Nuclear and Electron Spin Relaxation Techniques for delineation of bioinorganic and biological activities (original) (raw)
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Classification of binary carbon-13 nuclear magnetic resonance spectra
Analytical Chemistry, 1977
This ensures similarity in relaxation rates and, hence, observed NOE. This allows the procedure to be applied not only to isomers but also to many systems where other methods would be impractical. In large systems, such as steroids, proton magnetic resonance can prove too complex to yield quantitative results; yet this is when CMR becomes most useful. For, in general, as the size of the molecule increases, the relaxation times decrease and the CMR experimental time decreases making it a practical analytic tool. In summary, this method overcomes problems present in previous methods of quantitation by CMR which required either very long experimentai times or sacrificing resolution. Our technique affords a method of quantifying mixtures which are not simply isomers in a reasonable length of time without expensive instrumentation or contamination of the sample by relaxation reagents.
Carbon-13 NMR spectroscopy of biological systems
Academic Press eBooks, 1995
This book provides both an introduction for the novice and a review for the expert to the rapidly developing field of 13 C NMR spectroscopy of biological systems. It consists of a forward by Joachim Seelig, a preface by the author, and six chapters dealing with basic principles and key applications. The mix of theory and application defines the unique quality of this book. Chapter 1, by Nicolau Beckmann, provides a Ž . brief summary 5 pages, 26 references of basic principles from a historical perspective. The reader is referred to basic texts for details, and landmark developments are cited. Beginning with continuous wave NMR spectroscopy, it describes the introduction of Fourier transform and double resonance techniques. Highlights of solid state NMR include polarization transfer, decoupling, and magic-angle spinning methods. The chapter ends with a description of heteronuclear polarization transfer, indirect proton NMR detection of 13 C, and spectral editing techniques. Chapter 2, Gemmeker and Kessler, is unique in providing a coherent view of the multidimensional NMR methods applied to proteins and nucleic acids by structural biologists and the analytical NMR methods used by organic chemists. The success in bridging this gap makes this an extraordinarily valuable contribution; perhaps these authors are the only ones with sufficient experience to show that these two branches of NMR spectroscopy are not nearly as disparate as they may seem. The wide range of individual experiments are unified by the focus on the 13 C nucleus, which in most applications is observed through the nearby 1 H nuclei, leading naturally to multidimensional experiments that display the effects of the available chemical shift and spin coupling interactions. The analytical applications emphasize those experiments that are performed Ž . Ž .
Journal of the American Chemical Society, 2001
We describe magic-angle-spinning NMR methods for the accurate determination of internuclear dipole-dipole couplings between homonuclear spins-1 / 2 in the solid state. The new sequences use symmetry principles to treat the effect of magic-angle sample-rotation and resonant radio frequency fields. The pulsesequence symmetries generate selection rules which reduce the interference of undesirable interactions and improve the robustness of the pulse sequences with respect to chemical shift anisotropies. We show that the pulse sequences may be used to estimate distances between 13 C spins in organic solids, including bond lengths in systems with large chemical shift anisotropies, such as conjugated systems. For bond-length measurements, the precision of the method is (2 pm with a systematic overestimate of the internuclear distance by 3 ( 1 pm. The method is expected to be a useful tool for investigating structural changes in macromolecules.
Journal of Biomolecular NMR, 1991
A method to determine heteronuclear long-range couplings to carbon and nitrogen at natural abundance is presented and applied to two cyclic hexapeptides and the peptidomacrolide FK506. The method is applicable for proton-bearing heteronuclei. By introduction of heteronuclear half-filters in two-or three-dimensional experiments the spectra exhibit an E.COSY pattern ;vhen executed without heteronuclear decoupling. The extraction of the heteronuclear coupling constants is.therefore independent of linewidth.
Carbon-13 NMR spectroscopy of heterocyclic compounds—IV
Tetrahedron, 1975
Complete assignments of chemical shifts and extensive assignments of carbon-proton coupling constants are presented for ail the monohyd~xyc~ma~ns except the S-derivative, together with similar data for 6.7-and 7,8dihydroxy-, band f-methoxy-, ?-hydroxy~-me~yl-and 6,7-and 7,8-dihydroxy~methyl-coum~ns. It is shown that shifts in the polysubstituted molecules can be predicted with high precision from substituent effects evaluated for the more simple derivatives. The approach is extended to some simple glucosyl derivaiives, and it is demonstrated that not only the anomeric configuration but also the exact site of the sugar substitution can be determined from "C data.
Angewandte Chemie International Edition, 2012
For many years the practical use and measurement of longrange proton-carbon coupling constants ( n J(CH); n > 1) in natural abundant molecules have been a timely topic in NMR spectroscopy and there are still a number of unresolved issues in this area. There have always been doubts about the correct choice of the best NMR method to be used and many discussions have focused on the accuracy, reliability, and simplicity of the data analysis and determination of the n J(CH) coupling constant. Despite the extensive number of NMR techniques that have been developed, there are still two unsolved experimental problems pertaining basically to nonprotonated carbon atoms, namely, a) an accurate measurement of very small coupling constants (less than 2-3 Hz) and b) the absence of a general and robust approach to determine the sign of the coupling constant. Widely used pulse sequences like a/b-HSQC-TOCSY, [2] HETLOC, or HECADE that consist of a dual-step HSQC-type block followed by a TOCSY transfer ( 1 J(CH) + J(HH), Scheme 1A) provide the magnitude and the sign of n J CH coupling constants irrespective of their values (0-10 Hz) but only for protonated carbons. On the other hand, long-range correlation schemes such as HSQMBC, EXSIDE, or J-HMBC experiments based on a direct n J(CH) transfer (Scheme 1 B), typically fail to measure very small coupling constants (0-3 Hz) as well as they do not provide information about the sign.