Seymour Steven Brody

Fluorescence lifetime, yield, energy transfer and spectrum in photosynthesis, 1950–1960

The fluorescence lifetime of chlorophyll agives information about the primary photo-physical events in photosynthesis. Most of the light energy absorbed by chlorophylls is utilized for photochemistry. There are two main additional pathways competing for the absorbed light energy: fluorescence and radiationless internal conversion (heat). Only a few percent of the absorbed energy proceeds along these two pathways. This historical minireview focuses on the first direct measurements of the lifetime of chlorophyll fluorescence, the time it takes to transfer energy from phycoerythrin to chlorophyll a, and the discovery of the fluorescence band at 720 nm (F720; then attributed to a dimer of chlorophyll). These works were carried out during the the late 1950s to the early 1960s in the laboratory of Professor Eugene Rabinowitch at the University of Illinois, Urbana-Champaign [Brody (1995) Photosynth Res 43: 67–74].

ABSORPTION AND FLUORESCENCE SPECTRA OF CHLOROPHYLL‐a IN POLAR SOLVENTS AS A FUNCTION OF TEMPERATURE

Abstract— Absorption and fluorescence spectra of chlorphyll‐a in aqueous alcohol were determined as a function of temperature between 173° and 293°K. From a comparison of these spectra with ones obtained in pure methanol, it is suggested that changes in molecular association occur within aggregates of chlorophyll‐a in aqueous‐alcoholic solution induced by variation of the dielectric constant. The latter varies over a wide range in aqueous alcohol as a function of temperature.

Absorption properties of aggregated (dimeric) chlorophyll

Abstract The absorption spectrum of an aggregated form of chlorophyll a in ethanol is given. This aggregate, which could be a dimer, has major absorption maxima at 682, 648, and 455 mμ. A geometry is suggested for it, based upon the spectral changes which result from aggregation. The shape of the red band of the dimer, and an estimate of dimer concentration (relative to total chlorophyll) is given for two different kinds of algae. There is good correlation between the absorption properties of the aggregate and the ligh-induced changes in absorption observed in photo-synthetic material.

SPECTRAL PROPERTIES OF CHLOROPHYLL a MONOLAYERS: MONOLAYERS OF CHLOROPHYLL a AND PHEOPHYTIN AT A GAS‐WATER INTERFACE*

Abstract— Surface and spectral properties of chlorophyll a monolayers were studied at a nitrogen‐water interface. Direct spectral analysis of Chl monolayers indicated that compression results in a heterogenous mixture of Chl species. Fourth derivative and difference spectra showed the presence of minor bands at 692, 726 and 748 nm. The state of compression determines the quantity and type of spectral species formed. A Chl monolayer on an acid subphase results in the formation of a long wavelength absorbing species (705 nm) similar to that of pheophytin. The half‐band width, optical density/monolayer, and extinction coefficients of Chl monolayers are given. It is concluded that in the monolayer the formation of various aggregated species of Chl can be induced.

Absorption difference spectroscopy of chlorophyll a in ethanol solution

Abstract Absorption difference spectra between highly concentrated and dilute solutions of chlorophyll a have been measured in ethanol, maintaining the product of concentration and path length constant. A log-log plot of dimer versus monomer concentration, derived from the data, was linear with a slope of 2.0, which is consistent with the interpretation that dimers are present in this solvent. The absorption spectrum of the dimer in ethanol was calculated, and a value of 4.5 ± 0.8 M −1 was obtained for the equilibrium constant for dimerization.

We remember Eugene : (Rabinowitch and his laboratory, during the fifties).

This article is written in memory of Eugene Rabinowitch, one of the major prophets of photosynthesis. I speak on behalf of all the students and post-doctorial associates who were fortunate to be associated with and to have loved this wonderful man. I shall also describe my research with Eugene. We all remember him on the 1995 anniversary of his death (May 15, 1973).

Spectral properties of chloroplast membranes as a function of physiological temperatures

Abstract The absorption spectrum of chloroplasts changes as a function of temperature. As chloroplasts are cooled from room temperature to 10°C there are increases in absorption at 675, 500 and 436 nm, plus a small decrease at 685 nm. As the chloroplasts are heated to 34°C there are decreases in absorption at 675, 500 and 436 nm plus increases in absorption at 690 and 400 nm. It is concluded that the temperature dependent change in phase of the membrane lipids (solid to liquid crystal state) modifies the state of chlorophyll aggregation.

Effects of pH on the binding of hematoporphyrin derivative to monolayer and bilayer membranes

The effects of pH on the binding of hematoporphyrin derivative (HpD) to monolayer and bilayer membranes have been studied. Absorption spectra of HpD bound to phosphatidylcholine (PC) liposomes indicate that there is greater binding of HpD to lipid films at acidic, tumoricidal pH conditions than at normal tissue pH. These results were found to correlate with surface pressure measurements of monolayer films formed under similar conditions. Surface potential measurements in conjunction with surface pressure measurements from monolayer films suggest that at low pH (i.e. less than or equal to 6.6) porphyrin intercalates within the lipid film to reach relatively high concentrations, while at higher pH (i.e. greater than or equal to 7.4) the porphyrin preferably adsorbs to the lipid film at the monolayer/water interface.

Oxyhemoglobin A and oxyhemoglobin S films at an air-water interface: Absorption spectra studies

Abstract Properties of oxyhemoglobin at an interface are important to further the understanding of tertiary and quaternary changes in hemoglobin. Absorption spectra of oxyhemoglobin films were studied directly at the air-water interface. Both oxy Hb A and oxy Hb S show a bathochromic shift in the Soret band as compared to the solution spectra. No spectral difference is observed between oxy Hb A and oxy Hb S. However, surface isotherms show a greater unfolding of the molecule for oxy Hb S than oxy Hb A. Hemolysates appear to be more stable on the surface than their corresponding chromatographed material. The lack of spectral shift upon compression might be the consequence of the high dielectric constant of the medium. A model for this surface phenomenon with respect to observed mechanical precipitation of oxy Hb S is discussed.

Absorption spectra of mixed monomolecular films of chlorophyll and photosynthetic electron carriers at a gas-water interface.

Abstract Absorption spectra of mixed monomolecular films containing chlorophyll and endogenous redox reagents are studied at a gas-water interface. Overlapping absorption spectra are resolved by difference spectroscopy and fourth derivative analysis. Monomolecular films are formed in a Langmuir trough using a Wilhelmy film balance. A reaction between vitamin K 1 and chlorophyll is observed both in the dark and after illumination. A smaller interaction occurs between α-tocopherolquinone and chlorophyll. A light-driven reaction occurs between oxidized plastocyanin and chlorophyll, but not between reduced plastocyanin and chlorophyll. An interaction is observed between cytochrome c and chlorophyll both in the dark and after illumination. Evidence is obtained indicating that the presence and amount of aggregated species of chlorophyll are dependent on the presence of specific reagents. We suggest that redox reagents of Photosystem II and Photosystem I of photosynthesis also serve to “induce” the formation of distinct chlorophyll species.