Conformational analysis in carbohydrate chemistry. II. Equilibria between reducing sugars and their glycosidic anhydrides

1968 ◽  
Vol 21 (11) ◽  
pp. 2747 ◽  
Author(s):  
SJ Angyal ◽  
K Dawes
Keyword(s):  
Gas Chromatography ◽  
Conformational Analysis ◽  
Reducing Sugars ◽  
Interaction Energies ◽  
Carbohydrate Chemistry ◽  
Conformational Interaction ◽  
Good Agreement

The position of the equilibria between aldohexoses and 3-deoxyaldohexoses and their 1,6-anhydrides, and between heptuloses and their 2,7-anhydrides, has been determined by gas chromatography. The results are in good agreement with data calculated from conformational interaction energies. D-Talose gives equal amounts of the 1,6-anhydropyranose and the 1,6-anhydrofuranose. D-glycero-D-gulo-Heptose gives 66% of the 1,7- and only 9% of the 1,6-anhydride.

Conformational analysis in carbohydrate chemistry. I. Conformational free energies. The conformations and α : β ratios of aldopyranoses in aqueous solution

1968 ◽  
Vol 21 (11) ◽  
pp. 2737 ◽  
Author(s):  
SJ Angyal
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Conformational Analysis ◽  
Reasonable Agreement ◽  
Anomeric Effect ◽  
Interaction Energies ◽  
Free Energies ◽  
Carbohydrate Chemistry ◽  
Predominant Conformation

The relative free energies of the aldopyranoses in aqueous solution have been calculated, taking non-bonded interaction energies and the anomeric effect into account. It is shown that the calculated free-energy values correctly predict the predominant conformation of the α- and β-pyranose forms of each aldose. The α- to β-pyranose ratios of the aldoses in aqueous solution, calculated from these values, are in reasonable agreement with those determined experimentally.

Universal Gaussian basis functions in relativistic quantum chemistry: atomic Dirac–Fock–Coulomb and Dirac–Fock–Breit calculations

1992 ◽  
Vol 70 (6) ◽  
pp. 1822-1826 ◽  
Author(s):  
G. L. Malli ◽  
A. B. F. Da Silva ◽  
Yasuyuki Ishikawa
Keyword(s):  
Relativistic Quantum ◽  
Basis Set ◽  
Basis Sets ◽  
Interaction Energies ◽  
Gaussian Basis Sets ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field ◽  
Gaussian Basis Set ◽  
Good Agreement

Matrix Dirac–Fock–Coulomb and Dirac–Fock–Breit self-consistent field calculations are performed for a number of neutral atoms. He (Z = 2) through Xe (Z = 54), using the universal Gaussian basis set (18s, 12p, 11d) reported recently by Da Silva etal. The total Dirac–Fock–Coulomb, the Dirac–Fock–Breit, and the Breit interaction energies calculated with this universal Gaussian basis set are in good agreement with the corresponding values obtained by using an extensive well-tempered Gaussian basis set for the He through Ca (Z = 20) atoms. Although this universal Gaussian basis set is inadequate for the calculation of total Dirac–Fock–Coulomb and Dirac–Fock–Breit energies for the Kr, Sr, and Xe atoms, the Breit interaction energies calculated with this basis for these three atoms are in very good agreement with the corresponding Breit interaction energies obtained by using the extensive well-tempered Gaussian basis sets. Work is in progress to generate a more extensive and energetically better universal Gaussian basis set for He through Xe for its use in non-relativistic Hartree–Fock as well as Dirac–Fock self-consistent field calculations on polyatomics involving heavy atoms.

Filler-Elastomer Interactions. Part VI. Characterization of Carbon Blacks by Inverse Gas Chromatography at Finite Concentration

1992 ◽  
Vol 65 (5) ◽  
pp. 890-907 ◽  
Author(s):  
Meng-Jiao Wang ◽  
Siegfried Wolff
Keyword(s):  
Gas Chromatography ◽  
Energy Distribution ◽  
Inverse Gas Chromatography ◽  
General Trend ◽  
High Energy ◽  
Carbon Blacks ◽  
Finite Concentration ◽  
Good Agreement

Abstract Carbon blacks ranging from N110 to N990 were characterized by means of inverse gas chromatography at finite concentration. The isotherms, net heat, and spreading pressures for benzene and cyclohexane adsorption suggest a general trend of increasing surface activity with increases in specific surface area. This is in good agreement with surface-energy measurements reported previously. The energy-distribution function of adsorption shows that while the concentrations of low-energy sites are comparable for most of the carbon blacks, differences exist with regard to high-energy sites. These suggest that small-particle-size blacks possess a greater number of high-energy centers. The graphitization of carbon blacks results in a considerable reduction in their adsorption capacity and narrows the energy distribution of their surfaces. One can therefore conclude that high-energy sites play an important role in the determination of the surface energies and reinforcing ability of carbon blacks.

scholarly journals Conformational analysis in carbohydrate chemistry. V. Formation of glycosidic anhydrides from heptoses

1981 ◽  
Vol 59 (2) ◽  
pp. 379-383 ◽  
Author(s):  
Stephen John Angyal ◽  
Trung Quang Tran
Keyword(s):  
Conformational Analysis ◽  
Major Product ◽  
Carbohydrate Chemistry ◽  
Dioxane Ring

The position of the equilibrium between aldoheptoses and their glycosidic anhydrides depends crucially on the configuration of the heptose. Depending on that configuration, the 1,6-anhydropyranose, the 1,7-anhydropyranose, or the 1,6-anhydrofuranose is the major product, its proportion varying from 99% to less than 1%. The position of the equilibrium is predictable from conformational considerations. 1,7-Anhydrofuranoses have not been encountered. The 1,3-dioxane ring of the 1,7-anhydropyranoses was found to assume a skew form.

scholarly journals Anomeric modification of carbohydrates using the Mitsunobu reaction

2018 ◽  
Vol 14 ◽  
pp. 1619-1636 ◽  
Author(s):  
Julia Hain ◽  
Patrick Rollin ◽  
Werner Klaffke ◽  
Thisbe K Lindhorst
Keyword(s):  
Reducing Sugars ◽  
The Other ◽  
Mitsunobu Reaction ◽  
Carbohydrate Chemistry ◽  
Glycoside Synthesis ◽  
Glycosyl Phosphates ◽  
First Choice ◽  
The One ◽  
Hydroxy Groups ◽  
Anomeric Center

The Mitsunobu reaction basically consists in the conversion of an alcohol into an ester under inversion of configuration, employing a carboxylic acid and a pair of two auxiliary reagents, mostly triphenylphosphine and a dialkyl azodicarboxylate. This reaction has been frequently used in carbohydrate chemistry for the modification of sugar hydroxy groups. Modification at the anomeric position, leading mainly to anomeric esters or glycosides, is of particular importance in the glycosciences. Therefore, this review focuses on the use of the Mitsunobu reaction for modifications of sugar hemiacetals. Strikingly, unprotected sugars can often be converted regioselectively at the anomeric center, whereas in other cases, the other hydroxy groups in reducing sugars have to be protected to achieve good results in the Mitsunobu procedure. We have reviewed on the one hand the literature on anomeric esterification, including glycosyl phosphates, and on the other hand glycoside synthesis, including S- and N-glycosides. The mechanistic details of the Mitsunobu reaction are discussed as well as this is important to explain and predict the stereoselectivity of anomeric modifications under Mitsunobu conditions. Though the Mitsunobu reaction is often not the first choice for the anomeric modification of carbohydrates, this review shows the high value of the reaction in many different circumstances.

Zur Abscheidung von Methyljodid and Silberzeolithen / Investigations on the Fixation of Methyl Iodide by Silver Zeolites

1972 ◽  
Vol 27 (8-9) ◽  
pp. 1323-1328 ◽  
Author(s):  
C. Donner ◽  
T. Tamberg
Keyword(s):  
Gas Chromatography ◽  
Infrared Spectroscopy ◽  
Water Content ◽  
Methyl Iodide ◽  
Silver Ions ◽  
Reaction Products ◽  
Total Fixation ◽  
Heat Treated ◽  
Alkyl Iodides ◽  
Good Agreement

Abstract Alkyl iodides especially methyl iodide from the offgas of reactors and of reprocessing plants are difficult to remove.In earlier investigations it was shown that silver zeolites are qualified for a total fixation of methyl iodide, only when these sieves were exhaustively loaded with silver ions.In order to explain why only exhaustively loaded silver zeolites of type X are able to remove methyl iodide completely from the air, the reaction products from the chemisorption reaction were identified. The proportion of the silver ions that had reacted was calculated.Exhaustively loaded Ag-LMS-X pellets heat-treated at 400 °C (water content 0.94% by wt.) react with CH3I to form dimethylether.If the same pellets were gently dried with P2O5 (water content 15% by wt.) dimethylether and methanol were the products.The identification was done by gas chromatography and infrared spectroscopy.The chemisorption reaction can be described in the following way:a) CH3I + HOH+Ag+ →AgI + CH3OH + H+b) CH3I + CH3OH+Ag+ → AgI + CH3OCH3 + H+If only small concentrations of methyl-iodide and an excess of water vapour are present only methanol is expected.The experimental results are in good agreement with the assumptions.

scholarly journals Evaluation of Bionike One-Step Tests for the Detection of Drugs of Abuse in Urine

1997 ◽  
Vol 34 (1) ◽  
pp. 74-80 ◽  
Author(s):  
E R S Brown ◽  
D R Jarvie ◽  
D Simpson
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Drugs Of Abuse ◽  
Urine Samples ◽  
Gas Chromatography Mass Spectrometry ◽  
Site Testing ◽  
Immunoassay Technique ◽  
Or Groups ◽  
One Step ◽  
Good Agreement

Bionike one-step tests were used to screen urine samples for amphetamines, methamphetamines, benzodiazepines, cannabinoids, methadone and opiates, and results were compared with those obtained using enzyme multiplied immunoassay technique d.a.u. assays. Taking into consideration different threshold levels and possible differences in cross-reactivities, there was good agreement between the methods. Results of Bionike tests correlated well with amphetamines, methadone and opiates detected in urine using gas chromatography—mass spectrometry. Bionike methods are rapid, simple to use, and relatively inexpensive for on-site testing of individual drugs or groups of drugs in urine.

Implications of Monosaccharides in Sticky Cotton Processing

1976 ◽  
Vol 46 (5) ◽  
pp. 374-380 ◽  
Author(s):  
C. W. Roberts ◽  
H. S. Koenig ◽  
R. G. Merrill ◽  
P. S. R. Cheung ◽  
H. H. Perkins
Keyword(s):  
Gas Chromatography ◽  
Analytical Method ◽  
Reducing Sugars ◽  
Cotton Fibers ◽  
Processing History ◽  
Trimethylsilyl Derivatives ◽  
Growing Conditions ◽  
Derivatives Of ◽  
Semiquantitative Method ◽  
Soluble Components

The analytical method for gas chromatography of trimethylsilyl derivatives of the water-surfactant-soluble components and/or natural contaminants of cotton fibers was refined and utilized. Results of this semiquantitative method support the findings that content of reducing sugars is correlated with “stickiness” of cotton, and that growing conditions, processing history, and maturity of cotton directly affect the components present and their concentrations.

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