76
Kj = [BHP]/([BH]([Pt/2]-2[BHP])2) (3-4)
Ks and are the apparent association constants for the
surface-bound and intercalatively-bound drug-DNA complexes,
respectively. These equations were tested to certify their
validity under our experimental conditions. Recall that
plots of log ( [BHP]/ [BH] ) vs. log ( [P^m] -q [BHP] ) yield lines
whose slopes are equal to q and whose intercepts are equal
to log K. Tables 18 through 21 include calculated values
of log ( [BHP]/[BH]), log([Pt/3]-[BHP]), and log([Pfc/2]-2[BHP])
for representative titrations. Figures 7 and 8 are plots
of log([BHP]/[BH]) vs. log([Pty3]-[BHP]) for the reactions
in the presence of 0.0025M Cs+ and 6.3 x 10 Mg++; and in
0.15M Cs+, 0.010N Mg++, and 0.010M Cs+, respectively.
Figures 9 and 10 are plots of log ( [BHP] / [BH] ) vs. logUP^.^]-
2 [BHP]) for the same systems. Three general features are
particularly significant. One, the shapes and slopes of
the curves are essentially the same whether log ([P^^] [BHP] )
or log( IP32[BHP]) is plotted against log([BHP]/[BH]).
(Calculated slopes are tabulated in Table 23.) Only in the
latter portions of the titrations done in the more dilute
alkali metal electrolytes does this rule begin to break down.
Two, except for 0.15M Cs^PO., all plots of the data in
volving the presence of monovalent cations exhibit definite
curvature the lower the concentration, and further down
a series of the periodic chart, the greater the curvature.
2+
Conversely, all concentrations of all M salts yield