Abstract:
The absolute fhotoelectron quantum yield
spectra for benzo[ a ]pyrene an dimethylbenzanthracene are
present~d in th~ wavelength range 180-230 nm. These polycyclic
aromatic carcmogens have photoelectron quantum yields of
approximately 2 X 10-3 electrons per incident photon at 180 nm.
The quantum yields fall off quickly and monotonically at
wavelengths longer than 210 nm (5.9 eV). Threshold values for
benzo[ a ]pyrene and dimethylbenzanthracene are 5.25 ± 0.06
eV and 5.27 ± 0.04 eV, respectively. The photoelectron quantum
yields of benzo[ a ]pyrene and dimethylbenzanthracene are
several orders of magnitude greater than typical components
of biological membranes (amino acids, phospholipids, and
polysaccharides). Preliminary micrographs of benzo[a]pyrene
and dimethylbenzanthracene sublimed onto poly(L-lysine) and
onto dimyristoyl phosphatidylcholine demonstrate the high
contrast of small crystallites of carcinogens against a background
of membrane components. These results and calculations
involving relative contrast factors suggest that the distribution
of these carcinogens in biological membranes can be
determined by using photoelectron microscopy.