Solvent effects on protomeric equilibriums: quantitative correlation with an electrostatic hydrogen-bonding model

Beak, Peter; Covington, Johnny B.

doi:10.1021/ja00480a069

Cited by 32 publications

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“…As a working hypothesis, it seems that molecules whose tautomers are rigid extrapolate well, whereas tautomers that are conformationally imprecise tend to gain, in water, a kind of ''entropic advantage'' that exaggerates their importance; see Sections 11.3.1 and 11.3.2 for more detailed discussion. Nevertheless, there are exceptions: in both anthrone 27 [18] and 6-chloropyrid-2-one 28 [45], both of them rigid molecules, K T for the oxo form in water is underpredicted by the LSER regression equation [17] by factors of about two and three, respectively. A possible explanation in the first case, indicated in Figure 11.11, is that the two peri interactions between CH and carbonyl inhibit its solvation by alkanols while still allowing water to approach.…”

Section: Overviewmentioning

confidence: 99%

“…Explaining the second is more involved. In preparation for their studies on lactam tautomerism which included that of 28 [45], Beak and coworkers carried out experiments [47] to find out whether lactam dimerization might be a serious distorting factor. The result was negative, yet nobody seems to have considered the possibility that lactim dimerization could be a problem, a serious threat given the much greater strength of OH .…”

Section: Overviewmentioning

confidence: 99%

“…O hydrogen bonding [35], vide Figure 11.13. While this is improbable for solutions in which the lactam tautomer dominates, the data on 28 from which log K T can be extrapolated [45] consist entirely of organic solvents in which 28a is the major tautomer. There may be other ways in which rigid tautomers can misbehave, but so far none has been reported.…”

Section: Overviewmentioning

confidence: 99%

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The Scope and Limitations of LSER in the Study of Tautomer Ratio

Taylor

2013

Tautomerism

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A change in solvent commonly gives rise to major changes in the rates and equilibria of chemical reactions. While solvent effects have long been studied, their quantitative analysis is a relatively recent achievement. The crucial step in this development lies in the solvatochromic approach, above all associated with Taft and coworkers [1, 2], which is a multiple regression technique that relies on giving numerical values to the solvent properties concerned. In this methodology, spectroscopic shifts, mostly ultraviolet (UV) or nuclear magnetic resonance (NMR) but sometimes of other sorts, are used to generate values for each property by comparison with a standard nonpolar solvent, for example, cyclohexane, as described in the following sections. The thermodynamic status of these shifts is uncertain: they were originally supposed to be free-energy related but they are not free energies per se and some have been demonstrated [3] to represent blends of G with H. As used in linear solvation energy relationships (LSER), however (see discussion below), the values themselves are unexceptionable provided that they are proportional to the energy of the molecular property they purport to describe, and even their precise thermodynamic status is of muted importance if they are mutually orthogonal. Essentially, LSER is an empirical topic and here will be treated as such. The Taft-Kamlet LSER MethodologyThe overall LSER equation in its most comprehensive form [1] is set out as follows:where XYZ is the free energy of the process, rate, or equilibrium, in a given solvent, XYZ 0 is the value expected for the solvent cyclohexane, and the remaining terms list * This author is deceased.Tautomerism: Methods and Theories, First Edition. Edited by Liudmil Antonov.

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Section: Overviewmentioning

confidence: 99%

Section: Overviewmentioning

confidence: 99%

Section: Overviewmentioning

confidence: 99%

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The Scope and Limitations of LSER in the Study of Tautomer Ratio

Taylor

2013

Tautomerism

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“…Furthermore, increasing interest is being shown in the tautomeric equilibrium between 4-hydroxypyridine and 4-pyridone in connection with the physiological action of pyridine and pyrimidine derivatives, e.g. pyrimidine nucleic acid bases [10][11][12][13][14]. On the other hand, cholestery benzoate is the first liquid crystalline compound [15], and in this connection, we have studied the reaction of nucleic acid bases with cholestery p-(ω-bromoalkyloxy)benzoates (1) [16,17].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and liquid crystalline properties of novel pyridine derivatives

Itahara

2008

Journal of Heterocyclic Chem

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“…19,20 The tautomeric equilibria shown in Scheme 1 have also been shown to depend on environment. 7,[21][22] While in gas phase or in nonpolar solvents the hydroxypyridine forms dominate, in aqueous solution or in polar solvents the pyridone forms predominate. The change in equilibrium constants may be attributed to the greater stability of pyridone---solvent complexes.…”

Section: Introductionmentioning

confidence: 99%

Steady-state and time-resolved fluorescence investigation of 2-pyridone and 3-pyridone in solution and their specific binding to human serum albumin

Abou‐Zied

Al-Shihi

2008

SPIE Proceedings

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2-pyridone (2Py) and 3-pyridone (3Py) were examined in different solvents and their binding to human serum albumin (HSA) was studied using steady-state spectroscopy and time-resolved fluorescence. Solvation of 2Py and 3Py by water was examined in binary mixtures of 1,4-dioxane and water. Analysis of the absorption and fluorescence data reveals the solvation of the hydrogen bonding center in 2Py by one water molecule and in 3Py by three water molecules. A zwitterionic tautomer of 3Py is formed in water and shows distinct absorption peaks from the absorption of the neutral tautomer. Fluorescence of 3Py was observed in polar solvents only, whereas 2Py is fluorescent in polar and nonpolar solvents. The absorption and fluorescence spectra of 2Py in different solvents indicate less solute-solvent interaction in nonpolar solvents. This observation was confirmed by the measured longer fluorescence lifetime of 2Py in cyclohexane compared to that in water. The mechanism of binding of 2Py and 3Py as probe ligands to HSA was investigated by following the intensity change and lifetime of HSA fluorescence after excitation at 280 nm. The presence of 2Py and 3Py causes a reduction in the fluorescence intensity and lifetime of HSA. This observation indicates that subdomain IIA binding site (Sudlow site I) is the host of the probes and the reduction in the fluorescence of HSA is due to energy transfer from the Trp-214 residue to the probe in each case. The distance between Trp-214 and each of the probes was calculated using Förster theory for energy transfer to be 1.99 nm for HSA/2Py and 2.44 nm for HSA/3Py. The shorter distance in the former complex indicates more efficient energy transfer than in the latter. This was confirmed by estimating the quenching rate constant (k q ) in each complex. k q was calculated to be 1.44 x 10 12 M -1 s -1 for HSA/2Py and 3.45 x 10 11 M -1 s -1 for HSA/3Py. The calculated distances and the k q values indicate a static quenching mechanism operative in the two complexes. The binding constants were estimated to be K = (3.4 ± 0.4) x 10 4 M -1 for the HSA/2Py complex and K = (2.3 ± 0.3) x 10 4 M -1 for the HSA/3Py complex. The number of binding sites of HSA was calculated to be one in both complexes. The latter results, along with the quenching results, indicate that both probes, 2Py and 3Py, bind only in Sudlow site I in subdomain IIA.

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Solvent effects on protomeric equilibriums: quantitative correlation with an electrostatic hydrogen-bonding model

Cited by 32 publications

References 5 publications

The Scope and Limitations of LSER in the Study of Tautomer Ratio

The Scope and Limitations of LSER in the Study of Tautomer Ratio

Synthesis and liquid crystalline properties of novel pyridine derivatives

Steady-state and time-resolved fluorescence investigation of 2-pyridone and 3-pyridone in solution and their specific binding to human serum albumin

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