APS & TEMED in acid gels

Edmundo Castro ecastro at physci.ucla.edu
Thu Jan 23 19:01:19 EST 1997


Steven Cohen wrote:
> 
> This does not make sense to me either. Perhaps the kinetics of the
> polymerization will be increased, but it is the amount of Bis-Acrylamide and
> total Acrylamide concentration  that controls the quantity of cross-linking
> which controls the porosity of the gel. Just like other catalysts, APS and
> TEMED do not effect the final product but the speed in which equalibrium is
> reached.

> >
> >Is this really true?  I was under the impression that the porosity
> >was governed by the % acrylamide and by the ratio of acrylamide/bis
> >(or other cross-linker).  The concentration of TEMED and/or persulphate
> >shouldn't have any effect unless they become limiting - so that the
> >gel fails to polymerise completely no matter how long it is left.
> >Since they only catalyse the polymerisation of the acrylamide monomer
> >they play no real role in the eventual structure of the gel.
> >       Can someone correct or confirm my assumption?


If you have an excess of APS  the ratio of radicals generated would be changed.  
Instead of having an optimal number of acrylamide radical being generated (which will 
react with the bis-acrylamide) you will have an excess of APS radicals which: 

1- will react with each other thereby terminating the reaction (they can no longer 
generate acrylamide radicals).

2- more importantly: will react with  acrylamide radicals thereby preventing the 
acrylamide radical reaction with other acrylamide radicals and bis-acrylamide.

But, I have increased the amounts of APS and TEMED in the past (usually APS by 
50%) and have had no problems.  Usually, I only use freshly made APS for 
sequencing gels, when I use old APS (up to 4 weeks old) in gels for westerns I bump 
up the amount of APS.

BTW, warming up the mix slightly can significantly speed up the polymerazation 
process.

EC



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