129Xe NMR as a probe of polymer blends

The miscibility of two-component polymer blends has been investigated using xenon-129 (¹²⁹Xe) nuclear magnetic resonance (NMR) to probe the phase morphology. The chemical shift of ¹²⁹Xe dissolved in a given polymer is unique, thus heterogeneous blends with large domain sizes exhibit two ¹²⁹Xe NMR lines. When a single resonance is obtained, the data are consistent with miscibility, yielding an upper bound on the domain size. The temperature dependence of the relative solubilities and chemical shifts of ¹²⁹Xe dissolved in the pure components may allow a determination of the phase morphology in blends exhibiting a single resonance. The method is used to demonstrate that polychloroprene and 25% epoxidized 1,4-polyisoprene form a miscible blend.     

83Kr nuclear magnetic moment in terms of that of 3He

High resolution NMR spectroscopy was applied to precisely determine the ⁸³Kr nuclear magnetic dipole moment on the basis of new results available for nuclear magnetic shielding in krypton and helium‐3 atoms. Small amounts of ³He as the solutes and ⁸³Kr as the buffer gas were observed in ³He and ⁸³Kr NMR spectra at the constant external field, B₀ = 11.7578 T. In each case, the resonance frequencies (ν^He and ν^Kr) were linearly dependent on the density of gaseous solvent. The extrapolation of experimental points to the zero density of gaseous krypton allowed for the evaluation of both resonance frequencies free from intermolecular interactions. By combining these measurements with the recommended ⁸³Kr chemical shielding value, the nuclear magnetic moment could be determined with much better precision than ever before, μ(⁸³Kr) = ?0.9707297(32)μ_N, with the improvement due to the greater accuracy of the spectral data. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of 6FDA‐based hyperbranched and linear polyimide–silica hybrid membranes by gas permeation and 129Xe NMR measurements

Physical and gas transport properties of novel hyperbranched polyimide–silica hybrid membranes were investigated and compared with those of linear‐type polyimide–silica hybrid membranes with similar chemical structures. Hyperbranched polyamic acid, as a precursor, was prepared by polycondensation of a triamine, 1,3,5‐tris(4‐aminophenoxy)benzene (TAPOB), and a dianhydride, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA). 6FDA‐TAPOB hyperbranched polyimide–silica hybrids were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) by sol–gel reaction. 5% weight‐loss temperature of the 6FDA‐TAPOB hyperbranched polyimide–silica hybrids determined by TG‐DTA measurement considerably increased with increasing silica content, indicating effective crosslinking at polymer–silica interface. CO₂, O₂, N₂, and CH₄ permeability coefficients of the 6FDA‐based polyimide–silica hybrids increased with increasing silica content. In addition, CO₂/CH₄ selectivity of the 6FDA‐TAPOB–silica hybrids remarkably increased with increasing silica content. From ¹²⁹Xe NMR analysis, characteristic distribution and interconnectivity of cavities created around polymer–silica interface were suggested in the 6FDA‐TAPOB–silica hybrids. It was indicated that size‐selective separation ability is effectively brought by the incorporation of silica for the 6FDA‐TAPOB hyperbranched polyimide–silica hybrid membranes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 291–298, 2006     

Enantiopure cryptophane-129Xe nuclear magnetic resonance biosensors targeting carbonic anhydrase

The (+) and ( ? ) enantiomers for a cryptophane-7-bond-linker-benzenesulfonamide biosensor (C7B) were synthesised and their chirality was confirmed by electronic circular dichroism spectroscopy. Biosensor binding to carbonic anhydrase II (CAII) was characterised for both enantiomers by hyperpolarised (HP) ¹²⁹Xe NMR spectroscopy. Our previous study of the racemic ( ± ) C7B biosensor–CAII complex [Chambers, J.M.; Hill, P.A.; Aaron, J.A.; Han, Z.H.; Christianson, D.W.; Kuzma, N.N.; Dmochowski, I.J. J. Am. Chem. Soc.2009, 131, 563–569] identified two ‘bound’ ¹²⁹Xe@C7B peaks by HP ¹²⁹Xe NMR (at 71 and 67 ppm, relative to ‘free’ biosensor at 64 ppm), which led to the initial hypothesis that (+) and ( ? ) enantiomers produce diastereomeric peaks when coordinated to Zn²⁺ at the chiral CAII active site. Unexpectedly, the single enantiomers complexed with CAII also identified two ‘bound’ ¹²⁹Xe@C7B peaks: (+) 72, 68 ppm and ( ? ) 68, 67 ppm. These results are consistent with X-ray crystallographic evidence for benzenesulfonamide inhibitors occupying a second site near the CAII surface. As illustrated by our studies of this model protein–ligand interaction, HP ¹²⁹Xe NMR spectroscopy can be useful for identifying supramolecular assemblies in solution.     

MCM-41分子筛的合成及129Xe核磁共振的研究

ＭＣＭ４１中孔分子筛是１９９２年由Ｍｏｂｉｌ公司的科学家Ｋｒｅｓｇｅ［１］等人首次合成的,并在《自然》杂志发表。这种中孔分子筛具有六角形孔径,孔径２ｎｍ～１０ｎｍ,这种分子筛的孔径可以通过水晶模板来控制［２］。已报道的合成ＭＣＭ４１,孔径一般在２．０ｎｍ～３．５ｎｍ,使用的水晶模板一般是单一或两种阳离子季铵盐表面活性剂［３,４］。本论文通过引入第二种扩孔模板,与阳离子季铵盐协同作用,合成了孔径５．２ｎｍ（ＢＥＴ法测）的ＭＣＭ４１。通过氮气的吸脱附,测定了分子筛的比表面和孔径等性质。Ｊ．Ｆｒａｉｓｓａｒｄ…     

Gas-phase 21Ne NMR studies and the nuclear magnetic dipole moment of neon-21

Gas-phase ²¹Ne nuclear magnetic resonance spectra were measured at the natural abundance of ²¹Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B₀ = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the ²¹Ne nuclear magnetic moment, μ(²¹Ne) = 0.6617774(10) μ_N. The present value of μ(²¹Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(²¹Ne).     

The dependence on temperature and concentration of 129Xe NMR chemical shift values of organoxenon(II) salts [RXe][Y] and of the parent molecule XeF2

The dependence of the 129Xe NMR chemical shift value of XeF2 on temperature and concentration was determined in a variety of prototypic media: in acidic (anhydrous HF, aHF), nonprotic but polar (dichloromethane), and basic (CD3CN-EtCN, 1:3 v/v) solvents. The 129Xe NMR spectra of a representative series of organoxenon(II) salts [RXe][Y] (R = C6F5, heptafluoro-1,4-cyclohexadien-1-yl (cyclo-1,4-C6F7), pentafluoro-1,4-cyclohexadien-3-on-1-yl (cyclo-3-O-1,4-C6F5), CF2=C(CF3), (CF3)2CFC[triple bond]C, C4H9C[triple bond]C; Y = BF4, AsF6) in aHF showed, compared with XeF2-aHF, a quantitatively less distinct but qualitatively related dependence of delta(129Xe) vs temperature. The dependence of their delta(129Xe) values on concentration in aHF is negligible. An explanation for the different behavior of [RXe][Y] and XeF2 is offered.     

129Xe NMR Studies of Pecan Shell-Based Biochar and Structure-Process Correlations

Pecan shell-based biochar is utilized as a filtration medium, sequestrant for metallic ions, soil conditioner, and other applications. One process for creating the biochar involves the use of phosphoric acid at high temperature in a partial oxygen atmosphere to produce a highly porous carbonaceous material. In this work, we found ¹²⁹Xe NMR to be an excellent technique to study micropores in biochar. Thus, the ¹²⁹Xe chemical shift in biochar was found to vary linearly with the xenon pressure; from the data an estimate of about 8–9 Å could be proposed for the average pore diameter in pecan shell-based biochar. Through saturation recovery and 2-D NMR exchange experiments, information on the exchange between free versus bound xenon was obtained. Furthermore, correlations of ¹²⁹Xe NMR data with the carbonization process conditions were made.     

ChemInform Abstract: NMR of 129Xe Trapped in Clathrates and Some Other Solids.

129Xe NMR chemical shifts, obtained for Xe trapped in the cages of clathrate hydrates and a clathrasil sample, together with shift data for solid Xe correlate linearly with the mean free radius of the cage.     

129Xe NMR chemical shift in Xe@C60 calculated at experimental conditions: Essential role of the relativity,dynamics, and explicit solvent

The isotropic ¹²⁹Xe nuclear magnetic resonance (NMR) chemical shift (CS) in Xe@C₆₀ dissolved in liquid benzene was calculated by piecewise approximation to faithfully simulate the experimental conditions and to evaluate the role of different physical factors influencing the ¹²⁹Xe NMR CS. The ¹²⁹Xe shielding constant was obtained by averaging the ¹²⁹Xe nuclear magnetic shieldings calculated for snapshots obtained from the molecular dynamics trajectory of the Xe@C₆₀ system embedded in a periodic box of benzene molecules. Relativistic corrections were added at the Breit–Pauli perturbation theory (BPPT) level, included the solvent, and were dynamically averaged. It is demonstrated that the contribution of internal dynamics of the Xe@C₆₀ system represents about 8% of the total nonrelativistic NMR CS, whereas the effects of dynamical solvent add another 8%. The dynamically averaged relativistic effects contribute by 9% to the total calculated ¹²⁹Xe NMR CS. The final theoretical value of 172.7 ppm corresponds well to the experimental ¹²⁹Xe CS of 179.2 ppm and lies within the estimated errors of the model. The presented computational protocol serves as a prototype for calculations of ¹²⁹Xe NMR parameters in different Xe atom guest–host systems. © 2013 Wiley Periodicals, Inc.     

Gas sorption environments in poly(2,6‐dimethyl‐1,4‐phenylene oxide) by xenon‐129 nuclear magnetic resonance: Effects of processing

One‐ and two‐dimensional xenon‐129 nuclear magnetic resonance (¹²⁹Xe NMR) experiments were performed on a series of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PXE) samples to characterize the sorption environments and the relative mobility of xenon in the samples. Samples of PXE in sealed NMR tubes pressurized with xenon were studied as a function of temperature, pressure, and processing. In a dense cast film of PXE, the shift relative to the free gas resonance is smaller than that observed for typical glassy polymers, indicating a higher free volume environment. Solubility rises rapidly as temperature decreases. The lower shift and rapid increase in solubility with decreasing temperature are consistent with a relatively high free volume environment for gas sorption. If PXE is antiplasticized, the shift is slightly larger, the increase in signal intensity with decreasing temperature is smaller, and the line widths are greater. This sample is a better packed glass with less free volume and slower diffusion. Samples of PXE produced by rapid precipitation have broad lines and even lower shifts corresponding to a wide distribution of higher free volume environments. The appearance of two lines at low temperatures is consistent with the presence of a bimodal distribution of environments similar to what has been observed with positron annihilation lifetime spectroscopy. The resonance closest to the free gas resonance is associated with very large free volume elements relative to those of traditional glassy polymers. In two‐dimensional experiments, there is a rapid exchange of xenon by diffusion between the two environments, indicating the close spatial proximity of the environments. Two‐dimensional experiments and one‐dimensional progressive saturation experiments reflect a rapid exchange of xenon between the sorbed state and the free gas resonance for the precipitated samples. At low temperatures, the high field peak exchanges more rapidly with the free gas. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1965–1974, 2002     

An improved 33S nuclear magnetic shielding scale from the gas‐phase study of COS

The ³³S NMR signal of gaseous carbonyl sulfide (COS) was monitored as a function of density for the first time. An extrapolation to the zero‐density limit permitted the measurement of nuclear magnetic shielding of an isolated COS molecule. An improved ³³S shielding scale was established taking the value of 817(12) ppm as the absolute shielding of COS. The new ³³S shielding scale is certainly more accurate than any previous estimation and contains some reference standards, e.g. an isolated SF₆ molecule, a saturated solution of (NH₄)₂SO₄ in D₂O, 2 M aqueous Cs₂SO₄ solution or liquid SF₆, CS₂ and SO₂. The latter results can be applied for the easy estimation of sulfur shielding available from all the measurements of ³³S NMR chemical shifts. Copyright © 2002 John Wiley & Sons, Ltd.     

NMR shielding in helium-3 atoms modified by gaseous nitrogen and oxygen

Helium-3 nuclear magnetic resonance (³He NMR) measurements were carried out for the gaseous mixtures of helium-3 with pure nitrogen and synthetic air as the solvents. It was found that ³He shielding is linearly dependent on solvent density up to approx. 6 mol/L. At higher density of the gaseous solvent, the change of ³He shielding is nonlinear and especially distinct when helium-3 atoms can interact with two O₂ molecules. The interaction with paramagnetic oxygen molecules can induce two kinds of ³He shielding changes: (1) due to the isotropic Fermi contact interaction and (2) from the dipolar magnetic interaction between unpaired O₂ electrons and ³He nuclear magnetic dipole moment. The two paramagnetic effects in helium-3 shielding cannot be experimentally separated, although for such small molecular objects, they could be presumably modeled by advanced theoretical calculations.     

From proton nuclear magnetic resonance spectra to pH. Assessment of H NMR pH indicator compound set for deuterium oxide solutions

In this study, a protocol for pH determination from D₂O samples using ¹H NMR pH indicator compounds was developed and assessed by exploring the pH-dependency of 13 compounds giving pH-dependent ¹H NMR signals. The indicators cover the pH range from pH* 0 to 7.2. Equations to transform the indicator chemical shifts to pH estimates are given here for acetic acid, formic acid, chloroacetic acid, dichloroacetic acid, creatine, creatinine, glycine, histidine, 1,2,4-triazole, and TSP (2,2,3,3-tetradeutero-3-(trimethylsilyl)-propionic acid). To characterize the method in presence of typical solutes, the effects of common metabolites, albumin and ionic strength were also evaluated. For the ionic strengths, the effects were also modelled. The experiments showed that the use of pH sensitive ¹H NMR chemical shifts allows the pH determination of typical metabolite solutions with accuracy of 0.01-0.05 pH units. Also, when the ionic strength is known with accuracy better than 0.1 mol dm⁻³ and the solute concentrations are low, (the NMR estimate of pH) can be assumed to be within 0.05 pH units from potentiometrically determined pH.     

利用二维核磁共振方法研究取代茚基金属钛、锆配合物 的空间结构

通过^1H-^1HTOCSY和^1H-^1HNOESY谱对一系列新型结构的取代茚基钛、锆配合物进行了结构上的解析，并由此发现夹心结构的锆配合物中，两个茚环(或茚环和茂环)以及茚环上的取代基之间存在核的Overhauser效应，这对于茚环相对空间结构的判断提供了有效的证据。     

Spin‐orbit ZORA and four‐component Dirac–Coulomb estimation of relativistic corrections to isotropic nuclear shieldings and chemical shifts of noble gas dimers

Hartree–Fock and density functional theory with the hybrid B3LYP and general gradient KT2 exchange‐correlation functionals were used for nonrelativistic and relativistic nuclear magnetic shielding calculations of helium, neon, argon, krypton, and xenon dimers and free atoms. Relativistic corrections were calculated with the scalar and spin‐orbit zeroth‐order regular approximation Hamiltonian in combination with the large Slater‐type basis set QZ4P as well as with the four‐component Dirac–Coulomb Hamiltonian using Dyall's acv4z basis sets. The relativistic corrections to the nuclear magnetic shieldings and chemical shifts are combined with nonrelativistic coupled cluster singles and doubles with noniterative triple excitations [CCSD(T)] calculations using the very large polarization‐consistent basis sets aug‐pcSseg‐4 for He, Ne and Ar, aug‐pcSseg‐3 for Kr, and the AQZP basis set for Xe. For the dimers also, zero‐point vibrational (ZPV) corrections are obtained at the CCSD(T) level with the same basis sets were added. Best estimates of the dimer chemical shifts are generated from these nuclear magnetic shieldings and the relative importance of electron correlation, ZPV, and relativistic corrections for the shieldings and chemical shifts is analyzed. © 2015 Wiley Periodicals, Inc.     

The F NMR spectrum of bis-trifluoromethylmercury Hg(CF3)2 in the nematic phase: DAISY — a novel program system for the analysis and simulation of NMR spectra

The ¹⁹F NMR spectrum of bis-trifluoromethylmercury in the nematic phase has been analysed using the DAISY program system. The scalar and the dipolar coupling constants have been obtained.     

Excited state dipole moments of N,N-dimethylaniline from thermochromic effect on electronic absorption and fluorescence spectra

The effect of temperature on absorption and fluorescence spectra of N,N-dimethylaniline (DMA) in ethyl acetate has been studied for temperature ranging from 293 to 388 K. The permittivity ε and refractive index n of the solvent decrease with temperature increase and the absorption and fluorescence bands are blue shifted (so-called “thermochromic shift”). Based on this phenomenon, the dipole moment μ_e in the excited singlet state and the Onsager interaction radius a for DMA were determined using the Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621; 18a (1963) 10, 256].

For the known dipole moment in the ground state μ_g = 1.61 D and for /a³ = 0.54 ( is the polarizability of the solute) the average value of μ_e = 3.55 D and a = 3.1 Å were determined. The obtained values for DMA are compared with the experimental values determined by other authors.     

FT-IR, NIR-FT-Raman and gas phase infrared spectra of 3-aminoacetophenone by density functional theory and ab initio Hartree-Fock calculations

The gas phase infrared spectrum of 3-aminoacetophenone (3AAP) was measured in the range 5000-500cm(-1) and with a resolution of 0.5cm(-1). The Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectra of 3AAP were recorded in the solid phase. Geometry optimizations were done without any constraint and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and density functional theory (DFT) levels invoking 6-311G(2df 2p) basis set and the results are compared with the experimental values. Harmonic-vibrational wavenumber was also calculated for the minimum energy conformer at ab initio and DFT levels using 6-31G(d,p) basis set and the results are compared with related molecules. With the help of specific scaling procedures, the observed vibrational wavenumbers in gas phase, FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrogram for the FT-IR spectra of the title molecule is also constructed.     

Preparative three-dimensional GC and nuclear magnetic resonance for the isolation and identification of two sesquiterpene ethers from Dictyota Dichotoma

Separation science plays a crucial role in the isolation of novel compounds contained in complex matrices. Yet their rationale employment needs preliminary structure elucidation, which usually requires sufficient aliquots of grade substances to characterize the molecule by nuclear magnetic resonance experiments. In this study, two peculiar oxa-tricycloundecane ethers were isolated by means of preparative multidimensional gas chromatography from the brown alga species Dictyota dichotoma (Huds.) Lam., aiming to assign their 3D structures. Density functional theory simulations were carried out to select the correct configurational species matching the experimental NMR data (in terms of enantiomeric couples). In this case, the theoretical approach was crucial as the protonic signal overlap and spectral overcrowding were preventing any other unambiguous structural information. Just after the identification through the density functional theory data matching of the correct relative configuration it was possible to verify an enhanced self-consistency with the experimental data, confirming the stereochemistry. The results obtained further pave the way toward structure elucidation of highly asymmetric molecules, whose configuration cannot be inferred by other means or strategies.