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 ¹ H 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.

Keywords: arylazopyrazoles; cucurbit[8]uril; host-guest systems; photo-responsive; stimuli-responsive.

Figure 1

a) UV/Vis spectrum of the photo‐isomerization of AAP in the presence of CB[8]/paraquat (1:1:1) at 100 μm in water with corresponding switching cycles (see text for details). b) ¹H NMR spectrum of the re‐isomerization of a 1:1:1 mixture irradiated with λ=520, 365 and 520 nm for 10 min ((E‐Z‐E) from top to bottom) at 100 μm. c) Scheme of heteroternary inclusion complex formation and dissociation (R₁: CH₂CONH‐(OCH₂CH₂)₄‐OH). d) Isothermal calorimetry of CB[8]/paraquat with E‐AAP and the corresponding 1:1 fit. e) ¹H NMR titration with 100 μm CB[8]/paraquat and E‐AAP. f) Job plot based on a ¹H NMR titration.

Figure 2

Assembly of heteroternary complex on antifouling SAMs. After cell adhesion, UV irradiation releases AAP–RGD and cells.

Figure 3

Concentration‐dependent E‐AAP assembly to a MV²⁺/CB[8] surface studied by a) SPR and b) QCM‐D. c) SPR response of flowing E‐ and Z‐AAP over MV²⁺/CB[8] SAMs. d) Change in SPR angle shift (square) and QCM‐D frequency (circle) vs. E‐AAP concentration (1:1 Langmuir fit is shown).

Figure 4

a) Fluorescence microscopy image of fixed C2C12 cells seeded for 1 h on CB[8]/MV²⁺/AAP–RGD SAMs. Cells were stained for nucleus (blue), actin (red) and vinculin (green), scale bar 100 μm. Inset is a magnified image of same surface, scale bar 50 μm. b) Quantitative analysis of C2C12 cells before (no UV) and after (UV) irradiation of λ=365 nm of the CB[8]/MV²⁺/AAP–RGD and cRGD SAMs.