Preparation of low-molecular-weight carboxymethyl chitosan and their superoxide anion scavenging activity

Low-molecular-weight carboxymethyl chitosans (CMCTSs) were prepared by oxidative degradation method involving hydrogen peroxide (H₂O₂) without or with microwave radiation. Viscosity determination and end group analysis were applied to measure molecular weights of CMCTSs. Effects of concentration of H₂O₂ and degradation time on molecular weights of CMCTSs were studied. The degradation process of CMCTSs will be accelerated with the aid of microwave radiation and degradation time may be reduced greatly. The superoxide anion scavenging activity of CMCTSs was evaluated by application of flow injection chemiluminescence technology. The 50% inhibition concentrations (IC₅₀s) of CMCTSs A, B, and C (1130, 2430 and 4350 Da) were 10.36, 17.57, and 23.38 mg/mL, respectively. The above results showed that CMCTSs with lower molecular weight had better superoxide anion scavenging activity.     

模拟酶研究进展

综述了近年来模拟酶的研究及进展，着重介绍了配合物模拟水解酶、超氧化物模拟歧化酶的进展及其他模拟酶的合成研究进展。     

Organoiron activation combined with electron- and proton transfer: implications in biology, organic synthesis, catalysis and nanosciences

This Account summarizes the results obtained in our research group on the intra- and intermolecular organoiron activation of substrates by combining the coordination of arenes by CpFe^+/0 and electron and/or proton transfer. The concepts involved are those of electron and proton reservoirs, activation of O₂ by single electron transfer in solution, mimic and inhibition of the reactivity of superoxide radical anion, materials synthesis (for instance fullerene anions), electronic communication between two metals connected by a hydrocarbon bridge, activation of arene ligands for multiple functionalization, giant dendrimer synthesis and electron transfer in catalysis (redox and electron-transfer-chain).     

二十员六氮大环双核铜（Ⅱ）配合物与超氧离子的反应

合成了以2,6-二乙酰基吡啶缩丙二胺为配体,以OH~-、Cl~-、Br~-、I~-、SCN~-及N_3~-为桥基的6种大环双核铜配合物,用光照法研究了这类配合物催化O_2~-的歧化反应的活性,通过顺磁共振波谱,探讨了各种桥基的配合物与O_2~-反应的两种反应机理:催化歧化机理及氧化还原机理。     

Antioxidant potential of styrene pyrone polyphenols from Inonotus obliquus: A combined experimental,density functional theory (DFT) approach and molecular dynamic (MD) simulation

Polyphenols containing styrene pyranone skeleton are unique to porous fungi. Inonotus obliquus (IO) is a medicinal and edible porous fungus. Twelve phenolic compounds containing four styryl pyranone polyphenols from IO were isolated and identified in this work. The antioxidant ability of the isolates was characterized utilizing the ferric reducing antioxidant power (FRAP) assay and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) radical scavenging test. Styrylpyranone polyphenols, especially methylinoscavin B, could capture free radicals better than other phenolic compounds, and quantum chemical calculations also confirmed this evaluation. The density functional theory (DFT) calculation data showed that Styrylpyranone polyphenols, especially methylinoscavin B, have a lower energy gap, higher softness and higher electronic chemical potential than other phenolic compounds. The bond dissociation energy values of the bond in C7ʹ O–H of the methylinoscavin B molecule are less than those in C11 and C6ʹ O–H when reacting with ∙OOH (selected as a representative free radical). On the basis of calculations, hydrogen atom transfer (HAT) is supposed to be a preferred mechanism over single electron transfer (SET) when phenolic compounds react with free radicals. Moreover, after treatment with final concentrations of 0.5, 1, 2, 3, 4 and 5 μM phelligridin E (PHE), the activity of SOD1 increased by 70.15%, 11.36%, 145.45%, 172.73%, 205.05% and 275.23%, respectively. The molecular dynamics simulation (MD) study of PHE employed SOD1 (PDB ID: 6FN8). The MD results showed that the hydrogen bonds between ASP147 of SOD1 and PHE promote GLU223-ARG224 to form a stable C coil after combining with PHE. The formation of the C Coil enhanced the stability of the electrostatic loop (EL) of SOD1 and the rate of diffusion of the superoxide anion to the active site. Styrylpyrone polyphenols of Inonotus obliquus origin have the potential to be a source of vigorous free radical scavengers and antioxidant enzyme activators.     

New 8-hydroxybriarane diterpenoids from the gorgonians Junceella juncea and Junceella fragilis (Ellisellidae)

Four new 8-hydroxybriarane diterpenoids, including junceols A-C (1-3) and fragilide D (4), have been isolated from the gorgonian corals Junceella juncea and Junceella fragilis, respectively. The structures of briaranes 1-4 were elucidated by the interpretations of spectral data analysis. Briaranes 1-3 have displayed inhibitory effects on superoxide anion generation by human neutrophils.     

Oxidations by copper metalloenzymes and some biomimetic approaches

This paper illustrates the various aspects of the reactivity of the Cu(II)–Cu(I) system in biological systems, with one example of an enzymatic reaction in which Cu(II) alone is oxidizing enough to carry out the reaction (superoxide dismutase), one example in which a Cu(II)-bound peroxo intermediate is the active species (tyrosinase) and the examples of galactose oxidase and copper amine oxidases in which Cu(II) is associated with a redox active organic cofactor. In some cases, we will show some illustrations of biomimetic approaches developed in our laboratories, aimed at a better understanding of reaction mechanisms and at an original design of new catalysts with potential applications in synthetic chemistry. Some comments are given concerning the respective features of copper and iron.     

Hydrogen Storage and Selective,Reversible O2 Adsorption in a Metal–Organic Framework with Open Chromium(II) Sites

A chromium(II)‐based metal–organic framework Cr₃[(Cr₄Cl)₃(BTT)₈]₂ (Cr‐BTT; BTT³⁻=1,3,5‐benzenetristetrazolate), featuring coordinatively unsaturated, redox‐active Cr²⁺ cation sites, was synthesized and investigated for potential applications in H₂ storage and O₂ production. Low‐pressure H₂ adsorption and neutron powder diffraction experiments reveal moderately strong Cr–H₂ interactions, in line with results from previously reported M‐BTT frameworks. Notably, gas adsorption measurements also reveal excellent O₂/N₂ selectivity with substantial O₂ reversibility at room temperature, based on selective electron transfer to form Cr^III superoxide moieties. Infrared spectroscopy and powder neutron diffraction experiments were used to confirm this mechanism of selective O₂ binding.     

A Study on Some Copper (II) Complexes of Polyaza Cryptands and Planar Macrocycles—Synthesis,Characterization and Superoxide Dismutase Activity

Two kinds of macrocyclic copper(II) complexes were synthesized. One of them is composed of copper(II) cryptates of ligands L¹‐L⁴ which are condensation products of 5‐R‐2‐methoxy‐1,3‐phenyldialdehyde (R=OCH₃, L¹) with tris(2‐aminoethyl) amine and 5‐R‐2‐methothoxy‐1, 3‐phenyldialdehyde (R= CH₃, L³) with tris(2‐aminopropyl)amine as well as their reduced products of L¹ and L³ (L² and L⁴). The other is composed of two‐dimensional macrocyclic copper(II) complexes of ligands L⁵‐L⁸ of condensation products of diethylene triamine with 4‐R‐l‐methoxy‐2,6‐phenyldialdehyde (R= Cl, Br. CH₃, OCH₃). The relationship between their structures and superoxide dismutase (SOD) activity was investigated. The results can provide some clues to the synthesis of SOD mimics.     

Chemical Modification of Tryptophan Residues in Superoxide Dismutase from Camellia Pollen and Its Fluorescence Spectrum

The amino acid composition of the superoxide dismutase（SOD） from camellia pollen was measured and the tryptophan（Trp） residues were modified by using N-bromosuccinimide（NBS）. The results show that there are 21 Trp residues in an SOD molecule and seven of which are located on the surface of the enzyme. By researching the fluorescence spectra of the native SOD and the modified SOD, we have found that the emission wavelength of Trp is at 335 nm and the fluorescence intensity will decrease when the enzyme is modified. The results also show that potassium iodide（KI） can significantly quench the fluorescence of the native SOD, but it has a less pronounced effect on the modified enzyme. Glycerin as a surface activation reagent can stabilize the fluorescence of the modified enzyme.