COMMUNICATIONS TO THE EDITOR
Sept. 20, 1962
3587
Acknowledgment.-We are indebted to the National Science Foundation for financial support (Grant No. G-17345).
Chlorophyll a, isolated from spinach and carefully purified, exhibited three sharp, low field resonance bands ( T = 0.62, 0.85, and 1.81, measured in CDC13, tetramethylsilane as internal indicator). DEPARTMENT OF CHEMISTRY UNIVERSITY OF NORTH DAKOTA VICTOR J. HRUBY These bands correspond to the three bands found GRANDFORKS,NORTHDAKOTA A. WILLIAM JOHNSON in chlorin e6 trimethyl ester and assigned to the a-, RECEIVED JUNE 22, 1962 p- and &bridge hydrogen atoms by Woodward and Skaric.5 All other hydrogen resonances in chlorophyll a, including the C-10 hydrogen, lie a t higher SITE OF EXCHANGEABLE HYDROGEN IN fields. When chlorophyll a was treated with excess CHLOROPHYLL D FROM PROTON MAGNETIC RESONANCE MEASUREMENTS ON DEUTERIOCH30D in CClk for 48 hours,2 the band a t r = 1.81 CHLOROPHYLL 01 disappeared, in a manner entirely analogous to Sir : that reported for chlorin by Woodward and S k a r i ~ . ~ When the exchanged chlorophyll a was treated with As shown by an indirect infrared method, chlorophyll a possesses one slowly exchangeable hydrogen CHaOH, the band reappeared. These facts indicate atom when the chlorophyll is treated with methanol that the &bridge hydrogen atom undergoes the exin carbon tetrachloride solution a t room tempera- change. To minimize uncertainties and ambiguities in the ture in the dark.2 Although the position of the exchangeable hydrogen could not be established by interpretation of the very complex chlorophyll the exchange method, considerations had indicated n.m.r. spectrum, we followed the hydrogen exthat the active hydrogen probably was located a t change in deuterio-chlorophyll a.4 This substance showed no proton resonances. On treatment with the C-10 position (I).3 We have now carried out proton magnetic reso- CHaOH in CC1, for 48 hours, one, and only one, = 1.81. Again, nance measurements (Varian A-60 n.m.r. spec- proton resonance appeared a t treatment with CH30D caused t h e resonance peak trometer equipped with an audio oscillator and counter) that confirm the presence of but one to disappear. These results with deuterio-chloroexchangeable hydrogen atom in chlorophyll a phyll a demonstrate unequivocally that only one (under our exchange conditions). The exchange- hydrogen atom undergoes exchange under the reacable hydrogen is not located a t the C-10 position, tion conditions used here, and that the labile hydrobut is in fact on the &bridge carbon atom of the gen is located on the porphyrin ring a t the 6 posiporphyrin ring (I). The n.m.r. observations were tion. The remarkable observations of Woodward and made with two materials; not only was theexchange followed in ordinary chlorophyll a, but also in the Skaric5 on the chemical and exchange behavior of fully deuteriated chlorophyll a that we have avail- chlorins thus also appear to be valid for chlorophyll able.4 The use of the deuterio-chlorophyll made it a itself. That the hydrogen a t the 6 position is possible to detect hydrogen resonances that might more labile than the one a t C-10 could only be otherwise have been obscured in ordinary chloro- established by measurements on chlorophyll itself rather than on derivatives lacking the central phyll. magnesium atom and the cyclopentanone ring. Although the conditions used for the hydrogen exchange are certainly not physiological, nevertheless the lability of the &hydrogen atom in chlorophyll a as established here may also be pertinent to the chemical behavior of chlorophyll a in photosynthesis, We are deeply indebted to Dr. Gerhard L. Closs of the University of Chicago for guidance and instruction in the interpretation of the n.m.r. spectra. ( 5 ) R. B. Wnndwarrl and V. Skaric. J . A m . Chem. Sor., 8 3 , 4076 (1961).
CH2
I
I
"-;;IO COOCH3 C00G20H39 CHZ
I
I
JOSEPH J. KATZ ARGONNEXATIONAL LABORATORY MARYR. THOMAS ARGONNE, ILLINOIS HAROLD II. STRAIN RECEIVED JULY 25, 10632
c. 0 9
(1) Based on work performed under the auspices of the U . S.
Atomic Energy Commission. (2) J. J. Katz, M. R. Thomas, H. L. Crespi and H. H. Strain, J . A m . Chem. Soc., 83, 4180 (1961). (3) H. Fischer and S. Goebel, A n n . , 633, 168 (1936); S. Aronoff, Encyclopedia of Plant Physiology, 6, 234 (1960); W. Vishniac and I. A. Rose, Naluie, 133, 1089 (1958). (4) H. H. Strain, M. R. Thomas, H. L. Crespi, M. I. Blake and J. J. Katz, A n n . New York Acad. Sci., 84, 617 (1960).
THE EFFECT OF H?O ON THE y-RADIOLYSIS OF AERATED CHaOH'
Sir : We wish to report a previously overlooked2 effect of Ha0 on the y-radiolysis of aerated methanol which gives promise of serving as a useful tool in the study of radiolytic mechanism. (1) Research performed under the auspices of the United States Atomic Energy Commission. (2) E. Hayon and J. J. Weiss, J. Chem. Soc., 3970 (1961).
