498. The dissociation constants of some symmetrically disubstituted succinic acids

Dippy, J. F. J.; Hughes, S. R. C.; Różański, Andrzej

doi:10.1039/jr9590002492

Cited by 105 publications

(93 citation statements)

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“…Hydroxyl, acetoxyl, and trifluoroacetoxyl groups confer an especially wide range of electron-withdrawing ability. These functional groups have conjugate acid pK a values of 15.6, 4.76, and 0.23, respectively, 18 and F values (which report on inductive effects) of 0.33, 0.42, and 0.58, respectively. 19 To reveal the consequences of O-acylation of 4-hydroxyproline residues, compounds 1-6 were synthesized by the routes shown in Scheme 1.…”

Section: Resultsmentioning

confidence: 99%

O‐acylation of hydroxyproline residues: Effect on peptide‐bond isomerization and collagen stability

et al. 2004

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In collagen, strands of the sequence XaaYaaGly form a triple‐helical structure. The Yaa residue is often (2S,4R)‐4‐hydroxyproline (Hyp). The inductive effect of the hydroxyl group of Hyp residues greatly increases collagen stability. Here, electron withdrawal by the hydroxyl group in Hyp and its 4S diastereomer (hyp) is increased by the addition of an acetyl group or trifluoroacetyl group. The crystalline structures of AcHyp[C(O)CH3]OMe and Achyp[C(O)CH3]OMe are similar to those of AcHypOMe and AcProOMe, respectively. The O‐acylation of AcHypOMe and AchypOMe increases the 13C chemical shift of its Cγ atom: AcHyp[C(O)CF3]OMe ≅ Achyp[C(O)CF3]OMe > AcHyp[C(O)CH3]OMe ≅ Achyp[C(O)CH3]OMe ≥ AcHypOMe ≅ AchypOMe. This increased inductive effect is not apparent in the thermodynamics or kinetics of amide bond isomerization. Despite apparently unfavorable steric interactions, (ProHypGly)10, which is O‐acylated with 10 acetyl groups, forms a triple helix that has intermediate stability: (ProHypGly)10 > {ProHyp[C(O)CH3]Gly}10 ≫ (ProProGly)10. Thus, the benefit to collagen stability endowed by the hydroxyl group of Hyp residues is largely retained by an acetoxyl group. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2005

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Section: Resultsmentioning

confidence: 99%

O‐acylation of hydroxyproline residues: Effect on peptide‐bond isomerization and collagen stability

et al. 2004

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“…The pKa values given here are the acid dissociation constants in an aqueous solution of the anion molecule constituting the IL. 34 EMIm-ACE was purchased from Aldrich Chemical Co., and BMIm-BEN and BMIm-MAN were synthesized by the anion-exchange resin method. 35 To remove as much moisture as possible, the ILs were heated at 85°C in a vacuum for 24 h. The water contents were measured by a Karl Fischer Moisture Meter (KF-100 Mitsubishi Chemical Corporation) before the polarization experiment.…”

Section: Methodsmentioning

confidence: 99%

Anodization Behavior of Aluminum in Ionic Liquids with a Small Amount of Water

et al. 2013

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We investigated the anodic oxidation of aluminum in ionic liquids (ILs) by the constant-voltage rising rate (C-V) method and constant-current density (C-C) method, with characterization by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The structure of the oxide layer and the reaction efficiency varied with the type of IL, the applied voltage, the forming method, and the water content. A homogeneous Al 2 O 3 film with a superior dielectric property was formed by the C-V method (100 mV/s) in 1-butyl-3-methylimidazolium benzoate (BMIm-BEN, water content 0.81 wt%) at 40 V. Although a homogeneous barrier-type Al 2 O 3 film was also formed in 1-butyl-3-methylimidazolium mandelate (BMIm-MAN, water content 0.34 wt%) at 40 V, some anion species existed in the film, and its jump-voltage characteristics was inferior to that of the film formed in BMIm-BEN. The relative permittivity of the film formed in BMIm-BEN was almost equal to that of the Al 2 O 3 film formed in adipate (1.0 wt%) aqueous solution, but the dielectric constant of the film formed in BMIm-MAN was 1.5 times larger. In contrast, a heterogeneous porous Al 2 O 3 film containing a large amount of anion molecules was formed in 1-ethyl-3-methylimidazolium acetate (EMIm-ACE, water content 0.79 wt%) at 40 V. Since the source of oxygen for anodic oxidation is the small amount of water in the ILs, the water content strongly affected the characteristics of the formed Al 2 O 3 layer.

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“…The importance of steric inhibition of solvation in the ionization equilibria has been demonstrated (43,44). The reduced solvation will preferentially decrease the stability of the anion with respect to the acid.…”

Section: Efect Of Ortho or "Ortho" Fused Ring Substituentsmentioning

confidence: 99%