Dynamic Carbon-13 MAS NMR: Application to Benzene Ring Flips in Polyaryl Ethers

2000 ◽  
Vol 18 (1-4) ◽  
pp. 17-36 ◽  
Author(s):  
Detlef Reichert ◽  
Günter Hempel ◽  
Horst Schneider ◽  
Herbert Zimmermann ◽  
Zeev Luz
Keyword(s):  
Benzene Ring ◽  
Mas Nmr ◽  
Polyaryl Ethers

Electron Microscopic and Isozyme Study of a Case of Ochronosis

1972 ◽  
Vol 30 ◽  
pp. 88-89
Author(s):  
Jay W. Cha ◽  
Perry J. Melnick
Keyword(s):  
Benzene Ring ◽  
Enzyme System ◽  
Homogentisic Acid ◽  
Degenerative Changes ◽  
Acid Oxidase ◽  
Electron Microscopic ◽  
Tyrosine Metabolism ◽  
Collagenous Tissues

Hereditary ochronosis in very few cases has been examined electron microscopically or histochemically. In this disease homogentisic acid, a normal intermediary of tyrosine metabolism, forms in excessive amounts. This is believed to be due to absence or defective activity of homogentisic acid oxidase, an enzyme system necessary to break the benzene ring and to further break it down to fumaric and acetoacetic acids. Ochronotic pigment, a polymerized form of homogentisic acid, deposits mainly in mesenchymal tissues. There has been a question whether the pigment originates from the collagenous tissues, or deposits passively, where in contrast to melanin it induces degenerative changes.

A MAS NMR STUDY OF THE STRUCTURE OF AMORPHOUS ALUMINA FILMS

1985 ◽  
Vol 46 (C8) ◽  
pp. C8-113-C8-117 ◽  
Author(s):  
R. Dupree ◽  
I. Farnan ◽  
A. J. Forty ◽  
S. El-Mashri ◽  
L. Bottyan
Keyword(s):  
Mas Nmr ◽  
Alumina Films ◽  
Nmr Study ◽  
Amorphous Alumina

The Nature of Chemisorbed CO2 in Zeolite A

2019 ◽  
Author(s):  
Przemyslaw Rzepka ◽  
Zoltán Bacsik ◽  
Andrew J. Pell ◽  
Niklas Hedin ◽  
Aleksander Jaworski
Keyword(s):  
Solid State ◽  
Ir Spectroscopy ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Surface Coverage ◽  
Gas Mixtures ◽  
Mas Nmr ◽  
Significant Fraction ◽  
Zeolite A

Formation of CO<sub>3</sub><sup>2-</sup> and HCO<sub>3</sub><sup>-</sup> species without participation of the framework oxygen atoms upon chemisorption of CO<sub>2</sub> in zeolite |Na<sub>12</sub>|-A is revealed. The transfer of O and H atoms is very likely to have proceeded via the involvement of residual H<sub>2</sub>O or acid groups. A combined study by solid-state <sup>13</sup>C MAS NMR, quantum chemical calculations, and <i>in situ</i> IR spectroscopy showed that the chemisorption mainly occurred by the formation of HCO<sub>3</sub><sup>-</sup>. However, at a low surface coverage of physisorbed and acidic CO<sub>2</sub>, a significant fraction of the HCO<sub>3</sub><sup>-</sup> was deprotonated and transformed into CO<sub>3</sub><sup>2-</sup>. We expect that similar chemisorption of CO<sub>2</sub> would occur for low-silica zeolites and other basic silicates of interest for the capture of CO<sub>2</sub> from gas mixtures.

Pharmacologically potentials of different substituted coumarin derivatives

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Benzene Ring ◽  
Bioactive Compounds ◽  
Biological Activities ◽  
Pharmacological Properties ◽  
Coumarin Derivatives ◽  
Wide Range ◽  
Anti Oxidant ◽  
Anti Inflammatory ◽  
Coumarin Compounds

Coumarin and its derivatives are widely spread in nature. Coumarin goes to agroup as benzopyrones, which consists of a benzene ring connected to a pyronemoiety. Coumarins displayed a broad range of pharmacologically useful profile.Coumarins are considered as a promising group of bioactive compounds thatexhibited a wide range of biological activities like anti-microbial, anti-viral,antiparasitic, anti-helmintic, analgesic, anti-inflammatory, anti-diabetic, anticancer,anti-oxidant, anti-proliferative, anti-convulsant, and antihypertensiveactivities etc. The coumarin compounds have immense interest due to theirdiverse pharmacological properties. In particular, these biological activities makecoumarin compounds more attractive and testing as novel therapeuticcompounds.

Hosoya polynomials of general spiro hexagonal chains

Filomat ◽  
2014 ◽  
Vol 28 (1) ◽  
pp. 211-215 ◽  
Author(s):  
Xianyong Li ◽  
Xiaofan Yang ◽  
Guoping Wang ◽  
Rongwei Hu
Keyword(s):  
Organic Chemistry ◽  
Benzene Ring ◽  
Spiro Compounds

Spiro hexagonal chains are a subclass of spiro compounds which are an important subclass of Cycloalkynes in Organic Chemistry. This paper addresses general spiro hexagonal chains in which every hexagon represents a benzene ring, and establishes the formulae for computing the Hosoya polynomials of general spiro hexagonal chains.

Proximity and conformation effects in 29Si and 13C NMR spectra of di-ortho substituted trimethylsiloxybenzenes

1990 ◽  
Vol 55 (8) ◽  
pp. 2027-2032 ◽  
Author(s):  
Jan Schraml ◽  
Robert Brežný ◽  
Jan Čermák
Keyword(s):  
Benzene Ring ◽  
13C Nmr ◽  
Proximity Effect ◽  
Nmr Spectra ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Proximity Effects ◽  
13C Nmr Spectra ◽  
Methoxy Groups ◽  
C Nmr

29Si and 13C NMR spectra of five 4-substituted 2,6-dimethoxytrimethylsiloxybenzenes were studied with the aim to elucidate the nature of the deshielding proximity effects observed in the spectra of ortho substituted trimethylsiloxybenzenes. The sensitivity of 29Si chemical shifts to para substitution is in the studied compounds essentially the same as in mono ortho methoxytrimethylsiloxybenzenes. The deshielding proximity effect of the ìsecondî methoxy group is somewhat smaller than that of the ìfirstî group. The present results indicate that the two methoxy groups assume coplanar conformations with the benzene ring and are turned away from the trimethylsiloxy group which is not in the benzene plane. It is argued that in mono ortho methoxytrimethylsiloxybenzenes the two substituent groups adopt the same conformations as in the compounds studied here.

scholarly journals Sensitivity gains, linearity, and spectral reproducibility in nonuniformly sampled multidimensional MAS NMR spectra of high dynamic range

2014 ◽  
Vol 59 (2) ◽  
pp. 57-73 ◽  
Author(s):  
Christopher L. Suiter ◽  
Sivakumar Paramasivam ◽  
Guangjin Hou ◽  
Shangjin Sun ◽  
David Rice ◽  
...  
Keyword(s):  
Nmr Spectra ◽  
Dynamic Range ◽  
High Dynamic Range ◽  
Mas Nmr ◽  
High Dynamic
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