Crosslinking Gelatin

Gelatin is used in many products. From medicine capsules to photograhy film. I would like to start a thread so some of the chemistry brains out there may help me understand the full process that gelatin undergoes when it is crosslinked by one means or another. Below is what I have so far and I ask...

I'll have to think about these new posts later, but this all sounds promising, good leads....

...meanwhile:

Ionic diameters:

Cr(VI): 0.088 nm
Cr(V): 0.098 nm
Cr(III): 0.123 nm

Ok, I think I see where you are going now. And this is exactly they type of info I have been looking for to gain that last bit of knowledge on the matter.



Applications of Environmental ... - Google Book Search

So now to apply Ionic exchange and ionic diameter with the process....

So are we saying the higher charged lower diameter Cr(VI) will displace Cr(V) and Cr(III). Thus if a Cr(V) does attach to a site, a Cr(VI) will displace it and be used.

This makes sense because other studies have confirmed that during exposure
a gelatin-Cr(V) species is instantly produced and that this
species has been tracked by ESR measurements and shown
to be capable of lasting for many hours at room temperature
before finishing up as Cr(III).

No, certainly not displacement, but perhaps transformation into the higher oxidation states.
...I still need to think more on this part also, but I'm focusing on the collagen rather than the Cr (but the "coll-Cr" complex thing is neat).

I'm still needing to read those last 2 from page 1; but my first impression is that it is not the hydrogen bonds being broken, but maybe the "Schiff bonds" being broken (or other covalent bonds).

I need to recheck specifics of the "denaturation" part, but I don't think we're going all the way down to amino acids in this denaturing. The H-bonds are within the triple helix. Many helices form the (bundle)-collagen; and denaturation separates the bundles into (roughly) the still fully H-bonded triple helices.

Hope this provides a bit more inspiration.
More later as I have time to delve....

Look at the third image in my first post. It seems to me that the individual amino strands are broken from the triple heix structure in addition to the triple helices breading from one another.

I'm not missing a link to a picture, am I?
You're referring to the line drawings?
My monitor doesn't seem to resolve the image down to the amino acid scale.

...from your link #8:
The structure and properties of solid gelatin and the principles of their modification
Statements such as this make me think that we're talking about the more collagen-ish end of a spectrum, from long-amino-chain macromolecules, up to the supra-molecular, helical collagen.

Does the part about 3 left-handed coils coming together to create a large right-handed helix make sense to you?
...and then the covalent bonding of these large helices to form gelatin (at one end of the spectrum)?

3 coils = 1 helix
H-bonds = intrahelix
covalent bonds = interhelix

Is that right?

At least half of our problem understanding all of this stems from the limitation of using a single word, gelatin, to talk about a substance with extreme variability along many different parameters.
...and then there's the word, collagen....

...meanwhile....
I am finding all the hydration effects interesting; thanks for the link.
~Be Back Later

In my first post there are three images. For some reason this forum scales the image down very small. If you click on the image it does bring up a new window and the image is enlarged. The image that has the subtitle "Denaturation of collagen" right below it is the one I was refering to. If you cannot see it, I can post it on my web page and post a link. I find this representation very good because it shows the form of collagen and then the form of gelatin. At lease so far the research I have done seems to support this.

I am not sure if the part about 3 left-handed coils coming together to create a large right-handed helix makes sense to me or not as far as why and how, but here is a very good representation of the molecule.
Collagen, What is Collagen? About its Science, Chemistry and Structure
The top picture shows the coil of the amino strands and the opposite coil of the entire molecule.

Here is anther technical article for your reading pleasure.
About Collagen : Koken Co.,Ltd.

Well, that is exactly what I am trying to nail down. I wasn't so concerned with collagen as I am working with gelatin, but it seems the bonding applies to bot. So, yes, that seems correct to me. But I would imagine some covalent bonding within the colagen molecule and some H-Bonding from molecule to molecule also. Don't you think?

From what I understand both types of bonds are broken in the denaturing process, that is using a heavy acid or base along with heat to break up the individual collagen molecules from one anther and actually break up the triple helix molecule itself into individual amino strand. Now, it seems not all bonds are broken and this give the different gelatins it's different properties, mainly bloom.

Let's look at two extreems in the denaturing process. In one extreem of gelatin denaturing, all of the intra and inter bonds are broken and when the gelatin is dried you have a bowl of cooked spaghetti that has been alowed to dry. Each strand can bond to a neighboring strand. But I assume with minimal covalent bonding and mostly H-bonding. But in another type of gelatin during the denaturing, not so many intra and inter bonds are broken so you have some triple helices remaining, you have some partial triple helices with three dangling amino strands and you have some completely loose amino strands. When this is dried you alos get minimal covalent bonding and mostly H-bonding but because some of the collagen was not broken into the individual strand and because some collagen was not broken from its bond with other collagen molecules, there remains more rigidity and more covalent bonds (left over from not being fully denatured).

As you can see this would give gelatin very different properites. The first much more spungy the second more rigid.

Now when I apply energy to gelatin, it seems to me I am exciting some part of it such that it wants to lose and electron to the Chromium. In doing so, it must have a tendoncy to want to share that empty spot with another part of the amino chain or another amino chain all together. This would be a strong covalent bonding. If all or nearly all the covalent bonding potential are used up, the sturcture become very rigid and cannot absorb water any more.

It's nice to have feedback of any type on this subject, because it let's me research different perspectives and keeps me thinking of that next part or step. I want to thank you for your time in discussing this with me. I wish I has more chemistry in my education.