scholarly journals Proton transfer equilibria, temperature and substituent effects on hydrogen bonded complexes between chloranilic acid and anilines

2000 ◽  
Vol 14 (3) ◽  
pp. 99-107 ◽  
Author(s):  
Gamal A. Gohar ◽  
Moustafa M. Habeeb
Keyword(s):  
Hydrogen Bond ◽  
Complex Formation ◽  
Proton Transfer ◽  
Equilibrium Constants ◽  
Bond Formation ◽  
Substituent Effects ◽  
Substituted Anilines ◽  
Chloranilic Acid ◽  
Hydrogen Bond Formation ◽  
Linear Relationships

The proton transfer equilibrium constants (KPT) for 1 : 1 complex formation between Chloranilic Acid (CA) and a series ofp- andm‒substituted anilines have been measured in 1,4-dioxane spectrophotometrically. The results supported the concept of amine-solvent hydrogen bond formation (short range solvation effect). Beside, this effect, theKPTvalues were apparently affected by the electron donation power of the aniline ring substituent, which was transmitted to the interaction center via resonance and inductive effects. Linear relationships betweenKPTand σ-Hammett substituent constants, or pKvalues formandpanilines,were obtained verifying the above conclusions. The solute-solvent hydrogen bond formation might increase the reactivity of the aniline nitrogen than would the inductive effect of the alkyl group, in case of CA-N-alkyl aniline complexes. The thermodynamic parameters for the proton transfer complex formation were estimated and it was indicated that the solvent–aniline hydrogen bond formation was preferred in the case ofp-substituted aniline complexes more than in the case of the correspondingm‒isomer. It has been found that the proton transfer process was enthalpy and entropy controlled.

scholarly journals Excited-state intramolecular proton transfer in a bioactive flavonoid provides fluorescence observables for recognizing its engagement with target proteins

2019 ◽  
Vol 18 (9) ◽  
pp. 2270-2280 ◽  
Author(s):  
Davide Vanossi ◽  
Monica Caselli ◽  
Giorgia Pavesi ◽  
Chiara Borsari ◽  
Pasquale Linciano ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Excited State ◽  
Proton Transfer ◽  
Bond Formation ◽  
Intermolecular Hydrogen Bond ◽  
Intramolecular Proton Transfer ◽  
Hydrogen Bond Formation ◽  
Target Proteins ◽  
Emission Properties

Intra- vs. intermolecular hydrogen-bond formation and ESIPT in a bioactive flavonoid result in different emission properties and provide a clue for recognizing its binding to target proteins.

Stabilities in the gas phase of the hydrogen bonded complexes, YC6H4OH-X−, of substituted phenols, YC6E4OH, with the halide anions X− (Cl−, Br−, I−)

1990 ◽  
Vol 68 (11) ◽  
pp. 2070-2077 ◽  
Author(s):  
Gary J. C. Paul ◽  
Paul Kebarle
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Proton Transfer ◽  
Gas Phase ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Closed Shell ◽  
Bond Energies ◽  
Substituted Phenols ◽  
Hydrogen Bonded

The equilibria, YPhOH + Br− = YPhOH-Br−, involving 26 differently substituted phenols, were determined with a pulsed high pressure mass spectrometer. The −ΔG0 evaluated from the equilibrium constants represent the hydrogen bond free energies in YPhOH-Br−. These data and data for X− = Cl− and I−, determined previously in this laboratory, are used to examine the substituent effects on the hydrogen bonding. It was found that the hydrogen bond energies in YPhOH-X− increase approximately linearly with the gas phase acidities of the phenols, YPhOH. This is in agreement with earlier observations that showed the bond energies in AH-B−, where AH were oxygen and nitrogen acids and B− closed shell anions, increase with increasing acidity of AH.A detailed analysis of the substituent effects, which is possible for YPhOH-X−, shows that the relationship with the acidity of AH can be divided into two parts. One is the increasing extent of actual proton transfer from AH on formation of the hydrogen bonded complex. Such proton transfer occurs in YPhOH-X− only for the series X− = Cl−. The second effect, which occurs for Cl− and is dominant for Br− and I−, is not directly related to the acidity of the phenols (or AH in general) but depends on a similarity of the substituent effects on the acidity and the stabilization of YPhOH-X− (or AH-B− in general). The dominant contribution to YPhOH-X− stabilization in this case is due to the field effects of the substituents, i.e., π delocalization plays only a small part. Therefore, the correlation with the acidity of YPhOH, where π delocalization is important, is not very close. Keywords: hydrogen bonding, substituent effects, ion–molecule equilibria, stability constants, thermochemistry.

Anion Receptors Containing -NH Binding Sites: Hydrogen-Bond Formation or Neat Proton Transfer?

2005 ◽  
Vol 11 (1) ◽  
pp. 120-127 ◽  
Author(s):  
Valeria Amendola ◽  
Massimo Boiocchi ◽  
Luigi Fabbrizzi ◽  
Arianna Palchetti
Keyword(s):  
Hydrogen Bond ◽  
Proton Transfer ◽  
Binding Sites ◽  
Bond Formation ◽  
Anion Receptors ◽  
Hydrogen Bond Formation

Studies on Charge-Transfer and Hydrogen Bond Formation with Cyproheptadine

2001 ◽  
Vol 215 (7) ◽  
Author(s):  
J. Gangopadhyay ◽  
Sujit Chandra Lahiri
Keyword(s):  
Hydrogen Bond ◽  
Charge Transfer ◽  
Complex Formation ◽  
Hydrogen Bonds ◽  
Bond Formation ◽  
Charge Transfer Complexes ◽  
Hydrogen Bond Formation

Cyproheptadine, an antihistaminic and antipruritic drug, forms fairly stable charge-transfer complexes with quinone (Q), chloranil (Chl-Q) and anthraquinone (AQ) in chloroform. It also forms stable hydrogen bonds with alcohols (methanol and propanol) and phenols (α-naphthol,The results suggest that cyproheptadine can form loose association with receptors through charge-transfer and hydrogen bond complex formation.

scholarly journals Theoretical Investigation of Excited-State Intramolecular Double-Proton Transfer Mechanism of Substituent Modified 1, 3-Bis (2-pyridylimino)-4,7-dihydroxyisoindole in Dichloromethane Solution

2021 ◽  
Author(s):  
Xiumin Liu ◽  
Wenzhi Li ◽  
Yuxi Wang ◽  
Yaping Tao ◽  
Yi Wang ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Excited State ◽  
Proton Transfer ◽  
Density Functional ◽  
Photophysical Properties ◽  
Substituent Effects ◽  
Intramolecular Proton Transfer ◽  
Hydrogen Bond Formation ◽  
Dichloromethane Solution ◽  
Double Proton Transfer

Abstract Density functional theory (DFT) and time-dependent DFT (TDDFT) methods were used to investigate substituent effects and excited-state intramolecular double-proton transfer in 1, 3-bis (2-pyridylimino)-4, 7-dihydroxyisoindole (BPI-OH) and its derivatives. The results of a systematic study of the substituent effects of electron-withdrawing groups (F, Cl, and Br) on the adjacent sites of the benzene ring were used to regulate the photophysical properties of the molecules and the dynamics of the proton-transfer process. Geometric structure comparisons and infrared spectroscopic analysis confirmed that strengthening of the intramolecular hydrogen bond in the first excited state (S1) facilitated proton transfer. Functional analysis of the reduction density gradient confirmed these conclusions. Double-proton transfer in BPI-OH is considered to occur in two steps, i.e., BPI-OH (N) →BPI-OH (T1) →BPI-OH (T2), in the ground state (S0) and the S1 state. The potential-energy curves for two-step proton transfer were scanned for both the S0 and S1 states to clarify the mechanisms and pathways of proton transfer. The stepwise path in which two protons are consecutively transferred has a low energy barrier and is more rational and favorable. This study shows that the presence or absence of coordinating groups, and the type of coordinating group, affect the hydrogen-bond strength. A coordinating group enhances hydrogen-bond formation, i.e., it promotes excited-state intramolecular proton transfer.

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