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Default for Solubility gain per charge in the Compound block #38

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TatianaAlieva opened this Issue Jul 3, 2017 · 3 comments

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TatianaAlieva commented Jul 3, 2017

Hi to everybody,
Excuse me, what rational is behind the default value of 1000 for Solubility gain per charge?
Thank you in advance!!

@msevestre msevestre added the question label Jul 3, 2017

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Yuri05 Jul 5, 2017

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The logP is typically reduced by 3-4 units.
According to our observations, however, it is mostly near 3 (factor 1000).
Since solubility is reciprocal to lipophilicity, a solubility increase of 1000 is assumed.

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Yuri05 commented Jul 5, 2017

The logP is typically reduced by 3-4 units.
According to our observations, however, it is mostly near 3 (factor 1000).
Since solubility is reciprocal to lipophilicity, a solubility increase of 1000 is assumed.

@Yuri05 Yuri05 added the answer label Jul 5, 2017

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TatianaAlieva Jul 7, 2017

Hi,
when I asked, I hoped to learn a new thing for myself, and not to make another argument here. However, this answer is in obvious contradiction with solubility and LogP octanol-water definitions. So, I clarify this, but I will not argue further.

Aqueous solubility is not reciprocal to LogP.
Solution process is a transfer from pure liquid state of the solute to solution (aqueous in our case). Solution energy can be represented as
Gsolution=Gvaporization+Gsolvation_in_H20
(Solvation is the gas-to-solvent transfer according to IUPAC).
In contrast, octanol-water partitioning refers to transfer: solution in water ->solution in octanol
Go-w= Gsolvation_oct -Gsolvation_in_H20
A very good diagram illustrating the difference between solubility and partitioning is represented in Zhang and Gobas (1995), Fig 2.

The first terms in the eqs. above (Gvaporization and Gsolvation_oct) are not negligible, therefore LogS and LogP are not reciprocal.

Further,

The logP is typically reduced by 3-4 units.

I guess you mean here that LogP for the ionized species is typically 3-4 units lower than that one for the neutral one, correct? Therefore LogD never goes 3-4 units below logP at any pH.
As far as I understand, this property is related to solvation in octanol process (because the residual water in octanol ~2,5%; high dielectric constant, due to which octanol effectively stabilizes charged species, so on) .
Therefore the observed relation between LogP and LogD has nothing to do with solubility limitations for electrolytes.

TatianaAlieva commented Jul 7, 2017

Hi,
when I asked, I hoped to learn a new thing for myself, and not to make another argument here. However, this answer is in obvious contradiction with solubility and LogP octanol-water definitions. So, I clarify this, but I will not argue further.

Aqueous solubility is not reciprocal to LogP.
Solution process is a transfer from pure liquid state of the solute to solution (aqueous in our case). Solution energy can be represented as
Gsolution=Gvaporization+Gsolvation_in_H20
(Solvation is the gas-to-solvent transfer according to IUPAC).
In contrast, octanol-water partitioning refers to transfer: solution in water ->solution in octanol
Go-w= Gsolvation_oct -Gsolvation_in_H20
A very good diagram illustrating the difference between solubility and partitioning is represented in Zhang and Gobas (1995), Fig 2.

The first terms in the eqs. above (Gvaporization and Gsolvation_oct) are not negligible, therefore LogS and LogP are not reciprocal.

Further,

The logP is typically reduced by 3-4 units.

I guess you mean here that LogP for the ionized species is typically 3-4 units lower than that one for the neutral one, correct? Therefore LogD never goes 3-4 units below logP at any pH.
As far as I understand, this property is related to solvation in octanol process (because the residual water in octanol ~2,5%; high dielectric constant, due to which octanol effectively stabilizes charged species, so on) .
Therefore the observed relation between LogP and LogD has nothing to do with solubility limitations for electrolytes.

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Upcoming version 7.3 will include a way to load a Table pH vs Solubility. This will be very easy to override the default behavior if required

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msevestre commented Apr 6, 2018

Upcoming version 7.3 will include a way to load a Table pH vs Solubility. This will be very easy to override the default behavior if required

@msevestre msevestre closed this Apr 6, 2018

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