Electronic cigarettes enabling
enhanced airflow have grown in popularity in recent years. The objective
of this study is to show that flow rates modulate the levels of specific
aerosol toxicants produced in electronic cigarettes. Flow rates used
in various laboratory investigations involving e-cigarettes have varied
widely to date, and can thus promote interlaboratory variability in
aerosol product profiles. The thermal decomposition of hydroxyacetone
and glycolaldehyde is less favorable at lower temperatures, supporting
the observations of these products at higher flow rates/lower heating
coil temperatures. Higher temperatures promote the formation of acetaldehyde
from hydroxyacetone and formaldehyde from both hydroxyacetone and
glycolaldehyde. A separate finding is that greater airflow can also
expose users to concerning levels of e-liquid solvents. Under the
modest conditions studied, propylene glycol aerosol levels are found
at above the acceptable inhalation levels defined by NASA, and in
range of the generally recognized as safe levels for daily ingestion.
The electronic cigarette solvents propylene glycol and glycerol are known to produce toxic byproducts such as formaldehyde, acetaldehyde and acrolein. However, the aerosol toxin yield depends upon a variety of chemical and physical variables. The formaldehyde hemiacetals derived from these solvents were reported as major electronic cigarette aerosol components by us in 2015. In the study described herein, the formaldehyde hemiacetals were found at higher levels than those of free formaldehyde via an orthogonal sample collection protocol. In addition, the common aldehyde collection methods for electronic cigarettes, such as impingers and sorbent tubes containing DNPH, significantly underestimate the levels of formaldehyde. The reason for this is that formaldehyde hemiacetals follow other reaction pathways, such as the formation of a less reactive full cyclic acetal catalyzed by the acidity of the DNPH solution and the silica. We found that formaldehyde hemiacetals are a considerable fraction of the total formaldehyde produced in electronic cigarette that cannot be determined accurately by DNPH derivatization methods. Although the health effects of the hemiacetals are not yet known, they warrant further investigation.
Fluorescent small molecules enable
researchers and clinicians to
visualize biological events in living cells, tissues, and organs in
real time. Herein, the focus is on the structure and properties of
the relatively rare benzo[a]xanthenes that exhibit
enhanced steric and electronic interactions due to their annulated
structures. Three types of fluorophores were synthesized: (i) pH-
and solvent-dependent seminaphthorhodafluors, (ii) pH- and solvent-independent
seminaphthorhodafluors, and (iii) pH-independent but solvent-sensitive
seminaphthorhodamines. The probes exhibited promising far-red to near-infrared
(NIR) emission, large Stoke shifts, broad full width at half-maximum
(fwhm), relatively high quantum yields, and utility in immunofluorescence
staining. Deviation of the π-system from planarity due to changes
in the fluorophore ionization state resulted in fluorescence properties
that are atypical of common xanthene dyes.
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