Cross-polarization dynamics in polycrystalline samples

Taylor, Robert E.; Chim, Nicholas; Dybowski, Cecil

doi:10.1016/j.molstruc.2006.07.006

Cited by 6 publications

(24 citation statements)

References 41 publications

(63 reference statements)

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“…For a better data fitting, the authors modified the original CP model from Müller et al 20 in order to account for the proton spin lattice relaxation time and for all the possible crystallite orientations relative to the applied magnetic field. With this new approach, Taylor et al 17 showed that a nonmonotonic cross polarization can explain better the CP dynamics in polycrystalline molecules.…”

Section: Resultsmentioning

confidence: 99%

“…The aims of the present paper are: 1) to study the CP dynamics of two humic substances (from a soil sample and a coal sample) by applying the model proposed by Taylor et al 17 modified in order to account for the natural heterogeneity and amorphism of NOM; 2) to suggest a possible conformation in the solid state of the two humic substances.…”

Section: Dynamics Of Cross Polarization Inmentioning

confidence: 99%

“…3 However, it has been shown that the monotonic CP model fails when it is applied for studying cross polarization either in polycrystalline materials 17 or in amorphous natural organic matter. 18,19 In fact, Taylor et al 17 reported that the best fit for variable contact time (VCT) experiments done on crystalline organic systems is a nonmonotonic model, in which two different cross polarization mechanisms are introduced. The faster CP mechanism is governed by the H-C internuclear distance, whereas the slower one is mediated by fast local segmental motions.…”

Section: Introductionmentioning

confidence: 99%

“…The faster CP mechanism is governed by the H-C internuclear distance, whereas the slower one is mediated by fast local segmental motions. 17 Proton-tocarbon distances and local segmental motions were also used by Abelmann et al 19 to interpret the CP behavior of humic substances from two different coals. Conversely, Dria et al 18 attributed the non-monotonic CP behavior of heterogeneous and amorphous NOM extracted from different sources only to different local dynamics experienced by the molecular groups resonating at the same chemical shift values.…”

Section: Introductionmentioning

confidence: 99%

“…The model proposed by Müller et al 20 for the interpretation of the CP dynamics in crystalline materials was modified by Taylor et al 17 by considering the longitudinal proton relaxation time term averaged over all the possible crystallite orientations in the applied magnetic field. In addition, two other different mathematical models were applied by Dria et al 18 and Abelmann et al 19 to study the CP dynamics of NOM.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Dynamics of Cross Polarization in Solid State Nuclear Magnetic Resonance Experiments of Amorphous and Heterogeneous Natural Organic Substances

Conte

Berns

2008

ANAL. SCI.

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Section: Resultsmentioning

confidence: 99%

Section: Dynamics Of Cross Polarization Inmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Dynamics of Cross Polarization in Solid State Nuclear Magnetic Resonance Experiments of Amorphous and Heterogeneous Natural Organic Substances

Conte

Berns

2008

ANAL. SCI.

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Variable temperature NMR characterization of α-glycine

Taylor¹,

Dybowski²

2008

Journal of Molecular Structure

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Proton NMR spin-lattice relaxation times in the laboratory frame (T 1) and in the rotating frame (T 1ρ) were measured as a function of temperature for a static sample of αglycine. Both T 1 and T 1ρ data can be fit quantitatively by a single thermally-activated motion (the modulation of the dipolar coupling by random hopping about the threefold axis of the-NH 3 group), with no addition of other mechanisms at any temperature between 173 K and 415 K. An activation energy of 21.7 ± 1 kJ/mol was extracted and is compared with previously reported values for both αand γ-glycine. Such comparisons allow the correction of glycine polymorphs misidentified in the literature. The minimum in T 1 at 325 K corresponds to a correlation time of 0.53 ns. Chemical shifts as a function of temperature were measured by 1 H CRAMPS and by 13 C and 15 N CP/MAS experiments. These results are discussed relative to a previous report of anomalous electrical behavior in α-glycine within this temperature range.

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Single-Core PAHs in Petroleum- and Coal-Derived Asphaltenes: Size and Distribution from Solid-State NMR Spectroscopy and Optical Absorption Measurements

et al. 2016

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Using solid-state 13C NMR spectroscopy of two different asphaltenes, one derived from petroleum and the other from coal liquids, it was shown that the asphaltene molecular architecture consists of a spectrum of sizes, ranging from smaller polyaromatic hydrocarbons (PAHs; <5 condensed rings) to much larger ones (>9 condensed rings), but their distribution varies between the two. It is shown that smaller PAHs are likely more abundant in the coal-derived asphaltenes, while the largest PAH cores of the two different asphaltenes are similar in size. These observations are reinforced by optical absorption. The coal-derived asphaltenes were found to contain a small fraction of archipelago-type structures, where a small PAH is tethered to the larger PAH core via an aryl linkage, which are less evident, and likely less abundant, in the petroleum asphaltenes. An important difference between the two asphaltenes lies in their alkyl fraction, with the petroleum asphaltenes possessing significantly longer and more mobile alkyl side chains, on average ∼7 carbons long, as opposed to an average chain length of ∼3–4 in the coal asphaltenes. The petroleum asphaltenes also possess a larger fraction of alicyclics. The longer length increases the propensity of the petroleum asphaltene alkyl side chains to intercalate between the aromatic rings of adjacent asphaltene aggregates, which is not observed in coal-derived asphaltenes. This work demonstrates the utility of combining cross-polarization dynamics and directly polarized 13C solid-state NMR spectroscopy in studying asphaltenes, while adding to the body of evidence supporting the single-core model of asphaltenes, which appears to be the dominant structural motif for this fraction of petroleum.

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Cross-polarization dynamics in polycrystalline samples

Cited by 6 publications

References 41 publications

Dynamics of Cross Polarization in Solid State Nuclear Magnetic Resonance Experiments of Amorphous and Heterogeneous Natural Organic Substances

Dynamics of Cross Polarization in Solid State Nuclear Magnetic Resonance Experiments of Amorphous and Heterogeneous Natural Organic Substances

Variable temperature NMR characterization of α-glycine

Single-Core PAHs in Petroleum- and Coal-Derived Asphaltenes: Size and Distribution from Solid-State NMR Spectroscopy and Optical Absorption Measurements

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