Resonance Study Of Molecular Motion Research Articles

Two-dimensional transferred-echo double resonance study of molecular motion in a fluorinated polycarbonate

A two-dimensional version of the transferred-echo double resonance (TEDOR) experiment is introduced to measure strong heteronuclear magnetic dipolar interactions between rare spins. A quantitative description of this 2D-TEDOR experiment is given for an I– S pair of spins undergoing relative motion. 2D-TEDOR calculations are consistent with data for a calibration model: the directly bound 13 C– 31 P pair in [3- 13 C] glyphosate, HO 3 31P 13CH 2NHCH 2COOH. Analysis shows that the indirect spin–spin interaction and the dipole–dipole interaction have opposite signs in this system. The 2D-TEDOR experiment is then used to measure heteronuclear 13 C– 19 F interactions in a fluorinated polycarbonate in which an aromatic proton is replaced by a fluorine on every fourth ring. Results from the 2D-TEDOR experiment show that the aromatic ring flips that occur in ordinary polycarbonate are blocked for a fluorinated ring.

What's water got to do with it? A nuclear magnetic resonance study of molecular motion in pig stratum corneum.

The 1H and 2H magnetic resonance signals from pig stratum corneum were measured as a function of hydration. The 1H free induction decay contained two components, one motionally restricted and the other isotropically mobile on the timescale of 10(-5) s. From its T2 decay, the mobile signal was further subdivided into two components; one, which was 11% of the signal and 5.5% of the mass of the dehydrated stratum corneum, was assigned to nonaqueous tissue (likely hydrocarbons) and the other to water. As water content increased from 0 to 0.25 gH2O/gSC, the second moment of the motionally restricted signal decreased from 5.4 x 10(9) to 3.6 x 10(9) s(-2), whereas the water T2 time increased from less than 0.3 ms to 3.3 ms. The 2H quadrupolar echo from stratum corneum hydrated in 2H2O had a signal from motionally restricted deuterons, attributed to deuterons exchanged onto O-H and N-H groups, and a mobile signal from 2H2O. The amount of exchange, 9.5% of the hydrogen sites in the motionally restricted fraction, was close to the number of exchangeable sites on keratin, the most abundant protein in stratum corneum. Our results are consistent with a model in which the bulk of the water interacts closely with the corneocytes in stratum corneum.

Pulsed electron nuclear double resonance study of molecular motions of radicals in a high-strength liquid-crystalline polymer

Radicals in a liquid-crystalline copolyester are studied by pulsed electron paramagnetic resonance (EPR) and pulsed electron nuclear double resonance (ENDOR). For the first time transient ENDOR techniques are used to investigate molecular motion of radicals in a disordered solid. The nuclear phase memory relaxation of hyperfine coupled protons is measured in a temperature region between 250 and 350 K in the solid state. Remarkably, the relaxation rate increases linearly rather than quadratically with the strength of the hyperfine coupling | A zz |. This results from a thermally activated process, characterized by small-angle fluctuations of radicals with an amplitude of the order of 1°. The corresponding activation energy of 24 kJ/mol indicates that the radicals are chain ends in the polymer.

Magic angle spinning nuclear magnetic resonance studies of molecular motion in cross-linked polyethylene

Magic angle spinning nuclear magnetic resonance spectroscopic investigations were performed on solid state high density polyethylene (HDPE) and low density polyethylene (LDPE) crosslinked by γ-irradiation using doses up to 40 Mrad. The free induction decay was measured at various spinning frequencies in order to obtain information on the influence of crosslinks and branches on molecular mobility in the amorphous regions of the semicrystalline material. The anisotropy of motion caused by crosslinks and entanglements is characterized by the anisotropy parameter, a, and the correlation time of anisotropy fluctuations τ ca . It was found that in HDPE the values of a are larger and those of τ ca are smaller than in LDPE. In HDPE crosslinking leads to a shift of the spectrum of a to larger values whereas in LDPE no change is observed upon irradiation. However, if the material is molten, upon irradiation the molecular mobility is markedly decreased in both HDPE and LDPE. The results are discussed comparing densities of crosslinks and entanglements.

Nuclear Magnetic Resonance Study of Molecular Motions in Poly(γ-n-alkyl L-glutamate)s

The temperature dependence of the NMR line-width and second moment of poly(γ-n-alkyl L-glutamate)s having methyl, ethyl, n-propyl, and n-butyl groups were measured at temperatures ranging from -150°C to 150°C. Three motional narrowing processes were found and are ascribed to the motions of the main chain (the α-process), the side chain as a whole (the β-process), and part of the side chain (the γ-process). The correlation spectra for the β-process in these samples were determined, and the shapes of the spectra were compared with each other, with those of the dielectric-relaxation spectra of the same samples, and with those of the dielectric-relaxation spectra of the β-process in poly(n-alkyl methacrylate)s caused by the motion of similar side chains. It is shown that the shapes of these spectra are the same irrespective of the difference in side-chain length and in main-chain conformation.

Nuclear magnetic resonance studies of molecular motion in guanidinium chloride, bromide, and iodide

Guanidinium [Formula: see text] chloride, bromide, and iodide salts have been studied by 1H and 2H nmr as a function of temperature. The 2H powder lineshapes show conclusively that reorientation of the guanidinium ion occurs about the principal three-fold axis in the chloride, bromide, and high temperature phase of the iodide. Activation energies for this process have been obtained from 1H spin-lattice relaxation results. The question of whether or not there are concurrent two-fold flips of the —NH2 units is discussed, but must presently remain unresolved. It was found that the high temperature phase of the iodide can be supercooled.

Glassy crystals. 2. Electron paramagnetic resonance study of molecular motions and free-radical diffusion near the glass transition in cycloalkanols: evidence for chemical diffusion

Etude par RPE, des radicaux libres produits par irradiation γ a 77 K de cycloalcanols «cristallins vitreux» en fonction de la temperature: mouvements intramoleculaires dans le domaine 10 7 -10 9 Hz au voisinage de la temperature de transition vitreuse, Tg. Analyse de la recombinaison radicalaire autour de T g : elle est regie par diffusion «chimique» dans le cas du cyclooctanol. Mouvements de reorientation rapide

Proton and fluorine nuclear magnetic resonance studies of molecular motion in dimethyl sulfoxide-boron trifluoride complex

Proton and fluorine second moments and spin-lattice relaxation times have been studied over a wide temperature range in solid dimethyl sulfoxide-boron trifluoride (CH 3) 2SO · BF 3 and in its deuterated analog (CD 3) 2SO · BF 3. The results indicate that the two methyl groups are dynamically inequivalent within the molecule and reorient at and above 77 K about their threefold symmetry axes ( C 3) with different frequencies and with activation energies of 6.69 and 10.45 kJ/mol. The BF 3 group is rigid at 77 K, while above 135 K it reorients about its C 3 symmetry axis with an activation energy of 15.93 kJ/mol. The low-temperature fluorine relaxation is controlled by the reorientation of the methyl groups which is faster than that of BF 3. This allows one to deduce for the fluorine-proton second moment a value indicating that the BF3 group is closer to one of the two methyl groups in the proton-containing compound.

A nuclear magnetic resonance study of molecular motion in (2,4,5-Trichlorophenoxy)acetic acid

Proton magnetic resonance data in polycrystalline (2,4,5-trichlorophenoxy)acetic acid in the temperature range 77-400 K are reported in this communication. After a correction is made for the H-H distance in the methylene group the rigid lattice second moment (S2) coincides with the experimental value in the temperature range 77-170 K. The observed fall in S2 in the temperature range 170- 208 K is interpreted as the result of the CH2COOH group reorientation. The barrier height associated with the reorientation is found to be 8.728 kJ mol- which indicates non-cleavage of hydrogen-bonding in the dimeric unit during reorientation.

A nuclear magnetic resonance study of molecular motion in solid l-glutamic acid

Proton magnetic resonance absorption and spin-lattice relaxation time measurements have been carried out on solid l-glutamic acid, NH 3 +CH(CH 2) 2COOHCOO −, in the temperature range 77 to 400 K. The absorption line measurements show that the structure is rigid on the NMR time scale at the lowest temperatures studied, while at higher temperatures the amino group executes hindered rotation about the NC bond. The proton spin-lattice relaxation measurements in both the Zeeman and rotating frames of reference ( T 1 and T 1 ϱ ) reveal a single minimum in each case due to the dominant amino group motion. Analysis of the relaxation data yields an activational energy barrier of 31.1 ± 0.3 kJ mol − to the amino group motion. An additional motional process involving, the rotational oscillation of the methylene side chain has been invoked to explain the slight discrepancy in the second moment and the rotating-frame relaxation data. Both the absorption and the relaxation data are in accord with the fact that this amino acid exists as a zwitterion, wherein the α-amino group is protonated.

13C nuclear magnetic resonance study of molecular motions in natural rubber

T 1 and T2 have been measured at two frequencies and the nuclear Overhauser enhancement at one for the methylene and methine 13C n.m.r. signals from natural rubber. They are shown to be highly consistent with the predictions of a “three-τ” model, which assumes two librational modes of motion at different rates and amplitudes, superimposed on a very slow isotropic motion. Also, they are reasonably consistent with a combined libration and reptation model, but inconsistent with all non-librational models.

Pulsed nuclear magnetic resonance study of molecular motion in solid imipramine hydrochloride, desipramine hydrochloride, and iminobibenzyl

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPulsed nuclear magnetic resonance study of molecular motion in solid imipramine hydrochloride, desipramine hydrochloride, and iminobibenzylDavid W. Larsen, Ted A. Smentkowski, Barbara A. Soltz, and Frank E. StaryCite this: J. Am. Chem. Soc. 1978, 100, 16, 4982–4987Publication Date (Print):August 1, 1978Publication History Published online1 May 2002Published inissue 1 August 1978https://doi.org/10.1021/ja00484a011RIGHTS & PERMISSIONSArticle Views44Altmetric-Citations4LEARN 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 (677 KB) Get e-Alerts Get e-Alerts

Pulsed 1H nuclear magnetic resonance studies of molecular motion and plastic crystallinity in dodecamethylcyclohexasilane

Dodecamethylcyclohexasilane exhibits plastic crystalline behaviour from 77 to 253 °C, with molecular rotation taking place both in the crystalline ( 77 °C) phases; activation energies for various molecular motions are reported.

Proton magnetic resonance study of molecular motion in (NH4)2HAsO4 and (NH4)2HPO4

The temperature dependences of the second moments of the proton magnetic resonance absorption spectra and spin-lattice relaxation times are measured in (NH4)2HAsO4 and (NH4)2HPO4. Characteristic T1 minima and proton line width transitions are found demonstrating the existence of two chemically different NH4 groups in the unit cell. The anomalous increase in the As75 NQR frequency with increasing temperature in (NH4)2HAsO4 is explained as a result of thermally induced “acid” proton fluctuations in the HAsO4 groups. In (NH4)2HAsO4 and (NH4)2HPO4 werden die Temperaturabhängigkeiten der zweiten Momente der magnetischen Protonenresonanzabsorptionsspektren und Spin—Gitter-Relaxationszeiten gemessen. Charakteristische T1-Minima und Übergänge der Protonenlinienbreiten werden gefunden und zeigen die Existenz von zwei chemisch verschiedenen NH4-Gruppen in der Einheitszelle an. Der anomale Anstieg in der As75-NQR-Frequenz mit steigender Temperatur in (NH4)2HAsO4 wird als Ergebnis thermisch induzierter „azider”︁ Protonenfluktuationen in den HAsO4-Gruppen interpretiert.

Carbon-13 nuclear magnetic resonance study of molecular motions and conformational transitions in muscle calcium binding parvalbumins

13C nuclear magnetic resonance is used to detect the Ca2+ ion controlled conformational transition in muscle calcium binding parvalbumin and to study its intramolecular motions. Nuclear relaxation parameters are used to evaluate the reorientation rates of the protein and some of the amino acid side chains. While peripheral residues exhibit greater motional freedom than the protein interior, an interesting finding is that significant rapid internal motion is present in the phenylalanine rings comprising the hydrophobic core of the protein.

A wide-line nuclear magnetic resonance study of molecular motions in piperidinium salts

Wide line nmr and differential scanning calorimetric studies confirm the existence of crystal phase transitions in piperidinium iodide. The highest temperature phase involves isotropic rotation of the piperidinium ion. No crystal structure transitions occur in the chloride, bromide, or hexafluorophosphate salts although these compounds undergo second moment transitions indicating probable rotation of the piperidinium ion about the N—C3 axis.

13C T1 nuclear magnetic resonance study of molecular motion: rotational barriers in hindered methyl groups

Analysis of spin–lattice relaxation (T1) data can give information on restricted rotation which is otherwise inaccessible. This study investigates the influence of substituents on the rotation of a neighbouring methyl group in a series of related polycyclic compounds.

Hydrogen bond studies. 107. A proton magnetic resonance study of molecular motion in solid trimethylammonium iodide, bromide, and hydrogen oxalate

Proton magnetic resonance data are reported for polycrystalline trimethyl-ammonium iodide and bromide, and for poly and monocrystalline trimethyl-ammonium hydrogen oxalate. The second moments at the lowest temperatures correspond to values calculated for rigid structures. Line narrowings occur in the temperature region 120–220 K; the values of the second moments at higher temperatures are consistent with combined reorientations of the methyl groups and the cations as a whole around their respective threefold pseudo-symmetry axes.

Wide line nuclear magnetic resonance study of molecular motions in solid sulpholan

Sulpholan has been studied by the wide line n.m.r. method over the temperature range 77 to 310 K. Two transitions were observed. The transition centred at 210 K is probably due to molecular reorientation about the two-fold axis, and the transition at 288 K is due to both isotropic rotation and self diffusion. The higher temperature transition shows a hysteresis effect.

Proton magnetic resonance study of molecular motion in trimethylamine-trimethylaluminium and trimethylamine-trimethylgallium

Proton magnetic resonance second moments and spin-lattice relaxation times of trimethylamine-trimethylaluminium and trimethylamine-trimethylgallium have been measured between liquid nitrogen temperature and their melting points. The second moments show that the methyl groups attached to Al or Ga are reorientating fast enough to narrow the n.m.r. line at the lowest observed temperatures. Reorientation of the N-methyl groups about their C3 axes and of the whole molecule about the N—Al or N—Ga bond at n.m.r. line width frequencies can be distinguished from the second moment curves as separate processes occurring at higher temperatures. The variation with temperature of the spin-lattice relaxation time has been interpreted for each compound in terms of reorientation with one correlation time of methyl groups on Al or Ga, reorientation with a longer correlation time (at given temperature) of methyl groups on N, and reorientations with yet longer correlation times about the central bond. Separate motions are distinguished for reorientation of the two moieties in the gallium complex. Phase transitions are found in both solids, and in the highest temperature phase of each solid the spin-lattice relaxation results, augmented by values of the spin-lattice relaxation time in the rotating frame, have been interpreted as showing a combined motion of isotropic rotation and self-diffusion. Activation energies have been found for the several motional processes.