Re: Glutaraldehyde: a different kind of cautionary tale

MARTINM wrote:

>
> That's very interesting. This seems to confirm what is stated in a paper
> dealing with dichromated gelatin: there is a fundamental difference between
> chrome hardening and aldehyde hardening. "When the commonest organic
> hardener (formaldehyde) is used, the gelatin molecules bind to their amino
> groups at relatively high pH values and the carboxylic groups are considered
> absolutely free."(Mazakova et al, Dichromated gelatin for volume holographic
> recording with high sensitivity. Part II, Optical and Quantum Electronic 14,
> 1982, p.318)
> "The results from the experiments show that if for bias hardening of
> dichromated layers a hardening agent is used which binds not the carboxylic
> but, say, the amino groups of the gelatin molecules, the light energy is
> used more thoroughly, i.e. the sensitivity improves." ( p.319)
> I ignore how this relates to gum crosslinking though.

This is interesting, thanks. How it relates to gum crosslinking is
anyone's guess, since there is little or no information extant on gum
crosslinking per se and what is thought about it is mostly extrapolated
from other processes. But I think it's unlikely that amine groups are
involved. Amino acids form only about 1% of the total gum (N is then a
fraction of 1%) and furthermore, most of that is locked so deep in the
molecule (which is thought to be somewhat spherical in shape) that it
can't be attacked by proteolytic enzymes; it seems reasonable (to me
anyway) to assume that entities that are unavailable to be attacked by
enymes are also unavailable for crosslinking.

But your information serves to illustrate the folly of assuming that
just because a reaction has a similar result, the chemistry must be the
same. This should be self-evident, but I can't tell you how hard it is
to convince people that just because something is true for gelatin it
doesn't follow that it's also true for gum, which has a completely
different molecular structure, completely different composition, very
different properties, different melting point, different etc etc etc
etc.
Katharine
Received on Thu Apr 29 14:02:00 2004