Fuel-driven
dissipative self-assemblies play essential roles in
living systems, contributing both to their complex, dynamic structures
and emergent functions. Several dissipative supramolecular materials
have been created using chemicals or light as fuel. However, electrical
energy, one of the most common energy sources, has remained unexplored
for such purposes. Here, we demonstrate a new platform for creating
active supramolecular materials using electrically fueled dissipative
self-assembly. Through an electrochemical redox reaction network,
a transient and highly active supramolecular assembly is achieved
with rapid kinetics, directionality, and precise spatiotemporal control.
As electronic signals are the default information carriers in modern
technology, the described approach offers a potential opportunity
to integrate active materials into electronic devices for bioelectronic
applications.
Molecular self-assembly is pervasive
in the formation of living
and synthetic materials. Knowledge gained from research into the principles
of molecular self-assembly drives innovation in the biological, chemical,
and materials sciences. Self-assembly processes span a wide range
of temporal and spatial domains and are often unintuitive and complex.
Studying such complex processes requires an arsenal of analytical
and computational tools. Within this arsenal, the transmission electron
microscope stands out for its unique ability to visualize and quantify
self-assembly structures and processes. This review describes the
contribution that the transmission electron microscope has made to
the field of molecular self-assembly. An emphasis is placed on which
TEM methods are applicable to different structures and processes and
how TEM can be used in combination with other experimental or computational
methods. Finally, we provide an outlook on the current challenges
to, and opportunities for, increasing the impact that the transmission
electron microscope can have on molecular self-assembly.
Liquid-phase
transmission electron microscopy (LP-TEM) enables
the real-time visualization of nanoscale dynamics in solution. This
technique has been used to study the formation and transformation
mechanisms of organic and inorganic nanomaterials. Here, we study
the formation of block-copolymer-supported bilayers using LP-TEM.
We observe two formation pathways that involve either liquid droplets
or vesicles as intermediates toward supported bilayers. Quantitative
image analysis methods are used to characterize vesicle spread rates
and show the origin of defect formation in supported bilayers. Our
results suggest that bilayer assembly methods that proceed via liquid
droplet intermediates should be beneficial for forming pristine supported
bilayers. Furthermore, supported bilayers inside the liquid cells
may be used to image membrane interactions with proteins and nanoparticles
in the future.
Metal−organic frameworks (MOFs) are a class of porous nanomaterials that have been extensively studied as enzyme immobilization substrates. During in situ immobilization, MOF nucleation is driven by biomolecules with low isoelectric points. Investigation of how biomolecules control MOF self-assembly mechanisms on the molecular level is key to designing nanomaterials with desired physical and chemical properties. Here, we demonstrate how molecular modifications of bovine serum albumin (BSA) with fluorescein isothiocyanate (FITC) can affect MOF crystal size, morphology, and encapsulation efficiency. Final crystal properties are characterized using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), fluorescent microscopy, and fluorescence spectroscopy. To probe MOF self-assembly, in situ experiments were performed using cryogenic transmission electron microscopy (cryo-TEM) and X-ray diffraction (XRD). Biophysical characterization of BSA and FITC-BSA was performed using ζ potential, mass spectrometry, circular dichroism studies, fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The combined data reveal that protein folding and stability within amorphous precursors are contributing factors in the rate, extent, and mechanism of crystallization. Thus, our results suggest molecular modifications as promising methods for fine-tuning protein@ MOFs' nucleation and growth.
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