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Intercalation binding of 6‐substituted naphthothiopheneamides to DNA: Enthalpy and entropy components
Author(s) -
Hopkins Harry P.,
Ming Yang,
Wilson W. David,
Boykin David W.
Publication year - 1991
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360310910
Subject(s) - chemistry , intercalation (chemistry) , enthalpy , trifluoromethyl , substituent , stereochemistry , exothermic reaction , crystallography , titration , medicinal chemistry , inorganic chemistry , organic chemistry , thermodynamics , alkyl , physics
N‐(3‐dimethylaminopropyl) naphtho [2, 1‐ b ] thiophene‐4‐carboxamide and the 6‐substituted methoxy, methyl, fluoro, chloro, bromo, trifluoromethyl, and cyano derivatives have been shown to bind to DNA via intercalation with binding constants in the 35–900 × 10 3 range at 25°C, pH 7, and [Na + ] = 0.019 M . Both electron‐donating and ‐withdrawing substituents enhance intercalation binding, but the binding affinity is most enhanced by the cyano substituent. Calorimetric titrations for calf thymus DNA differ dramatically from those reported for ethidium [Hopkins et al. (1990) Biopolymers Vol. 29, pp. 449–459]. Apparent enthalpy parameters (Δ H B ) for intercalation are constant only at low coverage of sites and become much more positive as saturation is approached. In the plateau region, Δ H B values for the parent and the cyano‐, fluoro‐, chloro‐, and bromo‐substituted compounds are nearly the same (∼ −5.9 kcal/mol). For the methyl‐ (−6.8 kcal/mol) and methoxy‐ (−7.5 kcal/mol) substituted compounds, the Δ H B values are more exothermic than that for the un‐substituted compound, whereas Δ H B for the trifluoromethyl compound is approximately 1 kcal/mol less exothermic. The corresponding Δ S B values, corrected for mixing effects, are in the 7–15‐cal/deg/mol range and are approximately linearly related to Δ H B if the cyano derivative is excluded.