The voltammetric responses of Pt disk electrodes 5-50 nm in radii in the presence of excess inert electrolyte were investigated to verify the applicability of the conventional diffusion-based voltammetric theory to nanoscale electrochemical interfaces. A so-called "inverted heat-sealing" procedure was introduced in the electrode fabrication process to eliminate the possible tiny interstice between the glass sheath and electrode wire that could severely distort the voltammetric curves of nanometer-szied electrodes. Linear relations between the limiting currents (i L ) and the concentrations of electroactive ions (c a ) were found at electrodes as small as 5 nm, seemingly inferring that the classic voltammetric theory is applicable at such small electrodes. However, a delicate analysis on the dependences of i L on the electroactive size of electrode and the charge carried by the electroactive ions revealed that the i L ∼ c a linearity is altered from the predication of the conventional voltammetric theory as the size of electrode approaches nanometer scales (e. g., <10 nm). The altered i L ∼ c a linearity at nanoelectrodes is explainable in terms of size-induced merging of electric double layer (EDL) and concentration depletion layer (CDL) and is well-predictable from the previous dynamic double layer model for nanoelectrode based on Poisson-Nernst-Planck theory (J. Phys. Chem. B 2006, 110, 3262). It is thus concluded that the enhanced EDL effects at nanoscale electrochemical interfaces do cause deviations from the predication of the conventional voltammetric theory, but the deviations are quantitatively small (e.g., within 20% even at electrodes of a few nanometers) and in most cases might be hardly distinguished with the experimental uncertainties.
We reported a novel injectable doxorubicin-loaded hydrogel based on host-guest interaction and Schiff's base reaction. A supramolecular polymeric prodrug was prepared through the inclusion of adamantane-modified doxorubicin into the β-cyclodextrin cavity on the polyaldehyde dextran chain, which was in situ crosslinked by carboxymethyl chitosan.
Chili peppers exhibit antiobesity, anticancer, antidiabetic, and pain- and itch-relieving effects on animals and humans; these effects are due to capsaicin, which is the main pungent and biologically active component of pepper. Capsiate, a nonpungent capsaicin analogue, is similar to capsaicin in terms of structure and biological activity. In this study, we investigated whether capsaicin and capsiate exhibit the same hypoglycemic effects on rats with type 1 diabetes (T1D). Experimental rats were categorized into four groups: control, model, capsaicin, and capsiate groups. The two treatment groups were treated orally with 6 mg/kg bw capsaicin and capsiate daily for 28 days. Treatment with capsaicin and capsiate increased body weight, increased glycogen content, and inhibited intestinal absorption of sugar in T1D rats. Particularly, insulin levels were increased from 14.9 ± 0.76 mIU/L (model group) to 22.4 ± 1.39 mIU/L (capsaicin group), but the capsiate group (16.7 ± 0.79 mIU/L) was increased by only 12.2%. Analysis of the related genes suggested that the transient receptor potential vanilloid 1 (TRPV1) receptor was activated by capsaicin. Liver X receptor and pancreatic duodenum homeobox 1 controlled the glycometabolism balance by regulating the expression levels of glucose kinase, glucose transport protein 2 (GLUT2), phosphoenolpyruvate carboxykinase, and glucose-6-phosphatase, leading to reduced blood glucose levels in T1D rats. Meanwhile, the hypoglycemic effect was enhanced by the down-regulated expression of sodium glucose cotransporter 1, GLUT2, and GLUT5 in the intestine. The results showed that the spicy characteristics of capsaicin might be the root of its ability to decrease blood glucose.
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