Because of its relatively high natural abundance and the
broad range of chemical shifts (900 ppm), 113Cd is
a
potentially excellent istope for NMR studies of metal
binding
sites of natural organic matter (NOM). This paper
presents
a 113Cd NMR study of the effects of pH and, to a
lesser
extent, Cd/C molar ratio on the complexation of cadmium
ion
by Suwannee River NOM. Spectra are presented for
solutions ranging in pH from 3.6 to 9.0 and ranging in
Cd/C
ratio from 0.0013 to 0.0068. At acidic pH, a single
somewhat
sharp peak is observed, but more complex spectra are
obtained at alkaline pH. These changes indicate that
Cd−NOM exchange rates are much faster at acidic pH, where
the concentration of free Cd2+ is greatest. Under
nearly
all the conditions of Cd/C ratio and pH that were used,
Cd2+ is primarily coordinated by O donor atoms,
probably
in carboxyl groups. At high pH, some evidence of
Cd2+
coordination by N donor atoms is observed. No
evidence
of Cd2+ ions coordinated by S donor atoms was
observed
in the NMR spectra, even at Cd/C ratios that were
significantly
lower than the S/C ratio of the NOM.
Dietary polysaccharides provide various beneficial effects for our health. We investigated the protective effects of wild jujube (Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chou) sarcocarp polysaccharides (WJPs) against experimental inflammatory bowel disease (IBD) by enabling enhanced intestinal barrier function. Colitis was induced in rats by the intrarectal administration of TNBS. We found that WJPs markedly ameliorated the colitis severity, including less weight loss, decreased disease activity index scores, and improved mucosal damage in colitis rats. Moreover, WJPs suppressed the inflammatory response via attenuation of TNF-α, IL-1β, IL-6 and MPO activity in colitis rats. And then, to determine the effect of WJPs on the intestinal barrier, we measured the effect of WJPs on the transepithelial electrical resistance (TER) and FITC-conjugated dextran permeability in Caco-2 cell stimulation with TNF-α. We further demonstrated that the alleviation of WJPs to colon injury was associated with barrier function by assembly of tight junction proteins. Moreover, the effect of WJPs on TER was eliminated by the specific inhibitor of AMPK. AMPK activity was also up-regulated by WJPs in Caco-2 cell stimulation with TNF-α and in colitis rats. This study demonstrates that WJPs protect against IBD by enabling enhanced intestinal barrier function involving the activation of AMPK.
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