scholarly journals Revisiting paramagnetic relaxation enhancements in slowly rotating systems: how long is the long range?

2020 ◽  
Author(s):  
Giovanni Bellomo ◽  
Enrico Ravera ◽  
Vito Calderone ◽  
Mauro Botta ◽  
Marco Fragai ◽  
...  
Keyword(s):  
Chemical Exchange ◽  
Protein Structure Determination ◽  
Bulk Water ◽  
Water Proton ◽  
Proton Relaxation ◽  
Relaxation Rates ◽  
Rotating Systems ◽  
Complete Relaxation ◽  
Nuclear Magnetization ◽  
Order Of Magnitude

Abstract. Cross relaxation terms in paramagnetic systems that reorient rigidly with slow tumbling times can increase the effective longitudinal relaxation rates of protons of more than one order of magnitude. This is evaluated by simulating the time evolution of the nuclear magnetization using a complete relaxation matrix approach. The calculations show that the Solomon dependence of the relaxation rates on the metal-proton distance (as r−6) can be incorrect for protons farther than 15 Å from the metal, and thus can originate sizable errors in R1-derived distance restraints used, for instance, for protein structure determination. Furthermore, the chemical exchange of these protons with bulk water protons can enhance the relaxation rate of the solvent protons by far more than expected from the Solomon equation. Therefore, it may contribute significantly to the water proton relaxation rates measured at MRI magnetic fields in the presence of slow-rotating nanoparticles containing paramagnetic ions and a large number of exchangeable surface protons.

scholarly journals Revisiting paramagnetic relaxation enhancements in slowly rotating systems: how long is the long range?

2021 ◽  
Vol 2 (1) ◽  
pp. 25-31
Author(s):  
Giovanni Bellomo ◽  
Enrico Ravera ◽  
Vito Calderone ◽  
Mauro Botta ◽  
Marco Fragai ◽  
...  
Keyword(s):  
Relaxation Rate ◽  
Chemical Exchange ◽  
Protein Structure Determination ◽  
Bulk Water ◽  
Paramagnetic Relaxation ◽  
Water Proton ◽  
Proton Relaxation ◽  
Relaxation Rates ◽  
Rotating Systems ◽  
Order Of Magnitude

Abstract. Cross-relaxation terms in paramagnetic systems that reorient rigidly with slow tumbling times can increase the effective longitudinal relaxation rates of protons of more than 1 order of magnitude. This is evaluated by simulating the time evolution of the nuclear magnetization using a complete relaxation rate-matrix approach. The calculations show that the Solomon dependence of the paramagnetic relaxation rates on the metal–proton distance (as r−6) can be incorrect for protons farther than 15 Å from the metal and thus can cause sizable errors in R1-derived distance restraints used, for instance, for protein structure determination. Furthermore, the chemical exchange of these protons with bulk water protons can enhance the relaxation rate of the solvent protons by far more than expected from the paramagnetic Solomon equation. Therefore, it may contribute significantly to the water proton relaxation rates measured at magnetic resonance imaging (MRI) magnetic fields in the presence of slow-rotating nanoparticles containing paramagnetic ions and a large number of exchangeable surface protons.

scholarly journals Analysis of Conformational Exchange Processes using Methyl-TROSY-Based Hahn Echo Measurements of Quadruple-Quantum Relaxation

2021 ◽  
Author(s):  
Christopher Andrew Waudby ◽  
John Christodoulou
Keyword(s):  
Chemical Shift ◽  
Chemical Exchange ◽  
Relaxation Dispersion ◽  
Conformational Exchange ◽  
Parameter Estimates ◽  
Relaxation Rates ◽  
Exchange Processes ◽  
Methyl Trosy ◽  
Quantum Transitions ◽  
Order Of Magnitude

Abstract. Transverse nuclear spin relaxation is a sensitive probe of chemical exchange on timescales on the order of microseconds to milliseconds. Here we present an experiment for the simultaneous measurement of the relaxation rates of two quadruple-quantum transitions in 13CH3-labelled methyl groups. These coherences are protected against relaxation by intra-methyl dipolar interactions, and so have unexpectedly long lifetimes within perdeuterated biomacromolecules. However, these coherences also have an order of magnitude higher sensitivity to chemical exchange broadening than lower order coherences, and therefore provide ideal probes of dynamic processes. We show that analysis of the static magnetic field dependence of zero-, double- and quadruple-quantum Hahn echo relaxation rates provides a robust indication of chemical exchange, and can determine the signed relative magnitudes of proton and carbon chemical shift differences between ground and excited states. We also demonstrate that this analysis can be combined with established CPMG relaxation dispersion measurements, providing improved precision in parameter estimates, particularly in the determination of 1H chemical shift differences.

Etude des complexes aqueux d'uranium(IV) en milieu acide par résonance magnétique nucléaire

1976 ◽  
Vol 54 (2) ◽  
pp. 303-312 ◽  
Author(s):  
C. Kiener ◽  
G. Folcher ◽  
P. Rigny ◽  
J. Virlet
Keyword(s):  
Exchange Rate ◽  
Chemical Shift ◽  
Exchange Process ◽  
Bound Water ◽  
Outer Sphere ◽  
Bulk Water ◽  
Proton Relaxation ◽  
Water Molecules ◽  
Relaxation Rates ◽  
The Exchange Rate

The hydration of tetravalent uranium in acid solutions has been studied by proton magnetic resonance. Longitudinal and transversal relaxation rates of water are reported as a function of temperature, acidity, and added ions. The relaxation rates observed in perchloric solutions at high temperature are governed by the exchange process of water molecules between the inner coordination sphere of uranium(IV) and the bulk water. The bound proton's lifetime τM lies between 10 ms and 1 s. At pH > 0, the exchange rate depends upon acidity according to the law 1/τM ≈ A + B/[H+]. At high concentrations of diamagnetic ions the exchange rate depends linearly upon water activity. At low temperature, the proton relaxation rates are dominated by an outer sphere effect and the electronic relaxation time of uranium(IV) is found to be about 10−13 s. No signal is observed from protons of the water molecules in the first sphere, firmly bound to uranium(IV), which undergo rapid relaxation. The chemical shift of the proton absorption signal in hydrochloric solutions arise from tightly bound water molecules in paramagnetic interaction with uranium(IV) in a second sphere, and in fast exchange with the bulk water. Above a chlorine concentration of 6 M, the monochloro complex of uranium(IV) contributes to the chemical shift.

scholarly journals The binding of lanthanides to non-immune rabbit immunoglobulin G and its fragments

1975 ◽  
Vol 149 (1) ◽  
pp. 73-82 ◽  
Author(s):  
S K Dower ◽  
R A Dwek ◽  
A C McLaughlin ◽  
L E Mole ◽  
E M Press ◽  
...  
Keyword(s):  
Heavy Chain ◽  
Immunoglobulin G ◽  
Metal Binding ◽  
Binding Sites ◽  
Water Proton ◽  
Proton Relaxation ◽  
Relaxation Rates ◽  
Protein Fluorescence ◽  
Chain Dimer ◽  
Rabbit Igg

The binding of Gd(III) to rabbit IgG (immunoglobulin G) and the Fab (N-terminal half of heavy and light chain), (Fab')2 (N-terminal half of heavy and light chains joined by inter-chain disulphide bond), Fc (C-terminal half of heavy-chain dimer)and pFc' (C-terminal quarter of heavy-chain dimer) fragments was demonstrated by measurements of the enhancement of the solvent-water proton relaxation rates in the appropriate Gd(III) solutions. At pH 5.5 there are six specific Gd(III)-binding sites on the IgG. These six sites can be divided into two classes; two very ‘tight’ sites on the Fc fragment (Kd approx. 5 μM) and two weaker sites on each Fab region (Kd approx. 140 μM). Ca(II) does not apparently compete for these metal-binding sites. The metal-binding parameters for IgG can be explained as the sum of the metal binding to the isolated Fab and Fc fragments, suggesting that there is no apparent interaction between the Fab and Fc regions in the IgG molecule. The binding of Gd(III) to Fab and Fc fragments was also monitored by measuring changes in the electron-spin-resonance spectrum of Gd(III) in the presence of each fragment and also by monitoring the effects of Gd(III) on the protein fluorescence at 340 nm (excitation 295 nm). The fluorescence of Tb(III) solutions of 545 nm (excitation 295 nm) is enhanced slightly on addition of Fab or Fc.

scholarly journals Analysis of conformational exchange processes using methyl-TROSY-based Hahn echo measurements of quadruple-quantum relaxation

2021 ◽  
Vol 2 (2) ◽  
pp. 777-793
Author(s):  
Christopher A. Waudby ◽  
John Christodoulou
Keyword(s):  
Chemical Shift ◽  
Chemical Exchange ◽  
Relaxation Dispersion ◽  
Conformational Exchange ◽  
Parameter Estimates ◽  
Relaxation Rates ◽  
Exchange Processes ◽  
Methyl Trosy ◽  
Quantum Transitions ◽  
Order Of Magnitude

Abstract. Transverse nuclear spin relaxation is a sensitive probe of chemical exchange on timescales on the order of microseconds to milliseconds. Here we present an experiment for the simultaneous measurement of the relaxation rates of two quadruple-quantum transitions in 13CH3-labelled methyl groups. These coherences are protected against relaxation by intra-methyl dipolar interactions and so have unexpectedly long lifetimes within perdeuterated biomacromolecules. However, these coherences also have an order of magnitude higher sensitivity to chemical exchange broadening than lower order coherences and therefore provide ideal probes of dynamic processes. We show that analysis of the static magnetic field dependence of zero-, double- and quadruple-quantum Hahn echo relaxation rates provides a robust indication of chemical exchange and can determine the signed relative magnitudes of proton and carbon chemical shift differences between ground and excited states. We also demonstrate that this analysis can be combined with established Carr–Purcell–Meiboom–Gill (CPMG) relaxation dispersion measurements, providing improved precision in parameter estimates, particularly in the determination of 1H chemical shift differences.

scholarly journals Water Diffusion Modulates the CEST Effect on Tb(III)-Mesoporous Silica Probes

2020 ◽  
Vol 6 (3) ◽  
pp. 38
Author(s):  
Fabio Carniato ◽  
Giuseppe Ferrauto ◽  
Mónica Muñoz-Úbeda ◽  
Lorenzo Tei
Keyword(s):  
Mesoporous Silica ◽  
Chemical Exchange ◽  
Mesoporous Silica Nanoparticles ◽  
Bulk Water ◽  
Water Diffusion ◽  
Chemical Exchange Saturation Transfer ◽  
Order Of Magnitude ◽  
Tem Microscopy ◽  
Magnetic Resonance Imaging Mri ◽  
Mcm 41

The anchoring of lanthanide(III) chelates on the surface of mesoporous silica nanoparticles (MSNs) allowed their investigation as magnetic resonance imaging (MRI) and chemical exchange saturation transfer (CEST) contrast agents. Since their efficiency is strongly related to the interaction occurring between Ln-chelates and “bulk” water, an estimation of the water diffusion inside MSNs channels is very relevant. Herein, a method based on the exploitation of the CEST properties of TbDO3A-MSNs was applied to evaluate the effect of water diffusion inside MSN channels. Two MSNs, namely MCM-41 and SBA-15, with different pores size distributions were functionalized with TbDO3A-like chelates and polyethylene glycol (PEG) molecules and characterized by HR-TEM microscopy, IR spectroscopy, N2 physisorption, and thermogravimetric analysis (TGA). The different distribution of Tb-complexes in the two systems, mainly on the external surface in case of MCM-41 or inside the internal pores for SBA-15, resulted in variable CEST efficiency. Since water molecules diffuse slowly inside silica channels, the CEST effect of the LnDO3A-SBA-15 system was found to be one order of magnitude lower than in the case of TbDO3A-MCM-41. The latter system reaches an excellent sensitivity of ca. 55 ± 5 μM, which is useful for future theranostic or imaging applications.

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