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Biomedical subjects

M Calvin

Publications and source records attributed to M Calvin.

At least 91 records · Page 5Linked to original sources
PubMed1969

Biradical spin labeling for nerve membranes.

We have explored the behavior of pair interaction in a suitable biradical when it is bound by van der Waals' forces in a nerve membrane. We have concomitantly examined a set of model solvents to represent this situation. It appears that the biradical suffers a restriction of internal motion with a minimal restraint on its external motion in the nerve medium. The biradical is so situated as not to respond to the passage of the action potential.

Electron Spin Resonance Spectroscopy↗
PubMed1969

Chemical evolution.

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Biological Evolution↗
PubMed1967

Thermodynamics of light emission and free-energy storage in photosynthesis.

A Planck law relationship between absorption and emission spectra is used to compute the fluorescence spectra of some photosynthetic systems from their absorption spectra. Calculated luminescence spectra of purple bacteria agree well but not perfectly with published experimental spectra. Application of the Planck law relation to published activation spectra for Systems I and II of spinach chloroplasts permits independent calculation of the luminescence spectra of the two systems; if the luminescence yield of System I is taken to be one-third the yield of System II, then the combined luminescence spectrum closely fits published experimental measurement.Consideration of the entropy associated with the excited state of the absorbing molecules is used to compute the oxidation-reduction potentials and maximum free-energy storage resulting from light absorption. Spinach chloroplasts under an illumination of 1 klux of white light can produce at most a potential difference of 1.32 ev for System I, and 1.36 ev for System II. In the absence of nonradiative losses, the maximum amount of free energy stored is 1.19 ev and 1.23 ev per photon absorbed for Systems I and II, respectively. The bacterium Chromatium under an illumination of 1 mw/cm(2) of Na D radiation can produce at most a potential difference of 0.90 ev; the maximum amount of free energy stored is 0.79 ev per photon absorbed.The combined effect of partial thermodynamic reversibility and a finite trapping rate on the amount of luminescence is considered briefly.

Chloroplasts↗
PubMed1966

Thymine addition to ethanol: induction by gamma irradiation.

When thymine in dilute, deaerated, aqueous solution was irradiated with gamma-rays in the presence of ethanol, a high yield of products containing both the thymine and ethanol moieties was obtained. These were shown to be isomers formed by the attack of CH(3)CHOH radicals at the carbon No. 6 position of thymine. A similar reaction was observed with N, N'-dimethylthymine, but O,O'-dimethylthymine did not react. The reaction may be relevant to the resistance of certain cells to ionizing radiation.

Chemical Phenomena↗