Abstract
Varied concentrations of tetramethyl- (TMAB), tetraethyl- (TEAB), tetrapropyl- (TRAB), tetrabutyl- (TBAB), tetrapentylammonium bromide (TPAB) and ammonium bromide are monitored for effects on DNA sedimentation, viscosity and melting temperature. No changes are observed at 25–30°C for the hydrodynamic properties of DNA when treated with the quaternary ammonium bromide. At higher temperatures, 30–100°C, the tetraalkyl-ammonium bromides reduce the temperature required for conversion of the DNA double-strand helix to the coil (T m). A form of Debye-Huckel equation ( T m=a mu; 2 + b ) accurately describes the results. Ionic strength of the quaternary ammonium compounds is represented by μ/2. The potency of tetraalkylammonium bromide in reducing T m (“a” in the T m equation) is correlated with the hydrophobicity of the molecule (number of carbon atoms), r = 0.999 and F = 526 (r represents the correlation coefficient and F represents the test value for significance of the equation evaluated by least squares analysis). The T m of rat liver chromatin is also reduced in a similar fashion by TPAB. The T m of poly(dG-dC) is not altered by 0.1 M TBAB whereas the T m of poly(dA-dT) is greatly reduced by the compound. It is thought that the tetraalkylammonium bromide preferentially binds to the coil of DNA during heating and that a preferentially hydrophobic interaction may occur with the adenine-thymine bases.
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