Aqueous bimolecular proton transfer in acid–base neutralization

Mohammed, Omar F.; Pines, Dina; Pines, Ehud; Nibbering, Erik T. J.

doi:10.1016/j.chemphys.2007.06.040

Cited by 73 publications

(153 citation statements)

References 149 publications

(225 reference statements)

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“…With increasing delay, these absorption bands decay and a new absorption at 1503 cm −1 grows in that is assigned to the conjugated photobase PTS * − . [14][15][16][17][18][19][20][21] Therefore, the decay and rise of these bands reflect the release of the proton by HPTS * . [14][15][16][17][18][19][20][21] The transient spectra in the frequency region between 1600 and 2100 cm −1 are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…13 Recently, the proton transfer between HPTS and different carboxylate bases dissolved in water has been studied by probing the vibrations of the photoacid and an accepting base with femtosecond midinfrared laser pulses. [14][15][16][17][18][19][20][21] These studies showed that the SCK model does not provide an adequate description of the data at all delay times. It was also found that there is not a single well-defined reaction distance at which proton transfer takes place.…”

Section: -3mentioning

confidence: 99%

“…12,[14][15][16][17][18][19][20][21] If the strength and concentration of the base are sufficient, the release of the proton by HPTS * is strongly accelerated. In this acid-base reaction, the diffusion of the reactants through the water medium can play an essential role, as the reactants have to come sufficiently close to let the proton transfer take place.…”

Section: -3mentioning

confidence: 99%

“…Instead, there exists a distribution of hydrogen-bonded reaction complexes that differ in the number of water molecules separating the acid and the base. 14,15,20,21 Additionally, at high base concentrations, most of the proton transfers occur in complexes that are already present in the solution before the HPTS molecule is excited. [14][15][16][17][18][19][20][21] Of course, at low base concentrations, diffusion is important as it is required to generate the hydrogenbonded reaction complexes.…”

Section: -3mentioning

confidence: 99%

“…Such a mechanism has been identified in previous work on proton transfer between HPTS and carboxylate bases. [14][15][16][17][18][19][20][21] It is to be expected that for small acid-base separations of one or two water molecules the second channel will be much faster than the first channel.…”

Section: -3mentioning

confidence: 99%

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Parallel proton transfer pathways in aqueous acid-base reactions

Cox

Bakker

2008

The Journal of Chemical Physics

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We study the mechanism of proton transfer ͑PT͒ between the photoacid 8-hydroxy-1,3, 6-pyrenetrisulfonic acid ͑HPTS͒ and the base chloroacetate in aqueous solution. We investigate both proton and deuteron transfer reactions in solutions with base concentrations ranging from 0.25M to 4M. Using femtosecond midinfrared spectroscopy, we probe the vibrational responses of HPTS, its conjugate photobase, the hydrated proton/deuteron, and chloroacetate. The measurement of these four resonances allows us to follow the sequence of proton departure from the acid, its uptake by the water solvent, and its arrival at the base. In recent studies it was shown that proton transfer to carboxylate bases proceeds via Grotthuss conduction through a water wire connecting the acid and the base ͓Mohammed et al., Science 310, 83 ͑2005͒;Agnew. Chem. Int. Ed. 46, 1458 ͑2007͒;Siwick and Bakker, J. Am. Chem. Soc. 129, 13412 ͑2007͒; J. Phys. Chem. B 112, 378 ͑2008͔͒. Here we show that, for the weaker base chloroacetate, an alternative channel for proton transfer arises. In this channel the proton is first transferred to the water solvent and only later taken up from the water by the base. We study the base concentration dependence of the two competing channels.

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Section: Resultsmentioning

confidence: 99%

Section: -3mentioning

confidence: 99%

Section: -3mentioning

confidence: 99%

Section: -3mentioning

confidence: 99%

Section: -3mentioning

confidence: 99%

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Parallel proton transfer pathways in aqueous acid-base reactions

Cox

Bakker

2008

The Journal of Chemical Physics

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Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution

Kaiser

Halbritter

Heckel

et al. 2021

Chemistry A European J

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Photoacids attract increasing scientific attention, as they are valuable tools to spatiotemporally control protonrelease reactions and pH values of solutions. We present the first time-resolved spectroscopic study of the excited state and proton-release dynamics of prominent merocyanine representatives. Femtosecond transient absorption measurements of a pyridine merocyanine with two distinct protonation sites revealed dissimilar proton-release mechanisms: one site acts as a photoacid generator as its pK a value is modulated in the ground state after photoisomerization, while the other functions as an excited state photoacid which releases its proton within 1.1 ps. With a pK a drop of 8.7 units to À 5.5 upon excitation, the latter phenolic site is regarded a super-photoacid. The 6-nitro derivative exhibits only a phenolic site with similar, yet slightly less photoacidic characteristics and both compounds transfer their proton to methanol and ethanol. In contrast, for the related 6,8-dinitro compound an intramolecular proton transfer to the orthonitro group is suggested that is involved in a rapid relaxation into the ground state.

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Influence of Ions on Aqueous Acid–Base Reactions

2009

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We study the effects of bromide salts on the rate and mechanism of the aqueous proton/deuteron-transfer reaction between the photoacid 8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS) and the base acetate. The proton/deuteron release is triggered by exciting HPTS with 400 nm femtosecond laser pulses. Probing the electronic and vibrational resonances of the photoacid, the conjugate photobase, the hydrated proton/deuteron and the accepting base with femtosecond visible and mid-infrared pulses monitors the proton transfer. Two reaction channels are identified: 1) direct long-range proton transfer over hydrogen-bonded water bridges that connect the acid and base and 2) acid dissociation to produce fully solvated protons followed by proton scavenging from solution by acetate. We observe that the addition of salt affects the long-range reaction pathway, and reduces both the rate at which protons are released to solution by HPTS and the rate at which solvated protons are scavenged from solution by acetate. We study the dependence of these effects on the nature and concentration of the dissolved salt.

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Aqueous bimolecular proton transfer in acid–base neutralization

Cited by 73 publications

References 149 publications

Parallel proton transfer pathways in aqueous acid-base reactions

Parallel proton transfer pathways in aqueous acid-base reactions

Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution

Influence of Ions on Aqueous Acid–Base Reactions

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