=0ASent: Thursday, 3 May 2012, 22:42=0ASubject: CC= L: Large value of equilibrium constants=0A =0A=0ADear Colleagues,=0AI carri= ed out some theoretical calculations on complexation of some transition met= al ions with a polypyridine ligand and I predicted the equilibrium constant= s for the assumed reversible reactions. I got values of K as high as 1 x 10= ^400 and in fact, an infinite value in one case.What do you think about the= se large values? I interpretated them to mean that the reactions are essent= ially irreversible.=0AThank you all.=0A=0A=A0=0AOlasunkanmi Lukman Olawale= =0A________________________________=0ACurrent Address:=0ADepartment of Chem= istry,=0AObafemi Awolowo University,=0AIle-Ife, Osun State.=0ANigeria.=0A= =0A+234-0-80-52401564 Or +234-0-80-67161091=0A_____________________________= ___ ---146335258-1435714669-1336199315=:26910 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable

Dear Olasunkanmi,

I am not sure if entropy an= d enthalpy values calculated at PM6 are OK or not. You had better see the b= inding energy between your ligand(s) and the metal ion; the energy for the = following reaction

M + (= n) L--> ML(n)

E(binding) =3D E(complex) - [E(meta= l) + E(ligands)]

It = must be in an acceptable range, something around 60-100 kJ per mole for eac= h metal-ligand bond. I mean if your complex is six coordinated, it's bindin= g energy cannot be greater than ~600 kJ per mole.

<= div>In the free energy equation, the effect of temperature in the sec= ond term, RHS of the equation can be very large, particularly, if the entropy is large. It may affects the final result seriously. Discuss about= the binding energy instead of the free energy and equilibrium constants...=

Finally, if it is possible for you, examine the val= idity of your data by computing binding energies at different theoretical l= evels (ab initio and DFT) and/or experimental values.

Good luck!

Cina=

**********************************************************= *******************************************

Cina For= outan-Nejad, Ph.D.

School of Chemistry, College of S= cience,

Univesity of Tehran, Tehran, Iran

http://independent.academia.edu/CinaForoutanNejad

From: Olasunkanmi Lukman Olawale walecomuk.:.yah= oo.co.uk <owner-chemistry a ccl.net>
To: "Foroutan-Nejad, Cina " <canyslopus a yahoo= .co.uk>
Sent: Frid= ay, 4 May 2012, 20:24
Subject: CCL: Large value of equilibrium constants

<= div id=3D"yiv463207733">

= Cina & Andrew: Thank you for your response. Here is the brief des= cription of what I actually did. M+ + L= =3D ML+

<= span>Delta G(rxn) =3D Delta H(rxn) - TxDelta S(rxn).

I used PM= 6 Hamiltonian in semiempirical quantum chemical calculation software (MOPAC= ). I got Delta H(rxn) from the Delta H(formation) of the species; and Delta= S(rxn) from the difference in absolute entropies of the species. I calcula= ted K (equilibrium constant) from Delta G(rxn).

Valu= es of K as high as 1 x 10^400 and infinity were obtained.

= What do you suggest?

Thank you.

Olasunkanmi Lukman Olawale

Current Address:
Department of Chemistry,
Obafemi Awolowo University,
Ile-Ife, Osun State.
Nigeria.

+234-0-80-52401564 = Or +234-0-80-67161091

From: cina forouta= n canyslopus()yahoo.co.uk <owner-chemistry%x%ccl.net>
To: "Olasunkanmi, Olawale Lukman " <= ;walecomuk%x%yahoo.co.uk>
Sent= : Thursday, 3 May 2012, 13:48
Subject: CCL: Large value of equilibrium constants

Dear Olasunkanmi,

<= span>

Would you please=0A mention at which theoretic= al level you performed the computations. Is it an ab initio or DFT or it is= of semi-empirical/molecular mechanic level? This might be a systematic err= or due to the computational level. Would you please also mention the amount= of the binding energies between the metal and ligands. If the binding ener= gy is very large, you must improve your computational level.

See this reference as an example of wrong computational level sele= ction: Sensors, 2007, 7, 3119.

Good Luck!

Cina

******= ***************************************************************************= ***************

Cina=0A Foroutan-Nejad, Ph.D.

School of Chemistry, College of Science

University of Tehran, Tehran, Iran

http://i= ndependent.academia.edu/CinaForoutanNejad

From:<= /b> Olasunkanmi Lukman Olawale walecomuk^_^yahoo.co.uk <owner-chemistry]= ^[ccl.net>
To: "Foro= utan-Nejad, Cina " <canyslopus]^[yahoo.co.uk>
Sent: Thursday, 3 May 2012, 22:42
Subject: CCL: Large value of equil= ibrium constants

Dear Colleagues,
I carried = out some theoretical calculations on complexation of some transition metal = ions with a polypyridine ligand and I predicted the equilibrium constants f= or the assumed reversible reactions. I got values of K as high as 1 x 10^40= 0 and in fact, an infinite value in one case.What do you think about these = large values? I interpretated them to mean that the reactions are essential= ly irreversible.
Thank you all.

Ol= asunkanmi Lukman Olawale
Current Address:
Department of=0A Chemistry,Obafemi Awolowo University,
Ile-Ife, Osun State.
Nigeria.
+2<= span style=3D"color:rgb(0, 0, 191);font-weight:bold;">34-0-80-52401564 Or += 234-0-80-67161091

---146335258-1435714669-1336199315=:26910-- From owner-chemistry@ccl.net Sat May 5 20:47:00 2012 From: "Nancy nancy5villa^-^gmail.com" To: CCL Subject: CCL: Chelation of Calcium with Citrate Message-Id: <-46859-120505204544-18232-5+IuoX2ol6nRDODmqTUQvg]*[server.ccl.net> X-Original-From: Nancy Content-Type: multipart/alternative; boundary=002354333c4ea17a3f04bf53783c Date: Sat, 5 May 2012 17:45:33 -0700 MIME-Version: 1.0 Sent to CCL by: Nancy [nancy5villa() gmail.com] --002354333c4ea17a3f04bf53783c Content-Type: text/plain; charset=ISO-8859-1 Hi All, I would like to find the stoichiometry for the chelation of a calcium ion (Ca 2+) with a citrate ion (citrate 3-), as well as the equilibrium constant or free energy of calcium-citrate complex formation. x*Ca2+ + y*citrate3- <=> z*calcium-citrate-complex (x, y, and z are the stoichiometric coefficients) Thanks in advance, Nancy --002354333c4ea17a3f04bf53783c Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi All,

I would like to find the stoichiometry for the chelation of = a calcium ion (Ca 2+) with a citrate ion (citrate 3-), as well as the equil= ibrium constant or free energy of calcium-citrate complex formation.

x*Ca2+=A0 +=A0 y*citrate3-=A0 <=3D>=A0 z*calcium-citrate-complex= =A0 (x, y, and z are the stoichiometric coefficients)

Thanks in adva= nce,
Nancy

--002354333c4ea17a3f04bf53783c-- From owner-chemistry@ccl.net Sat May 5 22:40:00 2012 From: "cina foroutan canyslopus+*+yahoo.co.uk" To: CCL Subject: CCL: Chelation of Calcium with Citrate Message-Id: <-46860-120505222735-14092-EYzDy1PlYpuGoNN37fB/BA/a\server.ccl.net> X-Original-From: cina foroutan Content-Type: multipart/alternative; boundary="-146335258-710115717-1336271245=:7495" Date: Sun, 6 May 2012 03:27:25 +0100 (BST) MIME-Version: 1.0 Sent to CCL by: cina foroutan [canyslopus[-]yahoo.co.uk] ---146335258-710115717-1336271245=:7495 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Dear Nancy,=0A=0AFinding the stoichiometric coefficient might be possible i= f you carefully probe the PES of the calcium citrate at an ab initio of DFT= level of theory (selecting a computational level depends on your computati= onal resources). However, I am not sure if you can find equilibrium constan= ts! Please remember that an equilibrium constant must be derived from the G= ibbs free energy equilibrium. So, you must have both the enthalpy and entro= py of your reaction as well as enthalpy and entropies of solvation. This ne= eds a precise solvation model, but to the best of my knowledge all solvatio= n models suffer from shortcomings more or less. That is why interactions li= ke hydrogen bonding are not included in such models. (Dear CCLers please co= mment on this statement if I am not right).=0A=0AI recommend you to discuss= about the energy changes upon complexation. You can easily discuss about t= he binding energies instead of equilibrium constants!=0A=0AGood luck=0ACina= =0A************************************************************************= ******************=0ACina Foroutan-Nejad,=0ASchool of Chemistry, College of= Sciences,=0AUniversity of Tehran, Tehran, Iran.=0Ahttp://independent.acade= mia.edu/CinaForoutanNejad=0A=0A=A0 =0A=0A=0A=0A____________________________= ____=0A From: Nancy nancy5villa^-^gmail.com =0ATo:= "Foroutan-Nejad, Cina " =0ASent: Sunday, = 6 May 2012, 4:45=0ASubject: CCL: Chelation of Calcium with Citrate=0A =0A= =0AHi All,=0A=0AI would like to find the stoichiometry for the chelation of= a calcium ion (Ca 2+) with a citrate ion (citrate 3-), as well as the equi= librium constant or free energy of calcium-citrate complex formation.=0A=0A= x*Ca2+=A0 +=A0 y*citrate3-=A0 <=3D>=A0 z*calcium-citrate-complex=A0 (x, y, = and z are the stoichiometric coefficients)=0A=0AThanks in advance,=0ANancy ---146335258-710115717-1336271245=:7495 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Dear Nancy,

Finding the stoichiometric coeffi= cient might be possible if you carefully probe the PES of the calcium citra= te at an ab initio of DFT level of theory (selecting a computational level = depends on your computational resources). However, I am not sure if you can= find equilibrium constants! Please remember that an equilibrium constant m= ust be derived from the Gibbs free energy equilibrium. So, you must have bo= th the enthalpy and entropy of your reaction as well as enthalpy and entrop= ies of solvation. This needs a precise solvation model, but to the best of = my knowledge all solvation models suffer from shortcomings more or less. Th= at is why interactions like hydrogen bonding are not included in such model= s. (Dear CCLers please comment on this statement if I am not right).
I recommend you to discuss about the e= nergy changes upon complexation. You can easily discuss about the binding e= nergies instead of equilibrium constants!

Good luck
Cina
***********************************************************************= *******************
Cina Foroutan-Nejad,
School of Chemistry, College of Sciences,
University of Tehran, Tehran, Iran.
http://indepen= dent.academia.edu/CinaForoutanNejad

From: Nancy nancy5villa^-^gmail.com= <owner-chemistry*o*ccl.net>
= To: "Foroutan-Nejad, Cina " <canyslopus*o*yahoo.co.uk&g= t;
Sent: Sunday, 6 Ma= y 2012, 4:45
Subject: = CCL: Chelation of Calcium with Citrate

Hi All,

I would like to find the stoichiometry for the = chelation of a calcium ion (Ca 2+) with a citrate ion (citrate 3-), as well= as the equilibrium constant or free energy of calcium-citrate complex form= ation.
=0A
x*Ca2+ + y*citrate3- <=3D> z= *calcium-citrate-complex (x, y, and z are the stoichiometric coeffici= ents)

Thanks in advance,
Nancy

=0A

<= /div>

---146335258-710115717-1336271245=:7495-- From owner-chemistry@ccl.net Sat May 5 23:57:00 2012 From: "Nancy nancy5villa-#-gmail.com" To: CCL Subject: CCL: Chelation of Calcium with Citrate Message-Id: <-46861-120505235601-10398-aTpKAAVAUeNvfKwPyi46Iw~~server.ccl.net> X-Original-From: Nancy Content-Type: multipart/alternative; boundary=485b397dd53b4b163e04bf56215f Date: Sat, 5 May 2012 20:55:53 -0700 MIME-Version: 1.0 Sent to CCL by: Nancy [nancy5villa],[gmail.com] --485b397dd53b4b163e04bf56215f Content-Type: text/plain; charset=ISO-8859-1 I am interested in experimentally derived equilibrium constants or free energies for the calcium-citrate complex formation. I would appreciate it if anyone has info on this. Thanks, Nancy On Sat, May 5, 2012 at 7:27 PM, cina foroutan canyslopus+*+yahoo.co.uk < owner-chemistry*o*ccl.net> wrote: > Dear Nancy, > > Finding the stoichiometric coefficient might be possible if you carefully > probe the PES of the calcium citrate at an ab initio of DFT level of theory > (selecting a computational level depends on your computational resources). > However, I am not sure if you can find equilibrium constants! Please > remember that an equilibrium constant must be derived from the Gibbs free > energy equilibrium. So, you must have both the enthalpy and entropy of your > reaction as well as enthalpy and entropies of solvation. This needs a > precise solvation model, but to the best of my knowledge all solvation > models suffer from shortcomings more or less. That is why interactions like > hydrogen bonding are not included in such models. (Dear CCLers please > comment on this statement if I am not right). > I recommend you to discuss about the energy changes upon complexation. You > can easily discuss about the binding energies instead of equilibrium > constants! > > Good luck > Cina > > ****************************************************************************************** > Cina Foroutan-Nejad, > School of Chemistry, College of Sciences, > University of Tehran, Tehran, Iran. > http://independent.academia.edu/CinaForoutanNejad > > > > ------------------------------ > *From:* Nancy nancy5villa^-^gmail.com > *To:* "Foroutan-Nejad, Cina " > *Sent:* Sunday, 6 May 2012, 4:45 > *Subject:* CCL: Chelation of Calcium with Citrate > > Hi All, > > I would like to find the stoichiometry for the chelation of a calcium ion > (Ca 2+) with a citrate ion (citrate 3-), as well as the equilibrium > constant or free energy of calcium-citrate complex formation. > > x*Ca2+ + y*citrate3- <=> z*calcium-citrate-complex (x, y, and z are > the stoichiometric coefficients) > > Thanks in advance, > Nancy > > > > > > --485b397dd53b4b163e04bf56215f Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable I am interested in experimentally derived equilibrium constants or free ene= rgies for the calcium-citrate complex formation.=A0 I would appreciate it i= f anyone has info on this.

Thanks,
Nancy

On Sat, May 5, 2012 at 7:27 PM, cina foroutan canyslopus+*+yahoo.co.uk <owner-chemistry*o*ccl.net> wrote:

Dear Nancy,

<= span>

Finding the stoichiometric coefficient might be possible if you = carefully probe the PES of the calcium citrate at an ab initio of DFT level= of theory (selecting a computational level depends on your computational r= esources). However, I am not sure if you can find equilibrium constants! Pl= ease remember that an equilibrium constant must be derived from the Gibbs f= ree energy equilibrium. So, you must have both the enthalpy and entropy of = your reaction as well as enthalpy and entropies of solvation. This needs a = precise solvation model, but to the best of my knowledge all solvation mode= ls suffer from shortcomings more or less. That is why interactions like hyd= rogen bonding are not included in such models. (Dear CCLers please comment = on this statement if I am not right).
I recommend you to discuss about the e= nergy changes upon complexation. You can easily discuss about the binding e= nergies instead of equilibrium constants!

Good luck
Cina
***= ***************************************************************************= ************
Cina Foroutan-Nejad,
School of Chemistry, College of Sciences,
Univ= ersity of Tehran, Tehran, Iran.
http://independ= ent.academia.edu/CinaForoutanNejad

=A0

From: Nancy nancy5villa^-^gmail.com <owner-chemistry^-^ccl.net>
To: "Foroutan-Nejad, C= ina " <canyslopus^-^yahoo.co.uk>
Sent:= Sunday, 6 May 2012, 4:45
Subject: CCL: Chelation of = Calcium with Citrate

Hi = All,

I would like to find the stoichiometry for the chelation of a c= alcium ion (Ca 2+) with a citrate ion (citrate 3-), as well as the equilibr= ium constant or free energy of calcium-citrate complex formation.

x*Ca2+=A0 +=A0 y*citrate3-=A0 <=3D>=A0 z*calcium-citrate-complex= =A0 (x, y, and z are the stoichiometric coefficients)

Thanks in adva= nce,
Nancy

--485b397dd53b4b163e04bf56215f--