= Derek A. Pratt
{c}
\b[Derek A. Pratt] studies the mechanisms and products of <radical (chemistry)> reactions, including hydrocarbon and <lipid> oxidation and its inhibition by <antioxidants>. His University of Ottawa profile identifies this research programme and his chemistry affiliation.<Derek Pratt at the University of Ottawa>[Official biography and research interests]{ref} With <Evan A. Haidasz> and <Antonius T. M. Van Kessel>, he coauthored the visible-light spectrophotometric method for <radical-trapping antioxidant> reactivity.<A Continuous Visible Light Spectrophotometric Approach To Accurately Determine the Reactivity of Radical-Trapping Antioxidants by Evan A. Haidasz and others>[Byline and Abstract]{ref}
\Image[https://www.uottawa.ca/faculty-science/sites/g/files/bhrskd386/files/2022-08/D.Pratt_.jpg]
{title=Derek A. Pratt, portrait identified by the University of Ottawa}
{description=External portrait labelled Derek Pratt on the official Faculty of Science profile.}
An original steady-state model illustrates why adding a trap can change oxidation kinetics. Let radicals enter at rate $R_i$, disappear by bimolecular <radical chain termination> at rate $2k_tR^2$, and be removed by trapping at rate $aR$. Radical balance gives
$$
R_i=2k_tR^2+aR,\qquad
R=\frac{\sqrt{a^2+8k_tR_i}-a}{4k_t}.
$$
With no trapping, $R=\sqrt{R_i/(2k_t)}$; with sufficiently strong trapping, $R\simeq R_i/a$. A substrate-oxidation rate proportional to $R$ consequently follows different initiation-rate scalings in those regimes.
For chosen $R_i=2\,\mathrm{\mu mol\,L^{-1}\,s^{-1}}$ and $k_t=1\,\mathrm{L\,\mu mol^{-1}\,s^{-1}}$, the no-trap radical concentration is $1\,\mathrm{\mu mol\,L^{-1}}$. Adding $a=3\,\mathrm{s^{-1}}$ gives $R=0.5\,\mathrm{\mu mol\,L^{-1}}$. These are illustrative model parameters, not measurements from Pratt's work. Experimental interpretation must identify which reactions the optical reporter follows; a reduced signal alone does not locate the inhibited chemical step or establish an effect in a living system.
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