The critical size of hydrogen-bonded alcohol clusters as effective Brønsted bases in solutions

Park, Sunyoung; Kim, Taeg Gyum; Ajitha, M.; Kwac, Kijeong; Lee, Young Min; Kim, Heesu; Jung, Yousung; Kwon, Oh‐Hoon

doi:10.1039/c6cp01650b

Cited by 14 publications

(27 citation statements)

References 53 publications

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“…In neat ACN, AH + * was found to decay mainly in 9.1 ns (93%), which is ascribed to the lifetime of AH + * in the absence of ESPT. The minor component (7%) of the fluorescence decay is attributed to the complex of AH + with residual water as reported 4b …”

Section: Resultssupporting

confidence: 68%

“…For proton transfer to occur, the formation of an encounter acid–base complex by hydrogen (H)‐bonding is prerequisite. Through a series of studies, this group has revealed the cooperative nature of H‐bonding of alcohol as a base in the acid–base reactions with a strong photoacid 4 . The cooperative nature of H‐bonds in alcohol clusters originates from the increase of negative charge density on the proton‐accepting oxygen atom of the alcohol molecule, which donates a H‐bond to another alcohol molecule.…”

Section: Introductionmentioning

confidence: 99%

“…Depending on the pH of the surrounding medium, the cationic form (C) and the deprotonated zwitterionic form (Z) of NM7HQ + in the ground state can coexist with the p K a value of 5.9 in water. When NM7HQ + is photoexcited to the lowest excited singlet state (C*), electron rearrangement occurs, and the partial electronic charge of the hydroxyl oxygen atom is transferred to the aromatic moiety promoting NM7HQ + to a strong acid with p K a * of −2.3 4,10 . Deprotonation then readily follows to form a keto species in the excited state (K*).…”

Section: Introductionmentioning

confidence: 99%

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Acid–base reaction of a super‐photoacid with a cooperative amide hydrogen‐bonded chain

Choi

Kim

Kwon

2022

Bulletin Korean Chem Soc

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The excited-state proton transfer (ESPT) of the strong photoacid, N-methyl-7-hydroxyquinolium (NM7HQ + ), was studied in the presence of N-methylbenzamide (NMB) as a base in the aprotic polar solvent, acetonitrile. According to the Benesi-Hildebrand relation, it was revealed that the hydrogen (H)-bonded complex of NM7HQ + and NMB exists in the ground state in a 1:1 stoichiometry with the association constant of 22.2 AE 1.7 M À1 . The fluorescence quenching of the 1:1 complex was observed to follow the Stern-Volmer relation with the molecularity of one for NMB indicating that the ESPT of NM7HQ + occurs with the H-bonded chain of two NMB molecules. Our study highlights the cooperative nature of Hbonding in the chemical reactivity of amide in acid-base reactions as has already been reported for alcohol. K E Y W O R D S amide, chemical kinetics, cooperativity, diffusion, excited-state proton transfer, hydrogen bond

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Section: Resultssupporting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Acid–base reaction of a super‐photoacid with a cooperative amide hydrogen‐bonded chain

Choi

Kim

Kwon

2022

Bulletin Korean Chem Soc

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“…63 The concerted action of a pair of water or alcohol molecules in proton transfer reactions has also been demonstrated. [64][65][66][67] Electron transfer from water or alcohols to other excited chromophores has also been established. Femtosecond experiments in bulk solvents showed that excited oxazine 750 is reduced by different aliphatic alcohols.…”

Section: Involvement Of An Electron Transfer Process In the Quenchingmentioning

confidence: 99%

Fluorescence quenching of the N-methylquinolinium cation by pairs of water or alcohol molecules

Rodríguez‐Prieto

Corbelle

Fernández

et al. 2018

Phys. Chem. Chem. Phys.

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N-Methylquinolinium cation (MQ+) in its first-excited singlet state is a strong oxidant commonly used as a photosensitizer, whose fluorescence is therefore quenched by electron donors. Interestingly, the fluorescence of MQ+ is also quenched by hydroxy compounds such as water and alcohols, more difficult to oxidize. We investigated the quenching mechanism of MQ+ fluorescence by small amounts of water and alcohols in acetonitrile solution. The fluorescence intensities and lifetimes exhibited a nonlinear dependence on the quencher concentration. We found evidence that emissive exciplexes MQ+*-ROH are formed between the excited quinolinium and the hydroxy compounds. An accurate quantitative description of the results was obtained with a model in which the exciplex reacts with a second molecule of the hydroxy compound, which quenches the fluorescence. The rate constant of this process increased as the quencher ionization energy decreased. We showed also that a low basicity of the hydroxy compound inhibits the quenching process. These results are consistent with the existence of a concerted photoinduced proton-coupled electron transfer (PCET) involving an intermediate complex of the excited quinolinium with a H-bonded molecular pair of the hydroxy compounds. In these pairs, a water or an alcohol molecule is able to donate an electron to the photoexcited quinolinium cation and a proton to the second H-bonded hydroxy molecule, showing an enhanced reducing power in comparison with the isolated molecule. The structure of the intermediate complex was investigated using high-level quantum mechanical calculations. At high water concentrations in acetonitrile/water mixtures, the quenching process is slowed down, indicating that higher water aggregates are less effective for a PCET process. The results obtained may be relevant to the study of water oxidation and electron transfer in biological systems.

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“…A hydrogen bond is an important interaction dominating the structural conformation of a DNA double chain and the reactivity of clusters . The strength of the hydrogen bond sometimes determines the reaction mechanism of the clusters …”

Section: Introductionmentioning

confidence: 99%

Effects of zero point vibration on the reaction dynamics of water dimer cations following ionization

Tachikawa

2017

J Comput Chem

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Reactions of water dimer cation (H2O)2+ following ionization have been investigated by means of a direct ab initio molecular dynamics method. In particular, the effects of zero point vibration and zero point energy (ZPE) on the reaction mechanism were considered in this work. Trajectories were run on two electronic potential energy surfaces (PESs) of (H2O)2+: ground state ( A″-like state) and the first excited state ( A'-like state). All trajectories on the ground-state PES lead to the proton-transferred product: H O (Wd)-H O(Wa) → OH(Wd)-H O (Wa), where Wd and Wa refer to the proton donor and acceptor water molecules, respectively. Time of proton transfer (PT) varied widely from 15 to 40 fs (average time of PT = 30.9 fs). The trajectories on the excited-state PES gave two products: an intermediate complex with a face-to-face structure (H O-OH ) and a PT product. However, the proton was transferred to the opposite direction, and the reverse PT was found on the excited-state PES: H O(Wd)-H O (Wa) → H O (Wd)-OH(Wa). This difference occurred because the ionizing water molecule in the dimer switched between the ground and excited states. The reaction mechanism of (H2O)2+ and the effects of ZPE are discussed on the basis of the results. © 2017 Wiley Periodicals, Inc.

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The critical size of hydrogen-bonded alcohol clusters as effective Brønsted bases in solutions

Cited by 14 publications

References 53 publications

Acid–base reaction of a super‐photoacid with a cooperative amide hydrogen‐bonded chain

Acid–base reaction of a super‐photoacid with a cooperative amide hydrogen‐bonded chain

Fluorescence quenching of the N-methylquinolinium cation by pairs of water or alcohol molecules

Effects of zero point vibration on the reaction dynamics of water dimer cations following ionization

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