UV‐Visible Spectra and Photoacidity of Phenols, Naphthols and Pyrenols

Pines, Ehud

doi:10.1002/9780470682531.pat0283

Cited by 4 publications

(5 citation statements)

References 81 publications

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“…For this purpose, we selected 2 oxygen bases with structures and pK a s relevant to biological systems: the HPTS base 8hydroxy-1,3,6-trisulfonate anion, and the 1N4S base 1-naphthol-4-sulfonate anion. The pK o a s (I = 0) of these 2 bases' conjugate Brønsted acids (H + Bs) are 7.95 and 8.2, respectively (54,55). HPTS and 1N4S have basicity similar to that of many important physiological bases such the amine groups in small peptides, the hydroxyl group in tyrosine, and the imine group in histidine, whose conjugate acids' pK o a s all fall in the range of 8 ± 2 (56).…”

Section: Resultsmentioning

confidence: 99%

Intact carbonic acid is a viable protonating agent for biological bases

Aminov

Pines

Kiefer

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Carbonic acid H2CO3 (CA) is a key constituent of the universal CA/bicarbonate/CO2 buffer maintaining the pH of both blood and the oceans. Here we demonstrate the ability of intact CA to quantitatively protonate bases with biologically-relevant pKas and argue that CA has a previously unappreciated function as a major source of protons in blood plasma. We determine with high precision the temperature dependence of pKa(CA), pKa(T) = −373.604 + 16,500/T + 56.478 ln T. At physiological-like conditions pKa(CA) = 3.45 (I = 0.15 M, 37 °C), making CA stronger than lactic acid. We further demonstrate experimentally that CA decomposition to H2O and CO2 does not impair its ability to act as an ordinary carboxylic acid and to efficiently protonate physiological-like bases. The consequences of this conclusion are far reaching for human physiology and marine biology. While CA is somewhat less reactive than (H+)aq, it is more than 1 order of magnitude more abundant than (H+)aq in the blood plasma and in the oceans. In particular, CA is about 70× more abundant than (H+)aq in the blood plasma, where we argue that its overall protonation efficiency is 10 to 20× greater than that of (H+)aq, often considered to be the major protonating agent there. CA should thus function as a major source for fast in vivo acid–base reactivity in the blood plasma, possibly penetrating intact into membranes and significantly helping to compensate for (H+)aq’s kinetic deficiency in sustaining the large proton fluxes that are vital for metabolic processes and rapid enzymatic reactions.

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Section: Resultsmentioning

confidence: 99%

Intact carbonic acid is a viable protonating agent for biological bases

Aminov

Pines

Kiefer

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…Both values are in the typical p K a -range of pyrenol-derived photoacids. 31 After polymerization the acidity of the 1-pyrenols was found to increase slightly yielding p K a values ranging from 8.7 for P[(OEG 9 MA) 0.88 - co -HPSAPMA 0.12 ] to 9.8 in P[(OEG 3 MA) 0.86 - co -HPSAPMA 0.14 ] (see Table 2 for more details). In case of the OEG 3 MA-based copolymers, i.e.…”

Section: Resultsmentioning

confidence: 99%

“…26,27 The most prominent photoacids known are hydroxyarenes such as phenols, naphthols, or pyrenols. [28][29][30][31] In our previous work we successfully demonstrated that the UV light initiated ESPT in micelles formed of 1-naphthol-carrying copolymers with photoacid moieties in the micellar core contributes to the release of the encapsulated model compound Nile red. 21,22 However, the necessity of UV light to release the drug from the nanoparticles reduces the potential of these polymers in biomedical applications.…”

Section: Introductionmentioning

confidence: 99%

Multi-stimuli-responsive copolymers based on 1-pyrenol polyphotoacids

et al. 2023

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“…Table S6). This is within expectations, given that the Förster’s method provides a rough estimate of photoacidity because of the assumption that the entropy change is same in the ground and excited states and also because of errors associated in determining the 0–0 transition energies of the conjugate acid and base forms …”

Section: Resultsmentioning

confidence: 99%

Dual Excited State Proton Transfer Pathways in the Bifunctional Photoacid 6-Amino-2-naphtol

Jagushte,

Sadhukhan,

Upadhyaya

et al. 2023

J. Phys. Chem. B

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This study investigates the photoacidity and excited state proton transfer (ESPT) pathways of a bifunctional molecule, 6amino-2-naphthol (6N2OH), using absorption, steady-state fluorescence, time-resolved fluorescence, and theoretical calculations. 6N2OH attains four different prototropic forms in the excited state (cation, neutral, anion, or zwitterion) depending on pH of the solution. Interestingly, ESPT at the OH site of the molecule can be controlled by the protonation state of the amino substituent. Conversion of the electron donating NH 2 group to the electron withdrawing NH 3+ group brings about a reduction of more than 7 pK a units for the deprotonation of OH in the excited state. Further, the position of the NH 2 substituent on the naphthalene framework is found to play an important role in dictating the ESPT pathways of aminonaphthols. Unlike most aminonaphthol derivatives that undergo ESPT only at the OH site, akin to substituted naphthols, 6N2OH undergoes ESPT at both OH and NH 3 + sites, indicating its similarity to substituted naphthols and substituted naphthylamines. ESPT at the NH 3 + site resulting in cation ↔ neutral equilibrium of 6N2OH in the excited state is well-corroborated by comparative studies with another reference photoacid, 6-amino-2-methoxynaphthalene (6N2M). Correlation of the acidity constants of 6N2OH with the σ p parameters according to the Hammett model reveals that while 6N2OH can be treated either as naphthol or as naphthylamine in the ground state, the structure−function correlation cannot be extrapolated directly in the excited state, thus highlighting the rich and complex photophysics of bifunctional photoacids.

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UV‐Visible Spectra and Photoacidity of Phenols, Naphthols and Pyrenols

Abstract: Introduction The Thermodynamic Aspects of Photoacidity On the Origin of Photoacidity The Electronic Structure of Photoacids Free‐Energy Correlations Between Photoacidity and Reactivity Concluding Remarks: Evaluation of our Current Understanding of the Photoacidity of Hydroxyarenes

Cited by 4 publications

References 81 publications

Intact carbonic acid is a viable protonating agent for biological bases

Intact carbonic acid is a viable protonating agent for biological bases

Multi-stimuli-responsive copolymers based on 1-pyrenol polyphotoacids

Dual Excited State Proton Transfer Pathways in the Bifunctional Photoacid 6-Amino-2-naphtol

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