Re: glutaraldehyde

From: T. E. Andersen ^lt;postlister@microscopica.com>
Date: 03/17/04-05:43:17 PM Z
Message-id: <4058E295.9090606@microscopica.com>

Hi there,

You may be absolutely right, of course, but I'll through in a couple of
question marks anyway...

Ryuji Suzuki wrote:
> Increased crosslinking is very beneficial in hardening gelatin. It
> makes gelatin more durable during wet processing, and commercial
> photographic films, paper, and other non-photographic printing papers
> where gelatin size is used, are hardened with glutaraldehyde, often
> with some other non-aldehyde hardeners to achieve very strong
> hardening effect.

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

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.

>
>> On the other hand, it may well prove to reduce the archival
>> properties of the coating. I do not know this to be the case, but I
>> would not be surpriced if it did. After all, the more cross-linked
>> the proteins are, the more brittle the gelatin will be, and the
>> less of the protein molecules will be free to adhere to the paper
>> and image layers. Again, I do not know this to be a problem, but
>> it's fair assumption.
>
>
> I suggest you study literature before making such a speculative
> comment. Hardening of gelatin have little influence on mechanical
> properties of dry gelatin. Also note that gelatin is degraded
> collagen product and is a bit different from proteins you are
> accustomed to.

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?

>
>> I have not used glyoxal (HOCCOH) yet (but I've bought a bottle to
>> test). It's similar to glutar aldehyde (HOC(CH2)3COH) in being a
>> dialdehyde, so it too, is cross-linking.
>
>
> 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?
(As far as I know glyoxal is not used in microscopy, and I have no
scientific knowledge of this compound, other than what I have read in
the Merck Index. If you have references dealing with the reactions of
glyoxal with proteins, I'd very much like to get a short list if possible.)

Regards,

Tom Einar Andersen

Ps. I saw the ref. list you sent in another posting. That paper dealing
with the effect of aldehydes on bread and croissants really makes me
want to bake my own bread.... Why on earth would anyone want to use
aldehydes on bread????
Received on Wed Mar 17 18:10:32 2004

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