Oxygen-17 and nitrogen-14 NMR studies of amide systems

Burgar, M.; Amour, Thomas E. St.; Fiat, D.

doi:10.1021/j150605a011

Cited by 69 publications

(53 citation statements)

References 5 publications

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“…This can presumably be attributed to the fact that, in water, the Gly2 and Gly3 peptide oxygens of Leu-enkephalin and Gly-Ala and Gly-Leu peptide oxygens are mainly hydrated by one molecule of H,O, in contrast to the case of model amides and cyclic peptide oxygens, which are hydrated by two molecules of water. This agrees with the finding of Burgar et al 22 that the temperature coefficients of the 170 chemical shifts for the peptide Gly-Ala are 60% of those observed in N,N-dimethylformamide in water. Nevertheless, further research is needed in order to delineate the exact hydration numbers of Gly2 and Gly3 peptide oxygens in Leu-enkephalin.…”

Section: Conformation Of Leu-enkephalin In Ch3cn/ Dmso (4 : 1)supporting

confidence: 93%

¹⁷O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

et al. 1989

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The synthesis of Leu-enkephalin selectively 17O-enriched in Gly2 and Gly3 is reported. The 17O-nmr chemical shifts of [17O-Gly2, Leu5]- and [17O-Gly3, Leu5]-enkephalins in H2O are almost identical and independent of the pH. Since hydrogen bonding is the dominant factor governing the chemical shifts of the peptide oxygen, it can be concluded that the hydration state of both oxygens is identical and independent of the pH. The 17O chemical shifts of the [17O-Leu5]-enkephalin terminal carboxyl group at pH approximately 1.9 and 5.6 are very different in H2O but very similar in CH3CN/DMSO (4:1) solution. This suggests that the protonation state of the carboxyl group at both pH values in CH3CN/DMSO solution is the same and consequently that Leu-enkephalin exists in the neutral form at pH approximately 5.6. In this organic mixed solvent system both Gly2 and Gly3 oxygen resonances exhibit a significant shift to high frequency by the same extent (delta delta approximately 30 ppm). It is concluded that both peptide oxygens are not hydrogen bonded to an appreciable extent and that no specific 2----5 hydrogen bonding exists to an appreciable extent. This conclusion is in agreement with the energy of activation for molecular rotation, as determined from T1 measurements, which was found to be almost identical for both [17O-Gly2, Leu5]- and [17O-Gly3, Leu5]-enkephalins in CH3CN/DMSO (4:1) mixed solvent.

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Section: Conformation Of Leu-enkephalin In Ch3cn/ Dmso (4 : 1)supporting

confidence: 93%

¹⁷O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

et al. 1989

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“…The NMP 170 resonance showed no consistent trend in freqnency as SO2 was added. The frequency was at 4-8240 Hz relative to D 2 0 , in reasonable agreement with the data for other amides such as dimethyl formamide (14). The 170 resonance is broad, especially in NMP, so that its position is accurate to at best 4-20 Hz.…”

Section: (F) Nuclear Magnetic Resonancesupporting

confidence: 85%

“…The signal (at 24°C) shifts from 8257 Hz (XH,O = 0) to 7574 Hz (XHzO = 0.635) to 7184 Hz (XH,O = 0.792). Large 170 shifts of oxygens in C=O bonds on-adding water have been noted previously (14). Figure 8 shows the shift in the SO, 170 resonance as a function of XSOZ.I There is considerable decrease in the 170 resonance as NMP is initially added to SO,, but at Xso, < 0.33, it no longer changes.…”

Section: (F) Nuclear Magnetic Resonancesupporting

confidence: 52%

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The system sulfur dioxide – N-methyl-2-pyrrolidinone

Adams¹,

Kruus²,

Patraboy³

1983

Can. J. Chem.

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Solubility and freezing point data are presented for the system sulfur dioxide – N-methyl-2-pyrroIidinone (NMP). The enthalpy and entropy of solution are determined as −33.7 kJ mol−1 and −94.6 J K−1 mol−1, respectively. The freezing point diagram shows maxima at [Formula: see text], suggesting the presence of 2:1 and 1:1 NMP:SO2 complexes. The existence of such complexes in the liquid state is supported by viscosity and permittivity data. Nuclear magnetic resonance and Raman spectroscopic data suggest an overall shift of electron density from the nitrogen and the carbonyl carbon of NMP to the O of SO2, with weakening of the CO bond of NMP.

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“…-The carbonyl 0-atoms of aldehydes and ketones show increased shielding in 170-NMR when participating in an intermolecular or intramolecular H-bond with an H-donor group [8a]. For amide 0-atoms similar but smaller intermolecular shielding effects have been reported [9]. Using 170-NMR, intramolecular H-bonds in aromatic o-hydroxy-carbonyl compounds were demonstrated to yield shielding effects, measured as ~l d ( '~O ) = [6(170)(CO; ortho-OH)] -[6(I7O)(CO; para-OH)], of -31 ppm for salicylaldehyde [lo], -40 ppm for o-hydroxyacetophenone [ll], and -9 ppm for methyl salicylate [12]; the difference between these values has been attributed to differences in basicity of the carbonyl groups.…”

mentioning

confidence: 99%

NMR of Terminal Oxygen. Part 14. Kinetically stabilized simple enols containing methylated uracil groups: Application of a ¹⁷O‐NMR test of H‐bonding

Zhuo

Wyler

Péchy

et al. 1994

Helvetica Chimica Acta

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In the crystalline N,N'-dimethylated uracil derivatives Za, b, the kinetically stabilized enol group forms an H-bond with 0-C(4), as demonstrated by increased shielding of specifically labelled 2a and 2b in the I70-NMR spectra (~lS('~o)(C(4)-0) = -30 ppm); absence of dilution and solvent effects show that the H-bridge is intramolecular, forming an eight-membered chelate ring. The (apparent) shielding effect dS("O) in Za,h is larger than that in salicylamide. The strong H-bond explains why the enols 2, in spite of the absence of steric hindrance, are kinetically stabilized.Introduction. -In spite of their lower thermodynamic stability, simple nonconjugated enols are often not too unstable under appropriate conditions (absence of catalysts, aprotic solvents) and can sometimes even be isolated, before being tautomerized to the more stable carbonyl compounds [2]. Even vinyl alcohol has a lifetime of several min at room temperature in MeCN solution 131. The reason for this sluggishness of ketonisation is that the rate-determining step, uiz. the transfer of a proton to C(a), is not a rapid reaction [4]; this contrasts with the reactions of the same enols with halogen or similar electrophiles, which are nearly diffusion-controlled [5]. Increased kinetic stability is

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Oxygen-17 and nitrogen-14 NMR studies of amide systems

Cited by 69 publications

References 5 publications

¹⁷O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

¹⁷O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

The system sulfur dioxide – N-methyl-2-pyrrolidinone

NMR of Terminal Oxygen. Part 14. Kinetically stabilized simple enols containing methylated uracil groups: Application of a ¹⁷O‐NMR test of H‐bonding

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Oxygen-17 and nitrogen-14 NMR studies of amide systems

Cited by 69 publications

References 5 publications

17O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

17O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

The system sulfur dioxide – N-methyl-2-pyrrolidinone

NMR of Terminal Oxygen. Part 14. Kinetically stabilized simple enols containing methylated uracil groups: Application of a 17O‐NMR test of H‐bonding

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¹⁷O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

¹⁷O‐nmr studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

NMR of Terminal Oxygen. Part 14. Kinetically stabilized simple enols containing methylated uracil groups: Application of a ¹⁷O‐NMR test of H‐bonding