Concepts in Magnetic Resonance Part A最新文献

{"title":"Conservation of energy, density of states, and spin lattice relaxation","authors":"Navin Khaneja","doi":"10.1002/cmr.a.21457","DOIUrl":"https://doi.org/10.1002/cmr.a.21457","url":null,"abstract":"<p>The starting point of all NMR experiments is a spin polarization which develops when we place the sample in static magnetic field <i>B</i>₀. There are excess of spins aligned along <i>B</i>₀ (spin up with lower energy) than spins aligned opposite (spin down with higher energy) to the field <i>B</i>₀. A natural question is what is the source of this excess spin polarization because relaxation mechanisms can flip a up spin to a down spin and vice-versa. The answer lies in the density of states. When a molecule with spin down flips to spin up it loses energy. This energy goes into increasing the kinetic energy of the molecule in the gas/solution phase. At this increased kinetic energy, there are more rotational-translational states accessible to the molecule than at lower energy. This increases the probability the molecule will spend in spin up state (higher kinetic energy state). This is the source of excess polarization. In this article, we use an argument based on equipartition of energy to explicitly count the excess states that become accessible to the molecule when its spin is flipped from down to up. Using this counting, we derive the familiar Boltzmann distribution of the ratio of up vs down spins. Although prima facie, there is nothing new in this article, we find the mode counting argument for excess states interesting. Furthermore, the article stresses the fact that spin polarization arises from higher density of states at increased kinetic energy of molecules.</p>","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"46A 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21457","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91838675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"NMR Concepts","authors":"","doi":"10.1002/cmr.a.21436","DOIUrl":"https://doi.org/10.1002/cmr.a.21436","url":null,"abstract":"","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"46A 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21436","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"109174259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"DVD Review","authors":"","doi":"10.1002/cmr.a.21368","DOIUrl":"https://doi.org/10.1002/cmr.a.21368","url":null,"abstract":"","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"46A 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21368","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"109174258","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Steady-state free precession signals of arbitrary dephasing order and their sensitivity to T2∗","authors":"Jochen Leupold","doi":"10.1002/cmr.a.21435","DOIUrl":"10.1002/cmr.a.21435","url":null,"abstract":"<p>A simple approach how to calculate analytical expressions for unbalanced steady-state free precession (ubSSFP) signals of arbitrary dephasing order is presented. Dephasing order is the number of effective gradient dephasing cycles that magnetization immediately after an RF-pulse has experienced during the ubSSFP sequence. Based on the obtained equations, which are in accordance with existing literature, the sensitivity of ubSSFP signals to <i>T</i>₂^∗ is derived under the assumption of a Lorentzian frequency distribution resulting from static field inhomogeneities. Further, the phases of all ubSSFP signals are calculated and a general expression of how to use them for B₀-fieldmapping is given. The derivation is supported by the extended phase graph (EPG) model, and as such the work also acts as a comprehensive introduction to the formal description of SSFP. In addition, the balanced SSFP (bSSFP) sequence is explored. The connection of bSSFP to ubSSFP is shown, and potential <i>T</i>₂^∗-sensitivity of bSSFP is examined based on numerical simulations. It is shown that ubSSFP signals with negative dephasing order have a refocusing character and behave similar to spin-echo signals. Conversely, ubSSFP signals with zero or positive dephasing order can be regarded as <i>T</i>₂^∗-weighted. The behavior of bSSFP depends largely on the exact distribution of frequencies. For instance, for a narrow spherical distribution, bSSFP acts like a spin-echo sequence, while for a Lorentzian distribution a refocusing behavior does not occur.</p>","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"46A 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21435","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87722707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Continuous wave electron paramagnetic resonance of nitroxide biradicals in fluid solution","authors":"Sandra S. Eaton,&nbsp;Lukas B. Woodcock,&nbsp;Gareth R. Eaton","doi":"10.1002/cmr.a.21426","DOIUrl":"10.1002/cmr.a.21426","url":null,"abstract":"<p>Nitroxide biradicals have been prepared with electron-electron spin-spin exchange interaction, <i>J</i>, ranging from weak to very strong. EPR spectra of these biradicals in fluid solution depend on the ratio of <i>J</i> to the nitrogen hyperfine coupling, <i>A</i>_N, and the rates of interconversion between conformations with different values of <i>J</i>. For relatively rigid biradicals EPR spectra can be simulated as the superposition of <i>AB</i> splitting patterns arising from different combinations of nitrogen nuclear spin states. For more flexible biradicals spectra can be simulated with a Liouville representation of the dynamics that interconvert conformations with different values of <i>J</i> on the EPR timescale. Analysis of spectra, factors that impact <i>J</i>, and examples of applications to chemical and biophysical problems are discussed.</p>","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"47A 2","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21426","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45562301","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"DVD Review","authors":"","doi":"10.1002/cmr.a.21431","DOIUrl":"https://doi.org/10.1002/cmr.a.21431","url":null,"abstract":"","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"45A 6","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21431","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"109175464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A tribute to Alexander Davidson Bain: An NMR pioneer and mentor at McMaster University","authors":"Christopher Anand,&nbsp;Bob Berno,&nbsp;Stephen Boulton,&nbsp;Michael A. Brook,&nbsp;Richard Epand,&nbsp;Timothy R. Field,&nbsp;Gillian R. Goward,&nbsp;Paul Hazendonk,&nbsp;Giuseppe Melacini","doi":"10.1002/cmr.a.21418","DOIUrl":"10.1002/cmr.a.21418","url":null,"abstract":"<p>In this tribute to our friend, mentor and colleague Alexander Davidson Bain we have collectively recapitulated the milestones of his career at McMaster university. We start from Alex's scientific and educational achievements and continue with his accomplishments as a community and infrastructure builder. We attempt to provide a sense of the breadth and depth of his seemingly endless scientific contributions while at McMaster by briefly summarizing selected representative examples from his body of work. Following Alex's lead, the scientific account is mixed with anecdotes and “bits of wisdom” we fondly remember from our interactions and collaborations with him. We also touch upon his brilliant and nurturing educational style and his “aggregator” role within the McMaster and wider NMR communities. We conclude with a more personal picture of Alex D. Bain, in which his scientific excellence and profound intellect are inextricably tied to his kind, nurturing and optimistic character and to his uniquely wry humor. He was not just a “good guy,” he was the epitome of the “good guy.”</p>","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"45A 6","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21418","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81401056","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Solid-state NMR studies of chemical exchange in ion conductors for alternative energy applications","authors":"Danielle L. Smiley,&nbsp;Gillian R. Goward","doi":"10.1002/cmr.a.21419","DOIUrl":"10.1002/cmr.a.21419","url":null,"abstract":"<p>Here we describe the selective inversion methodology for quantifying the rates of site-specific ion exchange in materials such as lithium ion battery cathode frameworks. This strategy is shown to be robust in the presence of paramagnetic centers and viable and efficient for the evaluation of hopping rates, in spite of varying initial conditions for the NMR experiment. This is contrasted with 2D EXSY methodology, and selective inversion is shown to be preferable for a number of reasons articulated herein. Work in this area in our group was guided by insights into chemical exchange processes provide by our friend and colleague, Prof. Alex D. Bain. We dedicate this short review to him.</p>","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"45A 6","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21419","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79560665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A special issue in honor of the late Professor Alex D. Bain (1948-2016)","authors":"William F. Reynolds PhD,&nbsp;Eugene P. Mazzola PhD,&nbsp;Roderick E. Wasylishen PhD","doi":"10.1002/cmr.a.21421","DOIUrl":"10.1002/cmr.a.21421","url":null,"abstract":"&lt;p&gt;The NMR community lost one of its most brilliant and original thinkers when Alex Bain died in late 2016. Many of his friends and former colleagues felt that Alex deserved some form of special recognition in view of his many contributions to NMR, both in Canada and elsewhere. Since Alex had published a number of important articles in &lt;i&gt;Concepts in Magnetic Resonance&lt;/i&gt; and also served on the Editorial Board of Concepts, it was decided that a special issue of this journal in his honor would be an appropriate form of recognition of Alex's accomplishments, and three of us agreed to be Guest Editors for the issue.&lt;/p&gt;&lt;p&gt;Alex Bain graduated with a double Honors B.Sc. in Mathematics and Chemistry from the University of Toronto in 1970. He then received a National Research Council of Canada Fellowship for M.Sc. studies at the University of British Columbia where he carried out research on photoelectron spectroscopy. Next, he received a Shell Canada Fellowship for Ph.D. studies at Cambridge University. There he began his NMR career, working with Dr. Ruth Lynden-Bell. Returning to Canada in 1974, a time when full-time academic positions in Chemistry were few and far between, he first had an NRC Postdoctoral Fellowship with Professor John Martin at the University Alberta, followed by a series of limited term appointments at McMaster University and the Scarborough Campus of the University of Toronto. Finally, in 1980, Bruker Canada hired him as research scientist with particular responsibility for NMR programming, including for 2D NMR. He remained there until 1987 when McMaster attracted him back as an Associate Professor and later he became a Full Professor. In 2008, due to health concerns, he opted for early retirement to become an Emeritus Professor. However, he still kept very active in research, both at McMaster and as an unpaid research associate in Lewis Kay's group at Toronto. His contributions there are described in the article by Lewis.&lt;/p&gt;&lt;p&gt;Alex's research combined a strong desire to fully understand complex NMR phenomena with a knowledge and depth of understanding of advanced mathematical methods relevant to NMR that very few in the NMR community could match. Thus, use of Liouvillian operators, Floquet theory and sparse matrices featured prominently in his research. His Ph.D. research included elucidation of alternative relaxation pathways in heteronuclear AX&lt;sub&gt;2&lt;/sub&gt; and AX&lt;sub&gt;3&lt;/sub&gt; spin systems, knowledge that is still used today by Lewis Kay and others in designing 3D and 4D pulse sequences for protein NMR research. His Postdoctoral research included the use of Liouvillian operators to calculate NMR transitions. During his first spell at McMaster, he pioneered the use of Superspin to simulate 2D spectra. He also programmed a borrowed computer from a Nicolet FT-IR spectrometer to acquire and process 2D data on a Bruker spectrometer. This is what likely led to his job offer from Bruker. While at Bruker, he published a very useful pap","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"45A 6","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21421","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80174019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spin precession: A spin-1 case study using irreducible tensor operators","authors":"David J. Siminovitch","doi":"10.1002/cmr.a.21411","DOIUrl":"10.1002/cmr.a.21411","url":null,"abstract":"<p>Using a Cartesian operator basis set, precession equations have previously been derived for spin-1 systems using some 23 Cartesian operator commutators. We avoid the explicit evaluation of these commutators, and use instead fundamental properties of irreducible tensor operators (ITO) to obtain these precession equations. First, advantage is taken of the angle-axis parametrization of the rotation matrices that transform second-rank ITO under rotation to define the unitarily equivalent rotation matrix that transforms second-rank Cartesian tensors. From this latter transformation, and using simple matrix analysis techniques, all the equations that describe spin-1 precession in the presence of radiofrequency fields and resonance offsets are obtained. Second, information on the ITO commutation relations can be encoded in angular momentum coupling coefficients in a generalized spin precession equation. In the case of spin-1, this leads to a set of coupled differential equations for the statistical tensor components . After transformation of these components to their Cartesian counterparts, the corresponding vector differential equations that define the time evolution of the Cartesian operator expectation values are easily solved, again using simple matrix analysis. This solution yields all the equations that describe spin-1 precession in the presence of radiofrequency fields, resonance offsets, and the quadrupolar interaction.</p>","PeriodicalId":55216,"journal":{"name":"Concepts in Magnetic Resonance Part A","volume":"45A 6","pages":""},"PeriodicalIF":0.6,"publicationDate":"2018-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.a.21411","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81924358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}