Expt4 - B I/CH 3 68 L aboratory E xperiment 4 A B etter...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
BI/CH 368 – Laboratory Experiment 4 A Better Herbicide? An Investigation in Rational Molecular Design Case Background You have begun your new job in chemical manufacturing, and your first assignment is to design a new herbicide that is broadly effective, but relatively short-lived in the environment. One of the most widely used general herbicides is DCMU, developed by DuPont in 1954 and marketed as Diuron. However, DCMU is relatively persistent in the environment and can inhibit subsequent growth of desired plants (Field et al. 2003; Tomlin 2003). While most agricultural workers have not been complaining too much about DCMU, you see this assignment as a means to firmly establish yourself in the company as a Wunderkind . You know from your undergraduate days that many substituted quinones are structurally similar to an important intermediate in photosynthesis, and that they break down relatively quickly in the environment. You decide to use these quinones to inhibit photosynthesis and then use a computer program to study the correlation between quinone structure and inhibitory effectiveness (high inhibition of photosynthesis will kill a plant more quickly). You plan to use these data to design a molecule with the perfect features for killing weeds by inhibiting their photosynthesis that will not persist in the environment. (Source: Reuters) Experimental Background Photosynthetic electron transport can be inhibited in the presence of certain compounds that act as herbicides. The compounds that you will investigate are structural analogues of the mobile electron carrier Q B , a nonpolar plastoquinone. Q B shuttles reducing equivalents from the membrane-bound protein complex Photosystem II to the cytochrome bf complex. Oxidized Q B binds via specific interactions to one of the protein components of Photosystem II and acts as a two-electron acceptor. The reduced form then diffuses through the membrane until it encounters a specific binding site on the cytochrome bf complex, where it donates its electrons.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
BI/CH 368 Laboratory - Experiment 4- Spring 2012 2 Analogues of Q B inhibit electron transport by blocking the binding site on Photosystem II within a protein called D1. You will measure the rate of electron transfer within illuminated chloroplasts by monitoring reduction of DCPIP spectrophotometrically (DCPIP changes from blue to colorless as it is reduced). In an aqueous solution of chloroplasts, DCPIP accepts electrons from Photosystem II via Q B . Blocking the Q B binding site on D1 results in decreased reduction of DCPIP. You will use the decreased rate in DCPIP reduction to assess the efficiency of a wide range of potential inhibitors of Q B binding. By analyzing the structures of these compounds and determining what molecular features lead to maximal inhibition, you will determine a quantitative structure-activity relationship (QSAR) that should allow you to characterize the binding site of D1 and postulate the structure of the ideal inhibitor. Structures of Quinones to be Analyzed
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/31/2012 for the course CHEM 360 taught by Professor Millard during the Spring '12 term at Colby.

Page1 / 8

Expt4 - B I/CH 3 68 L aboratory E xperiment 4 A B etter...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online