Understanding the stability of zeolitic imidazolate framework-8 (ZIF-8) under physiological conditions is critical in biotechnology and biomedicine for biosensing, biocatalysis, and drug delivery.
We present a model and web-based tool for rapid and efficient prediction and rationalization of chemical membrane degradation in PEMFCs including protection mechanisms.
The formation of
a stable triacylgermenolate
2
as
a decisive intermediate was achieved by using three pathways. The
first two methods involve the reaction of KO
t
Bu or
alternatively potassium with tetraacylgermane
1
yielding
2
via one electron transfer. The mechanism involves the formation
of radical anions (shown by EPR). This reaction is highly efficient
and selective. The third method is a classical salt metathesis reaction
toward
2
in nearly quantitative yield. The formation
of
2
was confirmed by NMR spectroscopy, UV–vis
measurements, and X-ray crystallography. Germenolate
2
serves as a starting point for a wide variety of organo-germanium
compounds. We demonstrate the potential of this intermediate by introducing
new types of Ge-based photoinitiators
4b
–
4f
. The UV–vis absorption spectra of
4b
–
4f
show considerably increased band intensities
due to the presence of eight or more chromophores. Moreover, compounds
4d
–
4f
show absorption tailing up to 525
nm. The performance of these photoinitiators is demonstrated by spectroscopy
(time-resolved EPR, laser flash photolysis (LFP), photobleaching (UV–vis))
and photopolymerization experiments (photo-DSC measurements).
We show the synthesis of a redox-active quinone, 2methoxy-1,4-hydroquinone (MHQ), from a bio-based feedstock and its suitability as electrolyte in aqueous redox flow batteries. We identified semiquinone intermediates at insufficiently low pH and quinoid radicals as responsible for decomposition of MHQ under electrochemical conditions. Both can be avoided and/or stabilized, respectively, using H 3 PO 4 electrolyte, allowing for reversible cycling in a redox flow battery for hundreds of cycles.
Tetraacylgermanes are known as highly efficient photoinitiators. Herein, the synthesis of mixed tetraacylgermanes 4 a–c and 6 a–e with a nonsymmetric substitution pattern is presented. Germenolates are crucial intermediates of these new synthetic protocols. The synthesized compounds show increased solubility compared with symmetrically substituted tetraacylgermanes 1 a–d. Moreover, these mixed derivatives reveal broadened n–π* absorption bands, which enhance their photoactivity. Higher absorption of these new compounds at wavelengths above 450 nm causes efficient photobleaching when using an LED emitting at 470 nm. The quantum yields are in the range of 0.15–0.57, depending on the nature of the aroyl substituents. On the basis of these properties, mixed‐functionalized tetraacylgermanes serve as ideal photoinitiators in various applications, especially in those requiring high penetration depth. The synthesized compounds were characterized by elemental analysis, IR spectroscopy, NMR and CIDNP spectroscopy, UV/Vis spectroscopy, photolysis experiments, and X‐ray crystallography. The CIDNP data suggest that the germyl radicals generated from the new tetraacylgermanes preferentially add to the tail of the monomer butyl acrylate. In the case of 6 a–e only the mesitoyl groups are cleaved off, whereas for 4 a–c both the mesitoyl and the aroyl group are subject to α‐cleavage.
We present a systematic
investigation of the photophysical properties
of diazocines in aqueous media. The Z–E photoconversion yields of CH2CH2- and CH2S-bridged diazocines decrease with increasing
water content in acetonitrile. However, there is one exception. A
CH2-NAc-bridged diazocine mostly retains its photostationary
state in water (85 to 72%) because of the high quantum yields for
the Z → E conversion. Moreover,
it is water-soluble without further substitution and is therefore
ideally suited as a photoswitch in biological (aqueous) environments.
We show the synthesis of a redox-active quinone, 2methoxy-1,4-hydroquinone (MHQ), from a bio-based feedstock and its suitability as electrolyte in aqueous redox flow batteries. We identified semiquinone intermediates at insufficiently low pH and quinoid radicals as responsible for decomposition of MHQ under electrochemical conditions. Both can be avoided and/or stabilized, respectively, using H 3 PO 4 electrolyte, allowing for reversible cycling in a redox flow battery for hundreds of cycles.
Cyclopolymerizable
monomers (CPMs) are rarely described as cross-linkers,
as their most prominent feature is the ability to form soluble polymer
chains. In this study, we design a dimalonate-based CPM and investigate
its ability as a low-shrinkage reactive diluent in a commercial resin.
It demonstrates high reactivity in radical photopolymerization with
significantly reduced volumetric shrinkage and shrinkage stress compared
to commercial monomers. The investigated CPM is copolymerizable with
conventional methacrylates and yields photopolymers with similar mechanical
properties. Additionally, an in-depth evaluation of the propagation
step during cyclopolymerization was performed via NMR studies. Considering
the low volumetric shrinkage of the CPM-cross-linker, additive manufacturing
or dental resins represent highly promising applications.
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