Intermolecular Proton Transfer in the Excited Hydrogen‐Bonded Complex in Nonpolar Solvent and Fluorescence Quenching Due to Hydrogen Bonding

The time-dependent density functional theory (TD-DFT) method was used to study the excited-state proton transfer (ESPT) properties of the hydrogen-bonded cinnamonitrile (3TPAN)–methanol (MeOH) complex (3TPAN–MeOH). The intermolecular hydrogen bonds N1···H11 in both the ground state S0 and the excited state S1 were demonstrated by the optimized geometric structures of the hydrogen-bonded 3TPAN–MeOH complex. While in the excited state S3, a new hydrogen bond H11···O1 was formed after the ESPT took place from the hydrogen-bonded MeOH molecule to the 3TPAN moiety. It was demonstrated that the electronic transitions of the S1 states for both the 3TPAN monomer (including the S3 state) and the hydrogen-bonded 3TPAN–MeOH complex should be of a localized-excited (LE) nature on the 3TPAN molecule, while the S3 state of the hydrogen-bonded 3TPAN–MeOH complex should be of charge transfer (CT) character from the hydrogen-bonded MeOH molecule (through O1···H11) to the 3TPAN moiety. The S3-state proton transfer and charge transfer due to the intermolecular hydrogen-bonding interaction should be the reasons for the remarkable redshift (0.91 eV) of the S3-state electronic energy for the hydrogen-bonded 3TPAN–MeOH complex compared with that of the 3TPAN monomer.

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Controlled protonation of iron–molybdenum cofactor by nitrogenase: a structural and theoretical analysis

Biochemical Journal ◽

10.1042/bj3550569 ◽

2001 ◽

Vol 355 (3) ◽

pp. 569-576 ◽

Cited By ~ 51

Author(s):

Marcus C. DURRANT

Keyword(s):

Hydrogen Bonding ◽

Theoretical Analysis ◽

Proton Transfer ◽

Water Channel ◽

Molybdenum Cofactor ◽

Functional Differences ◽

Iron Molybdenum Cofactor ◽

Transfer Channels ◽

Protein Environment ◽

Hydrogen Bonded

Qualitative molecular modelling has been used to identify possible routes for transfer of protons from the surface of the nitrogenase protein to the iron–molybdenum cofactor (FeMoco) and to substrates during catalysis. Three proton-transfer routes have been identified; a water-filled channel running from the protein exterior to the homocitrate ligand of FeMoco, and two hydrogen-bonded chains to specific FeMoco sulphur atoms. It is suggested that the water channel is used for multiple proton deliveries to the substrate, as well as in diffusion of products and substrates between FeMoco and the bulk solvent, whereas the two hydrogen-bonded chains each allow a single proton to be added to, and subsequently depart from, FeMoco during the catalytic cycle. Possible functional differences in the proton-transfer channels are discussed in terms of assessment of the protein environment and specific hydrogen-bonding effects. The implications of these observations are discussed in terms of the suppression of wasteful production of dihydrogen by nitrogenase and the Lowe–Thorneley scheme for dinitrogen reduction.

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

Canadian Journal of Chemistry ◽

10.1139/v90-316 ◽

1990 ◽

Vol 68 (11) ◽

pp. 2070-2077 ◽

Cited By ~ 12

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.

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Interaction Site and Proton Transfer Equilibrium in the 4-Aminoantipyrine-Pentachlorophenol Hydrogen–Bonded Adduct

Journal of Chemical Research ◽

10.3184/030823402103172095 ◽

2002 ◽

Vol 2002 (6) ◽

pp. 255-256 ◽

Cited By ~ 2

Author(s):

Moustafa M. Habeeb

Keyword(s):

Hydrogen Bonding ◽

Proton Transfer ◽

Crystalline Form ◽

Hydrogen Bonding Interaction ◽

Interaction Site ◽

Bonding Interaction ◽

Ft Ir ◽

C Nmr ◽

Hydrogen Bonded

The hydrogen-bonding interaction site between 4-aminoantipyrine (4AAP) and pentachlorophenol (PCP) was investigated in the crystalline form using FT-IR and in solution using FT-IR, UV-Vis and 1H,13C NMR spectroscopies.

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