In the OSTI Collections: Nuclear Magnetic Resonance

Dr. Watson computer sleuthing scientist

Article Acknowledgement:

Dr. William N. Watson, Physicist

DOE Office of Scientific and Technical Information

 

Alternate Text Placeholder

All of the protons and neutrons in the nucleus of any atom are magnets.  Since the set of protons in a nucleus has its smallest possible energy when the protons are configured in pairs with opposite magnetic alignments, a nucleus with an even number of protons in its lowest-energy state will have its protons’ magnetic fields cancel out.  Likewise, neutrons tend to form pairs with opposite magnetic alignments, so a nucleus with an even neutron number has no net magnetic field from its neutrons in its lowest-energy state.  Thus for a nucleus to exhibit one pair of magnetic poles (north and south) at its minimum energy, it has to have either an odd number of protons, an odd number of neutrons, or both.  Nuclei that do have odd numbers of either protons or neutrons will inevitably be magnets in their lowest-energy state, and will tend to be oriented so that their own magnetic fields align with any others in their environment. 

 

This tendency was discovered by 1938[APS], and was later found to be helpful in determining the compositions, structures, and chemical activities of materials that contain magnetic nuclei.  The way this works depends on several features of matter.    

 

First, the electrons that surround an atom’s nucleus are also magnetic particles.  Every electron and magnetic nucleus thus has its own magnetic field, which is strongest near the particle and weaker further away.  Each particle is affected by the magnetic fields of all the others, and by any other magnetic fields whose origin is outside the atom.  At any particle’s location, all of the other magnetic fields may have different orientations and cancel each other out to some extent; whatever part of the total field is left uncancelled will exert a torque on the magnetic particle if its own magnetic field isn’t precisely aligned in the same direction.  The strength of this torque increases as the angle between the two fields’ directions becomes more perpendicular.  Other torques, e.g. from electrostatic[Wikipedia] or nuclear[Wikipedia] forces, may compete with the magnetic torque and influence the particle’s orientation further. 

 

The energy of a magnetic particle and magnetic field is greater, the more nearly opposite the orientations of the particle and field are.  If an atom, a molecule, or a whole set of molecules in (e.g.) a liquid or solid has a fixed total amount of energy for which different sets of particle orientation are possible, then pairs of particles with different orientations may exchange energy with each other and reorient themselves.  If a system of magnetic particles is given some additional energy from outside in the form of a radio pulse—which consists of electromagnetic fields that oscillate at different frequencies, reinforce each other within the pulse, and cancel each other elsewhere—the system may absorb portions of the radio pulse’s energy as the pulse’s varying magnetic field twists some of the particles toward a single general direction.  Alternatively, the radio pulse might stimulate the system to lose energy if its magnetic field reorients some particles in a different general direction, thus changing the particles’ own magnetic fields so that they instigate small electromagnetic ripples of their own—that is, new radio pulses.  In this case the system adds energy to the original radio pulse instead of absorbing energy from it. 

 

Because of the particles’ quantum-mechanical properties, unless the size of the angle between a particle’s orientation and the total magnetic field from its environment has one of a few specific values, that angle’s size cannot remain constant for any length of time.  How much energy the particle-and-field system has at any of the stable angular sizes is proportional to the strength of the magnetic field, which depends on the field’s sources.  For example, a nucleus with no electrons around it, oriented in a particular way in the field of a strong external magnet, will have a particular energy.  But a similarly located nucleus in an atom with electrons may have a different environmental magnetic field, namely the sum of the external field and the fields of all the electrons around the nucleus.  In this case the energy of the nucleus+field may be different, even if angle between the nucleus and external field is the same.  So if identical radio pulses in the same magnetic field were applied to both the lone nucleus and the nucleus in the atom, different amounts of energy might be absorbed or emitted from the pulses.  Still other amounts of energy could be absorbed or emitted if the same pulses were instead applied to a molecule of many atoms and nuclei in the same external field.  In this case the magnetic field at any one nucleus would be the sum of the external magnet’s field, the magnetic fields of all the atoms’ electrons, and the fields of the other atoms’ nuclei; the nucleus’ orientation may also be further affected electrically, not magnetically, by asymmetric neighboring-electron distributions, if the distribution of its own protons is asymmetric enough.  The different patterns of the radio pulses’ energy changes would provide clues about whether a lone nucleus, single atom, or multiatom molecule had interacted with each pulse. 

 

The quantum physics of electromagnetic waves is such that the energy changes would be associated with particular frequencies in each radio pulse.  Each quantum of energy absorbed or emitted by either particle system would affect the radio pulse’s spectrum at a frequency proportional to the quantum’s energy.[Wikipedia]  Radio pulse components with frequencies that don’t match an energy difference between a particle system’s stable states are unchanged by the system; component frequencies that do match energy differences are resonant frequencies for the system.  Thus the phenomenon of energy emission or absorption related to the reorientation of nuclear magnetic fields is known as nuclear magnetic resonance, or NMR.  It is this effect of magnetic nuclei on the energy of radio pulses that provides information about the properties of materials that contain the nuclei, since the total magnetic field from each nucleus’ environment depends on what kinds of nuclei the material contains, how its different kinds of atoms and their electrons are arranged, and how strong the external magnetic field is at the location of each nucleus.  The resonance’s dependence on external field strength even provides a way to locate nuclei in a material sample.  If an external magnetic field has different strengths at different points of the sample, nuclei interacting with the different-strength fields at those different points—even if the nuclei are of the same type and are surrounded by similar sets of electrons and other nuclei—will absorb and emit waves of different frequencies; the affected frequencies thus provide information about where the nuclei are. 

 

Since its discovery, nuclear magnetic resonance has become a standard way to help determine materials’ compositions, structures, and chemical activities.  The basic problems in using nuclear magnetic resonance this way involve either finding a particular resonance effect on radio waves that yields some desired information about a material, or seeing what a given effect says about the material that produced it.  As an example, the slide presentation “Predictive Modeling in Actinide Chemistry and Catalysis”[SciTech Connect] describes how one research group studied actinide compounds using multiple techniques, one of which was measurement of nuclear magnetic resonance in some of the compounds.  The way radio pulses were affected by passage through the compounds gave the researchers information to work out how their electrons are arranged, which determines how the compounds function as catalysts.  How the strength of the compounds’ effects varied with radiowave frequency for even similar compounds clearly differed, as shown by the slides displaying nuclear magnetic resonance results. 

 

As other recent research reports indicate, nuclear magnetic resonance continues to be used to learn about the atomic structures of many materials, gain insight into how chemical reactions proceed at material surfaces, and better understand how atoms move during various other physical processes.  The reports also show the numerous considerations generally involved in translating the effects of nuclear magnetic resonance into information about the materials that exhibit it. 

 

Top

Separator line

Structure

 

About 80% of the active ingredients used in medicines are solids.  In about 80% of these solids, the atoms can be arranged in more than one way, and each arrangement can have significantly different effects.  Thus knowing how the atoms are actually arranged is important in the exploration of new medicines and in assuring the quality of existing ones.  Since nitrogen atoms are commonly found in the functional portions of organic molecules and, in solids, play an important role in intermolecular bonding, locating the nitrogen atoms in a medicine’s active ingredients would provide very useful clues to the ingredients’ complete atomic arrangements.  As noted above, the set of radio frequencies at which nuclei absorb energy is significantly affected by how other electric charges are distributed near the nuclei, so nuclear magnetic resonance of an active pharmaceutical ingredient’s nitrogen nuclei can provide clues to how those atoms are arranged with respect to the ingredient’s other atoms. 

 

While for many pharmaceutical molecules nitrogen is an important component, hydrogen is even more so.  But while nuclear magnetic resonance of an active ingredient’s hydrogen atoms can show how they’re arranged in the ingredient’s bulk form, the method doesn’t do the same as easily for drugs in the forms actually administered to patients; hydrogen atoms are also common in additional ingredients like binders and fillers, so the magnetic resonance of those atoms obscures that of the active ingredients’ hydrogen.  One way to get around this problem is to locate atoms of elements that aren’t found in the added ingredients.  Electrically charged atoms (ions[Wikipedia]) of chlorine, for example, are absent from drugs’ added ingredients, but exist in many drugs whose active ingredients are synthesized as hydrogen chloride salts.  Observing nuclear magnetic resonance from chlorine ions can thus provide information about those ions’ locations and environments, therefore indicating the atomic arrangement of the active ingredients of drugs that contain them—which, as noted above, significantly affects the ingredients’ pharmaceutical action. 

 

But interpreting the clues provided by the magnetic resonance of nitrogen or chlorine nuclei is problematic.  Nitrogen nuclei come in just two stable isotopes:  nitrogen-15 (seven protons, eight neutrons), which produces a more distinct resonance signal with a smaller frequency range but typically constitutes less than 1% of all the nitrogen in a sample; and the very common nitrogen-14 (seven protons, seven neutrons), which produces a less distinct signal by interacting with waves that have a broader range of frequencies—very broad, unless the electric charges in their neighborhood are distributed very symmetrically.  Chlorine-35, which constitutes about 76% of all stable chlorine atoms, also interacts with radio waves of a broad range of frequencies.  Getting the desired information about how the atoms in drugs or drug components are arranged by observing nuclear magnetic resonance in the nitrogen or chlorine atoms has been largely a matter of designing a suitable sequence of radio pulses to make the resonance effects of energy absorption and emission clearly observable.  At least some pulses directly energize resonance effects, while other pulses reorient appropriate nuclei to produce those effects when energized.  How this was done for nitrogen and chlorine nuclei in drugs is described in the two papers “Natural abundance 14N and 15N solid-state NMR of pharmaceuticals and their polymorphs”[DoE PAGES] and “35Cl dynamic nuclear polarization solid-state NMR of active pharmaceutical ingredients”[DoE PAGES], both published in the journal Physical Chemistry Chemical Physics

 

The exact molecular form a pharmaceutical has when a patient takes it can affect how it starts producing the desired results in his body, possibly accompanied by side effects.  Materials that do nonbiomedical jobs may, as a result of doing them, undergo some side effects themselves, which can change their molecular structures enough to limit how long or well they can do those jobs.  For example, elastic, viscous polymers (“elastomers”[Wikipedia]) do many different jobs that subject them to things like mechanical stress, temperature fluctuations, or irradiation—any of which may change the molecular structures that give these materials their useful elastomeric character.  As a step toward understanding and controlling the changes,[SciTech Connect] researchers at Lawrence Livermore National Laboratory measured many properties of a polydimethylsiloxane[Wikipedia] elastomer named TR-55 that were aged by controlled exposure to gamma rays[Wikipedia] emitted by cobalt-60[Wikipedia] nuclei; the properties measured included a type of magnetic resonance in which the magnetic moments of hydrogen nuclei in the elastomer are first brought from independent orientations into coherent alignment.[SciTech Connect]  Unstressed samples of TR-55 that were exposed to higher gamma-ray doses became easier to stretch; samples exposed to higher and higher doses while in a stretched state relaxed afterward to lengths that were longer and longer than their original unstretched lengths. 

 

TR-55 is basically a set of what would be separate polymer molecules with various lengths, most of them hundreds of SiO(CH3)2 units long, except that each “separate molecule” is actually a segment in a network, chemically bonded to other segments at one or both ends, with the entire network of segments being embedded in a different filler material.  The nuclear magnetic resonance measurements indicate what fractions of the network’s segments are one unit long, two units long, &c., up to several hundred units long.  Measurements made after exposing the material to greater and greater radiation doses showed narrower distributions of segment lengths, with the most common lengths in the more-irradiated samples being shorter, indicating that irradiation induces cross-linking among the network’s segments. 

 

To see whether radiation-induced cross-linking alone could account for the changes observed in TR-55’s elasticity, the Lawrence Livermore researchers modeled its polymer network mathematically and worked out whether additional chemical bonding between atoms in the middles of existing polymer segments would result in the kinds of segment-length distributions deduced from nuclear magnetic resonance of actual samples.  The matches were close for radiation doses up to 10 megarads[Wikipedia] (or 100 kilograys[Wikipedia], which would deposit 100 kilojoules of energy per kilogram of sample), but greatly underestimated the chain-shortening of samples that were given 25-megarad doses (250 kilojoules per kilogram).  Mathematical models that also included dangling polymer segments or loops had more realistic segment distributions. 

 

The atomic arrangements of several uranyl hydroxide materials determine their geophysical precipitation reactions in our environment and how uranium-based nuclear fuel and waste products can be processed.  The arrangements of some of these materials had been incompletely determined since the locations of their hydrogen atoms were unknown.  To help locate the hydrogen in such materials, researchers at Sandia National Laboratories used nuclear magnetic resonance on rotating material samples as described in their report “Insight into hydrogen bonding of uranyl hydroxide layers and capsules by use of 1H magic-angle spinning NMR spectroscopy”[DoE PAGES].   The “magic-angle spinning” referred to in the title is a common way to narrow the range of resonant frequencies in a solid.[Wikipedia]  Different nuclei may interact enough as described in this article’s introduction to give nuclei of the same type a wider range of orientations than they would have otherwise.  A way to average out some of these effects is to spin the sample; this is most effective when the rotation axis has a particular “magic” angle (the arccosine of ).   By providing information about which hydrogen atoms were close enough neighbors to couple magnetically, the techniques proved useful for monitoring changes in the electrostatic bonds between positive hydrogen nuclei in one set of molecules and negatively-charged regions in neighboring molecules.  For example, the researchers found that hydrogen nuclei in the hydroxyl (OH) segments of the material α-UOH were magnetically coupled, while in metaschoepite materials, they not only found that hydrogen nuclei in the materials’ water molecules were magnetically coupled, but also that hydrogen nuclei of the water molecules were coupled to those of hydroxyl segments.  Variations in the metaschoepite materials’ magnetic resonance during dehydryation showed a disruption in the hydrogen bond strengths as water molecules were removed, along with the formation of multiple mixed phases.  The details of this and other data showed that the materials studied have extensive networks of intermolecular hydrogen bonds, and that the water molecules in them move slowly. 

 

Top

Separator line

Surface chemistry

 

Nuclear magnetic resonance also provides clues to how atoms rearrange in various chemical reactions, such as those in which uranium atoms are removed from nitric acid solutions by reacting with silica-based materials at their surfaces.  The report “Probing the interaction of U(VI) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy” from Lawrence Livermore National Laboratory[DoE PAGES] tells how nuclear magnetic resonance was used to gain insight into how the extraction works and what the process’ limits are. 

 

Two other reports describe how researchers used one method of aligning certain nuclei in materials to enhance their resonance, thus enabling the researchers to better understand chemical reactions occurring at the materials’ surfaces.  The fastest way to get the magnetic fields of these nuclei mainly oriented in the same general direction was an indirect one:  first, use radio pulses to orient the magnetic fields of neighboring hydrogen atoms the same way, and then let the hydrogens interact with those nuclei so that their magnetic fields become oriented as desired.  Locating the nuclei within a sample of the material by their resonance frequencies then provided further information about their arrangement among the materials’ other atoms, which clarified how the materials functioned in particular chemical processes. 

 

In investigations described by one of the reports[DoE PAGES], researchers located platinum-195 atoms in different porous materials that each consisted of a framework of metal compounds and organic molecules.  Many different structures of this type are possible, each one having properties that suit it for particular purposes like water purification, catalyzing certain chemical reactions, hydrogen storage, or serving as precursors[Wikipedia] for making metal nanoparticles.  Determining where the platinum-195 atoms were in the materials examined helped clarify the materials’ overall atomic structures and thus how the materials performed various functions.  The other report[DoE PAGES] described how orienting hydrogen atoms in order to reorient oxygen-17 nuclei allowed NMR studies of the atomic arrangements at the surfaces of silica nanoparticles.  The chief problem here is that oxygen-17, the only stable magnetic isotope of oxygen, is also the rarest oxygen isotope:  99.96% of the stable oxygen atoms on earth are nonmagnetic, so nuclear magnetic resonance can only locate the very few oxygen nuclei that have 9 neutrons each.  However, the few oxygen-17 nuclei were plentiful enough for the researchers to determine how atoms at the silica nanoparticles’ surfaces behave when various chemical and physical reactions occur there. 

 

Top

Separator line

Motion

 

Atoms can, of course, also move even when they’re not rearranging themselves into different molecules during chemical reactions.  Atoms can move without changing the identity of the molecules they constitute if the molecules simply bend, change their orientations, or move from one place to another.  Even these motions are significant processes in many materials, and several experiments have used nuclear magnetic resonance to determine the exact nature of such motions. 

 

Liquids that consist of electrically positive and negative molecules have been replacing volatile organic compounds for certain uses.  The new liquids offer the advantages of being less volatile, remaining liquid within large temperature ranges, not changing their molecular structure at high temperatures, being relatively unreactive with other materials, and having properties that can be easily tuned by adjusting their compositions.  However, their generally higher viscosity and resulting lower conductivity for charged atoms or molecules makes their use problematic in some cases.  One group of researchers has investigated how the viscosity of a two-component liquid (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, or BMIM TFSA), is affected by the structures of its molecules, using nuclear magnetic resonance of the liquid’s hydrogen and fluorine atoms under a wide range of conditions to better understand the effect of the BMIM component’s long carbon-hydrogen chains.  The researchers’ described their experiments and conclusions in a paper[DoE PAGES] for the Journal of the Electrochemical Society, particularly noting what the experimental results imply about where hydrogen bonds tend to form between the positively-charged BMIM and the negatively-charged TFSA molecules, and how much more readily the BMIM molecules diffuse than the TFSA molecules do under similar conditions. 

 

Figure 1

Figure 1.  Molecular diagrams of 1-butyl-3-methylimidazolium (BMIM) and bis(trifluoromethylsulfonyl)amide (TFSA).  For nuclear magnetic resonance experiments on BMIM TFSA reported in the Journal of the Electrochemical Society, some of the more common hydrogen-1 atoms, whose nuclei are single protons, were replaced in BMIM molecules by the magnetically different hydrogen-2 atoms, whose nuclei consist of single protons bound to single neutrons.  The hydrogen-1 and hydrogen-2 atoms are represented by white and green spheres respectively.  (Figure from “Investigation of Dynamics in BMIM TFSA Ionic Liquid through Variable Temperature and Pressure NMR Relaxometry and Diffusometry”[DoE PAGES], p. 3.) 

 

Unlike these liquids, some solid materials have been found to conduct charged atoms very rapidly.  An investigation of why this happens in solid salts composed of positive lithium or sodium ions combined with negative ions consisting of hydrogen, boron, and possibly carbon (B10H10 or CB9H10) is reported in the Journal of Physical Chemistry C (“Comparison of Anion Reorientational Dynamics in MCB9H10 and M2B10H10 (M = Li, Na) via Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Studies” [DoE PAGES]).  Nuclear magnetic resonance was one of the techniques used to see how the negative ions in these materials reoriented at high temperatures, on the assumption that their reorientation makes it easier for the positive ions to move among the materials’ atoms, and possibly even helps drag or push the positive ions along—an assumption corroborated by recent mathematical modeling of Na2B10H10

 

Figure 2

Figure 2.  Center top:  diagram of negatively charged molecular ion, either CB9H10- or B10H102-, depending on whether the large sphere near the right end of the diagram represents a carbon atom or another boron atom.  Bottom:  intensities of nuclear magnetic resonance (NMR) at different radio-wave frequencies and of quasielastic neutron scattering (QENS) for different-sized energy transfers E in the material Na2B10H10, which consists of positive sodium (Na) ions and negative B10H10 ions; the different-colored curves correspond to different experimental temperatures (upper left).  The magnetic resonance and neutron scattering data were used to determine how often the CB9H10- or B10H102- ion orientations jump—frequencies that are thought to affect how rapidly positive ions move through the material.  (Figure from “Comparison of Anion Reorientational Dynamics in MCB9H10 and M2B10H10 (M = Li, Na) via Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Studies”[DoE PAGES], p. 1000.)

 

By combining observations of nuclear magnetic resonance and the scattering of neutrons from nuclei in these materials in different temperature ranges spanning roughly 300 kelvins (or 540 Fahrenheit degrees), the researchers found how rapidly the different salts’ negative ions rotate around which axes at different temperatures.  NaCB9H10 was found to reorient faster than either LiCB9H10 or Na2B10H10 at various temperatures, and also had both the highest mobility of positive ions and highest ion conductivity at temperatures between 300 and 400 kelvins (about 27°C to 127°C, or 80°F to 260°F)—findings consistent with the idea that fast negative-ion reorientation can enhance the conduction of ions.  (Li2B10H10 observations proved hard to interpret since that salt begins to decompose at temperatures above 560 kelvins.)  Other studies by the same researchers of similar materials suggest that the conductivity enhancement may decrease as the reorientation frequencies drop from 10-100 jumps per nanosecond to 1-10 per nanosecond.  The neutron scattering experiments suggest that small-angle jumps dominate the negative ion reorientations, and that all the reorientations tend to be around just one axis at lower temperatures and multidimensional at higher temperatures, but that even at the highest temperatures studied, the set of rotations isn’t fully three-dimensional. 

 

Molecular reorientation in important two-dimensional materials—namely, membranes in living cells—has also been explored by nuclear magnetic resonance, with one group’s findings summarized in the title of their paper, “1H NMR Shows Slow Phospholipid Flip-Flop in Gel and Fluid Bilayers”[DoE PAGES].  The term “bilayers” refers to the basic structure of the membranes, which consist of two layers of long phospholipid[Wikipedia] molecules (see Figure 3).  The molecules in each layer lay alongside each other so that one layer’s thickness equals one molecule’s length.  Water attracts one end of each molecule but not the other; thus the water-attracted ends (or “heads”) become the outer, water-facing surfaces of bilayer while the water-nonattracted ends (“tails”) face inward, constituting the inner portion of the bilayer.  While the molecules of a fluid bilayer can diffuse among each other within their layer’s two dimensions the way molecules of an ordinary fluid can diffuse in three dimensions, a gel bilayer is a two-dimensional solid whose molecules have much less molecular mobility.  But a phospholipid molecule may move from one layer to the other, most easily where the two layers merge into one at membrane edges such as pores.  This process was investigated in bilayers of the phospholipid DPPC[Wikipedia] in which the hydrogen in most of the molecules’ heads consist of hydrogen-2 atoms (one proton, one neutron) instead of the more common hydrogen-1 (one proton, no neutrons).  Since the few hydrogen-1 nuclei in the heads of the remaining DPPC molecules had different nuclear magnetic moments than the hydrogen-2 atoms, their positions could be distinguished by their different nuclear magnetic resonance, and their DPPC molecules’ occasional “flip-flopping” across the bilayer membrane could thus be tracked.  The flip-flop rate was found to match expectations from mathematical modeling in its dependence on the bilayer’s temperature, density of pores, and whether the bilayer was in a fluid or gel phase. 

 

Figure 3

Figure 3.  Schematic illustration of a bilayer of phospholipid[Wikipedia] molecules on a solid support.  The two layers merge at a pore, shown in cross section.  In the bilayer’s fluid phase, the molecules can move within a layer; at the pore, where the upper and lower layers merge, molecules can also move between the upper and lower layers more easily.  Researchers monitored the interlayer transfer rate in real bilayers of phospholipid molecules that contained hydrogen-2 atoms, which were easily distinguished by nuclear magnetic resonance from the more numerous phospholipids containing only hydrogen-1 atoms.  (Figure from “1H NMR Shows Slow Phospholipid Flip-Flop in Gel and Fluid Bilayers”[DoE PAGES], p. 3731.) 

 

While nuclear magnetic resonance can provide important information about molecular-scale motions, it has also proven useful for indicating the existence of long-range motions within a large organism—some of which can be significant indicators of the general health of natural resources.  “In vivo observation of tree drought response with low-field NMR and neutron imaging”[DoE PAGES] describes how researchers at Los Alamos National Laboratory used some fairly simple nuclear magnetic resonance equipment, whose magnetic fields were much weaker than those used in many other NMR devices, to see daily cycling in the water content of a greenhouse aspen tree.  In additional experiments that compared magnetic resonance observations of a juniper tree and a pinon pine tree with the way those trees interacted with neutron beams as they each took up water made with hydrogen-2 atoms, the researchers found that the magnetic resonance didn’t involve water in the trees’ cells or cell walls, but did involve water that was being rapidly transported through the trees.  From this they learned that nuclear magnetic resonance alone indicate determine how a tree is transporting water, with no need for neutron-beam observations.  By simulating drought conditions in the aspen and accounting for effects of temperature on their nuclear magnetic resonance observations, the researchers further demonstrated that such observations could detect effects of drought on a tree’s daily water cycle:  “[l]arge variations in water content indicate ready access to water; a constant water content indicates a lack of access to water; and a declining signal indicates drought or even tree death”. 

 

All these measurements did more than just show that nuclear magnetic resonance can reveal the healthiness of a greenhouse tree’s environment.  The noninvasive way they were obtained also demonstrated the possibility that many trees in the wild could be monitored simultaneously, with relatively simple equipment, to see if their environment is providing enough water.  While these findings represent an advance in managing natural resources, the researchers did not think they constituted the last word on the subject, but that further improvements of the technique were possible:  for instance, they planned to model the effects of heat flow through the space examined to better predict how temperature affects the nuclear magnetic resonance observations. 

 

Figure 4 Top

Figure 4 Bottom

Figure 4.  Top:  (i) Schematic of a low field NMR system used to measure the water content in a tree shows (a) the 41-cm diameter Helmholtz coils which produce a magnetic field; (b) copper shielding, with one panel removed for clarity, used to block radiofrequency noise; and (c) the solenoid, wrapped around a former on the tree’s trunk, which both produces a second magnetic field and detects the resulting NMR signal.  (ii) A representative neutron image of a branch showing (A) the stem; (B) the NMR solenoid; (C) the cup holding heavy water made with hydrogen-2 atoms; and the regions of interest as highlighted by the white boxed.  (iii) Subtracting subsequent neutron images from the first creates difference images. Such images clearly show the uptake of the heavy water through the branch, even revealing a section of non-conductive heartwood running down the center of this branch.  Difference images also help reveal any physical movement of the system, and provide a direct measurement of the amount of water taken up by the plant (D).  Bottom:  Red line represents a mathematical model that accounts for most of the NMR signal variation while the plant’s watering was limited, but not while the plant was either well-watered or drying, since the plant’s water content wasn’t constant.  To encourage water loss, the tree was manipulated in several ways: (a) watering was stopped; (b) the crown was removed 1 meter above the detector coil, with the cut sealed with an impermeable barrier; (c) the crown was removed 10 centimeters from the detector coil and the cut left unsealed; (d) strips of phloem were removed above and below the detector coil to cease carbohydrate transport.  The “well watered”, “water limited”, and “drying” epochs were determined based on NMR signal response to the manipulations.  (After “In vivo observation of tree drought response with low-field NMR and neutron imaging”[DoE PAGES], pp. 3 and 5.) 

Top

Separator line

 

References

 

Wikipedia

 

 

Top

Separator line

Reports available through OSTI’s SciTech Connect

 

  • “Predictive Modeling in Actinide Chemistry and Catalysis” [Metadata] (slides)

2016-05-16

Technical Report

Intended for presentation for Chemistry Department at Shaanxi Normal University [English] and Shaanxi University of Technology [English]. 

(By one of the authors of a journal paper[DoE PAGES] featured in last month’s “In the OSTI Collections” article about density functional theory[OSTI].  That paper and this slide presentation dealt with multiple techniques for studying materials, including both nuclear magnetic resonance and density functional theory.) 

 

  • “Radiation-induced aging of PDMS Elastomer TR-55: a summary of constitutive, mesoscale, and population-based models” [Metadata]

2016-11-16

Technical Report

Cp. https://www.osti.gov/scitech/biblio/1111129 (see https://www.osti.gov/home/osti-collections-mesoscale-science#Experiments)

 

  • “Multiple-quantum nuclear magnetic resonance spectroscopy” [Metadata]

1986-08-01

Journal Article; published in Science, Volume 233, Issue 4763, pp. 525-531

  • Amoco Research Center

A description of the nuclear magnetic resonance method used in the study of TR-55 cited immediately above.  

 

Top

Separator line

Reports available through DoE PAGES

 

  • “Natural abundance 14N and 15N solid-state NMR of pharmaceuticals and their polymorphs” [Metadata]

Reviews, and annotated copy of changes made after reviews, are accessible with the manuscript accepted by the journal that published it. 

2016-06-08

Physical Chemistry Chemical Physics, Volume 18, Issue 26

 

  • 35Cl dynamic nuclear polarization solid-state NMR of active pharmaceutical ingredients” [Metadata]

2016-08-24

Physical Chemistry Chemical Physics, Volume 18, Issue 37

 

  • “Insight into hydrogen bonding of uranyl hydroxide layers and capsules by use of 1H magic-angle spinning NMR spectroscopy” [Metadata]

[Insight into the hydrogen bonding for uranyl hydroxides using 1H MAS NMR spectroscopy]

2016-04-27

Journal of Physical Chemistry C, Volume 120,Issue 19

 

  • “Probing the interaction of U(VI) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy” [Metadata]

2016-05-30

Dalton Transactions, Volume 45, Issue25

 

  • “DNP-enhanced ultrawideline solid-state NMR spectroscopy: Studies of platinum in metal–organic frameworks” [Metadata]

2016-06-06

Journal of Physical Chemistry Letters, Volume 7, Issue 13

 

  • “Probing surface hydrogen bonding and dynamics by natural abundance, multidimensional, 17O DNP-NMR spectroscopy” [Metadata]

2016-05-06

Journal of Physical Chemistry C, Volume 120, Issue 21

 

  • “Investigation of Dynamics in BMIM TFSA Ionic Liquid through Variable Temperature and Pressure NMR Relaxometry and Diffusometry” [Metadata]

2017-05-11

Journal of the Electrochemical Society, Volume 164, Issue 8

 

  • “Comparison of Anion Reorientational Dynamics in MCB9H10 and M2B10H10 (M = Li, Na) via Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Studies” [Metadata]

2016-12-13

Journal of Physical Chemistry C, Volume 121, Issue 2; Journal ID: ISSN 1932-7447

 

  • 1H NMR Shows Slow Phospholipid Flip-Flop in Gel and Fluid Bilayers” [Metadata]

2017-01-20

Langmuir, Volume 33, Issue 15; Journal ID: ISSN 0743-7463

 

  • In vivo observation of tree drought response with low-field NMR and neutron imaging” [Metadata]

2016-05-06

Frontiers in Plant Science, Volume 7

 

Top

Separator line

Additional references

 

 

  • High Resolution Nuclear Magnetic Resonance by John A. Pople[OSTI], William G. Schneider, and Harold J. Bernstein.

A textbook published in 1959.