Photo‐responsive Bioactive Surfaces Based on Cucurbit[8]uril‐Mediated Host–Guest Interactions of Arylazopyrazoles

Abstract

A photoswitchable arylazopyrazole (AAP) derivative binds with cucurbit[8]uril (CB[8]) and methylviologen (MV2+) to form a 1:1:1 heteroternary host–guest complex with a binding constant of K a=2×103 m −1. The excellent photoswitching properties of AAP are preserved in the inclusion complex. Irradiation with light of a wavelength of 365 and 520 nm leads to quantitative E‐ to Z‐ isomerization and vice versa, respectively. Formation of the Z‐isomer leads to dissociation of the complex as evidenced using 1H NMR spectroscopy. AAP derivatives are then used to immobilize bioactive molecules and photorelease them on demand. When Arg‐Gly‐Asp‐AAP (AAP–RGD) peptides are attached to surface bound CB[8]/MV2+ complexes, cells adhere and can be released upon irradiation. The heteroternary host–guest system offers highly reversible binding properties due to efficient photoswitching and these properties are attractive for designing smart surfaces.

Multivalency in Heteroternary Complexes on Cucurbit[8]uril‐Functionalized Surfaces: Self‐assembly, Patterning, and Exchange Processes

“…The maleimide moieties of type 1 and type 2 surfaces were then functionalized by a Michael addition with thiol‐substituted methyl viologen 4 b . Successful immobilization of CB[8] and the formation of ternary complexes on those surfaces has been verified by QCM‐D control experiments (Figures S5 and S6) and revealed results comparable to previously reported examples …”

“…The observed exothermic binding curve has an inflection point at a molar ratio of one indicating the formation of a 1 : 1 assembly. The data fitting of the titration to a 1 : 1 binding model gave an association constant K 1 ⋅ 4a ⊂CB[8] =(1.7±0.1)×10 4 M −1 , in line with values found for similar complexes …”

“…CB[8] binds electron‐deficient methyl viologen with an association constant, K , of 10 5 –10 6 M −1 , and the resulting methyl viologen⊂CB[8] complex can efficiently include a second electron‐rich aromatic guest. These ternary complexes were already used to selectively adhere cells, bacteria or proteins to surfaces and releasing them on demand …”

Stimuli‐Responsive Cucurbit[n]uril‐Mediated Host‐Guest Complexes on Surfaces

“…[102] Ravoo and coworkers reported heterocomplexation of arylazopyrazole-modified integrin-binding peptides onto pseudorotaxane-based CB [8] SAMs (Figure 13). [103] Arylazopyrozoles are of interest to improve the photoswitching characteristics of the CB [8] SAMs. Previous work on arylazopyrazoles demonstrated excellent switchability with a photostaionary state up to 96 % and half-lifetimes of several days.…”

“…[104][105][106] Myoblast cells were adhered onto the supramolecular surfaces and released by UV induced isomerization of the arylazopyrazoles. [103] Another photoswitchable molecule, cinnamamide, has been attached to the surface of silica nanoparticles and undergoes, similar to azobenzene, a trans to cis isomerization after irradiation with light of l = 300 nm. As a consequence CB [7] dissociated away from the surface thereby releasing of guest molecules out of the porous nanoparticles.…”