Determination of configurational isomers in polybutadienes by <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR spectroscopy

The NMR spectra (600 MHz) of polybutadienes containing different amounts of cis-1,4, trans- 1,4 and 1,2 units are analyzed. The critical consideration of signal assignment and the comparison of ¹H and ¹³C NMR data reveal that there are significant limitations to the quantitative characterization of polybutadienes with the use of NMR spectroscopy.     

Potential and Limitations of 2D <Superscript>1</Superscript>H–<Superscript>1</Superscript>H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids

Summary.  A brief overview of our recent results concerning the application of 2D CRAMPS experiments to investigate a wide range of materials is presented. The abilities of the 2D ¹H–¹H spin-exchange technique to characterize the structure of organic solids as well as the limitations resulting from segmental mobility and from undesired coherence transfer are discussed. Basic principles of ¹H NMR line-narrowing and procedures for analysis of the spin-exchange process are introduced. We focused to the qualitative and quantitative analysis of complex spin-exchange process leading to the determination of domain sizes and morphology in heterogeneous multicomponent systems as well as the characterization of clustering of surface hydroxyl groups in polysiloxane networks. Particular attention is devoted to the determination of the ¹H–¹H interatomic distances in the presence of local molecular motion. Finally we discuss limitations of the ¹³C–¹³C correlation mediated by ¹H–¹H spin exchange to obtain structural constraints. The application of Lee-Goldburg cross-polarization to suppress undesired coherence transfer is proposed. Corresponding author. E-mail: brus@imc.cas.cz Received May 28, 2002; accepted (revised) July 1, 2002     

Complete <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR signal assignments and chemical shift calculations of four 1,2,4-oxadiazole-based light-emitting liquid crystals

In this article, we describe the complete ¹H and ¹³C NMR signal assignments of four 1,2,4-oxadiazoles possessing light-emitting liquid crystal properties. These results were obtained by using one- and two-dimensional NMR techniques as well as GIAO (PCM) calculations at B3LYP/6-311++G(d,p) level for compounds 1 and 2a–d. The computed values are in good agreement with the ones obtained experimentally. In addition, some previously unexplained thermotropic features of compounds 2a–d could be clarified with the help of the geometry optimization calculations carried out by us.     

Extraction of metal ions (Fe<Superscript>3+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) using immobilized-polysiloxane iminobis(n-2-aminophenylacetamide) ligand system

A new insoluble solid functionalized ligand system bearing chelating ligand group of the general formula P-(CH₂)₃-N[CH₂CONH(C₆H₄)NH₂]₂, where P represents [Si–O] _n polysiloxane network, was prepared by the reaction of the immobilized diethyliminodiacetate polysiloxane ligand system, P-(CH₂)₃N(CH₂CO₂Et)₂ with 1,2-diaminobenzene in toluene. ¹³C CP-MAS NMR, XPS and FTIR results showed that most ethylacetate groups (–COOEt) were converted into the amide groups (–N–C=O). The new functionalized ligand system exhibits high capacity for extraction and removal of the metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with efficiency of 95–97% after recovery from its primary metal complexes. This functionalized ligand system formed 1:1 metal to ligand complexes.     

Through space spin-spin coupling <Superscript>19</Superscript>F-<Superscript>1</Superscript>H as the base for comparative analysis of conformational equilibrium in fluorine-substituted aryl vinyl selenides and sulfides

The analysis of long-range spin-spin coupling ¹⁹F-¹H and the other conformation-dependent parameters of ¹H NMR spectra shows that aryl vinyl selenides like aryl vinyl sulfides exist as mixtures of s-cis and s-trans rotational isomers. The combined data of ¹H and ¹³C NMR spectra reveal the increase in the torsional angle ϑ at the bond X-CH=CH₂ (X = S, Se) in selenides compared to sulfides due to diminished interaction energy of the unshared electron pairs of selenium with the π*-orbitals of the double bond as compared to analogous interaction in sulfides.     

Evaluation of <Superscript>13</Superscript>C NMR spectra of cyclopropenyl and cyclopropyl acetylenes by theoretical calculations

A convenient methodology was developed for a very accurate calculation of ¹³C NMR chemical shifts of the title compounds. GIAO calculations with density functional methods (B3LYP, B3PW91, PBE1PBE) and 6-311+G(2d,p) basis set predict experimental chemical shifts of 3-ethynylcyclopropene (1), 1-ethynylcyclopropane (2) and 1,1-diethynylcyclopropane (3) with high accuracy of 1–2 ppm. The present article describes in detail the effect of geometry choice, density functional method, basis set and effect of solvent on the accuracy of GIAO calculations of ¹³C NMR chemical shifts. In addition, the particular dependencies of ¹³C chemical shifts on the geometry of cyclopropane ring were investigated.     

Accurate assignments in PMR and <Superscript>13</Superscript>C NMR spectra of anhydrolycoctonine using 2D spectroscopy

Resonances in PMR and ¹³C NMR spectra of anhydrolycoctonine were fully assigned based on a series of 1D and 2D NMR experiments. The conformation of ring A was concluded to be a distorted boat with H-1β from a comprehensive analysis of chemical shifts, SSCC, and the NOE for two possible conformations. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 267–269, May–June, 2008.     

Hydridosilazanes hydrolysis-condensation reactions studied by <Superscript>1</Superscript>H and <Superscript>29</Superscript>Si liquid NMR spectroscopy

Hydridosilazane compounds containing Si–N and Si–H bonds can be used as precursors of SiO_x materials. The hydrolysis-condensation reactions of tetramethyldisilazane, as a polyhydridosilazane model compound, were investigated by ¹H and ²⁹Si liquid NMR spectroscopy. These reactions were carried out at room temperature for up to 120 min in presence of water. The identified products are short linear siloxane species (hydride terminated polydimethylsiloxanes M^HD_xM^H) and cyclosiloxanes. Silicon hydride persistence in the reactional mixture suggested that silazane group is more sensitive to hydrolysis reaction than silicon hydride group. Moreover, additional experiments evidenced that the low steric hindrance of the silicon hydride influences the silazane hydrolysis kinetic. Hence the presence of ammonia released during silazane hydrolysis reaction was demonstrated to be a catalyst of the silicon hydride hydrolysis reaction.     

Quantitative <Superscript>2</Superscript>H NMR spectroscopy

The selectivity of deuterium distribution between the nonequivalent positions in 3-carene (1), 4-α-acetyl-2-carene (2), and 4-(1-hydroxyethyl)-2-carene (3) has been measured by ²H-{¹H} NMR spectroscopy at the natural abundance of deuterium. These “H/D-isotope portraits” were shown to be typical of terpenes and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six-membered ring in compound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2) atom from the anti position with respect to the three-membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group. For Part 2, see Ref. 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1657–1664, August, 2008.     

Structure of lipid A from the marine gram-negative bacterium <Emphasis Type="Italic">Pseudoalteromonas nigrifaciens</Emphasis> IAM 13010<Superscript>T</Superscript>

The structure of lipid A from the marine γ-proteobacterium Pseudoalteromonas nigrifaciens IAM 13010^T that was prepared by hydrolysis of the corresponding lipopolysaccharide by acetic acid (1%) was determined by chemical analysis, ¹³C NMR spectroscopy, and MALDI/TOF and LSIMS mass spectrometry. It was shown that lipid A is a β-1,6-bonded disaccharide of glucosamine that is substituted by two phosphoric acids (in the C1 and C4′ positions), two (R)-3-hydroxyalkanoic (normal and branched) acids with ester bonding (at the C3 and C3′-positions), and (R)-3-hydroxydodecanoic and (R)-3-dodecanoyloxydodecanoic acids (both with amide bonding at C2′ and C2, respectively). It was hypothesized that this type of structure is typical of lipid A from bacteria of the genus Pseudoalteromonas in general. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 425–429, September–October, 2007.     

pH optimization for a reliable quantification of brain tumor cell and tissue extracts with <Superscript>1</Superscript>H NMR: focus on choline-containing compounds and taurine

The aim of this study was to define the optimal pH for ¹H nuclear magnetic resonance (NMR) spectroscopy analysis of perchloric acid or methanol–chloroform–water extracts from brain tumor cells and tissues. The systematic study of the proton chemical shift variations as a function of pH of 13 brain metabolites in model solutions demonstrated that recording ¹H NMR spectra at pH 10 allowed resolving resonances that are overlapped at pH 7, especially in the 3.2–3.3 ppm choline-containing-compounds region. ¹H NMR analysis of extracts at pH 7 or 10 showed that quantitative measurements of lactate, alanine, glutamate, glutamine (Gln), creatine + phosphocreatine and myo-inositol (m-Ino) can be readily performed at both pHs. The concentrations of glycerophosphocholine, phosphocholine and choline that are crucial metabolites for tumor brain malignancy grading were accurately measured at pH 10 only. Indeed, the resonances of their trimethylammonium moieties are cleared of any overlapping signal, especially those of taurine (Tau) and phosphoethanolamine. The four non-ionizable Tau protons resonating as a singlet in a non-congested spectral region permits an easier and more accurate quantitation of this apoptosis marker at pH 10 than at pH 7 where the triplet at 3.43 ppm can be overlapped with the signals of glucose or have an intensity too low to be measured. Glycine concentration was determined indirectly at both pHs after subtracting the contribution of the overlapped signals of m-Ino at pH 7 or Gln at pH 10.     

Determination of <Superscript>3</Superscript>H and <Superscript>14</Superscript>C in the Dry Active Wastes (DAW) generated from the Light Water Reactors (LWR) by a wet oxidation method

³H and ¹⁴C Measurements of the dry active waste (DAW), such as the cotton, paper, and vinyl, generated from a nuclear power plant (NPP) were conducted with wet oxidation using open vessel equipment based on simulation results. The recovery efficiency with the simulated samples was around 93% with a relative standard deviation (RSD) of 1–3%. A liquid scintillation counter (LSC) was used for counting and adjusted to a quenching correction curve. The counting value was evaluated for the minimum detectable activity (MDA), which was found to be about 4 × 10⁻¹ Bq/g for ³H and 2 × 10⁻² for ¹⁴C when approximately 5 g of the samples were measured. The measured DAW samples for the cotton, paper, and vinyl generated from NPP achieved of RSD values of 25, 25, and 60%, respectively, for ³H and 0–50% for ¹⁴C.     

PMR and <Superscript>13</Superscript>C NMR spectra of biologically active compounds. XIII.* Structure and stereochemistry of a new phenylpropanoid glycoside isolated from <Emphasis Type="Italic">Onopordum acanthium</Emphasis> seeds

The structure of a new compound was determined using PMR and ¹³C NMR spectroscopy (HHCOSY, HSBC, HMBC, ROESY) as 2-[3′-methoxy,4-O-β-D-galactopyranos-1-yl)benzyl]-3-(3″,4″-dimethoxybenzyl)-4hydroxybutyric acid, which was isolated for the first time from seeds of Scotch thistle Onopordum acanthium L. *For No. XII, see [1]. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 53–55, January–February, 2009.     

<Superscript>1</Superscript>H NMR spectra of water contained in solutions of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) and its modification products in CDCl<Subscript>3</Subscript>

¹H NMR spectra in CDCl₃ of poly(N-vinylpyrrolidone), epoxidized poly(N-vinyl-pyrrolidone), and products derived from the latter by modification with amino acids (glycine, β-alanine, γ-aminobutyric acid, and ε-aminocaproic acid) were examined. The ¹H NMR spectra of the modified polymers contain signals for water protons due to different centers of water sorption. These signals differ in chemical shift and integral intensity and indicate a changed spatial packing of the polymer as the result of its modification. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2377–2380, October, 2005.     

Ionic mobility in heptafluorozirconantes with a mixed cationic sublattice as probed by <Superscript>1</Superscript>H and <Superscript>19</Superscript>F NMR

The ionic mobility in heptafluorozirconates (NH₄)_2.7Rb_0.3ZrF₇ and (NH₄)_2.75Cs_0.25ZrF₇ has been studied by ¹H and ¹⁹F NMR in the temperature range 150–430 K. The types of ion motion were determined and their activation energies were estimated. A phase transition results in a modification in which diffusion in the ammonium sublattice and orientational disorder of ZrF₇³⁻ anions are observed. Owing to diffusion of ammonium ions, the compounds have relatively high ionic conductivity (σ ≥ 5 × 10⁻⁵ S/cm at 420 K).     

New coumarin glucoside from <Emphasis Type="Italic">Angelica dahurica</Emphasis>

A new linear furanocoumarin glycoside named dahurin B (1) was isolated from the fresh roots and rhizomes of Angelica dahurica. The structure of the new compound was elucidated by spectral techniques including ¹H NMR, ¹³C NMR, as well as HSQC, HMBC, and COSY. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 330–331, July–August, 2007.     

Determination of <Superscript>137</Superscript>Cs and <Superscript>85</Superscript>Sr transport parameters in fucoidic sand columns and groundwater system

The determination is based on the evaluation of experimentally obtained breakthrough curves using the erfc-function. The first method is founded on the assumption of a reversible linear sorption/desorption isotherm of radionuclides on solid phase with constant distribution and retardation coefficients, whereas the second one is based on the assumption of a reversible non-linear sorption/desorption isotherm described with the Freundlich equation, i.e., with non-constant distribution and retardation coefficients. Undisturbed cores of 5 cm in diameter and 10 cm long were embedded in the Eprosin-type cured epoxide resin column. In this study the so-called Cenomanian background groundwater was used as transport medium. The groundwater containing radionuclides was introduced at the bottom of the columns at about 4 mL h⁻¹ constant flow-rate. The results have shown that in the investigated fucoidic sands: (i) the sorption was in principle characterized by linear isotherms and the corresponding retardation coefficients of ¹³⁷Cs and ⁸⁵Sr, depending on the type of sample, were approximately 13 or 44 and 5 or 15, respectively; (ii) the desorption was characterized by non-linear isotherms, and the retardation coefficients of the same radionuclides ranged between 23–50 and 5–25, respectively. The values of the hydrodynamic dispersion coefficients of these radionuclides varied between 0.43–1.2 cm² h⁻¹.      

Determination of the molecular weight of polyoxypropylenepolyols by <Superscript>1</Superscript>H NMR spectroscopy

Commercial and laboratory samples of polyoxypropylenepolyols were studied by ¹H NMR spectroscopy at operating frequencies of 100 and 500 MHz. Various methods depending on the solvent used were suggested for determining the equivalent weight (molecular weight of the polyether per terminal hydroxy group). The ¹H NMR data are compared to the data obtained by chemical methods and gel permeation chromatography.     

Structure of binuclear platinum(III) acetamidate complexes in solutions as probed by <Superscript>195</Superscript>Pt, <Superscript>13</Superscript>C,and <Superscript>1</Superscript>H NMR spectroscopy

¹⁹⁵Pt, ¹H, and ¹³C NMR spectroscopy was used to study the structure of binuclear platinum(III) acetamidate complexes with 1,10-phenanthroline and 2,2′-bipyridine ligands [Pt₂(phen)₂(acam)₄](NO₃)₂ (1) and [Pt₂(bipy)₂(acam)₄](NO₃)₂ (2) in aqueous solutions. The ¹⁹⁵Pt NMR spectra of solutions of complexes 1 and 2 in D₂O exhibit two signals with satellites due to the ¹⁹⁵Pt–¹⁹⁵Pt spin-spin coupling (¹ J(Pt–Pt) ≈ 6345 Hz), whereas their ¹H and ¹³C NMR spectra contain four sets of signals for the protons and the carbon atoms of the heterocyclic and acetamidate ligands. The signals were assigned using the COSY, NOESY, and HSQC/ HMBC experiments and comparing the coordination shifts of the signals for the protons of heterocycles. These data allowed us to draw a conclusion that binuclear complexes 1 and 2 in solution have a head-to-head structure with nonequivalent platinum(III) atoms (coordination cores PtN₅ and PtN₃O₂), the axial-equatorial coordination of the bidentate heterocyclic molecules, and two bridging and two terminal acetamidate ligands.     

The structure of chain segments and <Superscript>1</Superscript>H NMR spectra of polychloroprene

The ¹H NMR spectra (working frequencies of 500 and 600 MHz) of polychloroprenes are studied. The spin systems of protons for monomer units of different configurations (1,2, 3,4, 1,4-cis-and 1,4- trans- units), as well as for dyad and triad combinations of 1,4 units, are classified. A high working frequency, the method of double resonance, and the calculation of chemical shifts by empirical increments make it possible to refine the assignment of ¹H NMR signals.