Biotin acidity help

Question

Hello,

I need help figuring out the acidity of biotin? I want to say it is acidic because of the carboxylic acid group. I know biotin is highly soluble in water so does that also indicate it is a strong acid?

I also need help with pka values.

1.  Identification of the value(s) for pKa for your molecule based on information available in the PubChem database A pKa is the pH at which a weak acid and its conjugate base exist in equal concentrations. An analogous relationship applies to weak bases and their conjugate acids, commonly expressed in terms of pKb (with the corresponding pKa = 14 – pKb at room temperature). The lower a pKa, the stronger an acid; the higher a pKa, the stronger a base. If your molecule has multiple acidic/basic functional groups (where even alcohols can act as extremely weak acids), there likely will be reported multiple values for pKa, one for each type of functional group.

I don't understand what to find on pubmed to solve the values. I am so confused. I have watched multiple youtube videos and I am confused. I really am trying to learn this so please help. I need someone to dumb it down for me.

Thank you

Answer 1

Hello franklin, Biotin is an acid, in biochemistry research which I did during my undergraduate study. We discovered that Biotin has a Pka value of 4.52 but it does alter, Which means it has stereoisomers which means it is a moderately weak acid.

For the Pka=14-Pkb; Base on data base biotin pka is 4.52. Hence let's calculate it conjugate base to determine its affinity level;

When Pka=4.52 let's calculate pkb

and substitute the value;

4.52=14-pkb

pkb=14-4.52=9.48

pkb=9.48

With a pkb of this level, biotin will dissociate or dissolve completely.

A simple method of understanding it;

Pka when it has extremely low value like -7,-6 it is very strong just like HCL, HF

And when it is high like from 2-50 it is regarded as weak at this stage it will be having a strong pkb value.

So they both work together to balance nature. You can ask questions if you are lost I can use a basic means and explain.

Answer 2

Hi Frank!

Great question-- the solubility indeed stems from the carboxylic acid group, but solubility doesn't necessarily correspond with acidity, necessary (for example, salts). But you are correct-- biotin is acidic because of the carboxylic acid; this group generally makes for weak acids (think acetic acid/vinegar), as the carboxylate that results from deprotonation is a decent enough base (a strong acid would, for one reason or another, have a very poor conjugate base- think HCl and Cl^-). You can see this reflected in PubChem where it states, "It is a conjugate acid of a biotinate."

With regard to pKa, I'm seeing 4.5 cited in other literature¹. PubChem doesn't seem to have anything on its dissociation constant/pH/etc. pKa is just the negative decimal log of the acid dissociation constant, which must be observed by dissolving the acid in water (or predicted by a computer simulating the same), not calculated by hand. It's normally listed in PubChem under "Dissociation constants" (e.g. for sulfuric acid's PubChem entry, 3.2.22).

Hope this helps!

¹Hamid M. Said, Cell and Molecular Aspects of Human Intestinal Biotin Absorption, The Journal of Nutrition, Volume 139, Issue 1, January 2009, Pages 158–162, https://doi.org/10.3945/jn.108.092023