[gmx-users] Surface tension calculation for organic monolayer

[Naga Rajesh Tummala]

Few things to check:

Do you observe that the cis-pinonic acid or alcohol forms a monolayer at
the water-vacuum interface?
If yes, are solvation energies considered in the force filed development
for this organic molecule (that can make the difference) An example of
where we observed "http://pubs.acs.org/doi/abs/10.1021/la904615u"





On Thu, Jul 7, 2016 at 11:51 AM, gozde ergin <gozdeeergin at gmail.com> wrote:

> Dear Spoel,
> Thanks for your respond.
> For this simulations I used acids however I got the similar results when I
> used alcohol (pK values are lower than acids).
> I doubt this error coming from the pH effects.
> But how could i get the protonated molecules configuration?
> > On 07 Jul 2016, at 17:11, David van der Spoel <spoel at xray.bmc.uu.se>
> wrote:
> >
> > On 07/07/16 16:06, gozde ergin wrote:
> >> Dear users,
> >>
> >> I simulated three different systems in cubic box and calculated their
> surface tension as shown below;
> >>
> >> 1. Pure water , surface tension = 61.5 mN/m
> >> 2. Water with 3M NaCl salt, surface tension = 66.5 mN/m
> >> 3.Water surface covered with cis-pinonic organic, surface tension =
> 63.5 mN/m
> >>
> >> For system 1 and 2, the results are almost correct however the result
> for system 3 is not correct.
> >>
> >> Cis-pionic is an surface active molecule and should lower the surface
> tension.
> >> However in my simulations I could not capture this trend.
> >> I used GAFF force field and LINCS for the constraints.
> >> Does anyone has any idea?
> >> Or is there anyone that calculated the surface tension for organic
> coated surfaces with GAFF force field?
> >>
> >> Thanks
> >>
> > Maybe you should consider pH effects? Since this is an acid I would
> guess part of these are deprotonated in solution, did you consider the pK?
> You probably need to mix different amounts of protonated and deprotonated
> molecules and plot the surface tension as a function of the protonation
> state.
> >
> > --
> > David van der Spoel, Ph.D., Professor of Biology
> > Dept. of Cell & Molec. Biol., Uppsala University.
> > Box 596, 75124 Uppsala, Sweden. Phone:        +46184714205.
> > spoel at xray.bmc.uu.se    http://folding.bmc.uu.se
> > --
> > Gromacs Users mailing list
> >
> > * Please search the archive at
> http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before
> posting!
> >
> > * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
> >
> > * For (un)subscribe requests visit
> > https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or
> send a mail to gmx-users-request at gromacs.org.
>
> --
> Gromacs Users mailing list
>
> * Please search the archive at
> http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before
> posting!
>
> * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
>
> * For (un)subscribe requests visit
> https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or
> send a mail to gmx-users-request at gromacs.org.
>



-- 
Naga Rajesh Tummala