Carbon-13 and Fluorine-19 NMR Spectroscopy of the Supramolecular Solid p-tert-Butylcalix[4]arene ·α,α,α-trifluorotoluene

The supramolecular 1 : 1 host–guest inclusion compound, p-tert-butylcalix[4]arene ·α,α,α-trifluorotoluene, 1, is characterized by ¹⁹F and ¹³C solid-state NMR spectroscopy. Whereas the ¹³C NMR spectra are easily interpreted in the context of earlier work on similar host–guest compounds, the ¹⁹F NMR spectra of solid 1 are, initially, more difficult to understand. The ¹⁹F{¹H} NMR spectrum obtained under cross-polarization and magic-angle spinning conditions shows a single isotropic resonance with a significant spinning sideband manifold. The static ¹⁹F{¹H} CP NMR spectrum consists of a powder pattern dominated by the contributions of the anisotropic chemical shift and the homonuclear dipolar interactions. The ¹⁹F MREV-8 experiment, which minimizes the ¹⁹F–¹⁹F dipolar contribution, helps to identify the chemical shift contribution as an axial lineshape. The full static ¹⁹F{¹H} CP NMR spectrum is analysed using subspectral analysis and subsequently simulated as a function of the ¹⁹F–¹⁹F internuclear distance (D_FF = 2.25 ± 0.01 Å) of the rapidly rotating CF₃ group without including contributions from additional libration motions and the anisotropy in the scalar tensor. The shielding span is found to be 56 ppm. The width of the centerband in the ¹⁹F{¹H} sample-spinning CP NMR spectrum is very sensitive to the angle between the rotor and the magnetic field. Compound 1 is thus an attractive standard for setting the magic angle for NMR probes containing a fluorine channel with a proton-decoupling facility.     

Molecular Structure of the Eudesmanolide Septulinolide

The molecular structure of septuplinolide from Calea septuplinerva was determined by single crystal X-ray diffraction analysis. This requires revision of stereochemistry at C4 from 4β-OH to 4α-OH in the septuplinolide molecule. Also, high-field ¹H and ¹³C NMR spectral assignments of the lactone are given.     

<Superscript>1</Superscript>H and<Superscript>13</Superscript>C chemical shift assignments and stereochemistry of matrine and oxymatrine

Matrine and oxymatrine were extracted fromSophora flavescens, and their¹H and¹³C nuclear magnetic resonances (NMR) were unambiguously assigned by a combination of different two-dimensional 2-D¹H-¹³C and¹H-¹H correlation experiments of HMQC, HMQC-TOCSY and MAXY. The technique of using those experiments to make the assignment of the heavily overlapped spectrum is demonstrated. The coupling constants of matrine were measured by 2-DJ-resolved spectrum and 1-D spectra extracted from the slices of 2-D MAXY spectrum. The stereochemistry of the titled compounds was established from the NMR spectroscopy.     

Assignments of the 13C NMR Spectra of Enhydrin and 2′,3′-Dehydromelnerin A and the Molecular Structure of Enhydrin

Abstract

Two melampolide-type sesquiterpene lactones, enhydrin and 2,′ 3′-dehydromelnerin A, were isolated from a Louisiana population of Polymnia uvedalia. Their ¹³C NMR spectra were assigned using ¹³C-¹H correlation, DEPT and COLOC experiments. The molecular structure of enhydrin was established by single crystal X-ray diffraction.     

Clustering and polymerization of Li15C60

The structural and electronic properties of lithium intercalated fullerides (of which Li₁₅C₆₀ is the most representative) are still puzzling and unclear. Above 520 K, x-ray/neutron diffraction shows an fcc phase in which the 15 Li atoms clusterize in the octahedral interstices. However, at lower temperatures, a change in the crystalline symmetry and also in the electronic properties takes place as observed from ¹³C, ⁷Li/⁶Li NMR and x-ray diffraction measurements. X-ray diffraction data suggest the presence of two different stable structures: a tetragonal monomeric and an orthorhombic polymerised phase. Detailed ¹³C magic angle spinning NMR experiments in the latter phase indicate sp ³ bondings among the carbon atoms, whereas the relative (sp ²/sp ³) intensities, together with x-ray data, suggest the C₆₀ polymerization to be a [2+2] cycloaddition. Multiple quantum NMR experiments on ⁷Li confirm the presence of lithium clusters, as observed by x-ray diffraction in the high temperature phase, also at lower temperatures. However, the inferred cluster size is significantly smaller than that suggested by the stoichiometry. The distortion in the low-T structure of L₁₅C₆₀ is supposed to induce the migration of Li atoms from octahedral to tetrahedral voids, thus accounting for the lower number of Li atoms in the clusters. Further evidence of this scenario is obtained also from preliminary measurements of line shapes and T ₁ relaxation times, which exhibit a multiexponential recovery with very different constants that are hardly compatible with a single family of Li atom sites.     

A C solid-state NMR analysis of vitamin D compounds

¹³C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscopy has been employed to analyze four vitamin D compounds, namely vitamin D3 (D3), vitamin D2 (D2), and the precursors ergosterol (Erg) and 7-dehydrocholesterol (7DHC). The ¹³C NMR spectrum of D3 displays a doublet pattern for each of the carbon atoms, while that of Erg contains both singlet and doublet patterns. In the cases of 7DHC and D2, the ¹³C spectra display various multiplet patterns, viz. singlets, doublets, triplets, and quartets. To overcome the signal overlap between the ¹³C resonances of protonated and unprotonated carbons, we have subjected these vitamin D compounds to 1D ¹H-filtered ¹³C CP/MAS and {¹H}/¹³C heteronuclear correlation (Hetcor) NMR experiments. As a result, assisted by solution NMR data, all of the ¹³C resonances have been successfully assigned to the respective carbon atoms of these vitamin D compounds. The ¹³C multiplets are interpreted due to the presence of s-cis and s-trans configurations in the α- and β-molecular conformers, consistent with computer molecular modeling determined by molecular dynamics and energy minimization calculations. To further characterize the ring conformations in D3, we have successfully extracted chemical shift tensor elements for the ¹³C doublets. It is demonstrated that ¹³C solid-state NMR spectroscopy provides a robust and high sensitive means of characterizing molecular conformations in vitamin D compounds.     

Separate Quantification of Doubly and SinglyC-Labeled Metabolites by HSQC-FilteredJSpectroscopy

NMR detection of multiply labeled compounds in biological samples is often used to follow metabolic pathways. Detection of protons bound to¹³C atoms offers a more sensitive approach than direct¹³C detection, but generally results in the loss of carbon–carbon coupling information. We have modified an HSQC sequence to refocus the carbon chemical shifts in order to obtain a proton-correlated¹³C homonuclearJspectrum, which allows us to measure singly and doubly labeled compounds in the same spectrum.     

Solid-State NMR Studies on the Guest Ordering and Dynamics in α,ω-Dibromoalkane/Urea Inclusion Compounds

Solid-state nuclear magnetic resonance (NMR) spectroscopy is utilized to study the molecular behavior of 1,10-dibromodecane and 1,11-dibromoundecane in their urea inclusion compounds. The guest dynamics and conformational order are explored by ¹³C cross polarization magic-angle spinning (CP/MAS) and ¹H MAS NMR spectroscopy which confirm an all-trans conformation of the guest chains. Dynamic ²H NMR experiments are carried out on two guest molecules selectively deuterated at both end groups. A quantitative analysis of the experimental data, obtained from variable-temperature line shape, spin–spin and spin–lattice relaxation measurements, shows that both guest molecules undergo similar motions within the investigated temperature range between 100 and 298 K. The combination of nondegenerate 6-site (or 3-site) rotational jumps and small-angle overall chain wobbling provides an appropriate motional model for the guest motions in these compounds. It is found that the populations of the jump sites exhibit a characteristic temperature dependence, although a discontinuity is missing at the solid–solid phase transition. The same holds for the guest motions which also remain unaffected by the change of the urea lattice structure. Rather, a discontinuity of the guest dynamics at about 30 and 10 degrees above the corresponding solid–solid phase transition is observed for 1,10-dibromodecane and 1,11-dibromoundecane in urea, respectively. Likewise, there is no clear evidence for an odd–even effect due to the change of the guest chain length on the molecular properties of the present inclusion compounds. As a general result, it is concluded that the intermolecular interactions in the present materials are stronger than in n-alkane/urea inclusion compounds. Authors' address: Klaus Müller, Institut für Physikalische Chemie, Universit?t Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany     

Study of diamond film by dynamic nuclear polarization-enhanced13C nuclear magnetic resonance spectroscopy

Three chemical vapor deposited diamond films were studied by dynamic nuclear polarization (DNP)-enhanced high-resolution solid-state¹³C nuclear magnetic resonance (NMR) spectroscopy. Enhanced¹³C direct-polarization spectra of diamond films were obtained by irradiating the samples with microwaves at or near electron spin resonance Larmor frequency of carbon center free radicals. No NMR signal for sp² hybridized carbons could be observed. From the curve of the DNP enhancement as a function of frequency, it is found that the dominant DNP mechanism is the solid-state effect. The¹³C cross-polarization spectrum, which is an evidence for existence of the proton defect in the lattice of diamond films, is much broader than the¹³C single pulse spectrum. The reason is discussed shortly.     

Deuterium NMR studies of guest motions in urea inclusion compounds of 1,6-dibromohexane with analytical evaluation of spectra in the fast motion limit

²H NMR (nuclear magnetic resonance) spectroscopy, in conjunction with X-ray diffraction experiments, was used to characterize the guest motions of 1,6-dibromohexane in its urea inclusion compound. These motions are characterized by alkyl chain jumps between two conformations, each approximately gauche to the terminal bromines, which remain stationary. In this distorted urea channel, one conformer is heavily preferred, but thermally activated population of the unfavorable conformer leads to reversible, temperature-dependent changes in the unit cell parameters. Although rapid motions of the guest chain give rise to ambiguities in the interpretation of the²H NMR spectra, fortuitous temperature-independent spectral features of guests containing deuterium at the α, β and γ positions indicate that the guest motion resembles a two-site jump with unequal probabilities. Analytical lineshape calculations on the three sets of²H NMR spectra indicate a single jump mechanism in which the range of jump angles is narrowly prescribed. This NMR model provided a starting point for successful solution and refinement of the crystal structures at 213 and 298 K, which had been complicated by motional disorder.     

Growth and characterization of a new organic nonlinear optical crystal: Vanillylideneaniline

Vanillylideneaniline with chemical formula C₁₄H₁₃NO₂ (VAN), a second order nonlinear optical (SONLO) organic single crystal was synthesized and grown for the first time from dimethyl formamide (DMF) employing slow solvent evaporation technique. Single crystal X-ray diffraction data reveals that the crystal belongs to noncentrosymmetric orthorhombic space group C222₁. The high-resolution diffraction curve containing single peak with full width at half maximum (FWHM) of 62 arc s ascertains VAN was perfectly crystallized and free from structural grain boundaries. The formation of the material was confirmed quantitatively by FTIR, ₁H¹ and ¹³C NMR spectral analyses. The UV–vis–NIR spectrum reveals the percentage of the transmission of VAN crystal in the entire region. The variations of dielectric constant (?_r) and dielectric loss (D) with frequency at different temperatures were investigated. The SHG of VAN crystal is confirmed by Kurtz Powder technique. The mechanical strength of the crystal was estimated by Vickers hardness test. VAN has yield strength of 8.70 MPa. Thus the grown organic VAN single crystal can be recommended as a promising candidate for SONLO application and device fabrication technology.     

NMR Analysis of a Complex Spin System from a Siruo-Chamigrene

The compound 2,10-dibromo-3-chloro-8-hydroxy-β-chamigrene was analysed in detail by NMR Spectroscopy. the complete assignment of the signals in the ¹H and ¹³C NMR spectra and the determination of the relative configurations were achieved by 2D NMR techniques, AM1 data and ¹H spectrum simulation. Comparisons of the results with related spiro chamigrene systems are also presented.     

Crystal growth, FTIR and thermal characterization of bis(ethyltriphenylphosphonium) tetrabromomanganate(II) dihydrate crystals

Single crystals of a novel compound, bis(ethyltriphenylphosphonium) tetrabromomanganate(II) dihydrate (BTP-Mn) were grown by solution growth-slow evaporation technique from aqueous solution of the compound at ambient temperature. The grown crystals were characterized by elemental analysis, powder X-ray diffraction, thermal analysis, nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infra-red spectroscopy (FTIR) techniques. The chemical composition of the compound was revealed by elemental analysis and its crystallinity was confirmed by powder X-ray diffraction. Thermal analysis confirmed that the compound was stable up to 125°C. The various kinds of protons and carbons present in the compound were confirmed by ¹H NMR and ¹³C NMR technique respectively and the presence of phosphorous was confirmed by ³¹P NMR spectrum in the compound. The modes of vibration of different molecular groups present in the compound were identified by FTIR spectral analysis. The second harmonic generation behaviour was tested by Nd:YAG laser source.     

Nuclear Magnetic Resonance Spectra of Polyhydroxylated Fullerene C60(OH)n

Polyhydroxylated fullerene C₆₀(OH)_n (with an estimated number of hydroxyl groups n = 38–44) synthesized from pure fullerene by mixing a benzene solution of C₆₀ with a NaOH aqueous solution in the presence of a catalyst was studied with ¹H and ¹³C solid-state nuclear magnetic resonance. Possible features of the structure of a molecule shell were revealed from ¹H NMR data. The ¹³C spectrum showed a peak splitting with an increase in temperature, which is probably due to fullerenol isomers.

     

Stable isotope-enhanced two- and three-dimensional diffusion ordered C NMR spectroscopy (SIE-DOSY C NMR)

The feasibility of obtaining high quality homonuclear or heteronuclear diffusion-ordered ¹³C NMR data is shown to be greatly improved by using ¹³C isotopically-enriched samples. Stable isotope-enhanced diffusion ordered (SIE-DOSY) ¹³C NMR has been applied to ¹³C-enriched carbohydrates, and has been used to determine diffusion coefficients for pentose and hexose monosaccharides, and a disaccharide and trisaccharide. These 2D spectra were obtained with as little as 8 min of acquisition time. Fully resolved 3D DOSY-HMQC NMR spectra of [U-¹³C]xylose, [U-¹³C]glucose, and [1-¹³C^gal]lactose were obtained in 5 h. Sample derivatization with [carbonyl-¹³C]acetate (peracetylation) extends the usefulness of the technique to included non-labeled sugars; the ¹³C-carbonyl – carbohydrate ring proton ¹H–¹³C correlations also provide additional structural information, as shown for the 3-D DOSY-HMQC analysis of a mixture of maltotriose and lactose per-[carbonyl-¹³C]acetates.     

Study of the electronic structure and properties of 13C-isotope-based composites

The morphology and electronic structure of ¹³C-isotope-based graphite composites were studied by transmission electron microscopy (TEM), x-ray diffraction, and x-ray fluorescence spectroscopy. High-resolution TEM images showed that composites contain several forms of carbon particles. According to an x-ray diffraction analysis, the size of graphene stacks of graphite particles is 20 and 40 Å. The CK _α x-ray fluorescence spectra of the initial ¹³C isotope powder and composites based on it detected an increase in the density of high-energy occupied states in comparison with the graphite spectrum. Ab initio quantum chemical calculation of the structure of C₁₅₀ graphene showed that the increase in the density of states stems from the electrons of dangling bonds of boundary carbon atoms of particles ～20 Å in size. Electrical properties of ¹³C-isotope-based samples were studied by analyzing the temperature dependence of the conductivity. It was assumed that the change in the logarithmic dependence of the conductivity observed at liquid-helium temperatures to the linear dependence as the temperature increases is caused by carrier transfers between the disordered graphene layers forming a nanocomposite.     

13C NMR of tunnelling methyl groups

The dipolar interactions between the protons and the central ¹³C nucleus of a ¹³CH₃ group are used to study rotational tunnelling and incoherent dynamics of such groups in molecular solids. Single-crystal ¹³C NMR spectra are derived for arbitrary values of the tunnel frequency ν_t. Similarities to ESR and ²H NMR are pointed out. The method is applied to three different materials. In the hydroquinone/acetonitrile clathrate, the unique features in the ¹³C NMR spectra which arise from tunnelling with a tunnel frequency that is much larger than the dipolar coupling between the methyl protons and the ¹³C nucleus are demonstrated, and the effects of incoherent dynamics are studied. The broadening of the ¹³C resonances is related to the width of the quasi-elastic line in neutron scattering. Selective magnetization transfer experiments for studying slow incoherent dynamics are proposed. For the strongly hindered methyl groups of L-alanine, an upper limit for ν_t is derived from the ¹³C NMR spectrum. In aspirin? (acetylsalicylic acid), incoherent reorientations dominate the spectra down to the lowest temperatures studied; their rate apparently increases with decreasing temperature below 25 K.     

Influence of impurities and thermal treatment on spectroscopic properties and laser performance of thulium-doped yttrium vanadate crystals

Influence of impurities and thermal treatment on spectroscopic properties and laser performance of thulium-doped yttrium vanadate crystals was examined. YVO₄ crystals nominally pure, single doped with Tm³⁺ and co-doped with Tm³⁺ and Ca²⁺ were grown by the Czochralski method and then thermally treated at 1150 °C for several hours in a reducing atmosphere (vacuum) or oxidizing atmosphere (air). Samples of crystals were investigated by nuclear magnetic resonance spectroscopy (NMR) and by optical spectroscopy methods. Laser performance of samples was examined upon laser diode pumping. For pure YVO₄ and for YVO₄ containing 0.5 at. % of Tm a single-site NMR spectrum of ⁵¹V nuclei was observed with central line widths of 2.5 and 3.2 kHz (FWHM), respectively. For samples containing 5 at. % of Tm the NMR spectrum was a superposition of multi-site spectra indicating at least three kinds of vanadium sites with axial symmetry. Optical absorption spectra did not contain bands that could be ascribed to V⁴⁺ ions in tetragonal sites. Level of matrix absorption in the visible region and its increase with decreasing wavelength from about 600 to 370 nm was found to be substantially dependent on conditions of thermal treatment. Thermal treatment of crystals and additional doping with Ca did not influence the ³ F ₄ lifetime of thulium and laser performance of crystals, however. Infrared absorption spectra revealed OH^- contamination in all samples. It has been concluded that the quenching of the ³ F ₄ emission in samples containing 5 at. % of thulium is related to migration-accelerated energy transfer to hydroxyl ions acting as energy sinks. PACS 42.55.Xi; 42.62.Fi     

A New Method of Obtaining Structural Information from 2M Exchange NMR and NQR Spectra of Powders

A method of calculating the singularities of two-dimensional correlation spectra of powders and determining the structural parameters with the help of a computer program is described. The opportunities of the method are illustrated on examples of experimental 2M exchange ¹³ C NMR spectra of dimethylsulfone, 2M exchange ² H NMR spectrum of hexamethylbenzene, and model 2M exchange nutational NQR spectrum for spin I = 3/2. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 72–75, August, 2005.     

Structure and NMR properties of 6‐substituted‐5,6‐dihydrobenzo[c]phenanthridine alkaloids

We report a preparation of new 6‐substituted‐5,6‐dihydrobenzo[c]phenanthridines by the reaction of azoles with quaternary benzo[c]phenanthridine alkaloids sanguinarine and chelerythrine. The prepared compounds have been characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. Conformational behaviors of carbazole derivatives in solution have been investigated by low‐temperature NMR experiments. Barriers to rotation around newly formed C6–N bonds were determined to be 12–13 kcal/mol. Quantum chemical calculations have been used to reproduce the experimental observations. Large structural effects on several ¹H NMR resonances were observed experimentally, analyzed by Density Functional Theory (DFT) calculations at B3LYP/6‐311+G(d,p)/PCM level, and interpreted by ring‐current effects of the benzo[c]phenanthridine and carbazole units. Copyright © 2013 John Wiley & Sons, Ltd.