From owner-chemistry: at :ccl.net Fri Aug 29 00:00:00 2014 From: "busra dereli bsradereli---gmail.com" To: CCL Subject: CCL: Solvation Free Energy of Proton in THF Message-Id: <-50453-140828235830-9180-nANl1vHuUK5L3Wevg0uu4Q..server.ccl.net> X-Original-From: busra dereli Content-Type: multipart/alternative; boundary=bcaec52c5dfb2b8d6f0501bcaa18 Date: Fri, 29 Aug 2014 06:58:23 +0300 MIME-Version: 1.0 Sent to CCL by: busra dereli [bsradereli _ gmail.com] --bcaec52c5dfb2b8d6f0501bcaa18 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable When I modeled protonated THF, I got more reasonable numbers. However, I observe a significant deviation for the anionic system that makes me think about the anionic nature of the complex. Thanks a lot for all suggestions. Busra On Wed, Aug 27, 2014 at 2:33 PM, Andreas Klamt klamt/./cosmologic.de < owner-chemistry(!)ccl.net> wrote: > > Sent to CCL by: Andreas Klamt [klamt^^cosmologic.de] > Dear Busra, > > obviously Mariusz is absolutely right. If you really should like to try t= o > calculate absolute pKa, then you should get aware that the state of the > proton in THF surely is not an isolated proton, but a protonated THF. As = in > water you have H3O+. > > But I also would not expect that you can get an accurate prediction of th= e > total free energy of the protonated H3O+ with a continuum model. > > Best regards > > Andreas > > Am 27.08.2014 11:38, schrieb Mariusz Radon mariusz.radon[A]gmail.com: > > Sent to CCL by: Mariusz Radon [mariusz.radon::gmail.com] >> On 08/25/2014 08:23 PM, BUSRA DERELI bsradereli++gmail.com wrote: >> >>> Sent to CCL by: "BUSRA DERELI" [bsradereli::gmail.com] >>> Hello, >>> >>> I am trying to calculate pKa values of two systems, one is anionic and >>> the >>> other is cationic copper systems. I got so weird numbers not close to t= he >>> experimental values when I computed the free energy of proton in THF >>> which is >>> the solvent of interest. I use M11-L local functional with SDD basis se= t >>> on Cu >>> atom and 6-31G(d) on all other atoms in the system. Thus, I want to >>> compare the >>> computed solvation free energy of proton in THF with the experimental >>> value. In >>> some literature reports, I have seen absolute solvation free energy of >>> proton >>> in a couple of solvents but not in THF. >>> >>> Thanks, >>> Busra Dereli >>> >>> Dear Busra: >> >> Not very strange that you get weird number for solvation energy of >> proton which (unlike other ions) is just a point charge! As far as I >> know, it is extremely difficult to reproduce solvation energy of proton >> in such calculations. >> >> If your goal is to compare acidity of two substances, you are probably >> more interested in the difference of their pKa values, than in the >> individual pKa values. The point is that when you compute the >> difference, the (huge) error on the proton solvation energy cancels out >> exactly. Alternatively, you can compute relative pKa values of both >> substances with respect to some other chemical, treated as reference, >> whose actual pKa you take from experiment. That is much easier than >> trying to reproduce absolute pKa values. >> >> Best regards, >> Mariusz Radon >> >> > > -- > Prof. Dr. Andreas Klamt > CEO / Gesch=C3=A4ftsf=C3=BChrer > COSMOlogic GmbH & Co. KG > Imbacher Weg 46 > D-51379 Leverkusen, Germany > > phone +49-2171-731681 > fax +49-2171-731689 > e-mail klamt::cosmologic.de > web www.cosmologic.de > > [University address: Inst. of Physical and > Theoretical Chemistry, University of Regensburg] > > HRA 20653 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt > Komplementaer: COSMOlogic Verwaltungs GmbH > HRB 49501 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt > > > > > -=3D This is automatically added to each message by the mailing script = =3D-http://www.ccl.net/chemistry/sub_unsub.shtmlConferences: http://server.ccl.net/ > chemistry/announcements/conferences/> > > --bcaec52c5dfb2b8d6f0501bcaa18 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
When I modeled protonated THF, I got more reasonable numbe= rs. However, I observe a significant deviation=C2=A0=C2=A0for the anionic s= ystem that makes me think about the anionic nature of the complex.

=
Thanks a lot for all suggestions.

Busra


On Wed, Aug = 27, 2014 at 2:33 PM, Andreas Klamt klamt/./cosmologic.de <owner-chemistry(!)ccl.net> wrote:

Sent to CCL by: Andreas Klamt [klamt^^cosmologic.de]
Dear Busra,

obviously Mariusz is absolutely right. If you really should like to try to = calculate absolute pKa, then you should get aware that the state of the pro= ton in THF surely is not an isolated proton, but a protonated THF. As in wa= ter you have H3O+.

But I also would not expect that you can get an accurate prediction of the = total free energy of the protonated H3O+ with a continuum model.

Best regards

Andreas

Am 27.08.2014 11:38, schrieb Mariusz Radon mariusz.radon[A]gmail.com:

Sent to CCL by: Mariusz Radon [mariusz.radon::gmail.com]
On 08/25/2014 08:23 PM, BUSRA DERELI bsradereli++gmail.com wrote:
Sent to CCL by: "BUSRA=C2=A0 DERELI" [bsradereli::gmail.com]
Hello,

I am trying to calculate pKa values of two systems, one is anionic and the<= br> other is cationic copper systems. I got so weird numbers not close to the experimental values when I computed the free energy of proton in THF which = is
the solvent of interest. I use M11-L local functional with SDD basis set on= Cu
atom and 6-31G(d) on all other atoms in the system. Thus, I want to compare= the
computed solvation free energy of proton in THF with the experimental value= . In
some literature reports, I have seen absolute solvation free energy of prot= on
in a couple of solvents but not in THF.

Thanks,
Busra Dereli

Dear Busra:

Not very strange that you get weird number for solvation energy of
proton which (unlike other ions) is just a point charge! As far as I
know, it is extremely difficult to reproduce solvation energy of proton
in such calculations.

If your goal is to compare acidity of two substances, you are probably
more interested in the difference of their pKa values, than in the
individual pKa values. The point is that when you compute the
difference, the (huge) error on the proton solvation energy cancels out
exactly. Alternatively, you can compute relative pKa values of both
substances with respect to some other chemical, treated as reference,
whose actual pKa you take from experiment. That is much easier than
trying to reproduce absolute pKa values.

Best regards,
Mariusz Radon



--
Prof. Dr. Andreas Klamt
CEO / Gesch=C3=A4ftsf=C3=BChrer
COSMOlogic GmbH & Co. KG
Imbacher Weg 46
D-51379 Leverkusen, Germany

phone=C2=A0 =C2=A0+49-2171-731681
fax=C2=A0 =C2=A0 =C2=A0+49-2171-731689
e-mail=C2=A0 klamt::cosm= ologic.de
web=C2=A0 =C2=A0 =C2=A0www.cosmologic.de

[University address:=C2=A0 =C2=A0 =C2=A0 Inst. of Physical and
Theoretical Chemistry, University of Regensburg]

HRA 20653 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt
Komplementaer: COSMOlogic Verwaltungs GmbH
HRB 49501 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt




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