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Oxidative stress, which involved in several inflammatory and degenerative diseases, has become interesting in most of biomedical disciplines and many types of clinical research. Antioxidants can protect biological systems from the harmful effects of oxidative stress. It can reflect the monitor effect to oxidative stress from another aspect by detecting the antioxidant capacity. Therefore, it is particularly significant to assay the antioxidant capacity of biological fluids. Herein, for the first time a fluorescence-tunable probe was developed based on polydopamine-quenched fluorescent graphitic carbon nitride (g-C 3 N 4 ) for assessing the antioxidant capacity of biological fluids. Dopamine (DA) can self-polymerize on the surface of g-C 3 N 4 to produce a polydopamine (PDA) uniform coating layer in which the fluorescence of g-C 3 N 4 is efficiently quenched by the PDA layer, showing the fluorescence “off” state. However, in the presence of antioxidants, the self-polymerized effect of DA can be effectively inhibited and leading to the fluorescence “on” state. Therefore, detecting antioxidants can be achieved by monitoring the fluorescent emission of g-C 3 N 4 . Moreover, endowed with high sensitivity and selectivity, the proposed sensing system was successfully applied to assessment antioxidant capacity in biological fluid and the results matched well with commonly used antioxidant detection method. [ABSTRACT FROM AUTHOR]

Regioselective modification is an effective approach to synthesize polysaccharides with different structure features and improved properties. In this study, regioselective sulfation of Artemisia sphaerocephala polysaccharide (S RS ASP) was prepared by using triphenylchloromethane (TrCl) as protecting precursor. The decrease in fractal dimension ( d f ) values (1.56–2.04) of S RS ASP was observed in size-exclusion chromatography combined with multi angle laser light scattering (SEC-MALLS) analysis. Compared to sample substituted at C-6, S RS ASP showed a more expanded conformation of random coil, which was attributed to the breakup of hydrogen bonds and elastic contributions. Circular dichroism (CD), methylene blue (MB) and congo red (CR) spectrophotometric method and atomic force microscopy (AFM) results confirmed the conformational transition and stiffness of the chains after sulfation. S RS ASP exhibited enhanced antioxidant activities in the DPPH, superoxide and hydroxyl radical scavenging assay. Sulfation at C-2 or C-3 was favorable for the chelation which might prevent the generation of hydroxyl radicals. It concluded that the degree of substitution and substitution position were the factors influencing biological activities of sulfated polysaccharides. [ABSTRACT FROM AUTHOR]