Norris J R, Uphaus R A, Crespi H L, Katz J J
Proc Natl Acad Sci U S A. 1971 Mar;68(3):625-8. doi: 10.1073/pnas.68.3.625.
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)(+.).
对信号I（与光合作用中的初级光转换行为相关的光电子自旋共振信号）与体外各种叶绿素物种中产生的自由基信号进行了比较。从叶绿素单体（Chl.L）(+)、叶绿素二聚体（Chl(2)）(+)和叶绿素寡聚体（Chl(2)）(n) (+)获得的电子自旋共振信号比信号I宽，而叶绿素 - 水加合物（Chl.H₂O）(n) (+)给出的信号比信号I窄得多。（Chl.H₂O）(n) (+)异常窄的信号归因于自旋迁移，或未成对自旋在大量叶绿素分子上的离域。信号I的线宽可以用类似的离域过程来解释。电子自旋共振线宽与未成对自旋离域的叶绿素分子数N之间的理论关系为ΔH(N)=1/√N·ΔH(M)，其中ΔH(M)是单体（Chl.L）(+)的线宽。对于N = 2，这种关系很好地解释了绿藻、蓝绿藻和光合细菌中（1）H型和（2）H型信号I的线宽。信号I的线宽（以及反应中心叶绿素的光学性质）与未成对自旋在包含两个叶绿素分子的实体（Chl.H₂O.Chl）(+)上的离域一致。
