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 Ka =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 520â 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 Hâ 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.
Subject(s)
Macrocyclic Compounds/chemistry , Oligopeptides/chemistry , Paraquat/chemistry , Pyrazoles/chemistry , Animals , Cell Adhesion , Cell Line , Humans , Isomerism , Kinetics , Light , Macrocyclic Compounds/radiation effects , Mice , Oligopeptides/radiation effects , Paraquat/radiation effects , Photochemical Processes , Pyrazoles/radiation effects , Surface PropertiesABSTRACT
Cell adhesion is studied on multivalent knottins, displaying RGD ligands with a high affinity for integrin receptors, that are assembled on CB[8]-methylviologen-modified surfaces. The multivalency in the knottins stems from the number of tryptophan amino acid moieties, between 0 and 4, that can form a heteroternary complex with cucurbit[8]uril (CB[8]) and surface-tethered methylviologen (MV2+). The binding affinity of the knottins with CB[8] and MV2+ surfaces was evaluated using surface plasmon resonance spectroscopy. Specific binding occurred, and the affinity increased with the valency of tryptophans on the knottin. Additionally, increased multilayer formation was observed, attributed to homoternary complex formation between tryptophan residues of different knottins and CB[8]. Thus, we were able to control the surface coverage of the knottins by valency and concentration. Cell experiments with mouse myoblast (C2C12) cells on the self-assembled knottin surfaces showed specific integrin recognition by the RGD-displaying knottins. Moreover, cells were observed to elongate more on the supramolecular knottin surfaces with a higher valency, and in addition, more pronounced focal adhesion formation was observed on the higher-valency knottin surfaces. We attribute this effect to the enhanced coverage and the enhanced affinity of the knottins in their interaction with the CB[8] surface. Collectively, these results are promising for the development of biomaterials including knottins via CB[8] ternary complexes for tunable interactions with cells.
Subject(s)
Bridged-Ring Compounds/chemistry , Imidazoles/chemistry , Animals , Cell Adhesion , Cystine-Knot Miniproteins , Mice , TryptophanABSTRACT
Evaluating cooperativity for cucurbit[8]uril (CB[8])-mediated ternary complexation is required for understanding and advancing designs of such ternary self-assembled systems. A key issue is to dissect the contributions of the binding steps of the first and second guest molecules to the overall ternary complex formation energy. This is addressed by performing concentration-dependent titrations between CB[8] and guests by means of concentration-dependent calorimetric and 1 H-NMR titrations. The sensitivity of the fitting of the cumulative heat of complexation of the calorimetric titrations is evaluated in terms of fitting error and enthalpy-entropy compensation and, together with the NMR spectroscopic analysis of the separate species, non-cooperative binding is conceived to be the most probable binding scenario. The binding behavior of CB[8] homoternary complexes is similar to CB[8] heteroternary complexes, with an enthalpy-driven tight fit of the guests in the CB[8] cavity overcoming the entropic penalty. Also for these types of complexes, a non-cooperative binding is the most probable.
Subject(s)
Bridged-Ring Compounds/chemistry , Imidazoles/chemistry , Peptides/chemistry , Calorimetry/methods , Ligands , Magnetic Resonance Spectroscopy/methods , Protein Binding , ThermodynamicsABSTRACT
Supramolecular amphiphiles, consisting of ternary complexes of cucurbit[8]uril (CB[8]), an alkylated paraquat derivative and a tetraethylene glycol-functionalized azobenzene, self-assemble into vesicles of about 200 nm in diameter. The outer surface of the vesicles was functionalized with cell-targeting ligands. These vesicles were employed for loading and delivery of proteins into cells. Supramolecular amphiphile-derived vesicles show great promise as nanocarriers of functional molecules to be transferred into cells.
ABSTRACT
Multiple naphthol ligands were installed on the glycocalyx of white blood cells via metabolic labeling and subsequent strain promoted azide-alkyne cycloaddition. Only when cucurbit[8]uril was present to drive the formation of ternary complexes, cells specifically assembled on a methylviologen functionalized supported lipid bilayer through multivalent interactions.
Subject(s)
Alkynes/chemical synthesis , Azides/chemical synthesis , Bridged-Ring Compounds/metabolism , Glycocalyx/metabolism , Imidazoles/metabolism , Naphthols/metabolism , Alkynes/chemistry , Alkynes/metabolism , Azides/chemistry , Azides/metabolism , Bridged-Ring Compounds/chemistry , Cell Membrane/chemistry , Cell Membrane/metabolism , Cells, Cultured , Glycocalyx/chemistry , Humans , Imidazoles/chemistry , Jurkat Cells , Leukocytes/chemistry , Leukocytes/metabolism , Ligands , Lipid Bilayers/chemistry , Lipid Bilayers/metabolism , Macromolecular Substances/chemistry , Macromolecular Substances/metabolism , Molecular Structure , Naphthols/chemistryABSTRACT
This article reviews the state of the art in the development of strategies for generating supramolecular systems for dynamic cell studies. Dynamic systems are crucial to further our understanding of cell biology and are consequently at the heart of many medical applications. Increasing interest has therefore been focused recently on rendering systems bioactive and dynamic that can subsequently be employed to engage with cells. Different approaches using supramolecular chemistry are reviewed with particular emphasis on their application in cell studies. We conclude with an outlook on future challenges for dynamic cell research and applications.
