15N NMR spectroscopy acids: 7�solvent effects on a-and ?-amino (original) (raw)
Related papers
15N NMR spectroscopy acids: 7—solvent effects on α-and ω-amino
Organic Magnetic Resonance, 1979
The natural abundance "N NMR spectra of several a-and o-amino auds were measured in various protic solvents. Increasing acidity of the solvents results in an upfield shift in the case of the a-amino acids, while o-amino acids are almost insensitive to solvent effects.
17O NMR Studies of Solid Amino Acids
Springer eBooks, 1990
15 n labeled amino acids are routinely used to label proteins or nucleic acids for study by nMR. However, nMR studies of 15 n labeled amino acids in metabolite studies have not been pursued extensively, presumably due to line broadening present under standard experimental conditions. in this work, we show that lowering the temperature to −5 °C allows facile characterization of 15 n-labeled amino acids. further, we show that this technique can be exploited to measure 15 nH 3 produced in an enzyme catalyzed reaction and the transport and metabolism of individual amino acids in mammalian cell culture. With respect to 13 c-labeled amino acids, 15 n-labeled amino acids are less costly and enable direct characterization of nitrogen metabolism in complex biological systems by nMR. in summary, the present work significantly expands the metabolite pools and their reactions for study by NMR.
Tetrahedron Letters, 2004
The hypothesis and the conclusions of previous 17 O NMR studies on the detection of both oxygens of the carboxylic group of Boc-[ 17 O]Tyr(2,6-diClBzl)-OH in DMSO-d 6 solution (V. Tsikaris et al., Tetrahedron Lett. 2000, 41, 8651) are reconsidered. The appearance of two discrete resonances at 340 and 175 ppm of this protected amino acid is not now attributed: (a) to the reduction of the intramolecular conformational exchange rate, due to the effect of intramolecular hydrogen bonding of the hydroxy part of the carboxyl with the carbonyl oxygen of the Boc-group, and (b) to the effect of solvent viscosity, suggested in the mentioned study. The cause of this phenomenon is now attributed to a strong hydrogen bonding of the polar proton acceptor solvent DMSO with the carboxy group, which effectively reduces the proton exchange rate, thus becoming slow on the 17 O NMR time scale. Ó 2004 Elsevier Ltd. All rights reserved. 17 O NMR spectroscopy provides a powerful and sensitive tool for studying intra-and intermolecular hydrogen bonding effects both in solution and in the solid state. 1-4 Since the oxygen atom is one of the most important atoms constituting hydrogen-bonding structures, 17 O NMR might provide novel and complementary information not readily available from other methods.
The Journal of Physical Chemistry, 1991
The I 7 0 NMR line widths of the a-carboxyl groups of the protein amino acids includin 4-hydroxyproline, sarcosine, linear correlation was found between the line widths and the molecular weights of the amino acids at the pH values 0.5, 6.0, and 12.5, which are characteristic of the three ionization states of the neutral amino acids. The slopes of the straight lines were independent of pH; however, the line widths at acidic pH were increased by 98 f 13 Hz relative to those at neutral or basic pH. Since the I7O quadrupole coupling constant is only weakly influenced by the protonation state of the amino acids, it can be concluded that the a-carboxylic group is hydrated by an excess of two molecules of water relative to the a-carboxylate group. The lifetime of the water association is far below the NMR chemical shift time scale. Of the oxygen-containing functional groups of the amino acid side chains, only the phenolate ion of tyrosine was found to form water complexes that are stable within the range of the correlation times. It is shown that the I7O line widths of the a-carboxyl groups reflect the overall rotational correlation time of the amino acids. In contrast, the a-carbons are characterized by shorter effective correlation times presumably due to internal rotation of the C,-H vector. N,N-dimethylglycine, and Omethyltyrosine were measured in aqueous solution at 40 O C (I ! 0 enrichment 10 atom W). A
Canadian Journal of Chemistry, 1976
The acid–base chemistry of 2,3-diaminopropionic acid (dap), 2,4-diaminobutyric acid (dab), ornithine (orn), and lysine (lys) has been studied by 13C and proton nmr spectroscopy. Macroscopic acid dissociation constants for titration of the two ammonium groups of each molecule have been calculated from the 13C chemical shift titration curves for the alkyl carbon atoms by nonlinear least squares curve fitting methods. Microscopic acid dissociation constants for the simultaneous titration of the two ammonium groups of protonated orn and lys have been obtained from their proton chemical shift titration curves and from the 13C titration curves for orn and dap. The results indicate that the α-ammonium group of each of these α,ω-diaminocarboxylic acids is more acidic than its ω-ammonium group, but that the difference decreases as the number of carbons separating the ammonium groups decreases so that the acidities of the two ammonium groups of dap are almost identical. Results of pmr studies...
The nuclear magnetic resonance spectra ofN-nitroso-N-alkyl amino acids
Organic Magnetic Resonance, 1981
Structurally related acyclic and cyclic N-nitroso-N-alkyl amino acids were prepared and their 'H,-C and 15N NMR spectra were investigated. The changes in the 13C NMR spectra of the N-nitroso a-amino acids after dissolving in solvents suggest that they possess the 2-configuration in the crystalline state; in solution some of them isomerize to mixtures of the 2-and Eisomers whose composition appear to depend on steric factors. The 13C chemical shifts were assigned on the basis of anisotropic effects of the nitrosamino group and configurational stability. The 13C chemical shifts were correlated with those of the nitrosamines of the same carbon skeletons and the effects of changing a methyl group to the carboxylic acid are deshielding on the a-carbons and shielding on the &carbons.
Solid state 19F NMR parameters of fluorine-labeled amino acids. Part II: Aliphatic substituents
Journal of Magnetic Resonance, 2008
Structural parameters of peptides and proteins in biomembranes can be directly measured by solid state NMR of selectively labeled amino acids. The 19 F nucleus is a promising label to overcome the low sensitivity of 2 H, 13 C or 15 N, and to serve as a background-free reporter group in biological compounds. To make the advantages of solid state 19 F NMR fully available for structural studies of polypeptides, we have systematically measured the chemical shift anisotropies and relaxation properties of the most relevant aromatic and aliphatic 19 F-labeled amino acids. In this first part of two consecutive contributions, six different 19 F-substituents on representative aromatic side chains were characterized as polycrystalline powders by static and MAS experiments. The data are also compared with results on the same amino acids incorporated in synthetic peptides. The spectra show a wide variety of lineshapes, from which the principal values of the CSA tensors were extracted. In addition, temperature-dependent T 1 and T 2 relaxation times were determined by 19 F NMR in the solid state, and isotropic chemical shifts and scalar couplings were obtained in solution.
1H NMR spectroscopic criteria for the configuration of N‐acyl‐α, β‐dehydro‐α‐amino acid esters
Magnetic Resonance …, 2005
The diagnostic values of the following three spectral criteria for the configuration of N-acyl-a,b-dehydroa-amino acid esters were examined: (i) the proton at the b-position at the double bond of a Z-isomer is shielded if compared with the respective E-isomer (d Z b hd E b ); (ii) the proton at the nitrogen atom is shielded in a Z-isomer in comparison with the corresponding E-isomer (d Z NH hd E NH ); and (iii) changing of the solvent from CDCl 3 to deuterated trifluoroacetic acid (TFA) causes shielding of the H b vinylic proton of an E-isomer or deshielding of the respective proton of the Z-isomer (d E CDCl 3 id E TFA or d Z CDCl 3 hd Z