Nuclear Magnetic Resonance: Volume 39 (Specialist Periodical Reports, Band 39) - Hardcover

Hardcover

ISBN 10: 1847550606 ISBN 13: 9781847550606

Verlag: Royal Society of Chemistry, 2010

Inhaltsangabe

As a spectroscopic method, nuclear magnetic resonance (NMR) has seen spectacular growth, both as a technique and in its applications. Today's applications of NMR span a wide range of scientific disciplines, from physics to biology to medicine. Each volume of Nuclear Magnetic Resonance comprises a combination of annual and biennial reports which together provide comprehensive coverage of the literature on this topic. This Specialist Periodical Report reflects the growing volume of published work involving NMR techniques and applications, in particular NMR of natural macromolecules, which is covered in two reports: NMR of Proteins and Nucleic Acids and NMR of Carbohydrates, Lipids and Membranes. For those wanting to become rapidly aquainted with specific areas of NMR, Nuclear Magnetic Resonance provides unrivalled scope of coverage. Seasoned practitioners of NMR will find this an invaluable source of current methods and applications.

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Nuclear Magnetic Resonance Volume 39

A Review of the Literature Published Between January 2008 and May 2009

By G. A. Webb, K. Kamienska-Trela

The Royal Society of Chemistry

Copyright © 2010 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84755-060-6

Contents

Preface G. A. Webb and K. Kamiennska-Trela, v, 
Books and reviews W. Schilf, 1, 
Theoretical and physical aspects of nuclear shielding Cynthia J. Jameson and Angel C. De Dios, 42, 
Applications of nuclear shielding Shigeki Kuroki, Shingo Matsukawa and Hidekazu Yasunaga, 70, 
Theoretical aspects of spin–spin couplings Hiroyuki Fukui, 151, 
Applications of spin-spin couplings Krystyna Kamienska-Trela and Jacek Wójcik, 179, 
Solid state NMR spectroscopy A. E. Aliev and R. V. Law, 227, 
NMR of proteins and nucleic acids P. J. Simpson, 268, 
NMR of carbohydrates, lipids and membranes Elizabeth F. Hounsell, 290, 
Synthetic macromolecules Hiromichi Kurosu and Takeshi Yamanobe, 322, 
NMR in living systems M. J. W. Prior, 363, 
Nuclear magnetic resonance imaging Tokuko Watanabe, 398, 
NMR of liquid crystals and micellar solutions Gerardino D'Errico and Luigi Paduano, 424, 
Oriented molecules K. V. Ramanathan, Nitin P. Lobo and C. L. Khetrapal, 456, 

CHAPTER 1

Theoretical and physical aspects of nuclear shielding

Cynthia J. Jameson and Angel C. De Dios

DOI: 10.1039/9781849730846-00042

1. Theoretical aspects of nuclear shielding

1.1 General theory

Several methodologies are being developed for including relativistic effects in the calculation of molecular magnetic properties, in particular the nuclear magnetic shielding tensor. Approaches used can be grouped as follows: four-component or fully relativistic, two-component or quasi-relativistic, and perturbational. Volume 36 of this series gives an overview and newer developments have been discussed in succeeding volumes. In the four-component relativistic treatment of nuclear shielding, the Dirac operator is linear with respect to the vector potential such that the second order energy consists only of a single term, the paramagnetic term, when the first order wave function is directly expanded in the full space of unperturbed states. This standard linear response theory has been used by several groups. Alternative formulations of four-component treatments of nuclear magnetic properties including shielding have been proposed by Kutzelnigg and others by explicitly incorporating the magnetic balance condition between the small and large components of the Dirac spinor in the presence of magnetic fields. But, is it mandatory to resort to a magnetically balanced basis set for calculations of magnetic properties with perturbative fully relativistic methods? Calculations of molecular properties using finite basis sets in relativistic quantum mechanics are contaminated with spurious states. In order to eliminate them, kinetically balanced basis sets were suggested. Kutzelnigg has shown that the exact relativistic wavefunction of the ground state of H-like ions is expandable in a kinetically balanced even-tempered Gaussian basis. Two kinetically balanced bases have previously been investigated, restricted kinetic balanced (RKB) and unrestricted kinetic balanced (UKB). In this reporting period, the application of different kinetic balance prescriptions using the four-component polarization propagator approach in the calculation of nuclear magnetic shielding were investigated. They find that working with relativistic polarization propagators there is no formal requirement to enforce the application of magnetic kinetic balance prescription. On the contrary, the RKB prescription is found to be a necessary condition, but is not enough to obtain reliable results. The kinetic balance prescription ensures that the matrix representation of the kinetic energy operator of the unperturbed system will properly be described in the non-relativistic limit. Both the RKB and the UKB prescriptions were applied to generate small components from large components in the four component basis set. Calculations with both RKB and UKB prescriptions are found to converge to the same value, although UKB was found to be more efficient; i.e., the UKB prescription ensures basis set convergence with quite smaller basis sets than RKB, leading to potentially large time savings. Convergence threshold was defined as the difference within RKB calculations were less than 0.5%. Also UKB is de- fined as converged when the difference between converged RKB and the UKB calculations were less than 0.5%.

The performance of the UKB prescription in such calculations was studied for molecules containing more than one heavy atom in order to examine the electronic effects on the shielding of a heavy atom due to the presence of vicinal heavy atoms. The shieldings of X, Y, and H nuclei in XYH3 molecular systems with X = C, Si, Ge, Sn and Y = Br, I were calculated. Relativistic effects on the shielding of X due to heavy halogen atoms are larger for heavier X nuclei. For example, for substituent Y = I, the difference between Rel and non-rel shielding for X = C in CH3I is 235.57 ppm–198.31 ppm, i.e., (235.57 – 198.31)/198.31 = 18.79%, which the authors refer to as a HALA effect (vicinal heavy atom effect on the shielding of the light atom). For Sn in SnH3I, this difference is 4059.63 ppm – 3111.44 ppm, i.e., (4059.63 – 3111.44)/3111.44 = 30.47%, much larger. The authors refer to the latter as HAVHA + HAHA effects (heavy atom effects on the shielding of the vicinal heavy atom + heavy atom effects on its own shielding). The total shielding for C in CH3I is 235.57 ppm compared to C in CH4 where the total shielding is 195.55 ppm, i.e., (235.57 – 195.55)/ 195.55 = 20.50%. We compare this with the total shielding for Sn in SnH3I is 4059.63 ppm compared to Sn in SnH4 where the total shielding is 4110.16 ppm, i.e., (4059.63 – 4110.16)/4110.16 = 1.23%. For I shielding, the relativistic effects in SnH3I is (6652.74 – 5505.12)/5505.12 = 20.84%. We compare this with the relativistic effects on I shielding in CH3I, (5636.10 – 4429.34)/4429.34 = 27.24%, which is somewhat larger than 20.84%. The hydrogen shieldings exhibited an effect from the two-bond distant heavy atom Br or I; this effect is found to be more pronounced when the central atom is X = Si. The authors found that UKB is much more efficient, and that one can obtain reliable results working with Sadlej basis sets for calculations of paramagnetic components at RPA level. They also found that calculations of the diamagnetic components at PZOA level give a time savings of 50% when compared with RPA calculations of the same. All of these results are at the RPA level. These calculations were all carried out at the RPA level and so did not include electron correlation.

As mentioned above, various alternative formulations of four-component treatments of NMR properties have been proposed by Kutzelnigg and others, which explicitly incorporate the magnetic balance condition between the small and large components of the Dirac spinor in the presence of magnetic fields. These methods have achieved the same goal of capturing the diamagnetic part of the shielding in a natural manner, i.e., without using negative energy states in the computation or interpretation of the diamagnetic part. The essence of these methods is that the contributions of negative energy states are reduced to order c -2 or higher so as to guarantee the correct...

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 2010
• Sprache: Englisch
• ISBN 10: 1847550606
• ISBN 13: 9781847550606
• Einband: Gebundene Ausgabe
• Anzahl der Seiten: 512
• Herausgeber: Webb G A, Kamienska-Trela Krystyna
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: gpsr@libri.de; gpsr@libri.de; ; Europaallee 1; Bad Hersfeld; 36244; Deutschland