Heteromultivalent Ligand Display on Reversible Self-Assembled Monolayers (rSAMs): A Fluidic Platform for Tunable Influenza Virus Recognition.

We report on the design of heteromultivalent influenza A virus (IAV) receptors based on reversible self-assembled monolayers (SAMs) featuring two distinct mobile ligands. The principal layer building blocks consist of α-(4-amidinophenoxy)alkanes decorated at the ω-position with sialic acid (SA) and the neuraminidase inhibitor Zanamivir (Zan), acting as two mobile ligands binding to the complementary receptors hemagglutinin (HA) and neuraminidase (NA) on the virus surface. From ternary amphiphile mixtures comprising these ligands, the amidines spontaneously self-assemble on top of carboxylic acid-terminated SAMs to form reversible mixed monolayers (rSAMs) that are easily tunable with respect to the ligand ratio. We show that this results in the ability to construct surfaces featuring a very strong affinity for the surface proteins and specific virus subtypes. Hence, an rSAM prepared from solutions containing 15% SA and 10% Zan showed an exceptionally high affinity and selectivity for the avian IAV H7N9 (Kd = 11 fM) that strongly exceeded the affinity for other subtypes (H3N2, H5N1, H1N1). Changing the SA/Zan ratio resulted in changes in the relative preference between the four tested subtypes, suggesting this to be a key parameter for rapid adjustments of both virus affinity and selectivity.

Reversible Self-Assembled Monolayers with Tunable Surface Dynamics for Controlling Cell Adhesion Behavior.

Cells adhering onto surfaces sense and respond to chemical and physical surface features. The control over cell adhesion behavior influences cell migration, proliferation, and differentiation, which are important considerations in biomaterial design for cell culture, tissue engineering, and regenerative medicine. Here, we report on a supramolecular-based approach to prepare reversible self-assembled monolayers (rSAMs) with tunable lateral mobility and dynamic control over surface composition to regulate cell adhesion behavior. These layers were prepared by incubating oxoacid-terminated thiol SAMs on gold in a pH 8 HEPES buffer solution containing different mole fractions of ω-(ethylene glycol)2-4- and ω-(GRGDS)-, α-benzamidino bolaamphiphiles. Cell shape and morphology were influenced by the strength of the interactions between the amidine-functionalized amphiphiles and the oxoacid of the underlying SAMs. Dynamic control over surface composition, achieved by the addition of inert filler amphiphiles to the RGD-functionalized rSAMs, reversed the cell adhesion process. In summary, rSAMs featuring mobile bioactive ligands offer unique capabilities to influence and control cell adhesion behavior, suggesting a broad use in biomaterial design, tissue engineering, and regenerative medicine.

Discrimination of deletion to point cytokine mutants based on an array of cross-reactive receptors mimicking protein recognition by heparan sulfate.

Differential sensing of proteins based on cross-reactive arrays and pattern recognition is a promising technique for the detection and identification of proteins. In this study, a rational biomimetic strategy has been used to prepare sensing materials capable of discriminating structurally similar proteins, such as deletion and point mutants of a cytokine, by mimicking the biological properties of heparan sulfate (HS). Using the self-assembly of two disaccharides, lactose and sulfated lactose at various ratios on the surface of a chip, an array of combinatorial cross-reactive receptors has been prepared. Coupling with surface plasmon resonance imaging (SPRi), the obtained cross-reactive array is very efficient for protein sensing. It is able to detect HS binding proteins (HSbps) such as IFNγ at nanomolar concentrations. Moreover, such a system is capable of discriminating between IFNγ and its mutants with good selectivity.

Lipid Bilayer-like Mixed Self-Assembled Monolayers with Strong Mobility and Clustering-Dependent Lectin Affinity.

Glycans at the surface of cellular membranes modulate biological activity via multivalent association with extracellular messengers. The lack of tuneable simplified models mimicking this dynamic environment complicates basic studies of these phenomena. We here present a series of mixed reversible self-assembled monolayers (rSAMs) that addresses this deficiency. Mixed rSAMs were prepared in water by simple immersion of a negatively charged surface in a mixture of sialic acid- and hydroxy-terminated benzamidine amphiphiles. Surface compositions derived from infrared reflection-absorption spectroscopy (IRAS) and film thickness information (atomic force microscopy, ellipsometry) suggest the latter to be statistically incorporated in the monolayer. These surfaces' affinity for the lectin hemagglutinin revealed a strong dependence of the affinity on the presentation, density, and mobility of the sialic acid ligands. Hence, a spacer length of 4 ethylene glycol and a surface density of 15% resulted in a dissociation constant Kd,multi of 1.3 × 10-13 M, on par with the best di- or tri-saccharide-based binders reported to date, whereas a density of 20% demonstrated complete resistance to hemagglutinin binding. These results correlated with ligand mobility measured by fluorescence recovery after photobleaching which showed a dramatic drop in the same interval. The results have a direct bearing on biological cell surface multivalent recognition involving lipid bilayers and may guide the design of model surfaces and sensors for both fundamental and applied studies.

What is really driving cell-surface interactions? Layer-by-layer assembled films may help to answer questions concerning cell attachment and response to biomaterials.

Layer-by-layer (LbL) assembled multicomponent films offer the opportunity to control and to fine-tune cell attachment and behavior on solid surfaces [Layer-by-Layer Films for Biomedical Applications, edited by Picart et al. (Wiley, Weinheim, 2014) and El-Khouri et al., "Multifunctional layer-by-layer architectures for biological applications," in Functional Polymeric Ultrathin Films, edited by Advincula and Knoll (Wiley, Weinheim, 2011), Vol. 1]. At the same time, these films allow for quite detailed physicochemical characterization of static and dynamic surface properties that are typically not available in classic cell culture. In this report, the authors investigate cell adhesion and cytocompatibility of compositionally and morphologically similar thin films composed of oppositely charged synthetic or natural polyelectrolytes in which different physical parameters such as surface charge or water content are varied through chemical composition and deposition conditions. Human adult dermal fibroblasts were chosen as a model because of the need for chemically defined matrix in the field of primary cell amplification. The growth and the stability of the multilayer films in the incubation media were studied dissipation-enhanced quartz crystal micobalance (QCM-D) and ellipsometry. The QCM-D signals observed during the film deposition were analyzed qualitatively to estimate the viscoelastic properties of the films. The authors used contact angle measurements with water to study the contribution of the chemical functionalities to wetting behavior of the films. Most importantly, they also studied the interaction of the films with serum components. Our results underline that cell adhesion is a highly complex process which is not only governed by the functionality of a surface but also by its morphology, its affinity for serum components, and also by changes of surface properties brought about by adsorbing molecules. Of the many LbL-films tested, poly(4-styrenesulfonate)/poly(allyl amine) multilayers were best suited for our fibroblast cultures, which opens a way to avoid gelatin based and similar substrates whose exact chemical composition is unknown.

Evidence for the formation of an intermediate complex in the direct metalation of tetra(4-bromophenyl)-porphyrin on the Cu(111) surface.

A strong molecule-surface interaction between free-base-tetra(4-bromophenyl)-porphyrin and Cu(111) results in a distortion of both the molecule and the underlying copper surface in the vicinity of the molecule. This in turn leads to the formation of an intermediate complex due to bonding between the iminic nitrogens and surface copper atoms.

Self-assembled rows of Ni porphyrin dimers on the Ag(111) surface.

The growth and ordering of 5-(10,15,20-triphenylporphyrinatonickel(ii))dimer (NiTPP-dimer) molecules on the Ag(111) surface have been investigated using scanning tunnelling microscopy/spectroscopy (STM/STS) and low-energy electron diffraction (LEED). At one monolayer (ML) coverage the NiTPP-dimer forms a well-ordered close-packed molecular layer in which the porphyrin molecules have a flat orientation with the molecular plane lying parallel to the substrate. STM and LEED data obtained from one monolayer of the NiTPP-dimer on the Ag(111) surface show the formation of three domains which grow along the main crystallographic directions of the substrate. Scanning tunnelling spectroscopy data obtained from the NiTPP-dimer on the Ag(111) surface show good agreement with optical band gap measurements and density functional theory calculations.