From owner-biophysics@net.bio.net Sat Mar 26 22:00:00 1994 Path: biosci!agate!library.ucla.edu!news.mic.ucla.edu!unixg.ubc.ca!thackray From: thackray@unixg.ubc.ca (David Thackray) Newsgroups: bionet.biophysics Subject: Re: Isobestic point def'n wanted Date: 27 Mar 1994 06:03:14 GMT Organization: University of British Columbia, Vancouver, B.C., Canada Lines: 21 Message-ID: <2n37j2$slj@nnrp.ucs.ubc.ca> References: <1994Mar23.143955.1@opal.tufts.edu> <1994Mar23.230900.4807@alchemy.chem.utoronto.ca> NNTP-Posting-Host: unixg.ubc.ca In article <1994Mar23.230900.4807@alchemy.chem.utoronto.ca>, Marc Roussel wrote: >In article <1994Mar23.143955.1@opal.tufts.edu> skrishna@opal.tufts.edu writes: >>Can anyone give me a good definition of "isobestic point"? I heard it used in >>a seminar in a way I did not understand. > > In spectroscopy, it's a point whose absorbance is constant over the >course of a chemical reaction. > > Marc R. Roussel > mroussel@alchemy.chem.utoronto.ca Its the point in a spectrum of a reaction mixture where the reactants and products have equal extinction coefficients (presumably non zero :)) AND either there is only one reactant and one product absorbing at that point OR if there are reactants in rapid equilibrium with each other and/or ditto amongst the products. I think thats clear... A common assumption is that isosbestic points signify a one reactant to one product step being monitored at that point in the spectrum - which is not necessarily true. .