Proton Spin Relaxation Research Articles

The effects of vegetation and burning on the chemical composition of soil organic matter in a volcanic ash soil as shown by 13C NMR spectroscopy. I. Whole soil and humic acid fraction

Soil samples were collected from the surface mineral horizon (Ah horizon) of four adjacent soils (sites I, II, III, IV) and one remote soil (site V) derived from volcanic ash in Japan. The four adjacent sites were managed as Miscanthus sinensis grassland for several hundred years by the use of annual burning to prevent the regrowth of native forest species. At site I, annual burning was still being practiced when soil samples were collected; however, at sites II, III and IV annual burning to maintain grassland vegetation ceased about 20–30, 40–50 and more than 100 years ago, respectively, and the sites were left to return to forest. At site V, a mature, broad-leaf, deciduous forest established by natural regeneration existed. The influence of annual burning and vegetative cover on the chemistry of the organic materials contained in the whole soil, the < 53 μm soil fraction, the residues remaining after photo-oxidation of the < 53 μm soil fraction, and the humic acid fraction present at each of the five sites was examined using solid-state 13C NMR. On site I, where grasses were still burned annually, SOM and humic acid fraction contained a greater proportion of aromatic and carbonyl carbons compared to the other sites. Alkyl carbon made a relatively small (19%) contribution to the composition of SOM on site I. When grassland was invaded by forest, the chemical nature of the SOM and humic acid fraction changed. The greatest changes occurred during the first 20–30 years, after which changes in the chemistry of SOM and humic acid fraction were of a smaller magnitude. The changes in SOM chemistry included a decrease in aromatic and an increase in alkyl carbon contents, indicating that SOM produced under forest was richer in alkyl carbon than that produced under grasses managed with annual burning. The SOM at the remote site, under deciduous forest (site V), was highly aliphatic in nature with alkyl carbon contributing 35% of the total soil carbon. Application of a proton-spin relaxation editing (PSRE) procedure to the SOM of each site indicated heterogeneity within the SOM structures, and subspectra of carbon associated with slower- and faster-relaxing protons were derived. Subspectra of the slowly-relaxing fractions from sites I, II and III were similar and resembled spectra of partly decomposed plant materials. The fast-relaxing subspectrum from site I contained a strong central resonance at 130 ppm and a small peak at 176 ppm, and was very similar to spectra obtained for charcoal and charred residues. The fast relaxing fractions from other sites included less aromatic carbon and had some O-alkyl materials. The Bloch decay spectrum of SOM from site I showed more aromatic and carbonyl carbons than the CP/MAS spectrum and highlighted an important limitation of the CP/MAS technique when it is applied to SOM containing charcoals or charred plant residues.

The effects of vegetation and burning on the chemical composition of soil organic matter of a volcanic ash soil as shown by 13C NMR spectroscopy. II. Density fractions

Soil samples from the surface mineral horizons (Ah) of two adjacent sites (sites I and III) and one remote site (site V), derived from volcanic ash in Japan, were collected and separated into fractions with densities < 1.0 free, < 1.6 free, < 1.6 occluded, 1.6–1.8, 1.8–2.0 and > 2.0 Mg m −3. The terms free and occluded were used to indicate density fractions in which organic materials weakly associated with soil mineral particles resided external to or within soil aggregates, respectively. The studied sites were under different vegetative covers and had different burning histories. Sites I and III were managed as grassland for several hundred years by the use of annual burning to prevent the regrowth of native forest. At site I, annual burning of Japanese pampa grass ( Miscanthus sinensis) was still occurring. However at site III vegetation burning was stopped more than 100 years ago and the site was left to return to forest. At site V a mature, broad leaf deciduous forest maintained by natural regeneration existed. Solid state 13C CP/MAS, Bloch decay, and proton-spin relaxation editing (PSRE) NMR were applied to various density fractions to study the effect of vegetative cover and burning on the chemical composition of soil organic matter (SOM) associated with different density separates. The components of SOM contained in density fractions were also studied using light microscopy. The 13C CP/MAS NMR spectra obtained for the fractions < 1.0 free and < 1.6 free density fractions from sites I and III were similar to spectra of plant material and litter. However, at site V these fractions had more alkyl and less O-alkyl carbon than the corresponding fractions from sites I and III, indicating an influence of vegetative cover and/or extent of decomposition of plant material on the chemistry of SOM contained in these fractions. Using light microscopy, the < 1.0 Mg m −3 free and < 1.6 Mg m −3 free fractions were observed to be dominated by large, undecomposed root and shoot fragments and included charcoal and charred plant residues. The chemistry of the 1.8–2.0 Mg m −3 fractions was comparable to that of the < 1.6 Mg m −3 free fractions. The fractions < 1.6 Mg m −3 occluded and 1.6–1.8 Mg m −3, however, had considerably less O-alkyl and more aromatic carbon contents than the free light fractions. The aromatic carbon in these fractions was suggested to originate in part from charcoal and charred plant residues resulting from burning. Lignin and its decomposition products were also another source of aromatic carbon for these fractions. Application of Bloch decay NMR to the fractions 1.6–1.8 Mg m −3, confirmed the presence of a source of aromatic carbon containing few protons similar to charcoal in all three sites studied and showed that the aromatic carbon content of the fractions were underestimated by the CP/MAS method. PSRE NMR separated the fractions 1.6–1.8 Mg m −3 into two components and subspectra for these components in site I resembled spectra of slightly decomposed plant residues and charcoal.

1H-NMR Investigations on the Description of Constrained Diffusion Processes of Structural Defects in Bulk Polymers

Proton spin relaxation measurements above the glass transition temperature have been used to investigate the effect of crosslinking on local and coherent segmental dynamics in cis-1,4-polybutadiene samples. The polymer chains in bulk polybutadiene were crosslinked by exposure to ionizing radiation. The transition of the 1H-NMR signal from a liquid-like spin system response to a solid-like one is due to crosslinking and network formation by the irradiation and depends on the radiation dose. The description of the relaxation data is based on a stochastic model of translational diffusion of structural defects between fluctuating and fixed junctions of polymer chains. The assigned composite stochastic process has non-Markovian character. It is shown that the radiation yields changes in the constrained defect diffusion processes modelling the chain dynamics. Correlation time and memory time for the local and coherent segmental motion strongly depend on radiation dose.

Phase transitions and cation dynamics in [(CH 3) 2NH 2] 3Bi 2Cl 9 (DMACB)—Proton spin relaxation studies

Tris(dimethylammonium nona chloro dibismuthate), [(CH 3] 2NH 2] 3Bi 2Cl 9, family has been investigated through proton magnetic resonance and relaxation measurements as a function of temperature. Results indicate the presence of two phase transitions at 152 and 78 K, accompanied by changes in the reorientational dynamics of the cation groups. Above 152 K, the [(CH 3) 2NH 2] + groups are undergoing isotropic reorientations with dynamic inequivalence, while in contrast they exhibit two-fold rotations in the low temperature phase. The phase transition at 78 K seems to be associated with considerable change in the orientational order of the molecular groups. Comparison is made with similar antimony (Sb) substituted compounds to discuss the microscopic effects of substitution of heavier bismuth (Bi) metal atom.

Detection of trace of impurities in some solids by proton spin-relaxation measurements

The amount of diamagnetic impurities occluded in the potassium hydrogen dibenzoate sample was estimated by proton spin-lattice relaxation measurements.

Distribution of pore sizes in white cement paste from proton NMR spin-lattice relaxation

The distribution of pore sizes in hardening white synthetic cement paste, after 100 h of hydration, is modelled using proton spin relaxation data. The results are consistent with a trimodal pore size power law distribution. Two different distribution functions obtained by small angle neutron scattering were employed: one obeys a power law r-a with a = 4·5 for the pores with diameters of 20-120 nm, and one obeys a power law with a = 3·8 for pores having diameters of 120-2600 nm. The third pore group obeys the same power law (a = 3·8) for pores with diameters of 2·6-14 μm.

Magnetic resonance imaging of bovine ovaries in vitro.

A sample of 20 bovine ovaries were imaged in vitro using nuclear magnetic resonance (NMR) techniques to determine the visibility of various physiologic structures. In particular, the possibility of using NMR imaging to differentiate atretic follicles from physiologically selected and ovulatory follicles was examined. Five of the 20 ovaries were preserved in formalin, whereas the remaining 15 were preserved in a saline solution and imaged within 18 hours of death. Images weighted by T1 and T2 proton spin relaxation rates were obtained along with some three-dimensional (3-D) data sets acquired via a fast imaging with steady-state precession technique. Physiologically different structures were easily identified in the images from their morphology, especially in the 3-D images. Weighting by T1 and T2 was able to separate structures in the fresh ovaries in the following manner. Atretic and "cohort" follicles appear dark in T1-weighted images and bright in T2-weighted images. Ovulatory follicles appear bright in both T1- and T2-weighted images, whereas prephysiologic selection follicles present an intermediate brightness in T1-weighted images and appear dark in T2-weighted images. The corpus luteum appears bright in T1-weighted images and dark in T2-weighted images, whereas cysts in the corpus luteum appear dark in T1-weighted images and bright in T2-weighted images. The varying brightness of the follicles at different stages of development is hypothesized to be related to different hormone and protein concentrations in the follicular fluid. For example, it is known that physiologically selected preovulatory follicles contain high concentrations of estrogens in a viscous follicular fluid. The increased viscosity may occur only when the follicle fluid contains high concentrations of estrogen and contributes to bright T1-weighted images. The possibility of using nuclear relaxation-weighted NMR imaging for the study of follicular dynamics and other ovarian biology therefore shows great promise.

Solid-State 13C Nuclear Magnetic Resonance Characterization of Cellulose in the Cell Walls of Arabidopsis thaliana Leaves.

Solid-state 13C nuclear magnetic resonance was used to characterize the molecular ordering of cellulose in a cell-wall preparation containing mostly primary walls obtained from the leaves of Arabidopsis thaliana. Proton and 13C spin relaxation time constants showed that the cellulose was in a crystalline rather than a paracrystalline state or amorphous state. Cellulose chains were distributed between the interiors (40%) and surfaces (60%) of crystallites, which is consistent with crystallite cross-sectional dimensions of about 3 nm. Digital resolution enhancement revealed signals indicative of triclinic and monoclinic crystalline forms of cellulose mixed in similar proportions. Of the five nuclear spin relaxation processes used, proton rotating-frame relaxation provided the clearest distinction between cellulose and other cell-wall components for purposes of editing solid-state 13C nuclear magnetic resonance spectra.

Angular and frequency dependent spin relaxation study of liquid crystalline cyanobiphenyls

Abstract NMR field-cycling measurements of the Larmor frequency (v) and angular (Δ) dependences of the longitudinal proton spin relaxation time T 1 for the nematic liquid crystals 5CB and 8CB allow a more detailed analysis of the underlying molecular motions than data available previously. All T 1 (v, Δ) dispersion profiles essentially distinguish three frequency ranges where T 1 is governed by either local field effects, collective motions (director order fluctuations), or rotational and translational diffusion of individual molecules or molecular groups, respectively. The angular dependence supports and extends previous conclusions about the significance of the order fluctuation term at low (kHz) and high (MHz) Larmor frequencies; in addition it is the basis for the disentanglement of local field effects, which involve Jeener's dipolar relaxation, and of the sophisticated rotational relaxation models suggested in the literature by Dong, Nordio and Vold. It is found that Vold's third rate concept gives t...

Metabolite 1H relaxation in normal and hyponatremic brain.

Proton spin relaxation rate constants in normal and hyponatremic rat brain were measured to determine the sensitivity of metabolite relaxation properties to cytotoxic edema and to quantify metabolite concentration in normal and edematous brain. Relaxation rate constants for protons of water and spectral regions with dominant contributions from methyl protons of cholines (Cho), creatines (Cr), N-acetylaspartate (NA), and lactate (Lac), and for methylene protons of glutamate (Glu) were measured at 7 T. Changes in metabolite relaxation properties associated with cytotoxic edema were a decrease in the Cr longitudinal rate constant, from 0.63 +/- 0.02 s-1 (mean +/- SE) in controls to 0.50 +/- 0.03 s-1 in edematous brain, and an increase in the transverse rate constant of NA from 5.3 +/- 0.2 s-1 in controls to 6.6 +/- 0.3 s-1 in edematous brain. Four hours after induction of hyponatremia, there was a 14% reduction in summed metabolite concentrations of Cho, Cr, and NA, and a 200% increase in Lac signal intensity. It is concluded that changes in both metabolite spin relaxation and detectable spin concentration accompany the cerebral pathology of cytotoxic edema complicated with secondary ischemia.

NMR probe for high pressure and high temperature

A description is given of a probe which is designed for nuclear magnetic resonance (NMR) experiments at 180 MHz on samples at hydrostatic pressure up to 10 kbar. Temperature control has been designed to allow experiments from room temperature up to 600 K, regulated with an accuracy of 0.1 K. Radio frequency feedthroughs can sustain high-voltage pulses of considerable length. The probe has been used successfully in a proton spin relaxation study at 180 MHz of polyethylene near the melting line.

A long-term effect of N fertilization on the 13C CPMAS NMR of de-ashed soil humin in a second-growth Douglas-fir stand of coastal British Columbia

Carbon-13 CPMAS NMR spectroscopy was used to examine long-term effects of thinning and N fertilization on the humin fraction of soil organic matter in a second-growth Douglas-fir stand of coastal British Columbia. De-ashed organic-matter-enriched humin fractions were prepared from three mineral soil horizons of four silvicultural treatments using 1.0 M HF accompanied by a magnetic stir bar to remove ferromagnetic iron particles, followed by a density separation. With some exceptions a higher proportion of mass was recovered in the denser, light-coloured fraction, and a higher proportion of C and N in the less-dense, dark fraction. In all cases, the less-dense fraction was enriched in total C compared to the original crude humin, and had a more favourable C/Fe ratio for NMR spectroscopy. The fraction of observable C was 33–37% for 8 of the samples, but as low as 7.6% for the remaining four. Carbon-13 CPMAS NMR spectra had typical features for humins (alkyl C, O-alkyl C, di-O-alkyl C, aromatic C, and carboxyl, ester and amide C). With fertilization, there was a small but consistent decrease in the ratio of alkyl to O-alkyl C, regardless of horizon or thinning, indicating a lower extent of decomposition. Carbon-13 subspectra based on proton spin relaxation time ( T 1( 1 H) ) were obtained for one fertilized and one unfertilized sample. Subspectra of the slowly-relaxing (long T 1( 1 H) ) domain were dominated by long-chain alkyl C. For the fertilized sample, the subspectrum of the fast-relaxing (short T 1( 1 H )) domain had a higher proportion of O- and di-O-alkyl C, consistent with results from the normal CPMAS NMR spectra. Despite the uncertainties introduced by the de-ashing treatment and the low fraction of observable C, 13C CPMAS NMR showed that fertilization has a long-term effect which is reflected in this humin fraction.

NMR Studies of Hindered Ligand Rotation, Magnetic Anisotropy, Curie Behavior, Proton Spin Relaxation, and Ligand Exchange in Some Novel Oxomolybdenum(V)/Iron(III) Porphyrinate Complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNMR Studies of Hindered Ligand Rotation, Magnetic Anisotropy, Curie Behavior, Proton Spin Relaxation, and Ligand Exchange in Some Novel Oxomolybdenum(V)/Iron(III) Porphyrinate ComplexesPartha Basu, Nikolai V. Shokhirev, John H. Enemark, and F. Ann WalkerCite this: J. Am. Chem. Soc. 1995, 117, 35, 9042–9055Publication Date (Print):September 1, 1995Publication History Published online1 May 2002Published inissue 1 September 1995https://doi.org/10.1021/ja00140a022RIGHTS & PERMISSIONSArticle Views191Altmetric-Citations33LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Molecular dynamics simulation of the zero-field splitting fluctuations in aqueous Ni(II)

The fluctuations in the zero-field splitting (ZFS) of the electronic ground state of the Ni(II) ion in aqueous solution have been studied through a combination of ab initio quantum chemistry calculations, including spin–orbit coupling, and molecular dynamics (MD) simulations. The ab initio calculations for the hexa-aquo Ni(II) complex have been used to generate an expression for the ZFS as a function of the distortions of the idealized Th symmetry of the complex along the normal modes of Eg and T2g symmetries. The MD simulations provide a 200 ps trajectory of motions in the system consisting of a Ni(II) ion and 255 water molecules, which is analyzed in detail in terms of both the structure and the dynamics in the solvation sphere around the ion. The time correlation function (TCF) for the ZFS interaction has been computed and analyzed. It is found that the mean square amplitude of the ZFS is about 5.2 cm−1, which is about twice the estimates based on the model-dependent analysis of the proton spin relaxation in the aqueous Ni(II) solution. The decay of the ZFS TCF is found to occur on a subpicosecond time scale, which is much faster than earlier proposals. It is also interesting to note, for comparison with theoretical models, that the ZFS tensor is far from cylindrical and that the normal modes of Eg och T2g symmetry both contribute to its fluctuations.

Separating subspectra from cross-polarization magic-angle spinning nuclear magnetic resonance spectra by proton spin relaxation editing

Differences in proton spin relaxation time constants can be exploited to edit cross-polarization magic-angle spinning nuclear magnetic resonance (CP-MAS NMR) spectra of heterogeneous mixtures of different types of organic matter. This paper describes an extension of the editing procedure from two-component to three-component mixtures. Clean separation of 13C NMR subspectra was achieved for three synthetic polymers mixed as powders. Applying the procedure to both 13C and 31P CP-MAS NMR spectra of solid dairy pond sludge provided clues to the location of the phosphorus relative to different types of organic matter, and provided estimates of the proportions of organic matter in categories labeled “plant fragments”, “partly degraded residues” and “recalcitrant structures”. The editing procedure increased noise levels by factors between 2 and 11 in these worked examples, depending on the degree of difficulty involved in distinguishing differences in proton spin relaxation time constants.

Solid State 13C NMR Study of Wood Degraded by the Brown Rot Fungus Gloeophyllum trabeum

Blocks of Pinus koraiensis wood were degraded by Gloeophyllum trabeum and examined by solid-state 13 C NMR spectroscopy, using proton spin relaxation editing and resolution enhancement. Chemical compositions were estimated from relative signal areas. There was no evidence for preferential degradation of the noncrystalline cellulose which accounted for about 4% by weight of the initial wood. Loss of partly ordered cellulose on crystal surfaces exceeded the loss of crystal-interior cellulose. The proportion of the monoclinic Iβ crystalline form increased. These results were interpreted in terms of preferential degradation of crystallites that were relatively narrow and/or of the triclinic Iα form. The spectra showed evidence for loss of hemicelluloses, particularly those associated with relatively sharp NMR signals suggesting some degree of molecular ordering. There was no detectable loss of lignin

A 1H NMR study of glycerol at high pressure

Relative proton chemical shifts and spin relaxation times T 1 and T 2 have been measured at 400 MHz and room temperature, as functions of pressure using the diamond anvil cell. Hydroxyl proton chemical shifts indicate a substantial increase in hydrogen bonding with increasing pressure, to 10 kbar. From T 1 data, a minimum is inferred at a negative pressure of ∼ − 2.5 kbar, yielding an average molecular correlation time in excellent agreement with a value based independently upon extensive recent measurements of glycerol viscosity. It is concluded that over the observed pressure range NMR correlation times are essentially identical to shear (viscosity) relaxation times in glycerol, and that a single, well-defined average structural correlation time, τ, determines all relaxation phenomena in this liquid. Dielectric susceptibility and Brillouin scattering line width measurements support this conclusion, the former to very high (∼ 20 kbar) pressure. It is also found that values of the spin-spin relaxation rate T 2 −1 yield approximately 2.2 × 10 11 s −2 for the coupling constant between this rate and the correlation time, τ, under slow-hopping conditions, and that differences between observed pressure dependences of viscosity and spin relaxation rates are well accounted for by the pressure dependence of the infinite-frequency shear modulus, G ∞.

Solid-State 13C NMR Investigation of Molecular Ordering in the Cellulose of Apple Cell Walls

A resolution-enhanced 13 C nuclear magnetic resonance (NMR) spectrum of cell wall material isolated from Braeburn apples has revealed a pair of signals assigned to cellulose chains exposed on crystal surfaces, providing evidence for a high degree of molecular ordering on those surfaces. Proton spin relaxation editing revealed no detectable amorphous cellulose and provided an estimate of about 23 chains in a typical crystallite. Cellulose in apple cell walls was found to be distinctive, with triclinic Iα and monoclinic Iβ crystalline forms present in similar proportions. Hence, its composition is intermediate between the family of bacterial and Valonia celluloses, rich in the triclinic crystalline form, and the family of cotton and ramie celluloses, in which the monoclinic form is dominant

Solid state proton spin relaxation and methyl and t-butyl reorientation

We have measured the temperature T and Larmor frequency ω/2π dependence of the proton spin-lattice relaxation rate R in solid 1-hydroxy-2,4,6-tri-butylbenzene. The data is interpreted in terms of the rotational motion of the t-butyl groups and their constituent methyl groups. Our data is much more extensive than a previous report [J. Yamauchi and C. A. McDowell, J. Chem. Phys. 75, 1051 (1981)] resulting in a revised dynamical model and considerably larger rotational barriers. Interesting thermal history effects are discussed.

Proton Nuclear Magnetic relaxation study of molecular dynamics in the Ferroelectric Liquid Crystal Val.DOC

Abstract Molecular dynamics studies were carried out in the S A and S * C mesophases of the Ferroelectric Liquid Crystal Val.DOC by means of longitudinal proton spin relaxation dispersion. Fast field-cycling and conventional Nuclear Magnetic Resonance (NMR) techniques were used to obtain the frequency dependence of T 1 covering frequencies from 102 to 3 × 108 Hz at two different temperatures in each mesophase. The T 1 dispersion in both mesophases could be well modeled by the proposed dominant relaxation mechanisms, namely collective motions, molecular self diffusion and local molecular rotations. A Soft mode contribution to the spin-lattice relaxation could not be singled out from the contribution of other collective motions. The diffusion constant D ⊥perpendicular to the director was obtained at all temperatures studied and involves an activation energy of about 35 kJ/mol. Effective correlation times characterizing the average molecular rotations around the long axis and fluctuations of this axis, respe...