Porous chitosan-MnO2 nanohybrid: a green and biodegradable heterogeneous catalyst for aerobic oxidation of alkylarenes and alcohols

Tumor microenvironment-responsive histidine modified-hyaluronic acid-based MnO2 as in vivo MRI contrast agent

Tumor microenvironment (TME)-responsive manganese dioxide (MnO₂) nanoparticles as a good T₁ contrast agent could reduce unwanted toxicity and improve the accuracy of cancer detection. Despite these distinct advantages of MnO₂-based nanoparticles, their synthesis involves multi-step processes with relatively long synthesis times. In this study, we synthesized histidine-modified hyaluronic acid (HA-His), and the prepared HA-His conjugates quickly reduce permanganate to MnO₂, leading to facile production of HA-His/MnO₂ nanoparticles with good water-dispersibility and stability under biological conditions. The synthesized HA-His/MnO₂ nanoparticles readily responded to the TME (low pH, high H₂O₂, and high glutathione), and they were internalized into SCC7 cells with high CD44 expression. Moreover, the systemically administered HA-His/MnO₂ nanoparticles with biocompatibility were specifically accumulated in tumor tissues, thereby efficiently enhancing T₁ contrast in MRI. Therefore, the HA-His/MnO₂ nanoparticles synthesized herein can be used as a promising T₁ contrast agent for tumor MR imaging.

Base-Assisted Aerobic C-H Oxidation of Alkylarenes with a Murdochite-Type Oxide Mg6MnO8 Nanoparticle Catalyst

Heterogeneously catalyzed aerobic oxidative C-H functionalization under mild conditions is a chemical process to obtain desired oxygenated products directly. Nanosized murdochite-type oxide Mg₆MnO₈ (Mg₆MnO₈-MA) was successfully synthesized by the sol-gel method using malic acid. The specific surface area reached up to 104 m² g^-1, which is about 7 times higher than those (2-15 m² g^-1) of Mg₆MnO₈ synthesized by previously reported methods. Mg₆MnO₈-MA exhibited superior catalytic performance to those of other Mn- and Mg-based oxides, including manganese oxides with Mn-O-Mn active sites for the oxidation of fluorene with molecular oxygen (O₂) as the sole oxidant under mild conditions (40 °C). The present catalytic system was applicable to the aerobic oxidation of various substrates. The catalyst could be recovered by simple filtration and reused several times without obvious loss of its high catalytic performance. The correlation between the reactivity and the pK_a of the substrates, basic properties of catalysts, and kinetic isotope effects suggest a basicity-controlled mechanism of hydrogen atom transfer. The ¹⁸O-labeling experiments, kinetics, and mechanistic studies showed that H abstraction of the hydrocarbon proceeds via a mechanism involving O₂ activation. The structure of Mg₆MnO₈ consisting of isolated Mn⁴⁺ species located in a basic MgO matrix plays an important role in the present oxidation.

Nanostructured Manganese Oxides within a Ring-Shaped Polyoxometalate Exhibiting Unusual Oxidation Catalysis

Nanosized manganese oxides have recently received considerable attention for their synthesis, structures, and potential applications. Although various synthetic methods have been developed, precise synthesis of novel nanostructured manganese oxides are still challenging. In this study, using a structurally defined nanosized cavity inside a ring-shaped polyoxometalate, we succeeded in synthesizing two types of discrete 18 and 20 nuclear nanostructured manganese oxides, Mn18 and Mn20, respectively. In particular, Mn18 showed much higher catalytic activity than other manganese oxides for the oxygenation of alkylarenes including electron-deficient ones, and the reaction proceeded through a unique reaction mechanism due to its unusual manganese oxide structure.

Oxygen-generating glycol chitosan-manganese dioxide nanoparticles enhance the photodynamic effects of chlorin e6 on activated macrophages in hypoxic conditions

This study aimed to investigate the use of glycol chitosan (GC) for the synthesis of MnO₂ nanoparticles (NPs) and to evaluate whether the prepared GC-MnO₂ NPs enhance the light-triggered photodynamic effects of chlorin e6 (Ce6) via the generation of oxygen and alleviation of hypoxia in lipopolysaccharide (LPS)-activated macrophages (RAW 264.7), which produce excessive amounts of reactive oxygen species (ROS). GC-MnO₂ NPs were synthesized by a simple reaction between GC and KMnO₄ in water. The prepared GC-MnO₂ NPs were spherical in shape, with a mean diameter of approximately 60 nm. The particles effectively generated oxygen via H₂O₂-induced degradation under hypoxic conditions, which led to an increase in the singlet oxygen levels upon laser irradiation. Furthermore, GC-MnO₂ NPs significantly enhanced the light-triggered photodynamic effects of Ce6 on activated macrophages under hypoxic conditions, as shown by the increased levels of cell death and cell membrane damage in activated macrophages. Therefore, these results suggest that GC can be used as an alternative natural polymer for the synthesis of MnO₂ NPs and that oxygen-generating GC-MnO₂ NPs enhance the light-triggered photodynamic effects of Ce6 on activated macrophages by alleviating hypoxia.

Cu(I) Coordination Polymers as the Green Heterogeneous Catalysts for Direct C-H Bonds Activation of Arylalkanes to Ketones in Water with Spatial Confinement Effect

To develop coordination polymers (CPs) as catalysts to selectively catalyze the reaction of C-H bond activation of arylalkanes to their homologous ketones, three new Cu(I)-based coordination polymers (Cu^I-CPs) [CuI(aas-TPB)]_n (1), [CuBr(ass-TPB)CH₃CN]_n (2), and {[Cu(ass-TPB)]Cl}_n (3) (TPB = N,N,N-tris(3-pyridinyl)-1,3,5-benzenetricarboxamide) were synthesized. Structural variations from a herringbone fashion one-dimensional framework of 1 to a two-dimensional framework of 2 containing a 48-membered macrocycle and a cationic three-dimensional framework of 3 filled with Cl^- anions were observed arising from the different halogen ions (I^-, Br^-, and Cl^-). 1-3 were used as the green heterogeneous catalysts to catalyze direct C-H bond activation reactions of arylalkanes to ketones under mild reaction conditions with water as solvent. Handy product separation, convenient reaction procedures, and recyclability of these catalysts make the catalytic system fascinating. Moreover, the Cu^I-CPs performed the reaction with high regioselectivity due to the unique spatial confinement effect of CPs.

Amino Acid-Aided Synthesis of a Hexagonal SrMnO3 Nanoperovskite Catalyst for Aerobic Oxidation

A simple and efficient synthetic method for preparing high-surface-area perovskites was investigated by focusing on the importance of the formation of an amorphous precursor. Hexagonal SrMnO₃ with high surface area was successfully synthesized by simple calcination of the amorphous precursor prepared using aspartic acid and metal acetates instead of metal nitrates, without pH adjustment. The specific surface area reached up to ca. 50 m² g^-1, which is much larger than that for SrMnO₃ synthesized by previously reported methods. The catalytic activity for heterogeneous liquid-phase aerobic oxidation was significantly improved in comparison with the polymerized complex method, and the present catalytic system was applicable to the oxidation of various substrates.

Highly selective aerobic oxidation of alkyl arenes and alcohols: cobalt supported on natural hydroxyapatite nanocrystals

Cobalt was successfully immobilized on natural hydroxyapatite nanocrystals which was obtained from cow bones (Co–NHAp). NHAp as the support enhanced both catalytic activity and selectivity in aerobic oxidation of alkyl arenes and alcohols.

Magnetically separable chicken feathers: a biopolymer based heterogeneous catalyst for the oxidation of organic substrates

Magnetically separable chicken feather nanoparticles were found to be efficient, green and heterogeneous catalyst for selective oxidation of alcohols to carbonyls and sulfides to sulfoxides using t-butyl hydroperoxide (TBHP) as oxidant.

Magnetic MIL-101-SO3H: a highly efficient bifunctional nanocatalyst for the synthesis of 1,3,5-triarylbenzenes and 2,4,6-triaryl pyridines

A magnetic MIL-101-SO₃H was synthesized and successfully used as a highly active nanocatalyst for the synthesis of 1,3,5-triarylbenzenes and 2,4,6-triaryl pyridines.