0
edits
Changes
NMR
,no edit summary
<p>NMR studies magnetic nuclei by aligning them with an applied constant magnetic field and perturbing this alignment using an alternating magnetic field, those fields being orthogonal. The resulting response to the perturbing magnetic field is the phenomenon that is exploited in NMR spectroscopy and magnetic resonance imaging, which use very powerful applied magnetic fields in order to achieve high resolution spectra, details of which are described by the chemical shift and the Zeeman effect.</p>
<p>NMR phenomena are also utilised in low field NMR and Earth's field NMR spectrometers, and some kinds of magnetometer.</p>
<p> </p>
<h2p><span class="mw-headline"><font size="5">History</font></span></h2p>
<p> </p>
<h3p><span class="mw-headline"><font size="4">Discovery</font></span></h3p>
<p>Nuclear magnetic resonance was first described and measured in molecular beams by Isidor Rabi in 1938.<sup class="reference" id="_ref-0">[1]</sup> Eight years later, in 1946, Felix Bloch and Edward Mills Purcell refined the technique for use on liquids and solids, for which they shared the Nobel Prize in physics in 1952.</p>
<p>Purcell had worked on the development and application of RADAR during World War II at Massachusetts Institute of Technology's Radiation Laboratory. His work during that project on the production and detection of radiofrequency energy, and on the absorption of such energy by matter, preceded his discovery of NMR.</p>
<p>The development of nuclear magnetic resonance as a technique of analytical chemistry and biochemistry parallels the development of electromagnetic technology and its introduction into civilian use.</p>
<p> </p>
<h2p><span class="mw-headline"><font size="5">Theory of nuclear magnetic resonance</font></span></h2p>
<p> </p>
<h3><span class="mw-headline">Nuclear spin and magnets</span></h3>
<h4><span class="mw-headline">Spin behavior in a magnetic field</span></h4>
<p>Consider nuclei which have a spin of one-half, like <sup>1</sup>H, <sup>13</sup>C or <sup>19</sup>F. The nucleus has two possible spin states: <em>m</em> = ½ or <em>m</em> = -½ (also referred to as up and down or α and β, respectively). The energies of these states are degenerate—that is to say that they are the same. Hence the <em>populations</em> of the two states (i.e. number of atoms in the two states) will be approximately equal at thermal equilibrium.</p>
<div class="floatright"><span><img height="195" alt="Splitting of nuclei spin states in an external magnetic field" width="300" border="0" src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/a9/EPR_splitting.jpg/300px-EPR_splitting.jpg" width="300" border="0" /></span></div>
<p>If a nucleus is placed in a magnetic field, however, the interaction between the nuclear magnetic moment and the external magnetic field mean the two states no longer have the same energy. The energy of a magnetic moment μ when in a magnetic field <em>B</em><sub>0</sub> (the zero subscript is used to distinguish this magnetic field from any other applied field) is given by the negative scalar product of the vectors:</p>
<dl><dd><img class="tex" alt="E = -{\mathbf B_0}\cdot{\mathbf \mu}= - \mu_z B_0" src="http://upload.wikimedia.org/math/c/a/a/caa447d9fefe8dcdeb1ba0804e52d0b8.png" /> </dd></dl>
<p>The precessing nuclei can also fall out of alignment with each other (returning the net magnetization vector to a nonprecessing field) and stop producing a signal. This is called <em>T</em><sub>2</sub> relaxation. It is possible to be in this state and not have the population difference required to give a net magnetization vector at its thermodynamic state. Because of this, <em>T</em><sub>1</sub> is always larger (slower) than <em>T</em><sub>2</sub>. This happens because some of the spins were flipped by the pulse and will remain so until they have undergone population relaxation. In practice, the <em>T</em><sub>2</sub> time is the life time of the observed NMR signal, the free induction decay. In the NMR spectrum, meaning the Fourier transform of the free induction decay, the <em>T</em><sub>2</sub> time defines the width of the NMR signal. Thus, a nucleus having a large <em>T</em><sub>2</sub> time gives rise to a sharp signal, whereas nuclei with shorter <em>T</em><sub>2</sub> times give rise to more broad signals. The length of <em>T</em><sub>1</sub> and <em>T</em><sub>2</sub> is closely related to molecular motion.</p>
<p> </p>
<h2p><span class="mw-headline"><font size="5">[[NMR spectroscopy]]</font></span></h2p>
<p>NMR spectroscopy is one of the principal techniques used to obtain physical, chemical, electronic and structural information about molecules due to the chemical shift and Zeeman effect on the resonant frequencies of the nuclei. It is a powerful technique that can provide detailed information on the topology, dynamics and three-dimensional structure of molecules in solution and the solid state. Also, nuclear magnetic resonance is one of the techniques that has been used to build elementary quantum computers.</p>
<p> </p>
</ul>
<p> </p>
<h2p><span class="mw-headline"><font size="5">Applications</font></span></h2p>
<p> </p>
<h3><span class="mw-headline">Medicine</span></h3>
<p>Various magnetometers use NMR effects to measure magnetic fields, including proton magnetometers or proton precession magnetometers (PPM), and Overhauser magnetometers. See also Earth's field NMR.</p>
<p> </p>
<h2p><span class="mw-headline"><font size="5">Makers of NMR equipment</font></span></h2p>
<p>Major NMR instrument makers include Bruker, General Electric, JEOL, Kimble Chase, Philips, Siemens AG, Varian, Inc. and SpinCore Technologies, Inc.</p>
<p> </p>
<h2p><span class="mw-headline"><font size="5">See also</spanfont></h2span><div/p>
<ul>
<li>Carbon-13 NMR </li>
<li>NMR spectroscopy </li>
<li>Nuclear quadrupole resonance (NQR) </li>
<li>Protein NMR </li> <li>[[Proteomics]] </li>
<li>Proton NMR </li>
<li>Rabi cycle </li>
<li>Solid-state NMR </li>
<li>Zeeman effect </li>
</ul>
<p> </divp>
<p><span class="mw-headline"><font size="5">References</font></span></p>
<ol class="references">
<li>Akitt, J.W.; Mann, B.E., ‘’NMR and Chemistry’’; Stanley Thornes: Cheltenham, UK, 2000. (p273) </li>
<li>Akitt, J.W.; Mann, B.E., ‘’NMR and Chemistry’’; Stanley Thornes: Cheltenham, UK, 2000. (p287) </li>
<li>Hornak, Joseph P. <a class="external text" title="http://www.cis.rit.edu/htbooks/nmr/" rel="nofollow" href="http://www.cis.rit.edu/htbooks/nmr/" rel="nofollow"><em>The Basics of NMR</em></a> </li> <li><a class="external text" title="http://www.spectroscopynow.com/Spy/basehtml/SpyH/1,,5-14-9-0-0-education_dets-0-1839,00.html" rel="nofollow" href="http://www.spectroscopynow.com/Spy/basehtml/SpyH/1,,5-14-9-0-0-education_dets-0-1839,00.html" rel="nofollow">J. Keeler, Understanding NMR Spectroscopy</a> </li>
<li>Wuthrich, Kurt <em>NMR of Proteins and Nucleic Acids</em> Wiley-Interscience, New York, NY USA 1986. </li>
<li>Tyszka, J. M. & Fraser, S. E. & Jacobs, R. E. (2005). <a class="external text" title="http://dx.doi.org/10.1016/j.copbio.2004.11.004" rel="nofollow" href="http://dx.doi.org/10.1016/j.copbio.2004.11.004" rel="nofollow">Magnetic resonance microscopy: recent advances and applications</a>. <em><a class="mw-redirect" title="Current Opinion in Biotechnology" href="http://en.wikipedia.org/wiki/Current_Opinion_in_Biotechnology">Current Opinion in Biotechnology</a>,</em> <strong>16</strong>(1):93-99. </li>
</ol>
<p><a id="External_links" name="External_links"></a></p>
<h2p><span class="mw-headline"><font size="5">External links</font></span></h2p>
<ul>
<li><a class="external text" title="[http://wwwbiosites.vegaorg Biosites.org.uk]</videoli> <li>[http:/programme/21" hrefproteins.ws Proteins.ws]</li> <li><a class="external text" title="http://www.vega.org.uk/video/programme/21" rel="nofollow">Richard Ernst, NL - href="http://www.vega.org.uk/video/programme/21">Richard Ernst, NL - Developer of Multdimensional NMR techniques</a> Freeview video provided by the Vega Science Trust. </li> <li><a class="external text" title="http://www.vega.org.uk/video/programme/115" rel="nofollow" href="http://www.vega.org.uk/video/programme/115" rel="nofollow">'An Interview with Kurt Wuthrich'</a> Freeview video by the Vega Science Trust (Wüthrich was awarded a Nobel Prize in Chemistry in 2002 "for his development of nuclear magnetic resonance spectroscopy for determining the three-dimensional structure of biological macromolecules in solution"). </li> <li><em><a class="external text" title="http://abbreviations.oxid.ro/Academic-and-Science/Nuclear-Magnetic-Resonance/" rel="nofollow" href="http://abbreviations.oxid.ro/Academic-and-Science/Nuclear-Magnetic-Resonance/" rel="nofollow">Acronyms, Abbreviations and Initialisms - Nuclear Magnetic Resonance</a></em> </li> <li><a class="external text" title="http://vam.anest.ufl.edu/forensic/nmr.html" rel="nofollow" href="http://vam.anest.ufl.edu/forensic/nmr.html" rel="nofollow">A free interactive simulation of NMR principles</a> </li> <li><a class="external text" title="http://www.bionmr.com" rel="nofollow" href="http://www.bionmr.com/" rel="nofollow">Bionmr.com - discussion of NMR applications in biological systems</a> </li> <li><a class="external text" title="http://www.nmrwiki.org" hrefrel="nofollow" href="http://www.nmrwiki.org/" rel="nofollow"><em>NMRW</em>iki.ORG</a> NMR resource you can edit </li> <li><a class="external text" title="http://www.ismar.org" rel="nofollow" href="http://www.ismar.org/" rel="nofollow">The International Society of Magnetic Resonance</a> </li> <li><a class="external text" title="http://www.auremol.de" rel="nofollow" href="http://www.auremol.de/" rel="nofollow">AUREMOL (Universitaet Regensburg)</a> </li> <li>NMR processing software from <a class="external text" title="http://www.acdlabs.com/" hrefrel="nofollow" href="http://www.acdlabs.com/" rel="nofollow">ACD/Labs</a> for <a class="external text" title="http://www.acdlabs.com/products/spec_lab/exp_spectra/nmr/" rel="nofollow" href="http://www.acdlabs.com/products/spec_lab/exp_spectra/nmr/" rel="nofollow">1D</a> and <a class="external text" title="http://www.acdlabs.com/products/spec_lab/exp_spectra/2d_nmr/" rel="nofollow" href="http://www.acdlabs.com/products/spec_lab/exp_spectra/2d_nmr/" rel="nofollow">2D</a> NMR spectra. DB interface available. </li> <li>NMR Prediction software <a class="external text" title="http://www.acdlabs.com/products/spec_lab/predict_nmr/" hrefrel="nofollow" href="http://www.acdlabs.com/products/spec_lab/predict_nmr/" rel="nofollow">ACD/NMR Predictors</a> </li> <li>Automated elucidation of chemical structures <a class="external text" title="http://www.acdlabs.com/products/spec_lab/complex_tasks/str_elucidator/" rel="nofollow" href="http://www.acdlabs.com/products/spec_lab/complex_tasks/str_elucidator/" rel="nofollow">ACD/Structure Elucidator</a> </li> <li>NMR simulation software <a class="external text" title="http://www.bpc.lu.se/QSim" rel="nofollow" href="http://www.bpc.lu.se/QSim" rel="nofollow">QSim</a> </li> <li>NMR processing software <a class="external text" title="http://spin.niddk.nih.gov/bax/software/NMRPipe" hrefrel="nofollow" href="http://spin.niddk.nih.gov/bax/software/NMRPipe" rel="nofollow">NMRPipe</a> </li> <li><a class="external text" title="http://www.bmrb.wisc.edu/" rel="nofollow" href="http://www.bmrb.wisc.edu/" rel="nofollow">BMRB</a> BioMagResBank - A repository for experimental data from NMR spectroscopy of proteins, peptides, nucleic acids and small biomolecules. </li> <li><a class="external text" title="http://www.chemistry.ohio-state.edu/~grandinetti/RMN" rel="nofollow" href="http://www.chemistry.ohio-state.edu/~grandinetti/RMN" rel="nofollow">RMN</a> - An NMR data processing program for the Macintosh. </li> <li><a class="external text" title="http://baker-atlas.bakerhughesdirect.com/NMR-data-acquisition-systems/" hrefrel="nofollow" href="http://baker-atlas.bakerhughesdirect.com/NMR-data-acquisition-systems/" rel="nofollow">Baker Hughes - NMR data acquisition systems</a> </li> <li><a class="external text" title="http://baker-atlas.bakerhughesdirect.com/NMR-data-logging/" rel="nofollow" href="http://baker-atlas.bakerhughesdirect.com/NMR-data-logging/" rel="nofollow">Baker Hughes - The benefits of NMR data logging</a> </li> <li><a class="external text" title="http://www.process-nmr.com/time_domain_process_nmr_spectrom.htm" rel="nofollow" href="http://www.process-nmr.com/time_domain_process_nmr_spectrom.htm" rel="nofollow">Applications of Time-Domain NMR in Process Control</a> </li> <li><a class="external text" title="http://www.process-nmr.com/process.htm" hrefrel="nofollow" href="http://www.process-nmr.com/process.htm" rel="nofollow">Applications of High Resolution FT-NMR in Real-Time Process Control</a> </li> <li><a class="external text" title="http://nmr.bham.ac.uk" rel="nofollow" href="http://nmr.bham.ac.uk/" rel="nofollow">HWB-NMR</a> Henry Wellcome Building for Biomolecular NMR, Birmingham, UK. </li> <li><a class="external text" title="http://www.nmr.ch/" rel="nofollow" href="http://www.nmr.ch/" rel="nofollow">CARA</a> - Computer Aided Resonance Assignment, freeware, developed at the group of Prof. Kurt Wüthrich </li> <li><a class="external text" title="http://www.ccpn.ac.uk/" hrefrel="nofollow" href="http://www.ccpn.ac.uk/" rel="nofollow">CCPN</a> - The Collaborative Computing Project for NMR, based at the University of Cambridge, UK </li> <li><a class="external text" title="http://structbio.vanderbilt.edu" rel="nofollow" href="http://structbio.vanderbilt.edu/" rel="nofollow">Vanderbilt Structural Biology</a> General site for structural biology at Vanderbilt University. NMR, x-ray crystallography, and computational biology all included. </li> <li><a class="external text" title="http://janocchio.sourceforge.net" rel="nofollow" href="http://janocchio.sourceforge.net/" rel="nofollow">Janocchio</a> Conformation-dependent coupling and NOE prediction for small molecules. </li> <li><a class="external text" title="http://www.teachspin.com/instruments/earths_field_NMR/index.shtml" hrefrel="nofollow" href="http://www.teachspin.com/instruments/earths_field_NMR/index.shtml" rel="nofollow">Earth's field NMR (EFNMR)</a> </li> <li><a class="external text" title="http://www.chem.queensu.ca/FACILITIES/NMR/nmr/webcourse/precess.htm" rel="nofollow" href="http://www.chem.queensu.ca/FACILITIES/NMR/nmr/webcourse/precess.htm" rel="nofollow">Animation of NMR spin 1/2 precession</a> </li> <li><a class="external text" title="http://www.ebyte.it/stan/blog.html#08Feb29a class="external text" title="http://www.ebyte.it/stan/blog.html#08Feb29" rel="nofollow" href="http://www.ebyte.it/stan/blog.html#08Feb29" rel="nofollow">Article on helium scarcity and potential effects on NMR and MRI communities</a> </li>
</ul>