Effect of solvent and anion upon the proton magnetic resonance spectrum of the 1-methylpyridinium ion

1968 ◽  
Vol 46 (17) ◽  
pp. 2787-2791 ◽  
Author(s):  
W. F. Reynolds ◽  
U. R. Priller
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Proton Magnetic Resonance Spectrum ◽  
Concentrated Solutions ◽  
Nonpolar Medium ◽  
Ion Proton ◽  
Acetonitrile Solutions ◽  
Proton Chemical Shifts ◽  
Pyridinium Ion

The proton magnetic resonance spectra of 1-methylpyridinium bromide and iodide have been measured over a range of concentrations in different solvents. It is found that, with the exception of acetonitrile solutions, the infinite dilution chemical shifts are related to solvent dielectric constant. Extrapolated shifts for a nonpolar medium agree with previously calculated chemical shifts for the pyridinium ion. Proton chemical shifts in concentrated solutions are affected by cation–anion interactions. These interactions are interpreted in terms of ion pair formation.

Self Association of Folic Acid in Aqueous Solution by Proton Magnetic Resonance

1972 ◽  
Vol 50 (14) ◽  
pp. 2357-2363 ◽  
Author(s):  
Yui-Fai Lam ◽  
George Kotowycz
Keyword(s):  
Aqueous Solution ◽  
Folic Acid ◽  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Disodium Salt ◽  
Intermolecular Association ◽  
Self Association ◽  
Hydrophobic Portion ◽  
Proton Chemical Shifts

Proton magnetic resonance experiments on the disodium salt of folic acid in aqueous solutions (pD 7.1) indicate that the folate ion exists in an unfolded, extended conformation in solution. However, based on a temperature and concentration dependence of the proton chemical shifts, folate ions are involved in intermolecular association consisting of a vertical stacking interaction. A stacking model is proposed for the association with the hydrophilic ends of the molecule alternating in orientation with respect to the hydrophobic portion of the neighboring molecules.

CONFORMATIONAL EQUILIBRIA IN DIETHYL KETONE

1961 ◽  
Vol 39 (11) ◽  
pp. 2214-2224 ◽  
Author(s):  
R. Norman Jones ◽  
K. Noack
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Chemical Shifts ◽  
Variable Temperature ◽  
Proton Magnetic Resonance Spectrum ◽  
Diethyl Ketone ◽  
Conformational Isomers ◽  
Significant Chemical ◽  
Thickness Variable

A variable-thickness, variable-temperature absorption cell, modified from the design of Holden, Taylor, and Johnston, has been used to compare the infrared spectrum of diethyl ketone at −75° and +25 °C. The Raman spectrum of diethyl ketone has also been measured at +6°, +25°, and +85 °C, and the proton magnetic resonance spectrum over the range −61° to 104 °C.Both the infrared and Raman spectra exhibit pronounced temperature sensitivity, which is attributed to the presence of at least two conformational isomers in the liquid phase. Possible structures for these isomers are considered. Small but significant chemical shifts are noted in the proton magnetic resonance spectrum.

Determination of the molecular conformation of uridine in aqueous solution by proton magnetic resonance spectroscopy. Comparison with β-pseudouridine

1970 ◽  
Vol 48 (18) ◽  
pp. 2866-2870 ◽  
Author(s):  
Barry J. Blackburn ◽  
Arthur A. Grey ◽  
Ian C. P. Smith ◽  
Frank E. Hruska
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Molecular Conformation ◽  
Chemical Shifts ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Complete Analysis ◽  
Resonance Spectroscopy ◽  
Proton Coupling ◽  
Anti Conformation

A complete analysis of the 220 MHz proton magnetic resonance spectrum of aqueous uridine is reported. From the data a model for the molecular conformation is presented and compared with that of β-pseudouridine. It is concluded that in both compounds the ribose rings are in rapid equilibrium between classical puckered structures. The temperature-independence of the ribose proton coupling constants and chemical shifts suggests that all the conformers involved in this equilibrium have very similar energies. Both compounds exhibit a preference for the gauche–gauche rotamer about the exocyclic 4′—5′ bond; this conclusion is shown to be independent of the parameters in the Karplus equation or the energy minima chosen for the rotamers. The anti conformation of the uracil base is shown to exist in both compounds. It is proposed that the special structural significance of β-pseudouridine in transfer RNA must be due to the potential hydrogen bond that may be formed by the nitrogen atom at position one in uracil.

Proton magnetic resonance spectra of Trichosporon aculeatum mannan and its borate complex and their relationship to chemical structure

1968 ◽  
Vol 46 (13) ◽  
pp. 2305-2310 ◽  
Author(s):  
P. A. J. Gorin ◽  
M. Mazurek ◽  
J. F. T. Spencer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Chemical Structure ◽  
Chemical Shifts ◽  
Periodate Oxidation ◽  
Proton Magnetic Resonance Spectrum ◽  
Chemical Structures ◽  
Borate Complex ◽  
Structural Differences ◽  
Borate Complexes

Methylation–fragmentation and periodate oxidation studies show that the mannan of Trichosporon aculeatum is branched with 2-O and 6-O-monosubstituted units and 2,6-di-O-substituted D-mannopyranosyl units. It contains up to five consecutive α-D-(1 → 2)-linkages. The proton magnetic resonance spectrum of the mannan (recorded in D2O at 70° using a VananHA-100 spectrometer) indicates structural differences from other yeast mannans. It contains four distinct H-1 signals, but more than four H-1 environments are present since addition of sodium tetraborate shifts two signals downfleld so that six signals are observed (Fig. 1). Two of the four signals in the mannan spectrum at τ 4.40, and τ 4.20 can be assigned to chemical structures. The former signal arises from nonreducing end units attached to the 2-positions of adjacent mannopyranose units and from 2,6-di-O-substituted units and the latter from 2-O-substituted mannopyranose units. These assignments are based on the above chemical evidence, comparison with H-1 chemical shifts of known compounds, and the magnitudes of the H-1 shifts on borate addition. Downfleld shifts of H-1 proton signals on borate addition to known mannopyranosides vary from a maximum with compounds that can form 2,3-borate complexes to virtually none with 2-O-substituted derivatives. The magnitude of the downfleld shifts observed with α-D-linked mannopyranose derivatives is greater than that of their β-linked counterparts.

Sign in / Sign up

Export Citation Format

Share Document