Assignment Of 13C NMR Signals Research Articles

Assignment of 13C NMR spectrum for blepharismin C based on biosynthetic studies

Blepharismins, toxic pigments of the ciliate Blepharisma japonicum, are polycyclic ring-condensed compounds. Assignment of 13C NMR signals for blepharismin C, a major constituent of blepharismins, was achieved by analyses of the HMQC, HMBC, and INADEQUATE spectra of 13C-enriched samples obtained by feeding experiments using sodium [1- 13C], [2- 13C], and [1,2- 13C 2]acetates.

Substituent effects on 15N and 13C NMR chemical shifts of 3‐phenylisoxazoles: a theoretical and spectroscopic study

The synthesis and assignment of 15N and 13C NMR signals of the isoxazole ring in a series of para-substituted 3-phenyl derivatives are reported. DFT calculations of 15N and 13C chemical shifts are presented and compared to observed values. Substituent effects are interpreted in terms of the Hammett correlation and calculated bond orders.

Propene‐Norbornene Copolymers: Synthesis and Microstructure

AbstractSeries of propene(norbornene (P–N) copolymers were synthesized in the presence of two C2 symmetric zirconocenes, rac‐Et(Indenyl)2ZrCl2 (1) and rac‐Me2Si(Indenyl)2ZrCl2 (2), and of the Cs symmetric zirconocene Me2C(Cp)(Fluorenyl)ZrCl2 (3) with MAO as cocatalyst. P–N copolymers were characterized by 13C NMR spectroscopy, SEC, and DSC. A first assignment of the main 13C NMR signals of P–N copolymers obtained with 1 and 2 containing isolated N units was obtained on the basis of DEPT experiments and by comparison with isotactic polypropene (i‐PP) and E–N copolymer spectra. Ab initio theoretical 13C NMR chemical shifts, combined with R.I.S. statistics of the P–N chain, gave important detailed indications for the assignment of the complex 13C spectra of these copolymers. Such assignments were used to estimate the N copolymer content. The comparison of N content values obtained from the areas of different regions of the spectra reveals that 1,3 propene misinsertions are formed in greater amount as the [N]/[P] ratio of the feed increases. This may be due to the steric hindrance of the Mt–tertiary carbon bond when N is the last inserted unit, which makes difficult the next propene insertion and causes the low polymerization activities, molecular masses and Tg. The spectra of P–N copolymers obtained with 3 revealed to be even more complex. A limited assignment of the spectrum has been achieved. This allowed us to evaluate the N content in the copolymers and to evidence the low tendency of the Cs symmetric 3 to give 1,3 propene misinsertions in P–N copolymers. This is in agreement with the results observed with this catalyst in propene homopolymerization.

Cytotoxic coumarins from Mammea harmandii.

Two new naturally occurring coumarins, isomesuol (1) and mammearin A (2), together with nine known Mammea coumarins 3-11 were isolated from the EtOAc extract of the leaves and twigs of Mammea harmandii. Coumarins 1, 3 and 4 showed cytotoxicity against a panel of mammalian cancer cell lines. Their structures were determined by spectroscopic methods. The assignments of 13C-NMR signals of isomesuol (1), which was isolated for the first time as a natural product, have been revised.

New Stereochemical Assignments of 13C NMR Signals for Predominantly Syndiotactic Polystyrene

ADVERTISEMENT RETURN TO ISSUEPREVNoteNew Stereochemical Assignments of 13C NMR Signals for Predominantly Syndiotactic PolystyreneFlorian Feil and Sjoerd HarderView Author Information Universität Konstanz, Postfach 5560-M738, 78457 Konstanz, Germany Cite this: Macromolecules 2003, 36, 9, 3446–3448Publication Date (Web):April 10, 2003Publication History Received26 February 2003Revised19 March 2003Published online10 April 2003Published inissue 1 May 2003https://doi.org/10.1021/ma0342473Copyright © 2003 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1440Altmetric-Citations63LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (51 KB) Get e-AlertsSUBJECTS:Aromatic compounds,Hydrocarbons,Mathematical methods,Polymers,Styrenes Get e-Alerts

Propene−Norbornene Copolymers: Synthesis and Analysis of Polymer Structure by 13C NMR Spectroscopy and ab Initio Chemical Shift Computations

A series of propene−norbornene (P−N) copolymers were synthesized in the presence of rac-Et(indeny)2ZrCl2/MAO in toluene at 30 °C. P−N copolymers were characterized by 13C NMR spectroscopy, SEC, and DSC. Results were compared with those of a series of P−N copolymers synthesized in the presence of rac-Me2Si(Indenyl)2ZrCl2/MAO under the same experimental conditions. Polymerization activity appears to be quite low in comparison with ethene−norbornene (E−N) copolymerization. A first assignment of the main 13C NMR signals of P−N copolymers containing isolated N units was obtained on the basis of distortionless enhancement by polarization transfer (DEPT) 13C spectra and by comparison with isotactic polypropene (i-PP) and E−N copolymer spectra. Ab initio theoretical 13C NMR chemical shifts, computed for the most relevant conformers of a rather simple model compound and averaged using the RIS conformer populations estimated for an isotactic chain (P4−N)x, gave important detailed indications for the assignment of the complex 13C spectra of P−N copolymers with N content up to 35 mol %. Such assignments were used to estimate the N copolymer content. The discrepancy between the values obtained from the areas of methyl signals and from the areas of the signals assigned to norbornene carbons was found to be partially due to the presence of 1,3-propene misinsertions, which are formed in significant amount when increasing the [N]/[P] ratio of the feed. Our results confirm that, despite the relatively lower polymerization activity, at low norbornene/olefin ratio it is possible to obtain P−N copolymers that are relatively richer in norbornene than the E−N copolymers prepared in similar conditions. However, at higher norbornene/olefin feed ratios the great amount of 1,3-propene misinsertions clearly reveals that the steric hindrance of the Mt−tertiary carbon bond when N is the last inserted unit makes difficult the next propene insertion, causing low polymerization activities, molecular masses, and Tg.

Ethene/Norbornene Copolymerization using the Catalyst System Pri[(3‐Pri‐Cp)Flu]ZrCl2: Determination of the Copolymerization Parameters and Mechanistic Considerations

AbstractThe 13C NMR spectra of ethene/norbornene copolymers in which there are no norbornene microblocks are much simpler than those of copolymers in which norbornene microblocks are present, making it possible to completely assign all the 13C resonances to the corresponding pentads in the copolymer chain. However, there is disagreement in the literature over several assignments of the ethene 13C NMR signals. In this paper these discrepancies are summarized and discussed. This contribution also reports ethene/norbornene copolymerizations carried out at various temperatures using the homogeneous catalyst system Pri[(3‐Pri‐Cp)Flu]ZrCl2. The 13C NMR spectra of the copolymers were analyzed in the light of the discussion above and the triad distributions were used to determine the copolymerization parameters by Markov first‐ and second‐order statistical models. On the basis of these results, the mechanism generating such an alternating microstructure in these copolymers is discussed and compared with the mechanism previously proposed in the literature. The 13C NMR spectrum with signal assignments of an ethene/norbornene copolymer without norbornene microblocks.magnified imageThe 13C NMR spectrum with signal assignments of an ethene/norbornene copolymer without norbornene microblocks.

Complete 1H and 13C NMR assignment of mono-sulfated galactosylceramides with four types of ceramides from human kidney

The full assignment of 1H and 13C NMR signals of galactosylceramide 3-sulfate (galactosyl sulfatide) and 1H signals of galactosylceramide 6-sulfate was achieved by using 1H– 1H DQF-COSY and 1H– 13C heteronuclear COSY. Analyses were performed on a mixture of galactosyl sulfatides with four representative ceramide types consisting of a combination of non-hydroxy or 2-hydroxy fatty acids and sphingenine or 4 D-hydroxysphinganine (trihydroxysphinganine) as the long-chain bases. The 1H and 13C NMR parameters of galactosyl sulfatide with 4-hydroxysphinganine as well as 13C signals of complex lipids with 4-hydroxysphinganine were elucidated for the first time. Not only sulfation of the galactosyl residue, but also modification of the aglycon, including hydroxylation of fatty acids and hydration of the double bond in sphingoid bases, altered the chemical shifts substantially. In addition, the unique long-range coupling constants, 4 J H,H and 5 J H,H, in the galactosyl residue of galactosyl sulfatide could be determined.

Assignment of 1H, 13C and 15N NMR signals in the toluene 4-monooxygenase effector protein.

Toluene-4-monooxygenase (T4MO) catalyzes the NADHand O2-dependent hydroxylation of toluene to form p-cresol (Fox, 1997). T4MO belongs to an evolutionarily related family including methane monooxygenase, other aromatic monooxygenases, and alkene epoxidases. In all of these complexes, a small protein is obligately required to effect catalysis. It is reasonable to assume that the role of a diiron effector protein is to produce essential conformational changes by formation of specific protein–protein complexes. Recently, NMR structures for the effector proteins from the methane monooxygenase (MMOB) and phenol hydroxylase (P2) complexes have been reported. While MMOB has a compact fold with βαββ and βααββ domains (Chang et al., 1999; Walters et al., 1999), multiple configurations of P2 were detected in solution. This heterogeneity was postulated to reflect conformational flexibility possibly associated with catalytic function (Qian et al., 1997). Here we report chemical shift assignments for T4MOD. The solution structure of T4MOD arising from further analysis of these NMR assignments will provide a useful comparison to the NMR structures of other members of the effector protein family. Furthermore, this work provides the basis for more detailed study of the protein surface and specific residue contacts required for catalytic protein–protein interactions in the T4MO complex.

Assignment of the 13C NMR signals of some 8‐azaadenine, 2,6‐diaminopurine and 2,6‐diamino‐8‐azapurine carbonucleosides

Assignment of the 13C NMR signals of some 8‐azaadenine, 2,6‐diaminopurine and 2,6‐diamino‐8‐azapurine carbonucleosides

Isolation, characterisation, and NMR study of xyloglucan from enzymatically depectinised and non-depectinised apple pomace

Xyloglucan extracted with 4 M KOH from enzymically-depectinated and non-depectinated apple pomace was shown to be fucogalactoxyloglucan. The xyloglucan from the enzymically-depectinated apple pomace was found to be of lower molecular weight than that from the non-depectinated pomace. Xyloglucan from the non-depectinated pomace had an intrinsic viscosity of 244 ml/g. The oligosaccharides XXFG and XLFG were isolated from the 1,4- β- d-glucanase hydrolysate of the xyloglucan and their 13C NMR spectra were obtained for the first time. Assignment of the anomeric 13C NMR signals of these oligosaccharides permitted the unambiguous assignment of the anomeric region of the 13C NMR spectra of the fucogalactoxyloglucan. In the spectra of the oligosaccharides, splitting was observed in the C-6 signal from the fucosyl residues, indicating their proximity to the reducing glucosyl residues and thus yielding information about the conformation of xyloglucan in solution. Integration of the anomeric signals of 1H NMR spectra permits the rapid and non-destructive screening of the composition of xyloglucans from different plants.

Methacrylic polymers containing permanent dipole azobenzene chromophores spaced from the main chain.13C NMR spectra and photochromic properties

Dynamics in solution and photochromic properties of radical copolymers of 4-(4-oxy-4′-cyanoazobenzene)but-1-yl methacrylate, 6-(4-oxy-4′-cyanoazobenzene)hex-1-yl methacrylate, and 8-(4-oxy-4′-cyanoazobenzene)oct-1-yl methacrylate with (–)-menthyl methacrylate were investigated. 13C NMR and 2D HETCOR spectroscopy allowed assignment of 13C NMR signals and evaluation of main chain tacticity. 13C T1 relaxation times evidenced a rather limited mobility of the azobenzene chromophores when inserted in polymer macromolecules. Mobility increased with increasing the length of the polymethylene spacer that acted as a flexible joint between the aromatic chromophore and polymer backbone. Both the trans to cis photoisomerization and the cis to trans thermal isomerization processes showed a small dependence on monomer structure and chemical composition of the investigated photochromic polymers. These data seem to suggest an appreciable contribution of the in-plane inversion mechanism to both isomerization processes of the azobenzene chromophores. The absence of appreciable dichroic bands in the copolymer CD spectra and the negative results obtained in preliminary second harmonic generation measurements are discussed in terms of the polymer structural features.

13C and 1H NMR Spectra of Synthetic (25R)-5α-Spirostanes

The assignment of 13C and 1H NMR signals of synthetic (25R)-5α-spirostanes is presented; the main effects on chemical shifts due to substitution at C-23 are briefly discussed.

13C and 1H NMR Spectra of Synthetic (25R)-5α-Spirostanes

The assignment of 13C and 1H NMR signals of synthetic (25 R)-5α-spirostanes is presented; the main effects on chemical shifts due to substitution at C-23 are briefly discussed.

Identification and determination of the glyceride and tris-(2-hydroxyethyl)isocyanurate structures in the average macromolecule of a polyester with carbon-13-NMR spectroscopy: Analysis of the polyester average structure

The 13C-NMR approach to quantitative analysis of a polyester resin synthesized from dimethylterephthalate, ethylene glycol, tris-(2-hydroxyethyl)isocyanurate (THEIC), and glycerol is presented. Various glyceride and isocyanurate structures formed during the esterification have been identified and analyzed, at first in simple model systems and then in the structure of the resin. The contents of particular structural units were determined as well as a hypothetical average macromolecule of the resin defined. The assignments of 13C-NMR signals were made and correlated with the 1H shifts using a 2D-HETCOR experiment. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 675–687, 1998

Comprehensive Assignments of 1H and 13C NMR Signals for the Vinylidene Chloride-Butyl Acrylate Copolymers Using 2D NMR Spectroscopy

Vinylidene chloride butyl acrylate copolymers were prepared by photopolymerization at room temperature. The molecular weight of these copolymers have been determined using Gel Permeation Chromatography and the copolymer composition estimated using Schoneger technique. 2D NMR techniques such as 1 H 13 C heteronuclear single quantum correlation (HSQC) was used for the compositional and configurational assignments of 1 H and 13 C{ 1 H} NM R spectra for various resonating signals. 2D 1 H homonuclear double quantum filter-correlated spectroscopy (DQF-COSY) is used to get better insight for the copolymer structure.

Assignment of 1H and 13C NMR signals of eight apocampholenic derivatives

Assignment of 1H and 13C NMR signals of eight apocampholenic derivatives

Investigation of the Branching Characteristic of Glycogen by Means of Two-Dimensional1H and 13C NMR Spectroscopy

The assignment of 13C and 1H NMR signals of three highly short-chain branched α-D-glucan samples from animal tissue (glycogen) of different provenience, dissolved in dimethylsulfoxide, was achieved using two-dimensional H-H and C-H correlated spectroscopy. The results were comparable to those recently obtained for plant derived short-chain branched α-D-glucans (amylopectin) and non-branched/long-chain branched α-D-glucans (amylose). From these assignments and the integration of pertinent proton signals, the branching degree of the glycogen samples was derived to amount 13.5%. These samples were also analyzed with respect to their degree of polymerization distribution by means of the SEC-DRI/LALLS method. These data and the line broadening of the 1H and 13C NMR spectra of the glycogen samples compared to those of amylopectin and amylose supported the assumption of a broad (homogeneous) distribution of glucose residues in glycogen.

Synthesis and characterization by 1H and 13C nuclear magnetic resonance spectroscopy of 17α-cyano, 17α-aminomethyl, and 17α-alkylamidomethyl derivatives of 5α-dihydrotestosterone and testosterone

17α-Aminomethyl, 17α-acetamidomethyl, and 17α-hemiglutaramidomethyl derivatives of dihydrotestosterone and testosterone have been prepared by hydrocyanation of 3,3′-(ethylenedioxy)-5α-androstan-17-one and 3,3′-ethylenedioxyandrost-5-en-17-one, reduction of the corresponding acetylated 17α-cyanohydrins with lithium aluminium hydride, and acylation of the resulting 17α-aminomethyl derivatives with either acetic anhydride or the mono acid chloride of glutaric acid mono methyl ester. Saponification of the 17α-hemiglutaramidomethyl methyl esters gave the corresponding hemiglutaramido derivatives, while acid hydrolysis of the 3-ethylene ketal group of 17α-acetamidomethyl and 17α-hemiglutaramidomethyl derivatives regenerated the 3-oxo and 3-oxo-4-ene functions. The 17α-configuration of 17-substituted steroids was determined by 1H and 13C NMR and confirmed by comparing with NMR data for 17α- and 17β-cyano-17-hydroxyandrost-4-en-3-one, 17β-cyano-3.3′-(ethylenedioxy)androst-5-en-17-ol, 17α-alkynyl, and 17α-hexanoic derivatives of dihydrotestosterone and testosterone, of known 17-configurations. Several ambiguous assignments of 13C NMR signals of 17α-substituted steroids and unsubstituted 17β-hydroxy or 17-oxo precursors have been resolved using steroid analogs deuterated at positions C5–7, or C16 for androstane derivatives, and at positions C6–7, or C7 for androstene derivatives. 17α-Aminomethyl and 17α-alkylamidomethyl derivatives of dihydrotestosterone and testosterone are useful intermediates for the access to potential ligands of androgen-binding proteins necessary for affinity chromatography purification or affinity-labeling experiments.

Chiral methacrylic polymers containing permanent dipole azobenzene chromophores. 13C NMR spectra and photochromic properties

AbstractDynamics in solution and photochromic properties of radical copolymers of (S)‐4‐[N‐(2‐methacryloyloxyethyl)‐N‐(2‐methylbutyl)]amino‐4′‐cyanoazobenzene with butyl methacrylate were investigated. 13C NMR and 2D heteronuclear correlated (HETCOR) spectroscopy allowed assignment of 13C NMR signals and evaluation of main chain tacticity. 13C relaxation times T1 evidenced a rather limited mobility of azobenzene chromophores. Mobility increases with increasing content of butyl methacrylate units, that acts as an internal plasticizer. The limited mobility of the spacer between azobenzene and methacrylate groups is attributed to an interaction between carbonyl oxygen and aminic nitrogen stabilized by the internal charge transfer from the amino to the cyano group. Trans to cis photoisomerization rates turned out to be independent of molecular weight and chemical composition of the investigated photochromic polymers, whereas cis to trans thermal isomerization rates increase with the content of aromatic units. These data suggest that photo‐ and thermal isomerization processes imply an in‐plane inversion and an out‐of‐plane rotation of one of the phenyl rings of the azobenzene chromophores, respectively. Preliminary second harmonic generation measurements indicate that the investigated polymers are endowed with significant non‐linear optical properties.