China 
Africa 
Explore chapters and articles related to this topic
*
Published in Luis Liz-Marzán, Colloidal Synthesis of Plasmonic Nanometals, 2020
Verónica Montes-García, Jorge Pérez-Juste, Isabel Pastoriza-Santos, Luis M. Liz-Marzán
Macrocycle-functionalized metal nanoparticles can also be used as catalysts. The main role of the macrocycle in this case is stabilizing the nanoparticles by providing a protective layer that prevents aggregation. Among the various reported catalyzed reactions, carbon-carbon cross coupling and hydrogenation reactions[13] are the most frequently studied ones. Palladium nanoparticles modified with thiolated β-CD can successfully catalyze Suzuki,[70] Heck,[71] and Sonogashira[72] cross-coupling reactions. It has been demonstrated that the covalent modification of the nanoparticle surface with cyclodextrins allows the modulation of catalytic activity. The addition of a potential inhibitor with high affinity towards CD complexation will decrease the surface density of catalytic active sites.[73] It has been reported that CB[n]-stabilized Pd nanoparticles successfully catalyze Suzuki cross-coupling reactions, with CB[n] acting merely as a protecting agent.[24] The reduction of para-nitrophenol by borohydride has also been studied as a catalytic model reaction for cucurbituril-[21] and pillararene-stabilized[27,42] gold nanoparticles. Finally, CB[6]-stabilized platinum nanoparticles showed enhanced electrocatalytic activity and high poison tolerance for methanol oxidation.[23]
Effect of confinement on the electronic and optical properties of azobenzene: cucurbituril as a means of confinement
Published in Molecular Physics, 2022
Peaush Gangwar, Saurabh Singh Negi, Venkatnarayan Ramanathan, C. N. Ramachandran
Like azobenzene, a great deal of attention has been received by the pumpkin-shaped macrocyclic molecules cucurbituril CBn, where n represents the number of glycoluril units present [13]. Cucurbituril is synthesised by the condensation of glycoluril and formaldehyde. The distinct cage structure of cucurbituril was determined by Freeman et al. in 1981 [14,15]. They possess high chemical and thermal stability and hence can be used under different conditions of temperature and pressure. The cavity of this macrocyclic compound is sufficient to host a variety of guest molecules inside, as revealed from the crystal structure [16]. The possibility of CBn to form host–guest complexes with different molecules has attracted a considerable amount of attention over the last decade. There are studies available highlighting the synthesis and host–guest interaction of CBn as well as their applications in catalysis and drug delivery [17,18]. Sudip et al. studied the hydrogen storage capacity of cucurbituril, and they reported that CB7 interacts with hydrogen molecules, five endohedrally and fourty seven exohedrally [19]. The same group further studied the encapsulation of different gas molecules inside CB6, including CH4, CO2, CS2, NO2, C2H2, and Cl2. The study demonstrated that cucurbiturils act as excellent gas storage materials similar to metal oxide clusters [20–22]. Cucurbiturils have also been proposed as means of confinement to carry out reactions akin to transition metal clusters [23–28]. These include the CB7 catalysed Diels–Alder reaction of N-allyl-2-furfurylamine and its derivatives although the reactant molecules possess high interaction energy with the cage [29]. Manas et al. theoretically studied the Diels–Alder reaction between 1,3 butadiene and ethylene inside CBn; n = 6-8 [30]. They reported that the rate of the reaction is decreased on confining the reactants in CB6 and CB8 compared to CB7. Although several studies have been done in the past about the encapsulation of molecules inside CBn, no studies are available on the encapsulation of azobenzene inside cucurbiturils or on the effect of the properties of azobenzene due to confinement in CBn. Azobenzene is expected to show interesting photophysical properties under the confinement of cucurbituril. A suitable balance between molecular crowding and conformational liberty is required for the isomerisation of the guest molecule inside the cavity. Several theoretical and experimental studies have been carried out on the encapsulation of molecules inside various cages [31]. However, none of the studies focused on the encapsulation and subsequent changes in the properties of azobenzene inside CBn cages. In the present study, the host–guest complexes of azobenzene with CBn are investigated using density functional theoretical methods. Keeping the size of azobenzene and the cavities of CBn into consideration, CB9 and CB10 were used for confining azobenzene. The azobenzene is oriented both horizontally (h) and vertically (v) inside the cucurbituril cages. The structure, electronic, optical and absorption properties of h-AB@CBn and v-AB@CBn are investigated to examine the effect of encapsulation of azobenzene on the above properties.