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Biomedical subjects

J R Norris

Publications and source records attributed to J R Norris.

At least 55 records · Page 3Linked to original sources
PubMed1975

The triplet state in bacterial photosynthesis: Possible mechanisms of the primary photo-act.

In vitro and in vivo triplet state electron paramagnetic resonance (epr) spectra of bacteriochlorophylls (Bchls) show important differences in (a) electron spin polarization (esp), and (b) zero field splitting (ZFS) parameters. The unusual esp and ZFS properties of the observed in vivo triplet state are best interpreted as arising from a short-lived radical pair precursor (not directly observable by epr) formed in or with the special pair of bacteriochlorophyll molecules involved in the primary photo-act.

Journal Article↗
PubMed1974

An electron-nuclear double resonance (ENDOR) study of the special pair model for photo-reactive chlorophyll in photosynthesis.

A comparison of hyperfine coupling constants obtained by electron-nuclear double resonance spectroscopy of in vitro monomer chlorophyll and bacteriochlorophyll free radicals with those of the photoesr (electron spin resonance) signal associated with light conversion in photosynthesis provides convincing support for the special pair model for the in vivo photo-reaction center.

Journal Article↗
PubMed1971

Electron spin resonance of chlorophyll and the origin of signal I in photosynthesis.

A comparison has been made between Signal I, the photo-electron spin resonance signal associated with the primary light conversion act in photosynthesis, and free-radical signals generated in various chlorophyll species in vitro. The esr signals obtained from chlorophyll.monomer, (Chl.L)(+.), chlorophyll dimer, (Chl(2))(+.), and chlorophyll oligomer, (Chl(2))(n) (+.), are broader than Signal I, whereas the chlorophyll-water adduct, (Chl.H(2)O)(n) (+.), gives a signal very much narrower than Signal I. The unusually narrow signal from (Chl.H(2)O)(n) (+.) has been ascribed to spin migration, or to unpaired spin delocalization over a large number of chlorophyll molecules. The linewidth of Signal I can be accounted for by a similar delocalization process. A theoretical relationship between the esr linewidth and the number of chlorophyll molecules, N, over which an unpaired spin is delocalized, takes the form DeltaH(N) = 1/ radicalN.DeltaH(M), where DeltaH(M) is the linewidth of monomer (Chl.L)(+.). This relationship for N = 2 accounts well for the linewidths of Signal I in green algae, blue-green algae, and photosynthetic bacteria in both the (1)H- and (2)H-forms. The linewidth of Signal I (as well as the optical properties of reaction-center chlorophyll) are consistent with unpaired spin delocalization over an entity containing two chlorophyll molecules, (Chl.H(2)O.Chl)(+.).

Chlorophyll↗