Binding Interactions between a Ferrocenylguanidinium Guest and Cucurbit[n]uril Hosts

Abstract

The binding interactions between a novel ferrocenylguanidinium derivative (FcG) and the macrocyclic hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solution. H NMR spectroscopic experiments indicated that both hosts form stable 1:1 inclusion complexes with FcG, in which the ferrocenyl group is engulfed by the host cavity. The stoichiometry of the CB7·FcG complex was also confirmed by electrospray mass spectrometric (ESI MS) experiments. The association equilibrium constants (K) were determined from NMR competition experiments. The measured K values were 3.5 × 10 and 2.5 × 10 M for CB7 and CB8, respectively, in 50 mM sodium acetate-d DO solution (pD 4.7). DFT computational studies confirmed the 1:1 stoichiometry and the inclusion character of both complexes. Voltammetric experiments were carried out to measure the complexation-induced shifts on the half-wave potentials for the one-electron oxidation of the ferrocenyl moiety. Complexation by CB7 led to a 12 mV anodic shift, while CB8 caused a larger 32 mV shift also in the positive direction. These potential shifts suggest that the delocalization of the positive charge on the side arm over the three nitrogens in the guanidinium unit results in electrochemical behavior similar to that observed with neutral ferrocene derivatives.

Cucurbit[n]uril Host‐Guest Complexes of Acids, Photoacids, and Super Photoacids

“…The small value for benzocaine may be a result of binding further away from ammonium group, partially over the ethyl ester moiety, diminishing the effect of the loss of the ion‐dipole interaction upon deprotonation. A related carboxylic acid is p ‐guanidinobenzoic acid ( 27 ), which, along with 6‐ amidino‐2‐naphthol ( 26 ), is a metabolite of the serine protease inhibitor nafamostat . Complexation of 27 to CB[7] results in a p K a shift of 0.3 units, which may be lower than that of p ‐aminobenzoic acid due to a more diffuse positive charge on the guanidinium group compared to the ammonium .…”

Relative Position and Relative Rotation in Supramolecular Systems through the Analysis of the Principal Axes of Inertia: Ferrocene/Cucurbit[7]uril and Ferrocenyl Azide/β-Cyclodextrin Case Studies

“…Beyond any identification, as proposed and discussed herein, the authors always have the option to address the complete coordinates of each arrangement investigated as the Supporting Information. 56 In summary, the critical idea of this work is the construction of a reference system (X, Y, and Z) over the principal axes of the host molecule. The additional development of the derived system (x, y, and z) over the principal axes of the guest allows us to evaluate a set of parameters accounting for the relative position and rotation between a pair of molecules.…”

Chemical Sensors Based on Cucurbit[n]uril Macrocycles

“…[105,109,167,168,169,170,171,172,173,174,175,176,177,178,179] For instance, the half-wave potential (E 1/2 ) for the first reduction and second reduction process of the dicationic herbicide paraquat shifted to more negative potentials in the presence of CB7 (Table 4). However, as was shown in multiple examples by the groups of Kaifer and Kim, increases and decreases of the redox potential are observed depending on the chemical nature of the analyte.…”

“…[105,109,167,168,169,170,171,172,173,174,175,176,177,178,179] For instance, the half-wave potential (E 1/2 ) for the first reduction and second reduction process of the dicationic herbicide paraquat shifted to more negative potentials in the presence of CB7 (Table 4). [105,167,168] These analyte-dependent potential changes may serve as characteristic fingerprints for redox-based analyte differentiations. [169] Similarly, the E 1/2 value for ferrocene decreased in the presence of CB7, [173] whereas that of substituted ferrocenes (in particular for those with a positively charged substituent) was found to (strongly) increase, see Table S2 in the Supporting Information.…”