Solution and ionization of some car☐ylic acids in water and dimethyl sulfoxide

Benoit, R. L.; Louis, C.; ́chette, M. Fre

doi:10.1016/0040-6031(91)80277-p

Cited by 11 publications

(16 citation statements)

References 16 publications

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“…Indeed, this micro acidity constant quantifying the acidity of the (N7)H site in the H 3 (PMEA) tautomer compares favorably with the value pK H H 2 PMEA 4.16 AE 0.02 (Table 1), which quantifies the acidity of the N1 site in H 2 (PMEA) AE . Evidently, N1 is more basic than N7 by DpK a 1.28 AE 0.14; [27,28] this quantitative result confirms earlier more qualitative conclusions [19,20,29,30] about the basicity order of the nitrogens in the adenine residue. Table 1 shows that the phosphate group is less basic than the phosphonate group (cf.…”

Section: 2supporting

confidence: 80%

“…Acidity constants: Definitions, results, and site attributions: From the structure of (Dien)Pt(PMEA-N1) (see Figure 1) it is evident that this species can accept three protons, two at the phosphonate group and one at the N7 site of the adenine residue. [19] A further protonation at N3, after the N1 and N7 sites are blocked, appears in principle possible, however, the basicity of such an N3 site is certainly very low; for example, deprotonation at (N3)H in H 3 (adenine) 3 occurs [20] with pK a 9 À 4.2 and such extreme acidic conditions are not of relevance in the present study. Consequently, the following three deprotonation reactions need to be considered:…”

Section: Resultsmentioning

confidence: 52%

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Formation of Ternary Complexes by Coordination of (Diethylenetriamine)Platinum(II) to N1 or N7 of the Adenine Moiety of the Antiviral Nucleotide Analogue 9-[2-(Phosphonomethoxy)ethyl]adenine (PMEA): Comparison of the Acid-Base and Metal-Ion-Binding Properties of PMEA, (Dien)Pt(PMEA-N1), and (Dien)Pt(PMEA-N7)

et al. 2001

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The synthesis of (Dien)Pt(PMEA-N1), where Dien = diethylenetriamine and PMEA2- = dianion of 9-[2-(phosphonomethoxy)ethyl]adenine, is described. The acidity constants of the threefold protonated H3[(Dien)Pt(PMEA-N1)]3+ complex were determined and in part estimated (UV spectrophotometry and potentiometric pH titration): The release of the proton from the (N7)H+ site in H4[(Dien)Pt(PMEA-N1)]3+ occurs with a rather low pKa (= 0.52+/-0.10). The release of the proton from the -P(O)2(OH) group (pKa = 6.69+/-0.03) in H[(Dien)Pt(PMEA-N1)]+ is only slightly affected by the N1-coordinated (Dien)Pt2+ unit. Comparison with the acidic properties of the H[(Dien)Pt(PMEA-N7)]+ species provides evidence that in the (Dien)Pt(PMEA-N7) complex in aqueous solution an intramolecular, outer-sphere macrochelate is formed through hydrogen bonds between the -PO3(2-) residue of PMEA2- and a PtII-coordinated (Dien)NH2 group; its formation degree amounts to about 40%. The stability constants of the M[(Dien)Pt(PMEA-N1)]2+ complexes with M2+ = Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+ were measured by potentiometric pH titrations in aqueous solution at 25 degrees C and I = 0.1 M (NaNO3). Application of previously determined straight-line plots of log K(M(R-PO3))M versus pK(H(R-PO3)H for simple phosph(on)ate ligands. R-PO3(2-), where R represents a non-inhibiting residue without an affinity for metal ions, proves that the primary binding site of (Dien)Pt(PMEA-N1) is the phosphonate group with all metal ions studied; in fact, Mg2+, Ca2+ and Ni2+ coordinate (within the error limits) only to this site. For the Cu[(Dien)Pt(PMEA-N1)]2+ and Zn[(Dien)Pt(PMEA-N1)]2- systems also the formation of five-membered chelates involving the ether oxygen of the -CH2-O-CH2-PO3(2-) residue could be detected; the formation degrees are about 60% and 30%, respectively. The metal-ion-binding properties of the isomeric (Dien)Pt(PMEA-N7) species studied previously differ in so far that the resulting M[(Dien)Pt(PMEA-N7)]2+ complexes are somewhat less stable, but again Cu2+ and Zn2+ also form with this ligand comparable amounts of the mentioned five-membered chelates. In contrast, both M[(Dien)Pt(PMEA-N1/N7)]2+ complexes differ from the parent M(PMEA) complexes considerably; in the latter instance the formation of the five-membered chelates is of significance for all divalent metal ions studied. The observation that divalent metal-ion binding to the phosphonate group of (Dien)Pt(PMEA-N1) and (Dien)Pt(PMEA-N7) is only moderately inhibited (about 0.2-0.4 log units) by the twofold positively charged (Dien)Pt2+ unit at the adenine residue allows the general conclusion, considering that PMEA is a nucleotide analogue, that this is also true for nucleotides and that consequently participation of, for example, two metal ions in an enzymatic process involving nucleotides is not seriously hampered by charge repulsion.

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Section: 2supporting

confidence: 80%

Section: Resultsmentioning

confidence: 52%

Formation of Ternary Complexes by Coordination of (Diethylenetriamine)Platinum(II) to N1 or N7 of the Adenine Moiety of the Antiviral Nucleotide Analogue 9-[2-(Phosphonomethoxy)ethyl]adenine (PMEA): Comparison of the Acid-Base and Metal-Ion-Binding Properties of PMEA, (Dien)Pt(PMEA-N1), and (Dien)Pt(PMEA-N7)

et al. 2001

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“…Moreover, the protonation constants of all the ligands in DMSO/20%(v)H 2 O solution are higher than those in aqueous solution. This observation can be mainly attributed to the less stabilization effect on the deprotonated ligand by hydrogen bonds donated from solvent molecules in DMSO/20%(v)H 2 O solution as compared to that in pure aqueous medium. ,, …”

Section: Resultsmentioning

confidence: 97%

“…This observation can be mainly attributed to the less stabilization effect on the deprotonated ligand by hydrogen bonds donated from solvent molecules in DMSO/20%(v)H 2 O solution as compared to that in pure aqueous medium. 22,31,32 Stability Constants of U(VI) Complexes. In DMSO/ 20%(v)H 2 O Solution.…”

Section: ■ Resultsmentioning

confidence: 99%

Complexation of U(VI) with BiPDA, DmBiPDA, and PhenDA: Comparison on Structures and Binding Strengths in Aqueous and DMSO/20%(v)H₂O Solutions

Yang

Zhang

Yang³

et al. 2019

Inorg. Chem.

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The stability constants (log β) of 1:1 uranyl complexes with three N,O-mixed donor ligands (L = 2,2′-dipyridyl-6,6′-dicarboxylate, 3,3′-dimethyl-2,2′-bipyridine-6,6′-dicarboxylate, and 1,10-phenanthroline-2,9-dicarboxylate, denoted as BiPDA, DmBiPDA, and PhenDA, respectively) in aqueous and DMSO/20%(v)H2O solutions were determined by spectrophotometry in 0.1 M tetraethylammonium perchlorate. The effects of ligand preorganization, steric hindrance, and solvation on the binding strength of U(VI) with the three ligands were discussed. In aqueous solution, PhenDA forms stronger complexes with U(VI) than BiPDA due to its well-preorganized structure. In DMSO/20%(v)H2O solution, in contrast, the strong solvation effect of DMSO on the ligands reduces the energy gap between the trans- and cis-conformations of BiPDA, resulting in log β(UO2(BiPDA)) > log β(UO2(PhenDA)). The steric hindrance of methyl groups on DmBiPDA makes the complex UO2(DmBiPDA) of the lowest stability in both aqueous and DMSO/20%(v)H2O solutions. Single-crystal structural data of U(VI) complexes with the three ligands indicate that the ligand coordinates with UO2 2+ via aromatic nitrogen atoms and carboxylate oxygen atoms. There is no clear correlation between the trend of the stability constants in solutions and the U–N/O bond lengths of the three crystal complexes. Nevertheless, DmBiPDA coordinates to UO2 2+ in a high-strain fashion as a result of the steric hindrance of methyl groups while BiPDA in a low-strain fashion, which is in accordance with the relative complexation strength of the two respective complexes. The results from this work help us understand the effect of ligand preorganization and solvation on the binding strength of actinides with multidentate N,O-mixed ligands in solid and solutions, which is of importance in designing ligands for the partitioning of actinides from nuclear wastes.

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“…Tartaric acid, malic acid, phthalic acid, and succinic acid and their alkali-metal salts have been of particular use as buffers for pH measurements in aqueous media as well as for pH* measurements in mixed solvents (Perrin and Dempsey, 1979). There have been extensive studies on the dissociation constants of acids in various mixed and nonaqueous solvents (Azab, 1992(Azab, , 1993aAzab et al, 1995;Benoit et al, 1991;Papanatasiou et al, 1984;Amira et al, 1987;Dash et al, 1987). In this paper we determined the apparent dissociation constants of the biologically important dicarboxylic acids, malic, tartaric, phthalic, and succinic, by potentiometric pH titrations in pure water and various water + methanol, water + ethanol, water + dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile mixtures containing different mass fractions of the organic solvent ranging between 0.0 and 0.55.…”

Section: Introductionmentioning

confidence: 99%

Potentiometric Determination of the Apparent Dissociation Constants of Some Dicarboxylic Acids in Various Hydroorganic Media

1997

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The apparent dissociation constants of malic acid (hydroxybutanedioic acid), tartaric acid (2,3dihydroxybutanedioic acid), phthalic acid (1,2-benzenedicarboxylic acid), and succinic acid (butane-1,4dioic acid) were determined at 25 °C and ionic strength I ) 0.10 mol dm -3 KNO 3 by potentiometric pH titration in pure water and water + methanol, water + ethanol, water + N,N-dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile. pK a values increase with an increase in the concentration of the organic solvents. These results are discussed in terms of solvent characteristics. Solvent basicity and stabilization of the conjugate acid free base by hydrogen-bonding interactions in hydroorganic solvent media relative to pure aqueous media as well as proton-solvent interaction play an important role in the acid dissociation equilibrium.

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Solution and ionization of some car☐ylic acids in water and dimethyl sulfoxide

Cited by 11 publications

References 16 publications

Complexation of U(VI) with BiPDA, DmBiPDA, and PhenDA: Comparison on Structures and Binding Strengths in Aqueous and DMSO/20%(v)H₂O Solutions

Potentiometric Determination of the Apparent Dissociation Constants of Some Dicarboxylic Acids in Various Hydroorganic Media

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Solution and ionization of some car☐ylic acids in water and dimethyl sulfoxide

Cited by 11 publications

References 16 publications

Complexation of U(VI) with BiPDA, DmBiPDA, and PhenDA: Comparison on Structures and Binding Strengths in Aqueous and DMSO/20%(v)H2O Solutions

Potentiometric Determination of the Apparent Dissociation Constants of Some Dicarboxylic Acids in Various Hydroorganic Media

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Complexation of U(VI) with BiPDA, DmBiPDA, and PhenDA: Comparison on Structures and Binding Strengths in Aqueous and DMSO/20%(v)H₂O Solutions