Melanins are well-known biopolymers that are ubiquitous in nature, distributed widely in microorganisms, plants, and animals, and play significant physiological roles. They are mostly biopolymers formed from phenolic compounds by polymerization via quinones. Poly(dopamine) (PDA), a melanin-like material, is similar in structure and properties to eumelanin and has attracted considerable interest for various types of biological applications. This review outlines the recent advances in the structure and synthesis of PDA and discusses applications of PDA in many biological fields, such as biological imaging, photothermal therapy, and drug delivery systems. The purpose of this review is to give a brief overview of the synthesized procedures, structure, biomedical applications, and prospects of melanin-like materials.
Noble metal nanocrystals (NCs) enclosed with high-index facets hold a high catalytic activity thanks to the high density of low-coordinated step atoms that they exposed on their surface. Shape-control synthesis of the metal NCs with high-index facets presents a big challenge owing to the high surface energy of the NCs, and the shape control for metal Rh is even more difficult because of its extraordinarily high surface energy in comparison with Pt, Pd, and Au. The successful synthesis is presented of tetrahexahedral Rh NCs (THH Rh NCs) enclosed by {830} high-index facets through the dynamic oxygen adsorption/desorption mediated by square-wave potential. The results demonstrate that the THH Rh NCs exhibit greatly enhanced catalytic activity over commercial Rh black catalyst for the electrooxidation of ethanol and CO.
Glycerol, a byproduct of biodiesel production, is an industrial waste because of its excess yield. Electrooxidation of glycerol is a promising way to utilize glycerol through harvesting electric energy as fuels in a fuel cell or hydrogen as sacrificial agent in electrolysis cellwhile generating valuable chemicals. Here, we report a detailed mechanistic study of the glycerol electrooxidation reaction (GOR) on a series of Pt/C, Pt x Ru y /C, and Pt x Rh y /C nanocatalysts synthesized by NaBH 4 reduction. The EC cyclic voltammetry characterization indicates that alloying Ru with Pt greatly enhanced the GOR activity, especially at low potential, but not as much with alloying Rh, as compared with Pt/C. In situ FTIR and 13 C NMR spectroscopies were used to investigate the GOR mechanism at a molecular level. The results demonstrate that the selectivity of products depends on the type of catalysts and the oxidation potential. Although both PtRu/C and PtRh/C could accelerate the oxygen insertion reactions that led to higher selectivity of carboxylic acids, tartronic acid was more favored at high potential on the PtRh/C surface.
Gelation kinetics of native and acetylated konjac glucomannan (KGM) samples in the presence of alkali (sodium carbonate) was studied by dynamic viscoelastic measurements. Molecular weight and other molecular parameters of KGM were determined by static light scattering and viscosity measurements. It was found that KGM molecules were degraded during acetylation treatment, but the molecular weights of acetylated samples were almost independent of the degree of acetylation (DA) and were about a half of that of a native sample. At a fixed alkaline concentration, increasing concentration of KGM or temperature shortened the gelation time, but increasing DA delayed it. The deacetylation reaction and subsequent aggregation process of acetylated samples needed longer time than that of native sample, and acetylated samples formed finally more elastic gels. It implied that the presence of acetyl groups exerts a strong influence on gelation behavior of KGM. It was suggested that the gelation rate of acetylated KGM and native KGM, which depends on the alkaline concentration and temperature, is an important factor that determines the elastic modulus of gels. This was supported by the experimental finding that the saturated elastic modulus tends to the same value when the ratio of alkali concentration to acetylated groups was kept constant. In slower gelation processes, junction zones are more homogeneously distributed and more numerous, leading to the more elastic gels.
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