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The Journal of Physical Chemistry, Vol. 83, No. 26, 1979
= 9.54 G and uN2= 7.95 G. The simulation is essentially identical if the values are 9.64 and 8.05 G. The simulations in parts D and F of Figure 9 are qualitatively equally good, but quantitative examination shows that Figure 9F is about 1G narrower. Consequently, the interval between the first and last maxima corresponds better to the experimental spectrum. The spacing of the closest lines varies in the reported spectra, but averages about 0.02 G less than in these simulations. This spacing is only weakly dependent upon the from values used for uo,p(nitro).Thus, reduction of ao(nitro) 0.39 to 0.35 decreases this line spacing by less than 0.02 G. Reduction in up(nitro)also affects the spacing only weakly, and introduces some bizarre changes in the shape of the spectrum envelope. It is clear that, while the appearance of the spectrum is quite sensitive to small changes in at least some of the hfcs, it cannot be used to establish the superiority of a particular set of values. In all of our simulations, the line width used is 0.14 G, the minimum value we found necessary to remove structure on the individual lines of the spectrum. Note that the spectrum produced by sets of 2 , 2 , 1 , 2 , 2 , 1 , 2hydrogen and 2, 1, 1, 1 nitrogen atoms contains 131 220 lines. The observed spectrum contains about 150 lines, and is so underdetermined that we consider it rash to claim superiority for a particular set of parameters on the basis of a qualitative fit to the ESR spectrum. Instead, we consider the consistency of the data reported here for DPPH at 180 K, at room temperature, and in the fast jump limit to be the best evidence for their validity. The simulations do support our claim that averaging over processes 1-111, but not IV, occurs at room temperature. This has been suggested previously by Balaban and c o - w ~ r k e ron s ~ the ~ basis of their analysis of the ESR spectra of certain DPPH analogues.
Acknowledgment. Support for early stages of the work at UICC was provided by Grant GP 33518X from the National Science Foundation. Summer support for S. E.O'C. was provided by grants from the UICC Research Board. Computer services were provided by the UICC Computer Center. The work at Berlin was supported by the Deutsche Forschungagemeinschaft (Sfb 161). Many helpful discussions with Dr. M. Plato are gratefully acknowledged.
References and Notes (1) (a) Bruker Analytische Messtechnik GmbH and Freie Universttit Berlin. (b) Frele Universitat Berlin. (c) University of Illinois; work taken from the Ph.D. thesis of S.E.O'C.; (d) University of Illinois. (e) MaxPlanck-Institut. (2) S. Goldschmldt and K. Renn, Berichfe, 55, 628-643 (1922).
van der Waals Work up to 1966 or 1967 is reviewed in A. R. Forrester, J. M. Hay, and R. H. Thomson, "Organic Chemistry of Stable Free Radicals", Academic Press, New York, 1968, Chapter 4. C. A. Hutchison, R. C. Pastor, and A. G. Kowalsky, J . Chem. Phys., 20, 534-535 (1952). J. S.Hyde, R. C. Sneed, Jr., and G. H. Rist, J . Chem. Phys., 51, 1404-1416 (1969). (a) For nitroxyl radicals: Y. Y. Lim and R. S.Drago, J. Am. Chem. SOC.,93, 891-894 (1971). (b) For para-substltuted nitrobenzene anion radicals: P. L. Kolker and W. A. Waters, J . Chem. SOC., 1136-1141 (1964). (a) N. S.Garifyanov, A. V. Ilyasov, and Yu. V. Yablokov, Lbk/. Akad. Nauk SSSR, 149, 876-879 (1963); (b) Yu. M. Ryzhmanov and A. A. Egorova, ibid., 191, 148-150 (1970). Y. Deguchi, J. Chem. Phys., 32, 1584-1585 (1960). (a) R. I.Walter, J . Am. Chem. Soc., 88, 1930-1936 (1966); (b) V. A. Gubanov, V. I.Koryakov, A. K. Chlrkov, and R. 0. Matevosyan, Zh. StrUkt. Khim., 11, 941-946 (1970); 12, 538-541 (1971). (a) V. A. Gubanov, V. I.Koryakov, and A. K. Chirkov, J. Magn. Reson., 11, 326-334 (1973); (b) R. E. Sagdeev, Yu. N. Molin, V. I. Koryakov, A. K. Chirkov, and R. 0. Matevosyan, Org. M g n . Reson., 4,365-368 (1972). (a) N. S. Dalai, D. E. Kennedy, and C. A. McDowell, Chem. Phys. Lett., 30, 186-189 (1975), and precedlng papers; (b) N. S. Daiai, J. A. Ripmeester, and A. H. Reddoch, J . Magn. Reson., 31, 471-477 (1976). (a) K. P. Dlnse, R. Biehl, and K. Moblus, J . Chem. Phys., 61, 4335-4341 (1974); (b) R. Blehl, M. Plato, and K. Moblus, ibid., 63, 3515-3522 (1975). K. Moblus and R. Biehl In "Multiple Electron Resonance Spectroscopy", M. M. Dorio and J. H. Freed, Ed., Plenum Press, New York, 1979. Unpublished work of W. A. Doak and G. Putz with R. I.Waiter. S.E. O'Connor and R. I.Walter, J . Org. Chem., 42, 577 (1977). (a) M. M. Chen, A. F. D'Adamo, Jr., and R. I.Walter, J. Org. Chem., 26, 2721-2727 (1961); (b) K. Clusius and M. Vecchi, Helv. Chlm. Acta, 38, 933-937 (1953); (c) R. H. Polrler, E. J. Kahler, and F. Benlngton, J. Org. Chem., 17, 1437-1445 (1952). G. A. Pearson and R. I.Walter, J. Am. Chem. Soc., 99, 5262-5266 (1977). For general reviews, see (a) R. W. Krelllck In "NMR of Paramagnetic Molecules", 0. N. LaMar, W. Dew. Horrocks, Jr., and K. H. Holm, Ed., Academlc Press, New York, 1973; (b) E. DeBoer and H. van Wllligen in "Progress in NMR Spectroscopy", Vol. 2, J. W. Emsley, J. Feeney, and L. H. Sutcllffe, Ed., Pergamon Press, Oxford, 1967. R. D. Allendoerfer and A. H. Maki, J . Magn. Reson., 3, 396-410 (1970). R. Blehl, K. Hinrichs, H. Kurreck, W. Lubltz, U. Mennenga, and K. Roth, J . Am. Chem. SOC.,99, 4278-4286 (1977). R. Biehl, Ph.D. Thesls, Free University of Berlin, 1974. D. E. Williams, J . Am. Chem. Soc., 88, 5665-5666 (1966). H. S. Gutowsky, D. M. McCall, and C. P. Slichter, J . Chem. Phys., 21, 279-292 (1953). M. Plato, R. Biehi, K. Mobius, and K. P. Dinse, 2.Naturforsch. A , 31, 169-176 (1976). C. v. Borczyskowski and K. Moblus, Chem. Phys., 12, 281-290 (1976). L. Pauling, "The Nature of the Chemical Bond", 3rd ed, Cornell University Press, Ithaca, N.Y., 1960, pp 341-343. R. G. Lawlor and 0. K. Fraenkel, J . Chem. Phys., 49, 1126-1139 (1966); R. G. Lawlor, J. R. Bolton, M. Karplus, and 0. K. Fraenkel, ibld., 47, 2149-2165 (1967). 2. Panlotis and H. H. Gunthard, Mh. Chlm. Acta, 51, 561-564 (1968). 0. A. Pearson, M. Rocek, and R. I.Walter, J. Phys. Chem., 82, 1165-1192 (1976). A. T. Balaban, M. T. Capriou, N. Nagolta, and R. Baican, Tetrahedron, 33, 2249-2253 (1977), and references quoted there.
Research on Quantum Beats in Phosphorescence at Leiden J. H. van der Waals Center for the Study of Exclted States of Molecules, Huygens Laboratory, Lelden, The Netherlands (Recelved September 18, 1070) Pubilcatlon costs assisted by Ruksuniversitelt Lelden
G. N. Lewis and his school1 identified the optical pumping cycle underlying the phosphorescence of organic molecules. On excitation into a higher singlet state, intersystem crossing (ISC) occurs to the metastable triplet state T, from which the molecules decay back to the ground state So with the emission of light. Weissman, in a n ingenious experiment, showed t h a t this 0022-3654/79/2083-3456$0 1.OO/O
"phosphorescence" corresponds to electric dipole radiationS2 We specifically consider azaaromatic molecules with an n r * state S1 and r r * state T. One then expects the spin-orbit coupling (SOC) to occur locally near the N nucleus and such that in the ISC process the spin S = 1 is "created" with S in the " n r plane" determined by the 0 1979 American Chemlcal Society
%I NMR Study
of Zinc-Nucleotide Triphosphate Complexes
The Journal of Physical Chemistry, Vol. 83, No. 26, 1979 3457
were observed in the phosphorescence at the T,-T, zerofield ESR frequency (858 M H Z ) . ~Then a magnetic free induction signal at this frequency was generated by picosecond laser excitation into the singlet systems7For a more extensive discussion of this work see two recent review^.^^^ References and Notes (1) G. N. Lewis, D. Lipkln, and T. T. Magel, J . Am. Chem. Soc., 63, 3005 (1941); 0. N. Lewis and M. Kasha, ibld., 66, 2100 (1944). (2) S. 1. Welssman and D. Llpkin, J. Am. Chem. Soc., 64, 1916 (1942). (3) J. H. van der Waals and M. S. de Groot In "The Triplet State", A. B. Zahlan, Ed., Cambrldge University Press, 1967. (4) R. A. Schadee, J. Schmidt, and J. H. van der Waals, Chem. Phys. Left., 41, 435 (1976). (5) M. I. Podgoretskii and 0. A. Khrustalev, Sov. Phys.-Usp. (Engl. Trans/.),6, 682 (1964); M. Bixon, J. Jortner, and Y. Dothan, Mol. Phys., 2, 109 (1969); S. Haroche, Top. Appl. Phys., 13 (1976). (6) R. A. Schadee, C. J. Nonhof, J. Schmldt, and J. H. van der Waals, Mol. Phys., 34, 171, 1497 (1977); R. A. Schadee, J. Schmldt, and J. H. van der Waals, Ibld., 36, 177 (1978). (7) C.J. Nonhof, F. L. Plantenga, J. Schmidt, C. A. 0. 0. Varma, and J. H. van der Waals, Chem. Phys. Left., 60, 353 (1979). (8) J. Schmldt and J. H. van der Waals, in "Time Domain Electron Spin Resonance Spectroscopy", L. Kevan, Ed., Wiley, New York, 1979. (9) J. H. van der Waals In "Journal of Molecular Structure", W. J. Orvllle-Thomas, Ed., Elsevier, Amsterdam, 1979.
Flgure 1.
2 p i ~and lone-pair orbitals on the nitrogen (7 = 0 in Figure l).394 The crucial SOC thus occurs between SIand a triplet component T for which S,T, = 0. Whenever tLe plane 7 = 0 does not coincide with one of the planes of quantization in zero field, the ISC should lead into a coherent superposition of zero-field states and the phosphorescence should pass through two parallel channels. In an experiment so designed that one cannot discriminate between the channels, quantum interference effects then are expected to arise, just as in Young's two-slit e ~ p e r i m e n t . This ~ picture has been verified for tetramethylpyrazine in a durene host. First, quantum beats
Chlorine-35 Nuclear Magnetic Resonance Study of Zinc-Nucleotide Triphosphate Complexes' J. A. Happe and R. L. Ward" Chemlstry and Materials Science Deparfment, Lawrence Llvermore Laboratory, Unlversity of California, Livermore, California 94550 (Received August 13, 1979) Publlcation costs assisted by Lawrence Livermore Laboratory
The interaction of Zn(I1) with nucleotide triphosphates has been studied by 36ClNMR and by 'H NMR. In 0.5 M NaCl solutions, enhanced 36Clrelaxation is produced by the metal ion in a Zn(I1)-nucleotide triphosphate complex, Zn(NTP). In equimolar metal-ligand solutions, the adenosine triphosphate complex, Zn(ATP)2-, produces about twice as much 36Clrelaxation as do the inosine triphosphate or uridine triphosphate complexes, Zn(ITP)2-and Zn(UTP)2-. 36Clrelaxation by the cytidine triphosphate complex, Zn(CTP)2-,is intermediate. In each case, the enhanced 36Clrelaxation found, relative to the Zn2+(aq)value, is removed by interaction with excess nucleotide. In the presence of excess Zn(I1) ions, purine nucleotides form complexes which have high 36Clmolar relaxivity metal ion environments. These observations are discussed in terms of possible structures which could lead to such relaxation environments.
Metal ions participate in the biochemical reactions of nucleotides and nucleic acids. Much interest has centered around the structures of the nucleotide complexes with the eventual aim of better understanding the mechanisms of these important reactions. There are several review articles in this aream2t3 The binding of Mg(I1) to ATP has been studied by various methods and the evidence indicates that this ion binds only to the phosphate portion of the m ~ l e c u l e . ~ - ~ Considerably more study has been devoted to the binding of Mn(I1) to nucleotides principally because of the ease with which these complexes can be studied by NMR. Experiments with presumably 1:l complexes indicate a strong ring-Mn(I1) interaction, although it has been proposed that this interaction is mediated by an intervening water molecule.g-12 NMR studies of Zn(I1) binding to nucleotides at high concentration levels suggest that Zn(I1) does bind to both phosphate groups and N atoms of 0022-3654/79/2083-3457$01 .OO/O
ATP.4l7 Optical methods also indicate similar interactions at low concentrations.8 ORD and CD studies of Zn(I1)nucleotide monophosphate systems demonstrate Zn(I1) induced based stacking interactions at millimolar conc e n t r a t i o n ~ .Recently ~~ IH NMR measurements have been interpreted in terms of Znz ATP formation where both metal ions react with the adenine ring.14 The study of Zn(I1)-nucleotide complexes by 36ClNMR has been of interest to us because this technique can probe the zinc ion environment in these complicated systems. The objective of our studies was to gather and analyze evidence for or against nucleotide base participation in the zinc chelation. We have previously reported ex eriments on nucleotide diphosphate system^.'^ The C1 NMR method is particularly attractive in that low (millimolar) concentration levels may be used and different metalligand concentration ratios can be easily studied. In this paper we report a aeries of experiments dealing with the
0 1979 Arnerlcan Chemlcal Soclety
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