Lysozyme, like many other well-folded globular proteins,
under
stressful conditions produces nanoscale oligomer assembly and amyloid-like
fibrillar aggregates. With engaging Raman microscopy, we made a critical
structural analysis of oligomer and other assembly structures of lysozyme
obtained from hen egg white and provided a quantitative estimation
of a protein secondary structure in different states of its fibrillation.
A strong amide I Raman band at 1660 cm–1 and a N–Cα–C
stretching band at ∼930 cm–1 clearly indicated
the presence of a substantial amount of α-helical folds of the
protein in its oligomeric assembly state. In addition, analysis of
the amide III region and Raman difference spectra suggested an ample
presence of a PPII-like secondary structure in these oligomers without
causing major loss of α-helical folds, which is found in the
case of monomeric samples. Circular dichroism study also revealed
the presence of typical α-helical folds in the oligomeric state.
Nonetheless, most of the Raman bands associated with aromatic residues
and disulfide (−S–S−) linkages broadened in the
oligomeric state and indicated a collapse in the tertiary structure.
In the fibrillar state of assembly, the amide I band became much sharper
and enriched with the β-sheet secondary structure. Also, the
disulfide bond vibration in matured fibrils became much weaker compared
to monomer and oligomers and thus confirmed certain loss/cleavage
of this bond during fibrillation. The Raman band of tryptophan and
tyrosine residues indicated that some of these residues experienced
a greater hydrophobic microenvironment in the fibrillar state than
the protein in the oligomeric state of the assembly structure.
Metal halide perovskite nanocrystals (NCs) have emerged as highly promising light emitting materials for various applications, ranging from perovskite light‐emitting diodes (PeLEDs) to lasers and radiation detectors. While remarkable progress has been achieved in highly efficient and stable green, red, and infrared perovskite NCs, obtaining efficient and stable blue‐emitting perovskite NCs remains a great challenge. Here, a facile synthetic approach for the preparation of blue emitting CsPbBr3 nanoplatelets (NPLs) with treatment by an organic sulfate is reported, 2,2‐(ethylenedioxy) bis(ethylammonium) sulfate (EDBESO4), which exhibit remarkably enhanced photoluminescence quantum efficiency (PLQE) and stability as compared to pristine CsPbBr3 NPLs coated with oleylamines. The PLQE is improved from ≈28% for pristine CsPbBr3 NPLs to 85% for EDBESO4 treated CsPbBr3 NPLs. Detailed structural characterizations reveal that EDBESO4 treatment leads to surface passivation of CsPbBr3 NPLs by both EDBE2+ and SO42– ions, which helps to prevent the coalescence of NPLs and suppress the degradation of NPLs. A simple proof‐of‐concept device with emission peaked at 462 nm exhibits an external quantum efficiency of 1.77% with a luminance of 691 cd m−2 and a half‐lifetime of 20 min, which represents one of the brightest pure blue PeLEDs based on NPLs reported to date.
The title compounds (IV) (51 examples) are efficiently obtained by reaction of enaminones, various 5‐substituted isatins, and indane‐1,3‐dione in water.
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