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.

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.

Reprint of: Antiproliferative activity of the Antrodia camphorata secondary metabolite 4,7-dimethoxy-5-methylbenzo[d][1,3]dioxole and analogues.

Both the traditional Chinese medicinal fungus, Antrodia camphorata, and its secondary metabolite, 4,7-dimethoxy-5-methylbenzo[d][1,3]dioxole, have been reported to possess promising anticancer activity. In this work the natural product and analogues bearing more polar substituents were synthesised and assessed for antiproliferative activity in the NCI-60 screen. Although each compound inhibited the growth of some cell lines at 10µM, none had sufficient activity to warrant further investigation.

Reversible Self-Assembled Monolayers (rSAMs) as Robust and Fluidic Lipid Bilayer Mimics.

Lipid bilayers, forming the outer barrier of cells, display a wide array of proteins and carbohydrates for modulating interfacial biological interactions. Formed by the spontaneous self-assembly of lipid molecules, these bilayers feature liquid crystalline order, while retaining a high degree of lateral mobility. Studies of these dynamic phenomena have been hampered by the fragility and instability of corresponding biomimetic cell membrane models. Here, we present the construct of a series of oligoethylene glycol-terminated reversible self-assembled monolayers (rSAMs) featuring lipid-bilayer-like fluidity, while retaining air and protein stability and resistance. These robust and ordered layers were prepared by simply immersing a carboxylic acid-terminated self-assembled monolayer into 5-50 µM aqueous ω-(4-ethylene glycol-phenoxy)-α-(4-amidinophenoxy)decane solutions. It is anticipated that this new class of robust and fluidic two-dimensional biomimetic surfaces will impact the design of rugged cell surface mimics and high-performance biosensors.

Reversible Self-Assembled Monolayers (rSAMs): Adaptable Surfaces for Enhanced Multivalent Interactions and Ultrasensitive Virus Detection.

We report on the design of pH-switchable monolayers allowing a reversible and ordered introduction of affinity reagents on sensor surfaces. The principal layer building blocks consist of α-(4-amidinophenoxy)alkanes decorated at the ω-position with affinity ligands. These spontaneously self-assemble on top of carboxylic acid terminated SAMs to form reversible homo or mixed monolayers (rSAMs) that are tunable with respect to the nature of the head group, layer order and stability while featuring pH responsiveness and the dynamic nature of noncovalent build assemblies. We show that this results in a range of unique biosensor features. As a first example a sialic acid rSAM featuring strong lectin affinity is here used to sense hemagglutinin and influenza virus (H5N1) at the pM and fM level by in situ ellipsometry in a fully reversible fashion. We believe that the rSAM concept will find widespread use in surface chemistry and overall for boosting sensitivity in affinity biosensors.

Antiproliferative activity of the Antrodia camphorata secondary metabolite 4,7-dimethoxy-5-methylbenzo[d][1,3]dioxole and analogues.

Both the traditional Chinese medicinal fungus, Antrodia camphorata, and its secondary metabolite, 4,7-dimethoxy-5-methylbenzo[d][1,3]dioxole, have been reported to possess promising anticancer activity. In this work the natural product and analogues bearing more polar substituents were synthesised and assessed for antiproliferative activity in the NCI-60 screen. Although each compound inhibited the growth of some cell lines at 10µM, none had sufficient activity to warrant further investigation.

An Epitope-Imprinted Biointerface with Dynamic Bioactivity for Modulating Cell-Biomaterial Interactions.

In this study, an epitope-imprinting strategy was employed for the dynamic display of bioactive ligands on a material interface. An imprinted surface was initially designed to exhibit specific affinity towards a short peptide (i.e., the epitope). This surface was subsequently used to anchor an epitope-tagged cell-adhesive peptide ligand (RGD: Arg-Gly-Asp). Owing to reversible epitope-binding affinity, ligand presentation and thereby cell adhesion could be controlled. As compared to current strategies for the fabrication of dynamic biointerfaces, for example, through reversible covalent or host-guest interactions, such a molecularly tunable dynamic system based on a surface-imprinting process may unlock new applications in in situ cell biology, diagnostics, and regenerative medicine.

Access to 1,2,3,4-Tetraoxygenated Benzenes via a Double Baeyer-Villiger Reaction of Quinizarin Dimethyl Ether: Application to the Synthesis of Bioactive Natural Products from Antrodia camphorata.

The first systematic investigation into the Baeyer-Villiger reaction of an anthraquinone is presented. The double Baeyer-Villiger reaction of quinizarin dimethyl ether is viable, directly providing the dibenzo[b,f][1,4]-dioxocin-6,11-dione ring-system, which is otherwise difficult to prepare. This methodology provides rapid access to 1,2,3,4-tetraoxygenated benzenes, and has been exploited by application to the total synthesis of a natural occurring benzodioxole and its biphenyl dimer, which both display noteworthy biological activity. Interestingly, the axially chiral biphenyl was found to be configurationally stable, but the resolved enantiomers exhibit no optical activity at the αD-line.