Halonium ion rearrangements. Temperature-dependent carbon-13 chemical shifts as indicators of equilibriums between cyclic halonium ions and open carbonium ions

1973 ◽  
Vol 95 (22) ◽  
pp. 7449-7457 ◽  
Author(s):  
P. Mark. Henrichs ◽  
Paul E. Peterson
Keyword(s):  
Chemical Shifts ◽  
Temperature Dependent ◽  
Carbonium Ions ◽  
Halonium Ion

Nuclear magnetic resonance studies. III. Rotational isomerism of some C-glucosylflavonoid acetates

1965 ◽  
Vol 18 (5) ◽  
pp. 715 ◽  
Author(s):  
RA Eade ◽  
WE Hillis ◽  
DHS Horn ◽  
JJH Simes
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Steric Hindrance ◽  
Chemical Shifts ◽  
Rotational Isomerism ◽  
Bulky Substituent ◽  
Temperature Dependent ◽  
Magnetic Resonance Studies ◽  
Rotational Isomers ◽  
Nuclear Magnetic

The temperature-dependent variations in the spectra of certain C-glucosyl-flavonoid acetates are attributed to the effect of steric hindrance of bulky substituent groups of the sugar and aromatic moieties on the rate of interconversion of the two rotational isomers present. The differences in the chemical shifts of the protons of the two isomers are attributed to differences in the orientation and position of the acetyl and phenyl groups.

scholarly journals Influence of urea on methyl $$\upbeta$$-D-glucopyranoside in alkali at different temperatures

Cellulose ◽  
2019 ◽  
Vol 26 (18) ◽  
pp. 9413-9422 ◽  
Author(s):  
Maria Gunnarsson ◽  
Merima Hasani ◽  
Diana Bernin
Keyword(s):  
Conformational Changes ◽  
Chemical Shifts ◽  
Regenerated Cellulose ◽  
Temperature Dependent ◽  
Hydroxymethyl Group ◽  
Overhauser Effect ◽  
Specific Manner ◽  
Acting Mechanism ◽  
Different Temperatures ◽  
Dissolution Efficiency

Abstract The dissolution efficiency plays an important role on the properties of regenerated cellulose-based products. Urea is known to be one of the additives aiding to improve cellulose dissolution in the NaOH(aq) system. The acting mechanism caused by urea has been debated and one of the hypothesis is that urea could induce a conformational change on cellulose, which promotes dissolution. Here we used NMR spectroscopy on a model system for cellulose, namely, methyl $$\upbeta$$β-D-glucopyranoside ($$\upbeta$$β-MeO-Glcp) and compared chemical shifts and J couplings, which both are indicators for conformational changes, as a function of temperature and upon the addition of urea. We found that in NaOH(aq), the hydroxymethyl group changes its conformation in favour of the population of the gt rotamer, while the presence of urea induced temperature dependent conformational changes. Heteronuclear Overhauser effect experiments showed that urea associates with cellulose but in a non-specific manner. This suggests that urea rather than binding to the carbohydrate, changes the chemical environment inducing a change in conformation of $$\upbeta$$β-MeO-Glcp and likely also for cellulose when dissolved in NaOH(aq) with urea.

Detection of myoglobin desaturation in Mirounga angustirostris during apnea

2002 ◽  
Vol 282 (1) ◽  
pp. R267-R272 ◽  
Author(s):  
Paul J. Ponganis ◽  
Ulrike Kreutzer ◽  
Napapon Sailasuta ◽  
Torre Knower ◽  
Ralph Hurd ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Elephant Seal ◽  
Metabolic Responses ◽  
Conformational Heterogeneity ◽  
Mirounga Angustirostris ◽  
Oxygen Regulation ◽  
Temperature Dependent ◽  
H Nmr ◽  
State Study

1H NMR solution-state study of elephant seal ( Mirounga angustirostris) myoglobin (Mb) and hemoglobin (Hb) establishes the temperature-dependent chemical shifts of the proximal histidyl NδH signal, which reflects the respective intracellular and vascular Po 2 in vivo. Both proteins exist predominantly in one major isoform and do not exhibit any conformational heterogeneity. The Mb and Hb signals are detectable in M. angustirostris tissue in vivo. During eupnea M. angustirostris muscle maintains a well-saturated MbO2. However, during apnea, the deoxymyoglobin proximal histidyl NδH signal becomes visible, reflecting a declining tissue Po 2. The study establishes a firm methodological basis for using NMR to investigate the metabolic responses during sleep apnea of the elephant seal and to secure insights into oxygen regulation in diving mammals.

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