Anal. Chem. 1998, 70, 1R-5R
Solid-State Nuclear Magnetic Resonance Cecil Dybowski
Department of Chemistry and Biochemistry, University of Delaware Newark, Delaware 19716-2522 Review Contents Scope Reviews and Books Instrumentation and Theory Chemical Shift Tensors of Spins 1/2 Quadrupolar Nuclei Surfaces and Catalysis Synthetic Polymers Whole Biological Solids Conclusions
1R 1R 1R 2R 2R 3R 3R 3R 4R
SCOPE The field of nuclear magnetic resonance is now so large that there are many subspecialties, each with its own jargon, its own special way of looking at the nature of the materials being studied, and its own technology. Frequently the thing that is common between two NMR spectroscopists is the fact that they both examine materials with radio frequency irradiation of a sample bathed in a magnetic field. Thus, I restrict discussion here to the subfield of nuclear magnetic resonance of solid materials, orsmore preciselysto that group of techniques known as solidstate nuclear magnetic resonance. Even covering that field is dauntingly difficult, and so I have taken the liberty of choosing examples that represent interesting uses of the technique rather than enumerating every use that has been made in the two years between October 1995 and October 1997. REVIEWS AND BOOKS More and more books and reviews of the application of NMR spectroscopy to solids have appeared. Many long-standing review series in NMR spectroscopy such as the Specialist Periodical Reports, Progress in NMR Spectroscopy, NMR: Basic Principles and Progress, Magnetic Resonance Reviews, and Advances in Magnetic Resonance contain reviews pertinent to NMR of solids; they should be routinely checked for information. The large and rather allencompassing Encyclopedia of Nuclear Magnetic Resonance has now appeared (1). In it there are many useful articles on applications of NMR spectroscopy to solids and solidlike materials. A particularly interesting section is the first volume, which contains a detailed history of the technique by Becker, Fisk, and Khetrapal (2) and personal remembrances of some of the participants in the development of NMR spectroscopy as a discipline. A short review of uses of NMR by Legrand has appeared, for persons wanting an introduction in French (3). Other reviews of possible interest are of analysis of zeolite catalysts with solid-state NMR techniques (4, 5), solid-state 31P NMR spectroscopy in environmental science included in a review that also covers solution-state NMR (6), NMR studies of packing in surfactantlipid systems (7), and application of solid-state NMR in oil-shale research (8). S0003-2700(98)00001-8 CCC: $15.00 Published on Web 03/21/1998
© 1998 American Chemical Society
A source of information that has come into more use lately is the Internet. Many sites specialize in collecting information and technology of interest to NMR spectroscopists, including information on theory, instrumental techniques, free software, example data, and persons and sites where one may find information. As these develop and more appear, this is sure to become a major resource for NMR spectroscopists. Several good starting points can be found, for example, the NMR server at the University of Florida [http://micro.ifas.ufl.edu/] and the server at the University of York [http://www.york.ac.uk/depts/chem/nmr/NMR Links.html], from which one can access a wide variety of information about NMR on the Internet. INSTRUMENTATION AND THEORY Improvements in spinning speed control is one factor in improving resolution in magic angle spinning NMR, and this has been discussed and demonstrated (9). Another major area where resolution can be enhanced is efficiency of dipolar decoupling. The efficiency of heteronuclear dipolar decoupling sequences has been examined by the ETH group. Several sequences where both frequency and phase modulation are used were studied (10). The concern for better sensitivity continues to be addressed with discussions of large-volume sample coils that have good B1 homogeneity across the sample (11). The effects of spinning speed on the temperature of the sample have been addressed in two recent publications, where the “internal” temperature is monitored by an internal NMR thermometer (12, 13). The use of the carbon and/or proton resonance shifts of vanadocene as an internal thermometer for solid-state NMR has been proposed (14). Off-magic-angle spinning of doubly 15N-labeled 5-methyl-2diazobenzenesulfonic acid hydrochloride was used to test average Hamiltonian theory, with comparison to previously single-label studies (15). The results were in close agreement. The Utah group reports a high-resolution 3D separated local field experiment with the slow-spinning experiment (16). In the experiment, isotropic chemical shift, anisotropic chemical shift, and C-H dipolar coupling are correlated. Thus, a substantial body of information about a system is available in a single experiment. A recent report gives an example of how to use a pair of onedimensional MAS experiments to disentangle overlapping sideband patterns, in this case applied to a sample containing phosphatidylcholine and dioleoylphosphatidylethanolamine (17). The side bands in magic-angle spinning spectra of materials subject to anisotropic J coupling have been analyzed, particularly for phophorus nuclei (18). Simulation of the expected spectra was used to extract information from these spectra. The use of J coupling for cross polarization in a solid has been demonstrated, and transient oscillations are observed, as expected (19). Analytical Chemistry, Vol. 70, No. 12, June 15, 1998 1R
Recoupling and/or correlating shift and dipolar interactions is an important theme in solid-state NMR spectroscopy. A windowless dipolar recoupling experiment has been demonstrated, with the acronym DRAWS, that allows accurate internuclear distance determinations (20). Of course, the use of the DRAMA sequence to make similar measurements continues, for example, with the measurement of dipolar couplings among 31P’s on side chains of a helical peptide (21). The analysis of adenosine monophosphate using a 3D experiment yields a succession of MELODRAMA transfers allowing one to disperse overlapping spectra (22). Use of time-resolved REDOR spectra to detect the resonances of enzyme intermediates or transients would seem to indicate that spectral editing by use of spectra gathered “on the fly” adds extra utility to this technique (23). Calculation of powder averages was investigated and a proposed numerical scheme (called REPULSION) is shown to converge faster and with fewer systematic errors induced by nonuniform distributions of crystallites than previous calculational devices (24). The study of the proton resonance by the CRAMPS experiment is always very complicated. A recent report studies the effects when fast magic-angle spinning is applied. The authors report that the high-speed MAS is found to play an important role in averaging dipolar couplings (25). Some new twists on a very old subject, spin diffusion, were investigated in the studies of driven spin diffusion between a spin1/ nucleus and a spin-1 nucleus (26). The report focused on 2 deuterated biphenyl where a molecular flip drives the spin diffusion. As for old subjects with new twists, a recent report examines a technique for improved CRAMPS spectroscopy of homonuclearcoupled systems (27). CHEMICAL SHIFT TENSORS OF SPINS 1/2 The principal tensor quantity for spins 1/2 is the chemical shift, although there is growing interest in the anisotropic J coupling. Reports of carbon NMR chemcal shift measurements continue to be seen. The study of other nuclei has also yielded interesting results. The chemical shift tensors of a wide range of lead salts have been reported (28). A study of the SnS, SnS2, and Sn2S3 structures with 119Sn NMR characterized the distortion from octahedral symmetry on the basis of the size of the chemical shift anisotropy (29). A strong deshielding of terminal phosphido complexes containing a P-metal triple bond has been reported (30). A comparison of phosphorus chemical shift measurements for zinc phosphonates demonstrated the connectivity of shift parameters such as asymmetry and anisotropy with structure (31). Quantitative 2D spin diffusion studies were used to assign 31P resonances in solid Cd3(PO4)2, followed by assignment of the Cd resonances with a phosphorus-filtered cross-polarization (32). These experiments demonstrate how complex questions of spectral interpretation may be resolved with a series of NMR studies tailored to the particular system. A recent report gives 171Yb chemical shift-tensor data on a series of Yb(II) bis(cyclopentadineyl) complexes (33) and information on the chemical shifts of the same nucleus in AYbI3, where A is K, Rb, or Cs, has been reported (34). 2R
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
QUADRUPOLAR NUCLEI For quadrupolar nuclei, the focus of investigations has been the quadrupole coupling constants, from which information about electronic structure and dynamics (by line shape analysis) can be gained. 17O NMR chemical shifts of certain titanates, zirconates, stannates, niobates, and aluminates have been reported (35). In these materials, it appeared that the 17O NMR was more diagnostic of chemical state than 27Al NMR. A measurement of the 33Cs chemical shift and electric field gradient tensors in CsCd(SCN)3 has been reported (36). By studying the field dependence of the 51V MAS spectra of V2O5 and γ-LiV2O5, the relative orientation of the chemical shift and electric field gradient tensors were determined (37). In a vanadium NMR study of doped anatase, both octahedral and tetrahedral coordinations of the vanadium centers were observed (38). The 47Ti and 49Ti NMR spectra of the three common phases of TiO2 have been studied. Line widths are dominated by the electric quadrupole interaction, with the authors pointing out that the line widths require one to assume a significant covalent interaction between the titanium and the oxygen. The 95Mo NMR parameters of sodium molybdate dihydrate, hexacarbonylmolybdenum, and pentacarbonylphosphinemolybdenum(0) have been reported (39). The use of deuterium NMR has allowed the study of dynamics of guest molecules included in complexes with tris(5-acetyl-3-thienyl)methane (40) and xenon enclathrated in p-tert-butylcalix[4]arene cavities (41). MAS 19F NMR was used to follow the ring inversion in a fluorocyclohexane-thiourea inclusion compound (42). Some experiments focus on ways to improve the technology of acquiring the spectra of quadrupolar nuclei. Theoretical (43) and experimental (44, 45) multiple-quantum studies continue to show the importance of developments in multiple-quantum magicangle-spinning techniques. This latter experiment combines the multiple-quantum technique with cross-polarization in studies of a fluorinated aluminophosphate. A technique for determining chemical shift tensors and the relative orientation of the chemical shift and quadrupolar principal axes has been discussed and demonstrated for rubidium and sodium (46). A discussion of high-power proton decoupling from 23Na in makatite demonstrates improvement in the spectral resolution in the isotropic dimension of a two-dimensional experiment (47). A method for providing Z-filtering of multiquantum spectra of quadrupolar nuclei such as 27Al has been reported (48). Rotor synchronization and threepulse Z-filtering was shown to improve the results of 2D multiplequantum MAS spectra of half-integer quadrupolar nuclei, such as rubidium in RbNO3 and sodium in Na5P3O10 and Na2C2O4 (49). A method to separate spinning side bands in the second-orderbroadened spectra of half-integer quadrupolar nuclei was demonstrated on 71Ga in β-Ga2O3 (50). A variety of transition-selective techniques applicable to the 14N resonance have been demonstrated (51). The dynamics of cross-polarization between silicon and the central transition of the sodium resonance of albite was investigated, and the authors indicate how to optimize cross-polarization under these circumstances (52). A recent report demonstrates a high-resolution heteronuclear correlation spectrum between the phosphorus and the sodium in Na3P3O9 (53).
SURFACES AND CATALYSIS The application of NMR spectroscopy to materials at surfaces, and especially at catalytic surfaces, is an area that has grown substantially, with many examples of how NMR can yield information on structure and dynamics of the surface phase. For example, the principal components of the carbon chemical shift tensor of H-bonded acetone in H-ZSM-5 and physisorbed acetone in silicalite have been reported (54). Other studies include an observation of species during alkylation of toulene by methanol over H-ZSM-5 (55), in the methanol-to-hydrocarbon production over H-SAPO-34 (56), in the reaction of methanol with a heteropolyanion structure (57), in the production of carboxylic acids over H-ZSM-5 (58), in the conversion of methanol over offretites (59), in the reactions of ethylbenzene (60), in the conversion of 2-propanol over H and rare-earth Y zeolites (61), in the alkylation of aromatics over zeolite beta (62), and in the carbonylation of benzene with carbon monoxide over sulfated zirconia (63). The preparation and NMR observation of benzenium, toluenium, and ethylbenzenium ion on a surface has been reported (64). Certain chlorinated organics adsorbed in Y zeolites were investigated by MAS NMR (65). The NMR investigation of cesium ions in various minerals shows that it is a powerful tool for identifying sites for these ions (66). A recent report uses 133Cs and 23Na to learn about the cesium and sodium sites in zeolite X (67). Of course, NMR can also be used to probe the incorporation or removal of NMR-active nuclei into the framework, as was done in the 71Ga NMR of an MFI-type gallium silicate (68) or in the studies of dealumination of kaolinite by CRAMPS and MAS NMR techniques (69). The isotherms of adsorption of selected organic materials on coal fly ash were aided by 13C NMR spectra of the materials (70). Adosrption studies of acrylic acid and maleic acid onto alumina were aided by 13C NMR, where the nature of the species on the surface were determined (71). Mobility of molecules in confined spaces has been an issue addressed in a number of papers with NMR spectroscopy. For example, the mobility of benzene and p-xylene in various zeolitic structures has been studied with carbon NMR (72). The deuteron resonance of deuterated water in activated carbon was investigated, and the difference of spectroscopy of materials in large and small pores was demonstrated (73). Cyclohexanemobility in the zeolite H-ZSM-5 has been investigated with temperaturedependent deuterium line shape studies (74). From the analysis, the authors obtain a value of 48 kJ/mol for the activation energy for the cyclohexane ring inversion. The study of molecules adsorbed on electrodes is a relatively new area of research. An interesting use of NMR in this area is given by a stud of carbon monoxide adsorbed on a platinum electrode (75). The surface structure of chromatography coatings is also an area that is of importance, and 13C NMR has been reported for silicone-coated silicas (76). An interesting report is the direct measurement of spectra of samples on resins used in the current combinatorial techniques of synthesis, using a J-resolved 2D NMR experiment (77). SYNTHETIC POLYMERS Polymer materials also have been widely investigated with solid-state techniques. In one interesting report, the use of rotational-echo double-resonance NMR (on site-specifically labeled
macromolecules) allowed specification of average 13C-19F distances in a fifth-generation dendrimeric system (78). The use of a two-dimensional MAS NMR technique to measure orientation in a uniaxially deformed polyethylene sample has been discussed (79). In this paper, the authors indicate that a strength of the NMR method is the sensitivity to phase and chemical structure. In a recent report, Spiess indicates how various multidimensional techniques may be used to probe length scales in heterogeneous polymers (80). An interesting use of solid-state NMR has been the examination of virgin and explanted silicone breast prostheses (81). In these studies, the authors were able to detect methyltrifluoropropylsiloxane units and diphenylsiloxane units, as well as silica, in the virgin materials. In explanted prostheses, a trace of lipid is detected with NMR spectroscopy. The solid-state NMR study of thermal degradation of poly(ethylene glycol) and poly(vinyl alcohol) in an alumina ceramic showed that both kinds of chains degrade independently of each other (82). Another interesting use of solids NMR was in the examination of flame retardation in ethylene-vinyl acetate copolymers, before and after burning (83). WHOLE BIOLOGICAL SOLIDS While the bulk of solid-state NMR of biological materials has been applied to laboratory preparations, there have been a number of interesting applications of the technique to reasonably whole biological materials. For example, carbon NMR studies of cell walls of wheat bran indicate structural features, such as the relative amounts of cellulose and lignin (84). Studies of the transformation of wheat straw by solid-state fermentation were aided by investigation with 13C MAS NMR spectroscopy (85). Studies of humic and fulvic soils continue to appear, in which various components are identified (86) or the decomposition of such materials as eucalyptus litter (87) or maple prunings (88) is monitored. 13C examination of sodium alginate from Sargassum brown algae from the Sargasso Sea indicated that its composition is distinctive from that of most other brown algae (89). A recent study demonstrates the use of 15N NMR to study composts grown with enriched KNO3 (90). 15N NMR indicated that an algal sapropel from Mangrove Lake in Bermuda had primarily amide linkages (91). The effect of burning of vegetation on nearby soils has been examined with NMR (92). The NMR spectroscopy of woods and wood products has become a major theme in studies of whole materials. Twodimensional NMR of wood was used to separate the main components’ contribution to the spectra (93). Pulp and sludge from paper were examined with NMR to determine various components (94), and a recent report uses NMR to investigate the effects of Streptomyces to decolor paper mill effluent (95). Investigations of T1F of protons in various starch preparations indicated that in native starch the dynamics were rather homogeneous but that glutens from wheats were somewhat inhomogeneous in the dynamics (96). A striking use of solid-state NMR was the determination of structural differences between silk I and silk II (97). A recent article tries to evaluate the feasibility of assigning resonance with multidimensional solid-state NMR of uniformally labeled proteins and peptides (98). For determination of structure, Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
3R
the observation of 15N in labeled peptides in lipid bilayers has been used to demonstrate the helicity of the peptide (99). Many reports deal with studies of laboratory preparations of biological materials. One particularly interesting report shows that large polarization enhancements can be obtained for frozen arginine and the protein T4 lysozyme in frozen glycerol-water solutions that contain nitroxide radicals (100). CONCLUSIONS The last two years have seen new developments in solid-state NMR and the enhancement of techniques reported earlier. However, the period is characterized most vividly by the proliferation of applications to the analysis of many different kinds of materialssfrom pure solids containing nontraditional subjects for NMR investigation such as ytterbium to materials with unusual orgins or complexities (such as studies of the decomposition of eucalyptus litter). It is likely that these trends will continue in the next years, as a wide variety of different materials yield interesting information when examined with the many different solid-state NMR techniques. Cecil Dybowski is professor of chemistry at the University of Delaware. He is a member of the American Chemical Society, the American Physical Society, the Society for Applied Spectroscopy, and the Delaware Academy of Sciences, among others. Aside from over 130 research papers, he is the coauthor of two books: Transient Techniques in the NMR of Solids (Academic Press: New York, 1985) with B. C. Gerstein, and NMR Spectroscopy Techniques (Dekker: New York, 1987) with R. L. Lichter. He is a member of the editorial boards of Solid State Nuclear Magnetic Resonance, Magnetic Resonance Reviews, and Applied Spectroscopy. He is currently Associate Editor of Applied Spectroscopy and Section Editor of the Encyclopedia of Analytical Chemistry. Since its inception, he has been a lecturer in the American Chemical Society Shortcourse on NMR Spectroscopy. LITERATURE CITED (1) Encyclopedia of Nuclear Magnetic Resonance; Grant, D. M., Harris, R. K., Eds.; John Wiley and Sons: Chichester, U.K., 1996. (2) Becker, E. D.; Fisk, C.; Khetrapal, C. L. In Encyclopedia of Nuclear Magnetic Resonance; Grant, D. M., Harris, R. K., Eds.; John Wiley and Sons: Chichester, U.K., 1996; Vol. 1, pp 1-160. (3) Legrand, A. P.; D’Espinose de la Caillerie, J. B. Spectra Anal. 1997, 26, 31-37. (4) Engelhardt, G. Surf. Sci. 1996, 321-330. (5) Doremieux-Morin, C.; Fraissard, J. Sekiyu Gakkaishi 1997, 40, 355-365. (6) Condron, L. M.; Frossard, E.; Newman, R. H.; Tekely, P.; Morel, J.-L. Nucl. Magn. Reson. Spectrosc. Environ. Chem. 1997, 247271. (7) Beyer, K. Prog. Colloid Polym. Sci. 1997, 103, 778-86. (8) Miknis, F. P. Annu. Rep. NMR Spectrosc. 1997, 33, 207-246. (9) Chopin, L.; Rosanske, R.; Gullion, T. J. Magn. Reson., Ser. A 1996, 122, 237-239. (10) Gan, Z.; Ernst, R. R. Solid State Nucl. Magn. Reson. 1997, 8, 153-159. (11) Privalov, A. F.; Dvinskikh, S. V.; Vieth, H.-M. J. Magn. Reson., Ser. A 1996, 123, 157-160. (12) Neue, G.; Dybowski, C. Solid State Nucl. Magn. Reson. 1997, 7, 333-336. (13) Grimmer, A.-R.; Kretschmer, A.; Cajipe, V. B. Magn. Reson. Chem. 1997, 35 86-90. (14) Koehler, F. H.; Xie, X. Magn. Reson. Chem. 1997, 35, 487-492. (15) Challoner, R.; Harris, R. K.; Tossell, J. A. J. Magn. Reson. 1997, 126, 1-8. (16) Hu, J. Z.; Alderman, D. W.; Pugmire, R. J.; Grant, D. M. J. Magn. Reson. 1997, 126, 120-126 (17) Shekar, S. C.; Hamilton, J. A. Magn. Reson. Chem. 1997, 35, 302305. (18) Wu, G.; Sun, B.; Wasylishen, R.; Griffin, R. G. J. Magn. Reson. 1997, 124, 366-371. (19) Verhoeven, A.; Verel, R.; Meier, B. H. Chem. Phys. Lett. 1997, 266, 465-472. (20) Mehta, M. A.; Gregory, D. M.; Kiihne, S.; Mitchell, D. J.; Hatcher, M. E.; Shiels, J. C.; Drobny, G. P. Solid State Nucl. Magn. Reson. 1996, 7, 211-228. (21) Klug, C. A.; Studelska, D. R.; Chen, G.; Gilbertson, S. R.; Schaefer, J. Solid State Nucl. Magn. Reson. 1996, 7, 173-176. (22) Sun, B.-Q.; Rienstra, C. M.; Costa, P. R.; Williamson, J. R.; Griffin, R. G. J. Am. Chem. Soc. 1997, 119, 8540-8546. 4R
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
(23) Mitchell, D..; Jakeman, D. L.; Igumenova, T. I.; Shittleworth, W. A.; Miller, K. D.; Evans, J. N. S. Chem. Commun. 1997, 10191020. (24) Bak, M.; Nielsen, N. C. J. Magn. Reson. 1997, 125, 132-139. (25) Hafner, S.; Spiess, H. W. Solid State Nucl. Magn. Reson. 1997, 8, 17-24. (26) Mueller, A.; Zimmerman, H.; Haeberlen, U. J. Magn. Reson. 1997, 126, 68-78. (27) Hohwy, M.; Bower, P. V.; Jakobsen, H. J.; Nielsen, N. C. Chem. Phys. Lett. 1997, 27, 297-303. (28) Neue, G.; Dybowski, C.; Smith, M. L.; Hepp, M. A.; Perry, D. L. Solid State Nucl. Magn. Reson. 1996, 6, 241-250. (29) Pietrass, T.; Taulelle, F. Magn. Reson. Chem. 1997, 35, 363366. (30) Wu, G.; Rovnyak, D.; Johnson, M. J. A.; Zanetti, N. C.; Musaev, D. G.; Morokuma, K.; Schrock, R. R.; Griffin, R. G. J. Am. Chem. Soc. 1996, 118, 10654-10655. (31) Massiot, D.; Drumel, S.; Janvier, P.; Busjoli-Doeuff, M.; Bujoli, B. Chem. Mater. 1997, 9, 6-7. (32) Dusold, S.; Kuemmerlen, J.; Schaller, T.; Sebald, A.; Dollase, W. A. J. Phys. Chem. B 1997, 101, 6359-6366. (33) Keates, J. M.; Lawless, G. A. Organometallics 1997, 16, 28422846. (34) Zhao, X.; Ma, X.; Wang, S.; Ye, C. J. Alloys Compd. 1997, 250, 409-411. (35) Bastow, T. J.; Dirken, P. J.; Smith, M. E.; Whitfield, H. J. J. Phys. Chem. 1996, 100, 18539-18545. (36) Kroeker, S.; Eichele, K.; Wasylishen, R.; Britten, J. F. J. Phys. Chem. B 1997, 101. 3727-3733. (37) Marichal, C.; Kempf, J.-Y.; Maigret, B.; Hirschinger, J. Solid State Nucl. Magn. Reson. 1997, 8, 33-46. (38) Luca, V.; Thomson, S.; Howe, R. F. J. Chem. Soc., Faraday Trans. 1997, 93, 2195-2202. (39) Eichele, K.; Wasylishen, R. E.; Nelson, J. H. J. Phys. Chem. 1997, 101, 5463-5468. (40) Sidhu, P. S.; Bel, J.; Penner, G. H.; Jeffrey, K. R. Can. J. Chem. 1996, 74, 1784-1794. (41) Brouwer, E. B.; Enright, G. D.; Ripmeester, J. A. Chem. Commun. 1997 939-940. (42) Nordon, A.; Harris, R. K.; Yeo, L.; Harris, K. D. M. Chem. Commun. 1997, 961-962. (43) Dumazy, Y.; Amoureaux, J. P.; Fernandez, C. Mol. Phys. 1997, 90, 959-970. (44) Pruski, M.; Lang, D. P.; Fernandez, C.; Amoureaux, J.-P. Solid State Nucl. Magn. Reson. 1997, 7, 327-331. (45) Fernandez, C.; Delevoye, L.; Amoureaux, J.-P.; Lang, D. P.; Pruski, M. J. Am. Chem. Soc. 1997, 119, 6858-6862. (46) Shore, J. S.; Wang, S. H.; Taylor, R. E.; Bell, A. T.; Pines, A. J. Phys. Chem. 1996, 100, 9412-9420. (47) Hanaya, M.; Harris, R. K. Solid State Nucl. Magn. Reson. 1997, 8, 147-151. (48) Amoureux, J.-P.; Fernandez, C.; Steuernagel, S. J. Magn. Reson., Ser. A 1996, 123, 116-118. (49) Hanaya, M.; Harris, R. K. J. Phys. Chem. A 1997, 101, 69036910. (50) Massiot, D.; Montouillout, V.; Fayon, F.; Florian, P. Bessada, C. Chem. Phys. Lett. 1997, 272, 295-300. (51) Hill, E. A.; Yesnowski, J. P. J. Chem. Phys. 1997, 107, 346-354. (52) De Paul, S. M.; Ernst, M.; Shore, J. S.; Stebbins, J. F.; Pines, A. J. Phys. Chem. B 1997, 101, 3240-3249. (53) Wang, S. H.; De Paul, S. M.; Bull, L. M. J. Magn. Reson. 1997, 125, 364-368. (54) Sepa, J.; Lee, C.; Gorte, R. J.; White, D. Kassab, E.; Evleth, E. M.; Jessri, H.; Allavena, M. J. Phys. Chem. 1996, 100, 1851518523. (55) Ivanova, I. I.; Corma, A. J. Phys. Chem. 1997, 101, 547-551. (56) Salehirad, F.; Anderson, M. J. Catal. 1996, 164, 301-314. (57) Ishimaru, S.; Ikeda, R. Ber. Bunsen-Ges. Phys. Chem. 1997, 101, 1090-1096. (58) Stepanov, A. G.; Luzgin, M. V.; Ronammikov, V. N.; Sidelnikov, V. N.; Zamaraev, K. I. J. Catal. 1996, 164, 411-421. (59) Alba, M. D.; Romero, A. A.; Poccelli, M. L.; Klinowski, J. J. Phys. Chem. B 1997, 101, 5166-5171. (60) Philippou, A.; Anderson, M. J. Catal. 1997, 167, 266-272. (61) Hunger, M.; Horvath, T. J. Catal. 1997, 167, 187-197. (62) Mitra, A.; Subramanian, S.; Das, D.; Satyanarayana, V.; Chilukuri, V.; Chakrabarty, D. K. Appl. Catal. 1997, 153, 233-241. (63) Clingenpeel, T. H.; Wessel, T. E.; Biaglow, A. I. J. Am. Chem. Soc. 1997, 119, 5469-5470. (64) Xu, T.; Barich, D.; Torres, P. D.; Haw, J. F. J. Am. Chem. Soc. 1997, 119, 406-414. (65) Hannus, I.; Konya, Z.; Nagy, J. B.; Kiricsi, I. J. Mol. Struct. 1997, 410-411, 89-93. (66) Kim, Y.; Kirkpatrick, R. J.; Cygan, R. T. Geochim. Cosmochim. Acta 1996, 60, 4059-4074. (67) Yagi, Fuyuki; Kanuka, Nariyasu; Tsuji, Hideto; Nakata, Hideaki; Hattori, Hideshi Microporous Mater. 1997, 9, 229-235. (68) Takeguchi, T.; Kagawa, K.; Kim, J.-B.; Inui, T.; Wei, D. Haller, G. L. Catal. Lett. 1997, 46, 5-9. (69) Fitzgerald, J. J.; Hamaza, A. I.; Bronniman, C. E.; Dec, S. F. J. Am. Chem. Soc. 1997, 119, 7105-7113.
(70) Netzel, D. A.; Miknis, F. P.; Lane, D. C.; Rovani, J. F.; Cox, J. D.; Clark, J. A. Nucl. Magn. Reson. Spectrosc. Environ. Chem. 1997, 91-119. (71) Mao, Y.; Fung, B. M. J. Colloid Interface Sci. 1997, 191, 216221. (72) Satozawa, M.; Kunimori, K.; Hayashi, S. Bull. Chem. Soc. Jpn. 1997, 70, 97-105. (73) Harris, R. K.; Thompson, T. V.; Forshaw, P.; Foley, N.; Thomas, K. M.; Norman, P. R.; Pottage, C. Carbon 1996, 35, 1275-1279. (74) Aliev, Abil E.; Harris, Kenneth D. M. J. Phys. Chem. A 1997, 101, 4541-4547. (75) Yhanke, M. S.; Rush, B. M.; Reimer, J. A.; Cairns, E. J. J. Am. Chem. Soc. 1996, 118, 12250-12251. (76) Ohkubo, A.; Kanda, T.; Ohtsu, Y.; Yamaguchi, M. J. Chromatogr. 1997, 779, 113-122. (77) Shapiro, M. J.; Chin, J.; Marti, R. E.; Jarosinski, M. A. Tetrahedron Lett. 1997, 38, 1333-1336. (78) Wooley, K. L.; Klug, C. A.; Tasaki, K.; Schaefer, J. J. Am. Chem. Soc. 1997, 119, 53-58. (79) Clayden, N. J.; Eaves, J. G.; Croot, L. Polymer 1997, 38, 159163. (80) Spiess, H. W. Macromol. Symp. 1997, 117, 257-265. (81) Picard, F.; Alikacem, N.; Guidoin, R.; Auger, M. Magn. Reson. Med. 1997, 37, 11-17. (82) Voorhees, K. J.; Stevenson, D. N.; Sun. Yahong; Maciel G. E. J. Mater. Sci. 1997, 32, 2115-2120. (83) Pecoul, N.; Bourbigot, S.; Revel, B. Macromol. Symp. 1997, 119, 309-315. (84) Ha, M.-A.; Jardine, W. G.; Jarvis, M. C. J. Agric. Food Chem. 1997, 45, 117-119. (85) Berrocal, M.; Hernandez-Coronado, M. J.; Hernandez, M.; Huerta, I.; Arias, M. E. Biotechnol. Pulp Pap. Ind., Proc. Int. Conf. 1996, 569-572.
(86) Sihombing, R.; Greenwood, P. F.; Wilson, M. A.; Hanna, J. V. Org. Geochem. 1996, 24, 859-873. (87) Skene, T. M.; Skjemstad, J. O.; Oades, J. M.; Clarke, P. J. Aust. J. Soil Res. 1997, 35, 73-87. (88) Vincelas-Akpa, M.; Loquet, M. Soil Biol. Biochem. 1997, 29, 751758. (89) Llanes, R.; Sauriol, F.; Morin, F. G.; Perlin, A. S. Can. J. Chem. 1997, 75, 585-590. (90) Knicker, H.: Freund, R.; Luedemann, H.-D. Nucl. Magn. Reson. Spectrosc. Environ. Chem. 1997, 272-294. (91) Knicker, H.; Hatcher, P. G. Naturwissenschaften 1997, 84, 231234. (92) Golchin, A.; Clarke, P.; Baldock, J. A.; Higashi, T.; Skjemstad, J. O.; Oades, J. M. Geoderma 1997, 76, 155-174. (93) Bardet, M.; Emsley, L.; Vincendon, M. Solid State Nucl. Magn. Reson. 1997, 8, 25-32. (94) Jackson. M. J.; LIne, M. A. J. Agric. Food Chem. 1997, 45, 23542358. (95) Hernandez, M.; Rodriguez, J.; Perez, M. I.; Ball, A. S.; Arias, M. E. Appl. Microbiol. Biotechnol. 1997, 47, 272-278. (96) Li. S.; Dickinson, L. C.; Chinachoti, P. Cereal Chem. 1996, 73, 736-743. (97) Asakura, T.; Demura, M.; Date, T.; Miyashita, N.; Ogawa, K.; Williamson, M. P. Biopolymers 1997, 41, 193-203. (98) Tycko, R. J. Biomol. NMR 1996, 8, 239-251. (99) Bechniger, B.; Gierasch, L. M.; Montal, M.; Zasloff, M.; Opella, S. Solid State Nucl. Magn. Reson. 1996, 7, 185-191. (100) Hall, Dennis A.; Maus, Douglas, C.; Gerfen, Gary J.; Inati, Souhei; Becerra, Lino R.; Dahlquist, Frederick W.; Griffin, Robert G. Science 1997, 276, 930-932.
A1980001N
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
5R
