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Enthalpy-Entropy Compensation for Some Drugs Dissociation in Aqueous Solutions
Authors: Meloun Milan | Ferenčíková Zuzana
Year: 2012
Type of publication: článek v odborném periodiku
Name of source: Fluid Phase Equilibria
Publisher name: Elsevier Science BV
Place: Amsterdam
Page from-to: 31-41
Titles:
Language Name Abstract Keywords
cze Kompenzace entalpie vůči entropii pro několik vybraných léčiv při disociaci ve vodných roztocích Naměřená závislost entalpie-entropie se jeví indikativní co do společného mechanismu disociace léčiv. Regresní triplet odhaluje lineární závislost mezi termodynamickými parametry odvozenými z naměřených disociačních konstant při dvou různých teplotách na základě Van´t Hoffovi rovnice. Ortogonální regresí bylo analyzováno 87 naměřených pKa od 44 léčiv a byl odhadnut regresní model DH0=40.43+0.966TDS0 s korelačním koeficientem r=0.8953. termodynamické disociační konstanty; disociační entropie; disociační entalpie; kompenzace entapllie-entropie
eng Enthalpy-Entropy Compensation for Some Drugs Dissociation in Aqueous Solutions The observed enthalpy-entropy compensation seems to be strongly indicative of a common mechanism of drugs dissociation. The regression triplet (data, model, method) is used for the estimation of dependencies between thermodynamic parameters Delta H-0, Delta S-0, Delta G(0) derived from dissociation constant measurements at two different temperatures and Van't Hoff equation. The orthogonal regression analysis involves 87 experimental pK(a) values performed on 44 drugs to give unbiased parameter estimates for a linear dependence Delta H-0 = 40.43 + 0.966 T Delta S-0 with the Pearson's correlation coefficient r = 0.8953. The standard free energy change Delta G(0) for the dissociation reaction may be decomposed on Delta H-0 vs. pK(a) dependence and T Delta S-0 vs. pK(a) dependence. The Delta H-0 is sensitive to changes in pK(a) because of electrostatic effects. Increasing the Bronsted basicity of the drug causes an increase of the Delta H-0 term and decreases the T Delta S-0 term. When Delta H-0 is negative, then the value T Delta S-0 is the dominant factor, which determines that Delta G(0) is positive. The ionization of a neutral acid involves formation of two ions so that the entropy decreases. On the second ionization of the same acid, there are now three ions and the anion has a charge, so the entropy again only decreases. Thermodynamic dissociation constant; Dissociation entropy; Dissociation enthalpy; Enthalpy-entropy compensation

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