thank you very much for your prompt reply! 
if i just want to  get the conformation change free energy, such as B --> B', how to do it ? is there a tutorial for it? with respect to 
A + B --> AB', can i devise a process like this, A + B --> A + B' --> AB', to compute the overall free energy?
Junjian
----- Original Message ----- 
From: "David Case" <dacase.rci.rutgers.edu>
To: "AMBER Mailing List" <amber.ambermd.org>
Sent: Wednesday, March 16, 2011 9:25 PM
Subject: Re: [AMBER] using thermodynamic integration,how to deal with absolute pka and conformation change
> 
> 
> On Mar 16, 2011, at 8:58 AM, "Junjian Miao" <junjianmiao.gmail.com> wrote:
> 
>> regarding  thermodynamic integration, i have a couple of questions, one is can i use it to simulate absolute pka, for example, CH3COOH + H2O --> 
>> CH3COO-  +  H3O+  ?the tutorial A6 demonstrates how to simulate the relative pka, however no comments about absolute one.
> 
> You can't get absolute pKa's from molecular mechanics.  Google on something like "DFT absolute pka".
> 
>> another is, for instance, as for reaction A + B --> AB', where the conformation of B changes significantly, in this case, how to simulate the reaction to get the absolute free energy?
> 
> There is no general answer, since it depends on the nature of A and B, and the amount of change.  The mailing list is not a good way to get such general questions answered.  Try to find papers or reviews that describe problems similar to yours.
> 
> ..dac
>> 
> 
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Received on Thu Mar 17 2011 - 21:00:03 PDT