ABSTRACT
The chelating reaction between glutathione peptides and divalent cadmium ion was used as a typical model for investigating the coordination chemistry of SH-containing peptides and heavy metal ions, which was essential to understand the mechanism of intracellular cadmium detoxification.Here, the mutant (CM113R)7 αHL protein nanopore equipped with a first synthesized per-6-quaternary ammonium-β-cyclodextrin (p-QABCD) was used as nanoreactor and detector to investigate the single-molecule reaction of GSH molecules and Cd2+ ions.Different reaction pathways, intermediates, and products could be recognized.Cd2+-GSH reaction was highly dependent on the solution pH.The Cd(GSH)2 was formed at pH 7.4, while the Cd(GSH)2 and Cd2(GSH)2 were formed at pH 9.0.Cd2(GSH)2 was formed by two possible pathways: (1) A Cd2+ ion primarily coordinated with the thiol group of two GSH molecules to form Cd(GSH)2, and then the second Cd2+ ion quickly incorporated with the deprotonated amino group of Cd(GSH)2 to form Cd2(GSH)2;(2) Two Cd2+ ions separately coordinated with the thiol and deprotonated amino group of one GSH molecule to form Cd2(GSH)1, and the second GSH molecule quickly bounded to Cd2+ ions to form Cd2(GSH)2.This work studied the chelating reaction between metal ions and bioactive glutathione at single-molecule level without labeling and chemical modification, and would be important to further understand intracellular mechanisms of detoxification of heavy metals and greatly expand the research field of nanopore single-molecule technique.
ABSTRACT
Abstract A new method was established to determine the free inorganic cadmium ion ( Cd2+) in marine bivalves using high performance liquid chromatography and inductively coupled plasma mass spectrometry ( HPLC-ICP-MS) . The free Cd2+ in shellfish was ultrasonic extracted for 40 min by 10 mmol/L Tris buffer solution ( with 0. 1 mol/L NaCl, pH=7. 5), and the separation of Cd2+ was achieved using an IonPac CS5A analytical column with an IonPac CG5A guard column. The mobile phase consisted of 50 mmol/L C2 H2 O4 and 95 mmol/L LiOH. The new method had a good linear relationship with the correlation coefficient of 0. 999 and the standard recoveries of Cd2+ were all above 84. 6%. The free Cd2+ content in several kinds of marine bivalves was determined using the method and the results showed that the percentage of free inorganic Cd2+ to the total Cd content in samples with high Cd content was higher than those with low Cd content.