The metal‐free hydrogen activator 1 catalyzes the unique P/B hydrogenation of the frustrated Lewis pair 3, which itself is inactive toward H2 under the applied conditions, to yield the hydrogenation product 4. System 1/2 (5 mol %) also catalyzes the hydrogenation of a bulky ketimine and of enamines under mild conditions (2.5 bar H2, RT) to yield the respective amines.
Nonspecific
adsorption of biomolecules to solid surfaces, a process
called biofouling, is a major concern in many biomedical applications.
Great effort has been made in the development of antifouling polymer
coatings that are capable of repelling the nonspecific adsorption
of proteins, cells, and micro-organisms. In this respect, we herein
contribute to understanding the factors that determine which polymer
brush results in the best antifouling coating. To this end, we compared
five different monomers: two sulfobetaines, a carboxybetaine, a phosphocholine,
and a hydroxyl acrylamide. The antifouling coatings were analyzed
using our previously described bead-based method with flow cytometry
as the read-out system. This method allows for the quick and automated
analysis of thousands of beads per second, enabling fast analysis
and good statistics. We report the first direct comparison made between
a sulfobetaine with opposite charges separated by two and three methylene
groups and a carboxybetaine bearing two separating methylene groups.
It was concluded that both the distance between opposite charges and
the nature of the anionic groups have a distinct effect on the antifouling
performance. Phosphocholines and simple hydroxyl acrylamides are not
often compared with the betaines. However, here we found that they
perform equally well or even better, yielding the following overall
antifouling ranking: HPMAA ≥ PCMA-2 ≈ CBMAA-2 > SBMAA-2
> SBMAA-3 ≫ nonmodified beads (HPMAA being the best).
RGD tripeptide motifs frequently mediate ligand binding to integrins. The type IV secretion system (T4SS) protein CagL of the gastric pathogen Helicobacter pylori also contains an RGD motif. CagL decorates the T4SS pilus and may function as an adhesin for host cells. Whether CagL binds integrins via its RGD motif is under debate. Here, we present crystal structures of CagL revealing an elongated four-helix bundle that appears evolutionarily unrelated to the proposed VirB5 orthologs. The RGD motif is surface-exposed but located within a long α helix. This is unprecedented as previously characterized integrin-binding RGD motifs are located within extended or flexible loops. Yet, adhesion of gastric epithelial cells to CagL was strictly RGD-dependent. Comparison of seven crystallographically independent molecules reveals substantial structural flexibility. Intramolecular disulfide bonds engineered to reduce CagL flexibility resulted in more stable protein, but unable to support cell adhesion. CagL may thus partly unfold during receptor binding.
To enhance the sensitivity and selectivity of surface-based (bio)sensors, it is of crucial importance to diminish background signals that arise from the nonspecific binding of biomolecules, so-called biofouling. Zwitterionic polymer brushes have been shown to be excellent antifouling materials. However, for sensing purposes, antifouling does not suffice but needs to be combined with the possibility to efficiently modify the brush with recognition units. So far this has been achieved only at the expense of either antifouling properties or binding capacity. Herein we present a conceptually new approach by integrating both characteristics into a single tailor-made monomer: a novel sulfobetaine-based zwitterionic monomer equipped with a clickable azide moiety. Copolymerization of this monomer with a well-established standard sulfobetaine monomer results in highly antifouling surface coatings with a large yet tunable number of clickable groups present throughout the entire brush. Subsequent functionalization of the azido brushes via widely used strain-promoted alkyne azide click reactions yields fully zwitterionic 3D-functionalized coatings with a recognition unit of choice that can be tailored for any specific application. Here we show a proof of principle with biotin-functionalized brushes on SiN that combine excellent antifouling properties with specific avidin binding from a protein mixture. The signal-to-noise ratio is significantly improved over that of traditional chain-end modification of sulfobetaine polymer brushes, even if the azide content is lowered to 1%. This therefore offers a viable approach to the development of biosensors with greatly enhanced performance on any surface.
Frustbewältigung: Der metallfreie Wasserstoffaktivator 1 katalysiert die ungewöhnliche P/B‐Hydrierung des „frustrierten“ Lewis‐Paars 3, das unter den Reaktionsbedingungen selbst nicht mit H2 reagiert, und liefert das zwitterionische Produkt 4. Das System 1/2 (5 Mol‐%) katalysiert auch die Hydrierung eines sperrigen Ketimins und von Enaminen unter milden Bedingungen (2.5 bar H2) zu den entsprechenden Aminen.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.