A Remarkably Efficient MnFe2O4‐based Oxidase Nanozyme

Nanomaterials‐based enzyme mimetics (nanozymes) have attracted considerable interest due to their applications in imaging, diagnostics, and therapeutic treatments. Particularly, metal‐oxide nanozymes have been shown to mimic the interesting redox properties and biological activities of metalloenzymes. Here we describe an efficient synthesis of MnFe₂O₄ nanomaterials and show how the morphology can be controlled by using a simple co‐precipitation method. The nanomaterials prepared by this method exhibit a remarkable oxidase‐like activity. Interestingly, the activity is morphology‐dependent, with nanooctahedra (NOh) exhibiting a catalytic efficiency of 2.21×10⁹ m ^?1 s^?1, the highest activity ever reported for a nanozyme.     

A Single Atom Change Facilitates the Membrane Transport of Green Fluorescent Proteins in Mammalian Cells

Direct delivery of proteins into mammalian cells is a challenging problem in biological and biomedical applications. The most common strategies for the delivery of proteins into the cells include the use of cell‐penetrating peptides or supercharged proteins. Herein, we show for the first time that a single atom change, hydrogen to halogen, at one of the tyrosine residues can increase the cellular entry of ～28 kDa green fluorescent protein (GFP) in mammalian cells. The protein uptake is facilitated by a receptor‐mediated endocytosis and the cargo can be released effectively into cytosol by co‐treatment with the endosomolytic peptide ppTG21.     

Synthesis, characterization, and antioxidant activity of some ebselen analogues

Simple synthetic routes for several analogues of the anti-inflammatory organoselenium drug, ebselen, are described. The compounds are characterized by (1)H, (13)C, and (77)Se NMR spectroscopy and mass spectral techniques and, in some cases, by single-crystal X-ray diffraction studies. The glutathione peroxidase (GPx)-like antioxidant activity has been studied by using H(2)O(2), tBuOOH, and Cum-OOH as substrates, and thiophenol (PhSH, 4-Me-C(6)H(4)SH) and glutathione (GSH) as cosubstrates. Density functional theory (DFT) calculations have been performed on these systems to understand the effects of various substituents on the (77)Se NMR chemical shifts; these results have been compared with the experimental data. The experimental and theoretical results suggest that the presence of a phenyl substituent on the nitrogen atom is important for the antioxidant activity of ebselen. While ebselen and its analogues are poor catalysts in aromatic thiol assays, these compounds exhibit high GPx activity when GSH is used as the cosubstrate. The poor catalytic activity of ebselen analogues in the presence of aromatic thiols such as PhSH and 4-Me-C(6)H(4)SH can be ascribed to the undesired thiol exchange reaction that takes place at the selenium center due to SeO nonbonding interactions. To understand the effects of different peroxides on the catalytic activities, we have determined the initial rates at various concentrations of GSH and peroxides. These data suggest that the nature of peroxide has little effect on the catalytic efficiencies, although the initial reaction rates observed with hydrogen peroxide were found to be higher than that with tBuOOH and Cum-OOH. In contrast to the effect of peroxides, the nature of thiols appears to have a dramatic effect on the catalytic activity of ebselen and its related derivatives.     

Interaction of single-walled carbon nanotubes with poly(propyl ether imine) dendrimers

We study the complexation of nontoxic, native poly(propyl ether imine) dendrimers with single-walled carbon nanotubes (SWNTs). The interaction was monitored by measuring the quenching of inherent fluorescence of the dendrimer. The dendrimer-nanotube binding also resulted in the increased electrical resistance of the hole doped SWNT, due to charge-transfer interaction between dendrimer and nanotube. This charge-transfer interaction was further corroborated by observing a shift in frequency of the tangential Raman modes of SWNT. We also report the effect of acidic and neutral pH conditions on the binding affinities. Experimental studies were supplemented by all atom molecular dynamics simulations to provide a microscopic picture of the dendrimer-nanotube complex. The complexation was achieved through charge transfer and hydrophobic interactions, aided by multitude of oxygen, nitrogen, and n-propyl moieties of the dendrimer.     

High-PL efficiency of polyaniline using various dopants

Polyaniline (PANI) was doped with hydrochloric acid (HCl), succinic acid (C₄H₆O₄) and sulphuric acid (H₂SO₄) by chemical oxidation method. The samples were characterized by using various techniques such as XRD, photoluminescence IR and UV spectroscopy. FTIR study confirmed the presence of dopant molecules in the molecular structure. UV spectra revealed that absorption peaks at 350 nm and 600 nm are due to π–π* transition of polyaniline. The strong band at 600 nm showed extension of polymer chains in the prepared samples. XRD pattern confirmed the amorphous nature of polymer samples. The photoluminescence (PL) spectrum shows good emission at 490 nm. The intensity of photoluminescence depends upon the dopants nature.     

A simple and efficient strategy to enhance the antioxidant activities of amino-substituted glutathione peroxidase mimics

The glutathione peroxidase (GPx) activities of some diaryl diselenides incorporating tertiary amino groups were studied with H(2)O(2), Cum-OOH, and tBuOOH as substrates and with PhSH as thiol co-substrate. Simple replacement of a hydrogen atom with a methoxy group dramatically enhances the GPx activity. The introduction of methoxy substituents ortho to selenium in N,N-dialkylbenzylamine-based compounds makes the basicity of the amino groups perfect for the catalysis. The presence of 6-OMe groups prevents possible SeN interactions in the selenols, increasing their zwitterionic characters. The methoxy substituents also protect the selenium in the selenenic acid intermediates from overoxidation to seleninic acids or irreversible inactivation to selenonic acid derivatives. The additional substituents also play a crucial role in the selenenyl sulfide intermediates, by preventing thiol exchange reactions-which would normally lead to an inactivation pathway-at the selenium centers. The strengths of SeN interactions in the selenenyl sulfide intermediates are dramatically reduced upon introduction of the methoxy substituents, which not only reduce the thiol exchange reactions at selenium but also enhance the nucleophilic attack of the incoming thiols at sulfur. The facile attack of thiols at sulfur in the selenenyl sulfides also prevents the reactions between the selenenyl sulfides and H(2)O(2) that can regenerate the selenenic acids (reverse-GPx cycle). These studies reveal that the simple 6-OMe groups play multiple roles in each of the catalytically active intermediates by introducing steric and electronic effects that are required for efficient catalysis.