High-Resolution <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR of Glycyrrhizic Acid and Its Esters

Resonances for protons and C atoms in the ¹H and ¹³C NMR spectra of glycyrrhizic acid and its esters were assigned using high-resolution ¹H (600 MHz) and ¹³C (150 MHz) NMR methods. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 347–350, July–August, 2005.     

<Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR spectra of some drimanic sesquiterpenoids

One- and two-dimensional homo- and heteronuclear correlation proton, carbon, proton—proton, and proton—carbon NMR spectra of fifteen drimanic sesquiterpenoids: 11,12-dibromodrima-5,8-dien-7-one, drim-8-en-7-one, 11-hydroxydrim-8-en-7-one, 11,12-dihydroxydrim-8-en-7-one, 11-hydroxy-11,12-epoxydrim-8-en-7-one, 11-hydroxy-11,12-epoxydrim-8-en-7-one, 8,9-epoxydriman-7-one, 8,9-epoxydriman-7-ol, 11,12-diacetoxydrim-8-en-7-ol, drimane-7,8,11-triol, 7,8-isopropylidenedioxydriman-11-al, 9, 11-dihydroxydrim-7-en-6-one, drimane-7,8,9-triol, drimane-7,8,11-triol, and drim-8-ene-7,11,12-triol were studied. The proton and carbon chemical shifts were assigned.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2589–2594, December, 2004.     

2-Amino-4-aryl-1-arylideneaminoimidazoles and Acylation Products: A Multinuclear (<Superscript>1</Superscript>H, <Superscript>13</Superscript>C, <Superscript>15</Superscript>N) NMR Study

Summary. The structure of 2-amino-4-aryl-1-arylideneaminoimidazoles in DMSO-d₆ solution was investigated by means of NMR spectroscopic methods (¹H, ¹³C, ¹⁵N). From these data the (E)-configuration at the excocyclic C=N bond and a strong preference for the conformer with the imidazole H-5 and the N=CH proton being spatially close (s-trans regarding the N–N bond) can be concluded. Reaction of the title compounds with acetic anhydride leads to mono and diacylation at the 2-amino group, whereas treatment with pivalic anhydride exclusively affords the corresponding monoacyl product. The mono- and diacylation products exhibit similar configurational and conformational properties as the parent compounds.     

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     

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.     

Quantitative analysis of hydrogen peroxide by <Superscript>1</Superscript>H NMR spectroscopy

A technique utilizing ¹H NMR spectroscopy has been developed to measure the concentration of hydrogen peroxide from 10^–3 to 10 M. Hydrogen peroxide produces a peak at around 10–11 ppm, depending upon the interaction between solvent molecules and hydrogen peroxide molecules. The intensity of this peak can be monitored once every 30 s, enabling the measurement of changes in hydrogen peroxide concentration as a function of time. ¹H NMR has several advantages over other techniques: (1) applicability to a broad range of solvents, (2) ability to quantify hydrogen peroxide rapidly, and (3) ability to follow reactions forming and/or consuming hydrogen peroxide as a function of time. As an example, this analytical technique has been used to measure the concentration of hydrogen peroxide as a function of time in a study of hydrogen peroxide decomposition catalyzed by iron(III) tetrakispentafluorophenyl porphyrin.Electronic Supplementary Material Supplementary material is available for this article at     

Comprehensive 1H and 13C NMR assignment of 13 protobassic acid saponins

This study aimed to carry out complete ¹H and ¹³C NMR assignment of 13 protobassic acid saponins, including arganins A–C ( 1 – 3 ) and F ( 4 ), butyrosides B–D ( 5 – 7 ), tieghemelin ( 8 ), 3′-O-glucosyl-arganin C ( 9 ), Mi-saponins A–C ( 10 – 12 ), and mimusopsin ( 13 ), recorded in methanol-d₄. This was accomplished by the analysis of high-resolution one-dimensional (1D) NMR (¹H and ¹³C), two-dimensional (2D) NMR (¹H–¹H COSY, HSQC, and HMBC), and selectively excited 1D TOCSY spectra. Before this study, ¹H and ¹³C NMR data of arganins A–C ( 1 – 3 ) and F ( 4 ) were partially assigned. Our effort leads to their complete assignment, especially the glycon residue, and revises some reported data. Some revisions of the ¹H and ¹³C NMR data in the glycon part of butyroside C ( 6 ), tieghemelin ( 8 ), Mi-saponin A ( 10 ), and mimusopsin ( 13 ) were made. Those data of butyrosides B and D ( 5 & 7 ) and Mi-saponin B ( 11 ), which had not been recorded in methanol-d₄, are provided. In addition, the ¹H and ¹³C NMR data of Mi-saponin C ( 12 ) are reported for the first time. These data, being recorded in methanol-d₄, should be more friendly for use as a reference for identifying the related triterpenoid saponins.     

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.     

<Superscript>1</Superscript>H and <Superscript>7</Superscript>Li NMR in defect cobaltite Li<Subscript>0.6</Subscript>CoO<Subscript>2</Subscript>

Within a temperature range of 120–330 K, ⁷Li NMR spectra in Li_0.6CoO₂ are obtained. It is shown that as the temperature increases, both smooth and stepwise variation of ⁷Li NMR contact shifts occurs. The observed effects are explained by the occupation of the excited levels of cobalt ions. The stepwise change of the resonance line width depending on the temperature is revealed. It is driven by the features of the diffusive motion of lithium ions. The calculation of the ¹H NMR line shape provides the determination of the ratio of one-, two-, and three-spin proton clusters in Li_0.6CoO₂·xH₂O.     

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.     

<Superscript>1</Superscript>H NMR study on microstructure of a novel acrylamide/methacrylic acid template copolymer in aqueous solution

A novel acrylamide/methacrylic acid template copolymer was prepared using polyallylammonium chloride (PAAC) as a template. This copolymer contains acrylamide (PAM), phenoxy acrylate (POA), and acylic acid (PAA) blocks. The investigation by high resolution nuclear magnetic resonance (¹H NMR) shows that intramolecular hydrogen bonds between the PAM and PAA blocks lead to compact molecular arrangement at quite low pH values, and the motion of the phenoxy side chain of the POA blocks is somewhat restricted. With the increase in pH value of the solution, the carboxylic acid of the PAA block gradually dissociates, which weakens hydrogen bonds between the PAM and PAA blocks. The decrease in D _w, self-diffusion coefficient of water, indicates the growth in aggregate size of the template copolymer. The cross peaks between amide protons and backbone protons shown in 2D nuclear overhauser spectroscopy (NOESY) spectra imply the existence of the intermolecular hydrogen bonding interaction between PAM and PAA blocks. After the carboxylic acid of the PAA block is completely dissociated in alkaline solution, the electrostatic repulsion of the carboxylic ion makes the molecular chain of the copolymer exhibit more outstretched. Consequently, the phenoxy groups (the side chain of the POA block) have more space to move.     

1H and 13C NMR spectral data of new saponins from Cordia piauhiensis

Two new bidesmoside triterpenoid saponins were isolated from stems of Cordia piauhiensis. Their structures, characterized as 3-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl pomolic acid 28-O-beta-D-glucopyranosyl ester (1) and 3-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl oleanolic acid 28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (2), were unequivocally established after extensive NMR (1H, 13C, DEPT 135 degrees, COSY, HSQC, HMBC, TOCSY, and NOESY) studies.     

<Superscript>1</Superscript>H NMR Study of Heteroassociation of Ethidium Homodimer and Propidium Iodide in Water

1D and 2D ¹H NMR spectroscopy (500 MHz) was used to study heteroassociation of the bifunctional intercalator ethidium homodimer (EBH) with a phenanthridine dye propidium iodide (PI) in an aqueous salt (0.1 mol/l NaCl). A physical model of equilibrium between various associated forms of ethidium homodimer and propidium in solution is suggested, the most probable forms being 1:1 and 1:2 complexes of PI with the EBH monomer and dimer. The chemical shifts of the EBH molecule in heterocomplexes, as well as the equilibrium constants and the thermodynamic parameters (enthalpy, entropy) of heteroassociations, were calculated from the concentration and temperature dependences of the proton chemical shifts. It is concluded that the propidium molecule is built (intercalated) into the EBH monomer and dimer to form 1:1 and 1:2 complexes mainly stabilized by dispersive and hydrophobic interactions.Original Russian Text Copyright © 2004 by A. N.Veselkov, M. P. Evstigneev, S. A. Hernandez, O. V. Rogova, D. A. Veselkov, and D. B. Davies__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 837–843, September–October, 2004.     

Comparison of the electronic and steric structures of 1-vinyl-and 1-(prop-1-en-1-yl)pyrroles according to the <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR data

According to the ¹H and ¹³C NMR data, 1-isopropenylpyrroles are characterized by larger dihedral angles between the heteroring and exocyclic double bond planes, as compared to isostructural 1-vinylpyrroles, due to steric effect of the α-methyl group in the propenyl fragment. As a result, p-π conjugation with the propenyl group is weaker than with the vinyl group. The propenyl group in 1-isopropenylpyrrole having no other substituents in the heteroring is forced out from the heteroring plane, while the 1-vinylpyrrole molecule is planar. If substituents are present in positions 2 and 5 of the pyrrole ring, the propenyl group on the nitrogen atom becomes orthogonal with respect to the pyrrole ring plane, so that no p-π conjugation is possible. The steric structures of (E)-1-(prop-1-en-1-yl)pyrrole and (Z)-1-(prop-1-en-1-yl)pyrrole are different: the propenyl group in the former is turned relative to the heteroring plane, while the latter molecule is planar.     

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.     

1H and 13C NMR study of 2‐hydroxyglutaric acid and its lactone

Determination of the level and absolute configuration of 2‐hydroxyglutaric acid in a patient's urine is a method of diagnosing two metabolic diseases. Such a determination can be done with the aid of NMR spectroscopic methods. In this paper the careful interpretation of ¹H and ¹³C NMR spectra of this metabolite and its lactone measured under conditions used in biomedical assays is reported. The ¹H chemical shifts and spin–spin coupling constants were derived using the total lineshape analysis method. Copyright © 2002 John Wiley & Sons, Ltd.     

Proof of principle of a generalized fuzzy Hough transform approach to peak alignment of one-dimensional <Superscript>1</Superscript>H NMR data

In metabolic profiling, multivariate data analysis techniques are used to interpret one-dimensional (1D) ¹H NMR data. Multivariate data analysis techniques require that peaks are characterised by the same variables in every spectrum. This location constraint is essential for correct comparison of the intensities of several NMR spectra. However, variations in physicochemical factors can cause the locations of the peaks to shift. The location prerequisite may thus not be met, and so, to solve this problem, alignment methods have been developed. However, current state-of-the-art algorithms for data alignment cannot resolve the inherent problems encountered when analysing NMR data of biological origin, because they are unable to align peaks when the spatial order of the peaks changes—a commonly occurring phenomenon. In this paper a new algorithm is proposed, based on the Hough transform operating on an image representation of the NMR dataset that is capable of correctly aligning peaks when existing methods fail. The proposed algorithm was compared with current state-of-the-art algorithms operating on a selected plasma dataset to demonstrate its potential. A urine dataset was also processed using the algorithm as a further demonstration. The method is capable of successfully aligning the plasma data but further development is needed to address more challenging applications, for example urine data. Figure Traces of NMR peaks visualizing the Generalized Fuzzy Hough Transform (GFHT) method for elucidating peak correspondence between samples. The spectra are sorted according to one shift sensitive peak and reveals that other peaks exhibit a similar shift pattern. This pattern(s) can now be searched for using the GFHT. The red and black spectra in the figure are the most shifting spectra (top and bottom), by following the GFHT traces peak correspondence is easily established although peaks change spatial location Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Superscript>13</Superscript>C NMR analysis of cellulose samples from different preparation methods

Alpha-cellulose is a part of the wooden material that preserves isotopic composition during tree-growth, and therefore provides important indirect data for paleoclimatological studies. For this reason, it is exceptionally important to extract the alpha-cellulose component from plants, e.g. from tree rings of wood. Since the cell wall of plant cells consists of multicomponent polysaccharides, the extraction of cellulose from wood is not an obvious task. In this paper, we describe, evaluate and compare nine methods, based on the literature and experimental observations, for obtaining cellulose from tree rings of wood. We show that the distortionless enhancement by polarization transfer (DEPT-135) variant of liquid-state ¹³C NMR spectroscopy is a powerful analytical method for monitoring the preparation process. Trifluoroacetic acid was applied as solvent for the NMR analysis. We proved that all the preparation methods give pure cellulose samples without hemicellulose and lignin content, and we propose methods resulting in non-fragmented cellulose. ¹³C and ¹⁸O isotope ratio measurements have shown that all the applied extraction methods result in similar isotope ratios, thus they are suitable for paleoclimatological studies.