X-Message-Number: 8437
From: Brian Wowk <>
Date: Sun, 3 Aug 1997 11:40:43 -0500 (CDT)
Subject: Adonitol

Brian Rowley <> writes:

>Doug Skrecky wrote:
>>Adonitol has a molecular weight of 152,
>>while glycerol's is 92.09. Adonitol perfuses well for a molecule of its
>>size because its cross section is no larger than that of glycerol, so it
>>can pass through pores in cell membranes.

>Right; just because a molecule or ion is bigger doesn't always mean it will
>permeate less effectively. A classic example is sodium vs. potassium...

	Most cryoprotectants pass through cell membranes by diffusion
through the lipid bilayer, not pores.  As far as I'm aware, glycerol is
no exception.


>Water also perfuses well, but according to biologists at UBC no one knows
>why. Tissue membranes are phospholipid bilayers, and there is no obvious
>reason why water should get through so easily.

	The momentum of a water molecule is given by solving kT ~ p^2/2m.
Because the mass of water molecules is so small, they have a very large
momentum and plow through the lipid bilayer like bullets despite their
lipophobic nature. 


>Lastly, something that is hydrophobic (e.g., less polar) will cross a
>membrane a lot easier than something that is hydrophilic as a rule,
>regardless of molecular mass. It might be profitable to compare the
>hydrophobicity of adonitol with that of glycerol. 

	Adonitol and glycerol are part of the homologous series of
fully hydroxylated alkanes: methanol, ethylene glycol, glycerol,
erythritol, adonitol.  The general trend in this series is one of
decreasing hydrophobicity, decreasing permeation, decreasing glass
forming ability, and increasing viscosity.

	Even if adonitol did penetrate well, I still wouldn't be
excited by it unless it was a better glass former and less viscous
in solution than glycerol.

***************************************************************************
Brian Wowk          CryoCare Foundation               1-800-TOP-CARE
President           Human Cryopreservation Services   
   http://www.cryocare.org/cryocare/
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