Échelles pKHB et enthalpique du pouvoir accepteur de liaison hydrogène de thioéthers, thiols et disulfures

2005 ◽  
Vol 83 (2) ◽  
pp. 138-145 ◽  
Author(s):  
Christian Laurence ◽  
Michel Berthelot ◽  
Karine Evain ◽  
Bertrand Illien
Keyword(s):  
Hydrogen Bond ◽  
Inductive Effect ◽  
Resonance Effect ◽  
Substituent Effects ◽  
Hydrogen Bond Acceptor ◽  
Frequency Shifts ◽  
Ir Spectrometry ◽  
Distinctive Features ◽  
Alkyl Groups ◽  
Polarizability Effect

The hydrogen bond acceptor (HBA) strength of 31 tetrahedral sulfur bases (thioethers, thiols, disulfides) has been measured by IR spectrometry from: (i) their 1:1 complexation constants with 4-fluorophenol in CCl4 at 25 °C (the pKHB scale); (ii) their HB enthalpies; and (iii) the frequency shifts, Δν(OH), of the ν(OH) band of 4-fluorophenol hydrogen bonded to sulfur. The comparison of the pKHB, ΔH°, and Δν(OH) scales points to their distinctive features. The HBA strength depends on: (i) the nature of the atomic site: oxygen bases are always stronger than sulfur bases, in agreement with the hard and soft acids and bases principle; (ii) the functionality of this atom (for sulfur bases: phosphine sulfur > thioamide > thioketone > thioether > thiol > isothiocyanate ~ disulfide); and (iii) the substituent effects on the function. The main substituent effects are: (i) the polarizability effect of alkyl groups; (ii) the field-inductive effect; (iii) the resonance effect; and (iv) the cyclization effect, which changes the percentage of the s character of sulfur lone pairs. In addition to the attachment to the sulfur atom, IR spectra show the attachment of 4-fluorophenol to the chlorine of MeSCH2Cl and MeSCH2CH2Cl, and the interaction to the π cloud of PhSMe, Ph2S, PhCH2SMe, and EtSCH=CH2. Key words: hydrogen bond, thioethers, thiols, disulfides, pKHB scale.

scholarly journals Substituent effects of nitro group in cyclic compounds

2020 ◽  
Vol 32 (1) ◽  
pp. 179-203 ◽  
Author(s):  
Anna Jezuita ◽  
Krzysztof Ejsmont ◽  
Halina Szatylowicz
Keyword(s):  
Nitro Group ◽  
System Analysis ◽  
Inductive Effect ◽  
Resonance Effect ◽  
Substituent Effects ◽  
Electron Delocalization ◽  
High Electron ◽  
Aromatic Character ◽  
Substituent Constants ◽  
Cyclic Compounds

AbstractNumerous studies on nitro group properties are associated with its high electron-withdrawing ability, by means of both resonance and inductive effect. The substituent effect of the nitro group may be well described using either traditional substituent constants or characteristics based on quantum chemistry, i.e., cSAR, SESE, and pEDA/sEDA models. Interestingly, the cSAR descriptor allows to describe the electron-attracting properties of the nitro group regardless of the position and the type of system. Analysis of classical and reverse substituent effects of the nitro group in various systems indicates strong pi-electron interactions with electron-donating substituents due to the resonance effect. This significantly affects the pi-electron delocalization of the aromatic ring decreasing the aromatic character, evidenced clearly by HOMA values. Use of the pEDA/sEDA model allows to measure the population of electrons transferred from the ring to the nitro group.

scholarly journals Synthesis and investigation of solvent effects on the ultraviolet absorption spectra of 1, 3-bis-substituted-5, 5-dimethylhydantoins

2003 ◽  
Vol 68 (10) ◽  
pp. 699-706 ◽  
Author(s):  
Gordana Uscumlic ◽  
Abdulbaseta Kshad ◽  
Dusan Mijin
Keyword(s):  
Hydrogen Bond ◽  
Absorption Spectra ◽  
Electronic Absorption Spectra ◽  
Alkyl Halide ◽  
Substituent Effects ◽  
Solvent Polarity ◽  
Hydrogen Bond Donor ◽  
Hydrogen Bond Acceptor ◽  
Isolation Techniques ◽  
Energy Relationships

A series of 1,3-bis-substituted-5,5-dimethylhydantoins was synthesized using the reaction of 5,5-dimethylhydantoin with the corresponding alkyl halide in the presence of trimethylamine as catalyst and sodium hydroxide, according to a modified literature procedure. The experimental investigation included modification of the synthetic procedure in terms of starting materials solvent, temperature, isolation techniques, as well as purification and identification of the products. The absorption spectra of the 1,3-bis-substituted-5,5-dimethylhydantoins were recorded in twelve solvents in the range 200?400 nm. The effects of the solvent polarity and hydrogen bonding on the absorption spectra were interpreted by means of linear solvation energy relationships using a general equation of the form ? = ?0 s?* + a? + b? and by two-parameter models presented by the equation ? = ?0 s?* + a?, where ?* is a measure of the solvent polarity/polarisability, ? is the scale of the solvent hydrogen bond donor acidities and ? is the scale of the solvent hydrogen bond acceptor basicities. The solvent and substituent effects on the electronic absorption spectra of the investigated hydantoins is discussed.

Dielectric enrichment in binary solvent mixtures. The intramolecular hydrogen bond in N-alkyl-substituted o-nitroanilines. Substituent effects

1992 ◽  
Vol 70 (10) ◽  
pp. 2677-2682 ◽  
Author(s):  
Rosa Cattana ◽  
Juana J. Silber ◽  
Jorge Anunziata
Keyword(s):  
Hydrogen Bond ◽  
Intramolecular Hydrogen Bond ◽  
Preferential Solvation ◽  
Substituent Effects ◽  
Solvent Mixture ◽  
Binary Solvent ◽  
Solvent Mixtures ◽  
Hydrogen Bond Acceptor ◽  
Intramolecular Hydrogen ◽  
Strong Intramolecular Hydrogen Bond

In this work we report solvatochromism studies on o-nitroaniline and several N-alkyl-o-nitroaniline derivatives used as solutes in solvent mixtures of an "inert" nonpolar cosolvent, cyclohexane, and THF as a solvent with hydrogen bond acceptor ability. These studies allowed us to establish the competition between inter- and intramolecular hydrogen bond in solutes. This was done by comparing the magnitude of the local inhomogeneity induced by the solute-in-solvent mixture, that is, "preferential solvation," using Suppan's dielectric enrichment model as modified by us to be applied to electronic transitions. Since preferential solvation accounts for dielectric as well as specific interactions while dielectric enrichment only for the former, it was shown by comparison that it is possible to separate both effects and even quantify them. It was deduced that N-alkyl-o-nitroanilines form a strong intramolecular hydrogen bond, which remains unbroken even in polar solvents and hydrogen bond acceptors such as dimethyl sulfoxide. This was also confirmed by solvatochromic studies in pure solvents. On the other hand, a symmetrical dependence of the effects of alkyl substituents and solvents on the shifts of the absorption spectra was observed.

Effects of Substituents on the Barriers to Rotation in Phenyl and Benzyl Carbamates

1986 ◽  
Vol 39 (3) ◽  
pp. 457 ◽  
Author(s):  
C Yamagami ◽  
N Takao ◽  
Y Takeuchi
Keyword(s):  
Free Energy ◽  
Steric Effect ◽  
Inductive Effect ◽  
Resonance Effect ◽  
Substituent Effects ◽  
Energy Of Activation ◽  
Resonance Effects ◽  
Free Energy Of Activation

The free energy of activation for rotation about the C-N bond (ΔG‡Tc) in substituted phenyl and benzyl N,N- dimethylcarbamates was determined by the 13C dynamic n.m.r. method. The ΔG‡Tc value depended linearly on Hammett's σ with positive p. We have separated the substituent effects into inductive and resonance effects by using dual substituent parameter ( d.s.p .) analysis, and found that the resonance effect is more important than the inductive effect for para derivatives, and vice versa for meta derivatives. General trends of electronic substituent effects on barriers to rotation in carbamates and structurally related amides are also discussed. The ortho steric effect was small.

Hydrogen-Bond Acceptor and Donor Properties of Divalent Sulfur (Y-S-Z and R-S-H)

1997 ◽  
Vol 53 (4) ◽  
pp. 696-701 ◽  
Author(s):  
F. H. Allen ◽  
C. M. Bird ◽  
R. S. Rowland ◽  
P. R. Raithby
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Ab Initio ◽  
Bond Formation ◽  
Hydrogen Bond Acceptor ◽  
Similar Frequency ◽  
Alkyl Groups ◽  
Donor Ability ◽  
Structural Database ◽  
Divalent Sulfur

The hydrogen-bond acceptor ability of divalent sulfur in Y—S—Z systems, Y, Z= C, N, O or S, and the donor ability of thiol S—H have been studied using crystallographic data retrieved from the Cambridge Structural Database. Of 1811 Y—S—Z substructures that co-occur with N—H or O—H donors, only 86 (4.75%) form S...H—N,O bonds within S...H < 2.9 Å. In dialkylthioethers, the frequency of S...H bond formation is 6.24%, but drops below 3% when the alkyl groups are successively replaced by Csp 2 centres. This parallels an increasing \delta-positivity of S as calculated using ab initio methods. A similar frequency trend is observed for O...H—N,O bond formation by analogous oxyethers. Mean intermolecular >S...H distances for O—H [2.67 (3) Å] and N—H [2.75 (2) Å] donors (with H positions normalized to neutron values) are ca 0.25 Å longer than in C=S...H—N,O systems, indicative of very weak hydrogen bonding to >S. Intramolecular >S...H are slightly more frequent (8.56%), with S...H slightly shorter than for the intermolecular case. In contrast, 26 (70.3%) out of 37 S—H donors that co-occur with suitable acceptors form X...H—S bonds. The C=O...H—S system is predominant with a mean O...H distance of 2.34 (4) Å, considerably longer (weaker) than in C=O...H—O systems.

Principal component analysis of substituent constants

1990 ◽  
Vol 55 (1) ◽  
pp. 55-62 ◽  
Author(s):  
Drahomír Hnyk
Keyword(s):  
Principal Component Analysis ◽  
Inductive Effect ◽  
Resonance Effect ◽  
Principal Component ◽  
Component Analysis ◽  
Total Variance ◽  
Data Matrix ◽  
Cumulative Proportion ◽  
Two Factors ◽  
Substituent Constants

The principal component analysis has been applied to a data matrix formed by 7 usual substituent constants for 38 substituents. Three factors are able to explain 99.4% cumulative proportion of total variance. Several rotations have been carried out for the first two factors in order to obtain their physical meaning. The first factor is related to the resonance effect, whereas the second one expresses the inductive effect, and both together describe 97.5% cumulative proportion of total variance. Their mutual orthogonality does not directly follow from the rotations carried out. With the help of these factors the substituents are divided into four main classes, and some of them assume a special position.

Chemometric Analysis of Substituent Effects. VII. Inductive Effect as a Basic Substituent Effect. Isoeffect Substituent Constant

1995 ◽  
Vol 60 (8) ◽  
pp. 1316-1332 ◽  
Author(s):  
Oldřich Pytela ◽  
Aleš Halama
Keyword(s):  
Inductive Effect ◽  
Chemical Shifts ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Intersection Point ◽  
Chemometric Analysis ◽  
Reaction Centre ◽  
Substituent Constant ◽  
Modified Method ◽  
Substituted Benzoic Acids

The paper deals with chemometric analysis of the inductive effect. The notion of inductive effect is discussed, and unambiguous definitions are given for the notions of triad: reaction centre-basic skeleton-substituent, and the therewith connected definitions of inductive effect. For a quantitative description of inductive effect 7 types of chemical models were selected including noncyclic compounds, cyclic, and bicyclic compounds, derivatives of quinuclidine, 3-substituted benzoic acids, sulfonamides and pyridines. Altogether 139 sets of experimental data from literature have been used including altogether 1 294 points (9.3 points per set, 5 points at least) reflecting substituent effects of 34 substituents. It has been found that for a standard model the dissociation of substituted bicycloalkanecarboxylic acids only is satisfactory, all the other models reflecting also the mesomeric effects to variable extent (up to 10%). A distinctly different substitution behaviour was observed with 19F and 13C NMR chemical shifts of 4-substituted 1-fluoro- or 1-methylbicyclo[2.2.2]octanes. The earlier suggested model of substituent effects based on different way of transmission of substituent effects (3 classes) has been used for separating the inductive and mesomeric effects: it is mathematically presented as a set of straight lines with the intersection point at the so-called isoeffect substituent constant. Using the modified method of conjugated deviations a chemometric scale has been created for the inductive effect which agrees very well with the conventional scales given in literature; the only differences were observed for F and CH=O substituents (which are overestimated and underestimated, respectively, in literature). In the context given the inductive effect appears as a fundamental quantity forming a basis for quantitative description of other effects transferred by electrons.

scholarly journals Identification of Novel Cathepsin B Inhibitors with Implications in Alzheimer’s Disease: Computational Refining and Biochemical Evaluation

Cells ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1946
Author(s):  
Nitin Chitranshi ◽  
Ashutosh Kumar ◽  
Samran Sheriff ◽  
Veer Gupta ◽  
Angela Godinez ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Hydrogen Bond ◽  
Virtual Screening ◽  
Cathepsin B ◽  
Amyloid Β ◽  
Proteolytic Degradation ◽  
Hydrogen Bond Acceptor ◽  
Starting Point ◽  
The Brain

Amyloid precursor protein (APP), upon proteolytic degradation, forms aggregates of amyloid β (Aβ) and plaques in the brain, which are pathological hallmarks of Alzheimer’s disease (AD). Cathepsin B is a cysteine protease enzyme that catalyzes the proteolytic degradation of APP in the brain. Thus, cathepsin B inhibition is a crucial therapeutic aspect for the discovery of new anti-Alzheimer’s drugs. In this study, we have employed mixed-feature ligand-based virtual screening (LBVS) by integrating pharmacophore mapping, docking, and molecular dynamics to detect small, potent molecules that act as cathepsin B inhibitors. The LBVS model was generated by using hydrophobic (HY), hydrogen bond acceptor (HBA), and hydrogen bond donor (HBD) features, using a dataset of 24 known cathepsin B inhibitors of both natural and synthetic origins. A validated eight-feature pharmacophore hypothesis (Hypo III) was utilized to screen the Maybridge chemical database. The docking score, MM-PBSA, and MM-GBSA methodology was applied to prioritize the lead compounds as virtual screening hits. These compounds share a common amide scaffold, and showed important interactions with Gln23, Cys29, His110, His111, Glu122, His199, and Trp221. The identified inhibitors were further evaluated for cathepsin-B-inhibitory activity. Our study suggests that pyridine, acetamide, and benzohydrazide compounds could be used as a starting point for the development of novel therapeutics.

On the potential role of the amino nitrogen atom as a hydrogen bond acceptor in macromolecules

1998 ◽  
Vol 279 (5) ◽  
pp. 1123-1136 ◽  
Author(s):  
Ben Luisi ◽  
Modesto Orozco ◽  
Jiri Sponer ◽  
Francisco J Luque ◽  
Zippora Shakked
Keyword(s):  
Hydrogen Bond ◽  
Nitrogen Atom ◽  
Potential Role ◽  
Amino Nitrogen ◽  
Hydrogen Bond Acceptor ◽  
Amino Nitrogen Atom
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