Application of 13C-n.m.r. spectroscopy to study the mechanism of N-demethylation of [NMe13C] codeine by cell-free extracts of Cunninghamella bainieri

Codeine was synthesized with 90% enrichment of the N-methyl group with carbon-13. N-Demethylation of this substrate by cell-free extracts of Cunninghamella bainieri in an n.m.r, tube gave norcodeine and ¹³C-labelled formaldehyde. Fourier-transform ¹³C-n.m.r. spectroscopy was used to observe the N-demethylation process at selected temperatures. The labelled formaldehyde liberated was trapped with sodium sulphite, and the sulphite adduct, as well as intermediates, were located in the n.m.r, spectrum at each temperature. Intermediate resonances assignable to codeine-N-oxide were not detected during these enzyme-transformation studies. These data suggest that the observed ¹³C-n.m.r. signals correspond to the chemically labile carbinolamine intermediate formed during N-demethylation. A methine ¹³C signal was not observed. Thus, N-demethylation of codeine by Cunninghamella bainieri occurs by direct C-oxidation and not via an N-oxide intermediate.     

Pteridine studies: III—13C n.m.r. data of pteridine,some of its derivatives and their covalent σ-adducts with ammonia and water

¹³C n.m.r. spectral data of pteridine and nineteen of its derivatives (containing one or more chloro, methylthio, methyl, t-butyl or phenyl substituents) are reported. The ¹³C n.m.r. spectrum of the title compound has been assigned conclusively. ¹³C n.m.r. substituent effects are shown to be very useful in discerning between 6- and 7-substituted pteridines. Additionally, the ¹³C n.m.r. spectra of several covalent amination products, i.e. the 3,4-dihydro-4- amino- and the 5,6,7,8-tetrahydro-6,7-diaminopteridine derivatives, formed by dissolving the appropriate pteridine in liquid ammonia, have been recorded. The ¹³C n.m.r. spectra of the corresponding covalent hydrates are also reported.     

Thermally Prepared Ti/RhO x Electrodes: Hydrogen Evolution in Alkaline Solution

Ti/RhO _x electrodes were prepared at 400–600° by thermal decomposition of RhCl₃. Oxide layers were characterized by cyclic voltammetry in H₂SO₄ as well as in KOH solution. The voltammetric charge exhibited a maximum at 470°C in both cases. ₂ evolution from KOH solution was studied by steady-state polarization curves. Only one Tafel slope close to 40 mV was observed over the explored current range. The reaction order with respect to ^– was negative and fractional. A mechanism is proposed for H₂ evolution on RhO _x in KOH solution. The stability of the electrodes was tested by comparing the voltammetric charge before and after the ₂ evolution experiments. Stability was observed to increase with increasing calcination temperature. The same is the case for the electrocatalytic activity normalized to unit surface charge.     

Effect of monomer molecular flow on electrode surface on the structure of poly(α-tetrathiophene) obtained by anodic polymerization

Different structures have been found for poly(α-tetrathiophene) [poly(α-4TF)] electrosynthesized on Pt by anodic oxidation of 1.0 mM monomer solutions in media such as 45:35:20 (v/v/v) acetonitrile/THF/DMF, 45:35:20 (v/v/v) acetonitrile/ethanol/DMF and 72:28 (v/v) acetonitrile/DMF containing 0.1 M LiClO₄; as well as 72:28 (v/v) acetonitrile/DMF with 0.1 M NaClO₃, under dynamic and static conditions at 25 °C. In all cases the polymer was generated by chronoamperometry at 1.000 V vs. Ag∣AgCl, corresponding to the first oxidation peak detected by cyclic voltammetry. Uniform, adherent, insoluble and black polymer films were obtained under these conditions. The resulting structures have been elucidated by combining the information of their IR spectrum, n_ox-value and doping level of the counterion. The degree of crosslinking of every polymer has been quantified and related to the molecular flow of monomer on the Pt electrode. A monomer concentration flow between 4 × 10⁻⁶ and 5 × 10⁻⁶ mmol cm⁻² s⁻¹ was determined as the limiting value below which the polymer grows with crosslinking. This value corresponds to the electropolymerization rate of α-4TF by Pt area unit at 25 °C.     

The case for a revised structure for hypophyllanthin - an analysis of the 13C N.M.R. spectra of aryltetralins

A revised structure for hypophyllanthin is proposed on the basis of its ¹³C n.m.r. spectrum. ¹³C n.m.r. spectra also support the previously proposed structure for nirtetralin and assist in the structural elucidation of a new aryltetralin lignan.     

Complete assignment of the 13C n.m.r. spectrum of mutarotated D-ribose by integration and specific deuteration

The ¹³C n.m.r. spectrum of mutarotated D -ribose is completely assigned by using 2- and 3-deuterio-D -ribose as reference compounds. The signal intensities of the largely relaxed ¹³C n.m.r. spectrum are evaluated, and the equilibrium mixture of mutarotated D -ribose is found to consist of 6·1% α-furanose, 11·6% β-furanose, 20·3% α-pyranose and 62% β-pyranose.     

Effects of simultaneous 13C?1H and 13C?11B decoupling on the carbon-13 n.m.r. spectra of some organoboron compounds

¹³C FT n.m.r. spectra were obtained from borates of methyl α-D -glucopyranoside, triethylboron, sodium tetraphenylboron and 1-butaneboronic acid employing a simultaneous ¹H and ¹¹B decoupling network. The effectiveness of the system was evident using the three latter organoboron compounds. Since no diminution in line broadening of signals occurred in the spectrum of the sugar borate, the absence of ¹³C? O? ¹¹B coupling was indicated. This finding was confirmed by comparing the effects of varying the temperatures of sugar borates and triethylboron on their conventional ¹³C n.m.r. spectra.     

New confined p-phenylenevinylene (PPV)-type polymer analogue of poly(phenylene sulfide)

A new confined p-phenylenevinylene (PPV)-type polymer (PPVS) has been synthesized using Wittig condensation. The chemical structure of the polymer was well defined by ¹H NMR, ¹³C NMR, and FTIR spectroscopic analysis. PPVS contains oligomeric PPV units separated by sulfide bridges in the main chain; it is fully soluble in common organic solvents and has a number-average molecular weight of 3500 g mol⁻¹. Thermogravimetric analysis and differential scanning calorimetry indicate that PPVS is amorphous, stable up to 360 °C in air and displays a glass transition temperature of 98 °C. The optical properties of the polymer were investigated by UV-visible absorption and photoluminescence spectroscopies. The polymer film absorbs at 375 nm and emits at 517 nm with a narrow emission spectrum. From the cyclic voltammetry analysis, the electrochemical bandgap was estimated to be 2.78 eV. A single-layer diode device of the configuration indium-tin oxide/PPVS/aluminium has been fabricated and has a relatively low turn-on voltage of 3.4 V. An electroluminescent emission similar to photoluminescence is demonstrated in a multilayer device.     

Structural influence of the carbon chain length in hybrid materials obtained from zirconium n-propoxide and diols

Zirconium n-propoxide Zr(OPr ⁿ )₄ has been chemically modified by 1,3-propanediol and 1,3-butanediol with molar ratio r=0.5, 1 and 2. The properties of the hybrid organic-inorganic materials obtained after drying at 100°C for 24 hours have been measured by thermal analysis, X-ray diffraction, infra-red spectroscopy and ¹³C NMR with cross-polarisation at magic angle spinning. Chemical modification of the zirconium precursor at a molecular level has been clearly detected, with a bridging coordination mode for both diols. If the coordination mode of the diols cannot be changed by increasing the carbon chain length, it was found using ¹³C CP MAS NMR that the local order is much more well-defined when the reactivity of both OH groups are not the same. Thus, using 1,3-butanediol which has a primary and a secondary OH group, it is possible to obtain after complete modification (r=2) a highly homogeneous hybrid polymer which transforms directly into tetragonal zirconia below 400°C. With other diols (1,2-ethanediol and 1,3-propanediol), the hybrid materials transform into tetragonal zirconia above 400°C through a decomposition process involving several steps. Then playing with the carbon chain length and/or the steric hindrance around the OH groups provides an easy way to monitor the ultrastructure of these hybrid materials, and allows a better control of the gel oxide transformation.     

13C NMR spectra of benzofuroxan and related compounds

The ¹³C n.m.r. spectrum of benzofuroxan at ?15°C is assigned on the basis of selective decoupling experiments and by comparison with the ¹³C chemical shifts of model compounds. The ¹³C spectra were also measured in trifluoroacetic acid as a solvent. From the temperature dependence of the ¹³C spectrum of benzofuroxan in CDCl₃, a barrier of 14·0 ± 0·2 kcal mol^?1 is obtained for the degenerate tautomerism in this compound.     

Etude en RMN du carbone 13 de dicoumarols substitués

The ¹³C n.m.r. spectrum of the bridge substituted dicoumarols are interpreted in order to obtain structural information for quantitative structure-activity relationships. The results are in agreement with those obtained by ¹H n.m.r. These dicoumarols exhibit double restricted rotation around both bridge bonds.     

Electronic structure and absorption spectra of verdazyl radicals,the corresponding cations,and leuco compounds

The wavelengths of transitions in electronic absorption spectra of verdazyl radicals, the corresponding cations, and leuco compounds were calculated in valence and -electron approximations with allowance for configuration interaction. It was shown that the longest-wave bands in the investigated compounds are due to ^* electron transitions. The effect of the nature of the substituents on the position of the bands in the spectrum is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 473–477, July–August, 1986.     

Synthesis and spectral studies ofo-hydroxyacetophenone (N-benzoyl)glycyl hydrazone and some of its lanthanide(III) complexes

Summary o-Hydroxyacetophenone (N-benzoyl)glycyl hydrazone (o-HABzGH) has been characterized by i.r.,¹H n.m.r.,¹³C n.m.r. and mass spectral studies, and its complexes of the types [Ln(o-HABzGH)Cl₂(H₂O)₂]Cl and [Ln(o-HABzGH–2H)OH(H₂O)₃], where Ln=La, Pr, Nd, Sm and Eu, have been synthesized. The structures of the complexes have been studied by conductance, magnetic, electronic, i.r.,¹H n.m.r. and¹³C n.m.r. spectral techniques. The hypersensitive bands of the electronic spectra suggest coordination numbers six and seven around Nd^III in its adduct and neutral complexes respectively. I.r. and n.m.r. spectral data suggest a neutral bidentate behaviour for the ligand in the adducts and a dinegative tridentate nature in the neutral complexes.     

Preparation of a bacterial polyester with carboxy groups in side chains

Unsaturated biopolyesters were produced by Pseudomonas oleovorans from two mixtures of sodium octanoate and 10-undecenoic acid (90:10 and 80:20 mol/mol) as a reserve of carbon and energy. Chemical modification of double bonds into carboxyl groups was carried out with potassium permanganate (KMnO₄). Oxidation reaction was proved by ¹H and ¹³C NMR spectroscopy. Molecular weights of modified biopolyesters were not highly affected by the oxidation reaction. Hydrophilicity was enhanced; polyester containing 25 % of repeating units pendant carboxylic acid end groups was soluble in polar solvents such as methanol, dimethylsulfoxide or a 85:15 (v/v) acetone/water mixture. Moreover, the presence of carboxy pendant groups was important with respect to the hydrolytic degradation. A fast hydrolysis was observed at pH = 11 in 24 hours for the carboxylated modified polyester containing 25 % of carboxyl groups.     

1H and 13C studies of alkenes,epoxides and cyclic thionocarbonates

¹H and ¹³C chemical shift data are presented and discussed for a number of di- and tri-alkyl substituted alkenes, epoxides and thionocarbonates. The completely stereospecific interconversion of these compounds, together with the n.m.r. data, allows a straightforward and quantitative stereochemical analysis. For ¹H n.m.r., the most useful intermediates proved to be the thionocarbonates. The differential shieldings between cis and trans isomers are tentatively explained in terms of the conformational change of the 5-membered thionocarbonate ring. In ¹³C n.m.r., either series can be useful to distinguish between stereoisomers. The conclusions stemming from the ¹³C n.m.r. results complement the ¹H n.m.r. studies.     

13C Fourier transform n.m.r.: XIII—reassignment of the 13C spectrum of ergosterol

The complete labeling pattern of ergosterol isolated from Saccharomyces cerevisiae grown with [1-¹³C] acetate is detailed and the results of this study have led to a reassignment of carbons 5, 8, 12, 16, 22 and 23 in the ¹³C n.m.r. spectrum of ergosterol.     

N-Heterocyclic carbene complexes of palladium(II) and rhodium(I) with pendant ferrocenylmethyl groups: synthesis and electrochemistry

1-Ferrocenylmethyl-3-benzylimidazolidinium iodide and 1-ferrocenylmethyl-3-(2,4,6-trimethylbenzyl)imi-dazolidinium iodide were prepared in good yields by boiling, under reflux, a solution of (ferrocenylmethyl)- trimethylammonium iodide and the appropriate N-alkyl-2-imidazoline in MeCN. From the 1-ferrocenylmethyl-3-ben- zylimidazolidinium iodide salt, N-heterocylic carbene complexes of Pd^II and Rh^I were synthesized by in situ deprotonation and subsequent trapping. The new compounds were characterized by C, H, N analyses, ¹H-n.m.r., ¹³C-n.m.r. and by cyclic voltammetry. The n.m.r. properties of the complexes are compared with those of non-ferrocenylated carbene derivatives. The c.v.'s of these compounds show a number of resolved redox processes, indicating that CH₂Fc substituents are electronically isolated from the remaining molecular framework.     

A Structural Study of Epoxidized Natural Rubber (ENR-50) and Its Cyclic Dithiocarbonate Derivative Using NMR Spectroscopy Techniques

A structural study of epoxidized natural rubber (ENR-50) and its cyclic dithiocarbonate derivative was carried out using NMR spectroscopy techniques. The overlapping ¹H-NMR signals of ENR-50 at δ 1.56, 1.68-1.70, 2.06, 2.15-2.17 ppm were successfully assigned. In this work, the ¹³C-NMR chemical shift assignments of ENR-50 were consistent to the previously reported work. A cyclic dithiocarbonate derivative of ENR-50 was synthesized from the reaction of purified ENR-50 with carbon disulfide (CS₂), in the presence of 4-dimethylaminopyridine (DMAP) as catalyst at reflux temperature. The cyclic dithiocarbonate formation involved the epoxide ring opening of the ENR-50. This was followed by insertion of the C-S moiety of CS₂ at the oxygen attached to the quaternary carbon and methine carbon of epoxidized isoprene unit, respectively. The bands due to the C=S and C-O were clearly observed in the FTIR spectrum while the ¹H-NMR spectrum of the derivative revealed the peak attributed to the methylene protons had split. The ¹³C-NMR spectrum of the derivative further indicates two new carbon peaks arising from the >C=S and quaternary carbon of cyclic dithiocarbonate. All other ¹H- and ¹³C-NMR chemical shifts of the derivative remain unchanged with respect to the ENR-50.     

13C-NMR-spektroskopische und stereochemische Untersuchungen: XI—Konformationen von Bicyclo[3.3.1]nonanen und ihre Unterscheidbarkeit durch lanthanideninduzierte Verschiebungen

The ¹³C chemical shifts of bicyclo[3.3.1]nonane and of the corresponding 9-hydroxy- and 9-oxo- derivatives are compared with chemical shifts calculated on the basis of stereospecific shift increments. These results as well as the ¹H n.m.r. spectrum of the ketone indicate a predominant chair-chair conformation CC. A low temperature ¹³C n.m.r. study as well as an analysis of the temperature dependence of ¹³C chemical shifts in bicyclo[3.3.1]nonane furnish a limit for the free energy difference between CC and BC conformations of ΔG ≧ 5,85 kJ mol^?1. The distinction between CC, BC and BB provides a test for the applicability of lanthanide-induced ¹H and ¹³C shifts for the assignment of flexible geometries. The typical occurrence of several and/or flat minima in the LIS geometry analysis allows only the exclusion of boat–boat conformations.     

Thermally Induced Phase Transformation on 12-Tungstophosphoric Acid/ZrO2 Sol-Gel

Zirconium (IV)-n-butoxide and tungstophosphoric acid (WP) were co-gelled at pH 3, 5 and 7 with HCl acid, C₂H₄O₂ acid and NH₄OH, respectively. Pyridine adsorption bands at 1610 and 1442 cm^–1 corresponding to Lewis acidic sites were observed by FTIR spectroscopy. Acidity determined by ammonia thermodesorption shows values around 1100 mol of NH₃/g, which correspond to solids showing super acidity. It was found that the incorporation of WP to gelling zirconia delay the formation of tetragonal zirconia. Raman spectroscopy shows the stabilization of the Keggin structure on zirconia thermally treated at 400°C.