Chemical‐shift encoding–based water–fat separation with multifrequency fat spectrum modeling in spin‐lock MRI

2019 ◽  
Vol 83 (5) ◽  
pp. 1608-1624
Author(s):  
Weitian Chen ◽  
Dimitrios C. Karampinos
Keyword(s):  
Chemical Shift ◽  
Spin Lock ◽  
Spectrum Modeling

scholarly journals Chemical shift imaging with spectrum modeling

2001 ◽  
Vol 46 (1) ◽  
pp. 126-130 ◽  
Author(s):  
Li An ◽  
Qing-San Xiang
Keyword(s):  
Chemical Shift ◽  
Chemical Shift Imaging ◽  
Spectrum Modeling

scholarly journals The Role of the Chemical Shift Difference in a Two-Site Exchange Model Under an On-Resonance Spin-Lock RF Field

2018 ◽  
Author(s):  
Jae-Seung Lee ◽  
Alexej Jerschow ◽  
Ravinder Regatte
Keyword(s):  
Chemical Shift ◽  
Spin Dynamics ◽  
Protein Nmr ◽  
Spin Lock ◽  
Mri Contrast ◽  
Chemical Shift Difference ◽  
Site Exchange ◽  
Resonance Spin ◽  
Insight Into

The manuscript investigates the role of the chemical shift difference between two exchanging pools under a spin-lock RF field. The results demonstrate that the width of the dispersion of R1rho is determined mainly by the chemical shift difference when the exchange is slow. This work may give a new insight into the spin dynamics under a spin-lock condition and the results may be relevant to the fields using the spin-lock technique, such as protein NMR and MRI contrast.<br>

scholarly journals 1H R1ρ relaxation dispersion experiments in aromatic side chains

2021 ◽  
Author(s):  
Matthias Dreydoppel ◽  
Roman J. Lichtenecker ◽  
Mikael Akke ◽  
Ulrich Weininger
Keyword(s):  
Chemical Shift ◽  
Active Sites ◽  
Isotope Labeling ◽  
Relaxation Dispersion ◽  
Conformational Exchange ◽  
Side Chains ◽  
Transverse Relaxation Rate ◽  
Spin Lock ◽  
Spin Pairs ◽  
Aromatic Side Chains

AbstractAromatic side chains are attractive probes of protein dynamic, since they are often key residues in enzyme active sites and protein binding sites. Dynamic processes on microsecond to millisecond timescales can be studied by relaxation dispersion experiments that attenuate conformational exchange contributions to the transverse relaxation rate by varying the refocusing frequency of applied radio-frequency fields implemented as either CPMG pulse trains or continuous spin-lock periods. Here we present an aromatic 1H R1ρ relaxation dispersion experiment enabling studies of two to three times faster exchange processes than achievable by existing experiments for aromatic side chains. We show that site-specific isotope labeling schemes generating isolated 1H–13C spin pairs with vicinal 2H–12C moieties are necessary to avoid anomalous relaxation dispersion profiles caused by Hartmann–Hahn matching due to the 3JHH couplings and limited chemical shift differences among 1H spins in phenylalanine, tyrosine and the six-ring moiety of tryptophan. This labeling pattern is sufficient in that remote protons do not cause additional complications. We validated the approach by measuring ring-flip kinetics in the small protein GB1. The determined rate constants, kflip, agree well with previous results from 13C R1ρ relaxation dispersion experiments, and yield 1H chemical shift differences between the two sides of the ring in good agreement with values measured under slow-exchange conditions. The aromatic1H R1ρ relaxation dispersion experiment in combination with the site-selective 1H–13C/2H–12C labeling scheme enable measurement of exchange rates up to kex = 2kflip = 80,000 s–1, and serve as a useful complement to previously developed 13C-based methods.

scholarly journals The Role of the Chemical Shift Difference in a Two-Site Exchange Model Under an On-Resonance Spin-Lock RF Field

2018 ◽  
Author(s):  
Jae-Seung Lee ◽  
Alexej Jerschow ◽  
Ravinder Regatte
Keyword(s):  
Chemical Shift ◽  
Spin Dynamics ◽  
Protein Nmr ◽  
Spin Lock ◽  
Mri Contrast ◽  
Chemical Shift Difference ◽  
Site Exchange ◽  
Resonance Spin ◽  
Insight Into

The manuscript investigates the role of the chemical shift difference between two exchanging pools under a spin-lock RF field. The results demonstrate that the width of the dispersion of R1rho is determined mainly by the chemical shift difference when the exchange is slow. This work may give a new insight into the spin dynamics under a spin-lock condition and the results may be relevant to the fields using the spin-lock technique, such as protein NMR and MRI contrast.<br>

Macrocycles of Higher Ortho-Phenylenes: Assembly and Folding

2019 ◽  
Author(s):  
Zacharias Kinney ◽  
Viraj Kirinda ◽  
Scott Hartley
Keyword(s):  
Chemical Shift ◽  
Higher Order ◽  
Order Structure ◽  
Complex Geometries ◽  
Spatial Relationships ◽  
Predominant Species ◽  
Bite Angle ◽  
Direct Assembly

<p>Higher-order structure in abiotic foldamer systems represents an important but largely unrealized goal. As one approach to this challenge, covalent assembly can be used to assemble macrocycles with foldamer subunits in well-defined spatial relationships. Such systems have previously been shown to exhibit self-sorting, new folding motifs, and dynamic stereoisomerism, yet there remain important questions about the interplay between folding and macrocyclization and the effect of structural confinement on folding behavior. Here, we explore the dynamic covalent assembly of extended <i>ortho</i>-phenylenes (hexamer and decamer) with rod-shaped linkers. Characteristic <sup>1</sup>H chemical shift differences between cyclic and acyclic systems can be compared with computational conformer libraries to determine the folding states of the macrocycles. We show that the bite angle provides a measure of the fit of an <i>o</i>-phenylene conformer within a shape-persistent macrocycle, affecting both assembly and ultimate folding behavior. For the <i>o</i>-phenylene hexamer, the bite angle and conformer stability work synergistically to direct assembly toward triangular [3+3] macrocycles of well-folded oligomers. For the decamer, the energetic accessibility of conformers with small bite angles allows [2+2] macrocycles to be formed as the predominant species. In these systems, the <i>o</i>-phenylenes are forced into unusual folding states, preferentially adopting a backbone geometry with distinct helical blocks of opposite handedness. The results show that simple geometric restrictions can be used to direct foldamers toward increasingly complex geometries.</p>

Macrocycles of Higher ortho-Phenylenes: Assembly and Folding

2019 ◽  
Author(s):  
Zacharias Kinney ◽  
Viraj Kirinda ◽  
Scott Hartley
Keyword(s):  
Chemical Shift ◽  
Higher Order ◽  
Order Structure ◽  
Complex Geometries ◽  
Spatial Relationships ◽  
Predominant Species ◽  
Bite Angle ◽  
Direct Assembly

<p>Higher-order structure in abiotic foldamer systems represents an important but largely unrealized goal. As one approach to this challenge, covalent assembly can be used to assemble macrocycles with foldamer subunits in well-defined spatial relationships. Such systems have previously been shown to exhibit self-sorting, new folding motifs, and dynamic stereoisomerism, yet there remain important questions about the interplay between folding and macrocyclization and the effect of structural confinement on folding behavior. Here, we explore the dynamic covalent assembly of extended <i>ortho</i>-phenylenes (hexamer and decamer) with rod-shaped linkers. Characteristic <sup>1</sup>H chemical shift differences between cyclic and acyclic systems can be compared with computational conformer libraries to determine the folding states of the macrocycles. We show that the bite angle provides a measure of the fit of an <i>o</i>-phenylene conformer within a shape-persistent macrocycle, affecting both assembly and ultimate folding behavior. For the <i>o</i>-phenylene hexamer, the bite angle and conformer stability work synergistically to direct assembly toward triangular [3+3] macrocycles of well-folded oligomers. For the decamer, the energetic accessibility of conformers with small bite angles allows [2+2] macrocycles to be formed as the predominant species. In these systems, the <i>o</i>-phenylenes are forced into unusual folding states, preferentially adopting a backbone geometry with distinct helical blocks of opposite handedness. The results show that simple geometric restrictions can be used to direct foldamers toward increasingly complex geometries.</p>

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