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Spin Dynamics in NMR
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Dipolar coupling is generally the main source of relaxation for spins such as 1H,31P or 19F, but quadrupolar relaxation is dominant for spins such as .
Instrumentation
Published in Clive R. Bagshaw, Biomolecular Kinetics, 2017
Slower motions within proteins such as domain rotations that occur on a time scale longer than their rotational correlation times, can be studied by NMR using residual dipolar coupling [554,555]. Here, low concentrations of inert polymers are added to the protein or nucleic acid of interest to deliberately prevent a completely isotropic distribution of orientations so that orientation-dependent signals are not fully averaged to zero [556].
Electron Paramagnetic Resonance of Copper Proteins
Published in René Lontie, Copper Proteins and Copper Enzymes, 1984
However, a contrary view can also be put forward. While dipolar coupling may well influence the relaxation times, it will also give a coupling of the spins of the individual ions. This is a case of coupling at a distance between two dissimilar ions, only one of which has a nuclear spin. A somewhat analogous case has been documented for some vitamin B-12-dependent enzyme reactions,105 where both dipolar and exchange coupling was observed between the cobalt(II) ion in the corrin ring and a radical at the active site some distance away. Even at a distance of 10 Å, the dipolar interaction had a significant effect on the appearance of the spectrum, which was unlike that of either the radical or the cobalt(II) ion. In the case of cytochrome c oxidase, dipolar coupling between a copper(II) ion and a high spin iron(III) ion (S = 5/2) at a distance of around 7 Å would be expected to produce a quite distinctive spectrum, particularly in view of the S = 5/2 nature of the iron(III) ion. If the iron were in the low spin state (S = 1/2), the situation would be even more closely analogous to that described by Boas et al.,105 and once again, a distinctive spectrum might be expected. There must therefore be some uncertainty regarding the explanation of the EPR spectral peculiarities of the intrinsic copper of cytochrome c oxidase in terms of a copper-iron interaction.
In vivo magnetic nanoparticle hyperthermia: a review on preclinical studies, low-field nano-heaters, noninvasive thermometry and computer simulations for treatment planning
Published in International Journal of Hyperthermia, 2020
Harley F. Rodrigues, Gustavo Capistrano, Andris F. Bakuzis
Unfortunately, MRI at least with present technology, cannot be used in combination with MNH, because the static magnetic field inhibits the rotation of the magnetic moment of the nanoparticles, and therefore does not promote heat generation [2,32]. Furthermore, the presence of MIONP in biological tissues modifies the magnetic field properties in its vicinity, leading to a dipolar coupling between the magnetic moments of water protons and the magnetic moments of MIONPs, driving a faster dephasing of the water proton spin ensemble, resulting in a lower transversal relaxation time T2 signal intensity (inversely proportional to the amount of MIONP present) [44]. Since physiological and pathological changes in the tissue environment, due to temperature and viscosity, can also affect MRI T2-mapping, it is clear that distinguishing the contribution of only the temperature is a very difficult task by this technique, for MIONP concentrations above 1 mg(Fe).g−1(tissue) [50,51].
CH2 domain orientation of human immunoglobulin G in solution: Structural comparison of glycosylated and aglycosylated Fc regions using small-angle X-ray scattering
Published in mAbs, 2019
Seiki Yageta, Hiroshi Imamura, Risa Shibuya, Shinya Honda
It has long been assumed that removal of the N-linked glycan might result in the alteration of the orientation of the CH2 domain in the aglycosylated Fc region (aFc).15–17 For example, an aFc crystal structure (Protein Data Bank accession number, PDB: 3S7G) revealed a closed CH2 domain orientation, with the two CH2 domains more proximal to one another than in the crystal structure of the glycosylated Fc region (gFc) (PDB: 4W4N).15,18 In contrast, a recent residual dipolar coupling (RDC) analysis by nuclear magnetic resonance (NMR)19 examined the CH2-CH3 domain orientation in both gFc and aFc in solution, as judged by the relative orientation of each observable N-H bond vector of 15N-labeled gFc and aFc. The experiment revealed that the CH2-CH3 domain orientation in both gFc and aFc is similar to that in a crystal structure of gFc (PDB: 1L6X20). The authors proposed that “the effect of glycosylation on CH2 domain orientation is restricted to small amplitudes or small populations”. Their finding suggested the observed perturbation of the CH2 domain orientation in the crystal structure of aFc was mainly attributed to the crystal packing forces.21
A long-lasting oral preformulation of the angiotensin II AT1 receptor antagonist losartan
Published in Drug Development and Industrial Pharmacy, 2018
Washington X. De Paula, Ângelo M. L. Denadai, Aline N. G. Braga, V. Prasad Shastri, Sérgio V. B. Pinheiro, Frederic Frezard, Robson A. S. Santos, Ruben D. Sinisterra
Possible architectures of the Los/βCD complex were evaluated by the 2D-ROESY experiment (Figure 3), which are able to detect dipolar coupling in solution through space upon 5 Å distance [15,27,28]. Cross-peaks correlations were found between aromatic Los hydrogens (region at δ ≈ 6.5–7.6) with H2, H3, H4, H5, and H6 βCD hydrogens. These data demonstrate the penetration of Los aromatic groups into the βCD cavity.