Photoelectron Quantum Yields and Photoelectron Microscopy of Chlorophyll and Chlorophyllin

Abstract

The absolute PE quantum yield curves of chls u and b,.chln, and phytol were examined over the wavelength range 50G180 nm. In the long wavelength region (500-240 nm) quantum yields are below 5 x electrons per incident photon. Below 240 nm the quantum yields rise sharply. The chls and chln exhibit similar yield curves; measured yields were of order 5 x lO-"electrons per incident photon at 240 nm, 1 x at 220 nm, and 1 x at 180 nm. These yields are at least 2 orders of magnitude greater than those of the amino acids and more than three orders of magnitude greater than that of phytol over this wavelength region. Photoemission observed in chl thin films is due to the porphyrin moiety of the molecule. High contrast is obtained in PE micrographs of chln deposited on substrates of bovine serum albumin, dipalmitoyl phosphatidylcholine, or starch. Chl is expected to be the dominant photoemissive component of thylakoid membranes and accounts for the image contrast observed previously in PE micrographs of spinach chloroplasts.

Photoelectron Quantum Yield Spectrum and Photoelectron Microscopy of Β‐carotene

“…Chemical Company. Chl a was isolated from fresh spinach leaves as previously described (Dam et al, 1975) and stored in the dark in ethanol at -20°C. Silica gel (Type G) thin layer chromatography (TLC) plates were purchased from Eastman and washed with the appropriate developing solvent immediately before use.…”

“…Vertical bars represent the maximum estimated error of the measurements. Also shown is the mean photoelectron quantum yield spectrum for Chl a (Dam et al, 1975). Error bars for the Chl a spectrum are the same as those for the /?-carotene spectrum and are omitted for clarity.…”

“…Toward this end, we have determined the absolute photoelectron quantum yield spectra for a variety of biological membrane components including phospholipids , mono-and polysaccharides (Dam et al, 1977) and common amino acids and their homopolymers (Dam et at., 1974). We have also measured the photoelectron quantum yield spectra of chlorophylls a and b (Dam et al, 1975). The chlorophylls are 100-5000 times more photoemissive in the 2 W 2 3 0 nm excitation range than other membrane components listed above, suggesting that photoelectron microscopy may be a good way to approach the problem of pigment distribution in photosynthetic membranes.…”

<title>Photoelectron Microscopy Of Biological Surfaces Excitation Source Brightness Requirements</title>

“…These are very preliminary low magnification images. Several additional reports examine specific aspects of PEM applications to organic and biological surfaces (3)(4)(5)(6)(7)(8)(9)(10). Metallurgical ap plications are reviewed elsewhere (H).…”