Ting Zhang,Li Xia Chen,Yun Qian Zhang,Qian Jiang Zhu,Ying Huang,Zhu Tao
The outer surface interaction of cucurbit[ n ]urils (Q[ n ]s) is an important supramolecular interaction that results from the positive electrostatic potential on the outer surface of Q[ n ]s. It cannot only result in the formation of various novel Q[ n ]-based supramolecular frameworks, but can also lead to clustering emission of Q[ n ]s. In this work, three different Q[8]-based supramolecular frameworks, assembled through the outer surface interaction of Q[ n ]s (OSIQ), were prepared according to the literature. The solid-state clustering-triggered emission (CTE) characteristics of the frameworks were also determined. Moreover, investigation of their adsorption properties showed that the solid-state CTE of the three Q[8]-based supramolecular frameworks was quenched in the presence of certain chemicals and that they exhibited high selectivity for pyridine. Framework B exhibited the highest adsorption of pyridine.
Ethylene was introduced into cucurbit[n]urils (CB[n]s, n = 5–7) by molecular encapsulation, for comparison with V-type crystalline starch (V-starch) and α-cyclodextrin (α-CD). The encapsulation capacity of inclusion complexes (ICs) followed the order of CB[5] > V-starch > CB[6] > CB[7] > α-CD. X-ray diffractometry, and 13C solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy confirmed the presence of ethylene gas in the solid matrices. The controlled release kinetics of the ICs were further studied under different storage temperature (4 and 25 °C) and relative humidity (52.9 and 75.5%) conditions. The Avrami equation was adapted to analyze the controlled release kinetics of ethylene gas, showing a diffusion limited mechanism for CB[n]-ICs under all the storage conditions. The ethylene release rate from CB[n]-ICs was accelerated by increasing ambient temperature, but was not sensitive to relative humidity. CB[5] showed the slowest ethylene release rate among the five solid matrices, up to 700 h under 4 °C storage conditions. Molecular simulation suggested two stable molecular conformations for ethylene molecules within the matrices, i.e., type I, two ethylene molecules in the cavity; and type II, one ethylene molecule in the cavity and the other one outside the cavity. CB[5] and CB[6] had a stable type II molecular conformation of ethylene, whereas CB[7] showed similar stability to type I and type II molecular conformations. For the first time, we demonstrated that CB[n]s (particularly CB[5]) are desirable gas storage and release systems for ethylene. This technology can enable precisely controlled and targeted applications of ethylene for food processing and agricultural applications.
A series of gold nanoparticles (AuNPs) was prepared in situ with different cucurbit[n]urils (CB[n]s) in an alkaline aqueous solution. The nanoparticle sizes can be well controlled by CB[n]s (n=5,6,7,8) with different ring sizes. The packing densities of CB[5–8] and free surface area on AuNPs were determined. A direct relationship was found between the ring size and packing density of CB[n]s with respect to the AuNP-catalyzed reduction of 4-nitrophenol in the presence of NaBH4. The larger particle size and higher surface coverage of bigger CB[n]-capped AuNPs significantly decreased the catalytic activity. Furthermore, this work could lead to new applications that utilize AuNPs under an overlayer of CB[n]s for catalysis, sensing, and drug delivery.Keywords:gold nanoparticles;cucurbit[n]urils;controllable synthesis;catalysis
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