Molecular recognition based on low-affinity polyvalent interactions: selective binding of a carboxylated polymer to fibronectin fibrils of live fibroblast cells

To explore molecular recognition of biomolecules in the complex environment of the extracellular matrix, we utilized two fluorescent poly(p-phenyleneethynylene)s bearing either cationic alkylammonium or negatively charged carboyxlate side chains. While incubation of live NIH 3T3 fibroblast cells with the cationic polymer yielded perinuclear punctate staining reminiscent of endocytotic vesicles, the carboxylated polymer revealed a characteristic filamentous staining pattern. Histochemical and immunofluorescence studies demonstrated that the anionic PPE selectively binds to fibronectin fibrils of the extracellular matrix. An in vitro binding study revealed a dissociation constant of approximately 100 nM for the fibronectin-polymer complex. Both polymers showed bright two-photon excited emission as well as low toxicity, rendering them well-suited for live cell imaging studies. The studies demonstrate that selective molecular recognition of biomolecules in the complex environment of the extracellular matrix can be achieved by means of nonspecific low-affinity polyvalent interactions.     

Scalable Production of Monodisperse Bioactive Spider Silk Nanowires

Elongated protein-based micro- and nanostructures are of great interest for a wide range of biomedical applications, where they can serve as a backbone for surface functionalization and as vehicles for drug delivery. Current production methods for protein constructs lack precise control of either shape and dimensions or render structures fixed to substrates. This work demonstrates production of recombinant spider silk nanowires suspended in solution, starting with liquid bridge induced assembly (LBIA) on a substrate, followed by release using ultrasonication, and concentration by centrifugation. The significance of this method lies in that it provides i) reproducability (standard deviation of length <13% and of diameter <38%), ii) scalability of fabrication, iii) compatibility with autoclavation with retained shape and function, iv) retention of bioactivity, and v) easy functionalization both pre- and post-formation. This work demonstrates how altering the function and nanotopography of a surface by nanowire coating supports the attachment and growth of human mesenchymal stem cells (hMSCs). Cell compatibility is further studied through integration of nanowires during aggregate formation of hMSCs and the breast cancer cell line MCF7. The herein-presented industrial-compatible process enables silk nanowires for use as functionalizing agents in a variety of cell culture applications and medical research.     

Calibrating the X‐ray attenuation of liquid water and correcting sample movement artefacts during in operando synchrotron X‐ray radiographic imaging of polymer electrolyte membrane fuel cells

Synchrotron X‐ray radiography, due to its high temporal and spatial resolutions, provides a valuable means for understanding the in operando water transport behaviour in polymer electrolyte membrane fuel cells. The purpose of this study is to address the specific artefact of imaging sample movement, which poses a significant challenge to synchrotron‐based imaging for fuel cell diagnostics. Specifically, the impact of the micrometer‐scale movement of the sample was determined, and a correction methodology was developed. At a photon energy level of 20 keV, a maximum movement of 7.5 µm resulted in a false water thickness of 0.93 cm (9% higher than the maximum amount of water that the experimental apparatus could physically contain). This artefact was corrected by image translations based on the relationship between the false water thickness value and the distance moved by the sample. The implementation of this correction method led to a significant reduction in false water thickness (to ～0.04 cm). Furthermore, to account for inaccuracies in pixel intensities due to the scattering effect and higher harmonics, a calibration technique was introduced for the liquid water X‐ray attenuation coefficient, which was found to be 0.657 ± 0.023 cm^?1 at 20 keV. The work presented in this paper provides valuable tools for artefact compensation and accuracy improvements for dynamic synchrotron X‐ray imaging of fuel cells.     

Scanning tunneling microscopy as a tool to study catalytically relevant model systems

The surface science approach to catalysis, pioneered by 2007 Nobel Laureate in chemistry Gerhard Ertl, has helped revolutionize our understanding of heterogeneous catalysis at the atomic level. In this tutorial review we show how the scanning tunnelling microscope (STM), in combination with this surface science approach, is a very important tool for the study of catalytically relevant model systems. We illustrate how the high spatial and temporal resolution of the STM can be used to obtain quantitative information on elementary processes involved in surface catalyzed reactions. Furthermore, we show that the STM is an outstanding surface science tool to bridge the materials gap and the pressure gap between surface science experiments and real catalysis. Finally, we show that we are approaching an era where the atomic-scale insight gained from fundamental STM surface science studies can be used for the rational design of new catalysts from first principles.     

Aggregation and interaction of cationic nanoparticles on bacterial surfaces

Cationic monolayer-protected gold nanoparticles (AuNPs) with sizes of 6 or 2 nm interact with the cell membranes of Escherichia coli (Gram-) and Bacillus subtilis (Gram+), resulting in the formation of strikingly distinct AuNP surface aggregation patterns or lysis depending upon the size of the AuNPs. The aggregation phenomena were investigated by transmission electron microscopy and UV-vis spectroscopy. Upon proteolytic treatment of the bacteria, the distinct aggregation patterns disappeared.     

Improved syntheses of precursors for PET radioligands [F]XTRA and [F]AZAN

Improved syntheses of 7-methyl-2-exo-[3′-(2-bromopyridin-3-yl)-5′-pyridinyl]-7-azabicyclo[2.2.1]heptanes (3) and 7-methyl-2-exo-[3’-(6-bromopyridin-2-yl)-5′-pyridinyl]-7-azabicyclo[2.2.1]heptanes (4), precursors for PET radioligands [¹⁸F]XTRA (1) and [¹⁸F]AZAN (2), involving a key Stille coupling step followed by deprotection of Boc group and N-methylation are described. The new synthetic procedures provided the title compounds in more than 40% overall yields.