FACTOID # 22: South Dakota has the highest employment ratio in America, but the lowest median earnings of full-time male employees.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Nuclear magnetic resonance
Pacific Northwest National Laboratory's high magnetic field (800 MHz, 18.8 T) NMR spectrometer being loaded with a sample.
Pacific Northwest National Laboratory's high magnetic field (800 MHz, 18.8 T) NMR spectrometer being loaded with a sample.
900MHz, 21.2 T NMR Magnet at HWB-NMR, Birmingham, UK being loaded with a sample
900MHz, 21.2 T NMR Magnet at HWB-NMR, Birmingham, UK being loaded with a sample

Nuclear magnetic resonance (NMR) is a physical phenomenon based upon the quantum mechanical magnetic properties of an atom's nucleus. NMR also commonly refers to a family of scientific methods that exploit nuclear magnetic resonance to study molecules. NMR may be an acronym for: Nuclear magnetic resonance. ... Pacific Northwest National Laboratory 800MHz NMR Spectrometer File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Pacific Northwest National Laboratory 800MHz NMR Spectrometer File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... The Pacific Northwest National Laboratory (PNNL) is a one of nine United States Department of Energy multiprogram national laboratories. ... SI unit. ... Image File history File linksMetadata HWB-NMRv900. ... Image File history File linksMetadata HWB-NMRv900. ... SI unit. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ... For other senses of this word, see magnetism (disambiguation). ... For other uses, see Atom (disambiguation). ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ...


All nuclei that contain odd numbers of protons or neutrons have an intrinsic magnetic moment and angular momentum. The most commonly measured nuclei are hydrogen-1 (the most receptive isotope at natural abundance) and carbon-13, although nuclei from isotopes of many other elements (e.g. 15N, 14N 19F, 31P, 17O, 29Si, 10B, 11B, 23Na, 35Cl, 195Pt) can also be observed. For other uses, see Proton (disambiguation). ... This article or section does not adequately cite its references or sources. ... A bar magnet. ... This gyroscope remains upright while spinning due to its angular momentum. ... A hydrogen atom is an atom of the element hydrogen. ... For other uses, see Isotope (disambiguation). ... Carbon-13 is a stable isotope of carbon. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Distinguished from fluorene and fluorone. ... General Name, symbol, number phosphorus, P, 15 Chemical series nonmetals Group, period, block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... This article is about the chemical element and its most stable form, or dioxygen. ... Not to be confused with Silicone. ... For other uses, see Boron (disambiguation). ... For sodium in the diet, see Salt. ... General Name, symbol, number chlorine, Cl, 17 Chemical series nonmetals Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ...


NMR resonant frequencies for a particular substance are directly proportional to the strength of the applied magnetic field, in accordance with the equation for the Larmor precession frequency. Larmor precession refers to the precession of the magnetic moments of electrons or atomic nucleii in atoms around the direction of an external magnetic field. ...


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. For the indie-pop band, see The Magnetic Fields. ... In mathematics, orthogonal is synonymous with perpendicular when used as a simple adjective that is not part of any longer phrase with a standard definition. ... Nuclear magnetic resonance spectroscopy most commonly known as NMR spectroscopy is the name given to the technique which exploits the magnetic properties of certain nuclei. ... MRI redirects here. ... In nuclear magnetic resonance (NMR), the chemical shift describes the dependence of nuclear magnetic energy levels on the electronic environment in a molecule. ... The Zeeman effect (IPA ) is the splitting of a spectral line into several components in the presence of a magnetic field. ...


NMR phenomena are also utilized in low field NMR and Earth's field NMR spectrometers, and some kinds of magnetometer. Low field NMR is a branch of nuclear magnetic resonance (NMR), that is also related to Earths field NMR. Categories: | ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ...

Contents

History

Discovery

Nuclear magnetic resonance was first described and measured in molecular beams by Isidor Rabi in 1938.[1] 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. Isidor Isaac Rabi (July 29, 1898 - January 11, 1988) was an American physicist of Austro-Hungarian origin. ... Year 1946 (MCMXLVI) was a common year starting on Tuesday (link will display full 1946 calendar) of the Gregorian calendar. ... Felix Bloch (October 23, 1905 – September 10, 1983) was a Swiss physicist, working mainly in the USA. // A stamp from Guyana commemorating Felix Bloch. ... Edward Mills Purcell (August 30, 1912 – March 7, 1997) was an American physicist who shared the 1952 Nobel Prize for Physics for his independent discovery (published 1946) of nuclear magnetic resonance in liquids and in solids. ... Hannes Alfvén (1908–1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ... Year 1952 (MCMLII) was a leap year starting on Tuesday (link will display full calendar) of the Gregorian calendar. ...


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. For other uses, see Radar (disambiguation). ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... “MIT” redirects here. ... The Radiation Laboratory or often RadLab at Massachusetts Institute of Technology was in operation from October 1940 until December 31, 1945. ...


They noticed that magnetic nuclei, like 1H and 31P, could absorb RF energy when placed in a magnetic field of a strength specific to the identity of the nuclei. When this absorption occurs, the nucleus is described as being in resonance. Interestingly, for analytical scientists, different atoms within a molecule resonate at different frequencies at a given field strength. The observation of the resonance frequencies of a molecule allows a user to discover structural information about the molecule. It has been suggested that this article or section be merged with Radio waves. ...


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. This article does not cite any references or sources. ... Biochemistry (from Greek: , bios, life and Egyptian kēme, earth[1]) is the study of the chemical processes in living organisms. ...


Theory of nuclear magnetic resonance

Nuclear spin and magnets

The elementary particles, neutrons and protons, composing an atomic nucleus, have the intrinsic quantum mechanical property of spin. The overall spin of the nucleus is determined by the spin quantum number I. If the number of both the protons and neutrons in a given isotope are even then I = 0, i.e. there is no overall spin; just as electrons pair up in atomic orbitals, so do even numbers of protons and neutrons (which are also spin ½ particles and hence fermions) pair up giving zero overall spin. In other cases, however, the overall spin is non-zero. For example 27Al has an overall spin I = 5/2. Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 940 MeV/c² (1. ... For alternative meanings see proton (disambiguation). ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... In atomic physics, the spin quantum number is a quantum number that parametrizes the intrinsic angular momentum (or spin angular momentum, or simply spin) of a given particle. ... For other uses, see Isotope (disambiguation). ... In mathematics, the parity of an object refers to whether it is even or odd. ... In chemistry, an atomic orbital is the region in which an electron may be found around a single atom. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ...


A non-zero spin is associated with a non-zero magnetic moment, μ, via

 mu = gamma I

where the proportionality constant, γ, is the gyromagnetic ratio. It is this magnetic moment that is exploited in NMR. In physics, the gyromagnetic ratio or Landé g-factor is a dimensionless unit which expresses the ratio of the magnetic dipole moment to the angular momentum of an elementary particle or atomic nucleus. ...


Electron spin resonance is a related technique which exploits the spin of electrons instead of nuclei. The basic principles are otherwise similar. Electron Paramagnetic Resonance (EPR) or Electron Spin Resonance (ESR) is a spectroscopic technique which detects species that have unpaired electrons, generally meaning that the molecule in question is a free radical if it is an organic molecule, or that it has transition metal ions if it is an inorganic complex. ...


Values of spin angular momentum

The angular momentum associated with nuclear spin is quantized. This means both that the magnitude of angular momentum is quantized (i.e. I can only take on a restricted range of values), and also that the 'orientation' of the associated angular momentum is quantized. The associated quantum number is known as the magnetic quantum number, m, and can take values from +I to –I in integral steps. Hence for any given nucleus, there is a total of 2I+1 angular momentum states. This gyroscope remains upright while spinning due to its angular momentum. ... Generally, quantization is the state of being constrained to a set of discrete values, rather than varying continuously. ... By virtue of its charge and spin motion, an electron develops a magnetic field. ...


The z component of the angular momentum vector, Iz, is therefore:

I_z = m hbar

where hbar is Planck's reduced constant. A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ...


The z component of the magnetic moment is simply

mu_z = gamma I_z = mgamma hbar

Spin behavior in a magnetic field

Consider nuclei which have a spin of one-half, like 1H, 13C or 19F. The nucleus has two possible spin states: m = ½ or m = -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 populations of the two states (i.e. number of atoms in the two states) will be approximately equal at thermal equilibrium. In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ...

Splitting of nuclei spin states in an external magnetic field

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 B0 (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: Image File history File links Size of this preview: 800 × 521 pixelsFull resolution (2376 × 1548 pixel, file size: 177 KB, MIME type: image/jpeg) Personal creation; no rights claimed I, the copyright holder of this work, hereby release it into the public domain. ... For the indie-pop band, see The Magnetic Fields. ...

E = -{mathbf B_0}cdot{mathbf mu}= - mu_z B_0

where the magnetic field has been oriented along the z axis.


Hence

E = - mhbargamma B_0

As a result the different nuclear spin states have different energies in a non-zero magnetic field. In hand-waving terms, we can talk about the two spin states of a spin ½ as being aligned either with or against the magnetic field. If γ is positive (true for most isotopes) then m = ½ is the lower energy state. The term handwaving is an informal term that describes either the debate technique of failing to rigorously address an argument in an attempt to bypass the argument altogether, or a deliberate gesture and admission that one is intentionally glossing over detail for the sake of time or clarity. ...


The energy difference between the two states is

Delta E = hbargamma B_0

and this difference results in a small population bias toward the lower energy state.


Resonance

Resonant absorption will occur when electromagnetic radiation of the correct frequency to match this energy difference is applied. The energy of a photon is E = , where ν is its frequency. Hence absorption will occur when This box:      Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...

nu = frac{Delta E}{h}= frac{gamma B_0}{2pi}

These frequencies typically correspond to the radio frequency range of the electromagnetic spectrum. It has been suggested that this article or section be merged with Radio waves. ... Although some radiations are marked as N for no in the diagram, some waves do in fact penetrate the atmosphere, although extremely minimally compared to the other radiations The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. ...


It is this resonant absorption that is detected in NMR.


Nuclear shielding

It might appear from the above that all nuclei of the same nuclide (and hence the same γ) would resonate at the same frequency. This is not the case. The most important perturbation of the NMR frequency for applications of NMR is the 'shielding' effect of the surrounding electrons. In general, this electronic shielding reduces the magnetic field at the nucleus (which is what determines the NMR frequency). As a result the energy gap is reduced, and the frequency required to achieve resonance is also reduced. This shift of the NMR frequency due to the chemical environment is called the chemical shift, and it explains why NMR is a direct probe of chemical structure. In nuclear magnetic resonance (NMR), the chemical shift describes the dependence of nuclear magnetic energy levels on the electronic environment in a molecule. ...


Unless the local symmetry is particularly high, the shielding effect depends on the orientation of the molecule with respect to the external field. In solid-state NMR, magic angle spinning is required to average out this orientation dependence. This is unnecessary in conventional NMR of molecules in solution since rapid molecular tumbling averages out the anisotropic component of the chemical shift. Sphere symmetry group o. ... Solid-state NMR (SSNMR) spectroscopy is a kind of nuclear magnetic resonance (NMR) spectroscopy, characterized by the presence of anisotropic (directionally dependent) interactions. ... In physics, magic angle spinning (MAS) is a technique often used to perform solid-state NMR experiments. ...


Relaxation

For more details on this topic, see Relaxation (NMR).

The process called population relaxation refers to nuclei that return to the thermodynamic state in the magnet. This process is also called T1 relaxation, where T1 refers to the mean time for an individual nucleus to return to its equilibrium state. Once the population is relaxed, it can be probed again, since it is in the initial state. This article or section is in need of attention from an expert on the subject. ...


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 T2 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, T1 is always larger (slower) than T2. 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 T2 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 T2 time defines the width of the NMR signal. Thus, a nucleus having a large T2 time gives rise to a sharp signal, whereas nuclei with shorter T2 times give rise to more broad signals. The length of T1 and T2 is closely related to molecular motion. Larmor precession refers to the precession of the magnetic moments of electrons or atomic nucleii in atoms around the direction of an external magnetic field. ... A free induction decay (FID) curve is generated as excited nuclei relax in an NMR machine. ... In mathematics, the Fourier transform is a certain linear operator that maps functions to other functions. ... A free induction decay (FID) curve is generated as excited nuclei relax in an NMR machine. ...


NMR spectroscopy

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. Nuclear magnetic resonance spectroscopy most commonly known as NMR spectroscopy is the name given to the technique which exploits the magnetic properties of certain nuclei. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... In nuclear magnetic resonance (NMR), the chemical shift describes the dependence of nuclear magnetic energy levels on the electronic environment in a molecule. ... The Zeeman effect (IPA ) is the splitting of a spectral line into several components in the presence of a magnetic field. ... The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers. ...


Continuous wave (CW) spectroscopy

In its first few decades, nuclear magnetic resonance spectrometers used a technique known as continuous-wave (CW) spectroscopy. Although NMR spectra could be obtained using a fixed magnetic field and sweeping the frequency of the electromagnetic radiation, this more typically involved using a fixed frequency source and varying the current (and hence magnetic field) in an electromagnet to observe the resonant absorption signals. (This is the origin of the now anachronistic but still common "high" and "low" field terminology for low frequency and high frequency regions respectively of the NMR spectrum.)


CW spectroscopy is inefficient in comparison to Fourier techniques (see below) as it probes the NMR response at individual frequencies in succession. As the NMR signal is intrinsically weak, the observed spectra suffer from a poor signal-to-noise ratio (S/N). This can be mitigated by signal averaging i.e. adding the spectra from repeated measurements. While the NMR signal is constant between scans and so adds linearly, the random noise adds more slowly — as the square-root of the number of spectra (see Random walk). Hence the overall ratio of the signal to the noise increases as the square-root of the number of spectra measured. Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering concept defined as the ratio of a signal power to the noise power corrupting the signal. ... Example of eight random walks in one dimension starting at 0. ...


Fourier spectroscopy

Most applications of NMR involve full NMR spectra, that is, the intensity of the NMR signal as a function of frequency. Early attempts to acquire the NMR spectrum more efficiently than simple CW methods involved irradiating simultaneously with more than one frequency. It was soon realised, however, that a simpler solution was to use short pulses of radio-frequency (centred at the middle of the NMR spectrum). In simple terms, a short square pulse of a given "carrier" frequency "contains" a range of frequencies centred about the carrier frequency, with the range of excitation (bandwidth) being inversely proportional to the pulse duration (the Fourier transform of an approximate square wave contains contributions from all the frequencies in the neighborhood of the principal frequency). The restricted range of the NMR frequencies made it relatively easy to use RF pulses to excite the entire NMR spectrum. In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz. ... In mathematics, the Fourier transform is a certain linear operator that maps functions to other functions. ... A square wave is a kind of basic waveform. ...


Applying such a pulse to a set of nuclear spins simultaneously excites all the NMR transitions. In terms of the net magnetisation vector, this corresponds to tilting the magnetisation vector away from its equilibrium position (aligned along the external magnetic field). The out-of-equilibrium magnetisation vector precesses about the external magnetic field at the NMR frequency of the spins. This oscillating magnetisation induces a current in a nearby pickup coil, creating an electrical signal oscillating at the NMR frequency. This signal is known as the free induction decay (FID) and contains the sum of the NMR responses from all the excited spins. In order to obtain the frequency-domain NMR spectrum (intensity vs. frequency) this time-domain signal (intensity vs. time) must be Fourier transformed. Fortunately the development of FT-NMR coincided with the development of digital computers and Fast Fourier Transform algorithms. Larmor precession refers to the precession of the magnetic moments of electrons or atomic nucleii in atoms around the direction of an external magnetic field. ... For magnetic induction, see Magnetic field. ... A free induction decay (FID) curve is generated as excited nuclei relax in an NMR machine. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... In mathematics, the Fourier transform is a certain linear operator that maps functions to other functions. ... The Cooley-Tukey algorithm, named after J.W. Cooley and John Tukey, is the most common fast Fourier transform (FFT) algorithm. ...


Richard R. Ernst was one of the pioneers of pulse (FT) NMR and won a Nobel Prize in chemistry in 1991 for his work on FT-NMR and his development of multi-dimensional NMR (see below). Richard Robert Ernst (born August 14, 1933) is a Swiss physical chemist and Nobel Laureate. ... This is a list of Nobel Prize laureates in Chemistry from 1901 to 2006. ...


Multi-dimensional

The use of pulses of different shapes, frequencies and durations in specifically-designed patterns or pulse sequences allows the spectroscopist to extract many different types of information about the molecule.


Multi-dimensional nuclear magnetic resonance spectroscopy is a kind of FT-NMR in which there are at least two pulses and, as the experiment is repeated, the pulse sequence is varied. In multidimensional nuclear magnetic resonance there will be a sequence of pulses and, at least, one variable time period. In three dimensions, two time sequences will be varied. In four dimensions, three will be varied.


There are many such experiments. In one, these time intervals allow—among other things—magnetization transfer between nuclei and, therefore, the detection of the kinds of nuclear-nuclear interactions that allowed for the magnetization transfer. Interactions that can be detected are usually classified into two kinds. There are through-bond interactions and through-space interactions, the latter usually being a consequence of the nuclear Overhauser effect. Experiments of the nuclear-Overhauser variety may establish distances between atoms. It has been suggested that this article or section be merged with Dynamic nuclear polarisation. ...


Although the fundamental concept of 2D NMR was proposed by the Belgian scientist Jean Jeener, professor at the Free University of Brussels (now split into the Université Libre de Bruxelles and the Vrije Universiteit Brussel), this idea was largely developed by Richard Ernst who won the 1991 Nobel prize in Chemistry for his work in FT and multi-dimensional NMR. Multi-dimensional NMR experiments were further developed into powerful methodologies for studying biomolecules in solution, in particular for the determination of the structure of biopolymers such as proteins or even small nucleic acids. Kurt Wüthrich shared the 2002 Nobel Prize in Chemistry for his work in protein nuclear magnetic resonance spectroscopy. The Free University of Brussels is the name of two Belgian universities both in Brussels: the Dutch-speaking Vrije Universiteit Brussel, and the French-speaking Université Libre de Bruxelles This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The Université Libre de Bruxelles (or ULB) is a French-speaking university in Brussels, Belgium. ... The Vrije Universiteit Brussel (VUB) is a Flemish university situated in Brussels, Belgium. ... Richard Robert Ernst (born August 14, 1933) is a Swiss physical chemist and Nobel Laureate. ... Year 1991 (MCMXCI) was a common year starting on Tuesday (link will display the 1991 Gregorian calendar). ... This is a list of Nobel Prize laureates in Chemistry from 1901 to 2006. ... Biopolymers are a class of polymers produced by living organisms. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Look up nucleic acid in Wiktionary, the free dictionary. ... Kurt Wüthrich lecturing at the 2005 European Forum held in Alpbach, Austria. ... Also see: 2002 (number). ... This is a list of Nobel Prize laureates in Chemistry from 1901 to 2006. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz) NMR spectrometer being loaded with a sample. ...


Solids

This technique complements biopolymer X-ray crystallography in that it is frequently applicable to biomolecules in a liquid or liquid crystal phase, whereas crystallography, as the name implies, is performed on molecules in a solid phase. Though nuclear magnetic resonance is used to study solids, extensive atomic-level biomolecular structural detail is especially challenging to obtain in the solid state. There is no signal averaging by thermal motion in the solid state, where molecules are held still, each in a slightly different electronic environment, giving a different signal. This variation in electronic environment lowers resolution greatly and makes interpretation more difficult. Raymond Andrew was a pioneer in the development of high-resolution solid-state nuclear magnetic resonance. He introduced the magic angle spinning (MAS) technique and allowed for an increase in resolution by several orders of magnitude. In MAS, the sample is averaged by spinning it at several kilohertz. X-ray crystallography, also known as single-crystal X-ray diffraction, is the oldest and most common crystallographic method for determining the structure of molecules. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... For other uses, see Liquid (disambiguation). ... Schlieren texture of Liquid Crystal nematic phase Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal. ... This box:      For other uses, see Solid (disambiguation). ... Solid-state 900 MHz (21. ... In physics, magic angle spinning (MAS) is a technique often used to perform solid-state NMR experiments. ...


Alex Pines together with John S. Waugh revolutionized the area with the introduction of the cross-polarization technique in order to enhance low abundance and sensitivity nuclei. Alexander Pines (born 1945) is the Glenn Seaborg Professor of Chemistry at the University of California, Berkeley, and Principal Investigator in the Materials Sciences Division of the Lawrence Berkeley National Laboratory. ... John S. Waugh is a chemist and Institute Professor at the Massachusetts Institute of Technology. ...


Sensitivity

Because the intensity of nuclear magnetic resonance signals and, hence, the sensitivity of the technique depends on the strength of the magnetic field the technique has also advanced over the decades with the development of more powerful magnets. Advances made in audio-visual technology have also improved the signal-generation and processing capabilities of newer machines.


The sensitivity of nuclear magnetic resonance signals is also dependent—as noted above—on the presence of a magnetically-susceptible nuclide and, therefore, either on the natural abundance of such nuclides or on the ability of the experimentalist to artificially enrich the molecules, under study, with such nuclides. The most abundant naturally-occurring isotopes of hydrogen and phosphorus—for instance—are both magnetically susceptible and readily useful for nuclear magnetic resonance spectroscopy. In contrast, carbon and nitrogen have useful isotopes but which occur only in very low natural abundance.


Other limitations on sensitivity arise from the quantum-mechanical nature of the phenomenon. For quantum states separated by energy equivalent to radio frequencies, thermal energy from the environment causes the populations of the states to be close to equal. Since incoming radiation is equally likely to cause stimulated emission (a transition from the upper to the lower state) as absorption, the NMR effect depends on an excess of nuclei in the lower states. Several factors can reduce sensitivity, including

  • Increasing temperature, which evens out the population of states. Conversely, low temperature NMR can sometimes yield better results than room-temperature NMR, providing the sample remains liquid.
  • Saturation of the sample with radio energy. This manifests itself in both CW and pulsed NMR, the first by using too much continuous power, and the second by pulsing frequently without allowing time for the nuclei to return to thermal equilibrium. For nuclei such as 29Si this is a serious problem as the relaxation time is measured in seconds.
  • Non-magnetic effects, such as electric-quadrupole coupling of spin-1 and spin-3/2 nuclei with their local environment, which broaden and weaken absorption peaks. 14N, a very common spin-1 nucleus, is difficult to study for this reason. High resolution NMR instead probes molecules using the rarer Nitrogen 15N isotope, which has spin-½.

Schematic quadrupole magnet(four-pole) used to focus particle beams in a particle accelerator. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ...

Isotopes

Many chemical elements can be used for NMR analysis. [1]

  • 1H, the most commonly used, very useful. Highly abundant, the most sensitive nucleus apart from tritium. Narrow chemical shift, but sharp signals. In particular, the 1H signal is that used in magnetic resonance imaging.
  • 2H, commonly used in the form of deuterated solvents to avoid interference of solvents in measurement of 1H. Rarely used in NMR measurents themselves, due to low resolution and low sensitivity; mainly utilized in determining of effectiveness of chemical deuteration.
  • 3He, very sensitive. Low percentage in natural helium, has to be enriched. Used mainly in studies of endohedral fullerenes.
  • 13C, commonly used. Low percentage in natural carbon, therefore spectrum acquisition takes a long time. Frequently used for labeling of compounds in synthetic and metabolic studies. Has low sensitivity and wide chemical shift, yields sharp signals. Low percentage makes it useful by preventing spin-spin couplings and makes the spectrum appear less crowded.
  • 15N, relatively commonly used. Can be used for labeling compounds. Nucleus very insensitive but yields sharp signals. Low percentage in natural nitrogen together with low sensitivity requires high concentrations or expensive isotope enrichment.
  • 14N, medium sensitivity nucleus with wide chemical shift. Its large quadrupole moment interferes in acquisition of high resolution spectra, limiting usefulness to smaller molecules.
  • 19F, relatively commonly measured. Sensitive, yields sharp signals, has wide chemical shift.
  • 31P, 100% of natural phosphorus. Medium sensitivity, wide chemical shift range, yields sharp lines. Used in biochemical studies.
  • 17O, low sensitivity and very low natural abundance.
  • 10B, lower sensitivity than 11B. Use quartz tubes, as borosilicate glass interferes with measurement.
  • 11B, more sensitive than 10B, yields sharper signals. Use quartz tubes, as borosilicate glass interferes with measurement.
  • 35Cl and 37Cl, broad signal. 35Cl significantly more sensitive, preferred over 37Cl despite its slightly broader signal. Organic chlorides yield very broad signals, use limited to inorganic and ionic chlorides and very small organic molecules.
  • 43Ca, used in biochemistry to study calcium binding to DNA, proteins, etc. Moderately sensitive, very low natural abundance, has to be enriched.
  • 195Pt, used in studies of catalysts and complexes.
  • Other nuclei, usually used in the studies of their complexes and chemical binding, or to detect presence of the element: 6Li, 7Li, 9Be, 19F, 21Ne, 23Na, 25Mg, 27Al, 29Si, 31P, 33S, 39K, 40K, 41K, 45Sc, 47Ti, 49Ti, 50V, 51V, 53Cr, 55Mn, 57Fe, 59Co, 61Ni, 63Cu, 65Cu, 67Zn, 69Ga, 71Ga, 73Ge, 77Se, 81Br, 87Rb, 87Sr, 95Mo, 109Ag, 113Cd, 125Te, 127I, 133Cs, 135Ba, 137Ba, 139La, 183W, 199Hg.

This article is about the chemistry of hydrogen. ... Tritium (symbol T or ³H) is a radioactive isotope of hydrogen. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Endohedral Fullerenes are fullerenes that have incorporated in their inner sphere atoms, ions or clusters. ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Schematic quadrupole magnet(four-pole) used to focus particle beams in a particle accelerator. ... Distinguished from fluorene and fluorone. ... General Name, symbol, number phosphorus, P, 15 Chemical series nonmetals Group, period, block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... This article is about the chemical element and its most stable form, or dioxygen. ... For other uses, see Boron (disambiguation). ... Hello Please take a look at my one of a kind custom pyrex glass dildos made in upstate Ny all hand sculpted not machined. ... For other uses, see Boron (disambiguation). ... Hello Please take a look at my one of a kind custom pyrex glass dildos made in upstate Ny all hand sculpted not machined. ... General Name, symbol, number chlorine, Cl, 17 Chemical series nonmetals Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... For other uses, see Calcium (disambiguation). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... It has been suggested that this article or section be merged into Catalysis. ...

Applications

Medicine

The use of nuclear magnetic resonance best known to the general public is in magnetic resonance imaging for medical diagnosis, however, it is also widely used in chemical studies, notably in NMR spectroscopy such as proton NMR and carbon-13 NMR. Biochemical information can also be obtained from living tissue (e.g human brain tumours) with the technique known as in vivo magnetic resonance spectroscopy. MRI redirects here. ... Nuclear magnetic resonance spectroscopy most commonly known as NMR spectroscopy is the name given to the technique which exploits the magnetic properties of certain nuclei. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz, 18. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz, 18. ... This article is about modern humans. ... Human brain In animals, the brain (enkephale) (Greek for in the skull), is the control center of the central nervous system, responsible for behavior. ... Tumor (American English) or tumour (British English) originally means swelling, and is sometimes still used with that meaning. ... In vivo (that is in the living organism) magnetic resonance spectroscopy is a specialised technique associated with magnetic resonance imaging (MRI). ...


These studies are possible because nuclei are surrounded by orbiting electrons, which are also spinning charged particles such as magnets and, so, will partially shield the nuclei. The amount of shielding depends on the exact local environment. For example, a hydrogen bonded to an oxygen will be shielded differently than a hydrogen bonded to a carbon atom. In addition, two hydrogen nuclei can interact via a process known as spin-spin coupling, if they are on the same molecule, which will split the lines of the spectra in a recognizable way. For other uses, see Magnet (disambiguation). ... This article is about the chemical element and its most stable form, or dioxygen. ... This article is in need of attention. ...


Chemistry

By studying the peaks of nuclear magnetic resonance spectra, skilled chemists can determine the structure of many compounds. It can be a very selective technique, distinguishing among many atoms within a molecule or collection of molecules of the same type but which differ only in terms of their local chemical environment.


By studying T2* information a chemist can determine the identity of a compound by comparing the observed nuclear precession frequencies to known frequencies. Further structural data can be elucidated by observing spin-spin coupling, a process by which the precession frequency of a nucleus can be influenced by the magnetization transfer from nearby nuclei. Spin-spin coupling is most commonly observed in NMR involving common isotopes, such as Hydrogen-1 (HNMR).


T2 information can give information about dynamics and molecular motion.


Because the nuclear magnetic resonance timescale is rather slow, compared to other spectroscopic methods, changing the temperature of a T2* experiment can also give information about fast reactions, such as the Cope rearrangement or about structural dynamics, such as ring-flipping in cyclohexane. It has been suggested that Cope reaction be merged into this article or section. ... Cyclohexane is a cycloalkane with the molecular formula C6H12. ...


An example of nuclear magnetic resonance being used in the determination of a structure is that of buckminsterfullerene. This now famous form of carbon has 60 carbon atoms forming a sphere. The carbon atoms are all in identical environments and so should see the same internal H field. Unfortunately, buckminsterfullerene contains no hydrogen and so 13C nuclear magnetic resonance has to be used. 13C spectra require longer acquisition times since carbon-13 is not the common isotope of carbon (unlike hydrogen, where 1H is the common isotope). However, in 1990 the spectrum was obtained by R. Taylor and co-workers at the University of Sussex and was found to contain a single peak, confirming the unusual structure of C60.[2] Buckminsterfullerene (C60) Fullerenes are molecules composed entirely of carbon, taking the form of a hollow sphere, ellipsoid, or tube. ... The University of Sussex (also known colloquially as Sussex Uni) is an English campus university which is situated next to the East Sussex village of Falmer, and is four miles from Brighton. ...


Non-destructive testing

Nuclear magnetic resonance is extremely useful for analyzing samples non-destructively. Radio waves and static magnetic fields easily penetrate many types of matter and anything that is not inherently ferromagnetic. For example, various expensive biological samples, such as nucleic acids, including RNA and DNA, or proteins, can be studied using nuclear magnetic resonance for weeks or months before using destructive biochemical experiments. This also makes nuclear magnetic resonance a good choice for analyzing dangerous samples. Ferromagnetism is the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. ... Highly simplified diagram of a double-stranded nucleic acid. ... For other uses, see RNA (disambiguation). ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ...


Data acquisition in the petroleum industry

Another use for nuclear magnetic resonance is data acquisition in the petroleum industry for petroleum and natural gas exploration and recovery. A borehole is drilled into rock and sedimentary strata into which nuclear magnetic resonance logging equipment is lowered. Nuclear magnetic resonance analysis of these boreholes is used to measure rock porosity, estimate permeability from pore size distribution and identify pore fluids (water, oil and gas). These instruments are typically low field NMR spectrometers. Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer. ... The oil industry is a type of industry which brings petroleum to a financial market. ... Petro redirects here. ... For other uses, see Natural gas (disambiguation). ... Water borehole in northern Uganda A borehole is a deep and narrow shaft in the ground used for abstraction of fluid or gas reserves below the earths surface. ... Low field NMR is a branch of nuclear magnetic resonance (NMR), that is also related to Earths field NMR. Categories: | ...


Process control

NMR has now entered the arena of real-time process control and process optimization in oil refineries and petrochemical plants. Two different types of NMR analysis are utilized to provide real time analysis of feeds and products in order to control and optimize unit operations. Time-domain NMR (TD-NMR) spectrometers operating at low field (2-20 MHz for 1H) yield free induction decay data that can be used to determine absolute hydrogen content values, rheological information, and component composition. These spectrometers are used in mining, polymer production, cosmetics and food manufacturing as well as coal analysis. High resolution FT-NMR spectrometers operating in the 60 MHz range with shielded permanent magnet systems yield high resolution 1H NMR spectra of refinery and petrochemical streams. The variation observed in these spectra with changing physical and chemical properties is modelled utilizing chemometrics to yield predictions on unknown samples. The prediction results are provided to control systems via analogue or digital outputs from the spectrometer. Process control is a statistics and engineering discipline that deals with architectures, mechanisms, and algorithms for controlling the output of a specific process. ... Process Optimization is the practice of making changes or adjustments to a process, to get results. ... View of the Shell/Valero Martinez oil refinery An oil refinery is an industrial process plant where crude oil is processed and refined into useful petroleum products. ... Petrochemicals are chemical products made from raw materials of petroleum (hydrocarbon) origin. ... A free induction decay (FID) curve is generated as excited nuclei relax in an NMR machine. ... This article is about the chemistry of hydrogen. ... Rheometry (from the Greek word rheos meaning stream) generically refers to the experimental techniques used to determine the rheological properties of materials, that is the quantitative and qualitative relationships between deformations and stresses, respectively their derivatives. ... This article is about mineral extractions. ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... Make-up redirects here. ... Coal Example chemical structure of coal Coal is a fossil fuel formed in ecosystems where plant remains were saved by water and mud from oxidization and biodegradation. ... A refinery is composed of a group of chemical engineering unit processes and unit operations used for refining certain materials or converting raw material into products of value. ... Petrochemicals are chemical products made from raw materials of petroleum (hydrocarbon) origin. ... Chemometrics is the application of mathematical or statistical methods to chemical data. ... A control system is a device or set of devices that manage the behavior of other devices. ...


Earth's field NMR

In the Earth's magnetic field, NMR frequencies are in the audio frequency range. EFNMR is typically stimulated by applying a relatively strong dc magnetic field pulse to the sample and, following the pulse, analysing the resulting low frequency alternating magnetic field that occurs in the earth's magnetic field due to free induction decay (FID). These effects are exploited in some types of magnetometers, EFNMR spectrometers, and MRI imagers[[2]]. Their inexpensive portable nature makes these instruments valuable for field use and for teaching. The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... A free induction decay (FID) curve is generated as excited nuclei relax in an NMR machine. ... A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ...


Magnetometers

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. A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ... A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...


Makers of NMR equipment

Major NMR instrument makers include Bruker, General Electric, JEOL, Kimble Chase, Philips, Siemens AG, Varian, Inc. and SpinCore Technologies, Inc. Bruker originally started as a German company specialized in nuclear magnetic resonance (NMR), but has evolved into an international company with products covering a gamut of biological, chemical and medical fields. ... “GE” redirects here. ... A manufacturer of scanning electron microscopes, transmission electron microscopes, electron microprobes, electron beam lithography systems. ... Kimble Chase, short for Kimble Chase Life Science and Research Products LLC, is headquartered in Vineland, NJ. Kimble Chase supplies laboratory equipment and consumables for analytical chemists in the pharmaceutical, scientific, clinical, educational, environmental, industrial, and agricultural markets. ... Philips HQ in Amsterdam Koninklijke Philips Electronics N.V. (Royal Philips Electronics N.V.), usually known as Philips, (Euronext: PHIA, NYSE: PHG) is one of the largest electronics companies in the world, founded and headquartered in the Netherlands. ... Siemens redirects here. ... Varian, Inc. ...


See also

Pacific Northwest National Laboratorys high magnetic field (800 MHz, 18. ... In nuclear magnetic resonance (NMR), the chemical shift describes the dependence of nuclear magnetic energy levels on the electronic environment in a molecule. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a technique for studying chemical species that have one or more unpaired electrons, such as organic and inorganic free radicals or inorganic complexes possessing a transition metal ion. ... Ferromagnetic resonance, or FMR, is a spectroscopic technique to probe the magnetization of ferromagnetic materials. ... A free induction decay (FID) curve is generated as excited nuclei relax in an NMR machine. ... In physics, the gyromagnetic ratio (also sometimes known as the magnetogyric ratio in other disciplines) of a particle or system is the ratio of its magnetic dipole moment to its angular momentum. ... In vivo (that is in the living organism) magnetic resonance spectroscopy is a specialised technique associated with magnetic resonance imaging (MRI). ... J-coupling (also called indirect dipole dipole coupling) is the coupling between two nuclear spins due to the influence of bonding electrons on the magnetic field running between the two nuclei. ... The Larmor equation in physics, named for Irish physicist Joseph Larmor, is ω = γ B The equation describes the relationship between the angular frequency ω of a precessing proton, and the strength of the magnetic field B. Here γ is the gyromagnetic ratio, a constant unique to the nucleus of... The Larmor formula is used to calculate the power radiated by a nonrelativistic electron as it accelerates. ... Larmor precession refers to the precession of the magnetic moments of electrons or atomic nucleii in atoms around the direction of an external magnetic field. ... Low field NMR is a branch of nuclear magnetic resonance (NMR), that is also related to Earths field NMR. Categories: | ... In physics, magic angle spinning (MAS) is a technique often used to perform solid-state NMR experiments. ... MRI redirects here. ... A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ... The backbone dihedral angles are included in the molecular model of a protein. ... Nuclear magnetic resonance spectroscopy most commonly known as NMR spectroscopy is the name given to the technique which exploits the magnetic properties of certain nuclei. ... Nuclear Quadrupole Resonance or NQR is a technique related to nuclear magnetic resonance (NMR) which is used to detect atoms whose nuclei have a nuclear quadrupole moment, such as 14N, 35Cl and 63Cu. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz) NMR spectrometer being loaded with a sample. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz, 18. ... The Rabi cycle is a term from the field of quantum optics. ... Relaxometry refers to the study and/or measurement of relaxation variables in Nuclear Magnetic Resonance and Magnetic Resonance Imaging. ... This article or section is in need of attention from an expert on the subject. ... Solid-state NMR (SSNMR) spectroscopy is a kind of nuclear magnetic resonance (NMR) spectroscopy, characterized by the presence of anisotropic (directionally dependent) interactions. ... The Zeeman effect (IPA ) is the splitting of a spectral line into several components in the presence of a magnetic field. ...

References

  1. ^ Rabi, I. I., Zacharias, J. R., Millman, S. and Kusch, P. (1938). A New Method of Measuring Nuclear Magnetic Moment. Physical Review 53, 318-318
  2. ^ Taylor, Roger & Hare, Jonathan P.; Abdul-Sada, Ala'a K.; Kroto, Harold W (1990), "Isolation, separation and characterization of the fullerenes C60 and C70: the third form of carbon", Journal of the Chemical Society, Chemical Communications 20: 1423-5
  1. Martin, G.E; Zekter, A.S., ‘’Two-Dimensional NMR Methods for Establishing Molecular Connectivity’’; VCH Publishers, Inc: New York, 1988 (p.59)
  2. Akitt, J.W.; Mann, B.E., ‘’NMR and Chemistry’’; Stanley Thornes: Cheltenham, UK, 2000. (p273)
  3. Akitt, J.W.; Mann, B.E., ‘’NMR and Chemistry’’; Stanley Thornes: Cheltenham, UK, 2000. (p287)
  4. Hornak, Joseph P. The Basics of NMR
  5. J. Keeler, Understanding NMR Spectroscopy
  6. Wuthrich, Kurt NMR of Proteins and Nucleic Acids Wiley-Interscience, New York, NY USA 1986.
  7. Tyszka, J. M. & Fraser, S. E. & Jacobs, R. E. (2005). Magnetic resonance microscopy: recent advances and applications. Current Opinion in Biotechnology, 16(1):93-99.

Current Opinion in Biotechnology [ISSN 0958-1669] is a review journal launched in 1990 and is one in a series of ten Current Opinion life-sciences journals published by Elsevier. ...

External links


  Results from FactBites:
 
Nuclear Magnetic Resonance (523 words)
When the nuclear magnetic moment associated with a nuclear spin is placed in an external magnetic field, the different spin states are given different magnetic potential energies.
Note that the electron spin magnetic moment is opposite to the electron spin while the proton spin magnetic moment is in the direction of the proton spin.
The Larmor frequency of the electron spin is in the microwave region of the electromagnetic spectrum and is used in electron spin resonance.
Nuclear magnetic resonance (1591 words)
Nuclear magnetic resonance (NMR) is a physical phenomenon described independently by Felix Bloch and Edward Mills Purcell[?] in 1946 both of whom shared the Nobel Prize in physics in 1952 for their discovery.
NMR is used as a spectroscopy technique to obtain physical, chemical, and electronic properties of molecules.
The external magnetic field into which the sample material is placed exerts a torque on the nucleus that acts to align the nuclear magnetic field with the external field; however, since the nucleus is spinning, it will precess about the magnetic field instead of aligning with it.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m