Spin-lattice Relaxation Time Measurements Research Articles

Study of stretched polypropylene fibres by [formula omitted] pulsed and CW NMR spectroscopy

A set of stretched isotactic polypropylene fibres prepared with the draw ratio λ = 4 at four different stretching temperatures was investigated by H 1 pulsed relaxation NMR methods and CW NMR spectroscopy. We have studied the influence of the stretching temperature and draw ratio upon the changes of structure and molecular mobility. Some information on the influence of these conditions was obtained from CW NMR measurements by means of the temperature dependences of second moment M 2 and decomposition of NMR spectra into elementary components corresponding to the chains with different mobility. H 1 CW NMR spectra were measured at two (14.1 and 10.5 MHz) Larmor frequencies in the temperature range 200–420 K. An analysis of the experimental data shows that the stretching of the fibres at different temperature results in a change of molecular mobility. Spin-lattice relaxation times in laboratory ( T 1 ) and rotating ( T 1 ρ ) frames were also measured on the set of the fibres in the temperature range 239–423 K at 30 MHz Larmor frequency employing a home made pulse spectrometer. In the rotating frame spin-lattice relaxation time measurements in the temperature range above 278 K three relaxation times T 1 ρ have been observed. The minima of the temperature dependences of the observed relaxation times reflect an α -relaxation process in crystalline regions and β -relaxation process related to a double glass transition in the non-crystalline regions of the studied fibres.

Synthesis, characterization, thermal degradation, and comparative chain dynamics studies of weak-link polysulfide polymers

Synthesis, spectroscopic and thermal characterization of two new classes of polysulfide polymers: poly[1-(phenoxymethyl) ethylene polysulfide] (PPMEP), and poly[1-(phenoxy) ethylene polysulfide] (PPEP) is presented. The direct pyrolysis mass spectrometry (DP-MS) technique, used to study the thermal degradation behavior of these polysulfide polymers, indicated that the polymers underwent degradation through the weak-links scission. The thermal stability of the polysulfide polymers decreased as the “rank” (number of sulfur atoms in the polysulfide linkage; n = 1, 2, 4) increased. The main-chain flexibility of these polysulfide polymers in terms of their 13C NMR spin-lattice relaxation time (T1) measurements on the backbone methine (-CH-) and methylene (-CH2-) carbons are reported here for the first time. A comparative study of the solution chain dynamics indicated that it increased as “rank” of the polysulfide linkages decreased as well as by introducing side chain spacers such as, ether (-O-) or methyleneoxy (-CH2O-) groups.

Proton dynamics of CsH 2PO 4 studied by quasi-elastic neutron scattering and PFG-NMR

To illuminate ionic conduction behavior of super protonic phase of CsH 2PO 4 (CDP), quasi-elastic neutron scattering (QENS), pulse field gradient nuclear magnetic resonance (PFG-NMR) and 1H NMR spin-lattice relaxation time ( T 1) measurements were carried out. Diffusion coefficient of protons obtained from PFG-NMR reproduced well the electrical conductivity by using Nernst–Einstein equation. Comparison of PFG-NMR and T 1 provided a hopping distance of protons as 2.7 Å, which agreed with the next nearest proton sites in CDP. On the other hand, QENS data was fitted well with a jump-diffusion model. Comparison of the jump diffusion coefficient and the correlation time obtained by QENS provided a librational correlation time of protons in the order of 10 − 12 s. The present investigation suggests that different techniques, QENS and NMR, can observe protonic motions having different time constants including librational and translational motions within the hydrogen bonding network of CDP.

Host-Guest Interactions between 2,4-Dichlorophenol and Humic Substances As Evaluated by 1H NMR Relaxation and Diffusion Ordered Spectroscopy

1H NMR measurements of spin-lattice (T1) and spin-spin (T2) relaxation times and diffusion ordered spectroscopy (DOSY) were applied to investigate the association of 2,4-dichlorophenol (DCP) with a soil fulvic (FA-VICO) and humic acid (HA(-)-VICO), and a lignite humic acid (HA-LIG). The 1H T1 and T2 values of DCP were found to decrease with increasing humic concentration, indicating reduction in molecular mobility due to formation of noncovalent interactions. The increased shortening of relaxation times observed upon addition of HA suggested more extensive association of DCP with HA than with FA. The extent of binding was inferred from diffusion coefficients (D) which showed slower diffusion for bound DCP. At 1 mg mL(-1) DCP was completely bound by 4.1 and 5.8 mg mL(-1) of HA-VICO and HA-LIG, respectively, while full DCP association was not observed even up to 20 mg mL(-1) of FA. This was reflected by association constants (Ka): 3.1 +/- 0.3 M(-1) for FA-DCP, and 15.5 +/- 3.1 M(-1) and 11.0 +/- 1.2 M(-1) for HA-VICO and HA-LIG DCP complexes, respectively. The stronger binding to HA is attributed to their larger hydrophobic character enabling formation of stable hydrophobic domains to which DCP becomes associated in host-guest complexes. DCP complexation within humic hydrophobic domains was confirmed by upfield chemical shifts and signal line broadenings observed in 1H NMR spectra. Similar chemical shift variations for the three DCP aromatic protons further indicated pi-pi interactions, rather than H-bonding, as the main driving force for noncovalent association between DCP and dissolved humic substances. Relaxation and diffusion 1H NMR techniques provide rapid and accurate measurements of binding constants and thermodynamic parameters for host-guest complexes between environmental contaminants and natural organic matter.

1H, 13C, 15N NMR and nJ(C, H) coupling constants investigation of 3-piperidino-propylamine: A combined experimental and theoretical study

Proton coupled and decoupled 13C, 1H, 15N, DEPT, COSY, HETCOR and INADEQUATE NMR spectra of 3-piperidino-propylamine (3-pipa) have been reported for the first time. In order to provide a precise structural elucidation, the magnitude of n J(C, H) ( n = 1, 2, 3) coupling constants of 3-pipa (C 8H 18N 2) have been determined. Solvent effects on chemical shifts have been investigated by using CDCl 3 and DMSO. Molecular mobility of the title molecule has also been investigated by performing 13C NMR spin-lattice relaxation time ( T 1) measurements. 13C, 1H and 15N NMR chemical shifts and 1–3J(C, H) coupling constants of 3-pipa have been calculated by means of B3LYP density functional method with 6-311++G(d,p) basis set. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.

Liquid crystal 8CB in random porous glass: NMR relaxometry study of molecular diffusion and director fluctuations

We present the measurements of the proton spin-lattice relaxation time T1 of liquid crystal 4-n-octyl-4'-cyanobiphenyl (8CB) confined into randomly oriented approximately 15 nm pores of untreated porous glass. In the low kilohertz range the spin-lattice relaxation rate in the nanoconfined 8CB is about ten times larger than in the bulk. We show that the increase is mainly due to molecular reorientations mediated by translational displacements (RMTD). In the paranematic phase the power law describing the RMTD dispersion, (T1(-1))RMTD proportional, omega(-p), is well characterized by the exponent p=0.5+/-0.06 and suggests an equipartition of diffusion modes with different wavelengths. The largest distance related to the decay of the orientational correlation function is about twice the diameter of the cavity. The situation is different in the nematic phase, where the orientational correlation is eventually lost at approximately 60 nm in the direction along the pore, a distance corresponding roughly to the length of a pore segment in the glassy matrix. The exponent p is between 0.65 and 0.9, depending on the temperature, which implies that in the nematic phase long wavelength modes are relatively more important--a consequence of the uniform director field along the pore. These observations are in agreement with the model of mutually independent pores with nematic director parallel to the pore axis in each segment. We point out that in strongly confined liquid crystals the proton NMR relaxometry does not provide the evidence of director fluctuations correlated over micrometer distances as was suggested earlier. The local translational diffusion of molecules within the cavities is found about as fast as in bulk.

Penta-coordinated Al 3+ ions as preferential nucleation sites for BaO on γ-Al 2O 3: An ultra-high-magnetic field 27Al MAS NMR study

We report the first observation of preferential anchoring of an impregnated catalytic phase onto penta-coordinated Al 3+ sites on the surface of γ-Al 2O 3. The interaction of barium oxide with a γ-alumina support was investigated by high resolution solid state 27Al magic angle spinning NMR at an ultra-high magnetic field of 21.1 T and at sample spinning rates of up to 23 kHz. Under these experimental conditions, a peak in the NMR spectrum at ∼23 ppm with relatively low intensity, assigned to 5-coordinated Al 3+ ions, is clearly distinguished from the two other peaks representing Al 3+ ions in tetra-, and octahedral coordination. Spin-lattice 27Al relaxation time measurements clearly show that these penta-coordinated Al 3+ sites are located on the surface of the γ-alumina support. BaO deposition onto this γ-alumina sample resulted in the loss of intensity of the 23 ppm peak. The intensity loss observed was linearly proportional to the amount of BaO deposited. The results of this study strongly suggest that, at least for BaO, these penta-coordinated Al 3+ ions are the nucleation sites.

Unique Helical Triangle Molecular Geometry Induced by Dipole–Dipole Interactions

Abstract Novel helix-peptide wheels, in which three helices were connected by using a template, were prepared, and the dipole–dipole interactions among the helices were studied in relation to the formation of a planar triangle structure containing three helices. The helical segments had a 310-helix structure. 13C spin-lattice relaxation time (T1) measurements showed that the helical segments had restricted mobility. Deuterium exchange rates of amide protons were accelerated in the helix-peptide wheels compared to the respective linear helix peptides, suggesting that there is torsion on the cylindrical shape. Therefore, the predominant structure of the helix-peptide wheels is a planar triangle in solution. Further, the triangle structure was successfully transferred onto a gold substrate.

Study of molecular reorientation and quantum rotational tunneling in tetramethylammonium selenate by 1H NMR

1H NMR spin–lattice relaxation time measurements have been carried out in [(CH 3) 4N] 2SeO 4 in the temperature range 389–6.6 K to understand the possible phase transitions, internal motions and quantum rotational tunneling. A broad T 1 minimum observed around 280 K is attributed to the simultaneous motions of CH 3 and (CH 3) 4N groups. Magnetization recovery is found to be stretched exponential below 72 K with varying stretched exponent. Low-temperature T 1 behavior is interpreted in terms of methyl groups undergoing quantum rotational tunneling.

Favorable magnetic fluctuation anisotropy for unconventional superconductivity inf-electron systems

We report spin-lattice relaxation time measurements in isostructural ($\mathrm{Ho}\mathrm{Co}{\mathrm{Ga}}_{5}$-type) actinide compounds with different ground states (paramagnet, antiferromagnet, and superconductor) using single-crystal samples. The anisotropy of local magnetic fluctuations due to $LS$ coupling on the actinide (magnetic) site is evaluated. In the superconductor $\mathrm{Pu}\mathrm{Rh}{\mathrm{Ga}}_{5}$, the $XY$-type magnetic anisotropy is strong compared with nonsuperconducting compounds. Favorable magnetic anisotropy for $d$-wave superconductivity in $f$-electron systems is discussed.

Structures of Linear Poly(ethylene oxide) Compounds and Potassium Complexes in Dichloromethane

The H-1 NMR spectra of a series of linear poly(ethylene oxides) compounds (POE compounds) were measured in dichloromethane-d2 at 25 degrees C, where the POE compounds (HO-(CH2CH2O-)n-R) were unsubstituted POE, HEOn (R=H, n=3, 4, 6), and alkyl-substituted POE, DEOn (R=C12H25, n=4, 6, 8) and MeEO6 (R=CH3, n=6). All the peaks of H-1 NMR signals were assigned to each methylene proton of POE. The chemical shifts and coupling constant between vicinal protons were evaluated by a complete spin analysis. The spectral changes of POE compounds by the addition of potassium ion were measured at various metal-to-POE ratios. The chemical shift change of each methylene proton by the formation of the complex was evaluated. The downfield shift of methylene protons caused by the complex formation indicates that the ethylene oxide that the ethylene oxide moiety is coordinating to surround the potassium ion in the same manner as the cyclic crown ether complexes. The results of spin lattice relaxation time measurements of DEO6 suggest that all the methylenes of the ethylene oxides are immobilized by the coordination to the metal ion. Thus, it was confirmed that all oxygens of POE are participating in the complex formation.

NMR study of noncentrosymmetric superconductor Li2Pt3B

Measurements of Knight shift and nuclear spin-lattice relaxation time for 7Li , 11B and 195Pt has been performed in powdered sample of newly discovered noncentrosymmetric superconductor, Li2Pt3B. We discuss the local density of states at each atomic site. The result shows the platinum 5d electrons plays a dominant role for the electrical properties in this compound.

Spectroscopic study of the effect of N and F codoping on the spatial distribution of Er3+ dopant ions in vitreous SiO2

Pulsed electron paramagnetic resonance (EPR) spectroscopy has been used to study the influence of codoping with N and/or F on the clustering of Er3+ ions in vitreous SiO2. Measurements of echo-detected EPR, spin-lattice and phase memory relaxation times, and electron spin-echo envelope modulation (ESEEM) were made in the X band. Er-N, Er-F, and Er-N-F codoped glasses show clear evidence of clustering of Er3+ ions at concentration levels ranging between 6.67×1018 cm−3 and 6.67×1019 cm−3. However, the relatively long phase memory relaxation time and the observability of ESEEM in the Er-N-F codoped glass strongly indicate that combined codoping with N and F is more effective in homogenization of the spatial distribution of Er3+ ions in vitreous SiO2, although, the structural mechanism remains unclear. The ESEEM results provide evidence in favor of the presence of N in the vicinity of the Er3+ ions in Er-N-F codoped vitreous SiO2.

Twist glass transition in regioregulated poly(3-alkylthiophene)

The molecular structure and dynamics of regioregulated poly(3-butylthiophene) (P3BT), poly(3-hexylthiophene) (P3HT), and poly(3-dodecylthiophene) (P3DDT) were investigated using Fourier-transform infrared absorption (FTIR), solid-state $^{13}\mathrm{C}$ nuclear-magnetic resonance (NMR), and differential-scanning calorimetry (DSC) measurements. In the DSC measurements, the endothermic peak was obtained around $340\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in P3BT, and assigned to enthalpy relaxation that originated from the glass transition of the thiophene-ring twist in crystalline phase from results of FTIR, $^{13}\mathrm{C}$ cross-polarization and magic-angle spinning (CPMAS) NMR, $^{13}\mathrm{C}$ spin-lattice relaxation-time measurements, and centerband-only detection of exchange (CODEX) measurements. We defined this transition as a twist-glass transition, which is analogous to the plastic crystal--glassy crystal transition.

The role played by the interactions of small molecules with chitosan and their transition temperatures. Glass-forming liquids: 1,2,3-Propantriol (glycerol)

Dynamic behaviour of chitosan and chitosan blended with 1,2,3-propantriol (glycerol) has been studied by dynamic mechanical analysis (DMTA), solid-state NMR and differential scanning calorimetry (DSC). Two relaxation processes appear in pure chitosan, one at high temperature, the α-relaxation which has been attributed to its glass transition temperature and interpreted as torsional oscillations between two glucopyranose rings across a glucosidic oxygen and a cooperative hydrogen bonds reordering. And the other, a low temperature relaxation, β, which is associated with local motions of lateral groups, namely, –NH 2 or as – NH + 3 - OOC – CH 3 (quitosonium acetate), –CH 2OH and in some extension –NH–OC–CH 3, mainly. The incorporation of glycerol in the blends results, as detected by DMTA analysis, in a substantial depression of the glass transition of the chitosan matrix due to a plasticization process. The β-relaxation in the blends, which also depends on glycerol concentration, has been interpreted as motions of the side chains of chitosan linked to glycerol by hydrogen bonding. The interaction between both components was also investigated by solid-state NMR, which revealed a decreasing of the glycerol mobility with increasing chitosan content in the blends and an increase of chitosan mobility for enriched glycerol blends. The measurements of the proton spin-lattice relaxation time in the rotating frame, T 1 ρ H for 50% mol chitosan blend revealed that the blend is homogeneous in a length scale of few nanometers. As the glycerol concentration is increased, two relaxation times could be distinguished, corresponding to glycerol and chitosan domains. For high concentration glycerol blends, we have assumed a “ clustering model” for the glycerol molecules sorbed on chitosan macromolecular chains consisting of a two-step mechanism. A first step, in which the solvent is sorbed by means of hydrogen bonds on polymer-specific sites such as –OH and –NH 2 or as – NH + 3 - OOC – CH 3 (quitosonium acetate), and a second one, a solvent clustering around the first sorbed solvent molecules forming a hydrogen bonded network of glycerol molecules.

Investigation of local chain dynamics in poly(di-n-alkylitaconate)s

13C NMR in solution and molecular dynamics simulations were used to discuss the respective roles of intramolecular constraints and intermolecular contributions in poly(di-n-alkylitaconate)s (PDAI) with various side chain lengths. These polymers exhibit the unusual phenomenon of two distinct glass transitions when the alkyl side chains contain at least six carbon atoms. Nuclear Overhauser enhancement and spin-lattice relaxation time measurements in solution for PDAI’s with different side-chain lengths clearly indicated the existence of a competition between internal plasticization and organization of the alkyl parts of the side chains. This organisation decreases the flexibility of the long side chains and slows down the internal mobility of the main chain and carbonyl groups. Molecular modelling of the relative organization of two polymer chains demonstrates the strong tendency of the long alkyl parts to order and form discrete regions, which can be related to the existence of the second low-temperature glass transition in PDAI’s with long side groups.

Relaxation in the glass former acetylsalicylic acid studied by deuteron magnetic resonance and dielectric spectroscopy

Supercooled liquid and glassy acetylsalicylic acid was studied using dielectric spectroscopy and deuteron relaxometry in a wide temperature range. The supercooled liquid is characterized by major deviations from thermally activated behavior. In the glass the secondary relaxation exhibits the typical features of a Johari-Goldstein process. Via measurements of spin-lattice relaxation times the selectively deuterated methyl group was used as a sensitive probe of its local environments. There is a large difference in the mean activation energy in the glass with respect to that in crystalline acetylsalicylic acid. This can be understood by taking into account the broad energy barrier distribution in the glass.

Molecular Properties of Flurbiprofen and its Solid Dispersions with Eudragit RL100 Studied by High- and Low-Resolution Solid-State Nuclear Magnetic Resonance

Investigation of the conformational and molecular dynamic properties of the acidic and sodium salt forms of Flurbiprofen and their solid dispersions with Eudragit RL100, obtained by two different preparation methods (physical mixtures and coevaporates), and of the mixing degree between the two components in the dispersions. 1H and 13C high-resolution solid state NMR techniques, including Single Pulse Excitation-MAS, CP-MAS, FSLG-HETCOR; low-resolution 1H FID analysis; 1H spin-lattice relaxation time measurements. Conformational, molecular packing and dynamic differences were observed between the two pure forms of flurbiprofen, as well as between the pure drugs and the corresponding coevaporates. In the coevaporates of the two flurbiprofen forms, drug and polymer appear intimately mixed; their chemical interactions were detected and characterized. A combined analysis of several 13C and 1H high- and low-resolution solid state NMR experiments allowed the investigation of the conformational and dynamic properties of the pure drugs and of the solid dispersions with the polymer, as well as of the degree of mixing between drug and polymer and of the chemical nature of their interaction. Such information could be compared to the in vitro drug release profiles given by these solid dispersions.

Measurements of tissue T1 spin-lattice relaxation time and discrimination of large draining veins using transient EPI data sets in BOLD-weighted fMRI acquisitions

The signal intensity during the dynamic approach to the equilibrium state of longitudinal magnetization is a function of sequence parameters, such as repetition time and flip angle, and depends on tissue characteristics, including longitudinal relaxation time of stationary tissue and the rate of blood inflow. A method is presented to extract information from data acquired during the transient state prior to T 1 equilibrium using echo-planar acquisitions in T 2*-weighted functional magnetic resonance imaging (fMRI) experiments. A voxel in a single slice acquisition is assumed to contain either stationary tissue or large vessels with flowing blood. Models are presented to characterize longitudinal magnetization relaxation of heterogeneous stationary tissue and blood inflow. The data were fitted to theoretical models for longitudinal relaxation of stationary tissue and inflowing blood assuming no residual signal prior to each RF excitation. Parameters were estimated at 3 T for each model using least squares estimation. A goodness-of-fit criterion was applied to exclude voxels that have transient data that does not fit the selected (best fit) model. Voxels that best fit the inflow model, measured at various TR and flip angles, were assumed to contain large draining veins and were excluded from functional maps. Histogram analysis of T 1 distributions for activated voxels in a visual paradigm demonstrated the distributions are centered at T 1 values of gray matter with tails at both sides of the center due to partial voluming of gray matter with white matter and CSF respectively. The mean gray matter volume fraction in activated voxels was about 0.9. The results indicate that transient data sets can provide additional information that is useful for both localization and characterization of the functionally relevant BOLD response.

Paramagnetic relaxation of protons in rotationally immobilized proteins

The proton magnetic relaxation dispersion profiles are reported over the proton Larmor frequency range from 0.01 to 30 MHz for cross-linked gels and for the dry lyophilized bovine serum albumin covalently labeled at lysine with diethylenetriaminepentaacetic acid chelates of either Gd(III) or Mn(II) ions. The proton spin-lattice relaxation dispersion for the cross-linked paramagnetic protein gel is accurately represented as a sum of two major relaxation contributions. The diamagnetic term is a power law from the magnetic field dependence of the protein protons. The paramagnetic term is approximately described by the Solomon-Bloembergen-Morgan class of models. However, the paramagnetic relaxation mechanism in the dry lyophilized protein is fundamentally different and we develop a new quantitative description of the dispersion profile. In the dry case, no peak in the proton relaxation dispersion profile is detected from the field dependence of the electron spin relaxation times. The high-field paramagnetic relaxation dispersion is a power law in the Larmor frequency with an exponent of -0.8, which results from modulation of the electron-nuclear coupling by the intramolecular dynamics of the protein which primarily propagates along the primary structure of the protein. The low-field plateau is caused by the interruption of the electron-nuclear spin correlation by electron spin relaxation. This new quantitative description provides a simple approach to the measurement of electron spin-lattice relaxation times in paramagnetic protein systems at room temperature based on the magnetic field dependence of the proton spin-lattice relaxation rate constant.