Glyphosate is the active ingredient of the common herbicide Roundup. The increasing presence of glyphosate and its byproducts has raised concerns about its potential impact on the environment and human health. In this research, we investigated abiotic pathways of glyphosate degradation as catalyzed by birnessite under aerobic and neutral pH conditions to determine whether certain pathways have the potential to generate less harmful intermediate products. Nuclear magnetic resonance (NMR) spectroscopy and high-performance liquid chromatography (HPLC) were utilized to identify and quantify reaction products, and density functional theory (DFT) calculations were used to investigate the bond critical point (BCP) properties of the C-N bond in glyphosate and Mn(IV)-complexed glyphosate. We found that sarcosine, the commonly recognized precursor to glycine, was not present at detectable levels in any of our experiments despite the fact that its half-life (∼13.6 h) was greater than our sampling intervals. Abiotic degradation of glyphosate largely followed the glycine pathway rather than the AMPA (aminomethylphosphonic acid) pathway. Preferential cleavage of the phosphonate adjacent C-N bond to form glycine directly was also supported by our BCP analysis, which revealed that this C-N bond was disproportionately affected by the interaction of glyphosate with Mn(IV). Overall, these results provide useful insights into the potential pathways through which glyphosate may degrade via relatively benign intermediates.

The dissipation behaviors of the two enantiomers of the organophosphorus pesticide malathion (MA) in environment samples were elucidated using a normal-phase high-performance liquid chromatography with a cellulose-tris(3,5-dimethylphenylcarbamate) (CDMPC) chiral column. A validated chiral residue analysis method in soil and water was established; the average recoveries for the two enantiomers were 88-102% in soil and 81-99% in water. Racemic and enantiopure R-(+)- and S-(-)-MA were incubated in five soil and water systems. The results of the degradation of racemate in all of the environment samples showed the inactive S-(-)-enantiomer degraded more rapidly than the active R-(+)-enantiomer, resulting in a relative enrichment of the R-form. Moreover, when the enantiopure S-(-)- and R-(+)-MA were incubated in three well-chosen soil and water samples, respectively, inversion from one enantiomer to another was found, indicating that using the optically pure enantiomer will not help to increase the bioactivity and reduce the environmental pollution.

Nanoparticles have been increasingly used as carriers for local and systemic drug delivery via the skin. Dendrimers are emerging as the new generation of nanocarriers in skin drug delivery mainly due to their small size, extreme molecular uniformity, and highly functional surfaces. Despite the abundance of investigations which demonstrate the dendrimer-mediated skin delivery enhancement both in vitro and in vivo, there are still controversies over the mechanisms of their action. Based on the critical analysis of currently available data in this field, it is found that the skin delivery enhancement by dendrimers depends on the drugdendrimer-skin interactions and three potential mechanisms are proposed. Firstly, for some drugs, dendrimers may act as a drug release modifier and speed up the drug dissolution that is the rate-limiting step of percutaneous drug absorption. Secondly, via particle engineering the properties of dendrimers can be tailored to preferably penetrate the skin via the follicular route. Finally, certain low generation dendrimers may impair the stratum corneum barrier function, particularly in the presence of potent vehicles.

Degradation of glyphosate in the presence of manganese oxide and UV light was analyzed using phosphate oxygen isotope ratios and density function theory (DFT). The preference of C-P or C-N bond cleavage was found to vary with changing glyphosate/manganese oxide ratios, indicating the potential role of sorption-induced conformational changes on the composition of intermediate degradation products. Isotope data confirmed that one oxygen atom derived solely from water was incorporated into the released phosphate during glyphosate degradation, and this might suggest similar nucleophilic substitution at P centers and C-P bond cleavage both in manganese oxide- and UV light-mediated degradation. The DFT results reveal that the C-P bond could be cleaved by water, OH or OH, with the energy barrier opposing bond dissociation being lowest in the presence of the radical species, and that C-N bond cleavage is favored by the formation of both nitrogen- and carbon-centered radicals. Overall, these results highlight the factors controlling the dominance of C-P or C-N bond cleavage that determines the composition of intermediate/final products and ultimately the degradation pathway.

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