Evaluating metal ion salts as acid hydrolase mimics: metal-assisted hydrolysis of phospholipids at lysosomal pH

Acceleration and centralization of a back-diffusion process: Effects of EDTA-2Na on cadmium migration in high- and low-permeability systems

Pollutant accumulation in the low-permeability zones (LPZs) in groundwater systems is regarded as a secondary source, and its consequent back-diffusion can extend the timeframe of pump-and-treat remediation. However, the bioavailability and mobility of heavy metals and the medium characteristics can be changed during the process. This study investigated the accumulation and back-diffusion law of toxic metals and the effects of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) on them by implementing a series of tank experiments. In these experiments, a cadmium solution was injected first, and deionized water or EDTA-2Na constantly washed the system consisting of different medium layers. The experimental results showed that the cadmium breakthrough curves had some concentration gradient reverse points where the curves fluctuated with elution by deionized water, which did not exist when EDTA-2Na was the eluent. In these scenarios, the mass of accumulated cadmium in the media before elution was large, with a value of 931 mg (153 mg/kg), when the low-permeability medium was clay. However, when EDTA-2Na was injected together with cadmium, the value dropped to 319 mg (52.3 mg/kg), greatly reducing the cadmium accumulation. Additionally, the use of EDTA-2Na as an eluent resulted in the appearance of a secondary peak in the breakthrough curve, showing that EDTA-2Na accelerated and centralized the back-diffusion. Notably, the reduced cadmium accumulation in LPZs with the elution by EDTA-2Na was partly due to a reduced adsorption capacity of the clay minerals. The above results can advance the technology related to pump-and-treat remediation.

Metal-Assisted Hydrolysis Reactions Involving Lipids: A Review

This report covers major advances in the use of metal ions and complexes to hydrolyze ester and phosphate ester lipid bonds. These metal-based Lewis acids have been investigated as catalysts to isolate fatty acids from biological sources, as probes to study phospholipid bilayer properties, as tools to examine signal transduction pathways, and as lead compounds toward the discovery of therapeutic agents. Metal ions that accelerate phosphate ester hydrolysis under mild conditions of temperature and pH may have the potential to mimic phospholipase activity in biochemical applications.

Tuning Cerium(IV)-Assisted Hydrolysis of Phosphatidylcholine Liposomes under Mildly Acidic and Neutral Conditions

With the goal of designing a lysosomal phospholipase mimic, we optimized experimental variables to enhance Ce(IV) -assisted hydrolysis of phosphatidylcholine (PC) liposomes. Our best result was obtained with the chelating agent bis-tris propane (BTP). Similar to the hydrolytic enzyme, Ce(IV) -assisted hydrolysis of PC phosphate ester bonds was higher at lysosomal pH (∼4.8) compared to pH 7.2. In the presence of BTP, the average cleavage yield at ∼pH 4.8 and 37 °C was: 67±1 %, 5.7-fold higher than at ∼pH 7.2 and roughly equivalent to the percent of phospholipid found on the metal-accessible exo leaflet of small liposomes. No Ce(IV) precipitation was observed. When BTP was absent, there was significant turbidity, and the amount of cleavage at ∼pH 4.8 (69±1 %) was 2.1-fold higher than the yield obtained at ∼pH 7.2. Our results show that BTP generates homogenous solutions of Ce(IV) that hydrolyze phosphatidylcholine with enhanced selectivity for lysosomal pH.