Double Hydrophilic Block Copolymer Templated Au Nanoparticles with Enhanced Catalytic Activity toward Nitroarene Reduction

We present a facile method for synthesizing water-dispersible gold nanoparticles (Au NPs) using a double hydrophilic block copolymer (DHBC), poly­(ethylene oxide)-<i>block</i>-poly­(acrylic acid) (PEO-<i>b</i>-PAA), as a template and demonstrate their application in the reduction of nitroarenes. Selective coordinative interactions between a gold precursor and the PAA block of the DHBC lead to the formation of micelles, which are subsequently transformed into Au NPs with an average diameter of 10 nm using a reducing agent. The DHBC-templated Au NPs (Au@DHBC NPs) remain stable in water for several months without any noticeable aggregation. Furthermore, Au@DHBC NPs are found to be highly effective in catalyzing the reduction of a series of nitroarenes. Remarkably, the turnover frequency in the case of 4-nitrophenol using Au@DHBP NPs reaches 800 h^–1, outperforming previously reported Au NP-based catalytic systems. We believe the enhanced catalytic activity is due to the DHBC shell around Au NPs, which templates the formation of spherical Au NPs and, more importantly, provides the confined interior for the enhanced catalytic activity in nitroarene reduction. Considering the wide potential application of DHBC as a template for the synthesis of novel metal NPs, we anticipate that the approach presented in this study will offer a new means to create a variety of water-stable catalytic nanomaterials in various fields of green chemistry

Intrinsic Structural Heterogeneity and Long-Term Maturation of Amyloid β Peptide Fibrils

Amyloid β peptides form fibrils that are commonly assumed to have a dry, homogeneous, and static internal structure. To examine these assumptions, fibrils under various conditions and different ages have been examined with multidimensional infrared spectroscopy. Each peptide in the fibril had a ¹³C¹⁸O label in the backbone of one residue to disinguish the amide I′ absorption due to that residue from the amide I′ absorption of other residues. Fibrils examined soon after they formed, and reexamined after 1 year in the dry state, exhibited spectral changes confirming that structurally significant water molecules were present in the freshly formed fibrils. Results from fibrils incubated in solution for 4 years indicate that water molecules remained trapped within fibrils and mobile over the 4 year time span. These water molecules are structurally significant because they perturb the parallel β-sheet hydrogen bonding pattern at frequent intervals and at multiple points within individual fibrils, creating structural heterogeneity along the length of a fibril. These results show that the interface between β-sheets in an amyloid fibril is not a “dry zipper”, and that the internal structure of a fibril evolves while it remains in a fibrillar state. These features, water trapping, structural heterogeneity, and structural evolution within a fibril over time, must be accommodated in models of amyloid fibril structure and formation

Symmetry-Mismatched SBU Transformation in MOFs: Postsynthetic Metal Exchange from Zn to Fe and Its Effects on Gas Adsorption and Dye Selectivity

This research explores the alteration of metal–organic frameworks (MOFs) using a method called postsynthetic metal exchange. We focus on the shift from a Zn-based MOF containing a [Zn4O(COO)6] secondary building unit (SBU) of octahedral site symmetry (ANT-1(Zn)) to a Fe-based one with a [Fe3IIIO(COO)6]+ SBU of trigonal prismatic site symmetry (ANT-1(Fe)). The symmetry-mismatched SBU transformation cleverly maintains the MOF’s overall structure by adjusting the conformation of the flexible 1,3,5-benzenetribenzoate linker to alleviate the framework strain. The process triggers a decrease in the framework volume and pore size alongside a change in the framework’s charge. These alterations influence the MOF’s ability to adsorb gas and dye. During the transformation, core–shell MOFs (ANT-1(Zn@Fe)) are formed as intermediate products, demonstrating unique gas sorption traits and adjusted dye adsorption preferences due to the structural modifications at the core–shell interface. Heteronuclear clusters, located at the framework interfaces, enhance the heat of CO2 adsorption. Furthermore, they also influence the selectivity of the dye size. This research provides valuable insights into fabricating novel MOFs with unique properties by modifying the SBU of a MOF with flexible organic linkers from one site symmetry to another