3 research outputs found
Defects as Color Centers: The Apparent Color of Metal–Organic Frameworks Containing Cu<sup>2+</sup>-Based Paddle-Wheel Units
As
in the case of other semiconducting materials, optical and electronic
properties of metal–organic frameworks (MOFs) depend critically
on defect densities and defect types. We demonstrate here that, in
addition to the influence of imperfections on MOF chemical properties
like guest binding energies and catalytic activity, the optical properties
of these crystalline molecular solids also crucially depend on deviations
from the perfect crystalline structure. By recording UV–vis
absorption spectra for MOF thin films of particularly high quality,
we demonstrate that low-defect samples of an important MOF, HKUST-1,
are virtually colorless. Electronic structure calculations of the
excited states by employing complete active space self-consistent
field (CASSCF) calculations show that the d–d excitations in
defects result in the typical green color of the MOF material synthesized
by conventional methods
Bioinstructive Coatings for Hematopoietic Stem Cell Expansion Based on Chemical Vapor Deposition Copolymerization
We
report the chemical vapor deposition (CVD) of dual-functional
polymer films for the specific and orthogonal immobilization of two
biomolecules (notch ligand delta-like 1 (DLL1) and an RGD-peptide)
that govern the fate of hematopoietic stem and progenitor cells. The
composition of the CVD polymer and thus the biomolecule ratio can
be tailored to investigate and optimize the influence of the relative
surface concentrations of biomolecules on stem cell behavior. Prior
to cell experiments, all surfaces were characterized by infrared reflection
adsorption spectroscopy, time-of-flight secondary ion mass spectrometry,
and X-ray photoelectron spectroscopy to confirm the presence of both
biomolecules. In a proof-of-principle stem cell culture study, we
show that all polymer surfaces are cytocompatible and that the proliferation
of the hematopoietic stem and progenitor cells is predominantly influenced
by the surface concentration of immobilized DLL1
Salt Sensitivity of the Thermoresponsive Behavior of PNIPAAm Brushes
We report investigations
on the salt sensitivity of the thermoresponsive
behavior of PNIPAAm brushes applying the quartz crystal microbalance
coupled with spectroscopic ellipsometry technique. This approach enables
a detailed study of the optical and mechanical behavior of the polymer
coatings. Additional conclusions can be drawn from the difference
between both techniques due to a difference in the contrast mechanism
of both methods. A linear shift of the phase-transition temperature
to lower temperatures with the addition of sodium chloride was found,
similar to the behavior of free polymer chains in solution. The thermal
hysteresis was found to be decreased by the addition of sodium chloride
to the solution, hinting to the interaction of the ions with the amide
groups of the polymer, whereby the formation of hydrogen bonds is
hindered. The results of this study are of relevance to the application
of PNIPAAm brushes in biological fluids and demonstrate the additional
potential of the ion sensitivity besides the better known thermosensitivity