Theoretical study of deuterium isotope effects on acid–base equilibria under ambient and hydrothermal conditions

Mora‐Diez, Nelaine; Egorova, Yu.; Plommer, Hart; Tremaine, Peter R.

doi:10.1039/c4ra14087g

Cited by 27 publications

(33 citation statements)

References 51 publications

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“…This is consistent with the fact that the pK a of an organic acid is in general higher in D 2 O than in H 2 O. 19 The difference in these intensity ratios indicates that the isotopic effects alter the rate of deprotonation of photo-excited pyranine. Releasing of heavier D + from deuterated pyranine and transferring it through the hydrogen-bonding network should be slower, leading to the higher Q.…”

Section: Methodssupporting

confidence: 76%

“…A higher Q value of deuterated pyranine (relatively higher I PyOD* and lower I PyO−* ) represents that PyOD* is less acidic than PyOH*. This is consistent with the fact that the pK a of an organic acid is in general higher in D 2 O than in H 2 O . The difference in these intensity ratios indicates that the isotopic effects alter the rate of deprotonation of photo‐excited pyranine.…”

Section: Resultssupporting

confidence: 65%

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Excited‐State Proton Transfer Reaction of Pyranine in Aqueous Sugar and Alcohol Solutions Investigated by Fluorescence Spectroscopy

Hong

Cheong

Cho

2017

Bulletin Korean Chem Soc

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The fluorescence emission behaviors of excited pyranine (PyOH*) and deprotonated pyranine (PyO−*) were studied to explore the effects of sugar or alcohol on the excited‐state proton transfer (ESPT) reaction of pyranine in aqueous solutions. The fluorescence intensity ratio, Q between the two emission bands of pyranine varies significantly with the type and concentration of sugar or alcohol in aqueous solution. The results clearly show that a higher Q value (more PyOH* and less PyO−*) reflects a lower ESPT rate due to less free water molecules for solvation of PyO−* and H+. Higher Q values were observed in sugar solutions while lower values in alcohol solutions. Larger alcohols yielded higher Q values and the values for polyols (ethylene glycol and glycerin) were between those of methanol and ethanol, revealing that the hydroxyl groups in polyols form intramolecular hydrogen‐bond. The location of the hydroxyl group was also found to affect the intensity ratio, Q. The conductivities of 0.01 M HCl in aqueous sugar and alcohol solutions are consistent with the Q values observed, and the inverse of Q show a quadratic relation with conductivity. The enthalpy and entropy changes for the deprotonation reaction of PyOH* in fructose and ethanol aqueous solutions were also determined, assuming that the deprotonation reaction was an equilibrated process. The higher ΔH in fructose solution reveal that deprotonation of PyOH* in sugar solution is energetically less favored than in ethanol solution because solvation of fructose requires more water molecules.

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Section: Methodssupporting

confidence: 76%

Section: Resultssupporting

confidence: 65%

Excited‐State Proton Transfer Reaction of Pyranine in Aqueous Sugar and Alcohol Solutions Investigated by Fluorescence Spectroscopy

Hong

Cheong

Cho

2017

Bulletin Korean Chem Soc

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“…57 The deuterium isotope effect due to zero-point energies has been determined both experimentally and computationally to be around 0.5 pK a units for several aromatic acids with varying acidities. 58 This corresponds to a difference of 0.67 kcal mol À1 in DG. If the observed amplitudes of the fast decay components in H 2 O and D 2 O are assumed to reect the relative CIP* populations, the difference in DG is estimated to be 0.55 kcal mol À1 , in close agreement with the above value.…”

Section: Comparison With Experimental Decaysmentioning

confidence: 99%

Broadband fluorescence reveals mechanistic differences in excited-state proton transfer to protic and aprotic solvents

et al. 2020

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“…[ 2 ] The fact that the actual percentage of anion is 18% (calculated from the integration value 0.70 of the peak at 4.47 ppm vs a total integration of 3.74 of the signals H20) can be explained considering the lower acidity of the organic compounds in D 2 O with respect to H 2 O. [ 24 ] Calculated chemical shifts for H20, H21, and H22 of the anion are 4.42, 6.12, and 6.55, which are in good agreement with the experimental values.…”

Section: Resultsmentioning

confidence: 99%

Tautomeric and E‐Z equilibria of the herbicide clethodim in water and organic solvents: A nuclear magnetic resonance and theoretical study

Caputo

Colasurdo

Allegretti

et al. 2020

J of Physical Organic Chem

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The herbicide clethodim can exist as different tautomeric forms and also as E‐Z isomers. Previous works have made some approach to the matter of tautomerization and have always stated that the E form was the only one stable. In this work, the investigation on the tautomeric equilibrium of clethodim is carried out in solution by means of proton nuclear magnetic resonance (1H NMR), carbon‐13 nuclear magnetic resonance (13C NMR), and correlation spectroscopy (COSY) experiments in four solvents (CDCl3, acetone‐d6, dimethylsulfoxide (DMSO)‐d6, and D2O). Major tautomeric species have been identified, and equilibrium constants have been calculated from the integration of hydrogens of the chloroallyl radical of clethodim. E‐ketoenolimine is the only detectable tautomer in CDCl3. Mixtures of E‐ketoenolimine and E‐diketoenamine tautomers are observed in acetone‐d6 and DMSO‐d6 (in ratios of 8:92 and 53:47, respectively). In water, the most abundant neutral tautomers are E‐ketoenolimine, E‐diketoenamine, and Z‐ketoenolimine (with a tautomeric ratio of 66:20:14). Identification of the E and Z tautomers is reported. Thermodynamic parameters (obtained by analysis of the effect of temperature) and theoretical calculations (energies and chemical shifts) support the assignations and tautomeric ratios when considering specific clethodim‐solvent hydrogen bonds. In the case of water, calculations suggest double bonded complexes that would be the cause of stability of the tautomers. These new observations on the structure of clethodim in solution open a new series of questions on its absorption mechanism, and they are also a tool for further chemical modification of this herbicide.

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Theoretical study of deuterium isotope effects on acid–base equilibria under ambient and hydrothermal conditions

Abstract: The calculated difference between pKa values in H2O and D2O is in excellent agreement with experiment.

Cited by 27 publications

References 51 publications

Excited‐State Proton Transfer Reaction of Pyranine in Aqueous Sugar and Alcohol Solutions Investigated by Fluorescence Spectroscopy

Excited‐State Proton Transfer Reaction of Pyranine in Aqueous Sugar and Alcohol Solutions Investigated by Fluorescence Spectroscopy

Broadband fluorescence reveals mechanistic differences in excited-state proton transfer to protic and aprotic solvents

Tautomeric and E‐Z equilibria of the herbicide clethodim in water and organic solvents: A nuclear magnetic resonance and theoretical study

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