Crosslinking Gelatin

[johnfp]

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 for any corrections, additions or deletions please. I am also favorable to any type of discussion concerning crosslinking gelatin. The writing of mine below pertains to crosslinking gelatin with Ammonium dichromate as a sensitizer and then exposed to light but many other processes/chemicals can be used to crosslink the gelatin. So here is what I have so far. As you read you will come across questions that are questions that I still need help with..hint, hint.

 

Basics of Gelatin

 

Type A - Acid process used in production of product. Primarily pork skins.

 

Type B - Alkaline process used in production of product. Primarily cattle hides.

 

Type B (bovine) - Alkaline process used in production of product. Specifically cattle bone. According to one supplier, this type may contain small amounts of silver salts which could increase speed of Silver Halide films although it was unknown how much (if any) effect this might have.

 

Bloom Stength - This is a standard measurement that determines hardness of gelatin after a specific period of time. The higher the Bloom number the harder the gelatin.

 

 

The Mechanics of Gelatin in the Dichromated Holography Process

There is a lot of information available on collagen, gelatin and Dichromated Gelatin (DCG) holography but a paper that ties together these facets and can be understood by the amateur holographer is simply hard if not impossible to find. The scope of this paper is to finally bring together a concise understanding of what is happening in the DCG process. As it is impossible to footnote exact portions studied from other works because I intend to combine all research, I will simply put the credit due to the works I studied at the bottom of this paper and leave it up to the reader to research the individual papers for verification of the information I found.

 

 

 

 

Collagen

Collagen is a protein found in the skin, bones, tendons, cartilage, teeth, ligaments and connective tissue. It is the supporting structure for most body tissue. The collagen molecule is about 300nm long and 1.5nm in diameter. It is made up of three polypeptide strands, each of which is a left handed helix. These three left handed helices are wound together into a right handed triple helix. The strands are stabilized by hydrogen bonds. There is also some covalent crosslinking within the collagen molecule and crosslinking between molecules. The more crosslinking the less soluble to water the collagen is. The smallest amino acid is Glycine and it is this amino acid that resides on the inside of the triple helix structure with its hydrogen atom facing inward. Two more common amino acids are Proline and Hydroxyproline and face outward. This gives the polypeptide chain its characteristic helical shape(2,3,4,5).

 

If collagen is hydrolyzed, the three amino chains are separated into a random glob, while still being bonded to adjacent chains with a peptide bonds and some hydrogen bonding. This is now the nature of gelatin. Because the structured arrangement has been broken down, the gelatin will have partial triple helices with loose ends bonded to other polypeptide strands and loose polypeptide strands bonded to other loose polypeptide strands forming a matrix of connected fully and partially broken down collagen molecules. It is this Random Coil that give gelatin its springy properties(6,7).

 

These two images were taken from source (16).

 

 

 

Triple helix of collagen (crosslinked to another molecule from peptides at end of molecule)

 

 

 

 

Collagen molecules line-up to form a fibril in "quarter staggered" array.

 

 

 

 

Gelatin

Gelatin is made by using the Hydrolysis process to get water to react with the Collagen. The Collagen undergoes partial hydrolysis and is broken down into the Random Coil Globs. The intermolecular and intramolecular bonds that render collagen insoluble to water has to be broken as well as the hydrogen bonds holding the triple helix together has to be broken. The amount of water bonded directly to the gelatin is about 12% - 14% after hydrolysis and after the gelatin is allowed to dry. As the newly formed gelatin cools, hydrogen bonds reform, forming the Random Coil Globs. Gelatin dehydrated to 2% water becomes insoluble in water because of the extensive crosslinking and is achieved by dehydraion. It is this water bonding to the polypeptide chains that keeps the chains from crosslinking. Crosslinking is the covalent (sharing of 1 or more electrons) bonding of the polypeptide chains. This gelatin can be reheated in water to break down the hydrogen bonds again and then redried. It is this latter part that we use to make emulsion(6,8,9).

 

Gel Strength of gelatin is a measure of the rigidity of a gel formed from a 6.67% solution and prepared according to certain arbitrary prescribed conditions(13,14).

 

Bloom (named after Mr Bloom whom invented the measuring device) is a measure of force (weight) required to depress a prescribed area of the surface of the samplee a distance of 4 mm. The more rigid the sample the higher the bloom(13,14).

 

This image was taken from source (16).

 

 

 

Denaturation of collagen

 

 

 

 

CrVI

Hexavalent chromium CrVI compounds are a group of chemical substances that contain the metallic element chromium in its positive-6 valence (hexavalent) state and can be found naturally in rocks but is most commonly produced by industrial processes. It has the ability to gain electrons from other elements (a strong oxidizer), which means it can react easily with them(10,12).

 

Research is needed using vitamin C with CrVI(11).

 

 

 

 

DCG

When Dichromate is added to a gelatin emulsion and then dried the compound is in a clear dissolved up state in a gelled solution. The Chromium is still in the CrVI state. On exposure to the appropriate light source (actinic radiation) the Chromium gains an electron by oxidizing some of the amino acid groups (Where from and how does it gain this electron?) and becomes CrV very quickly and easily. This CrV is bound more tightly then CrVI to the gelatin and cannot be easily washed away with just water. With continued exposure some of the CrV gains more electrons and becomes CrIII but this happens much more slowly then the creation of CrV from CrVI. After exposure the, in the light struck areas, there is a large amount of semi-strong bounded CrV and traces of CrIII causing crosslinking. If this latent hologram is allowed to sit in the dark, the CrV continues to gain electrons (from where?) and converts to CrIII causing additional crosslinking. Because the dark reaction of CrVI to CrV is also slow, more CrIII and more crosslinking in formed in the light struck areas CrV to CrIII, then in the non light struck areas, CrVI to CrV to CrIII (15).

 

During the first step of processing (reducing agent: Fixer or Sodium Metabisulfite) the CrV is very quickly changed to CrIII and ultimately causes more crosslinking in the light struck areas of the gelatin. The CrVI is washed out as the reducing agent works much more slowly on CrVI to CrV to CrIII. So we have now just increased the crosslinking much more in the light struck areas then in the non light struck areas. And it is this highly crosslinked area of the gelatin that has a higher index of refraction then the uncrosslinked areas yielding us our phase hologram(15).

 

The DCG hologram is then washed to remove all traces of the reducing agent, unbound Cr. and any loose gelatin. Remember, gelatin is soluble in water unless it is crosslinked. The water also has the effect of swelling the gelatin and thus the fringes so a hologram is still not visible until the gelatin and fringes have been shrunk back to their original size or at least shrunk to a size able to replay the visible wavelengths.

 

The Hologram is then put into an alcohol bath. Many techniques have yielded good results in varying the temperature, duration, concentration and the number of these alcohol baths with each variable changing the final appearance of the hologram. The goal of the alcohol is to remove the water bound in the gelatin structure without allowing a collapse of the delicate fringe lattice structure. (Does alcohol bond where the water was bonded?) (How does alcohol absorb water?) Once the water has been unbound the hologram can be dried with forced or latent heat thus evaporating the alcohol and more of the now scarce water. Again, the more moisture that is taken out of the emulsion, the more crosslinking there is (even in unexposed regions) and the more insoluble the emulsion is. When taken below 2% water content the emulsion is insoluble at room temperature due to being fully crosslinked.

 

References

1. Dark self-enhancement in dichromated-gelatin grating: a detailed study. Roma Grzymala and Tuula Keinonen

2. Collagen - Wikipedia, the free encyclopedia

3. protein :: Collagen --* Britannica Online Encyclopedia

4. Gelatin

5. http://www.stanford.edu/~spark7/

6. Gelatin - Wikipedia, the free encyclopedia

7. Gelatin

8. The structure and properties of solid gelatin and the principles of their modification

9. Gelatin Information

10. Hexavalent Chromium - NIOSH Topic Page

11. Hexavalent chromium - Wikipedia, the free encyclopedia

12. 3M US: OSHA Hexavalent Chromium Standard - An overview of the Chromium Six (CrVI) standard; Impacts of the New Hex Chrome standard

13. http://www.gelatin-gmia.com/PDFs/2.1%20Gel%20Strength.pdf

14. Gelatin information, news, history and more

15. Improving the remarkable photosensitivity of dichromated gelatin for hologram recording in green laser light. Jeff Blyth, Christopher R. Lowe, John F. Pecora

16. The Effects of Relative Humidity on Some Physical Properties of Modern Vellum

17. Gel: a short word with a long meaning

18. Broad Range of Types of Polymers and Composites Polymer and Composite Consulting, Contract Research, and Software

[Essay]

Wow, what a lot of whork! :)

 

"When taken below 2% water content the emulsion is insoluble at room temperature due to being fully crosslinked."

When you say fully, do you mean completely -overriding the 'Cr-variations', or just finished changing (preserving the Cr variations?

 

"Because the dark reaction of CrVI to CrV is also slow, more CrIII and more crosslinking in formed in the light struck areas CrV to CrIII, then in the non light struck areas, CrVI to CrV to CrIII (15)."

Can you restate this "question?"

 

...sounds as if the electrons come from different areas of the collagen molecules (depending on conditions) and that causes a different kind of crosslinking? Is this what you're focusing on?

:)

[UncleAl]

Add a percent or two glutaraldehyde to mildly acidic gelatin solution. Similar borax solution is interesting if somewhat reversible.

 

Gelatin capsules are typically gelatin plasticed with glycerin or sorbitol followed by slight sustained hydration with humidity.

[johnfp]

Wow, what a lot of whork! :eek:

 

"When taken below 2% water content the emulsion is insoluble at room temperature due to being fully crosslinked."

When you say fully, do you mean completely -overriding the 'Cr-variations', or just finished changing (preserving the Cr variations?

 

"Because the dark reaction of CrVI to CrV is also slow, more CrIII and more crosslinking in formed in the light struck areas CrV to CrIII, then in the non light struck areas, CrVI to CrV to CrIII (15)."

Can you restate this "question?"

 

...sounds as if the electrons come from different areas of the collagen molecules (depending on conditions) and that causes a different kind of crosslinking? Is this what you're focusing on?

:)

 

Thank you for your reply and interest. Now remember, I am learning this as I discuss it.

 

Fully crosslinked really has nothing to do with the Cr variations. There are many other ways to crosslink the gelatin. Formaldyhide would work. The crosslinking is the strong bonding of the amino chains, not the weak hydrogen bonds.

 

The Cr give up the electrons when struck with light and it is these electrons that are used in the gelatin crosslinking. - Incorrect

 

Corect answer is: the Cr has a strong tendoncy to accept electrons. The electron it accepts comes from the amino groups. But then, how does this losing of an electron allow the amino groups to bond?

 

I am trying to fully understand the whole process and having been out of school for so long, I would like to understand it more mechanically then scientifiically. I would also like to finish this writing such that anyone can understand it, not just chemists or science professionals.

[johnfp]

"Because the dark reaction of CrVI to CrV is also slow, more CrIII and more crosslinking in formed in the light struck areas CrV to CrIII, then in the non light struck areas, CrVI to CrV to CrIII (15)."

Can you restate this "question?"

 

Whoops, missed this one. This is not a question but a statement and I can explain it better if you wish. The question preceeding this is what I am a little unclear on.

 

The Chromium is still in the CrVI state. On exposure to the appropriate light source (actinic radiation) the Chromium gains an electron by oxidizing some of the amino acid groups (Where from and how does it gain this electron?) and becomes CrV very quickly and easily.

 

I guess I want to understand how oxidation works. In this case we hit the CrVI with light. It must excite the CrVI but how does it excite it to make it want to accept an electron? Or is the light exciting the electron on amino acid group to the point it becomes "loose" and it just so happens the CrVI is very willing to accept this free electron. And If the amino acid group does lose this electron, how does that allow the chains to bond? I guess the CrVI which is now CrV does not give up the electron so easily and thus the amino chain bonds with another amino chain by sharing and electron. Does this sound correct?

[johnfp]

Add a percent or two glutaraldehyde to mildly acidic gelatin solution. Similar borax solution is interesting if somewhat reversible.

 

Gelatin capsules are typically gelatin plasticed with glycerin or sorbitol followed by slight sustained hydration with humidity.

 

Are you stating there are other ways to crosslink (harden) gelatin and to uncrossling (soften)?

 

I have read with some time release capsules, the study of partially crosslinked gelatin usage is very imporatant. But the actuall papers must be guarded as they are hard to find. Any links to any papers on crosslinking or gelatin that you do not think I have seen (footnotes) please forward them to me.

[Essay]

re:

Whoops, missed this one.

 

Fully crosslinked really has nothing to do with the Cr variations. There are many other ways to crosslink the gelatin. Formaldyhide would work. The crosslinking is the strong bonding of the amino chains, not the weak hydrogen bonds.

Yep, but this misses the point of my poorly focused inquiry....

...let's see, when I said, "Cr variations," I meant the variations in crosslinking caused by the light-Cr interactions?

If you could re-read that first question (with that substitution) it should make more sense.

 

The Cr give up the electrons when struck with light and it is these electrons that are used in the gelatin crosslinking.

Where does this sentence come from? (you're right, it's incorrect, but...?) -did someone say this somewhere else?

 

"But then, how does this losing of an electron allow the amino groups to bond?"

The answer here should be basic chemistry to you. You need to understand that much, at least.

It's so fundamental, I can't think of an easy way to jot it off here, now.

 

...re: Next Post....

 

"This is not a question but a statement...."

Yep, that's why I put quotes around the word "question;" it's a statement that begs several questions.

 

"I guess I want to understand how oxidation works."

Yep, see above about basics of chemistry.

 

"In this case we hit the CrVI with light."

Yes, but you need to be thinking about the light and the collagen.

 

"Or is the light exciting the electron on amino acid group to the point it becomes "loose" and it just so happens the CrVI is very willing to accept this free electron."

 

Now you've got it!

 

"....CrV does not give up the electron so easily and thus .... Does this sound correct?"

:) ummmm. Don't get hung up on the 5 to 3 shift, though (if that's where you're heading; later...).

...but yes, ultimately some amino acids are crosslinking as electrons go to the Chromium.

...wait, maybe if you restated that as CrV does accept electrons so easily and thus.... Yes, that sounds correct.

 

This is the point though where I was becoming interested. From your description of the process, it seems as if the collagen has different sites from which to differentially donate electrons.

I wonder if the Chromium has a preferred position "on" the collagen (or vice versa).

...and if the Cr might shift (or attract, and access different areas of collagen) as it's oxidation state changes.

 

I hope I'm not making this worse, by being picky. That should just be for this first clarification.

Future...less picky?

Too bad there isn't an animation of this happening.

:eek:

 

"If this latent hologram is allowed to sit in the dark, the CrV continues to gain electrons (from where?) and converts to CrIII causing additional crosslinking."

 

But yes, this is the crux of the biscuit.

 

That this happens makes me think of the multiple (differential) donor sites.

...different "kinds" of cross-linking? Whoops, gotta run. BBL

[johnfp]

This is the point though where I was becoming interested. From your description of the process, it seems as if the collagen has different sites from which to differentially donate electrons.

I wonder if the Chromium has a preferred position "on" the collagen (or vice versa).

...and if the Cr might shift (or attract, and access different areas of collagen) as it's oxidation state changes.

 

We have to remember it is not collagen we are working with but collagen that has been bronken down and is now gelatin (individual amino chains haphazardly arranged).

 

 

Here is what I understand so far. The collagen is denatured and breaks down into animo acid chains. These chains have a tendency to bond weakly (not sure what bond this is but I venture to guess it uses the water molecule somehow or the simple fact that the two ends of the amino chain have opposite charges). It is harder to get the strong amino bonds, that were present when the chains were in the collagen arrangement, to form this strong bond. It is the catalyst of Cr which freely accepts the free electrons from the amino acids (not sure where this bond resides..Glycine, Proline, Hydroxyproline etc...) which allows them to form this strong bond with one anther as existed in the collagin triple helix. Although that since the strands are haphazardly arranged, even thought the stong bonds form, the triple helix may or may not be formed.

 

So let me try to explain observations I have seen. I make a gelatin solution with AmDi and coat a plate and let it dry (about 6 hours). I then expose half the plate with adequate light and do not expose the other half. I then remove the remaining AmDi (with sodium metabisulfite but we dont have to go there yet). I then place the plate in warm water. I see the unexposed half swell more in the water then the exposed half. This is telling me the crosslinking in the exposed half has formed some type of strong bond that makes the chains more rigid to one another and thus cannot expand to hold the water. Then I place the plate in Isopropyl Alcohol which absorbs the water out of the gelatin. The unexposed half then shrinks more then the exposed half. This also tells me the strands in the unexposed half are not rigidly bonded to one another and thus allows them to contract or fall down upon one another more tightly. The exposed half pretty much stays the same thickness in water and after alcohol drying. Furthmore, the unexposed area can actually lose some amino chains in the warm water and the exposed area does not. This also allows the unexposed area to shrink even a little more.

 

So this kind of reinforces the fact that there is some weak bond and some strong bond. The weak bond breaks in simply warm water while the other stong bond as I call it does not. The strong bond remains even in water temperature as high as 32C. I would love to know what these bonds are and with what amino acids and whatever else contributes to these bonds.

 

I wonder if the Chromium has a preferred position "on" the collagen (or vice versa).

...and if the Cr might shift (or attract, and access different areas of collagen) as it's oxidation state changes.

 

I wonder also and would love to know.

[johnfp]

Just found this. I may contact the author.

 

Sandwalk: Collagen

 

Collagen is the major protein component of the connective tissue of vertebrates; it constitutes about 25% to 35% of the total protein in mammals. Collagen molecules have remarkably diverse forms and functions. For example, collagen in tendons forms stiff, ropelike fibers of tremendous tensile strength; in skin, collagen takes the form of loosely woven fibers, permitting expansion in all directions.

 

The structure of collagen was worked out by G. N. Ramachandran (famous for his Ramachandran plots). The molecule consists of three left-handed helical chains coiled around each other to form a right-handed supercoil. Each lefthanded helix in collagen has 3.0 amino acid residues per turn and a pitch of 0.94 nm, giving a rise of 0.31 nm per residue.

 

The collagen triple helix is stabilized by interchain hydrogen bonds. The sequence of the protein in the helical region consists of multiple repeats of the form –Gly–X–Y–, where X is often proline and Y is often a modified proline called 4-hydroxyproline. The glycine residues are located along the central axis of the triple helix, where tight packing of the protein strands can accommodate no other residue. For each –Gly–X–Y– triplet, one hydrogen bond forms between the amide hydrogen atom of glycine in one chain and the carbonyl oxygen atom of residue X in an adjacent chain. Hydrogen bonds involving the hydroxyl group of hydroxyproline may also stabilize the collagen triple helix. Unlike the more common α helix, the collagen helix has no intrachain hydrogen bonds.

 

In addition to hydroxyproline, collagen contains an additional modified amino acid residue called 5-hydroxylysine. Some hydroxylysine residues are covalently bonded to carbohydrate residues, making collagen a glycoprotein. The role of this glycosylation is not known.

 

Hydroxyproline and hydroxylysine residues are formed when specific proline and lysine residues are hydroxylated after incorporation into the polypeptide chains of collagen. The hydroxylation reactions are catalyzed by enzymes and require ascorbic acid (vitamin C).

 

Collagen triple helices aggregate in a staggered fashion to form strong, insoluble fibers. The strength and rigidity of collagen fibers result in part from covalent cross-links. The groups of the side chains of some lysine and hydroxylysine residues are converted enzymatically to aldehyde groups producing allysine and hydroxyallysine residues. Allysine residues (and their hydroxy derivatives) react with the side chains of lysine and hydroxylysine residues to form Schiff bases, complexes formed between carbonyl groups and amines. These Schiff bases usually form between collagen molecules.

[johnfp]

For each –Gly–X–Y– triplet, one hydrogen bond forms between the amide hydrogen atom of glycine in one chain and the carbonyl oxygen atom of residue X in an adjacent chain.

 

So if this particular bond is broken during the denaturing process, is this a bond that will not reform on it's own when the gelatin is in solution form or drying because the denaturing process broke the bond and added and electron to one or both of the atoms.

 

Then, if this IS the strong bond, does light cause those gained electrons to move more excitedly and become less stable and thus could get knocked off and it just so happens the Cr attracts the elecron(s) very easy. So when the Cr gains the electron(s) the amind hydrogen atom and the carbonyl oxygen atom can then rebond to reform that strong bond?

 

That must be it.

[Essay]

The structure of collagen was worked out by G. N. Ramachandran (famous for his Ramachandran plots). The molecule consists of three left-handed helical chains coiled around each other to form a right-handed supercoil. Each lefthanded helix in collagen has 3.0 amino acid residues per turn and a pitch of 0.94 nm, giving a rise of 0.31 nm per residue.

 

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

[johnfp]

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....

[johnfp]

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

 

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).

[Essay]

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.

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. :hihi:

More later as I have time to delve....

:confused:

[johnfp]

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.

[Essay]

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.

:huh:

 

I'm not missing a link to a picture, am I?

You're referring to the line drawings?

:hihi: 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

"...studies of gelatin films have revealed that in films cast at room temperatures and lower, the gelatin macromolecules have mainly a collagen-like helical structure (hereafter such films will conventionally be referred to as 'cold' films and such gelatin as 'helical' gelatin). At the same time, in films prepared from aqueous solutions by evaporating the solvent off at temperatures above 35°C, gelatin macromolecules assume the conformation of a statistical coil with no indications of ordering (hereafter such films will conventionally be called 'hot' films and such gelatin 'coiled' gelatin)27,53,53,56.

Thus, the closer the temperature of drying to the gel melting temperature the higher the gelatin concentration needed to obtain as large a degree of renaturation of the collagen-like helical structure as possible.

The conformational state of the macromolecules in the solid gelatin (for instance, in films) depends on the presence of....

Macroscopically, the helix to coil conformational transition occurring in solid gelatin shows itself as an irreversible spontaneous sample supercontraction (of up to 30% of the initial sample length).... Supercontraction of gelatin is similar to that observed in collagen. Its magnitude depends directly on the initial conformational state of the gelatin macromolecules....

suggests that the degree of uncoiling (anisotropy) of gelatin macromolecules can be inferred from the magnitude of the thermal supercontraction."

 

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.... :doh:

 

...meanwhile....

I am finding all the hydration effects interesting; thanks for the link. ;)

~Be Back Later

;)

[johnfp]

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.

 

...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?

 

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. :)