TY - JOUR
T1 - Low Temperature Absorption Spectra of Chlorophyll a in Polar and Nonpolar Solvents
AU - Brody, S. S.
AU - Broyde, S. B.
N1 - Funding Information:
We gratefully acknowledge support for this research by the National Science Foundation under Grant GB-7244. S. S. Brody was supported (in part) by a Public Health Service Research Career Program Award K3-GM-17, 918. Received for publication 23 June 1968.
PY - 1968
Y1 - 1968
N2 - Absorption spectra of chlorophyll a were measured in polar and non-polar solvents, as a function of temperature from 298° to 77°K. Both dilute and concentrated solutions were examined. In both types of solvents at room temperature, the absorption spectra of concentrated solutions differ from dilute ones in that the half width of the main red absorption band is greater, and all bands are shifted to longer wavelengths. These differences are largely due to the presence of dimers when the pigment concentration is high. In dilute ethanol solutions, where the chlorophyll is unassociated, cooling causes a red shift in all bands which is due to the increased polarity of the solvent at low temperature. On cooling at high concentrations in ethanol and EPA, a new band appears near 700 nm. This band is attributed to dimers present prior to cooling, but absorbing at shorter wavelengths at room temperature. In nonpolar solvents, a band near 700 nm appears at the solvent freezing point. In these solvents, the “700” nm absorption is attributed to dimers, and/or small polymers, partly formed by cooling. A change in aggregate geometry when the solvent becomes viscous or frozen can account for the appearance of this “700” nm absorption band at low temperature, in polar and nonpolar media.
AB - Absorption spectra of chlorophyll a were measured in polar and non-polar solvents, as a function of temperature from 298° to 77°K. Both dilute and concentrated solutions were examined. In both types of solvents at room temperature, the absorption spectra of concentrated solutions differ from dilute ones in that the half width of the main red absorption band is greater, and all bands are shifted to longer wavelengths. These differences are largely due to the presence of dimers when the pigment concentration is high. In dilute ethanol solutions, where the chlorophyll is unassociated, cooling causes a red shift in all bands which is due to the increased polarity of the solvent at low temperature. On cooling at high concentrations in ethanol and EPA, a new band appears near 700 nm. This band is attributed to dimers present prior to cooling, but absorbing at shorter wavelengths at room temperature. In nonpolar solvents, a band near 700 nm appears at the solvent freezing point. In these solvents, the “700” nm absorption is attributed to dimers, and/or small polymers, partly formed by cooling. A change in aggregate geometry when the solvent becomes viscous or frozen can account for the appearance of this “700” nm absorption band at low temperature, in polar and nonpolar media.
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U2 - 10.1016/S0006-3495(68)86570-1
DO - 10.1016/S0006-3495(68)86570-1
M3 - Article
C2 - 5713456
AN - SCOPUS:0014398760
SN - 0006-3495
VL - 8
SP - 1511
EP - 1533
JO - Biophysical journal
JF - Biophysical journal
IS - 12
ER -