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Carradus AJ, Bradley JMP, Gowland PA, Mougin OE. Measuring chemical exchange saturation transfer exchange rates in the human brain using a particle swarm optimisation algorithm. NMR IN BIOMEDICINE 2023; 36:e5001. [PMID: 37452522 DOI: 10.1002/nbm.5001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 06/12/2023] [Accepted: 06/13/2023] [Indexed: 07/18/2023]
Abstract
The z-spectrum contains many pools with different exchange rates and T2 values, which can make it difficult to interpret in vivo data and complicates the design of experiments aimed at providing sensitivity to one pool. This work aims to characterise the main pools observable with MRI at 7T in the human brain. To achieve this, we acquired z-spectra at multiple saturation powers in the human brain at 7T. We used simulations to optimise the use of particle swarm optimisation (PSO) to fit these data, validating this approach using further simulations and creatine phantoms. We then used the PSO to fit data from grey and white matter for the pool size, exchange rate, and T2 of five proton pools (magnetisation transfer, amides, amines, nuclear Overhauser enhancement NOE-3.5ppm and NOE-1.7ppm in addition to water). We then devised an approach for using PSO to fit z-spectra while limiting the computational burden, and we investigated the sensitivity of the fit to T2 and k for three overlapping pools. We used this to measure the exchange rate of creatine and to show that it varied with temperature, as expected. In the brain we measured a significantly larger pool size in white matter than in grey matter for the magnetisation transfer pool and the NOE-3.5ppm pool. For all other parameters we found no significant difference between grey and white matter. We showed that PSO can be used to fit z-spectra acquired at a range of B1 to provide information about peak position, amplitude, exchange rate, and T2 in vivo in the human brain. These data could provide more sensitivity to change in some clinical conditions and will also provide key information for further experimental design.
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Affiliation(s)
- Andrew J Carradus
- Sir Peter Mansfield Imaging Centre and NIHR Nottingham Biomedical Research Centre, Nottingham University Hospitals NHS Trust, School of Physics and Astronomy, University of Nottingham, Nottingham, UK
| | - Joe M P Bradley
- Sir Peter Mansfield Imaging Centre and NIHR Nottingham Biomedical Research Centre, Nottingham University Hospitals NHS Trust, School of Physics and Astronomy, University of Nottingham, Nottingham, UK
| | - Penny A Gowland
- Sir Peter Mansfield Imaging Centre and NIHR Nottingham Biomedical Research Centre, Nottingham University Hospitals NHS Trust, School of Physics and Astronomy, University of Nottingham, Nottingham, UK
| | - Olivier E Mougin
- Sir Peter Mansfield Imaging Centre and NIHR Nottingham Biomedical Research Centre, Nottingham University Hospitals NHS Trust, School of Physics and Astronomy, University of Nottingham, Nottingham, UK
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Bobko AA. Chemical exchange induced Hahn echo modulation in pulsed electron paramagnetic resonance experiment. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 315:106742. [PMID: 32447257 PMCID: PMC7282351 DOI: 10.1016/j.jmr.2020.106742] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2019] [Revised: 05/03/2020] [Accepted: 05/04/2020] [Indexed: 06/11/2023]
Abstract
Triarylmethyl (TAM) radicals are probes well suited to study microenvironment parameters using pulse electron paramagnetic resonance (EPR) due to their long relaxation times. Here, we are reporting the study of relaxation properties of monophosphonated TAM radicals in the presence of chemical exchange processes. The dependence of Hahn and inversion recovery echo on the solution pH and the chemical exchange rate are discussed. The modulation of Hahn echo intensity in solutions due to chemical exchange is observed in pulse EPR experiments. An analysis of the Hahn echo intensity decay allows for the quantitative determination of the chemical exchange rate and solution pH value.
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Affiliation(s)
- Andrey A Bobko
- In Vivo Multifunctional Magnetic Resonance Center, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, USA; Department of Biochemistry, West Virginia University School of Medicine, Morgantown, WV 26506, USA.
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Friebel A, Specht T, von Harbou E, Münnemann K, Hasse H. Prediction of flow effects in quantitative NMR measurements. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 312:106683. [PMID: 32014660 DOI: 10.1016/j.jmr.2020.106683] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Revised: 12/31/2019] [Accepted: 01/02/2020] [Indexed: 06/10/2023]
Abstract
A method for the prediction of the magnetization in flow NMR experiments is presented, which can be applied to mixtures. It enables a quantitative evaluation of NMR spectra of flowing liquid samples even in cases in which the magnetization is limited by the flow. A transport model of the nuclei's magnetization, which is based on the Bloch-equations, is introduced into a computational fluid dynamics (CFD) code. This code predicts the velocity field and relative magnetization of different nuclei for any chosen flow cell geometry, fluid and flow rate. The prediction of relative magnetization is used to correct the observed reduction of signal intensity caused by incomplete premagnetization in fast flowing liquids. By means of the model, quantitative NMR measurements at high flow rates are possible. The method is predictive and enables calculating correction factors for any flow cell design and operating condition based on simple static T1 time measurements. This makes time-consuming calibration measurements for assessing the influence of flow effects obsolete, which otherwise would have to be carried out for each studied condition. The new method is especially interesting for flow measurements with compact medium field NMR spectrometers, which have small premagnetization volumes. In the present work, experiments with three different flow cells in a medium field NMR spectrometer were carried out. Acetonitrile, water, and mixtures of these components were used as model fluids. The experimental results for the magnetization were compared to the predictions from the CFD model and good agreement was observed.
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Affiliation(s)
- Anne Friebel
- Laboratory of Engineering Thermodynamics (LTD), University of Kaiserslautern, Germany
| | - Thomas Specht
- Laboratory of Engineering Thermodynamics (LTD), University of Kaiserslautern, Germany
| | - Erik von Harbou
- Laboratory of Engineering Thermodynamics (LTD), University of Kaiserslautern, Germany.
| | - Kerstin Münnemann
- Laboratory of Engineering Thermodynamics (LTD), University of Kaiserslautern, Germany
| | - Hans Hasse
- Laboratory of Engineering Thermodynamics (LTD), University of Kaiserslautern, Germany
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Liu K, Ye L, Wang Y, Du G, Jiang L. A Pseudopeptide Polymer Micelle Used for Asymmetric Catalysis of the Aldol Reaction in Water. Polymers (Basel) 2018; 10:E1004. [PMID: 30960929 PMCID: PMC6403597 DOI: 10.3390/polym10091004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2018] [Revised: 09/04/2018] [Accepted: 09/05/2018] [Indexed: 11/25/2022] Open
Abstract
Micelles assembled from amphiphilic molecules have proved to be ideal scaffolds to construct artificial catalysts mimicking enzymatic catalytic behavior. In this paper, we describe the synthesis of amphiphilic poly(2-oxazoline) derivatives with l-prolinamide units in the side chain and their application in asymmetric aldol reactions. Upon dissolution in water, the pseudopeptide polymers self-assembled into particles with different sizes, relying on the copolymer composition and distribution of hydrophilic/hydrophobic segments in the polymer chain. A preliminary study has demonstrated that the catalytic activity of these polymeric organocatalysts are strongly dependent on the aggregated architecture. The micelle-type assemblies can act as nanoreactors to efficiently promote the direct aldolisation of cyclohexanone with aromatic aldehydes in aqueous media, affording anti-aldol products in excellent yields (88⁻99%) and higher stereoselectivities (90/10 dr, 86% ee) compared to their nonmicellar systems under identical conditions.
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Affiliation(s)
- Keyuan Liu
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Long Ye
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Yao Wang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Ganhong Du
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Liming Jiang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
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Zhang L, Martins AF, Zhao P, Wu Y, Tircsó G, Sherry AD. Lanthanide-Based T 2ex and CEST Complexes Provide Insights into the Design of pH Sensitive MRI Agents. Angew Chem Int Ed Engl 2017; 56:16626-16630. [PMID: 29024242 PMCID: PMC5879776 DOI: 10.1002/anie.201707959] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Indexed: 02/02/2023]
Abstract
The CEST and T1 /T2 relaxation properties of a series of Eu3+ and Dy3+ DOTA-tetraamide complexes with four appended primary amine groups are measured as a function of pH. The CEST signals in the Eu3+ complexes show a strong CEST signal after the pH was reduced from 8 to 5. The opposite trend was observed for the Dy3+ complexes where the r2ex of bulk water protons increased dramatically from ca. 1.5 mm-1 s-1 to 13 mm-1 s-1 between pH 5 and 9 while r1 remained unchanged. A fit of the CEST data (Eu3+ complexes) to Bloch theory and the T2ex data (Dy3+ complexes) to Swift-Connick theory provided the proton-exchange rates as a function of pH. These data showed that the four amine groups contribute significantly to proton-catalyzed exchange of the Ln3+ -bound water protons even though their pKa 's are much higher than the observed CEST or T2ex effects. This demonstrated the utility of using appended acidic/basic groups to catalyze prototropic exchange for imaging tissue pH by MRI.
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Affiliation(s)
- Lei Zhang
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
| | - André F Martins
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
- Advanced Imaging Research Center, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX, 75390, USA
| | - Piyu Zhao
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
| | - Yunkou Wu
- Advanced Imaging Research Center, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX, 75390, USA
| | - Gyula Tircsó
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetemtér 1, 4010, Debrecen, Hungary
| | - A Dean Sherry
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
- Advanced Imaging Research Center, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX, 75390, USA
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Zhang L, Martins AF, Zhao P, Wu Y, Tircsó G, Sherry AD. Lanthanide-Based T2ex
and CEST Complexes Provide Insights into the Design of pH Sensitive MRI Agents. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201707959] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Lei Zhang
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
| | - André F. Martins
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
- Advanced Imaging Research Center; UT Southwestern Medical Center; 5323 Harry Hines Blvd. Dallas TX 75390 USA
| | - Piyu Zhao
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
| | - Yunkou Wu
- Advanced Imaging Research Center; UT Southwestern Medical Center; 5323 Harry Hines Blvd. Dallas TX 75390 USA
| | - Gyula Tircsó
- Department of Inorganic and Analytical Chemistry; University of Debrecen; Egyetemtér 1 4010 Debrecen Hungary
| | - A. Dean Sherry
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
- Advanced Imaging Research Center; UT Southwestern Medical Center; 5323 Harry Hines Blvd. Dallas TX 75390 USA
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