Spectroscopic studies of 2,6-dihydroxypyridine and some of its derivatives. Tautomerism in solution, and very strong hydrogen bonding in solid 2,6-dihydroxypyridine and its N-methylated derivative

1971 ◽  
Vol 24 (12) ◽  
pp. 2557 ◽  
Author(s):  
E Spinner ◽  
GB Yeoh
Keyword(s):  
Hydrogen Bonding ◽  
Solid State ◽  
Magnetic Resonance ◽  
Hydrogen Bonds ◽  
Proton Magnetic Resonance ◽  
Heavy Atom ◽  
Spectroscopic Studies ◽  
Macromolecular Structure ◽  
Present Evidence ◽  
Transmission Windows

Ultraviolet, infrared, and proton magnetic resonance spectra were measured for 2,6-dihydroxypyridine, 6-hydroxy-1-methylpyrid-2-one, α,α,γ-trichloro- and α,α,γ-tribromo-glutaconimide, with special reference to the hydroxypyridone-pyridinediol-glutaconimide equilibrium. The ratio [pyridol]/[pyridone] is much smaller for 2,6- dihydroxy-than for 6-methoxy-2-hydroxy-pyridine, especially in hydroxylic solvents. The hydroxypyridone form is the main or predominant tautomer for 2,6-dihydroxypyridine in water, dimethyl sulphoxide, ethanol, and 5% ethanol-95% cyclohexane, and for the 1- methylated derivative in ethanol. The glutaconimide form is the main or predominant tautomer for 2,6-dihydroxy-pyridine in dioxan, and for the 1-methylated derivative in water, dioxan, and chloroform. In the solid state 2,6-dihydroxypyridine and the 1-methylated derivative show a very broad intense infrared OH band with a plateau extending from c. 1300 cm-1 to, respectively, 800 and 450 cm-1, and with some transmission ?windows?; there is very strong hydrogen bonding, various aspects of which will be discussed. The solids probably consist of 6-hydroxypyrid- 2-one molecules linked by very short unsymmetrical hydrogen bonds; though, for the unmethylated compound, an alternative ?macromolecular? structure, consisting of units in which the heavy-atom skeletons have C2v symmetry, and are linked together by symmetrical hydrogen bonds, cannot be ruled out entirely on the present evidence.

THE INTERACTION OF SILICON TETRAFLUORIDE WITH METHANOL

1963 ◽  
Vol 41 (6) ◽  
pp. 1477-1484 ◽  
Author(s):  
J. P. Guertin ◽  
M. Onyszchuk
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Absorption Band ◽  
Hydrogen Bonds ◽  
Infrared Spectrum ◽  
Proton Magnetic Resonance ◽  
Methanol Solution ◽  
Silicon Tetrafluoride ◽  
Conductivity Measurements ◽  
Bond Stretching

Silicon tetrafluoride reacts with methanol in a 1:4 mole ratio, forming the complex SiF4.4CH3OH, which freezes to a glass at about −20° and is completely dissociated in the gaseous phase at 25°. Conductivity measurements show clearly that it is a very weak electrolyte in methanol solution. Its infrared spectrum does not contain an Si—O bond stretching absorption band. Proton magnetic resonance measurements provide strong evidence of hydrogen bonding between silicon tetrafluoride and methanol. These results indicate that the structure of the complex requires tetracovalent rather than hexacovalent silicon and strong hydrogen bonds between methanol and each of the four fluorine atoms.

scholarly journals Proton magnetic resonance spectroscopic studies using paramagnetics of primary and tertiary structure of proteins

1974 ◽  
Vol 40 (1-2) ◽  
pp. 83-92 ◽  
Author(s):  
J. H. Bradbury ◽  
L. R. Brown ◽  
M. W. Crompton ◽  
B. Warren
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Tertiary Structure ◽  
Spectroscopic Studies ◽  
Structure Of Proteins

scholarly journals Temperature-Dependent Solid-State NMR Proton Chemical-Shift Values and Hydrogen Bonding

2021 ◽  
Author(s):  
Alexander A. Malär ◽  
Laura A. Völker ◽  
Riccardo Cadalbert ◽  
Lauriane Lecoq ◽  
Matthias Ernst ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Hydrogen Bonding ◽  
Solid State ◽  
Chemical Shift ◽  
Hydrogen Bonds ◽  
Solid State Nmr ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Proton Chemical Shift ◽  
Temperature Dependent

Temperature-dependent NMR experiments are often complicated by rather long magnetic-field equilibration times, for example occurring upon a change of sample temperature. We demonstrate that the fast temporal stabilization of the magnetic field can be achieved by actively stabilizing the temperature which allows to quantify the weak temperature dependence of the proton chemical shift which can be diagnostic for the presence of hydrogen bonds. Hydrogen bonding plays a central role in molecular recognition events from both fields, chemistry and biology. Their direct detection by standard structure determination techniques, such as X-ray crystallography or cryo-electron microscopy, remains challenging due to the difficulties of approaching the required resolution, on the order of 1 Å. We herein explore a spectroscopic approach using solid-state NMR to identify protons engaged in hydrogen bonds and explore the measurement of proton chemical-shift temperature coefficients. Using the examples of a phosphorylated amino acid and the protein ubiquitin, we show that fast Magic-Angle Spinning (MAS) experiments at 100 kHz yield sufficient resolution in proton-detected spectra to quantify the rather small chemical-shift changes upon temperature variations.<br>

Solid-state oxygen-17 nuclear magnetic resonance spectroscopic studies of alkaline earth metasilicates

1987 ◽  
Vol 91 (5) ◽  
pp. 1054-1058 ◽  
Author(s):  
Hye Kyung C. Timken ◽  
Suzanne E. Schramm ◽  
R. James. Kirkpatrick ◽  
Eric. Oldfield
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Solid State ◽  
Magnetic Resonance ◽  
Alkaline Earth ◽  
Spectroscopic Studies ◽  
Nuclear Magnetic

scholarly journals Metabolic alterations in generalised anxiety disorder: a review of proton magnetic resonance spectroscopic studies

2017 ◽  
Vol 26 (6) ◽  
pp. 587-595 ◽  
Author(s):  
G. Delvecchio ◽  
J. A. Stanley ◽  
A. C. Altamura ◽  
P. Brambilla
Keyword(s):  
Anxiety Disorder ◽  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Spectroscopic Studies ◽  
Resonance Spectroscopy ◽  
Generalised Anxiety Disorder ◽  
Neural Basis ◽  
Comprehensive Overview ◽  
Neuropsychiatric Diseases ◽  
Dorsolateral Prefrontal

Generalised anxiety disorder (GAD) is a common psychiatric illness characterised by selective morpho-functional brain alterations. The breath of neuroimaging studies investigating the neural basis of GAD is extensive; however, its pathophysiology is still largely unknown. Specifically for proton Magnetic Resonance Spectroscopy (¹H MRS) investigations, which have the aim of identifying differences in metabolite levels between conditions in key brain areas, often showed contrasting results. Indeed, there are selected ¹H MRS studies reporting deficits of key metabolites in GAD patients; however, collectively the literature remains mixed with respect to consistency of major findings. In this review, we evaluate published ¹H MRS studies on GAD with the final aim of providing a comprehensive overview of the extent of neurometabolic dysfunctions associated with GAD. Interestingly, the majority of the studies reviewed showed altered metabolite levels in the dorsolateral prefrontal cortex and hippocampus suggesting regional specificity. These results also provide evidence of the utility of ¹H MRS not only for elucidating the pathophysiology of neuropsychiatric diseases, but also for the identification of more beneficial and targeted pharmacological interventions. Additionally, future studies are warranted to overcome methodological differences observed across the studies.

Solvent effects in ultraviolet spectral studies of hydrogen bonding between phenol and N,N-dimethylacetamide

1967 ◽  
Vol 45 (18) ◽  
pp. 2033-2038 ◽  
Author(s):  
F. Takahashi ◽  
W. J. Karoly ◽  
J. B. Greenshields ◽  
N. C. Li
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Complex Formation ◽  
Equilibrium Constant ◽  
Proton Magnetic Resonance ◽  
Mixed Solvent ◽  
Resonance Method ◽  
Spectral Studies ◽  
Magnetic Resonance Method ◽  
Hydrogen Bonded

Ultraviolet spectral studies of hydrogen bonding between phenol and N,N-dimethylacetamide (DMA) in several media are reported. The equilibrium constant for the formation of the phenol–DMA complex is strongly solvent dependent, varying from 295 1/mole in cyclohexane to 130 in CCl4 and 16 in CHCl3, all at 28°. The greatly reduced value in CHCl3 indicates that the measured equilibrium constant is only an apparent one which does not take into account the decrease in free DMA concentration resulting from hydrogen-bonded complex formation with the solvent acting as hydrogen donor. In CCl4/CHCl3 mixed solvent, in the range of [chloroform] = 0 to 1.227 M, the measured equilibrium constant, K′, varies linearly with K′ [chloroform]. The slope of the line corresponds to the equilibrium constant for the formation of the hydrogen-bonded complex between CHCl3 and DMA in CCl4. The value, 0.9 1/mole, agrees with that obtained from a proton magnetic resonance method. The agreement is particularly noteworthy when we consider that the concentrations of phenol used in the proton magnetic resonance and ultraviolet spectral methods differ by a factor of 200, which leads definitely to the conclusion that the hydrogen-bonded CHCl3–DMA complex formed is 1:1. In cyclohexane/CHCl3 mixed solvent, similar results are obtained.

Selective deshielding of aromatic protons in some ortho-substituted acetanilides

1968 ◽  
Vol 46 (15) ◽  
pp. 2593-2600 ◽  
Author(s):  
James R. Bartels-Keith ◽  
Ronald F. W. Cieciuch
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Solvent Effects ◽  
Proton Magnetic Resonance ◽  
Aromatic Proton ◽  
Intramolecular Hydrogen Bonding ◽  
Low Field ◽  
Intramolecular Hydrogen

Certain ortho-substituted acetanilides exhibit proton magnetic resonance signals at unusually low field for the amido proton and the aromatic proton adjacent to the acetamido group. This effect, explicable in terms of intramolecular hydrogen-bonding, has been observed for nitro, carbonyl, sulfamoyl, and sulfonyl substituents. Solvent effects are discussed.

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