>From: athel at ir2cbm.cnrs-mrs.fr (Athel Cornish-Bowden)
>Subject: Re: Heterogenous catalysis
>...the rate at which molecules diffuse depends on lots of things: ....
One of the biggest determinants of diffusion rates in liquids is the
properties of the solvent. In water, most small molecules (substrates)
have a diffusivity of ~ 10^-5 cm^2/s, and for these sorts of
order-of-magnitude analyses, that value is good enough.
>... a reaction between a small molecule and a large one resembles a
>reaction between two small molecules more than one between two large ones.
That may be. Certainly the size of a proteins will give them much lower
diffusivities (ie, an order of magnitude or two lower), so they will be
essentially immobile compared to many substrates.
-Paul Schlosser
