TABLE 4.

Partition coefficients determined from the apparent first-order rate constants for the reaction between MePEG-OPSS reagents and Cys-135 in L135C₇ αHL pores

MePEG-OPSS*	1000 mM KCl	300 mM KCl†
PEG-0.85k	0.34 ± 0.06	0.32 ± 0.04
PEG-1.7k	0.14 ± 0.03	0.13 ± 0.03
PEG-2.5k	0.069 ± 0.009	0.058 ± 0.008
PEG-5.0k	0.0040 ± 0.0008	0.0032 ± 0.0007

Values are the mean ± SD of four experiments. The buffer solutions also contained 10 mM Tris·HCl and 100 μM EDTA, pH 8.5. The polymer concentration in the trans bath was 4 mM. The applied potential was −40 mV for the experiments at 300 mM KCl and +100 mV for the experiments at 1000 mM KCl. The partition coefficients (Π) were calculated from the reaction rates by applying a scaling law, which has been shown to apply to the αHL pore (Movileanu and Bayley, 2001), , where k′ is the apparent first-order reaction rate constant; a, the persistence length of the polymer (3.5 Å) (Rex et al., 1998; Kienberger et al., 2000); D, the diameter of the transmembrane barrel; k, the second-order reaction rate constant; and [PEG]_sol, the PEG concentration in the bulk aqueous phase. The slope of a plot of ln k′ versus N was used to obtain (a/D)^5/3, which was used to obtain Π for the various polymers from .

^*M_n values are given for the MePEG part of the molecules only.

^†These values are from Movileanu and Bayley (2001).