[gmx-users] Order parameter for unsaturated lipid chain in UA model

2010-02-25 Thread Sarah Witzke
Dear gmx users,

 

I am sorry to ask this question again, but reading in the email achieve did not 
enlighten me. I found this email which describes my problem, but unfortunately 
it has no replies:

http://lists.gromacs.org/pipermail/gmx-users/2008-July/034950.html 

Also there are these two recently emails: 
http://lists.gromacs.org/pipermail/gmx-users/2010-January/047767.html 
http://lists.gromacs.org/pipermail/gmx-users/2010-January/047767.html , but I 
am still in doubt.

So my question is regarding the unsaturated lipid chain of POPC. I would like 
to calculate the order parameters for my united atoms so I make first an index 
file with the tail atoms from the carbonyl-C to the methyl-C and then I run 
g_order -od. Then I make a new index file with the two atoms of the double bond 
and the atom before and after the double bond (four atoms in total) running 
g_order -unsat -od

I then take the two values from the last g_order run and replace them with the 
order parameters for the double bond calculated without -unsat. When looking at 
the graph and comparing to the literature this graph it looks wrong: First 
there is a small dip in the order for the atom before the double bond, then it 
goes a bit up for the first double bonded C, and then for the next double 
bonded C and the atom after that the order is quite low. I know this 
description is not good, but it was just to explain, that the graph is not as 
expected.

I would very much appreciated if anyone could tell me, where I go wrong.

 

Thank you,

Sarah 

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Re: [gmx-users] Order parameter for unsaturated lipid chain in UA model

2010-02-25 Thread Justin A. Lemkul



Sarah Witzke wrote:

Dear gmx users,

 


I am sorry to ask this question again, but reading in the email achieve did not 
enlighten me. I found this email which describes my problem, but unfortunately 
it has no replies:

http://lists.gromacs.org/pipermail/gmx-users/2008-July/034950.html 


Also there are these two recently emails: 
http://lists.gromacs.org/pipermail/gmx-users/2010-January/047767.html 
http://lists.gromacs.org/pipermail/gmx-users/2010-January/047767.html , but I 
am still in doubt.

So my question is regarding the unsaturated lipid chain of POPC. I would like 
to calculate the order parameters for my united atoms so I make first an index 
file with the tail atoms from the carbonyl-C to the methyl-C and then I run 
g_order -od. Then I make a new index file with the two atoms of the double bond 
and the atom before and after the double bond (four atoms in total) running 
g_order -unsat -od

I then take the two values from the last g_order run and replace them with the 
order parameters for the double bond calculated without -unsat. When looking at 
the graph and comparing to the literature this graph it looks wrong: First 
there is a small dip in the order for the atom before the double bond, then it 
goes a bit up for the first double bonded C, and then for the next double 
bonded C and the atom after that the order is quite low. I know this 
description is not good, but it was just to explain, that the graph is not as 
expected.

I would very much appreciated if anyone could tell me, where I go wrong.



I don't see why a drop in the order parameter is unexpected.  I see it all the 
time in published papers of unsaturated lipids, for example:


http://pubs.acs.org/doi/abs/10.1021/jp902131b
http://www3.interscience.wiley.com/journal/114209721/abstract

-Justin

 


Thank you,

Sarah 



--


Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin


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