Nmr spectroscopy

Nmr spectroscopy

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  -TATHAGATA CHAKRABORTY B.Pharm , 4thYear , 1st Semester
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  INTRODUCTION • Nuclear magneticresonance spectroscopy is a powerful analytical technique used to characterize organic molecules by identifying carbon-hydrogen frameworks within molecules. • Two common types of NMR spectroscopy are used to characterize organic structure: 1H NMR is used to determine the type and number of H atoms in a molecule; 13C NMR is used to determine the type of carbon atoms in the molecule. • The source of energy in NMR is radio waves which have long wavelengths, and thus low energy and frequency. • When low-energy radio waves interact with a molecule, they can change the nuclear spins of some elements, including 1H and 13C.
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  Mechanism of NMR •When a charged particle such as a proton spins on its axis, it creates a magnetic field. Thus, the nucleus can be considered to be a tiny bar magnet. • Normally, these tiny bar magnets are randomly oriented in space. However, in the presence of a magnetic field B0, they are oriented with or against this applied field. More nuclei are oriented with the applied field because this arrangement is lower in energy.
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  Mechanism of NMR(2) • In a magnetic field, there are now two energy states for a proton: a lower energy state with the nucleus aligned in the same direction as B0, and a higher energy state in which the nucleus aligned against B0. • When an external energy source (h) that matches the energy difference (E) between these two states is applied, energy is absorbed, causing the nucleus to “spin flip” from one orientation to another. • The energy difference between these two nuclear spin states corresponds to the low frequency RF region of the electromagnetic spectrum.
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  The NMR Spectrometer
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  The NMR Graph
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  Continuous-Wave (CW) Spectrometers  Thespectrometer scans through a range of frequencies  The sample is interrogated with one frequency at a time. As the frequency range is scanned, a plot of signal intensity vs. frequency is generated.
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  Fourier Transform (FT) Spectrometers The sample is interrogated with a range of freqencies, “all frequencies at once.” The decay of the signal over time is observed as a Free Induction Decay (FID)  A Fourier transform changes the signal vs. time plot into a signal vs. frequency plot.
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  ADVANTAGES OF FTNMR  Dramatic increase in the sensitivity of NMR measurements .  Has widespread applications esp. for 13C NMR, 31P NMR and 19F NMR giving high signal to noise ratio facilitating rapid scanning.  Can be obtained with less than 5 mg of the compound.  The signals stand out clearly with almost no electronic background noise .  Used in engineering, industrial quality control and medicine.
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  Advantages of FTover CW Spectrometers  If a signal is weak, many scans must be averaged to enhance the signal/noise ratio. Signal/noise ratio rises as the square root of number of scans. Only FT instruments can obtain a large number of scans in a reasonable time.  A scan can be performed much more quickly. CW-NMR: 5 minutes; FT-NMR: 5 seconds.
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  APPLICATIONS OF NMR NuclearMagnetic Resonance (NMR) Spectroscopy is a non-destructive analytical technique that is used to probe the nature and characteristics of molecular structure. A simple NMR experiment produces information in the form of a spectrum, which is able to provide details about:  The types of atoms present in the sample  The relative amounts of atoms present in a sample  The specific environments of atoms within a molecule  The purity and composition of a sample  Structural information about a molecule, including constitutional and conformational isomerisation
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  APPLICATION OF NMR SPECTROSCOPY Today,NMR has become a sophisticated and powerful analytical technology that has found a variety of applications in many disciplines of scientific research, medicine, and various industries. Some of the applications of NMR spectroscopy are LISTED BELOW:  Solution structure Molecular dynamics Protein folding Ionization state Protein hydration
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  APPLICATION OF NMR SPECTROSCOPY Hydrogen bonding  Drug screening and design Particularly useful for identifying drug leads and determining the conformations of the compounds bound to enzymes, receptors, and other proteins.  Native membrane protein Solid state NMR has the potential for determining atomic-resolution structures of domains of membrane proteins in their native membrane environments, including those with bound ligands  Metabolite analysis A very powerful technology for metabolite analysis.  Chemical analysis A matured technique for chemical identification and conformational analysis of chemicals whether synthetic or natural.
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  DISCUSSION  Recently 19FNMR studies of the cyan variant of GFP conducted in a laboratory indicated conformational flexibility in or near the chromophore moiety with residue His148 being most likely involved in this process. NMR has been suggested as a tool for elucidating the dynamics of chromophore formation, water accessibility of the chromophore and conformational flexibility in GFP. In contrast to many spectroscopic techniques, NMR spectroscopy provides a large frequency range for studying dynamical processes from pico second to second timescales and even longer at atomic resolutions.