Regulating Host–Guest Interactions between Cucurbit[7]uril and Guests on Gold Surfaces for Rational Engineering of Gold Nanoparticles

Abstract

Although macrocyclic host engineered nanoparticles have drawn a lot of attention in the past decade, little attention was paid to the binding affinity between the host and guest assembled on nanoparticles. In this work, the interactions between cucurbit[7]­uril (CB[7]) and three guests with phenyl (1), adamantyl (2), and ferrocene (3) groups on a gold surface were investigated. Their interactions were classified into four groups. The binding constants between CB[7] and three guests in the solution (group I) were determined by proton nuclear magnetic resonance (1H NMR) and isothermal titration calorimetry (ITC) experiments. The binding constants between CB[7]-stabilized gold nanosphere and guests 1 and 3 (group II) and those between 1-stabilized gold nanosphere and CB[7] (group III) were determined by ITC experiments. The binding constants determined in groups II and III decrease to approximately 20% of those in group I. The interactions between CB[7] and three guests on gold (group IV) were measured by single-molecule force spectroscopy (SMFS). Much lower binding constants than those in other groups were deduced. The hydrophobic and ion–dipole interactions play important roles in the pulling-out process in a thorough SMFS analysis. Furthermore, the CB[7]-capped gold nanospheres with different sizes were prepared, and their binding constant with the free guest (group II) depends on the nanoparticle size. All of these results are of great benefit to the rational design of macrocyclic host engineered nanoparticles for drug delivery and many other applications.

Evidenced cucurbit[n]uril-based host–guest interactions using single-molecule force spectroscopy

“…S1, ESI †). 30 Although the values of the binding constants measured using SMFS differed greatly from those measured via NMR, they displayed the same tendency. In addition, the binding constants of G1-4 with CB [8] were calculated to be 4-6 times greater than G1-4 without CB [8], leading to an increase in the rupture forces of G1-4 before and after CB [8] addition.…”

“…29 Cucurbiturils (CB[n]s) can also form a well-defined self-assembled monolayer (SAM) on substrates, and their disassociation with guests has recently been determined by us and other groups. 30,31 SMFS results suggested that hydrophobic and ion-dipole interactions may dominate the separation process between charged guest molecules and CB [7], which cannot be addressed via bulk measurements.…”

“…Herein, in order to directly measure the CB [8] enhanced guest-pair interactions, four guest molecules (G1, G2, G3, and G4 in Fig. 1), which contain imidazole, benzene rings or polypeptide moieties, were connected onto an AFM tip, respectively, through a flexible PEG chain (about 4 nm in length) endfunctionalized with a maleimide group (Mal-PEG 8 -NHS) according to our reported procedures, 30 while mixed guest/ 1-butanethiolate self-assembled monolayers (SAMs) were formed on the flat Au (111) surface (Fig. S1, ESI †).…”

Host‐Guest Systems on the Surface of Functionalized Superparamagnetic Iron Oxide Nanoparticles (SPIONs) Utilizing Hamilton Receptors and Cyanurate Derivative Molecules

“…For instance, interactions of gold nanoparticles with various host and guest systems have been determined by using cyclic voltammetry, [15] isothermal titration calorimetry, [16] and singlemolecule force spectroscopy. [17] In this work, for the first time we utilize Hamilton receptor and cyanurate guest molecules to study the host-guest interactions on the surface of functionalized SPIONs (Scheme 1). We prepare two types of nanoparticles bearing either the Hamilton receptor (Fe 3 O 4 @HamPAc) or the cyanurate derivative (Fe 3 O 4 @CyaPAc) and investigate how the position of the interacting molecules affects the overall binding events on the surface.…”

“…For instance, interactions of gold nanoparticles with various host and guest systems have been determined by using cyclic voltammetry, [15] isothermal titration calorimetry, [16] and single‐molecule force spectroscopy. [17] …”