scholarly journals Peculiarities of NMR 13C spectra of benzoic acid and saturated alkylbenzoates. I. Chemical shift of benzoyl fragment hydrocarbon atoms

2008 ◽  
Vol 2 (2) ◽  
pp. 77-83
Author(s):  
Volodymyr Mizyuk ◽  
◽  
Volodymyr Shibanov ◽  
Lesya Kobrin ◽  
Galyna Marshalok ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Carbon Atom ◽  
Benzoic Acid ◽  
Alkyl Radical ◽  
Chemical Shifts ◽  
Degree Of Branching ◽  
Alkoxyl Group

It has been shown that chemical shift of 5 types of carbon nuclei of benzoyl fragment in saturated alkylbenzoates depends upon alkyl radical degree of branching near α-carbon atom of alkoxyl group. Typical values of chemical shifts of five nuclei for primary, secondary and tertiary alkylbenzoates have been admitted

Origin and Nature of Transmission Modes of Anomalous Effects of meta-Substituents on the 13C Chemical Shift of the Carboxyl Carbon (δCO) of Benzoic Acid

2010 ◽  
Vol 63 (2) ◽  
pp. 321 ◽  
Author(s):  
Susanta K. Sen Gupta ◽  
Rajendra Prasad
Keyword(s):  
Chemical Shift ◽  
Benzoic Acid ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Basis Set ◽  
Benzoic Acids ◽  
Anomalous Effect ◽  
Atomic Orbitals ◽  
13C Chemical Shift ◽  
Carboxyl Carbon

Studies of substituent effects on NMR chemical shifts are of great benefit in determining fine details of electron distribution in molecules. Interestingly, NMR substituent effects are often different and even opposite to those associated with chemical reactivity. Among molecules exhibiting anomalous (reverse) substituent effects is benzoic acid, the standard model for studying substituent effects. The substituent effect on the 13C chemical shift of its carboxyl carbon (δ CO) is just the opposite of that on its acid strength or reactivity. To develop insights into the origin of the anomalous effect of a substituent on δ CO, occupancies of natural atomic orbitals at the carboxyl and ring carbons of a set of 10 meta-substituted benzoic acids have been calculated at the density functional theory level using the B3LYP function with split valance 6–311G++** basis set. Statistical correlations obtained for the 13C chemical shifts, δ CO and δ C-ring of these benzoic acids with the natural atomic orbital occupancies calculated for respective carbon atoms on one hand and with Taft’s inductive and resonance parameters (σ I and σ R BA ) of the substituents on the other hand have been critically analyzed. The findings have established firmly that a meta-substituent’s anomalous effect on δ CO is caused by the substituent-induced changes in the total occupancy of only the p z natural atomic orbitals at the carboxyl carbon. The study has demonstrated further that the transmission of the anomalous effect can be successfully interpreted by a 5.5:–2.5:1 combination of the localized, extended, and resonance-induced π-polarization effects.

29Si NMR chemical shifts in pertrimethylsilylated 1,6-anhydro-β-D-glucopyranose derivatives. Empirical assignment from Hammett type dependence of the chemical shifts

1983 ◽  
Vol 48 (9) ◽  
pp. 2503-2508 ◽  
Author(s):  
Jan Schraml ◽  
Jaroslav Včelák ◽  
Miloslav Černý ◽  
Václav Chvalovský
Keyword(s):  
Chemical Shift ◽  
Carbon Atom ◽  
Silicon Atom ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Polar Effect ◽  
29Si Nmr ◽  
Nmr Chemical Shifts ◽  
Trimethylsilyl Groups

29Si chemical shift of Si-3 silicon atom of the trimethylsiloxy group attached to C(3) carbon atom in 1,6-anhydro-β-D-glucopyranose derivatives correlates linearly with the sum of Taft polar constants σσ of substituents R2 and R4 on C(2) and C(4) carbon atoms. Quality of this correlation allows assignment of Si-3 line in the spectra of derivatives containing two or three trimethylsilyl groups in the molecule. The shielding order δ(Si-4) < δ(Si-3) found in 1,6-anhydro-2,3,4-O-tris(trimethylsilyl)-β-D-glucopyranose is the same as recently found in other pyranose derivatives with the same configuration of substituents but the order is reversed by strong polar effect of the substituent in 1,6-anhydro-2-O-p-toluenesulphonyl-3,4-O-bis(trimethylsilyl)-β-D-glucopyranose. This finding warns against indiscriminate use of empirical assignment rules based on simple shielding order without considering possible substituent effects.

scholarly journals Use of13C-NMR as complementar identification tool in essential oil analysis

1997 ◽  
Vol 13 (4) ◽  
pp. 265-273 ◽  
Author(s):  
José Wilson Alencar ◽  
Maria Goretti de Vasconcelos Silva ◽  
Maria Iracema Lacerda Machado ◽  
Afrânio Aragão Craveiro ◽  
Francisco José de Abreu Matos ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Carbon Atom ◽  
Essential Oil ◽  
Chemical Shifts ◽  
Chemical Constituents ◽  
Structural Features ◽  
Oil Analysis ◽  
Nmr Data ◽  
C Nmr ◽  
Identification Tool

A program using13C-NMR data was developed to improve GC/MS identifications of chemical constituents in essential oils. Compiled data uses 2290 and 2370 chemical shifts of 229 monoterpenes and 158 sesquiterpenes, respectively, stored into two reference libraries. Each carbon atom was codified using rules that correlates its chemical shift with structural features of the carbon hybridization and vicinity.

Fluorescence Reagents for Labelling of Biomolecules. Part I. Synthesis and Spectral Characterization of 2- and 4-Substituted 9-Isothiocyanatoacridines

1994 ◽  
Vol 59 (1) ◽  
pp. 203-212 ◽  
Author(s):  
Dana Mazagová ◽  
Danica Sabolová ◽  
Pavol Kristian ◽  
Ján Imrich ◽  
Marián Antalík ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Carbon Atom ◽  
Fluorescence Intensity ◽  
Fluorescence Spectra ◽  
Chemical Shifts ◽  
H Nmr ◽  
Hammett Constants ◽  
Hydrolysis Of ◽  
C Nmr

9-Isothiocyanatoacridines VIII - XIV were prepared from the corresponding 9-chloroacridines I - VII. The IR, 1H NMR, 13C NMR and fluorescence spectra of the products are given. The 13C NMR chemical shifts of the C-9 ipso carbon atom exhibit a trend that is in accord with the Hammett constants of substituents bonded to the C-2 carbon. Effect of these substituents on the chemical shift of C-NCS was only small. The dependence of hydrolysis of isothiocyanates VIII - XIV on pH of the medium was studied. It was found that 9-isothiocyanatoacridines do not undergo hydrolysis at pH 7 - 10. The relative fluorescence intensities (F/F0) of compounds VIII - XIV at pH 7.4 have been determined in comparison with that of 9-aminoacridine. No direct dependence between the fluorescence intensity and the polar character of substituents has been found.

Probe of cadmium(II) binding on soil fulvic acid investigated by 113Cd NMR spectroscopy

1996 ◽  
Vol 74 (7) ◽  
pp. 1360-1365 ◽  
Author(s):  
Kun H. Chung ◽  
Seog W. Rhee ◽  
Hyun S. Shin ◽  
Christopher H. Moon
Keyword(s):  
Nmr Spectroscopy ◽  
Chemical Shift ◽  
Acrylic Acid ◽  
Benzoic Acid ◽  
Fulvic Acid ◽  
Binding Sites ◽  
Chemical Shifts ◽  
Cadmium Concentration ◽  
Synthetic Polymers ◽  
Cadmium Complexes

Binding of cadmium(II) on soil fulvic acid (FA) was investigated over a range of fulvate-to-cadmium concentration ratios (8 – 59 equiv. mol−1) using 113Cd NMR spectroscopy. The 113Cd chemical shift of cadmium bound on fulvate was observed in a more downfield region (δ −20.4 to −15.6) than that bound on synthetic polymers, poly(acrylic acid) (PAA: δ −36.6 to −38.2), poly(methacrylic acid) (PMAA: δ −34.0 to −25.4), and poly(vinyl benzoic acid) (PVBA: δ −34.7 to −31.2). The calculated values of individual chemical shifts for the species CdL+ and CdL2 (L: carboxylate) formed in Cd(II)–carboxylate systems (e.g., acetate, benzoate) are δ −22 to −24 and δ −39 to −40, respectively. The relative downfield shift of cadmium(II)–fulvate suggests that functional groups (e.g., hydroxyl and neutral N donor) other than carboxylates may be involved in cadmium coordination. The chemical shifts of cadmium complexes of hydroxycarboxylates (e.g., glycolate) or carboxylates containing neutral N donor (e.g., picolinate) were generally observed in more downfield regions than their carboxylate counterparts. Key words: fulvic acid, polyfunctionality, binding sites, chemical shift, 113Cd NMR.

scholarly journals Structure of Nanobody Nb23

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3567
Author(s):  
Mathias Percipalle ◽  
Yamanappa Hunashal ◽  
Jan Steyaert ◽  
Federico Fogolari ◽  
Gennaro Esposito
Keyword(s):  
Nmr Spectroscopy ◽  
Chemical Shift ◽  
Solution Structure ◽  
Chemical Shifts ◽  
Molecular Size ◽  
Side Chain ◽  
3D Nmr ◽  
Target Antigen ◽  
Internuclear Distances ◽  
2D And 3D

Background: Nanobodies, or VHHs, are derived from heavy chain-only antibodies (hcAbs) found in camelids. They overcome some of the inherent limitations of monoclonal antibodies (mAbs) and derivatives thereof, due to their smaller molecular size and higher stability, and thus present an alternative to mAbs for therapeutic use. Two nanobodies, Nb23 and Nb24, have been shown to similarly inhibit the self-aggregation of very amyloidogenic variants of β2-microglobulin. Here, the structure of Nb23 was modeled with the Chemical-Shift (CS)-Rosetta server using chemical shift assignments from nuclear magnetic resonance (NMR) spectroscopy experiments, and used as prior knowledge in PONDEROSA restrained modeling based on experimentally assessed internuclear distances. Further validation was comparatively obtained with the results of molecular dynamics trajectories calculated from the resulting best energy-minimized Nb23 conformers. Methods: 2D and 3D NMR spectroscopy experiments were carried out to determine the assignment of the backbone and side chain hydrogen, nitrogen and carbon resonances to extract chemical shifts and interproton separations for restrained modeling. Results: The solution structure of isolated Nb23 nanobody was determined. Conclusions: The structural analysis indicated that isolated Nb23 has a dynamic CDR3 loop distributed over different orientations with respect to Nb24, which could determine differences in target antigen affinity or complex lability.

The biosynthesis of ephedrine

1989 ◽  
Vol 67 (6) ◽  
pp. 998-1009 ◽  
Author(s):  
Gunnar Grue-Sørensen ◽  
Ian D. Spenser
Keyword(s):  
Carbon Atom ◽  
Benzoic Acid ◽  
Pyruvic Acid ◽  
Nmr Spectra ◽  
Carbon Skeleton ◽  
Resonance Spectroscopy ◽  
Methyl Group ◽  
Acid Incorporation ◽  
Group A ◽  
C Nmr

It is shown by 13C nuclear magnetic resonance spectroscopy that the labelled C2 fragment of [2,3-13C2]pyruvic acid is transferred intact into the C-methyl group and the adjacent carbon atom of the Ephedra alkaloids, norephedrine, ephedrine, norpseudoephedrine, and pseudoephedrine, in growing plants of Ephedragerardiana. This finding serves to identify pyruvate as the elusive precursor of the aliphatic C2 terminus of the skeleton of the alkaloids. In earlier experiments with C-labelled substrates, label from [3-14C]pyruvic acid was incorporated mainly, but not exclusively, into the C-methyl group of ephedrine, and label from [2-14C]pyruvate was incorporated similarly into the carbon atom adjacent to the C-methyl group. A C6–C1 unit related to benzaldehyde or benzoic acid has long been known to generate the benzylic fragment of the carbon skeleton of the Ephedra alkaloids. It is likely that the carbon skeleton of ephedrine is generated from pyruvate and either benzaldehyde or benzoic acid, by a reaction analogous to the formation of acetoin or diacetyl from pyruvate and acetaldehyde or acetic acid, respectively. Keywords: biosynthesis of ephedrine, Ephedra alkaloids, 13C NMR spectra, ephedrine, biosynthesis of pyruvic acid, incorporation into ephedrine13C NMR spectra.

Circular dichroism spectra of tetraamminecobalt(III) complexes of amino alcohols

1978 ◽  
Vol 31 (11) ◽  
pp. 2399 ◽  
Author(s):  
CJ Hawkins ◽  
GA Lawrance ◽  
JA Palmer
Keyword(s):  
Circular Dichroism ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Amino Alcohols ◽  
Circular Dichroism Spectra ◽  
Chemical Shift Difference ◽  
Solvent Dependence ◽  
Cotton Effects ◽  
Circular Dichroïsm ◽  
Chiral Amino Alcohols

The circular dichroism spectra are reported for tetraamminecobalt(III) complexes with the chiral amino alcohols 2-aminopropan-1-ol, 2- aminobutan-1-ol, 1-aminopropan-2-ol, 2-amino-1-phenyl-ethanol, ψ- ephedrine and ephedrine with the alcohol groups protonated (OH) and deprotonated (O-). The solvent dependence of the chemical shifts of the NH protons was investigated to determine the effects of stereoselective solvation on the circular dichroism, but, in contrast to some other related systems, the chemical shift difference between the two NH2 protons was relatively insensitive to solvent. Consistent with this, the circular dichroism spectra of the tetraphenylborate salts of the deprotonated complexes were found not to be markedly dependent on solvent. Tetraammine-{(-)-ψ-ephedrine)cobalt(III) and tetraammine{(-)- ephedrine}cobalt(III) were found to have the same signs of Cotton effects for the various d-d transitions, whereas bis{(-)-ψ- ephedrine}copper(II) and bis{(-)-ephedrine}copper(II) had opposite signs. This has been explained in terms of different conformer populations in the cobalt(III) and copper(II) systems.

The13C Chemical Shift of theipso Carbon Atom in Phenyllithium

1995 ◽  
Vol 128 (12) ◽  
pp. 1183-1186 ◽  
Author(s):  
Stefan Berger ◽  
Ulrich Fleischer ◽  
Christian Geletneky ◽  
John C. W. Lohrenz
Keyword(s):  
Chemical Shift ◽  
Carbon Atom

NMR studies of tandem WW domains of Nedd4 in complex with a PY motif-containing region of the epithelial sodium channel

1998 ◽  
Vol 76 (2-3) ◽  
pp. 341-350 ◽  
Author(s):  
Voula Kanelis ◽  
Neil A Farrow ◽  
Lewis E Kay ◽  
Daniela Rotin ◽  
Julie D Forman-Kay
Keyword(s):  
Chemical Shift ◽  
Sodium Channel ◽  
Chemical Shifts ◽  
Epithelial Sodium Channel ◽  
Chemical Shift Assignment ◽  
Nmr Studies ◽  
Ww Domains ◽  
Ww Ii ◽  
Py Motif ◽  
Shift Assignment

Nedd4 (neuronal precursor cell-expressed developmentally down-regulated 4) is a ubiquitin-protein ligase containing multiple WW domains. We have previously demonstrated the association between the WW domains of Nedd4 and PPxY (PY) motifs of the epithelial sodium channel (ENaC). In this paper, we report the assignment of backbone 1Hα, 1HN, 15N, 13C', 13Cα, and aliphatic 13C resonances of a fragment of rat Nedd4 (rNedd4) containing the two C-terminal WW domains, WW(II+III), complexed to a PY motif-containing peptide derived from the β subunit of rat ENaC, the βP2 peptide. The secondary structures of these two WW domains, determined from chemical shifts of 13Cα and 13Cβ resonances, are virtually identical to those of the WW domains of the Yes-associated protein YAP65 and the peptidyl-prolyl isomerase Pin1. Triple resonance experiments that detect the 1Hα chemical shift were necessary to complete the chemical shift assignment, owing to the large number of proline residues in this fragment of rNedd4. A new experiment, which correlates sequential residues via their 15N nuclei and also detects 1Hα chemical shifts, is introduced and its utility for the chemical shift assignment of sequential proline residues is discussed. Data collected on the WW(II+III)-βP2 complex indicate that these WW domains have different affinities for the βP2 peptide.Key words: WW domain, PY motif, Nedd4, ENaC, NMR.

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