complex with CB[8] in aqueous solution, in which the hydroxyphenol (HP) moiety is back-folded and inserted together with the viologen moiety into the cavity of CB[8]. When the ethyl viologen dication (EV(2+)) in 1 is reduced, chemically or electrochemically, an intramolecular partner radical (EV(+)*-HP)/CB[8] can be detected, meanwhile, a dynamic balance between the partner radical and the intermolecular radical dimer (EV(+)*-HP)(2)/CB[8] can be observed.

Study of the Counter Anions in the Host‐Guest Chemistry of Cucurbit[8]uril and 1‐Ethyl‐1′‐benzyl‐4,4′‐bipyridinium

“…After addition of 1 equivalent CB[8], the first peak potential was shifted to about −0.55 V while the second peak shifted to about −1.10 V. The reason that the second peak shifted so much can be ascribed to the formation of radical dimer in the cavity of CB[8]. All these are in good agreement with our previous result [23]. Not too much difference caused by different counter anions can be observed during the measurements, providing further evidence that the counter anions did not have much influence on the CB[8] host during electrochemistry.…”

Assessment of Cooperativity in Ternary Peptide‐Cucurbit[8]uril Complexes

“…With the second complexation, the interaction among the two guests in the cavity of the CB [8] caused an additional upfield shift. [26] Under non-saturation conditions for CB [8],t he HG complex is well visible at low concentrations for both peptides, thus excluding as trongly positivec ooperative system, in contrastt ow hat has been described in an earlier study. [13] By monitoring the signals of the aromatic protons (Figure 3a,d ), the distributions of all species G, HG, andH G 2 were determinedf or each titration step (Figure 3b,e ).…”

“…Upon the first complexation, the upfield shifts of the phenyl protons of the Phe residue verified the shielding of the surrounding CB[8] host molecule. With the second complexation, the interaction among the two guests in the cavity of the CB[8] caused an additional upfield shift 26. Under non‐saturation conditions for CB[8], the HG complex is well visible at low concentrations for both peptides, thus excluding a strongly positive cooperative system, in contrast to what has been described in an earlier study 13.…”

Light driven molecular lock comprises a Ru(bpy)2(hpip) complex and cucurbit[8]uril

“…For example, CB[8] can bind both methyl viologen ( N , N -dimethyl-4,4-bipyridinium, MV 2+ ) and methyl viologen radical (MV˙ + ) or radical dimer (MV˙ + ) 2 inside its cavity. 5 It is also noted that MV 2+ , a common electron acceptor, is often utilized together with electron donors such as ruthenium poly-bipyridyl complexes to construct donor–photosensitizer–acceptor (D–P–A) systems. 6 And these host–guest systems have been used for the assembly of molecular loop-lock, 7 molecular necklaces, 8 and molecular machines.…”