Methylation of aldehyde nodes in Covalent Organic Frameworks leads to enhanced BET surface areas and reduced pore collapse compared to their non-methylated counterparts, which has been rationalized by DFT computations.
Covalent organic frameworks (COFs) are porous materials with high surface areas, making them interesting for a large variety of applications including energy storage, gas separation, photocatalysis, and chemical sensing. Structural variation plays an important role in tuning COF properties. Next to the type of the building block core, bonding directionality, and linking chemistry, substitution of building blocks provides another level of synthetic control. Thorough characterization and comparison of various substitution patterns is relevant for the molecular engineering of COFs via rational design. To this end, we have systematically synthesized and characterized multiple combinations of several methylated and non-methylated building blocks to obtain a series of imine-based COFs. This includes the experimental assignment of the COF structure by solid-state NMR. By comparing the properties of all COFs, the following trends were found: (1) upon methylation of the aldehyde nodes, COFs show increased Brunauer−Emmett−Teller surface areas, reduced pore collapse, blue-shifted absorbance spectra, and ∼0.2 eV increases in their optical band gaps. (2) COFs with dimethylated amine linkers show a lower porosity. (3) In tetramethylated amine linkers, the COF porosity even further decreases, the absorbance spectra are clearly red-shifted, and smaller optical band gaps are obtained. Our study shows that methyl substitution patterns on COF building blocks are a handle to control the UV absorbance of the resulting frameworks.
We studied the mechanistic and biological origins of
anti-inflammatory
poly-unsaturated fatty acid-derived
N
-acylethanolamines
using synthetic bifunctional chemical probes of docosahexaenoyl ethanolamide
(DHEA) and arachidonoyl ethanolamide (AEA) in RAW264.7 macrophages
stimulated with 1.0 μg mL
–1
lipopolysaccharide.
Using a photoreactive diazirine, probes were covalently attached to
their target proteins, which were further studied by introducing a
fluorescent probe or biotin-based affinity purification. Fluorescence
confocal microscopy showed DHEA and AEA probes localized in cytosol,
specifically in structures that point toward the endoplasmic reticulum
and in membrane vesicles. Affinity purification followed by proteomic
analysis revealed peroxiredoxin-1 (Prdx1) as the most significant
binding interactor of both DHEA and AEA probes. In addition, Prdx4,
endosomal related proteins, small GTPase signaling proteins, and prostaglandin
synthase 2 (Ptgs2, also known as cyclooxygenase 2 or COX-2) were identified.
Lastly, confocal fluorescence microscopy revealed the colocalization
of Ptgs2 and Rac1 with DHEA and AEA probes. These data identified
new molecular targets suggesting that DHEA and AEA may be involved
in reactive oxidation species regulation, cell migration, cytoskeletal
remodeling, and endosomal trafficking and support endocytosis as an
uptake mechanism.
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