Nuclear Magnetic Resonance

Volume 44

Krystyna Kamienska-Trela, Krystyna Kamienska-Trela

• Editore: Royal Society of Chemistry
• Anno: 2015
• ISBN:
  9781782625155
• Edizione: 1
• Argomento: Scienze fisiche
• Categoria: Spettroscopia e analisi dello spettro

Applications of nuclear magnetic resonance span a wide range of scientific disciplines, from physics to medicine. This series has provided an essential digest of the NMR literature for more than four decades and each volume provides unrivalled coverage of the literature on this topic. Continuous coverage on some topics such as theoretical and physical aspects of nuclear shielding is balanced by the desire for coverage on newer topics like applications in biological systems and materials science. For those wanting to become rapidly acquainted with NMR or seasoned practitioners, this is an invaluable source of current methods and applications.

Applications of nuclear shielding

Shigeki Kuroki,*^a Tsunenori Kameda*^b and Hidekazu Yasunaga*^c

DOI: 10.1039/9781782622758-00076

This chapter reports a selection of recent publications on the application of nuclear shielding, related NMR chemical shifts and NMR lineshapes, which have been published from 1 June 2013 to 31 May 2014. The reports include not only experimental NMR results but also calculated ones. The number of the papers in this field is rapidly increasing, covering practically all magnetically active nuclei. Therefore, a selection of related publications was made and generally it is restricted to journal original articles and reviews published in English. The survey of the papers starts from those devoted to the group 1 elements (¹H, ²H, ³H, ^6,7Li, ²³Na, ³⁹K, ^85,87Rb, ¹³³Cs) and continues along the periodic table up to the group 18 elements (²¹Ne, ³⁹Ar, ^129,131Xe).

1 Introduction

The report introduces studies on the application of nuclear shielding, covering the chemical shifts and lineshapes of NMR spectra, which were made in the world from 1 June 2013 to 31 May 2014. The shieldings of particular nuclear species are described in the following section according to their position in the periodic table. Although there is a great number of articles on the research made by NMR spectroscopies and related theoretical calculations during the period, we have space limitation in this chapter. Therefore, the coverage of this chapter is restricted to widely available and common journals, which are written and published in English, as a general rule.

The NMR experiments reported in the chapter for most elements were made in the course of physical, chemical or biological studies during the period. The simple chemical assignments, chemical structure determinations and related studies for synthesised and natural products are excluded from the text as possible. The review and preprint articles are given when they provide valuable information.

2 Group 1 (¹H, ²H, ³H, ^6,7Li, ²³Na, ³⁹K, ^85,87Rb, ¹³³Cs)

2.1 Hydrogen (¹H) (I=1/2)

The shielding effect of fluoroaromatic compounds on nuclei was studied by using nucleus-independent chemical shift (NICS) calculations at the GIAO/B3LYP/6-311++G(2d,p) level.¹ It was found and demonstrated by ¹H NMR measurements on BINAP bearing C₆F₅ groups that the chemical shift of a proton located above the fluoroaromatic ring is shifted upfield owing to a relatively weak shielding effect of the ring. The poly[2,7-(9,9-bis(octyl)-fluorene)-alt-benzothiadiazole] (F8BT), poly[2,7-(9,9-bis(2′-ethylhexyl)-fluorene)-alt-thiophene-S,S-dioxide] (PFTSO2) and poly[2,7-(9,9-bis(2′-ethylhexyl)-fluorene)-alt-1,4-phenylene] (PFP) containing, benzothiadiazole (BT), thiophene-S,S-dioxide and phenylene groups, respectively, were investigated by ¹H and ¹³C NMR spectroscopies.² The obtained NMR spectra and corresponding shielding tensors of the ¹H and ¹³C nuclei were interpreted by density functional theory (DFT) with complete geometry optimisation using B3LYP functional. The DFT analysis provides the relationship between the structure and NMR, optical, electronic properties. This conformation of 3-(1,3-diphenylpropan-2-yl)-4-methyl-6-phenylisoxazolo[3,4-d]pyridazin-7(6H)-one in CDCl₃ solution was evidenced by distinct phenyl-shielding effects on the ¹H NMR signals.³ The isoxazolo[3,4-d]pyridazin ring system is virtually planar, whereas the N-bonded Ph group is inclined to the former by an ring–ring angle of 55.05(3)°. The 1D and 2D Very Fast Magic-Angle Spinning (VF MAS) NMR experiments with sample rotation up to 55 kHz were applied to study both the dihydrate form and the anhydrous form of Tyr-(D)Ala-Phe-Gly.⁴ It was shown by NMR measurements employing both homo-nuclear (¹H–¹H BABA and ¹³C–¹³C SHANGHAI) and hetero-nuclear 2D correlations (¹H–¹³C and ¹H–¹⁵N) that removing water from the crystal lattice of this tetrapeptide in thermal processes does not destroy its subtle pseudo-cyclic structure. The geometry of the peptides and the ¹³C σ_ii principal elements of the NMR shielding tensor parameters and ¹H isotropic NMR shifts were calculated using gauge including projector augmented wave (GIPAW) method. The ¹H NMR spectrum of diquat (6,7-dihydrodipyrido[1,2-b:1′,2′-e] pyrazine-5,8-diium or DQ²⁺) encapsulated by cucurbit[n]uril (n=7, 8) hosts was obtained using the density functional theory, and theoretical calculations showed that both CB[7] or CB[8] host possesses strong affinity toward DQ²⁺.⁵ It was revealed that H_α protons on bi-pyridinium rings of DQ²⁺@CB[8] complex are de-shielded owing to C=O⋯H interactions and aromatic H_β and H_δ protons of DQ²⁺ within the CB[8] cavity exhibit significant shielding. The effects of stress-shielding on both viscoelastic properties and microstructure of collagen fibers in the Achilles tendon were studied by proton double-quantum filtered (¹H-DQF) NMR spectroscopy.⁶ The ¹H-DQF NMR results demonstrated significantly reduced residual dipolar coupling in the Achilles tendons and evaluated the alterations of the collagen fiber orientation that contributed to the function of tendinous tissue. Pyrazolo[4,3-c]pyrazoles and three regioisomers of their N-Me derivatives were studied by ¹H, ¹³C and ¹⁵N NMR spectroscopies and the NMR spectroscopic data for all isomers were interpreted by DFT calculations of nuclear shielding constants and indirect spin–spin coupling constants⁷ The N-Me isomers were used as model compounds to investigate a potential N1–H/N4–H, N2–H/N4–H and N1–H/N5–H tautomerism of 3,6-substituted pyrazolo[4,3-c]pyrazoles by using low-temperature NMR spectroscopy, and the stabilities of individual tautomeric forms were calculated by DFT methods. Oligostyrene–perylenediimide–oligostyrene coil–rod–coil molecule, which does not show self-assembly of the perylene segment in solvents that are selective for oligostyrene, was investigated by ¹H NMR.⁸ The chemical shift of Ph-CH in ¹H NMR spectrum shows a small shift from 7.15 to 7.08 ppm due to the ring current of perylene shielding the chemical environment of Ph-CH in solution. Characteristic NMR spectra of proton transfer in protonated water clusters, H⁺(H₂O)_n complexes (n=2–5), were studied using ab initio calculations at the RIMP2/TZVP level and BOMD simulations.⁹ The results of RIMP2/TZVP calculations showed that the proton moving on the oscillatory shuttling path is characterised by the ¹H NMR shielding constant (σ^corr_H+) varying in a narrow range, whereas σ^corr_H+ changes exponentially with R_O–H due to the proton moving on the structural diffusion path. ¹H NMR spectra of N-substituted epoxy-fused cyclopentane-3,5-diol derivatives wer...