Urinary Concentrations of Diisoheptyl Phthalate Biomarkers in Convenience Samples of U.S. Adults in 2000 and 2018-2019.

We know little about the potential health risks from exposure to diisoheptyl phthalate (DiHpP), a plasticizer used in commercial applications. The production of DiHpP ended in the United States in 2010, but DiHpP may still be present in phthalate diester mixtures. To investigate human exposure to DiHpP, we used three oxidative metabolites of DiHpP: Monohydroxyheptyl phthalate (MHHpP), mono-oxoheptylphthalate (MOHpP), and monocarboxyhexyl phthalate (MCHxP) as exposure biomarkers. We analyzed urine collected anonymously in 2000 (N = 144) and 2018-2019 (N = 205) from convenience groups of U.S. adults using high-performance liquid chromatography coupled with isotope-dilution high-resolution mass spectrometry. We detected MCHxP in all the samples tested in 2000 (GM = 2.01 ng/mL) and 2018-2019 (GM = 1.31 ng/mL). MHHpP was also detected in 100% of the 2018-2019 samples (GM = 0.59 ng/mL) and 96% of the 2000 urine samples analyzed (GM = 0.38 ng/mL). MOHpP was detected in 57% (2018-2019, GM = 0.03 ng/mL) and 92% (2000, GM = 0.19 ng/mL) of samples. The presence of MHHpP, MOHpP, and MCHxP in the 2018-2019 samples suggests recent exposure to DiHpP. Intercorrelations between metabolite concentrations were more significant in samples collected in 2000 than in samples collected in 2018-2019. The differences in urinary metabolite profiles and intercorrelations from samples collected during 2000 and 2018-2019 likely reflects changes in the composition of commercial DiHpP formulations before and after 2010.

Engineering Proton Transfer in Photosynthetic Oxygen Evolution: Chloride, Nitrate, and Trehalose Reorganize a Hydrogen-Bonding Network.

Photosystem II oxidizes water at a Mn4CaO5 cluster. Oxygen evolution is accompanied by proton release through a 35 Šhydrogen-bonding network to the lumen. The mechanism of this proton-transfer reaction is not known, but the reaction is dependent on chloride. Here, vibrational spectroscopy defines the functional properties of the proton-transfer network using chloride, bromide, and nitrate as perturbative agents. As assessed by peptide C═O frequencies, bromide substitution yields a spectral Stark shift because of its increase in ionic radius. Nitrate substitution leads to more complex spectral changes, consistent with an overall increase in hydrogen-bonding interactions with the peptide backbone. The effects are similar to spectral changes previously documented in site-directed mutations in a putative lumenal pathway. Importantly, the effects of nitrate are reversed by the osmolyte, trehalose. Trehalose is known to alter hydrogen-bonding interactions in proteins. Trehalose addition also reverses a shift in an internal hydronium ion signal, consistent with an alteration in its p Ka value and a change in the basicity of bound nitrate. The spectra provide evidence that the proton-transfer pathway contains peptide carbonyl groups, internal water, a hydronium ion, and amino acid side chains. These experiments also show that the proton-transfer pathway functionally adapts to changes in electric field, p Ka, and hydrogen bonding and thereby optimizes proton transfer to the lumen.