NMR Spin-lattice Relaxation Time Measurements Research Articles

Ion transport in non-aqueous electrolyte mixtures of zinc chloride deep eutectic solvent (DES) and molecular solvents

The ion dynamics of null solvents 1ZnCl2:4EtG and 1ChCl:1ZnCl2:6EtG incorporating 1M water, propylene carbonate (PC) or acetonitrile (AcN) were investigated using 1H NMR spectra and spin-lattice relaxation time (T1) measurements combined with ionic conductivity, density, and viscosity, all as a function of temperature. Results show that the inclusion of all co-solvents increased the available free volume of the mixtures and followed the trend H2O ≤ PC < AcN. 1H NMR spectra and T1 inferred the presence of multiple ionic species with varying rates of mobilities. These dynamic heterogeneities were displayed by the broad T1 minima – especially for the 1ZnCl2:4EtG mixtures – and asymmetrically broadened linewidths. T1 results also revealed selective interaction sites between the hydrogen bond donors and acceptors, as well as with the co-solvents.

Chain-folded lamellar structure and dynamics of the crystalline fraction of Bombyx mori silk fibroin and of (Ala-Gly-Ser-Gly-Ala-Gly)n model peptides

Solid-state NMR is a powerful analytical technique to determine the composite structure of Bombyx mori silk fibroin (SF). In our previous paper, we proposed a lamellar structure for Ala-Gly copolypeptides as a model of the crystalline fraction in Silk II. In this paper, the structure and dynamics of the crystalline fraction and of a better mimic of the crystalline fraction, (Ala-Gly-Ser-Gly-Ala-Gly)n (n = 2–5, 8), and 13C selectively labeled [3-13C]Ala-(AGSGAG)5 in Silk II forms, were studied using structural and dynamical analyses of the Ala Cβ peaks in 13C cross polarization/ magic angle spinning NMR and 13C solid-state spin-lattice relaxation time (T1) measurements, respectively. Like Ala-Gly copolypeptides, these materials have lamellar structures with two kinds of Ala residues in β-sheet, A and B, plus one distorted β-turn, t, formed by repetitive folding using β-turns every eighth amino acid in an antipolar arrangement. However, because of the presence of Ser residues at every sixth residue in (AGSGAG)n, the T1 values and mobilities of B decreased significantly. We conclude that the Ser hydroxyls hydrogen bond to adjacent lamellar layers and fix them together in a similar way to Velcro®.

Effect of Noncovalent Dispersion of Poly(Ethylene Oxide) in Columnar Polyether-Based Discotic Liquid Crystal on the Ionic Conductivity and Dynamics of Lithium Ions

The ionic conductivity of an electrolyte is represented by a product of carrier density, charge (electric), and ionic mobility. The overall goal of this study was to provide an insight into the influence of lithium ion conductivity and dynamic when a continuous discotic liquid crystal (DLC) matrix of hexaazatrinapthylene-polyether, HATN-TEG-1, is doped with a small amount of polyethylene oxide (PEO, 5% of MW 8000). The favorable non-covalent interactions between PEO and the DLC triethylene glycol side-chains is supported by the maintenance of the mesophase. The lithium ionic conductivity of HATN-TEG-1 was found to be 1.1 × 10−6 S cm−1, which is better than the corresponding HATN-TEG-1-5%PEO-8000 with a value of 6.06 × 10−7 S cm−1. These results are further supported by the dynamics of the lithium ions in HATN-TEG-1 and HATN-TEG-1-5%PEO-8000 as characterized by 7Li, and 1H NMR spin-lattice relaxation time and self-diffusion coefficient measurements. Though the additional PEO was found to increase the ion carriers, the significant lowering of the ionic conductivity may be attributed to the more pronounced decrease of the mobility of the ionic part when the HATN-TEG-1 matrix is dispersed with PEO. This finding indicates that the doping of 5% PEO onto the matrix of HATN-TEG-1 DLC has an adverse effect on both its diffusion rate and ion conductivity.

Hybrid organic-inorganic bismuth(III)-based material [4-NH2C5H4NH]7[BiCl6]2Cl. Crystal structure, dielectric properties and molecular motions of 4-aminopyridinium cations

4-aminopyridinium analogue, [4-NH2PyH]7[BiCl6]2Cl, has been synthesized and characterized by single-crystal X-ray diffraction at 100 K, calorimetric, dilatometric and dielectric studies. The crystal structure is centrosymmetric with the monoclinic space group, P21/n. It consists of two discrete [BiCl6]3- octahedra, one loose Cl− anion and seven, partially disordered, 4-aminopyridinium cations. The compound reveals a reversible first-order phase transition (I→II) at 305/304 K of the ‘order-disorder’ type. The dielectric studies disclosed a relaxation process in the kilohertz frequency region, assigned to the dynamics of organic cations, described well by the Cole-Cole relation. The 1H NMR spin–lattice relaxation time measurements indicate a complex cations motion over the Phase II. The possible mechanism of the I → II phase transition in [4-NH2PyH]7[BiCl6]2Cl is discussed.

Identification of Li-Ion Battery SEI Compounds through (7)Li and (13)C Solid-State MAS NMR Spectroscopy and MALDI-TOF Mass Spectrometry.

Solid-state (7)Li and (13)C MAS NMR spectra of cycled graphitic Li-ion anodes demonstrate SEI compound formation upon lithiation that is followed by changes in the SEI upon delithiation. Solid-state (13)C DPMAS NMR shows changes in peaks associated with organic solvent compounds (ethylene carbonate and dimethyl carbonate, EC/DMC) upon electrochemical cycling due to the formation of and subsequent changes in the SEI compounds. Solid-state (13)C NMR spin-lattice (T1) relaxation time measurements of lithiated Li-ion anodes and reference poly(ethylene oxide) (PEO) powders, along with MALDI-TOF mass spectrometry results, indicate that large-molecular-weight polymers are formed in the SEI layers of the discharged anodes. MALDI-TOF MS and NMR spectroscopy results additionally indicate that delithiated anodes exhibit a larger number of SEI products than is found in lithiated anodes.

Nuclear magnetic resonance study on rotational dynamics of water and benzene in a series of ionic liquids: Anion and cation effects

The rotational correlation times (τ(2R)) for polar water (D(2)O) molecule and apolar benzene (C(6)D(6)) molecule were determined in ionic liquids (ILs) by means of the (2)H (D) NMR spin-lattice relaxation time (T(1)) measurements. The solvent IL was systematically varied to elucidate the anion and cation effects separately. Five species, bis(trifluoromethylsulfonyl)imide (TFSI(-)), trifluoromethylsulfonate (TfO(-)), hexafluorophosphate (PF(6)(-)), chloride (Cl(-)), and formate (HCOO(-)), were examined for the anion effect against a fixed cation species of 1-butyl-3-methyl-imidazolium (bmim(+)). Four species, bmim(+), N-methyl-N-butylpyrrolidinium (bmpy(+)), N,N,N-trimethyl-N-propylammonium (N(1,1,1,3)(+)), and P,P,P-trihexyl-P-tetradecylphosphonium (P(6,6,6,14)(+)), were employed for the cation effect against a fixed anion species of TFSI(-). The τ(2R) ratio of water to benzene, expressed as τ(W/B), was used as a probe to characterize the strength of Coulombic solute-solvent interaction in ILs beyond the hydrodynamic limit based on the excluded-volume effect. The τ(W/B) value was found to strongly depend on the anion species, and the solute dynamics are sensitive not only to the size but also to the chemical structure of the component anion. The cation effect was rather weak, in contrast. The largest and most hydrophobic P(6,6,6,14)(+) cation was exceptional and a large τ(W/B) was observed, indicating a unique solvation structure in [P(6,6,6,14)(+)]-based ILs.

Anomalous dielectric behaviour in centrosymmetric organic–inorganic hybrid chlorobismuthate(III) containing functional N,N-dimethylethylammonium ligand. Crystal structure and properties

The structure of [C2H5NH(CH3)2+]3[BiCl6−] (abbreviated as DCB) was determined by a single-crystal X-ray diffraction at 115K. The compound adopts tetragonal symmetry with the space group I41/acd; a=23.35Å, c=17.60Å, V=9598Å3 and Z=16. The crystal structure of DCB is built up of isolated [BiCl6]3− units and N,N-dimethylethylammonium counterions that are accommodated in the large voids. At ambient temperature two-thirds of the counterions appear to be dynamically disordered. Dynamics of this type of cations contributes to the enhanced dielectric permittivity of DCB. A low frequency dielectric relaxation process that takes place between 200 and 300K is characterized by an exceptionally large dielectric increment, Δϵ>100, which is unprecedented in nonferroelectric materials. The molecular motions of the N,N-dimethylethylammonium cations were studied by means of H1 NMR spin-lattice relaxation time measurements.

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.

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.

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.

Significantly Contrasting Solid State Dynamics of the Racemic and Enantiomerically Pure Crystalline Forms of an Amino Acid

Solid state dynamic properties have been investigated for the racemic (DL) and enantiomerically pure (L) crystalline forms of the amino acid serine [HO x CH2 x CH(NH3(+)) x CO2(-)] using 2H NMR line shape analysis and 2H NMR spin-lattice relaxation time measurements for samples of DL-serine and L-serine deuterated in the NH3(+) and OH groups. 2H NMR line shape analysis indicates that, for both L-serine and DL-serine, the ND3(+) group undergoes a 3-site 120 degrees jump motion, with jump frequencies in the intermediate motion regime (10(3) s(-1) to 10(8) s(-1)) in the temperature range 153-313 K. However, at a given temperature, the jump frequency is substantially higher for L-serine (e.g., at 233 K, the jump frequency is 5.0 x 10(6) s(-1) for L-serine and 6.0 x 10(4) s(-1) for DL-serine). The OD group is not dynamic on the 2H NMR time scale within the temperature range studied. The results from both 2H NMR line shape analysis (LA) and 2H NMR spin-lattice relaxation time measurements (SLR) indicate that the activation energy for the 3-site 120 degree jump motion of the ND3(+) group is significantly higher for DL-serine [38.0 +/- 1.0 kJ mol(-1) (LA); 39.7 +/- 0.8 kJ mol(-1) (SLR)] than for L-serine [23.4 +/- 0.8 kJ mol(-1) (LA); 23.8 +/- 0.3 kJ mol(-1) (SLR)]. The difference in activation energies between DL-serine and L-serine is substantially greater than any reported previously for an amino acid in different crystal forms.

Crowned dendron: ion-responsive flexibility of macromolecules induced by integrated crown ether moieties

Polybenzyl ether type dendrons bearing the crown ether moieties at the periphery, namely, crowned dendrons were synthesized, and the effect of complex formation on their flexibility with metal-ion binding properties was examined. Upon addition of Na +, 1H NMR spectra of the crowned dendrons in CD 3CN were significantly broadened, reflecting the flexibility restriction of the crowned dendrons by the complex formation with Na +. Such a significant flexibility restriction was observed only with Na +, although ESI-MS studies revealed that the crowned dendrons formed 1:2 complexes (a metal ion:the crown ether moiety) regardless of the kind of metal ions. The flexibility restriction became significant with increasing dendron generation on the basis of 1H NMR spectra and spin-lattice relaxation time ( T 1) measurements. Binding constants of the crowned dendrons with metal ions in CD 3CN decreased with the increase of the dendron generation, reflecting an influence of the charge repulsion as well as a dendrimer effect to cause the steric hindrance. The examination of UV–vis absorption spectra for complexes of the crowned dendron with metal picrates in THF displayed the formation of a loose ion-pair complex with Na +, namely, a typical sandwich type complex. However, in CH 3CN, all metal picrates were solvated to be in a loose ion-pair even without complex formation. These results suggested that the control of macromolecular flexibility with metal ions is feasible by the integration of crown ether moieties with a dendritic structure.

Pressure and Temperature Effects on the Molecular Rotation in Acetonitrile-Water Mixtures

NMR spin-lattice relaxation time (T1) measurements were performed for 14N of acetonitrile in acetonitrile (CH3CN)—H2O mixtures and for 2H of heavy water in CH3CN—D2O mixtures at 30°C up to 294.2 MPa together with those for 2H in CH3CN—D2O mixtures at 10 and 20°C under atmospheric pressure over the whole composition range of the mixtures. IR absorption spectra for CH3CN—H2O and CH3CN—10 mol% HDO/D2O mixtures were obtained at 30°C under atmospheric pressure. Densities and viscosities of CH3CN—H2O mixtures were also measured under high pressure. The rotational correlation times for D2O [τ c (D)] and acetonitrile [τ c (N)] were determined from T1 measurements. Under atmospheric pressure, τ c (D) exhibits a small maximum around 10 mol% of acetonitrile at each temperature, and the maximum position is almost independent of temperature. These results suggest that the dipole–dipole interaction between acetonitrile and water molecules plays an important role in determining the rotational motion of water molecules in the mixtures. This is supported by the variation of the peak for the bending vibration of water molecules with composition. The decreases in τ c (D) and τ c (N) at higher acetonitrile contents are ascribed to the formation of acetonitrile dimer, trimer, and oligomer aggregates. Except for τ c (D) in the water-rich region, the pressure coefficients of τ c (D) and τ c (N) are positive which is understood as a simple compression effect. Furthermore, the composition of mixture at which τ c (D) and τ c (N) show a maximum shifted to higher acetonitrile content with increasing pressure. These results are discussed in terms of the pressure effect on the equilibria of acetonitrile monomers with the aggregates of acetonitrile in the mixtures.

High temperature proton NMR study of yttrium doped barium cerates

The mobility of protons in BaCe1−xYxO3−δ perovskite (x=0.01 to 0.10) was investigated by high temperature 1H NMR spin-lattice relaxation time (T1) and ac conductivity measurements. The temperature variation of T1 was obtained from room temperature to 1073 K. The absolute magnitude of T1 shows a complex dependence on doping concentration. However, the shape of the temperature dependence of T1 was independent of the doping concentration, suggesting the absence of major differences of the proton hopping mechanism on doping level of this material. The measured conductivity was well reproduced by a simple hopping model using correlation times of proton migration and proton concentrations estimated from the NMR measurement.

Crystal Structure and Cationic Motion of o-Toluidinium Chloranilate and m-Toluidinium Chloranilate Studied by X-ray Diffraction and 1H NMR

The crystal structure of o-toluidinium chloranilate and m-toluidinium chloranilate, 2CH3C6H4-NH3 + · C6O4Cl2 2−, was determined by single crystal X-ray diffraction at room temperature. It was found that o-toluidinium chloranilate (I) is monoclinic, P21/n (#14), Z = 2, a = 5.2184(14), b = 7.825(2), c = 22.840(5) Å , and β = 92.015(19)°, and m-toluidinium chloranilate (II) is monoclinic, P21/c (#14), Z = 2, a = 11.214(2), b = 5.4844(10), c = 16.379(6) Å, and β = 105.21(2)°. In these salts, the cations are connected with the anions by N-H... O hydrogen bonds to form 2:1 units of 2CH3C6H4NH3 + · C6O4Cl2 2− that are located on inversion centers. The 2CH3C6H4NH3 + · C6O4Cl2 2− units in both salts are connected by other N-H... O hydrogen bonds to build a three-dimensional hydrogen-bond network. Motions of the toluidinium ions in solid (I) and (II) were studied by 1H NMR spin-lattice relaxation time measurements. Reorientations of the NH3 + group about the C-N bond axis and the CH3 group about the C-C bond axis were observed, and their motional parameters were evaluated. The internal rotational barriers of the NH3 + and CH3 groups of an isolated o-toluidinium ion were estimated from ab initio molecular orbital calculations at HF/6-31G(d,p), MP2/6-31G(d,p), and B3LYP/6-31G(d,p) levels of theory.

Probing Pore Size Distribution by Cryogenic- and Relaxation 2H-NMR

Cryogenic NMR and NMR spin-lattice relaxation time (NMRT) measurements of pore-confined water (D 2 O) have been performed using deuterium NMR to probe the pore size distribution (PSD) of silica materials and porous membranes. NMRT measurements were performed at a temperature slightly below the normal freezing point (277 K) of bulk water (D 2 O) to ensure that all interparticle water was frozen out. PSD derived from cryogenic NMR was in excellent agreement with PSD obtained from N 2 -adsorption measurements. Also, PSD obtained by NMRT revealed approximately the same average pore dimension as obtained by N 2 adsorption. However, the former experimental technique resulted in somewhat narrower PSD than obtained by cryogenic NMR and N 2 adsorption and is discussed in the text. An attempt to determine the PSD of a TiO 2 membrane on a silica support by NMRT will also be discussed. The main results obtained in this work suggest that a combined use of cryogenic NMR and NMRT may give information on both PSD and pore-connectivity.

Dynamic Properties of the Guest Molecules in the Pyrazine/α-Zirconium Phosphate Intercalation Compound: a Multinuclear Solid-State NMR Study

Dynamic properties of perdeuterated pyrazine (pyrazine-d(4)) guest molecules in the layered a-zirconium phosphate host structure have been established from solid-state H-2 NMR lineshape analysis and H-2 NMR spin-lattice relaxation time measurements. Both techniques indicate that the intercalation compound contains two different types of pyrazine-d(4) guest molecules, which undergo different dynamic processes. The relative proportions of the two types of pyrazine-d(4) guest molecules are approximately 30% (component A) and 70% (component B). The pyrazine-d(4) molecules representing component B undergo two-site 180degrees jumps about the N...N axis of the molecule, whereas the pyrazine-d(4) molecules representing component A undergo an effectively isotropic motion. The activation energy for the two-site 180degrees motion of component B is estimated to be 39 kJ mol(-1) from the H-2 NMR spin-lattice relaxation time measurements and 49 kJ mol(-1) from the H-2 NMR line-shape analysis. Structurally, it may be inferred that component B comprises guest molecules for which the N...N axis has a restricted orientation in space, presumably because of direct interactions with the alpha-zirconium phosphate host structure, whereas component A comprises guest molecules that are held rather weakly in the host structure (or on its external surfaces) such that their reorientation is relatively unestricted. Thermogravimetric analysis provides direct evidence for the existence of two different types of pyrazine guest molecules in the alpha-zirconium phosphate host structure, with different strengths of binding and with populations in the approximate ratio 30:70. High-resolution solid-state N-15 NMR and C-13 NMR spectra provide further support for the existence of two different types of pyrazine guest species within the alpha-zirconium phosphate host structure and provide direct evidence that the pyrazine guest molecules of component B are N-protonated (from the host structure).

Dynamical structure of AgxCu1-xI (x=0.99–0.80) in ionic and superionic phases studied by solid 63Cu and 127I NMR spin–lattice relaxation time measurements

The temperature dependences of the 63Cu and 127I NMR spin–lattice relaxation time T1 and the 63Cu NMR spin–lattice relaxation time in a rotating frame T1ρ were measured for AgxCu1−xI (x = 0.99–0.80). In the γ phase, T1 and T1ρ were dominated by the lattice vibration at low temperatures. The minimum of T1ρ caused by the diffusion of the Cu ion was observed at ca. 360 K. The temperature dependence of T1ρ in the range 420–300 K can be explained in terms of a distribution of correlation times which arises from a distribution of activation energies for the ionic diffusion. The mean and the width of the distribution for the activation energies increased with increasing Cu concentration. The rapid T1 decrease observed above ca. 400 K can be attributed to the motion of the thermally generated defects. The enthalpy for the formation of the defect was estimated as 120 ± 10 kJ mol−1 from 63Cu NMR T1 and T1ρ values. In the α phase, the relaxation of the 63Cu nucleus was in the fast motion region and the activation energy of the ionic diffusion was determined as 7 ± 1 kJ mol−1 from the temperature dependence of 63Cu NMR T1.

NMR interaction studies of aromatic guanyl hydrazones with micelles: model for mechanism of action of cationic antibiotics.

Interaction studies using hydrogen NMR spin-lattice relaxation time measurements of a series of five antiparasitic guanyl hydrazones with SDS and cetyl trimethylammonium bromide micelles are used as a simple model for the interaction of these compounds with the cell membrane of Trypanosoma cruzi. The results show that the activity of the compounds is related to their capacity to selectively interact with anionic micelles, which reinforces the hypothesis that the mechanism of action of these compounds is related to their selective interaction with the negatively charged parasite membrane.