Poison Ivy Exudates (fwd)

John M. Brown jbrown01 at MAIL.COIN.MISSOURI.EDU
Wed Mar 29 23:30:19 EST 1995

Date: Thu, 23 Mar 1995 11:01:29 -0600
From: Jeff Dean <jdeanx1 at uga.cc.uga.edu>
Subject: Re: Poison Ivy Exudates

        (I tried to post this back to the newsgroup since I thought
it might be of interest to a wider audience, but I am having a bit of
trouble with the link between the server and my threaded reader. Feel 
free to repost it if you can.)
	The "tar" you saw was a high molecular weight polymer of a
sesquiterpenoid catechol, commonly referred to as urushiol. The 
urushiol monomers (these are also the allergens that make you itch
after handling fresh poison oak, ivy or sumac) are polymerized in a
free radical-mediated reaction catalyzed by laccases when the sap
is exposed to oxygen. These sap components and the reaction are
common to all members of the Toxidendron family and even some of the
related Anacardaceae (eg. mango -- this is why some people feel itchy
after eating mangoes, particularly if they ingest any of the fruit 
skin). A high-quality version of this sap harvested from the 
Japanese lacquer tree (Rhus vernicifera) is the varnishing agent for
all the black lacquerware commonly seen throughout east Asia. If you
would like more info, a good general discussion of the topic was 
written by Don Snyder (1989 J. Chem Edu. 66:977-980.
	It's really a pretty interesting story.


*                              *                                      *
* Jeffrey F.D. Dean, Ph.D.     * "Ay," quoth my uncle Gloster,        *
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