N-Methyl- and N-Phenylpiperazine Functionalized Styryl Dyes Inside Cucurbiturils: Theoretical Assessment of the Factors Governing the Host-Guest Recognition.

The family of cucurbiturils (CBs), the unique pumpkin-shaped macrocycles, has received great attention over the past four decades owing to their remarkable recognition properties. They have found diverse applications including biosensing and drug delivery technologies. The cucurbituril complexation of guest molecules can modulate their pKas, improve their solubility in aqueous solution, and reduce the adverse effects of the drugs, as well as enhance the stability and/or enable targeted delivery of the drug molecule. Employing twelve cationic styryl dyes with N-methyl- and N-phenylpiperazine functionality as probes, we attempted to understand the factors that govern the host-guest complexation of such molecules within CB[7] and CB[8] host systems. Various key factors determining the process were recognized, such as the pH and dielectric constant of the medium, the cavity size of the host, the chemical characteristics of the substituents in the guest entity, and the presence/absence of metal cations. The presented results add to our understanding (at the molecular level) of the mechanism of encapsulation of styryl dyes by cucurbiturils, thus shedding new light on various aspects of the intriguing complexation chemistry and the underlying recognition processes.

Utilizing symmetrical tetramethyl cucurbit[6]uril-based supramolecular fluorescence probe for detection of paraquat in water.

A supramolecular fluorescence probe has been developed using a symmetrical tetramethyl cucurbit[6]uril (TMeQ[6]) and a styryl derivative (SPy) with a host-guest ratio of 2:1. The introduction of paraquat (PQ) competes with SPy for the TMeQ[6] cavity, resulting in fluorescent quenching. The addition of 17 common herbicides and ions had negligible effects on the fluorescence quenching, indicating that the 2TMeQ[6]/SPy complex exhibits excellent selectivity in detecting PQ. The detection limit was found to be 4.62 × 10-7 M. More importantly, the probe was engineered to detect paraquat in river water by examining post-treatment samples and noting alterations in fluorescence color. The red to blue (R/B) intensity ratio is subsequently calculated to ascertain the PQ concentration. Experimental trials conducted on river water samples yielded recovery rates between 98.21 % and 108 %, with a relative standard deviation of less than 5 %. By pairing this with a smartphone-based colorimetric analysis application, we can facilitate portable PQ detection, enabling efficient and convenient monitoring across various locations.