Re: glutaraldehyde

From: "T. E. Andersen" <postlister@microscopica.com>
Subject: Re: glutaraldehyde
Date: Thu, 18 Mar 2004 00:43:17 +0100

> This may well be the case, but the mechanical durability of the very
> hardened films comes at a cost.

You are not getting one point I said in my previous email. Mechanical
strength of dry gelatin is little influenced by hardening. Dry
properties of gelatin is mostly determined by the viscosity of the
gelatin sol used to coat, and the condition at which the gelatin was
gelated. All these can be modified by addition of plasticizing agents,
of course. See for example Kozlov 1983. The structure and properties
of solid gelatin and the principles of their modification. Polymer,
24, 651-666.

> If you want very hardened gelatin, you
> can get that even with formaldehyde, since even this cross-links to some
> extent (due to short-chain polymers, if I remember correctly).

That's not the same. Bonding between gelatin and glutaraldehyde is
more secure. Bonding of formaldehyde is weaker and somewhat
reversible, and this is the same with collagen, not just gelatin. If
you desire only a bit of hardening, you can achieve that with reduced
amount of glutaraldehyde with better reliability than with
formaldehyde or glyoxal. There are a lot of literature on this topic
in the field of bioprosthesis. For example, they excise heart valve
from pig, harden it in glutaraldehyde and implant in humans as a
prosthesis, and a lot of research has been done on it.

> My primary reason for wanting to do alt-photo in the first place, is the
> ability to produce prints with very high life expectancy. This is not
> the first consern for commercial print papers or photographic films.
> Rather they need to accomodate the demands of high-speed presses and
> developing machines. Most of what these machines produce is designed to
> last only for a short time.

With glutaraldehyde hardening, you only need to cross link a very
small fraction of gelatin molecules in order to get useful
hardening. This is less chemical modification than other aldehydes
hardening. You would have to worry about the opposite - the
consequence of binding too many gelatin molecules with monofunctional
aldehydes.

> You may again be right, of course, but I don't see how gelatin can be
> *that* different from other proteins? I have not read the literature
> from the photo industry on this, but I *have* read quite a few volumes
> and articles from tissue research. Are you suggesting that the basic
> mechanisms of fixation are somehow different in gelatin? If so, why is
> that the case?

Gelatin is very different from parent proteins in that it gels and
sols in a certain temp range. Also, the moisture retention is a bit
different, because the fraction of polar functional groups are
different. These are influenced by the method of gelatin production
from the protein tissue... acid process and lime process. Anyway, the
paper referred above as well as in my previous posting will give you a
good starting point. There are older gelatin literature that is quite
comprehensive and good, but they usually don't talk about
glutaraldehyde because GTA became industrially widely available in
late 60's or so.

> > Glutaraldehyde is superior cross linking agent to glyoxal and
> > formaldehyde because GTA is bifunctional, meaning that it can attach
> > to two separate gelatin molecules. I suggest you study literature
> > before making speculative comments here, again.
>
> Why do you consider the glyoxal monofunctional? It, too has two aldehyde
> groups. Does only one react with proteins?

It's the matter of distance between two groups of aldehydes, and the
structure of glutaraldehyde in aquaous solution. GTA also makes
stronger links to amino groups.

I'm heading out for St Patrick's night so I'll send you the ref info later.

Ryuji
Received on Wed Mar 17 19:51:45 2004