Mass transport kinetics of the DNA-binding dye Hoechst-33342 into bovine spermatozoa

The mass transport kinetics for the unmediated diffusion of Hoechst-33342 dye (HO-33342) into spermatozoa was established at varying pH and temperature. The mass transport diffusion coefficient kdiff at 41.5 °C and pH 6.2 was determined to be 0.0435 min−1 [M sperm/mL]−1 and the energy of activation Ea associated with the temperature dependency of kdiff at 14.2 kcal/gmoL. The relationship of kdiff to pH was based mechanistically on the premise that the HO-33342 dye becomes more hydrophobic as the pH becomes more alkaline and therefore facilitates transport. The kdiff dependency on pH was described mathematically using a form of the Henderson–Hasselbalch equation in which the pKa of the HO-33342 dye was 6.6. Using the kinetic parameters, an Excel-based model was developed capable of predicting the time required for the HO-33342 dye to reach any specified level of saturation in the spermatozoa.

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