scholarly journals Summation Solute Hydrogen Bonding Acidity Values for Hydroxyl Substituted Flavones Determined by NMR Spectroscopy

2013 ◽  
Vol 8 (1) ◽  
pp. 1934578X1300800 ◽  
Author(s):  
William L. Whaley ◽  
Ekua M. Okoso-amaa ◽  
Cody L. Womack ◽  
Anna Vladimirova ◽  
Laura B. Rogers ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Nmr Spectroscopy ◽  
Intramolecular Interactions ◽  
Hydroxyl Group ◽  
Accurate Estimation ◽  
Hydroxyl Groups ◽  
Linear Free Energy Relationship ◽  
Hydrogen Bond Donor ◽  
Linear Free Energy ◽  
Drug Molecules

The flavonoids are a structurally diverse class of natural products that exhibit a broad spectrum of biochemical activities. The flavones are one of the most studied flavonoid subclasses due to their presence in dietary plants and their potential to protect human cells from reactive oxygen species (ROS). Several flavone compounds also mediate beneficial actions by direct binding to protein receptors and regulatory enzymes. There is current interest in using Quantitative Structure Activity Relationships (QSARs) to guide drug development based on flavone lead structures. This approach is most informative when it involves the use of accurate physical descriptors. The Abraham summation solute hydrogen bonding acidity ( A) is a descriptor in the general solvation equation. It defines the tendency of a molecule to act as a hydrogen bond donor, or acid, when surrounded by solvent molecules that are hydrogen bonding acceptors, or bases. As a linear free energy relationship, it is useful for predicting the absorption and uptake of drug molecules. A previously published method, involving nuclear magnetic resonance (NMR) spectroscopy, was used to evaluate A for the monohydroxyflavones (MHFs). Values of A ranged from 0.02, for 5-hydroxyflavone, to 0.69 for 4′-hydroxyflavone. The ability to examine separate NMR signals for individual hydroxyl groups allowed the investigation of intramolecular interactions between functional groups. The value of A for the position 7 hydroxyl group of 7-hydroxyflavone was 0.67. The addition of a position 5 hydroxyl group (in 5,7-dihydroxyflavone) increased the value of A for the position 7 hydroxyl group to 0.76. Values of A for MHFs were also calculated by the program ACD-Absolve and these agreed well with values measured by NMR. These results should facilitate more accurate estimation of the values of A for structurally complex flavones with pharmacological activities.

scholarly journals Study on the Dissolution Mechanism of Cellulose by ChCl-Based Deep Eutectic Solvents

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 278 ◽  
Author(s):  
Heng Zhang ◽  
Jinyan Lang ◽  
Ping Lan ◽  
Hongyan Yang ◽  
Junliang Lu ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Oxalic Acid ◽  
Deep Eutectic Solvents ◽  
Solvent System ◽  
Hydroxyl Group ◽  
Regenerated Cellulose ◽  
Dissolution Mechanism ◽  
Hydroxyl Groups ◽  
Type I ◽  
Hydrogen Bond Donor

Four deep eutectic solvents (DESs), namely, glycerol/chlorocholine (glycerol/ChCl), urea/ChCl, citric acid/ChCl, and oxalic acid/ChCl, were synthesized and their performance in the dissolution of cellulose was studied. The results showed that the melting point of the DESs varied with the proportion of the hydrogen bond donor material. The viscosity of the DESs changed considerably with the change in temperature; as the temperature increased, the viscosity decreased and the electrical conductivity increased. Oxalic acid/ChCl exhibited the best dissolution effects on cellulose. The microscopic morphology of cellulose was observed with a microscope. The solvent system effectively dissolved the cellulose, and the dissolution method of the oxalic acid/ChCl solvent on cellulose was preliminarily analyzed. The ChCl solvent formed new hydrogen bonds with the hydroxyl groups of the cellulose through its oxygen atom in the hydroxyl group and its nitrogen atom in the amino group. That is to say, after the deep eutectic melt formed an internal hydrogen bond, a large number of remaining ions formed a hydrogen bond with the hydroxyl groups of the cellulose, resulting in a great dissolution of the cellulose. Although the cellulose and regenerated cellulose had similar structures, the crystal form of cellulose changed from type I to type II.

The Dielectic properties of Crystalline Alcohols containing sterically hindered Hydroxyl groups

1953 ◽  
Vol 6 (2) ◽  
pp. 104 ◽  
Author(s):  
RJ Meakins
Keyword(s):  
Hydrogen Bonding ◽  
Hydroxyl Group ◽  
Appreciable Amount ◽  
Hydroxyl Groups ◽  
Dipole Orientation ◽  
Hindered Rotation ◽  
Dielectric Absorption ◽  
Free Hydroxyl ◽  
Sterically Hindered ◽  
High Dielectric

It has been previously suggested that the high dielectric absorption of certain crystalline forms of long-chain alcohols is associated with hydrogen-bonding of the hydroxyl groups. This theory is supported by the results given in the present paper, which show that with other alcohols, in which the hydroxyl groups are sterically hindered, the loss is almost completely eliminated. The smallest losses are obtained with triphenylcarbinol and cholesterol which both possess hydroxyl groups embedded in a bulky molecular structure. For the former compound, infra-red data from the literature indicate the absence of any appreciable amount of hydrogen-bonding and are thus in agreement with the evidence from dielectric measurements. High frequency absorption observed in these compounds is considered to be associated with dipole orientation resulting from hindered rotation of the free hydroxyl groups. The effects of steric hindrance of the hydroxyl group are also observed in tert.-butanol.

Conformation of the esters of steroid hydroxyl groups by infrared spectroscopy

1969 ◽  
Vol 47 (9) ◽  
pp. 1601-1603 ◽  
Author(s):  
C. R. Narayanan ◽  
M. R. Sarma ◽  
T. K. K. Srinivasan ◽  
M. S. Wadia
Keyword(s):  
Hydrogen Bonding ◽  
Infrared Spectroscopy ◽  
Carbonyl Group ◽  
Hydroxyl Group ◽  
Spectral Studies ◽  
Hydroxyl Groups ◽  
Hydrogen Atoms ◽  
Infrared Spectral

Infrared spectral studies show that the carbonyl group of the esters of steroid hydroxyl groups are stabilized near the adjacent alkyl hydrogen atoms; this energy of stabilization appears to be more than that of hydrogen bonding between the carbonyl and a nearby hydroxyl group.

Alkaloids of the Australian Rutaceae: Melicope fareana. V. The Structure of the Alkaloids

1949 ◽  
Vol 2 (2) ◽  
pp. 282 ◽  
Author(s):  
WD Crow ◽  
JR Price
Keyword(s):  
Hydrogen Bonding ◽  
Oxygen Atom ◽  
Nitrous Acid ◽  
Degradation Products ◽  
Structural Formula ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Complete Structure ◽  
Methylenedioxy Group ◽  
Alternative Structures

Melicopine, melicopidine, and melicopicine are shown to be members of a new group of alkaloids derived from acridine. The structure of melicopicine, 1,2,3,4-tetramethoxy-10-methylacridone (II), is deduced from data reported in earlier papers. The presence of the same 10-methylacridone skeleton in melicopidine and melicopine is established by conversion of the trimethoxyphenols obtained from them by fission of the methylenedioxy ring with methanolic potash to the respective dimethoxy-o- and p-quinones previously prepared from melicopicine. This conversion also establishes the position of the methylenedioxy group in melicopine relative to the hydroxyl group in normelicopicine. Similar considerations applied to the ethoxydimethoxyphenols show the position of the methylenedioxy group in melicopidine relative to the hydroxyl group in normelicopicine, and in this case, lead to the complete structure for the alkaloid (XIII). The action of nitrous acid on normelicopine and normelicopidine gives two hydroxymethoxyquinones isomeric with that obtained by the action of sodium carbonate on the dimethoxy-o- and p-quinones. The same two hydroxymethoxyquinones also result from the action of caustic soda on the dimethoxy-o- and p-quinones respectively. Their structures, which can be deduced from the second method of preparation, confirm the positions of the methylenedioxy group in melicopine and melicopidine relative to the hydroxyl group of normelicopicine, and prove that the hydroxyl groups in normelicopine and normelicopidine are in the same position as that in normelicopicine, but they do not make possible a choice between alternative structures for melicopine. This choice depends on the position of the hydroxyl group of the noralkaloids relative to the remainder of the acridone molecule. By consideration of the mechanism of fission of the methylenedioxy ring, the hydroxyl group of the noralkaloids is shown to be situated peri to the acridone oxygen atom, i.e. at position 4. This is confirmed by the occurrence of hydrogen bonding. Consequently the complete structural formula for melicopine is XXIII. The properties of the alkaloids and a number of the degradation products are discussed.

Solvent Polarity, Hydrogen-Bonding and Solvophobicity Effects on the Nucleophilic Substitution of Benzenesulfonyl Chloride with Aniline in Aqueous and Non-Aqueous Solutions of Methanol

2011 ◽  
Vol 36 (4) ◽  
pp. 361-370 ◽  
Author(s):  
Ali Reza Harifi-Mood ◽  
Aazam Jafarinejad
Keyword(s):  
Ethyl Acetate ◽  
Solvent Polarity ◽  
Rate Coefficients ◽  
Linear Free Energy Relationship ◽  
Hydrogen Bond Donor ◽  
Factors Affecting ◽  
Linear Free Energy ◽  
Increasing Trend ◽  
Donor Ability ◽  
The Media

The reaction between benzensulfonyl chloride and aniline was studied in various compositions of methanol with ethyl acetate, propan-2-ol and water at 25° C. Second-order rate coefficients of this reaction were determined; those in pure solvents were in the order of water > methanol >propan-2-ol> ethyl acetate. Rates decreased sharply with the mole fraction of ethyl acetate in methanol- ethyl acetate mixtures and showed an increasing trend with water content in methanol-water mixtures. Linear free energy relationship regressions showed that the polarity, hydrogen-bond donor ability and hydrophobicity of the media were the main factors affecting the reaction rate coefficient.

Crystal structure of i -erythritol and its relationship to some derived d and l and racemic substances

1959 ◽  
Vol 250 (1262) ◽  
pp. 301-315 ◽  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Three Dimensional ◽  
Tetragonal Structure ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Main Structure ◽  
Hydrogen Bonded

Meso erythritol forms a tetragonal structure in which the molecules are centro-symmetric. Each α -hydroxyl group forms part of a tetragonal spiral of hydrogen bonds. These spirals alone are sufficient to link all the molecules of the crystal into a three-dimensional hydrogen-bonded complex. The β -hydroxyl groups of neighbouring molecules form closed circuits of four hydrogen bonds in a tetrahedron so flattened as to be almost a square. These closed circuits are also by themselves sufficient to link all molecules in the crystal into a three-dimensional complex. When some of the hydroxyl groups are replaced by fluorine atoms of approximately the same size, the main structure should be retained if sufficient hydrogen bonding is left. It is possible, therefore, to predict structures for meso , d , l and racemic forms of some of the fluoro-substituted derivatives. 2-deoxy-2-fluoro (±) erythritol has been examined and found to have the expected racemic structure. The possibility of forms transitional between dextro , racemic, and laevo , is discussed.

Recent Progress in Equilibrium Acidity Studies of Organocatalysts

Synlett ◽  
2019 ◽  
Vol 30 (17) ◽  
pp. 1940-1949 ◽  
Author(s):  
Zhen Li ◽  
Xin Li ◽  
Jin-Pei Cheng
Keyword(s):  
Hydrogen Bonding ◽  
High Accuracy ◽  
Heterocyclic Carbenes ◽  
Cinchona Alkaloids ◽  
Acid Catalysts ◽  
Hydrogen Bond Donor ◽  
Indicator Method ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Double Hydrogen

This account summarizes our recent work on the pK a scales of some frequently used organocatalysts, especially those of hydrogen-bond-donor catalysts and stronger Brønsted acid catalysts. Most of these pK a values were obtained by the Bordwell overlapping indicator method, which is known to provide high accuracy. Linear free-energy relationships associated with pK a values are discussed in relation to understanding of reaction mechanisms.1 Introduction2 Single Hydrogen-Bonding Donors2.1 Proline-Type Organocatalysts2.2 Cinchona Alkaloids Bearing a Hydrogen-Bonding Donor in the 6′-Position3 Double-Hydrogen-Bonding Donors3.1 Thioureas3.2 Squaramides3.3 BINOLs4 Stronger Brønsted Acids5 N-Heterocyclic Carbenes6 Summary and Outlook

scholarly journals Influence of Multiple & Cooperative Hydrogen Bonding on the Acidity of Polyhydroxylated Piperidines: Electron Density Topological Analysis

2021 ◽  
Author(s):  
Marjan Jebeli Javan
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Gas Phase ◽  
Topological Analysis ◽  
Three Dimensional ◽  
Solution Phase ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Gas Phase Acidity ◽  
Polarized Continuum Model

Abstract Hydrogen bonds are the presiding concepts for arranging the three-dimensional forms of biological molecules like proteins, carbohydrates and nucleic acids, and acts as guides for proton transfer reactions. Gas-phase acidity and pKa calculations in dimethyl sulfoxide on a line of polyhydroxylated piperidines specify that multiple hydrogen bonds lead to enhance acidities.The gas-phase acidity (GPA) of polyhydroxylated piperidines was investigated by MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) method. For each structure, varied primary and secondary hydroxyl groups were deprotonated. The natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses have also been used to realize the character of the hydrogen bonding interactions in these compounds. The results show by adding each hydroxyl group, ΔHacid in the gas phase (it becomes less endothermic) and pKa value in the solution phase was decreased. Therefore, intramolecular hydrogen bonds lead to enhance the acid strength. In both the gas phase and solution phase, the β-Nojrimycin-OH2 (β-1-OH2) was found to be the most acidic compound with calculated gas-phase acidity (GPA) of 349.4 kcal.mol-1 and the pKa value of 22.0 (8.0 pKa units more acidic than 1-propanol).It was also shown, applying the polarized continuum model (PCM), there is a superior linear correlation with the gas phase acidities (GPAs) of polyhydroxylated piperidines and their calculated pKa (DMSO) values.

Jahn-Teller Effect in Hexahydroxocuprate(II) Complexes

1995 ◽  
Vol 60 (9) ◽  
pp. 1429-1434
Author(s):  
Martin Breza
Keyword(s):  
Hydrogen Bonding ◽  
Quantum Chemical ◽  
Potential Surface ◽  
Hydroxyl Group ◽  
Chemical Calculation ◽  
Teller Distortion ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Extremal Values ◽  
Jahn Teller Distortion

Using semiempirical CNDO-UHF method the adiabatic potential surface of 2[Cu(OH)6]4- complexes is investigated. The values of vibration and vibronic constants for Eg - (a1g + eg) vibronic interaction attain extremal values for the optimal O-H distance. The Jahn-Teller distortion decreases with increasing O-H distance. The discrepancy between experimentally observed elongated bipyramid of [Cu(OH)6]4- in Ba2[Cu(OH)6] and the compressed one obtained by quantum-chemical calculation is explainable by hydrogen bonding of the axial hydroxyl group.

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