33 research outputs found
Modifying the Morphology of Silicon Surfaces by Laser Induced Liquid Assisted Colloidal Lithography
Single, or isolated small arrays of, spherical silica colloidal particles (with refractive index ncolloid = 1.47 and radius R = 350 nm or 1.5 ÎŒm) were placed on a silicon substrate and immersed in carbon tetrachloride (nliquid = 1.48) or toluene (nliquid = 1.52). Areas of the sample were then exposed to a single laser pulse (8 ps duration, wavelength λ = 355 nm), and the spatial intensity modulation of the near field in the vicinity of the particles revealed via the resulting patterning of the substrate surface. In this regime, ncolloid < nliquid and the near-field optical intensification is concentrated at and beyond the edge of the particle. Detailed experimental characterization of the irradiated Si surface using atomic force microscopy reveals contrasting topographies. The same optical behavior is observed with both liquids, i.e., the incident laser light diverges on interaction with the colloidal particle, but the resulting interaction with the substrate is liquid dependent. Topographic analysis indicates localized ablation and patterning of the Si substrate when using toluene, whereas the patterning induced under carbon tetrachloride is on a larger scale and extends well below the original substrate surfaceâhinting at a laser induced photochemical contribution to the surface patterning
âCrossâ Supermicelles via the Hierarchical Assembly of Amphiphilic Cylindrical Triblock Comicelles
Self-assembled
âcrossâ architectures are well-known
in biological systems (as illustrated by chromosomes, for example);
however, comparable synthetic structures are extremely rare. Herein
we report an in depth study of the hierarchical assembly of the amphiphilic
cylindrical PâHâP triblock comicelles with polar (P)
coronal ends and a hydrophobic (H) central periphery in a selective
solvent for the terminal segments which allows access to âcrossâ
supermicelles under certain conditions. Well-defined PâHâP
triblock comicelles MÂ(PFS-<i>b</i>-PtBA)-<i>b</i>-MÂ(PFS-<i>b</i>-PDMS)-<i>b</i>-MÂ(PFS-<i>b</i>-PtBA) (M = micelle segment, PFS = polyferrocenyldimethylsilane,
PtBA = polyÂ(<i>tert</i>-butyl acrylate), and PDMS = polydimethylsiloxane)
were created by the living crystallization-driven self-assembly (CDSA)
method. By manipulating two factors in the supermicelles, namely the
H segment-solvent interfacial energy (through the central H segment
length, <i>L</i><sub>1</sub>) and coronal steric effects
(via the PtBA corona chain length in the P segment, <i>L</i><sub>2</sub> related to the degree of polymerization DP<sub>2</sub>) the aggregation of the triblock comicelles could be finely tuned.
This allowed a phase-diagram to be constructed that can be extended
to other triblock comicelles with different coronas on the central
or end segment where âcrossâ supermicelles were exclusively
formed under predicted conditions. Laser scanning confocal microscopy
(LSCM) analysis of dye-labeled âcrossâ supermicelles,
and block âcrossâ supermicelles formed by addition of
a different unimer to the arm termini, provided complementary characterization
to transmission electron microscopy (TEM) and dynamic light scattering
(DLS) and confirmed the existence of these âcrossâ supermicelles
as kinetically stable, micron-size colloidally stable structures in
solution
Structural features distinguishing infectious ex vivo mammalian prions from non-infectious fibrillar assemblies generated in vitro
Seeded polymerisation of proteins forming amyloid fibres and their spread in tissues has been implicated in the pathogenesis of multiple neurodegenerative diseases: so called "prion-like" mechanisms. While ex vivo mammalian prions, composed of multichain assemblies of misfolded host-encoded prion protein (PrP), act as lethal infectious agents, PrP amyloid fibrils produced in vitro generally do not. The high-resolution structure of authentic infectious prions and the structural basis of prion strain diversity remain unknown. Here we use cryo-electron microscopy and atomic force microscopy to examine the structure of highly infectious PrP rods isolated from mouse brain in comparison to non-infectious recombinant PrP fibrils generated in vitro. Non-infectious recombinant PrP fibrils are 10ânm wide single fibres, with a double helical repeating substructure displaying small variations in adhesive force interactions across their width. In contrast, infectious PrP rods are 20ânm wide and contain two fibres, each with a double helical repeating substructure, separated by a central gap of 8-10ânm in width. This gap contains an irregularly structured material whose adhesive force properties are strikingly different to that of the fibres, suggestive of a distinct composition. The structure of the infectious PrP rods, which cause lethal neurodegeneration, readily differentiates them from all other protein assemblies so far characterised in other neurodegenerative diseases
De novo designed peptide and protein hairpins selfâassemble into sheets and nanoparticles
AFM, TEM, fluorescence microscopy image files and spectral data published in DOI:10.1002/smll.202100472. Preprint of this is available at bioRxiv DOI:10.1101/2020.08.14.25146
Dimensional control and morphological transformations of supramolecular polymeric nanofibers based on cofacially-stacked planar amphiphilic platinum(II) complexes
Square-planar
platinumÂ(II) complexes often stack cofacially to
yield supramolecular fiber-like structures with interesting photophysical
properties. However, control over fiber dimensions and the resulting
colloidal stability is limited. We report the self-assembly of amphiphilic
PtÂ(II) complexes with solubilizing ancillary ligands based on polyethylene
glycol [PEG<sub><i>n</i></sub>, where <i>n</i> = 16, 12, 7]. The complex with the longest solubilizing PEG ligand, <b>Pt-PEG</b><sub><b>16</b></sub>, self-assembled to form polydisperse
one-dimensional (1D) nanofibers (diameters <5 nm). Sonication led
to short seeds which, on addition of further molecularly dissolved <b>Pt-PEG</b><sub><b>16</b></sub> complex, underwent elongation
in a âliving supramolecular polymerizationâ process
to yield relatively uniform fibers of length up to <i>ca</i>. 400 nm. The fiber lengths were dependent on the <b>Pt-PEG</b><sub><b>16</b></sub> complex to seed mass ratio in a manner
analogous to a living covalent polymerization of molecular monomers.
Moreover, the fiber lengths were unchanged in solution after 1 week
and were therefore âstaticâ with respect to interfiber
exchange processes on this time scale. In contrast, similarly formed
near-uniform fibers of <b>Pt-PEG</b><sub><b>12</b></sub> exhibited dynamic behavior that led to broadening of the length
distribution within 48 h. After aging for 4 weeks in solution, <b>Pt-PEG</b><sub><b>12</b></sub> fibers partially evolved
into 2D platelets. Furthermore, self-assembly of <b>Pt-PEG</b><sub><b>7</b></sub> yielded only transient fibers which rapidly
evolved into 2D platelets. On addition of further fiber-forming Pt
complex (<b>Pt-PEG</b><sub><b>16</b></sub>), the platelets
formed assemblies <i>via</i> the growth of fibers selectively
from their short edges. Our studies demonstrate that when interfiber
dynamic exchange is suppressed, dimensional control and hierarchical
structure formation are possible for supramolecular polymers through
the use of kinetically controlled seeded growth methods