Accurate DOSY measure of out-of-equilibrium systems by permutated DOSY (p-DOSY)

NMR spectroscopy is an excellent tool for monitoring in-situ chemical reactions. In particular, DOSY measurement is well suited to characterize transient species by the determination of their sizes. However, here we bring to light a difficulty in the DOSY experiments performed in out-of-equilibrium systems. On such a system, the evolution of the concentration of species interferes with the measurement process, and creates a bias on the diffusion coefficient determination that may lead to erroneous interpretations. We show that a random permutation of the series of gradient strengths used during the DOSY experiment allows to average out this bias. This approach, that we name p-DOSY does not require changes in the the pulse sequences nor in the processing software, and restores completely the full accuracy of the measure. This technique is demonstrated on the monitoring of the anomerization reaction of \alpha- to \beta-glucose.Comment: Revised version - 15 pages, 8 figures program archived at 10.5281/zenodo.1926

Manipulating and monitoring nanoparticles in micellar thin film superstructures

Understanding the dynamics of discrete self-assembled structures under influence of external triggers is of interest to harvest the potential of nano- and mesoscale materials. In particular, controlling the hierarchical organization of (macro)molecular and nanoparticle building blocks in monolayer superstructures is of paramount importance for tuning properties and characteristics. Here we show how the electron beam in cryo-transmission electron microscopy can be exploited to induce and follow local migration of building blocks and global migration of micellar aggregates inside micrometer-sized superstructures. We employ stroboscopic exposure to heat up and convert the vitrified superstructure into a liquid-like thin film under cryogenic conditions, resulting in controlled evaporation of water that finally leads to rupture of the micelle-containing superstructure. Micelle-embedded nanoparticles prove a powerful tool to study the complex hierarchically built-up superstructures, and to visualize both global movement of individual dendrimicelles and local migration of nanoparticles inside the micellar core during the exposure series.</p

Nanoparticles reveal Extreme Size-Sorting and Morphologies in Complex Coacervate Superstructures

We here provide detailed insight in self-assembled complex coacervate systems exploiting gold nanoparticles for cryoTEM contrast. Nanoparticle-containing dendrimicelles are formed from fifth-generation dendrimer-encapsulated nanoparticles (DENs) and dendrimer-stabilized nanoparticles (DSNs). The complex coacervate structures self-organize in biconcave thin water layers into size-sorted monolayer superstructures. The embedded nanoparticles are a straightforward tool to visualize dendrimicelles and determine the aggregation number and polydispersity. The superstructure shows extreme size-sorting patterns which, contrary to related systems with higher generation dendrimers, consists not only of dendrimicelles but also much bigger complex coacervate nanoassemblies, such as vesicles.</p

Controlled mixing of lanthanide(III) ions in coacervate core micelles

This article presents a facile strategy to combine Eu3+ and Gd3+ ions into coacervate core micelles in a controlled way with a statistical distribution of the ions. Consequently, the formed micelles show a high tunability between luminescence and relaxivity. These highly stable micelles present great potential for new materials, e.g. as bimodal imaging probes

Controlling Trapping, Release, and Exchange Dynamics of Micellar Core Components

Whereas the formation and overall stability of hierarchically organized self-assembled supramolecular structures have been extensively investigated, the mechanistic aspects of subcomponent dynamics are often poorly understood or controlled. Here we show that the dynamics of polyamidoamine (PAMAM) dendrimer based micelles can be manipulated by changes in dendrimer generation, pH, and stoichiometry, as proven by NMR and FRET. For this, dendrimers were functionalized with either fluorescein (donor) or rhodamine (acceptor) and encapsulated into separate micelles. Upon mixing, exchange of dendrimers is revealed by an increase in FRET. While dendrimicelles based on dendrimer generations 4 and 5 show a clear increase in FRET in time, revealing the dynamic exchange of dendrimers between micellar cores, generation 6 based micelles appear to be kinetically trapped systems. Interestingly, generation 6 based dendrimicelles prepared at a pH of 7.8 rather than 7.0 do show exchange dynamics, which can be attributed to about 25% less charge of the dendrimer, corresponding to the charge of a virtual generation 5.5 dendrimer at neutral pH. Changing the pH of dendrimicelle solutions prepared at a pH of 7.8 to 7.0 shows the activated release of dendrimers. High-resolution NMR spectra of the micellar core are obtained from a 1.2 GHz spectrometer with sub-micromolar sensitivity, with DOSY discriminating released dendrimers from dendrimers still present in the micellar core. This study shows that dendrimer generation, charge density, and stoichiometry are important mechanistic factors for controlling the dynamics of complex coacervate core micelles. This knowledge can be used to tune micelles between kinetically trapped and dynamic systems, with tuning of exchange and/or release speeds, to be tailored for applications in, e.g., material science, sensors, or drug delivery