Nuclear Magnetic Resonance Shift Reagents Research Articles

Enantiomeric NMR signal separation mechanism and prediction of separation behavior for a praseodymium (III) complex with (S,S)-ethylenediamine-N,N-disuccinate.

Because choice of chiral nuclear magnetic resonance (NMR) shift reagents and concentration conditions have been made empirically by trials and errors for chiral NMR analyses, the prediction of NMR signal separation behavior is an urgent issue. In this study, the separation of enantiomeric and enantiotopic 1 H and 13 C NMR signals for α-amino acids and tartaric acid was performed by using the praseodymium(III) complex with (S,S)-ethylenediamine-N,N'-disuccinate ((S,S)-EDDS). All the present D-amino acids exhibited larger downfield shift of their α-protons and α-carbons compared with those for the corresponding L-amino acids in common. This regularity is applicable to absolute configurational assignment and determination of optical purity of amino acids. The chemical shifts of β-protons of d- and l-alanine fully bound with the Pr(III) ((S,S)-EDDS) complex (δb s) and the adduct formation constants of both enantiomers (Ks) were obtained by dependences of the observed downfield shifts of the β-protons on the total concentrations of the respective enantiomers in the presence of a constant concentration of the Pr(III) complex. The difference in the K values was found to be predominant determining factor for the enantiomeric signal separation. The chemical shifts of both enantiomers (δs) and the enantiomeric signal separations (Δδs) under given conditions could be calculated from the δb and K values. Furthermore, prediction of the signal separation behavior was enabled by using the calculated δ values and the signal broadening obtained by dependences of the half-height widths of the observed signals on the bound/free substrate concentration ratios for the respective enantiomers.

An antiaromatic-walled nanospace.

Over the past few decades, several molecular cages, hosts and nanoporous materials enclosing nanometre-sized cavities have been reported1-5, including coordination-driven nanocages6. Such nanocages have found widespread use in molecular recognition, separation, stabilization and the promotion of unusual chemical reactions, among other applications3-10. Most of the reported nanospaces within molecular hosts are confined by aromatic walls, the properties of which help to determine the host-guest behaviour. However, cages with nanospaces surrounded by antiaromatic walls have not yet been developed, owing to the instability of antiaromatic compounds; as such, the effect of antiaromatic walls on the properties of nanospaces remains unknown. Here we demonstrate the construction of an antiaromatic-walled nanospace within a self-assembled cage composed of four metal ions with six identical antiaromatic walls. Calculations indicate that the magnetic effects of the antiaromatic moieties surrounding this nanospace reinforce each other. This prediction is confirmed by 1H nuclear magnetic resonance (NMR) signals of bound guest molecules, which are observed at chemical shift values of up to 24 parts per million(ppm), owing to the combined antiaromatic deshielding effect of the surrounding rings. This value, shifted 15 ppm from that of the free guest, is the largest 1H NMR chemical shift displacement resulting from an antiaromatic environment observed so far. This cage may thus be considered as a type of NMR shift reagent, moving guest signals well beyond the usual NMR frequency range and opening the way to further probing the effects of an antiaromatic environment on a nanospace.

Simple Resolution of Enantiomeric NMR Signals of α-Amino Acids by Using Samarium(III) Nitrate With L-Tartarate.

Readily available L-tartaric acid, which is a bidentate ligand with two chiral centers forming a seven-membered chelate ring, was applied to the chiral ligand for the chiral nuclear magnetic resonance (NMR) shift reagent of samarium(III) formed in situ. This simple method does not cause serious signal broadening in the high magnetic field. Enantiomeric (13)C and (1)H NMR signals and enantiotopic (1)H NMR signals of α-amino acids were successfully resolved at pH 8.0 and the 1:3 molar ratio of Sm(NO3)3:L-tartaric acid. It is elucidated that the enantiomeric signal resolution is attributed to the anisotropic magnetic environment for the enantiomers induced by the chiral L-tartarato samarium(III) complex rather than differences in stability of the diastereomeric substrate adducts. The present (13)C NMR signal resolution was also effective for the practical simultaneous analysis of plural kinds of DL-amino acids.

ChemInform Abstract: Lanthanide Enolates as Nuclear Magnetic Resonance Shift Reagents

AbstractReview: 207 refs.

Optical resolution of (±)‐Threo‐9,10,16‐trihydroxy hexadecanoic acid using (−)brucine

AbstractThe optical resolution of (±)threo‐9,10,16‐trihydroxy hexadecanoic acid was achieved by fractional crystallization using (−)brucine. Formation of an estolide during decomposition of the (−)brucine complex was observed to interfere with the separation of the optically pure material. This was corrected by converting the estolide to (+)‐threo‐9,10,16‐trihydroxy hexadecanoic acid via alcoholic alkaline hydrolysis followed by neutralization. Enantiomeric purity was determined by chiral lanthanide nuclear magnetic resonance shift reagent.

Chiral nuclear magnetic resonance shift reagents: Lanthanide mixtures with 1-(1-naphthyl) ethylurea derivatives of amino acids

Esters of 1-(1-naphthly)ethylurea derivatives of L-valine, L-leucine, L-tert-leucine, and L-proline are examined as organic-soluble chiral nuclear magnetic resonance (NMR) resolving agents. The reagents are useful for resolving the spectra of chiral sulfoxides, amines, alcohols, and carboxylic acids. Enantiomeric resolution is caused by a combination of diastereomeric effects and the different association constants of the substrates with the resolving agents. Organic-soluble lanthanide species are added to resolving agent-substrate mixtures and often enhance the enantiomeric resolution. The enhancement occurs because the substrate that exhibits weaker binding with the resolving agent is more available to bond to the lanthanide. Broadening in the spectra with lanthanides is reduced at 50°C. Enantiomeric resolution is still observed at elevated temperatures. Chirality 9:1–9, 1997. © 1997 Wiley-Liss, Inc.

Chiral nuclear magnetic resonance shift reagents: Lanthanide mixtures with 1‐(1‐naphthyl) ethylurea derivatives of amino acids

Esters of 1-(1-naphthly)ethylurea derivatives of L-valine, L-leucine, L-tert-leucine, and L-proline are examined as organic-soluble chiral nuclear magnetic resonance (NMR) resolving agents. The reagents are useful for resolving the spectra of chiral sulfoxides, amines, alcohols, and carboxylic acids. Enantiomeric resolution is caused by a combination of diastereomeric effects and the different association constants of the substrates with the resolving agents. Organic-soluble lanthanide species are added to resolving agent-substrate mixtures and often enhance the enantiomeric resolution. The enhancement occurs because the substrate that exhibits weaker binding with the resolving agent is more available to bond to the lanthanide. Broadening in the spectra with lanthanides is reduced at 50°C. Enantiomeric resolution is still observed at elevated temperatures. Chirality 9:1–9, 1997. © 1997 Wiley-Liss, Inc.

Asymmetric reduction with 5-deazaflavin. III. Reduction of ethyl benzoylformate in the presence of chiral ligand.

A nonenzymatic asymmetric reduction of ethyl benzoylformate with an achiral 1, 5-dihydro-5-deazaflavin derivative in chiral media was investigated as a model system for reruced nicotinamide adenine dinucleotide (phosphate)-dependent dihydrogenase. The chiral media include chiral nuclear magnetic resonance shift reagent, chiral Lewis acid, and a combination of metal ion an chiral ligand (additive). Of these reductions, a substantial asymmetric induction was observed in the presence of tris-[3-(heptafluoropropylhydroxymethylene)(+)-camphorato]europium to give ethyl mandelate possessing prediominantly S-configuration, in a optical yield of 24 to 36%. These values are among the highest so far reported in nonenzymatic reduction of ethyl benzoylformate with a 5-deazaflavin model. The discrimination of the prochiral face of the carbonyl compound was effectvie even when a catalytic amount of the chiral shift reagent was employed.

Organic-soluble lanthanide nuclear magnetic resonance shift reagents for sulfonium and isothiouronium salts

Lanthanide complexes of the formula (Ln(fod)/sub 4/)/sup -/ (FOD, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione) are effective organic-soluble nuclear magnetic resonance shift reagents for sulfonium and isothiouronium salts. The shift reagent is formed in solution from Ln(fod)/sub 3/ and Ag(fod) or K(fod). The selection of Ag(fod) or K(fod) in forming the shift reagent is dependent on the anion of the organic salt. Ag(fod) is more effective with halide salts, whereas K(fod) is preferred with tetrafluoroborate salts. Resolution of diastereotopic hydrogen atoms was observed in the shifted spectra of certain substrates. Enantiomeric resolution was obtained in the spectrum of sec-butylisothiouronium chloride with a chiral shift reagent. The reagents can be employed in solvents such as chloroform and benzene.

Lack of transbilayer coupling in phase transitions of phosphatidylcholine vesicles.

Praseodymium and ytterbium chlorides were used as nuclear magnetic resonance shift reagents to resolve the inner and outer choline methyl resonances of single-walled dimyristoylphosphatidylcholine bilayer vesicles. The gel to liquid-crystalline phase transition of these vesicles was monitored by observing the proton and carbon-13 nuclear magnetic resonance line widths of the choline methyl group nuclei. In the absence of ions the transition occurred at 21.5 degrees C in both halves of the bilayer. With Pr3+ or Yb3+ added to the outside of the vesicles, the phase transition temperature of the outer half of the bilayer was raised several degrees, while the transition temperature of the inner half was unchanged. In vesicles containing 20 mol % cholesterol the phase transition of the outer monolayer was considerably broadened, while the inner half still melted sharply at 21.6 degrees C. By use of dipalmitoylphosphatidylcholine vesicles with UO2(2)+ added to the outside, phase transitions at 41.5 and 44 degrees C were detected by electron spin resonance with the spin-label 2,2,6,6-tetramethylpiperidinyl-l-oxy. These results imply that the two halves of the bilayer in phospholipid vesicles are so weakly coupled that they can undergo the gel to liquid-crystalline phase transition independently.

Application of lanthanide nuclear magnetic resonance shift reagents in conformational analysis of flexible chain molecules. A pseudocontact-shift and relaxation investigation

Application of lanthanide nuclear magnetic resonance shift reagents in conformational analysis of flexible chain molecules. A pseudocontact-shift and relaxation investigation

Atropisomerism of biflavones. Confirmation of the enantiomeric purity of WB1 by using a chiral nuclear magnetic resonance shift reagent.

The optical purity of WB1, (-)-4', 4'", 7, 7"-tetra-O-methylcupressuflavone (1) was estimated from proton nuclear magnetic resonance (1H-NMR) studies of its dimethyl ether (2) by using a chiral NMR-shift reagent and found to be satisfactory.

Application of Chiral Lanthanide Nuclear Magnetic Resonance Shift Reagents to Pharmaceutical Analysis. II. Determination of Dextroand Levoamphetamine Mixtures

Optically pure d- and l-amphetamine sulfate, as well as various mixtures of the 2 enantiomers, were analyzed using a europium chiral nuclear magnetic resonance shift reagent. The enantiomeric shift difference (delta delta delta) exhibited by the doublet associated with the alpha-methyl protons was large enough to differentiate between the levo- and dextro-isomers. The alpha-methyl protons were decoupled and the enantiomeric composition was determined by using the peak heights of the resulting singlets. As little as 5% of the levo-isomer in the presence of the dextro-isomer can be determined using this method. The method is applicable to the analysis of bulk drug and pharmaceutical preparations.

Specific deuteration of .delta.-aminolevulinic acid by pyridoxal-catalyzed exchange and analysis of products using an aqueous lanthanide nuclear magnetic resonance shift reagent

Specific deuteration of .delta.-aminolevulinic acid by pyridoxal-catalyzed exchange and analysis of products using an aqueous lanthanide nuclear magnetic resonance shift reagent

Structures of europium complexes and implications in lanthanide nuclear magnetic resonance shift reagent chemistry

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructures of europium complexes and implications in lanthanide nuclear magnetic resonance shift reagent chemistryJ. A. Cunningham and R. E. SieversCite this: Inorg. Chem. 1980, 19, 3, 595–604Publication Date (Print):March 1, 1980Publication History Published online1 May 2002Published inissue 1 March 1980https://doi.org/10.1021/ic50205a005RIGHTS & PERMISSIONSArticle Views174Altmetric-Citations24LEARN 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 PDF (1 MB) Get e-Alerts Get e-Alerts

ChemInform Abstract: COMPARISON OF MOLECULAR GEOMETRIES DETERMINED BY PARAMAGNETIC NUCLEAR MAGNETIC RESONANCE RELAXATION AND SHIFT REAGENTS IN SOLUTION

Chemischer InformationsdienstVolume 9, Issue 18 Physical Organic Chemistry ChemInform Abstract: COMPARISON OF MOLECULAR GEOMETRIES DETERMINED BY PARAMAGNETIC NUCLEAR MAGNETIC RESONANCE RELAXATION AND SHIFT REAGENTS IN SOLUTION D. H. WELTI, D. H. WELTISearch for more papers by this authorM. LINDER, M. LINDERSearch for more papers by this authorR. R. ERNST, R. R. ERNSTSearch for more papers by this author D. H. WELTI, D. H. WELTISearch for more papers by this authorM. LINDER, M. LINDERSearch for more papers by this authorR. R. ERNST, R. R. ERNSTSearch for more papers by this author First published: May 2, 1978 https://doi.org/10.1002/chin.197818045AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume9, Issue18May 2, 1978 RelatedInformation

Comparison of molecular geometries determined by paramagnetic nuclear magnetic resonance relaxation and shift reagents in solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComparison of molecular geometries determined by paramagnetic nuclear magnetic resonance relaxation and shift reagents in solutionD. H. Welti, M. Linder, and R. R. ErnstCite this: J. Am. Chem. Soc. 1978, 100, 2, 403–410Publication Date (Print):January 1, 1978Publication History Published online1 May 2002Published inissue 1 January 1978https://doi.org/10.1021/ja00470a009RIGHTS & PERMISSIONSArticle Views61Altmetric-Citations16LEARN 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 PDF (874 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: LANTHANIDE PORPHYRIN COMPLEXES. EVALUATION OF NUCLEAR MAGNETIC RESONANCE DIPOLAR PROBE AND SHIFT REAGENT CAPABILITIES

Chemischer InformationsdienstVolume 8, Issue 6 Physical Organic Chemistry ChemInform Abstract: LANTHANIDE PORPHYRIN COMPLEXES. EVALUATION OF NUCLEAR MAGNETIC RESONANCE DIPOLAR PROBE AND SHIFT REAGENT CAPABILITIES W. DEW. JUN. HORROCKS, W. DEW. JUN. HORROCKSSearch for more papers by this authorC.-P. WONG, C.-P. WONGSearch for more papers by this author W. DEW. JUN. HORROCKS, W. DEW. JUN. HORROCKSSearch for more papers by this authorC.-P. WONG, C.-P. WONGSearch for more papers by this author First published: February 8, 1977 https://doi.org/10.1002/chin.197706057Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue6February 8, 1977 RelatedInformation

Cyclodextrins as chiral nuclear magnetic resonance shift reagents

Although chemical shift non-equivalence between enantiotopic groups in n.m.r. spectra has often been observed employing optically active solvents or chiral lanthanide shift reagents, or when a substrate is complexed to a chiral crown compound, such methods are normally critically dependent upon suitable substrate functionality. We now report that guest binding within the chiral cavity of β-cyclodextrin in D2O provides a method for inducing 19F n.m.r. chemical shifts between the prochiral CF3 groups of compounds 1 [1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol] and 2 [1,1,1,3,3,3-hexafluoro-2-(p-tolyl)propane], it being particularly noteworthy that the latter molecule lacks the type of functional group usually required for such chiral effects.

Lanthanide porphyrin complexes. Evaluation of nuclear magnetic resonance dipolar probe and shift reagent capabilities.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLanthanide porphyrin complexes. Evaluation of nuclear magnetic resonance dipolar probe and shift reagent capabilitiesWilliam D. Horrocks Jr. and Ching-Ping WongCite this: J. Am. Chem. Soc. 1976, 98, 23, 7157–7162Publication Date (Print):October 1, 1976Publication History Published online1 May 2002Published inissue 1 October 1976https://doi.org/10.1021/ja00439a007RIGHTS & PERMISSIONSArticle Views661Altmetric-Citations90LEARN 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 PDF (794 KB) Get e-Alerts Get e-Alerts