Human
skin oils are significant scavengers of atmospheric oxidants
in occupied indoor environments, and squalene is a major ozone-active
constituent. Here, we present a combined spectroscopic and atomistic
modeling approach to elucidate the conformational and orientational
preferences of squalene at the air/oil interface and their implications
for reactions with ozone. We find that squalene chains have a tendency
to align with the surface normal, resulting in different concentrations
of the various types of its double bonds and thus different reactivities.
We also observe the presence of water at the surface of this hydrophobic
compound. Both findings have possible implications for the design
and outcomes of kinetic models describing this important aspect of
indoor air chemistry.
Radioisotopes
of Cu, such as 64Cu and 67Cu,
are alluring targets for imaging (e.g., positron emission tomography,
PET) and radiotherapeutic applications. Cyclen-based macrocyclic polyaminocarboxylates
are one of the most frequently examined bifunctional chelators in
vitro and in vivo, including the FDA-approved 64Cu radiopharmaceutical,
Cu(DOTATATE) (Detectnet); however, connections between the structure
of plausible reactive intermediates and their stability under physiologically
relevant conditions remain to be established. In this study, we share
the synthesis of a cyclen-based, N,N-alkylated spirocyclic chelate, H2DO3AC4H8
, which serves as a model for N-protonation.
Our combined experimental (in vitro and in vivo) and computational
studies unravel complex pH-dependent speciation and enable side-by-side
comparison of N- and O-protonated
species of relevant 64Cu radiopharmaceuticals. Our studies
suggest that N-protonated species are not inherently
unstable species under physiological conditions and demonstrate the
potential of N,N-alkylation as a
tool for the rational design of future radiopharmaceuticals.
The C–H and O–H oscillators on the surfaces
of thin
films of human-derived skin oil and squalene are probed under ambient
conditions (300 K, 1 atm total pressure, 40% RH) using second-order
vibrational spectroscopy and contact angle goniometry before and after
exposure to ppb amounts of ozone. Skin oil and squalene are found
to produce different vibrational sum frequency generation spectra
in the C–H stretching region, while exposure to ozone results
in surface spectra for both materials that is consistent with a loss
of C–H oscillators. The measured contact angles show that the
hydrophobicity of the films increases following exposure to ozone,
consistent with the reduction in CC···H2O (“πH”) bonding interactions that is
expected from CC double bond loss due to ozonolysis and indicating
that the polar functional groups formed point toward the films’
interiors. Implications for heterogeneous indoor chemistry are discussed.
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