Defined micelles: A completely uniform and structurally precise micelle spontaneously formed by exactly seven amphiphilic dendro‐calixarene molecules in aqueous solution has been determined by cryo‐TEM and 3D reconstruction techniques. The picture shows seven calixarene head groups, which have been fit visually into the reconstructed density map of the micelle.
Exactly eight amphiphilic fullerene dendrimer molecules form a globular micelle spontaneously in aqueous solution. This supramolecular organization can be turned on and off by an external stimulus (pH). Owing to the remarkable structure persistence of the micelles, their three‐dimensional structure could be determined from cryogenic transmission electron micrographic images and the molecular architecture was subsequently modeled (see picture).
Bolaamphiphiles (“bolas”) containing two secondary amide groups at the ends of an oligomethylene
chain and two amino acid type headgroups were synthesized. The structures of crystals, of noncovalent
fibers, and of surface monolayers on gold strongly depended on odd−even effects. In the crystal structures
of alanine−alanine dipeptides with C11- and C12-α,ω-amino acid linkers, helical (even number of methylene
groups in the chain) or sheetlike (odd) arrangements of the headgroups were found. Bolas containing two
different amino acid end groups, namely, d- or l-alanine and l-lysine, connected by the same C11- and C12
linkers did not crystallize. Only the even-numbered bolas gave fibers. l- and d- configurations of alanine
headgroups affected the curvature of the fibers. Diamido bolas with terminal SH-groups self-assembled
on gold. Only those with even-numbered chains gave rigid monolayers. Simple stereochemical arguments
concerning the fitting of amide hydrogen bond chains on both ends of the bolas are given to explain the
observed differences in crystals, fibers, and monolayers.
A new class of non‐ionic dendronized multiamphiphilic polymers is prepared from a biodegradable (AB)n‐type diblock polymer synthesized from 2‐azido‐1,3‐propanediol (azido glycerol) and polyethylene glycol (PEG)‐600 diethylester using Novozym‐435 (Candida antarctica lipase) as a biocatalyst, following a well‐established biocatalytic route. These polymers are functionalized with dendritic polyglycerols (G1 and G2) and octadecyl chains in different functionalization levels via click chemistry to generate dendronized multiamphiphilic polymers. Surface tension measurements and dynamic light scattering studies reveal that all of the multiamphiphilic polymers spontaneously self‐assemble in aqueous solution. Cryogenic transmission electron microscopy further proves the formation of multiamphiphiles towards monodisperse spherical micelles of about 7–9 nm in diameter. The evidence from UV–vis and fluorescence spectroscopy suggests the effective solubilization of hydrophobic guests like pyrene and 1‐anilinonaphthalene‐8‐sulfonic acid within the hydrophobic core of the micelles. These results demonstrate the potential of these dendronized multiamphiphilic polymers for the development of prospective drug delivery systems for the solubilization of poorly water soluble drugs.
We show by molecular-dynamics (MD) simulations and cryo-transmission electron microscopy (cryo-TEM) experiments that the size and form of structurally persistent micelles formed by the T-shaped amphiphile 1 are controlled by the counterions. The two techniques reveal that the micelles are specifically stabilized by sodium counterions relative to potassium ions. Both the simulations and the cryo-TEM experiments suggest that the micelles are stabilized by strongly conserved hydrated contact ion pairs with sodium counterions but not with potassium ions. We suggest that the TEM is observing local high density due to hydrated carboxylate/sodium ion pairs at the surface of the micelle. A high concentration of such structures is found in MD simulations with sodium counterions, but not with potassium.
Herein, we present the design and synthesis of a catalytically active peptide-nanoparticle conjugate whose activity is regulated by a defined conformational change in the self-assembled peptide monolayer. A catalytically active peptide, designed after the heterodimeric α-helical coiled-coil principle was immobilized onto gold nanoparticles, and kinetic studies were performed according to the Michaelis-Menten model. The formed peptide monolayer at the gold nanoparticle surface accelerated p-nitrophenylacetate (pNPA) hydrolysis by 1 order of magnitude compared to the soluble peptide while exhibiting no defined secondary structure as determined by infrared (IR) and circular dichroism (CD) spectroscopy. Addition of the complementary peptide-induced coiled-coil formation while significantly hindering the pNPA hydrolysis catalyzed by the peptide-nanoparticle conjugate. The heptad repeat sequence of a coiled-coil opens up the opportunity for regulation of conformation and thus catalytic activity of peptide-nanoparticle conjugates upon interaction with a complementary coiled-coil sequence. Strategies of regulation of catalytic activity by interaction with a complementary cofactor/ligand are well-established in nature and are introduced here into rationally designed peptide-nanoparticle conjugates.
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.