Wide line and pulsed NMR studies of carboxyl-terminated polybutadiene polymers and binders

Nuclear magnetic resonance relaxation and line width studies were performed on two carboxyl-terminated polybutadiene polymers and their corresponding binders at temperatures from ?170 to 25°C. It was observed that the line widths of the binders increased as the functionality of the corresponding liquid polymers increased. In addition, glass transition temperatures and activation energies obtained from line width measurements were determined. From pulse measurements the magnitude of the relaxation time T₁ and the temperature at which T₁ is a minimum were determined for a polymer and its corresponding binder. These empirical quantities for the carboxyl-terminated polybutadiene polymers were lower than those of the corresponding binders because of less restraints in the internal motions of the polymer chain.     

Line-Pro le Analysis of Excitation Spectroscopy in the Even 3p5(2P1/2)nl'[K']J(l'=1,3) Autoionizing Resonances of Ar

The even-parity autoionizing resonance series 3p⁵np'[3/2]_1,2, 3p⁵np'[1/2]₁, and 3p⁵nf'[5/2]₃ of Ar have been investigated exciting from the two metastable states 3p⁵4s[3/2]₂ and 3p⁵4s'[1/2]₀ in the photon energy range of 32500-35600 cm^-1 with an experimental bandwidth of ~0.1 cm^-1. The excitation spectra of the even-parity autoionizing resonance series show typical asymmetric line shapes. New level energies, quantum defects, line profile index and resonance widths, resonance lifetime and reduced widths of the autoionizing resonances are derived by a Fano-type line-shape analysis. The line profile index q and the resonance widths Γ are shown to be approximately proportional to the effective principal quantum number n^*. The line separation of the 3p⁵np' autoionizing resonances is discussed.     

Ultra‐wideline 27Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Ultra‐wideline ²⁷Al NMR experiments are conducted on coordination compounds with ²⁷Al nuclei possessing immense quadrupolar interactions that result from exceptionally nonspherical coordination environments. NMR spectra are acquired using a methodology involving frequency‐stepped, piecewise acquisition of NMR spectra with Hahn‐echo or quadrupolar Carr–Purcell Meiboom–Gill (QCPMG) pulse sequences, which is applicable to any half‐integer quadrupolar nucleus with extremely broad NMR powder patterns. Despite the large breadth of these central transition powder patterns, ranging from 250 to 700 kHz, the total experimental times are an order of magnitude less than previously reported experiments on analogous complexes with smaller quadrupolar interactions. The complexes examined feature three‐ or five‐coordinate aluminum sites: trismesitylaluminum (AlMes₃), tris(bis(trimethylsilyl)amino)aluminum (Al(NTMS₂)₃), bis[dimethyl tetrahydrofurfuryloxide aluminum] ([Me₂‐Al(μ‐OTHF)]₂), and bis[diethyl tetrahydrofurfuryloxide aluminum] ([Et₂‐Al(μ‐OTHF)]₂). We report some of the largest ²⁷Al quadrupolar coupling constants measured to date, with values of C_Q(²⁷Al) of 48.2(1), 36.3(1), 19.9(1), and 19.6(2) MHz for AlMes₃ , Al(NTMS₂)₃ , [Me₂‐Al(μ‐OTHF)]₂ , and [Et₂‐Al(μ‐OTHF)]₂ , respectively. X‐ray crystallographic data and theoretical (Hartree–Fock and DFT) calculations of ²⁷Al electric field gradient (EFG) tensors are utilized to examine the relationships between the quadrupolar interactions and molecular structure; in particular, the origin of the immense quadrupolar interaction in the three‐coordinate species is studied via analyses of molecular orbitals.     

Angular dependence of 1H- and 2H-NMR spectra of H2O and D2O absorbed in cellulose acetate film

¹H- and ²H-NMR spectra of H₂O and D₂O absorbed in cellulose acetate films were observed while changing the angle between the plane of the film and the magnetic field. ¹H-NMR spectra show dipolar splittings that vary depending on the angle. The splitting has a maximum when the surface of the film is perpendicular to the magnetic field. From the angular dependence of the dipolar splitting, it is recognized that the proton-proton dipolar axis of water molecules tends to orient perpendicularly to the surface of the film. ²H-NMR spectra that show quadrupolar splittings also indicate that the quadrupolar axis tends to orient perpendicularly to the film. The so-called bound water and free water in the film can exchange rapidly on the NMR time scale, so that the line width and the splitting of the NMR spectra become smaller as the amount of water in the film increases. From the temperature dependence of line widths, the apparent reorientational activation energy of water molecules in the film is estimated to be 25 kJ/mol from ¹H-NMR and 31 kJ/mol from ²H-NMR.     

Line-profile Analysis of Excitation Spectroscopy in Even 5p5(2P1/2)nl' [K']J (l'=1, 3) Autoionizing Resonances of Xe

The even-parity autoionizing resonance series 5p⁵np'[3/2]₁, [1/2]₁, and 5p⁵nf'[5/2]₃ of xenon have been investigated, excited from the two metastable states 5p⁵6s[3/2]₂ and 5p⁵6s'[1/2]₀ in the photon energy range of 28000-42000 cm^-1 with experimental bandwidth of ～0.1 cm^-1. The excitation spectra of the even-parity autoionizing resonance series show typical asymmetric line shapes. New level energies, quantum defects, line profile indices and resonance widths, resonance lifetimes and reduced widths of the autoionizing resonances are derived by a Fano-type line-shape analysis. The line profile index and the resonance width are shown to be approximately proportional to the effective principal quantum number. The line separation of the 5p⁵np' autoionizing resonances is discussed.     

Semi‐analytical description of the S = 9/2 quadrupole nutation NMR experiment: multinuclear application to 113In and 115In in indium phosphide

The density matrix of a spin S = 9/2 excited by a radiofrequency pulse is calculated. The interaction involved during the excitation of the spin system is first‐order quadrupolar. Consequently, the results are valid for any ratio of the quadrupolar coupling ω_Q to the pulse amplitude ω₁. The behavior of the central transition intensities versus the pulse length is discussed. The ¹¹⁵In and ¹¹³In nuclei in a powdered sample of indium phosphide (InP) are used to illustrate the results. It is found that the ratio of the quadrupolar coupling constants determined in this work is in excellent agreement with the ratio of the quadrupole moments of the two nuclei. Copyright © 2015 John Wiley & Sons, Ltd.     

Ion-solvent interaction in nonaqueous solutions. II. Spin-lattice relaxation times of23Na and133Cs

The spin-lattice relaxation time (T ₁) of ²³ Na was measured in solutions of NaClO ₄ and (or) NaBr in formamide,N-methylformamide,N,N-dimethylformamide (DMF), MeCN, Me₂CO, tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO), and ¹³³ Cs in a solution of CsCl in formamide. The values of (1/T ₁) ₀ obtained by extrapolation are discussed in terms of current theories of quadrupolar magnetic relaxation of ionic nuclei. A correlation was found between (1/T ₁) ₀ for ²³ Na and Gutmann's donor numbers.For Part I, see ref. 1.     

A study of the NMR relaxation mechanisms of ABCl3 (A=Rb, Cs, B=Cd, Mn) single crystals with the electric quadrupole and the electric magnetic types

The ⁸⁷Rb and ¹³³Cs spin-lattice relaxation rates of RbCdCl₃ and CsCdCl₃ single crystals grown using the slow evaporation method were measured over the temperature range 160-400 K. The changes in the ⁸⁷Rb spin-lattice relaxation rate near 340, 363, and 395 K correspond to phase transitions of the RbCdCl₃ crystal. The jump in T₁⁻¹ at 395 K is due to a shortening in the c-direction as a result of a phase transition from a cubic to a tetragonal structure. We suggest that the cubic Rb environment is favored above 395 K due to the fast motions and soft modes, which cause relaxation and average out the quadrupolar splittings. The temperature dependence of the relaxation rate below 340 K in RbCdCl₃ can be represented by and is thus in accordance with a Raman process. The ¹³³Cs nuclei in the CsCdCl₃ crystal produce only one resonance line, which indicates that the local structure around the Cs atoms is cubic. The temperature dependence of the relaxation rate of the Cs nuclei can also be described with the quadratic equation . In the case of the RbCdCl₃ and CsCdCl₃ crystals, which are of electric quadrupolar type, their relaxations proceed via Raman processes, whereas in RbMnCl₃ and CsMnCl₃ crystals, which are of magnetic relaxation type, the relaxations proceed via single phonon processes. Therefore, the relaxation mechanisms of these different types of ABCl₃ crystals (quadrupolar and magnetic) are completely different NMR behavior.     

23Na NMR in urethane cross-linked polyether solid polymer electrolytes

Sodium triflate/polyether urethane polymer electrolytes ranging in concentration from 0.05 molal to 1.75 molal have been investigated via ²³Na static solid-state NMR. Room temperature spectra and spin lattice relaxation times were consistent with a single narrow resonance indicating the presence of only mobile ionic species. The concentration and temperature dependence of relaxation times, chemical shifts, and linewidth have been investigated. The results suggest either a single species or rapid exchange between a number of species (even at temperatures below the glass transition temperature, T_g). The linewidth decreases with increasing concentration of ions and remains temperature independent below T_g. Below T_g a maximum quadrupolar interaction constant of 2 MHz is calculated. The addition of plasticizer to the polymer electrolyte causes significant chemical shift changes that depend on the solvent donicity of the plasticizer. The linewidth and T₁ relaxation times also depend on the T_g of the plasticized systems. Previous ²³Na NMR literature results are reviewed and qualitative models developed to account for the variation in results. © 1994 John Wiley & Sons, Inc.     

Li ion dynamics in Li3xLa2/3–x□1/3–2xTiO3 studied by NMR

⁷Li nuclear magnetic resonance relaxation times, T₁ and T_1ρ, versus temperature are reported in the 150–900 K temperature range on the lithium lanthanum titanates, Li_3xLa_2/3–x□_1/3–2xTiO₃, which are fast ionic conductors. Two characteristic frequencies of Li⁺ motions are evidenced in these compounds: the first is in the range of the Larmor frequency when the second one is in the range of the radio-frequency field. These frequencies are respectively attributed to motion of the Li⁺ ion inside the cage formed by the oxygen ions and to jumps between the cages. The T₁ and T_1ρ studies on ⁶Li nuclei confirm the above results and show that the relaxation is not due to quadrupolar interaction at a variance, which is generally accepted.     

Study of molecular motions and 14N quadrupolar coupling in 1,3- and 1,4- diethylpyridinium bromides using 13C and 14N relaxation time measurements

The internal and overall motions of 1,3- and 1,4-diethylpyridinium bromides have been studied by ¹³C relaxation. The enthalpies of activation for the rotation of the ethyl groups in positions 1 and 3 are deduced from the temperature dependence of the T₁ values of the methylene and methine carbons. The ¹⁴N quadrupolar relaxation time, T_q, together with ¹³C relaxation data provide an estimate of the ¹⁴N quadrupolar coupling constants.     

High resolution 1H-NMR relaxation study of polyisobutylene in solution

From the temperature dependence of integrated intensities and from line widths in high-resolution ¹H-NMR spectra, the relaxation times T₁ and T₂ of protons in CH₂ and CH₃ groups of polyisobutylene in CCl₄ solution have been determined. Although the relaxation time T₁ of methylene protons is determined mainly by intragroup interactions, intergroup interactions of two methyl groups from each two consecutive monomer units were found to contribute considerably to T₁ of methyl protons. The Structure and mobility of polyisobutylene (PIB) molecules in solution is discussed on the basis of the relaxation time data.     

Line-profile analysis of excitation spectroscopy in the even 4p5(2P1/2)nl′ [K′]J（l′=1,3） autoionizing resonances of Kr

The even-parity autoionizing resonance series 4p5np′[3/2]1,2,[1/2]1,and 4p5nf′[5/2]3of krytpon have been investigated by laser excitation from the two metastable states 4p55s[3/2]2and 4p55s′[1/2]0in the photon energy region of 29000–40000 cm 1at experimental bandwidth of~0.1 cm 1.The excitation spectra of the even-parity autoionizing resonance series,most of which are experimentally studied for the first time in this work,show typical asymmetric line shapes.Complementary information on level energies,quantum defects,line profile indices and resonance widths,resonance lifetimes and reduced widths of the autoionizing resonances are derived by Fano-type line-shape analyses of the experimental results.Results from this work indicate that the line profile index(q)and the resonance width()are approximately proportional to the effective principal quantum number(n*);the line separation of the 4p5np′autoionizing resonances is also in good agreement with theoretical model.     

Deuterium MAS NMR Studies of Dynamics on Multiple Timescales: Histidine and Oxalic Acid

Deuterium (²H) magic‐angle spinning (MAS) nuclear magnetic resonance is applied to monitor the dynamics of the exchanging labile deuterons of polycrystalline L ‐histidine hydrochloride monohydrate‐d₇ and α‐oxalic acid dihydrate‐d₆. Direct experimental evidence of fast dynamics is obtained from T_1Z and T_1Q measurements. Further motional information is extracted from two‐dimensional single‐quantum (SQ) and double‐quantum (DQ) MAS spectra. Differences between the SQ and DQ linewidths clearly indicate the presence of motions on intermediate timescales for the carboxylic moiety and the D₂O in α‐oxalic acid dihydrate, and for the amine group and the D₂O in L ‐histidine hydrochloride monohydrate. Comparison of the relaxation rate constants of Zeeman and quadrupolar order with the relaxation rate constants of the DQ coherences suggests the co‐existence of fast and slow motional processes.     

Ionic bonding in butadiene copolymers. II. Stress relaxation

The mechanical lability of quadrupolar links in cationic and anionic polyelectrolytes and of ion-pair links in mixed polyelectrolytes is investigated in terms of deviations from the WLF viscoelastic theory. The behavior of E(t), log A_T, and E_visc indicate that the quadrupolar links do not interchange below the second transition T_t^* found in these materials. The blended polyelectrolytes exhibit low yields of the desired ion pair linking and have transitions characteristic of quadrupolar migration of the unreacted polyelectrolytes.     

A Nuclear Singlet Lifetime of More than One Hour in Room‐Temperature Solution

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are supremely important techniques with numerous applications in almost all branches of science. However, until recently, NMR methodology was limited by the time constant T₁ for the decay of nuclear spin magnetization through contact with the thermal molecular environment. Long‐lived states, which are correlated quantum states of multiple nuclei, have decay time constants that may exceed T₁ by large factors. Here we demonstrate a nuclear long‐lived state comprising two ¹³C nuclei with a lifetime exceeding one hour in room‐temperature solution, which is around 50 times longer than T₁. This behavior is well‐predicted by a combination of quantum theory, molecular dynamics, and quantum chemistry. Such ultra‐long‐lived states are expected to be useful for the transport and application of nuclear hyperpolarization, which leads to NMR and MRI signals enhanced by up to five orders of magnitude.     

Atomic line profile measurements on hollow-cathode and electrodeless discharge lamps using a high-resolution echelle monochromator

Commercial r.f.-excited electrodeless discharge lamps (EDLs) and hollow-cathode lamps (HCLs) of the elements As, Bi, Cd, Sb, Se, Sn, Te and Zn were studied using a 2.54-m scanning echelle monochromator. The variation of the widths of the resonance lines from these lamps was investigated for a range of power and current levels. In general, the tendency to self-absorption and self-reversal is greater for the more volatile elements, although the strong self-reversal of the Pb 217.0 nm line from a HCl is an exception. EDLs for the less volatile elements, which are incorporated as iodides, show relatively little variation in line width except at the highest powers.The extent of the overlap between the Bi and I atomic lines at 206.2 nm is demonstrated and, for As, a hyperfine structure splitting constant (A-value) of 0.016 cm⁻¹ was determined for the 5s⁴P energy level.     

Optimization of signal-to-noise ratio in the <Emphasis Type="Italic">in vivo</Emphasis><Superscript>31</Superscript>P magnetic resonance spectra of the human brain

The main problem in ³¹P magnetic resonance spectroscopy is a low signal-to-noise ratio (SNR) of spectra acquired with clinical magnetic resonance imaging (MRI) scanners. Using spin-spin phosphorus-proton (³¹P-¹H) decoupling and heteronuclear Overhauser effect and taking into account the effect of the longitudinal relaxation time T₁ on the SNR, the method for localization and excitation of the region of interest (Image Selected in vivo Spectroscopy pulse sequence) was optimized to increase the SNR in the ³¹P magnetic resonance spectra of the human brain to ~50% without increasing signal acquisition time.     

A Combined Solid‐State NMR and X‐ray Crystallography Study of the Bromide Ion Environments in Triphenylphosphonium Bromides

Multinuclear (³¹P and ^79/81Br), multifield (9.4, 11.75, and 21.1 T) solid‐state nuclear magnetic resonance experiments are performed for seven phosphonium bromides bearing the triphenylphosphonium cation, a molecular scaffold found in many applications in chemistry. This is undertaken to fully characterise their bromine electric field gradient (EFG) tensors, as well as the chemical shift (CS) tensors of both the halogen and the phosphorus nuclei, providing a rare and novel insight into the local electronic environments surrounding them. New crystal structures, obtained from single‐crystal X‐ray diffraction, are reported for six compounds to aid in the interpretation of the NMR data. Among them is a new structure of BrPPh₄, because the previously reported one was inconsistent with our magnetic resonance data, thereby demonstrating how NMR data of non‐standard nuclei can correct or improve X‐ray diffraction data. Our results indicate that, despite sizable quadrupolar interactions, ^79/81Br magnetic resonance spectroscopy is a powerful characterisation tool that allows for the differentiation between chemically similar bromine sites, as shown through the range in the characteristic NMR parameters. ^35/37Cl solid‐state NMR data, obtained for an analogous phosphonium chloride sample, provide insight into the relationship between unit cell volume, nuclear quadrupolar coupling constants, and Sternheimer antishielding factors. The experimental findings are complemented by gauge‐including projector‐augmented wave (GIPAW) DFT calculations, which substantiate our experimentally determined strong dependence of the largest component of the bromine CS tensor, δ₁₁, on the shortest Br? P distance in the crystal structure, a finding that has possible application in the field of NMR crystallography. This trend is explained in terms of Ramsey’s theory on paramagnetic shielding. Overall, this work demonstrates how careful NMR studies of underexploited exotic nuclides, such as ^79/81Br, can afford insights into structure and bonding environments in the solid state.     

Nuclear magnetic relaxation of ionic nuclei moving in an external electric field

We have experimentally investigated nuclear magnetic relaxation of some quadrupolar ionic nuclei (²³Na⁺, ⁸⁷Rb⁺ and ³⁵Cl⁻ ) in electrolyte solutions in non-equilibrium states. The measurements of relaxation rates 1/T₁ in the presence of a direct electric field, and thus also an electric current, revealed that differences can occur in comparison with relaxation in the absence of the field. In some systems no change in the relaxation rate was observed, but in certain other (non-aqueous) systems there was a change in the quadrupolar relaxation rate in the presence of the field.