Pacific Northwest National Laboratory's high magnetic field (800 MHz, 18. The Pacific Northwest National Laboratory (PNNL is one of nine United States Department of Energy (DOE multiprogram national laboratories. 8 T) NMR spectrometer being loaded with a sample. The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic

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. The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom NMR also commonly refers to a family of scientific methods that exploit nuclear magnetic resonance to study molecules. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by

All nuclei that contain odd numbers of protons or neutrons have an intrinsic magnetic moment and angular momentum. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. In Physics, Astronomy, Chemistry, and Electrical engineering, the term magnetic moment of a system (such as a loop of Electric current In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position 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. A hydrogen atom is an atom of the chemical element Hydrogen. The electrically neutral Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Carbon-13 ( 13C) is a natural stable Isotope of Carbon and one of the Environmental isotopes. g. ¹¹³Cd, ¹⁵N, ¹⁴N ¹⁹F, ³¹P, ¹⁷O, ²⁹Si, ¹⁰B, ¹¹B, ²³Na, ³⁵Cl, ¹⁹⁵Pt) can also be observed. Cadmium (ˈkædmiəm is a Chemical element with the symbol Cd and Atomic number 48 Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 Phosphorus, (ˈfɒsfərəs is the Chemical element that has the symbol P and Atomic number 15 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78

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. In Physics, Larmor precession (named after Joseph Larmor) refers to the Precession of the Magnetic moments of Electrons atomic

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. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In Mathematics, two Vectors are orthogonal if they are Perpendicular, i 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 spectral resolution, details of which are described by the chemical shift and the Zeeman effect. Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei The spectral resolution or resolving power of a Spectrograph, or more generally of a Frequency spectrum, is a measure of its power to resolve features 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 (ˈzeɪmɑːn is the splitting of a Spectral line into several components in the presence of a static Magnetic field.

NMR phenomena are also utilized in low field NMR and Earth's field NMR spectrometers, and some kinds of magnetometers. Low field NMR is a branch of Nuclear magnetic resonance (NMR that is also related to Earth's field NMR. Nuclear magnetic resonance (NMR in the Geomagnetic field is conventionally referred to as Earth's field NMR (EFNMR. A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument

History

Discovery

Nuclear magnetic resonance was first described and measured in molecular beams by Isidor Rabi in 1938. Isidor Isaac Rabi ( July 29, 1898 &ndash January 11, 1988) Galician born Physicist, and Nobel laureate. ^[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. Year 1946 ( MCMXLVI) was a Common year starting on Tuesday (link will display full 1946 calendar of the Gregorian calendar. This page addresses only the Swiss physicist for the man accused of espionage see Felix Bloch (diplomatic officer Felix Bloch ( October 23 Edward Mills Purcell ( August 30, 1912 &ndash March 7, 1997) was an American physicist who shared the 1952 Nobel Prize for Physics The Nobel Prize in Physics (Nobelpriset i fysik is awarded once a year by the Royal Swedish Academy of Sciences. 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. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including Ernest Lawrence's laboratory at UC Berkeley now known as Lawrence Berkeley National Laboratory, was also known as the 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.

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. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz 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.

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. Analytical chemistry is the study of the Chemical composition of natural and artificial Materials. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as

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. This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin The overall spin of the nucleus is determined by the spin quantum number I. In Atomic physics, the spin quantum number is a Quantum number that parameterizes the intrinsic Angular momentum (or spin angular momentum or simply If the number of both the protons and neutrons in a given isotope are even then I = 0, i. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides In Mathematics, the parity of an object states whether it is even or odd 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. An atomic orbital is a Mathematical function that describes the wave-like behavior of an electron in an atom In Particle physics, fermions are particles which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In other cases, however, the overall spin is non-zero. For example ²⁷Al has an overall spin I = 5/2.

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

where the proportionality constant, γ, is the gyromagnetic ratio. 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 It is this magnetic moment that is exploited in NMR.

Electron spin resonance is a related technique which exploits the spin of electrons instead of nuclei. Electron paramagnetic resonance (EPR or electron spin resonance (ESR Spectroscopy is a technique for studying Chemical species that have one or more unpaired The basic principles are otherwise similar.

Values of spin angular momentum

The angular momentum associated with nuclear spin is quantized. In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position 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. In Atomic physics, the magnetic quantum number is the third of a set of Quantum numbers (the Principal quantum number, the Azimuthal quantum number Hence for any given nucleus, there is a total of 2I+1 angular momentum states.

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

where is Planck's reduced constant. The Planck constant (denoted h\ is a Physical constant used to describe the sizes of quanta.

The z component of the magnetic moment is simply

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

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:

where the magnetic field has been oriented along the z axis. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges

Hence

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. 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 If γ is positive (true for most isotopes) then m = ½ is the lower energy state.

The energy difference between the two states is

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. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. The energy of a photon is E = hν, where ν is its frequency. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Hence absorption will occur when

These frequencies typically correspond to the radio frequency range of the electromagnetic spectrum. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies

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. If the nucleus is more shielded, then it will be shifted upfield (lower chemical shift) and if it is more deshielded, then it will be shifted downfield (higher chemical shift).

Unless the local symmetry is particularly high, the shielding effect depends on the orientation of the molecule with respect to the external field. Symmetry generally conveys two primary meanings The first is an imprecise sense of harmonious or aesthetically-pleasing proportionality and balance such that it reflects beauty or In solid-state NMR, magic angle spinning is required to average out this orientation dependence. Solid-state NMR ( SSNMR) spectroscopy is a kind of Nuclear magnetic resonance (NMR spectroscopy characterized by the presence of anisotropic (directionally dependent Nuclear magnetic resonance, magic angle spinning (MAS is a technique often used to perform experiments in Solid-state NMR Spectroscopy. This is unnecessary in conventional NMR of molecules in solution since rapid molecular tumbling averages out the anisotropic component of the chemical shift.

Relaxation

For more details on this topic, see Relaxation (NMR). In nuclear magnetic resonance (NMR spectroscopy and magnetic resonance imaging (MRI the term relaxation describes several processes by which nuclear Magnetization

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.

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. In Physics, Larmor precession (named after Joseph Larmor) refers to the Precession of the Magnetic moments of Electrons atomic 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 Fourier Transform NMR, a free induction decay (FID is the observable NMR signal generated by non-equilibrium nuclear spin magnetisation precessing about the In the NMR spectrum, meaning the Fourier transform of the free induction decay, the T₂ time defines the width of the NMR signal. This article specifically discusses Fourier transformation of functions on the Real line; for other kinds of Fourier transformation see Fourier analysis and In Fourier Transform NMR, a free induction decay (FID is the observable NMR signal generated by non-equilibrium nuclear spin magnetisation precessing about the 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.

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. Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by 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 (ˈzeɪmɑːn is the splitting of a Spectral line into several components in the presence of a static Magnetic field. 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. A quantum computer is a device for Computation that makes direct use of distinctively Quantum mechanical Phenomena, such as superposition

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). Signal-to-noise ratio (often abbreviated SNR or S/N) is an Electrical engineering concept also used in other fields (such as scientific Measurements 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). A random walk, sometimes denoted RW, is a Mathematical formalization of a trajectory that consists of taking successive Random steps Hence the overall ratio of the signal to the noise increases as the square-root of the number of spectra measured.

Fourier spectroscopy

Most applications of NMR involve full NMR spectra, that is, the intensity of the NMR signal as a function of frequency. A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. 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). Bandwidth is the difference between the upper and lower Cutoff frequencies of for example a filter, a Communication channel, or a Signal spectrum This article specifically discusses Fourier transformation of functions on the Real line; for other kinds of Fourier transformation see Fourier analysis and A square wave is a kind of Non-sinusoidal waveform, most typically encountered in Electronics and Signal processing. The restricted range of the NMR frequencies made it relatively easy to use RF pulses to excite the entire NMR spectrum.

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. In Physics, Larmor precession (named after Joseph Larmor) refers to the Precession of the Magnetic moments of Electrons atomic This oscillating magnetisation induces a current in a nearby pickup coil, creating an electrical signal oscillating at the NMR frequency. Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of This signal is known as the free induction decay (FID) and contains the sum of the NMR responses from all the excited spins. In Fourier Transform NMR, a free induction decay (FID is the observable NMR signal generated by non-equilibrium nuclear spin magnetisation precessing about the In order to obtain the frequency-domain NMR spectrum (intensity vs. A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. frequency) this time-domain signal (intensity vs. time) must be Fourier transformed. This article specifically discusses Fourier transformation of functions on the Real line; for other kinds of Fourier transformation see Fourier analysis and Fortunately the development of FT-NMR coincided with the development of digital computers and Fast Fourier Transform algorithms. The Cooley-Tukey Algorithm, named after JW 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 The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry.

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. In magnetic resonance spectroscopy, the transfer of Spin polarization from one spin population to another via cross-relaxation is generally called the Overhauser Experiments of the nuclear-Overhauser variety may establish distances between atoms.

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. The Free University of Brussels can refer to either of the following universities in Brussels, Belgium: Université Libre de Bruxelles (French-speaking The Université Libre de Bruxelles (or ULB) is a French -speaking University in Brussels The Vrije Universiteit Brussel is a Flemish University located 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 full calendar of the Gregorian Calendar. The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. 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. Biopolymers are a class of Polymers produced by living organisms Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information Kurt Wüthrich shared the 2002 Nobel Prize in Chemistry for his work in protein nuclear magnetic resonance spectroscopy. Kurt Wüthrich (born October 4, 1938) is a Swiss chemist and Nobel Chemistry laureate. See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. Protein nuclear magnetic resonance spectroscopy (usually abbreviated protein NMR) is a field of Structural biology in which NMR spectroscopy is used

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. X-ray crystallography is a method of determining the arrangement of Atoms within a Crystal, in which a beam of X-rays strikes a crystal and scatters A biomolecule is any organic Molecule that is produced by living Organisms including large Polymeric molecules such as Proteins Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional Liquid, and those of a Solid A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. 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. Solid-state NMR ( SSNMR) spectroscopy is a kind of Nuclear magnetic resonance (NMR spectroscopy characterized by the presence of anisotropic (directionally dependent He introduced the magic angle spinning (MAS) technique and allowed for an increase in resolution by several orders of magnitude. Nuclear magnetic resonance, magic angle spinning (MAS is a technique often used to perform experiments in Solid-state NMR Spectroscopy. In MAS, the sample is spun at several kilohertz around an axis that makes the so-called magic angle with the static magnetic field and the spin interactions are averaged to their isotropic values.

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 is the Glenn T Seaborg Professor of Chemistry at the University of California Berkeley, Senior Scientist in the Materials Sciences Division of the John S Waugh (born 1929 is an American 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. A quadrupole or quadrapole is one of a sequence of configurations of — for example — electric charge or current or gravitational mass that can exist in ideal form but it ¹⁴N, a very common spin-1 nucleus, is difficult to study for this reason. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 High resolution NMR instead probes molecules using the rarer Nitrogen ¹⁵N isotope, which has spin-½. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14

Isotopes

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

• ¹H, the most commonly used, very useful. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Highly abundant, the most sensitive nucleus apart from tritium. Tritium (ˈtɹɪtiəm symbol or, also known as Hydrogen-3) is a radioactive Isotope of Hydrogen. 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. Deuterium, also called heavy hydrogen, is a Stable isotope of Hydrogen with a Natural abundance in the Oceans of Earth Often used in determining the behavior of lipids in lipid membranes and other solids or liquid crystals as it is a relatively non-perturbing label which can selectively replace ¹H. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1
• ³He, very sensitive. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Low percentage in natural helium, has to be enriched. Used mainly in studies of endohedral fullerenes.
• ¹³C, commonly used. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 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. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 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. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Its large quadrupole moment interferes in acquisition of high resolution spectra, limiting usefulness to smaller molecules. A quadrupole or quadrapole is one of a sequence of configurations of — for example — electric charge or current or gravitational mass that can exist in ideal form but it
• ¹⁹F, relatively commonly measured. Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 Sensitive, yields sharp signals, has wide chemical shift.
• ³¹P, 100% of natural phosphorus. Phosphorus, (ˈfɒsfərəs is the Chemical element that has the symbol P and Atomic number 15 Medium sensitivity, wide chemical shift range, yields sharp lines. Used in biochemical studies.
• ¹⁷O, low sensitivity and very low natural abundance. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the
• ¹⁰B, lower sensitivity than ¹¹B. Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. Use quartz tubes, as borosilicate glass interferes with measurement. Borosilicate glass is a type of Glass with the main glass-forming constituents Silica and Boron oxide.
• ¹¹B, more sensitive than ¹⁰B, yields sharper signals. Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. Use quartz tubes, as borosilicate glass interferes with measurement. Borosilicate glass is a type of Glass with the main glass-forming constituents Silica and Boron oxide.
• ³⁵Cl and ³⁷Cl, broad signal. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and 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. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Moderately sensitive, very low natural abundance.
• ¹⁹⁵Pt, used in studies of catalysts and complexes. Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst
• 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.

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. Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei Proton NMR (also Hydrogen-1 NMR, or 1HNMR) is the application of Nuclear magnetic resonance in NMR spectroscopy Biochemical information can also be obtained from living tissue (e. g human brain tumours) with the technique known as in vivo magnetic resonance spectroscopy. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain See also Cancer A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells (termed neoplastic In vivo (that is 'in the living organism' magnetic resonance spectroscopy (MRS 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. A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field. 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. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 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. In Quantum mechanics, the procedure of constructing Eigenstates of total angular momentum out of eigenstates of separate angular momenta is called angular momentum coupling

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. The Cope rearrangement is an extensively studied Organic reaction involving the [33]-sigmatropic rearrangement of 15-dienes. Cyclohexane is a Cycloalkane with the Molecular formula C 6 H 12

An example of nuclear magnetic resonance being used in the determination of a structure is that of buckminsterfullerene. "C60" and "C-60" redirect here For other uses see C60 (disambiguation. 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. The University of Sussex is a British Campus university which is situated next to the East Sussex village of Falmer, and is from Brighton ^[2]

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. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it 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. A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl This also makes nuclear magnetic resonance a good choice for analyzing dangerous samples.

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. Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer The petroleum industry includes the global processes of exploration, extraction, refining, transporting (often by Oil tankers and pipelines Petroleum ( L petroleum, from Greek πετρέλαιον, lit Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, A borehole is drilled into rock and sedimentary strata into which nuclear magnetic resonance logging equipment is lowered. A borehole is the generalised term for any narrow shaft drilled in the ground either vertically or horizontally 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. Low field NMR is a branch of Nuclear magnetic resonance (NMR that is also related to Earth's field NMR.

Process control

NMR has now entered the arena of real-time process control and process optimization in oil refineries and petrochemical plants. Process control is a Statistics and Engineering discipline that deals with Architectures mechanisms and Algorithms for controlling Process optimization is the discipline of adjusting a process so as to optimize some specified set of parameters without violating some constraint An oil refinery is an industrial Process plant where Crude oil is processed and refined into more useful Petroleum products, such as Gasoline Petrochemicals are chemical products made from raw materials of Petroleum or other Hydrocarbon origin 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. In Fourier Transform NMR, a free induction decay (FID is the observable NMR signal generated by non-equilibrium nuclear spin magnetisation precessing about the Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 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 These spectrometers are used in mining, polymer production, cosmetics and food manufacturing as well as coal analysis. Mining is the extraction of valuable Minerals or other geological materials from the earth usually (but not always from an Ore body A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Food is any substance usually composed primarily of Carbohydrates Fats water and/or Proteins that can be eaten or drunk by an 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. A refinery is composed of a group of Chemical engineering unit processes and Unit operations used for Refining certain materials or converting Petrochemicals are chemical products made from raw materials of Petroleum or other Hydrocarbon origin The variation observed in these spectra with changing physical and chemical properties is modelled utilizing chemometrics to yield predictions on unknown samples. Chemometrics is the application of mathematical or statistical methods to chemical data The prediction results are provided to control systems via analogue or digital outputs from the spectrometer. A control system is a device or set of devices to manage command direct or regulate the behavior of other devices or systems

Earth's field NMR

In the Earth's magnetic field, NMR frequencies are in the audio frequency range. Earth 's magnetic field (and the surface magnetic field) is approximately a Magnetic dipole, with one pole near the North pole (see 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). Nuclear magnetic resonance (NMR in the Geomagnetic field is conventionally referred to as Earth's field NMR (EFNMR. In Fourier Transform NMR, a free induction decay (FID is the observable NMR signal generated by non-equilibrium nuclear spin magnetisation precessing about the These effects are exploited in some types of magnetometers, EFNMR spectrometers, and MRI imagers[[2]]. A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument Their inexpensive portable nature makes these instruments valuable for field use and for teaching.

Magnetometers

Various magnetometers use NMR effects to measure magnetic fields, including proton magnetometers or proton precession magnetometers (PPM), and Overhauser magnetometers. The proton magnetometer, also known as the proton precession magnetometer (PPM uses the principle of Earth's field nuclear magnetic resonance ( EFNMR A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument See also Earth's field NMR. Nuclear magnetic resonance (NMR in the Geomagnetic field is conventionally referred to as Earth's field NMR (EFNMR.

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 and has evolved into a worldwide company with an extensive portfolio of products for the biological is a notable manufacturer of Electron microscopes and other scientific instruments Kimble Chase, short for Kimble Chase Life Science and Research Products LLC is headquartered in Vineland NJ. Koninklijke Philips Electronics NV ( Royal Philips Electronics Inc. Varian Inc ( is one of the largest manufacturers of Scientific instruments for the scientific industry they have offerings over the whole range of chemical analysis equipment

See also

References

1. ^ Rabi, I. In Physics, Larmor precession (named after Joseph Larmor) refers to the Precession of the Magnetic moments of Electrons atomic Low field NMR is a branch of Nuclear magnetic resonance (NMR that is also related to Earth's field NMR. Nuclear magnetic resonance, magic angle spinning (MAS is a technique often used to perform experiments in Solid-state NMR Spectroscopy. A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument Molecular modelling is a collective term that refers to theoretical methods and computational techniques to model or mimic the behaviour of Molecules The techniques Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei Nuclear quadrupole resonance or NQR is a technique related to nuclear magnetic resonance ( NMR) Protein nuclear magnetic resonance spectroscopy (usually abbreviated protein NMR) is a field of Structural biology in which NMR spectroscopy is used Proton NMR (also Hydrogen-1 NMR, or 1HNMR) is the application of Nuclear magnetic resonance in NMR spectroscopy In Physics, the Rabi cycle is the cyclic behaviour of a Two-state quantum system in the presence of an oscillatory driving field Relaxometry refers to the study and/or measurement of relaxation variables in Nuclear Magnetic Resonance and Magnetic Resonance Imaging. In nuclear magnetic resonance (NMR spectroscopy and magnetic resonance imaging (MRI the term relaxation describes several processes by which nuclear Magnetization Solid-state NMR ( SSNMR) spectroscopy is a kind of Nuclear magnetic resonance (NMR spectroscopy characterized by the presence of anisotropic (directionally dependent The Zeeman effect (ˈzeɪmɑːn is the splitting of a Spectral line into several components in the presence of a static Magnetic field. 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 is a series of review journals published by Elsevier on various subjects of biology

External links

• Richard Ernst, NL - Developer of Multdimensional NMR techniques Freeview video provided by the Vega Science Trust.
• 'An Interview with Kurt Wuthrich' 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").
• Acronyms, Abbreviations and Initialisms - Nuclear Magnetic Resonance
• A free interactive simulation of NMR principles
• Bionmr.com - discussion of NMR applications in biological systems
• NMRWiki.ORG NMR resource you can edit
• The International Society of Magnetic Resonance
• AUREMOL (Universitaet Regensburg)
• NMR processing software from ACD/Labs for 1D and 2D NMR spectra. DB interface available.
• NMR Prediction software ACD/NMR Predictors
• Automated elucidation of chemical structures ACD/Structure Elucidator
• NMR simulation software QSim
• Free software for simulation of spin coupled multiplets and DNMR spectra WINDNMR-Pro
• NMR processing software NMRPipe
• BMRB BioMagResBank - A repository for experimental data from NMR spectroscopy of proteins, peptides, nucleic acids and small biomolecules.
• RMN - An NMR data processing program for the Macintosh.
• Applications of Time-Domain NMR in Process Control
• Applications of High Resolution FT-NMR in Real-Time Process Control
• HWB-NMR Henry Wellcome Building for Biomolecular NMR, Birmingham, UK.
• CARA - Computer Aided Resonance Assignment, freeware, developed at the group of Prof. Kurt Wüthrich
• CCPN - The Collaborative Computing Project for NMR, based at the University of Cambridge, UK
• Vanderbilt Structural Biology General site for structural biology at Vanderbilt University. NMR, x-ray crystallography, and computational biology all included.
• Janocchio Conformation-dependent coupling and NOE prediction for small molecules.
• Earth's field NMR (EFNMR)
• Animation of NMR spin 1/2 precession
• Article on helium scarcity and potential effects on NMR and MRI communities