Carbon-13 Nuclear Magnetic Resonance Spectra Research Articles

Structural analysis of polychlorinated biphenyls from carbon-13 nuclear magnetic resonance spectra

The relationship between {sup 13}C NMR chemical shifts and polychlorinated biphenyl (PCB) conformation is investigated. Predictive model equations based on calculated structural descriptors were developed for PCBs and were used to simulate {sup 13}C NMR spectra for nine conformations of each compound. For each compound, the conformation that produced the most accurate simulated spectrum overall was used to develop new model equations for performing further simulations. The continuation of this iterative process allowed the conformations of the PCBs to be successively adjusted, based on spectral comparison results. Conformational profiles were developed for all 49 of the PCB compounds.

High-resolution carbon-13 nuclear magnetic resonance spectra and structure of amorphous and crystalline forms of stereoregular poly(methyl methacrylate)s

High-resolution carbon-13 nuclear magnetic resonance spectra and structure of amorphous and crystalline forms of stereoregular poly(methyl methacrylate)s

Nuclear Magnetic Resonance Spectroscopic Studies on the Action of Ammonium Chloride to Chloroquine

In order to study the medically important action of ammonium chloride toward chloroquine or 7-chloro-4-(4′-diethylamino-1′-methylbutylamino)quinoline, the proton and carbon-13 nuclear magnetic resonance (NMR) spectra of chloroquine have been examined using a 400-MHz NMR spectrometer. Quinoline ring protons exhibited highly resolved coupling patterns of the first-order. The distortionless enhancement by polarization transfer (DEPT) spectra discriminated methyl, methylene and methine carbons in the diamino-chain where diamagnetic effects by nitrogen atoms are complicated. All assignments were fulfilled with carbon-proton correlation spetroscopy (COSY), besides homo-spin decoupling and DEPT spectra. The affinity of ammonium chloride with the chloro atom of the quinoline ring was observed in the proton NMR spectra. This fact seems to be related to the dose of ammonium chloride used to reduce the amount of chloroquine given to patients suffering from retinopathies.

Effects of synthetic estrogens, ( R, R)-(+)-, ( S, S)-(−)-, dl- and meso-hexestrol stereoisomers on microtubule assembly

We previously reported on the inhibition of microtubule polymerization and the formation of ribbon structures by synthetic estrogens [Sato et al., J Biochem 101: 1247–1252, 1987]. The present investigation aimed to analyse these effects in vitro on stereochemical point of view, using hexestrol isomers (( R, R)-(+)-hexestrol, ( S, S)-(−)-hexestrol and meso-hexestrol) and dl-hexestrol. Among hexestrols, dl-hexestrol showed the highest activity in ribbon formation from microtubule proteins at 100 μM. On the other hand, meso-hexestrol was distinguished from others by inhibition of microtubule assembly and formation of a large amount of aggregates from purified tubulin in the presence of MgCl 2 and DMSO. These results were discussed with physico-chemical properties of hexestrols, e.g. absolute configurations as well as circular dichroism spectra and solid state carbon-13 nuclear magnetic resonance spectra.

Study of heterogeneous equilibria in saturated aqueous solutions of some 7-chloro-1,4-benzodiazepines

Acid-base equilibria in heterogeneous and homogeneous systems of some sparingly soluble benzodiazepines (diazepam, prazepam, chlordiazepoxide and medazepam) were investigated in aqueous solution and the corresponding equilibrium constants were determined by the application of pH-metric, spectrophotometric and solubility methods. The sites of protonation were predicted on the basis of the analysis of the corresponding carbon-13 nuclear magnetic resonance spectra. In addition, buffer characteristics of saturated aqueous solutions of these drugs in the presence of the solid phase were investigated and it was established that they possess a very high buffer capacity over a specific pH range.

Inhibitory effect of cis-dehydromatricaria ester isolated from Solidago altissima on the growth of mammalian cells.

A cell growth inhibitory substance was isolated from Solidago altissima, which is known as a naturalized weed. The data of infrared spectrum, proton and carbon-13 nuclear magnetic resonance spectrum, and mass spectrum were identical with those of cis-dehydromatricaria ester. The compound inhibited both tumor and normal mammalian cells.

Solid-state carbon-13 nuclear magnetic resonance spectra of selected metal carboxylate complexes

Eight anhydrous metal carboxylate complexes have been studied in the solid state by 13C cross-polarization magic-angle-spinning n.m.r. spectroscopy. A general assignment of the 13C n.m.r. spectra can be made by comparing the data obtained with definitive structural data previously reported in single-crystal X-ray crystallographic studies. Although a complete assignment of all n.m.r. peaks has not been achieved, the results highlight the important parameters involved and demonstrate that in many cases definitive structural data can be deduced for these complexes in the solid state using n.m.r. spectroscopy. Metal carboxylates are excellent compounds for a comparative study because of the very high quality of the solid-state spectra produced. A crystallographic splitting of 8 Hz can be seen clearly in some spectra. The chemical shift is very sensitive to the precise crystallographic environment.

Multivariate analysis of carbon-13 nuclear magnetic resonance spectra. Identification and quantification of average structures in petroleum distillates

Analyse des fractions C 10 a C 25 de deux petroles de la Mer du Nord par spectrometrie RMN du carbone 13, avec transfert de polarisation pour determiner la multiplicite des resonances. Etude comparative avec les analyses realisees par chromatographie en phase gazeuse

1'-Methylzeatin and its 9-b-D-Ribofuranoside: The Carbon-13 Nuclear Magnetic Resonance Spectra Revised

Revised carbon-13 chemical shift assignments are reported for the cytokinins (1'R)-1'-methylzeatin [(1'R)-I] and its 9-β-D-ribofuranoside [(1R)-II].Previous shift assignments for the two methyl carbons in the purine N 6 side chain of [(1'R)-I] and [(1R)-II], as well as those for the C(2') and C(3') carbons of [(1R)-II] , have now been reversed by comparison with the 1 3C nmr data for the diastereomeric nucleoside (1S)-II and the cis isomers (1'R)-1'-methyl-cis-zeatin and its 9-β-D-ribofuranoside.

Constituents of the seeds of Swietenia mahagoni Jacq. II. Structures of swietemahonin A, B, C, D, E, F, and G and swietemahonolide.

Eight new tetranortriterpenoids, swietemahonin A-G and swietemahonolide, were isolated from the cotyledons of seeds of Swietenia mahagoni. The structures 1-8 are proposed for these compounds, respectively, based mainly on detailed analyses of the proton and carbon-13 nuclear magnetic resonance(1H-and 13C-NMR)spectra by the use of two-dimensional NMR techniques(1H-1H chemical shift correlation spectroscopy (COSY), 1H-13C COSY, and 1H-13C long-range COSY.

Proton, carbon-13, and platinum-195 nuclear magnetic resonance spectroscopy of hydroxypyridinate-bridged dinuclear platinum(III) complexes. Equilibria and mechanism of bridging ligand rearrangement

The proton, carbon-13, and platinum-195 nuclear magnetic resonance spectra of some o-hydroxypyridinate-bridged dinuclear platinum(III) complexes have been analyzed and used to study some of their reactions. These complexes feature two Pt(III) ions joined by a metal-metal bond. Each Pt has two methyl groups on it in a cis configuration. Two hydroxpyridinate groups bridge the dinuclear unit. Derivatives of the parent compound have fluorine, chlorine, or a methyl group at the 6-position of the hydroxypyridinate. The bridging ligands may bind in head-to-head (HH) or head-to-tail (HT) arrangements. The HH complex has either a single pyridine or a single diethyl sulfide coordinated to the platinum ion to which the hydroxypyridinate oxygen atoms are also bound. In the HH complexes this ligand is in slow exchange with free ligand and binds at the sites coaxial to the metal-metal bond. For complexes with the bridging ligands hydroxypyridinate and 6-fluorohydroxypyridinate, increased pyridine concentration results in the isomerization of the ligand bridge to form HT complexes. The HT complexes have pyridine bound to both axial sites and in fast exchange with free pyridine at room temperature. The mechanism of the HH to HT rearrangement may involve a preequilibrium of the HH complex with pyridine. Rearrangement ofmore » the bridge is dissociative but does not involve complete dissociation from the complex. 14 refs., 1 fig., 6 tabs.« less

High-temperature NMR using inductive heating

We report a simple, efficient method for carrying out nuclear magnetic resonance (NMR) experiments at high temperature in any NMR probe without modification. The sample tube is coated with a thin film of metal and the rf coil used for the NMR experiment is used to inductively heat the film, thus heating the sample inside the tube. Using this approach, we have obtained both proton and high-resolution carbon-13 NMR spectra at temperatures as high as 730 K.

Carbon-13 nuclear magnetic resonance of ferroelectric liquid crystals with off-magic-angle spinning

The orientational ordering of three ferroelectric liquid crystals 4′-(3-methyl-2-chloropentanoyloxy)-4-alkyloxybiphenyls has been studied by 2D carbon-13 nuclear magnetic resonance (NMR) with variable angle sample spinning. The three homologs have hexyloxy (C6), heptyloxy (C7), and octyloxy (C8) chains, respectively, at the 4 position. They exhibit smectic A (SA) and chiral smectic C (S*C; ferroelectric) phases and have unusually large spontaneous polarization of the electric dipoles. In the SA phase, macroscopic alignment of the molecular director along the spinning axis can be achieved by cooling the sample rapidly from the isotropic liquid. For the S*C phase, the molecular alignment is different for the three compounds. At a magnetic field of 7.05 T, the helical structures of C6 and C8 unwind and the molecular directors align along the spinning axis at a spinning rate of 1 kHz. However, under the same conditions, the helical structure of C7 is retained and its carbon-13 NMR spectrum shows a partial powder pattern. On the other hand, the racemate of C7 has a normal smectic C (SC) phase without a helical structure, and the molecular director can be easily aligned for the NMR study. The racemate of C8 was also synthesized and studied for comparison. The 2D NMR technique used was separated local field (SLF) spectroscopy with an efficient proton–proton dipolar decoupling sequence BLEW-48 in the evolution period. The carbon–proton dipolar coupling constants were determined and the order parameters for different molecular segments of the liquid crystal were calculated. The carbon-13 chemical shifts were also measured as functions of temperature and the data were used to probe the temperature dependence of order parameters. The results show that the C–H bond at the first chiral center in these compounds has an unusually large negative order parameter. This could be due to restricted rotation of the molecular segment at the chiral center, which would be related to the high spontaneous polarization of these compounds.

Simulation of carbon-13 nuclear magnetic resonance spectra of linear cyclic aromatic compounds

Simulation of carbon-13 nuclear magnetic resonance spectra of linear cyclic aromatic compounds

Simulation of carbon-13 nuclear magnetic resonance spectra of piperidines

Calcul de spectre RMN du 13 C pour des piperidines methylees a partir de donnees experimentales et des conformations correspondantes. Prediction des spectres RMN a basse temperature et des conformations pour les piperidines substituees et pour des pyrrolidines

Carbon-13 nuclear magnetic resonance spectra of D-homoannulated 17-hydroxypregnan-20-ones

The 13C-NMR spectra of several groups of isomeric D-homoannulated 17α-hydroxypregnan-20-ones have been recorded. The chemical shifts of the various carbon atoms have been correlated with the structures of the different isomers.

Mercury(II) complexes of vitamin B 1

Mercury(II) complexes of thiamine and its derivatives have been synthesized and characterized by elemental analysis, conductivity measurements, infrared, proton and carbon-13 nuclear magnetic resonance spectra. These new complexes have been formulated as either M(Th)X 3 with a possibility of direct Hg(II)-N(I′) interaction or as ionic compounds of the type (MX 3) −(Th) + where M = Hg, Th = thiamine, X= Cl, Br or I and (M(Th)(OAc)X)X where X = SCN and OAc = acetato group.

Simulation of carbon-13 nuclear magnetic resonance spectra of alkyl-substituted cyclohexanones and decalones

Simulation of carbon-13 nuclear magnetic resonance spectra of alkyl-substituted cyclohexanones and decalones

Structure elucidation methodology for disaccharides based on carbon-13 nuclear magnetic resonance spectrum simulation.

Molecular mechanics techniques are used to derive structural parameters that allow carbon-13 nuclear magnetic resonance spectra of disaccharides to be modeled. On the basis of a collection of 40 disaccharide spectra, four linear models are derived that allow complete spectra to be simulated. On the basis of these 40 compounds, the average difference between simulated and observed chemical shifts is +/- 0.45 ppm. The majority of structural parameters used are based on interatomic distances computed from modeled three-dimensional atomic coordinates. Found particularly useful in modeling the disaccharide spectra are the effects of oxygen electron lone pairs and encodings of the structural environments of hydrogens alpha to the carbon whose chemical shift is being predicted. The computed models are examined, and their predictive ability is assessed. The potential application of the methodology to the structure elucidation of disaccharides is demonstrated.

Viscosity measurements of low temperature molten salts

Low temperature molten salts are a new class of electrolytes for battery applications (e.g. [1]). Viscosity measurements of low temperature molten salts based on mixtures of aluminium or copper halide and alkylpyridinium or dialkylimidazolium halide have been reported [1-5]. They have shown strong dependences of viscosity with changes in composition in basic (i.e. organic-rich) melts [1, 2, 4, 5]. Further, 'gaps' in the liquidus lines, i.e. regions where fusion does not occur, only a glass transition at very low temperatures, have been shown for binary melts containing 1-methyl-3-ethylimidazolium chloride (MEIC) [1] and bromide [2] as the organic salt. Finally, measurements of chemical shifts for proton and carbon nuclear magnetic resonance spectra of basic MEICA1C13 melts have been explained in terms of oligomeric structures [6, 7]. All of these measurements used viscometers based on variations of Cannon-Fenske devices [1-3, 5] or the falling ball method [4]. These methods do not provide shear stress-shear rate data, which could be used to determine whether the melts behave like non-Newtonian fluids. This paper reports viscosity measurements of MEIC-A1CI3 binary melts using a plate and cone viscometer (in order to obtain shear stress-shear rate data) and compares the viscosities measured using this technique with those of previous investigators.