Acidic/negative and basic/positive mindf***.

[Function]

Hi everyone

 

Just to get to the point:

 

• Hematoxylin is a dark blue or violet stain that is Basic / Positive. It binds to BASOPHILIC substances (such DNA/RNA -- which are Acidic / Negative).
  • DNA/RNA in the nucleus, and RNA in ribosomes in the rough endoplasmic reticulum are both acidic because the nucleic acid building blocks that come off the phosphate backbone are negatively charged. These form salts with basic dyes containing positive charges. Therefore, dyes like haemotoxylin will bind to them and stain them violet.

• Eosin is a red or pink stain that is Acidic / Negative. It binds to ACIDOPHILIC substances (such as proteins -- which are Basic / Positive).
  • Most proteins in the cytoplasm are basic because they are positively charged due to the Arginine and Lysine amino acid residues. These form salts with acid dyes containing negative charges, like eosin. Therefore, eosin binds to these amino acids/proteins and stains them pink. This includes cytoplasmic filaments in muscle cells, intracellular membranes, and extracellular fibers.

From wiki.

 

I find this very contracdictory to everything I've learned about acids and bases.

 

Someone please help me.

 

F.

[swansont]

!

Moderator Note

Edited the title. Please refrain from that in the future.

[John Cuthber]

Part of the confusion may be due to the fact that the stain called Hematoxylin isn't Hematoxylin.

The stuff in the bottle has aluminium added to it.

The Al + Hematoxylin complex has a +ve charge overall.

On the other hand eosin, at the sort of pH you get in normal tissue has a -ve charge.

 

This might help

 

http://mhpl.facilities.northwestern.edu/files/2013/10/The-Science-and-Application-of-Hematoxylin-and-Eosin-Staining-6-5-2012.pdf

[Function]

Still it says that haematoxylin has a net positive charge; as far as I'm aware of, this is acidic and should bind to acidophilic substances? :/

[John Cuthber]

I'm not sure that the terms "acid" and "basic" are useful here.

Lysine is illustrated here

http://en.wikipedia.org/wiki/Lysine

and it's got a positive charge on it because, at the sort of pH you get in the body, it carries an extra proton. (The amino and carboxylate groups at the other end don't get involved much, because they are part of a protein chain- each is combined to form an amide group)

The reason it picks up that proton is that lysine a base.

However, once it has picked it up, the resulting protonated form is an acid.

(and I think that's where the confusion lies)

 

So, in the body, it's got a positive charge, and it sticks to the -ve charge of eosin.

 

Look at a much simpler case- ammonia.

NH3 is a base- it has no charge.

However in the body, at about pH7 it is protonated to form the ammonium ion NH4+

NH4+ is acidic (albeit weakly so).

 

 

Here's the strange bit,

if ammonia wasn't a base, it wouldn't get converted into an acid in the body.

 

(in the longer term the ammonia will be removed from the body- probably as urea- but that's not the point)

[Ophiolite]

That's interesting John. Should I have known that from my chemistry in secondary school?

[John Cuthber]

It seems more sensible to me to label these things (dyes, proteins, structure, whatever) with their charges.