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Hydrophobic interactions of DNA with long‐chain amines
Author(s) -
Chatterjee R.,
Chattoraj D. K.
Publication year - 1979
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.1979.360180112
Subject(s) - chemistry , bromide , ammonium bromide , ligand (biochemistry) , amine gas treating , ionic strength , ammonium , binding energy , medicinal chemistry , inorganic chemistry , stereochemistry , pulmonary surfactant , organic chemistry , aqueous solution , biochemistry , receptor , physics , nuclear physics
The binding ratio, Γ a , for several long‐chain amines to calf‐thymus DNA was measured as function of the ligand concentration, C , using the equilibrium dialysis method. The different amines used in the binding experiments at constant temperature were dodecyl trimethyl ammonium bromide (DTAB), myristyl trimethyl ammonium bromide (MTAB), cetyl trimethyl ammonium bromide (CTAB), and cetyl pyridinium chloride (CPCL). The formation and dissociation of the saturated DNA–amine complex were reversible. The initial slope of the binding isotherm decreased sharply with the reduction of the electrostatic effect as a result of the increase of the ionic strength of the medium. A sharp inflexion region was noted in the binding isotherm where the ligands bound in significant numbers may undergo hydrophobic interactions with each other. Γ a increased with C until a maximum value, Γ a m , was reached, beyond which binding slowly decreased with an increase of concentration. Both Γ a m and Γ a increased significantly with the increase of the hydrocarbon chain length of a ligand. The free energy change Δ G m for each saturated DNA–amine complex was evaluated on the basis of a thermodynamic relation and the standard state for binding was defined. The average free energy change for the binding per CH 2 group of the amine was found to be −1550 cal/mol. The difference between Δ G m for CTAB and CPCL was examined on the basis of the structural difference of their head groups. The binding isotherms for MTAB and CPCL were obtained from the binding data at 15, 30, and 45°C. The binding increased with increasing temperature. From the plot of Δ G m / T vs 1/ T , the changes in enthalpy and entropy due to the binding were evaluated for MTAB and CPCL. The binding reactions in these two cases were driven primarily by the entropy change due to the hydrophobic interaction. Standard free energy changes Δ G 0 m for the unsaturated complexes were close to Δ G m for the saturated complexes. The binding isotherms also depended on the nature of the neutral salt of the medium. At a given salt concentration, the order of the binding of the inorganic salts was as follows: KCl > NaCl > LiCl > Na 2 SO 4 > MgCl 2 . The effect of pH on binding was also examined. The importance of these results on the formation of the reconstituted and natural nucleohistone complexes is discussed.