Multivalent recognition of concanavalin A by {Mo₁₃₂ } glyconanocapsules--toward biomimetic hybrid multilayers

Herein, we consider Müller's spherical, porous, anionic, molybdenum oxide based capsule, (NH4)42[{(Mo(VI))Mo(VI)5O21(H2O)6}12{Mo(V)2O4(CH3COO)}30]⋅10 CH3COONH4⋅300 H2O≡(NH4)42⋅1 a⋅crystal ingredients≡1, {Mo132}, as an effective sugar-decorated nanoplatform for multivalent lectin recognition. The ion-exchange of NH4(+) ions of 1 with cationic-sugars, D-mannose-ammonium chloride (2) or D-glucose-ammonium chloride (3) results in the formation of glyconanocapsules (NH4)(42-n)2n⋅1 a and (NH4)(42-m)3m⋅1 a. The Mannose (NH4)(42-n)2n⋅1 a capsules bind selectively Concanavalin A (Con A) in aqueous solution, giving an association avidity constant of K(a)(multi)=4.6×10(4) M(-1) and an enhancement factor of β=K(a)(multi)/K(ass)(mono)=21.9, reminiscent of the formation of "glycoside clusters" on the external surface of glyconanocapsule. The glyconanocapsules (NH4)(42-n)2n⋅1 a and (NH4)(42-m)3m⋅1 a self-assemble in "hybrid multilayers" by successive layer-by-layer deposition of (NH4)(42-n)2n⋅1 a or (NH4)(42-m)3m⋅1 a and Con A. These architectures, reminiscent of versatile mimics of artificial tissues, can be easily prepared and quantified by using quartz crystal microgravimetry (QCM). The "biomimetic hybrid multilayers" described here are stable under a continual water flow and they may serve as artificial networks for a greater depth of understanding of various biological mechanisms, which can directly benefit the fields of chemical separations, sensors or storage-delivery devices.

Size-selective permeation of water-soluble polymers through the bilayer membrane of cyclodextrin vesicles investigated by PFG-NMR

Cyclodextrin vesicles (CDVs) consist of a bilayer of amphiphilic cyclodextrins (CDs). CDVs exhibit CD cavities at their surface that are able to recognize and bind hydrophobic guest molecules via size-selective inclusion. In this study, the permeability of α- and β-CDVs is investigated by pulsed field gradient-stimulated echo (PFG-STE) nuclear magnetic resonance. Diffusion experiments with water and two types of water-soluble polymers, polyethylene glycol (PEG) and polypropylene glycol (PPG), revealed three main factors that influence the exchange rate and permeability of CDVs. First, the length of the hydrophobic chain of the CD amphiphile plays a crucial role. Reasonably, vesicles consisting of amphiphiles with a longer aliphatic chain are less permeable since both membrane thickness and melting temperature T(m) increase. Second, the exchange rate through the bilayer membrane depends on the molecular weight of the polymer and decreases with increasing weight of the polymer. Most interestingly, a size-selective distinction of permeation due to the embedded CDs in the bilayer membrane was found. The mechanism of permeation is shown to occur through the CD cavity, such that depending on the size of the cavity, permeation of polymers with different cross-sectional diameters takes place. Whereas PPG permeates through the membrane of β-CD vesicles, it does not permeate α-CD vesicles.

Self-assembly of soft hybrid materials directed by light and a magnetic field

Dual-responsive soft matter: A soft hybrid material composed of superparamagnetic nanoparticles and cyclodextrin vesicles self-assembles in microscale linear aggregates in water in response to magnetic field as well as light.

Layer-by-layer deposition of vesicles mediated by supramolecular interactions

Vesicles are dynamic supramolecular structures with a bilayer membrane consisting of lipids or synthetic amphiphiles enclosing an aqueous compartment. Lipid vesicles have often been considered as mimics for biological cells. In this paper, we present a novel strategy for the preparation of three-dimensional multilayered structures in which vesicles containing amphiphilic β-cyclodextrin are interconnected by proteins using cyclodextrin guests as bifunctional linker molecules. We compared two pairs of adhesion molecules for the immobilization of vesicles: mannose-concanavalin A and biotin-streptavidin. Microcontact printing and thiol-ene click chemistry were used to prepare suitable substrates for the vesicles. Successful immobilization of intact vesicles through the mannose-concanavalin A and biotin-streptavidin motifs was verified by fluorescence microscopy imaging and dynamic light scattering, while the vesicle adlayer was characterized by quartz crystal microbalance with dissipation monitoring. In the case of the biotin-streptavidin motif, up to six layers of intact vesicles could be immobilized in a layer-by-layer fashion using supramolecular interactions. The construction of vesicle multilayers guided by noncovalent vesicle-vesicle junctions can be taken as a minimal model for artificial biological tissue.

Incorporation of amphiphilic cyclodextrins into liposomes as artificial receptor units

In this article, we describe the introduction of amphiphilic β-cyclodextrins into liposomes to act as artificial receptor units. Using dynamic light scattering, dye encapsulation, and cryogenic transmission electron microscopy, we show that amphiphilic β-cyclodextrins can be mixed in any proportion with a typical mixture of phospholipids and cholesterol to provide stable, spherical, and unilamellar mixed vesicles. It is also possible to form giant unilamellar vesicles with mixtures of lipids and cyclodextrin. The permeability of the mixed vesicles increases with the percentage of cyclodextrin. The cyclodextrins can act as host molecules for hydrophobic guest molecules, even when they are dispersed at a low percentage in the vesicle membrane. It is shown that mixed vesicles can be decorated with carbohydrate-functionalized guest molecules, with photoresponsive guest molecules, and with dye-functionalized guest molecules. Taken together, it is demonstrated that the host-guest chemistry of amphiphilic cyclodextrins is fully compatible with a liposomal bilayer membrane and the advantages of each can be combined to give superior nanocontainers.

Modular synthesis of amphiphilic Janus glycodendrimers and their self-assembly into glycodendrimersomes and other complex architectures with bioactivity to biomedically relevant lectins

The modular synthesis of 7 libraries containing 51 self-assembling amphiphilic Janus dendrimers with the monosaccharides D-mannose and D-galactose and the disaccharide D-lactose in their hydrophilic part is reported. These unprecedented sugar-containing dendrimers are named amphiphilic Janus glycodendrimers. Their self-assembly by simple injection of THF or ethanol solution into water or buffer and by hydration was analyzed by a combination of methods including dynamic light scattering, confocal microscopy, cryogenic transmission electron microscopy, Fourier transform analysis, and micropipet-aspiration experiments to assess mechanical properties. These libraries revealed a diversity of hard and soft assemblies, including unilamellar spherical, polygonal, and tubular vesicles denoted glycodendrimersomes, aggregates of Janus glycodendrimers and rodlike micelles named glycodendrimer aggregates and glycodendrimermicelles, cubosomes denoted glycodendrimercubosomes, and solid lamellae. These assemblies are stable over time in water and in buffer, exhibit narrow molecular-weight distribution, and display dimensions that are programmable by the concentration of the solution from which they are injected. This study elaborated the molecular principles leading to single-type soft glycodendrimersomes assembled from amphiphilic Janus glycodendrimers. The multivalency of glycodendrimersomes with different sizes and their ligand bioactivity were demonstrated by selective agglutination with a diversity of sugar-binding protein receptors such as the plant lectins concanavalin A and the highly toxic mistletoe Viscum album L. agglutinin, the bacterial lectin PA-IL from Pseudomonas aeruginosa, and, of special biomedical relevance, human adhesion/growth-regulatory galectin-3 and galectin-4. These results demonstrated the candidacy of glycodendrimersomes as new mimics of biological membranes with programmable glycan ligand presentations, as supramolecular lectin blockers, vaccines, and targeted delivery devices.

Multivalent glycoliposomes and micelles to study carbohydrate-protein and carbohydrate-carbohydrate interactions

This tutorial review describes multivalent carbohydrate-protein and carbohydrate-carbohydrate interaction studies that utilize self-assembled aggregates of thermodynamically stable liposomes and micelles. Strategies to prepare multivalent glycoliposomes and micelles include: (i) insertion of synthetic glycolipids into matrix lipids; (ii) preparation of glycolipids that aggregate to liposomes and micelles and (iii) modification of the hydrophilic surfaces with desired sugars. Several design strategies have been developed in order to obtain constituent glycolipids, having multivalent sugar moieties and their subsequent interactions with proteins were assessed in relation to the type of linkers that connect the hydrophilic and lipophilic segments. Lipophilic segments other than alkyl chains have also been developed. Polymer based glycoliposomes and micelles form an emphasis. Further, glycoliposomes facilitate studies of carbohydrate-carbohydrate interactions. An overview of the various types of glycoliposomes and micelles used to study carbohydrate-protein and carbohydrate-carbohydrate recognition phenomena is presented.

Cyclodextrin-based multivalent glycodisplays: covalent and supramolecular conjugates to assess carbohydrate-protein interactions

Covalent attachment of biorecognizable sugar ligands in several copies at precise positions of cyclomaltooligosaccharide (cyclodextrin, CD) macrocycles has proven to be an extremely flexible strategy to build multivalent conjugates. The commercial availability of the native CDs in three different sizes, their axial symmetry and the possibility of position- and face-selective functionalization allow a strict control of the valency and spatial orientation of the recognition motifs (glycotopes) in low, medium, high and hyperbranched glycoclusters, including glycodendrimer-CD hybrids. "Click-type" ligation chemistries, including copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC), thiol-ene coupling or thiourea-forming reactions, have been implemented to warrant full homogeneity of the adducts. The incorporation of different glycotopes to investigate multivalent interactions in heterogeneous environments has also been accomplished. Not surprisingly, multivalent CD conjugates have been, and continue to be, major actors in studies directed at deciphering the structural features ruling carbohydrate recognition events. Nanometric glycoassemblies endowed with the capability of adapting the inter-saccharide distances and orientations in the presence of a receptor partner or capable of mimicking the fluidity of biological membranes have been conceived by multitopic inclusion complex formation, rotaxanation or self-assembling. Applications in the fields of sensors, site-specific drug and gene delivery or protein stabilization attest for the maturity of the field.

Mannose-decorated cyclodextrin vesicles: The interplay of multivalency and surface density in lectin-carbohydrate recognition

Cyclodextrin vesicles are versatile models for biological cell membranes since they provide a bilayer membrane that can easily be modified by host–guest interactions with functional guest molecules. In this article, we investigate the multivalent interaction of the lectin concanavalin A (ConA) with cyclodextrin vesicles decorated with mannose–adamantane conjugates with one, two or three adamantane units as well as one or two mannose units. The carbohydrate–lectin interaction in this artificial, self-assembled glycocalyx was monitored in an agglutination assay by the increase of optical density at 400 nm. It was found that there is a close relation between the carbohydrate density at the cyclodextrin vesicle surface and the multivalent interaction with ConA, and the most efficient interaction (i.e., fastest agglutination at lowest concentration) was observed for mannose–adamantane conjugates, in which both the cyclodextrin–adamantane and the lectin–mannose interaction is inherently multivalent.

Self-assembled multivalency: dynamic ligand arrays for high-affinity binding

Multivalency is a powerful strategy for achieving high-affinity molecular recognition in biological systems. Recently, attention has begun to focus on using self-assembly rather than covalent scaffold synthesis to organize multiple ligands. This approach has a number of advantages, including ease of synthesis/assembly, tunability of nanostructure morphology and ligands, potential to incorporate multiple active units, and the responsive nature of self-assembly. We suggest that self-assembled multivalency is a strategy of fundamental importance in the design of synthetic nanosystems to intervene in biological pathways and has potential applications in nanomedicine.

Applications of isothermal titration calorimetry in pure and applied research--survey of the literature from 2010

Isothermal titration calorimetry (ITC) is a biophysical technique for measuring the formation and dissociation of molecular complexes and has become an invaluable tool in many branches of science from cell biology to food chemistry. By measuring the heat absorbed or released during bond formation, ITC provides accurate, rapid, and label-free measurement of the thermodynamics of molecular interactions. In this review, we survey the recent literature reporting the use of ITC and have highlighted a number of interesting studies that provide a flavour of the diverse systems to which ITC can be applied. These include measurements of protein-protein and protein-membrane interactions required for macromolecular assembly, analysis of enzyme kinetics, experimental validation of molecular dynamics simulations, and even in manufacturing applications such as food science. Some highlights include studies of the biological complex formed by Staphylococcus aureus enterotoxin C3 and the murine T-cell receptor, the mechanism of membrane association of the Parkinson's disease-associated protein α-synuclein, and the role of non-specific tannin-protein interactions in the quality of different beverages. Recent developments in automation are overcoming limitations on throughput imposed by previous manual procedures and promise to greatly extend usefulness of ITC in the future. We also attempt to impart some practical advice for getting the most out of ITC data for those researchers less familiar with the method.

Surface modified liposomes by mannosylated conjugates anchored via the adamantyl moiety in the lipid bilayer

The aim of the present study was to encapsulate mannosylated 1-aminoadamantane and mannosylated adamantyltripeptides, namely [(2R)-N-(adamant-1-yl)-3-(α,β-d-mannopyranosyloxy)-2-methylpropanamide and (2R)-N-[3-(α-d-mannopyranosyloxy)-2-methylpropanoyl]-d,l-(adamant-2-yl)glycyl-l-alanyl-d-isoglutamine] in liposomes. The characterization of liposomes, size and surface morphology was performed using dynamic light scattering (DLS) and atomic force microscopy (AFM). The results have revealed that the encapsulation of examined compounds changes the size and surface of liposomes. After the concanavalin A (ConA) was added to the liposome preparation, increase in liposome size and their aggregation has been observed. The enlargement of liposomes was ascribed to the specific binding of the ConA to the mannose present on the surface of the prepared liposomes. Thus, it has been shown that the adamantyl moiety from mannosylated 1-aminoadamantane and mannosylated adamantyltripeptides can be used as an anchor in the lipid bilayer for carbohydrate moiety exposed on the liposome surface.

Design of photosensitizer/cyclodextrin nanoassemblies: spectroscopy, intracellular delivery and photodamage

The engineering of multifunctional nanoparticles carrying photosensitizer drugs (PS) and exposing binding groups for cellular receptors is of increasing interest in therapeutics and diagnostics applications. Natural and modified cyclodextrins (CDs) offer useful scaffolds to bind PS guests by supramolecular interactions. In particular, amphiphilic β-CDs, which form nanoaggregates of diverse shape and size according to the polarity of substituent groups on the rims, include in their different compartments as CD cavity, hydrophilic and hydrophobic portion, PS with different physicochemical properties. PS embedded in cationic amphiphilic CD nanoassemblies are effective in inducing photodynamic damage in cancer cells. For a carrier/PS system to be used in photodynamic therapy (PDT) or photodynamic diagnosis (PDD), the appropriate combination of the delivery characteristics with the preservation of the photodynamic activity of the PS is strictly required. Homogeneous multilayer films based on cationic amphiphilic β-CD entrapping anionic porphyrins can be constructed to exploit interfacial electrostatic interactions between the two components. The capability of CDs to generate restricted microenvironments for PS which can facilitate photoinduced energy transfer with suitable donor molecules was investigated for potential application in fluorescence diagnosis. Besides, recent findings suggest that PDT could represent a useful tool for properly addressing an alternative approach for killing pathogens and combating infections at a clinical level. Finally, modified CDs can bind gold nanoparticles, yielding hybrid organic/inorganic nanoparticles which were studied in water solution and after casting on solid substrates. These binary assemblies could further encapsulate PS or other conventional drugs, opening new intriguing routes on multimodal therapy.

Enhanced chiral recognition by cyclodextrin dimers

In this article we investigate the effect of multivalency in chiral recognition. To this end, we measured the host-guest interaction of a β-cyclodextrin dimer with divalent chiral guests. We report the synthesis of carbohydrate-based water soluble chiral guests functionalized with two borneol, menthol, or isopinocampheol units in either (+) or (−) configuration. We determined the interaction of these divalent guests with a β-cyclodextrin dimer using isothermal titration calorimetry. It was found that—in spite of a highly unfavorable conformation—the cyclodextrin dimer binds to guest dimers with an increased enantioselectivity, which clearly reflects the effect of multivalency.

Glyco-pseudopolyrotaxanes: carbohydrate wheels threaded on a polymer string and their inhibition of bacterial adhesion

We report glyco-pseudopolyrotaxanes composed of cucurbit[6]uril-based mannose wheels (ManCB[6]) threaded on polyviologen (PV), which not only effectively induce bacterial aggregation, but also exhibit high inhibitory activity against bacterial binding to host cells. Three glyco-pseudopolyrotaxanes (1-3), which have 10, 5, and 3 ManCB[6] wheels, respectively, on a PV string, were prepared and characterized. Bacterial aggregation assays and hemagglutination inhibition assays illustrated the specific and multivalent interaction between the glyco-pseudopolyrotaxanes and E. coli ORN178. Compound 3 was especially effective at inducing bacterial aggregation and showed 300 times higher inhibitory potency than monomeric methyl-α-mannoside (Me-αMan) for ORN178-induced hemagglutination. Furthermore, we demonstrated their inhibitory activities for the adhesion of ORN178 bacteria to urinary epithelial cells as a model of urinary tract infection. Our findings suggest that these supramolecular carbohydrate clusters are potentially useful in antiadhesion therapy.

Multivalent interaction of cyclodextrin vesicles, carbohydrate guests, and lectins: a kinetic investigation

An artificial glycocalix self-assembles when unilamellar bilayer vesicles of amphiphilic β-cyclodextrins are decorated with maltose- and lactose-adamantane conjugates by host-guest interactions. The maltose-decorated vesicles aggregate in the presence of lectin concanavalin A whereas the lactose-decorated vesicles aggregate in the presence of lectin peanut agglutinin. The kinetics of the orthogonal multivalent interfacial interactions present in this ternary system of vesicles, carbohydrates, and lectins were studied by time-dependent measurements of the optical density at 400 nm. The average vesicle and vesicle aggregate sizes were monitored by dynamic light scattering. The aggregation process was evaluated as a function of lectin concentration, vesicle concentration, and surface coverage of the vesicles by the carbohydrate-adamantane conjugates. The initial rate of vesicle aggregation scales linearly with the lectin as well as the cyclodextrin vesicle concentration. Furthermore, each lectin requires a characteristic critical density of carbohydrates at the vesicle surface. These observations allow a prediction of the response of the ternary supramolecular system at different concentrations of its components. Also, the effective binding site separation in a multivalent receptor such as a multiple binding site protein can be accurately determined. This methodology can be extended to multivalent noncovalent interactions in other ligand-receptor systems at interfaces.

A universal protocol for photochemical covalent immobilization of intact carbohydrates for the preparation of carbohydrate microarrays

A universal photochemical method has been established for the immobilization of intact carbohydrates and their analogues, and for the fabrication of carbohydrate microarrays. The method features the use of perfluorophenyl azide (PFPA)-modified substrates and the photochemical reaction of surface azido groups with printed carbohydrates. Various aldoses, ketoses, nonreducing sugars such as alditols, and their derivatives can be directly arrayed on the PFPA-modified chips. The lectin-recognition ability of arrayed mannose, glucose, and their oligo- and polysaccharides were confirmed using surface plasmon resonance imaging and laser-induced fluorescence imaging.