Lanthanide-induced Shifts Research Articles

Nuclear magnetic resonance study of Ln3+ complexes with aspartate and glutamate residues. Thermodynamic and structural analysis

Binding of aspartate and glutamate residues with the lanthanide cation Yb3+ has been studied in D2O, involving two kinds of peptide backbones: N-acetylamino acid methyl esters and cyclic dipeptides. A method is described for the quantitative analysis of the lanthanide-induced shifts (LIS) from which the best model of solution, the binding constants, the induced shifts, and the geometry of the complexes have been determined. Aspartate and glutamate derivatives are found to form both 1 : 1 and 2 : 1 complexes (peptide:cation). Backbone flexibility and, to a lesser extent, side-chain length seem to govern the magnitude of the binding constants. Only one oxygen of the carboxylate group is involved in the complex. The Yb3+⋯ O– distances are found to be different according to the Asp (2.70–2.75 Å) and Glu (2.50–2.55 Å) residues. The predominant conformer has an extended side-chain so no chelation occurs with the peptide backbone.

Conformational studies by dynamic nuclear magnetic resonance. Part 30. Exchange kinetics between the rotamers of 2-acyl-furans and -thiophenes

Low-temperature 13C n.m.r. spectra allowed the observation of two different groups of signals, corresponding to the O,O-anti- and O,O-syn-rotamers, of a number of 2-acylfurans with the following alkyl groups bonded to carbonyl: Me, Et, Pri, But, pentan-3-yl. The ratios of these rotamers in dimethyl ether were thus obtained, and the barriers for the syn-anti interconversion were found to decrease with increasing bulkiness of the alkyl groups. Although separate 13C signals could not be detected for the rotamers of the corresponding 2-acylthiophenes, line-broadening effects nonetheless allowed measurement of the interconversion barriers. Lanthanide-induced shift experiments carried out on the latter derivatives (at both 1H and 13C frequencies) showed that in all the 2-acylthiophenes investigated the S,O-syn rotamers are predominant.

Beitr�ge zur Chemie der Pyrrolpigmente, LVIII Phytochrommodellstudien: Konformationsanalytische Untersuchungen an 2,3-Dihydrobilatrien-abc-Derivaten

Two 3,4-dihydropyrromethenones and two 2,3-dihydrobilatrienes-abc O-methylated at rings A and D resp. have been prepared. Their configurations were established as (Z), (E), (Z, Z, Z) and (Z, Z, Z), respectively, using1H-NMR-techniques (NOE); they are also shown to exist predominantly in the lactam form. Within the pyrromethene fragment of the bilatrienes the pyrrolic and pyrroleninic ring type depends on the position of O-methylation. A helical all-synperiplanar conformation in solution could be established for all cases by applying the lanthanide induced shift (LIS) technique.

Carbon-13 NMR Spectra of 5-(4-Substituted Benzylidene)-2,3,4,5-tetrahydropyridines

Abstract Carbon-13 chemical shifts for a series of 5-(4-substituted benzylidene)-2,3,4,5-tetrahydropyridines were determined. The substituent chemical shifts (SCS) were correlated with σI and σRo values by means of DSP and DSP-NLR analysis. It was found that as a substituent the C=C–C=N moiety is as mild as C=C and that the former can be approximated as a vinylogue of the C=N moiety. C-13 lanthanoid-induced shifts (LIS) of the parent compound were also discussed.

Contact and dipolar contributions to lanthanide-induced NMR shifts of amino acid and peptide models for calcium binding sites in proteins

1H nuclear magnetic resonance has been employed to study the binding of N α-acetyl- l-aspartic acid and N α-acetyl- l-aspartyl- l-glycyl- l-aspartylamide to the series of six lanthanide ions Dy 3+ through Lu 3+. Values for the dissociation constants and the maximum lanthanide-induced shifts were obtained by fitting the titration data for each metal ion to appropriate binding curves. The shifts were separated into contact and dipolar terms without prior knowledge of the symmetry of the complex or the orientation of the principle axis system of the magnetic susceptibility tensor. The results indicate the contact shifts in 1H NMR are not always negligible, and that Yb 3+ appears to be the best calcium analog for structural studies when the contact interaction is significant.

Application of biosynthetic 13C‐enrichment using [1‐13C]‐, [2‐13C]‐ and [1,2‐13C2]‐acetate as precursor for 13C NMR spectral assignment of higher plant metabolites. The assignments of some bryonolic acid derivatives

AbstractThe 13C NMR spectra of some derivatives of bryonolic acid (1) (D:C‐friedoolean‐8‐en‐3β‐ol‐29‐oic acid) were assigned by means of 13C‐enrichment, lanthanide‐induced shifts (LIS) and comparison of chemical shift data between derivatives. The 13C‐enriched species of 1, i.e., 1a, 1b and 1c were biosynthesized by Luffa cylindrica (Cucurbitaceae) callus fed with [1‐13C]‐, [2‐13C]‐ or [1,2‐13C2]‐acetate, respectively. Methyl acetylbryonolates 2, 2a, 2b and 2c, methyl bryonolates 3, 3a, 3b and 3c, methyl bryononates 4 and 4a, diacetyl‐3β,29‐diols (3,29‐diacetyl‐D:C‐friedoolean‐8‐en‐β,29‐diol) 5, 5a, 5b and 5c, and 3‐acetyl‐3β,29‐diols 6, 6a and 6b were prepared from 1, 1a, 1b and 1c, and their 13C NMR spectra were recorded. The 13C concentration of the 13C‐enriched species was high enough to exhibit the satellite peaks clearly, and the analysed data were very useful for this study. Thus, total assignments for 2, 3, 4, 5 and 6 were established. It was found that conversion of the methoxycarbonyl group at C‐29 into an acetoxymethyl group caused complex changes in the chemical shifts of the C, D‐ and E‐ring carbons and those of the methyl carbons linked to these rings.

Conformational analysis. Part 7. A lanthanide induced shift (L.I.S.) nuclear magnetic resonance investigation of conformational isomerism in ortho- and meta-substituted benzaldehydes

A lanthanide induced shift n.m.r. investigation of conformational isomerism in o- and m-methyl- and -chloro-benzaldehydes and m-methoxybenzaldehyde has been carried out. With the 13C diamagnetic complexation shifts removed by use of La(fod)3 and the application of a previously described lanthanide ion complexing model, the pseudo-contact shifts have been used to obtain precise conformational preferences of the aldehydes. The m-methyl-, -chloro-, and -methoxy-benzaldehydes are 44, 42, and 32%, respectively in the O-trans conformation, whereas the o-methyl is 59% in the O-trans form and the o-chloro 100% in the O-trans form. Possible structural deformations in the ortho-substituted compounds have been considered. The technique is a sensitive probe of the methyl torsional angle for the O-cis conformer, the methyl being staggered with respect to the aldehyde group. The o-methylbenzaldehyde geometry is not appreciably distored and the aldehyde group is coplanar with the aromatic ring. In o-chlorobenzaldehyde the structural changes are small and are interpreted as arising from the attractive Cl ⋯ HCO interaction.

Carbon-13 N.M.R. lanthanide-induced shift study of some D:A-friedooleananes

Carbon-13 n.m.r. signal assignments for D:A-friedooleanan-28-ol (1), D:A-friedooleanan-29-ol (2), D:A-friedooleanan-30-ol (3)D:a-friedooleanan-30-ol (4, D:A-friedooleanan-21α-ol (5) and 21α- hydroxy-D:A-friedooleanan-3-one (6) are reported. Lanthanide-induced shifts of the hydroxy compounds indicate that the oxygenation in the vicinity of ring E in these molecules does not affect the chair-chair-chair-twistboat-boat conformation proposed for D:A-friedooleananes.

Conformational analysis of organic carbonyl compounds. Part 4. A 1H and 13C nuclear magnetic resonance study of formyl and acetyl derivatives of benzo[b]furan

A conformational study of formyl and acetyl derivatives of benzo[b] furan provides evidence that in the case of 2- and 7-derivatives the E,Z-conformational mixture is solvent dependent, the Z-form prevailing in solvents with higher polarity. The presence of the same substituents in the 3- and 4-position gives compounds with predominantly Z-conformation and no change is caused by solvents. These results show an interestingly different behaviour by carbonyl derivatives of benzo[b] furan with respect to the same benzo[b] thiophene derivatives. The conformational analysis was carried out by the n.m.r. method by employing 1H and 13C chemical shifts, long-range proton–proton coupling constants, and lanthanide-induced shifts (LIS) simulation. For the derivatives substituted in position 7, the LIS method is not a suitable approach for the determination of conformer populations since, in solution, a chelate is formed where bonding of Eu to the oxygen atoms of the carbonyl and of the heterocyclic ring stabilizes the Z-form. A quantitative approach for determining the relative conformer populations of benzo[b] furan-7-carbaldehyde was set up by statistical manipulation of long-range proton–proton coupling constants, proton chemical shifts, and the classical theory of dielectrics.

Synthesis and stereochemical characterization of 1,2,7,11b- tetrahydropyrrolo[1,2-d][1,4]benzodiazepine-3,6(5H)-diones, obtained via Raney nickel hydrogenation of tetrahydroisoxazolo[2,3-d][1,4]benzodiazepinones

Catalytic hydrogenation (Raney nickel) of 2-alkoxycarbonyl-1,2,7,11b-tetrahydroisoxazolo [2,3,-d][1,4]-benzodiazepin-6(5H)-ones (1)produces 1,2,7,11b-tetrahydro-2-hydroxypyrrolo[1,2-d][1,4]benzodi-azepine-3,6(5H)-diones (2a–c). Their stereochemical characterization has been accomplished by 1H n.m.r. spectroscopy, principally by computer simulation of the lanthanoid-induced shift of the proton resonances. The result show that some 10-chloro-1,2,7,11b-tetrahydro-2-hydroxy-7-methyl-11b-phenylpyrrolo[1,2-d][1,4]benzodiazepine-3,6(5H)-diones exits predominantly in the transoid conformation in chloroform solution at room temperature; a related 7-unsubstituted product shows rapid conformational equilibration in comparison with the n.m.r. time scale, characterized by a slight conformational bias to the cisoid form.

Application of chiral lanthanide-induced shift reagents to optically active cations: the use of tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorato]europium(III) to determine the enantiomeric purity of tris(phenanthroline)ruthenium(II) dichloride

In non-polar solvents, chiral europium complexes provide attractive n. m. r. shift reagents to resolve spectra of optically active cations, and, in particular, for tris(phenanthroline)ruthenium dichloride,1H n. m. r. shift differences of up to 0.7 p.p.m. between isomers easily permit the determination of absolute enantiomeric purity.

ChemInform Abstract: LANTHANIDE‐INDUCED SHIFT AND RELAXATION‐RATE STUDIES OF AQUEOUS L‐PROLINE SOLUTIONS

Chemischer InformationsdienstVolume 14, Issue 40 Physical Organic Chemistry ChemInform Abstract: LANTHANIDE-INDUCED SHIFT AND RELAXATION-RATE STUDIES OF AQUEOUS L-PROLINE SOLUTIONS M. SINGH, M. SINGHSearch for more papers by this authorJ. J. REYNOLDS, J. J. REYNOLDSSearch for more papers by this authorA. D. SHERRY, A. D. SHERRYSearch for more papers by this author M. SINGH, M. SINGHSearch for more papers by this authorJ. J. REYNOLDS, J. J. REYNOLDSSearch for more papers by this authorA. D. SHERRY, A. D. SHERRYSearch for more papers by this author First published: October 4, 1983 https://doi.org/10.1002/chin.198340052AboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue40October 4, 1983 RelatedInformation

The Conformational Analysis of 1-p-Tolyl-2-phenyl-1-propanols, 1-p-Tolyl-2-phenylethanol, and 1-p-Tolyl-2-phenyl-1-propanone by Means of NMR Spectroscopy

Abstract The conformations of the diastereomers of 1-p-tolyl-2-phenyl-1-propanols[(RS⁄SR)-3 and (RR⁄SS)-3], 1-p-tolyl-2-phenylethanol (4), and 1-p-tolyl-2-phenyl-1-propanone (5) were studied by means of NMR spectroscopy, mostly with the aid of the computer-simulation of the lanthanoid-induced shifts. It has been suggested that the rotamers in which the tolyl group lies close to the phenyl group are preferred in the conformational equilibria of (RS⁄SR)-3, 4, and 5. For(RR⁄SS)-3, the most stable rotamer (in CDCl3) has been suggested to have the tolyl group anti to the phenyl group and gauche to the methyl group. The results have been discussed in view of the general occurrence of the folded conformation.

17O nuclear magnetic resonance studies of lanthanide ion-proline complexes

17O lanthanide-induced paramagnetic shifts are reported for nine different lanthanide ion-proline complexes in aqueous solution at pH 3. The results indicate that the hyperfine coupling constant for the directly liganded proline and water oxygens is indeed invariant for the nine lanthanide cations examined. This suggests that previous breaks in data for lanthanide-induced shifts along the lanthanide cation series must arise from changes in the non-axial dipolar contributions to these shifts near the center of the series.

A lanthanide-induced shift investigation of the conformation of pseudoionone and its derivatives in solution

NMR conformational studies of several pseudoionone derivatives were performed, including the use of lanthanide shift reagents. The mathematical treatment of spectral data allowed us to choose the most probable rotamers with s- cis or s- trans orientations within the diene systems conjugated with the carbonyl group.

ChemInform Abstract: THE COMPLEXATION OF CALCIUM(II) AND LANTHANIDE(III) CATIONS WITH THE PHOSPHATE SUBSTITUTE (CARBOXYMETHOXY)SUCCINATE (CMOS), AS STUDIED BY MAGNETIC RESONANCE SPECTROSCOPY

AbstractDie Komplexbildung zwischen Trinatrium‐carboxymethoxysuccinat und Lanthanoid(III)‐ sowie Ca(ll)‐Kationen wird mittels 1H‐NMR‐Spektroskopie untersucht.

Lanthanide-induced shift and relaxation-rate studies of aqueous L-proline solutions

Lanthanide-induced shift and relaxation-rate studies of aqueous L-proline solutions

Interpretation of lanthanide-induced shifts in NMR spectra. The case of nonaxial symmetry

The approach to the treatment of low-symmetry systems by the method of lanthanide shift reagents (LSR) is considered. Analysis of the results obtained by optical spectroscopy (mostly by luminescense spectroscopy of Eu 3+ ion) is used for this purpose. From the spectra mentioned, a model of the LSR adduct and parameters describing anisotropy of magnetic susceptibility are obtained. The method is applied to several rare-earth complexes of nonaxial symmetry. Bleaney's theory connecting pseudocontact NMR shifts to crystal field parameters of the second order is verified and shown to be correct if the crystal field splittings are of the order of kT. The systems Ln(dpm) 3 and Ln(fod) 3 are discussed.

Solution structure of tris[hydridotris(pyrazol-1-yl)borato]ytterbium(III); rare example of solution rigid lanthanide complex

The /sup 1/H, /sup 13/C, and /sup 11/B NMR spectra of Lu(HBPz/sub 3/) and Yb(HBPz/sub 3/)/sub 3/ (Pz = pyrazolyl, C/sub 3/N/sub 2/H/sub 3/) complexes have been recorded. The complexes are stereochemically rigid on the NMR scale with solution structure approximating the known solid-state structure of Yb(HBPz/sub 3/)/sub 3/. The molecules have C/sub s/ symmetry in solution, and accordingly, the ytterbium complex gives rise to 21, 18, and 3 well-separated and lanthanide-shifted resonances in the /sup 1/H, /sup 13/C, and /sup 11/B NMR spectrum, respectively. Least-squares fits of the lanthanide-induced shifts in the paramagnetic Yb(HBPz/sub 3/)/sub 3/ complex to the solid-state structural data, using the full form of the McConnell-Robertson expression for the dipolar shifts, gave the molecular susceptibility anisotropies of the complex and the orientation of the magnetic axes in the complex. The C/sub s/ molecular symmetry fixes the z magnetic axis perpendicular to the mirror plane, while the magnetic x axis refines to a position close to the pseudo-C/sub 2/ axis of the coordination polyhedron, which has approximate C/sub 2//sub nu/ symmetry. The close agreement between calculated dipolar shifts and experimentally observed lanthanide-induced shifts confirms that the solid-state molecular structure remains essentially unchanged on dissolution and shows thatmore » contributions to the induced shifts in the ytterbium complex by a Fermi contact mechanism are minimal.« less

ChemInform Abstract: STRUCTURE ELUCIDATION WITH LANTHANIDE‐INDUCED SHIFTS. 15. BLOCKING GROUPS FOR R POLYFUNCTIONAL COMPOUNDS

Chemischer InformationsdienstVolume 14, Issue 3 Physical Organic Chemistry ChemInform Abstract: STRUCTURE ELUCIDATION WITH LANTHANIDE-INDUCED SHIFTS. 15. BLOCKING GROUPS FOR R POLYFUNCTIONAL COMPOUNDS D. J. RABER, D. J. RABERSearch for more papers by this authorG. J. PROPECK, G. J. PROPECKSearch for more papers by this author D. J. RABER, D. J. RABERSearch for more papers by this authorG. J. PROPECK, G. J. PROPECKSearch for more papers by this author First published: January 18, 1983 https://doi.org/10.1002/chin.198303080Read 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue3January 18, 1983 RelatedInformation