Jj. Lee et Wt. Ford, ACCELERATION OF O-IODOSOBENZOATE-CATALYZED HYDROLYSIS OF P-NITROPHENYL DIPHENYL PHOSPHATE BY CATIONIC POLYMER COLLOIDS, Journal of the American Chemical Society, 116(9), 1994, pp. 3753-3759
Cross-linked polystyrene latexes containing (styrylmethyl)trialkylammo
nium chloride repeat units greatly accelerate the o-iodosobenzoate (IB
A) catalyzed hydrolysis of p-nitrophenyl diphenyl phosphate (PNPDPP).
The half-life of PNPDPP is as short as 3 s with 0.10 mg mL(-1) of part
icles containing 24 mol % of (styrylmethyl)tributylammonium chloride r
epeat units (TBAQ24) and 4 x 10(-5) M IBA in TAPS buffer at pH 9.1 and
25.0 degrees C, and the apparent second-order rate constant (k(IBA))
exceeds that in the absence of latexes by 6300 times, the largest rate
enhancement reported for IBA-catalyzed hydrolysis of PNPDPP in any co
lloidal or polymeric medium. The k(IBA) value increases with increasin
g radius of the quaternary ammonium ion (trimethyl < triethyl < tripro
pyl < tributyl) and with decreasing mole % of (styrylmethyl)trimethyla
mmonium chloride (TMAQ) repeat units in the latexes. The amounts of IB
A and chloride ions bound to latexes were measured directly by UV spec
trophotometry and chloride-selective electrode analysis of ultrafiltra
tes from dispersions, and ion exchange selectivity coefficients for IB
A and TAPS anions relative to chloride were calculated. The sizes of w
ater-swollen particles were measured by dynamic and static light scatt
ering. Using an ion-exchange model, the second-order rate constants k(
2L) in the latex phase were estimated from observed rate constants, th
e percent of IBA bound, and the particle volumes. The 6300 times rate
enhancement in the TBAQ24 dispersion is due ten times to a higher intr
aparticle rate constant and 630 times to higher local concentrations o
f IBA and PNPDPP in the latex phase. With the most hydrophilic TMAQ la
tex particles, the rate enhancements are due entirely to higher reacta
nt concentrations in the particles. The intraparticle rate constants a
t pH 9.1 and the ion exchange selectivity coefficients can be used to
predict rate constants as functions of pH, amount of latex particles,
and amount of added NaCl.