Alanine as Developer Preservative

[relistan]

I was looking through the MSDS of the ADOX XT-3 (their XTOL-alike developer) and noticed that they are using Alanine, an amino acid, (CAS 164462-16-2) in the formula. Looking around for photographic uses of this amino acid, I found a Kodak patent that describes a set of amino acids that may be used to prevent aerial oxidation of color developing agents, among them alanine:

As described hereinabove, the novel color developer compositions according to the invention comprise an alpha amino acid which functions to retard the aerial oxidation of the developing agent.

I had not heard of this preservative before and don't see it in other Kodak formulas, though they mention it in various places with regard to motion picture film—possibly as a constituent of ECN-2 developer. Just thought this information might be interesting, as it may be that ADOX found it to help prevent aerial oxidation of ascorbic acid or perhaps Dimezone (the other developing agent). Searches on this forum turn up no previous discussions.

Alanine, in the form of Beta-Alanine, is available at most health food stores. Might be of interest for experimentation with water-based home made developers.

 

[Rudeofus]

I would not recognize this ingredient as a reducer or Oxygen scavenger, but it does look a lot like a sequestering agent. Its similarity to Trilon B is striking, in the sense that Trilon B is to CAS 164462-16-2" exactly what EDTA is to PDTA.

 

[grain elevator]

I would not recognize this ingredient as a reducer or Oxygen scavenger, but it does look a lot like a sequestering agent. Its similarity to Trilon B is striking, in the sense that Trilon B is to CAS 164462-16-2" exactly what EDTA is to PDTA.

Well if it's effective to prevent the sudden death of asorbic acid developers, that would be amazing news for us home-brewers! Should be environmentally benign too, I suppose.

 

[Rudeofus]

Well if it's effective to prevent the sudden death of asorbic acid developers, that would be amazing news for us home-brewers! Should be environmentally benign too, I suppose.

It would be amazing news, if this compound was easier to obtain than all the others. Etidronic Acid, ATMP, DTPA, Trilon B are all well known and probably a lot cheaper than this Alanin compound, but for whatever reason only sporadically available from the usual sources (Formulary, Artcraft, Suvatlar). I have no idea why Adox would use this compound, all relevant patents should have run out by now.

 

[relistan]

I would not recognize this ingredient as a reducer or Oxygen scavenger, but it does look a lot like a sequestering agent. Its similarity to Trilon B is striking, in the sense that Trilon B is to CAS 164462-16-2" exactly what EDTA is to PDTA.

Ah, very interesting. Of course patents are sometimes not about what they say they are about, so it may be that it's a good chelator and Kodak didn't want to say so.

Anyway, ADOX is *also* using DTPA in XT-3 so I assume that was either considered to be inadequate by itself, there is something to the aerial protection idea from the patent, or it somehow works in tandem with DTPA.

It would be amazing news, if this compound was easier to obtain than all the others. Etidronic Acid, ATMP, DTPA, Trilon B are all well known and probably a lot cheaper than this Alanin compound, but for whatever reason only sporadically available from the usual sources (Formulary, Artcraft, Suvatlar). I have no idea why Adox would use this compound, all relevant patents should have run out by now.

Interesting that you mention patents, because the Kodak patent I cited has run out also, in 2012. I don't know if the form of alanine ADOX are using is cheaper or more available, or if it's because it solves another problem. But I do know that beta-alanine—which I think would behave the same as alanine as a chelator given the exposed groups on the molecule—is quite easy to get ahold of and a lot cheaper than when I ordered etidronic acid from Suvatlar. Chemical purity may vary of course, but it's cheap. Might be worth a shot.

 

[Rudeofus]

The ability to sequester metals depends on the number of carboxylic or phosphonic groups on these molecules. More is often better. Aminoacetic acid is not a sequestrant at all, whereas EDTA is. EDTA sequesters Calcium and Magnesium well, but Iron and Copper not strongly enough to prevent Fenton reaction. DTPA with one addition carboxylic group does sequester Iron and Copper ions (c.f. XTol). There are some lists and tables of complexing constants of various metal complexes, but it's difficult to find good numbers for the few ones actually available to us. It doesn't help either, that these complexing constants are strongly pH dependent ...

And yes, Suvatlar is expensive, but at least he has the chems. BTW Etidronic Acid is the worst of them, because it produces white flakes in alkaline hard water. BTDT. Some formulas I saw use Lithium ions to prevent this (no idea where to get those from for a sane price), others combine Etidronic Acid with EDTA to prevent this precipitate.

 

[Nikola Dulgiarov]

Ah, very interesting. Of course patents are sometimes not about what they say they are about, so it may be that it's a good chelator and Kodak didn't want to say so.

Anyway, ADOX is *also* using DTPA in XT-3 so I assume that was either considered to be inadequate by itself, there is something to the aerial protection idea from the patent, or it somehow works in tandem with DTPA.

Interesting that you mention patents, because the Kodak patent I cited has run out also, in 2012. I don't know if the form of alanine ADOX are using is cheaper or more available, or if it's because it solves another problem. But I do know that beta-alanine—which I think would behave the same as alanine as a chelator given the exposed groups on the molecule—is quite easy to get ahold of and a lot cheaper than when I ordered etidronic acid from Suvatlar. Chemical purity may vary of course, but it's cheap. Might be worth a shot.

The alanine compound is industrially known as MGDA-3Na or Dissolvine M-40, and although it shares the name with b-Alanine, structurally and functionally they're quite different molecules. MGDA is like three amino acid molecules bound to the same amino nitrogen - one alanine and two glycines (the simplest AA out there). And the reported compound is the trisodium salt.

I haven't seen any credible proof that Adox use DTPA in their XT-3 formulation. It seems that they use a substantial amount of MGDA based on the MSDS. At those concentrations and at the working pH of the developer, maybe MGDA on its own is a decent sequestering agent and unlike EDTA, does not promote the Fenton reaction which troubles all ascorate formulations. With a pKa1 of 9.9, it doesn't immediately suggest itself as a buffering agent that can substitute borate (pKa approx 9.1), but borates experience a pK shift in the presence of polyhydroxylic compounds, such as ascorbates, so perhaps the final composition buffers well in the needed range.
Since it's primarily touted as a very biodegradable chemical, I presume that was the main motivation behind that substitution, but I wonder if there isn't a second sequestering agent added at much lower concentrations (say <1% wt/wt of part B), which ensures that Cu and Fe are kept in inactive complexes (The Dissolvine brochure linked above clams that MGDA is suitable for chelating Fe up to pH 8, and the attached K plots confirm that).

 

[relistan]

And yes, Suvatlar is expensive, but at least he has the chems. BTW Etidronic Acid is the worst of them, because it produces white flakes in alkaline hard water. BTDT. Some formulas I saw use Lithium ions to prevent this (no idea where to get those from for a sane price), others combine Etidronic Acid with EDTA to prevent this precipitate.

Yeah, I appreciate him! The only place to get some of this stuff. I got the Etidronic acid while testing peroxide bleach patents. I did not perform at all as far as I could tell. As you know I ended up with a formula based around EDTA and citric acid.

The alanine compound is industrially known as MGDA-3Na or Dissolvine M-40, and although it shares the name with b-Alanine, structurally and functionally they're quite different molecules. MGDA is like three amino acid molecules bound to the same amino nitrogen - one alanine and two glycines (the simplest AA out there). And the reported compound is the trisodium salt.

Ok, good to know.

I haven't seen any credible proof that Adox use DTPA in their XT-3 formulation. It seems that they use a substantial amount of MGDA based on the MSDS.

Maybe I'm misreading it. I'm not an expert. But it says "Pentetic acid, pentasodium salt". Is that not DTPA?

In any case, if understand you, the "alanine" in there is actually MGDA in that formulation?

At those concentrations and at the working pH of the developer, maybe MGDA on its own is a decent sequestering agent and unlike EDTA, does not promote the Fenton reaction which troubles all ascorate formulations. With a pKa1 of 9.9, it doesn't immediately suggest itself as a buffering agent that can substitute borate (pKa approx 9.1), but borates experience a pK shift in the presence of polyhydroxylic compounds, such as ascorbates, so perhaps the final composition buffers well in the needed range.
Since it's primarily touted as a very biodegradable chemical, I presume that was the main motivation behind that substitution, but I wonder if there isn't a second sequestering agent added at much lower concentrations (say <1% wt/wt of part B), which ensures that Cu and Fe are kept in inactive complexes (The Dissolvine brochure linked above clams that MGDA is suitable for chelating Fe up to pH 8, and the attached K plots confirm that).

That makes sense, thanks for the explanation.

 

[relistan]

Looks like Trilon that @Rudeofus mentions is actually a trade name for this formulation. So looks like this is quite a well known chelating agent. Weird that searches didn't turn up much about it.

 

[Nikola Dulgiarov]

Yeah, I appreciate him! The only place to get some of this stuff. I got the Etidronic acid while testing peroxide bleach patents. I did not perform at all as far as I could tell. As you know I ended up with a formula based around EDTA and citric acid.



Ok, good to know.



Maybe I'm misreading it. I'm not an expert. But it says "Pentetic acid, pentasodium salt". Is that not DTPA?

View attachment 324082

In any case, if understand you, the "alanine" in there is actually MGDA in that formulation?



That makes sense, thanks for the explanation.

Nope, you're not misreading it, it's right there on page 1 and I missed it )
So, MGDA is probably doing double duty as sequestrant and buffering agent, while DTPA handles the transition metal ions.

My formulation of an Xtol lookalike uses DTPA-5Na and Etidronic acid triodium salt and I've found it to be stable over the medium term (ca 6 months)

Nota bene:
Trilon C - DTPA sodium salt (5Na)
Trilon M - MGDA trisodium salt
Trilon B - EDTA sodium salt (4Na)
Trilon A - NTA (nitrilotriacetic acid, free acid)

 

[Rudeofus]

Looks like Trilon that @Rudeofus mentions is actually a trade name for this formulation. So looks like this is quite a well known chelating agent. Weird that searches didn't turn up much about it.

Sorry, I messed up. Some silly resource referred to Nitrilotriacetic Acid Trisodium Salt as "Trilon B", I went with the shorter term, and this is nonsense. Trilon B is EDTA-Na4 and should not have been part of this discussion.

Either way, this Nitrilotriacetic Acid Trisodium Salt is yet another compound, similar but different to this CAS 164462-16-2 compound you brought up here. CAS 164462-16-2 has an extra methyl group on one acetic acid group. No idea, what difference it makes. It does look like a sequestering agent to me. Based on the NTA --> EDTA --> DTPA sequence I would expect it to be a rather weak sequestering agent, it's wikipedia entry seems to confirm my suspicion.

The main advantage of dicarboxymethyl alaninates appears to be their biodegradability, which makes it attractive for developers with low ecological footprint.

 

[Alan Johnson]

Alanine, CAS 164462-16-2 = trilon -as, a chelating agent.

TRILON AS - Ataman Kimya

Ataman Kimya

www.atamanchemicals.com

 

[albada]

I was looking through the MSDS of the ADOX XT-3 (their XTOL-alike developer) and noticed that they are using Alanine, an amino acid, (CAS 164462-16-2) in the formula. Looking around for photographic uses of this amino acid, I found a Kodak patent that describes a set of amino acids that may be used to prevent aerial oxidation of color developing agents, among them alanine:


I had not heard of this preservative before and don't see it in other Kodak formulas, though they mention it in various places with regard to motion picture film—possibly as a constituent of ECN-2 developer. Just thought this information might be interesting, as it may be that ADOX found it to help prevent aerial oxidation of ascorbic acid or perhaps Dimezone (the other developing agent). Searches on this forum turn up no previous discussions.

Alanine, in the form of Beta-Alanine, is available at most health food stores. Might be of interest for experimentation with water-based home made developers.

The patent cited above (EP0530921B1) documents observed decomposition-rates for developers containing some amino acids compared to a reference developer with no preservative.
Glycine performed best, so the patent focuses on it. Kodak observed that glycine changes decomposition-rate to 1/3 to 1/4 of the unprotected rate.

Question: How does that level of preservation compare to sulfite?
A second question: Are there other effective preservatives?

Kodak also observed that glycine has minimal photographic effect. I have some glycine which I purchased to use as a halide solvent, so I'm curious about its effectiveness as a preservative.

Mark

 

[Alan Johnson]

IMO, sulfite [typically 3.5 g/L] and glycine [without sulfite] would act differently.
The sulfite would react with any oxygen in the container/solution until it is all used up before the oxygen reacts with the developing agent and the concentration of the agent starts to fall.
With glycine the reaction between the oxygen and the developing agent would start straight away, the concentration of developing agent would start falling immediately.

There was once some speculation that sodium benzene sulfonate was in Rodinal to slow its oxidation but no conclusion was reached..

 

[Rudeofus]

With glycine the reaction between the oxygen and the developing agent would start straight away, the concentration of developing agent would start falling immediately.

Any idea, what actually happens between PPD, Glycine and Oxygen?

 

[Alan Johnson]

They don't give any explanation in the Kodak patent linked in post 1.
I suggest that the amino acid glycine may reduce the rate of diffusion of oxygen into the solution. [Unlike sulfite it does not actually remove the oxygen, which remains free to react with the developing agent].
If this is correct there is no need to propose any ppd-glycine reaction.

I cannot find any data for diffusion of oxygen in amino acid solutions but there is data showing a nearly 4x reduction in diffusion coefficient in pure anionic surfactant vs clean water, see table 2 here:

https://core.ac.uk/download/pdf/12043274.pdf

 

[relistan]

They don't give any explanation in the Kodak patent linked in post 1.
I suggest that the amino acid glycine may reduce the rate of diffusion of oxygen into the solution. [Unlike sulfite it does not actually remove the oxygen, which remains free to react with the developing agent].
If this is correct there is no need to propose any ppd-glycine reaction.

I cannot find any data for diffusion of oxygen in amino acid solutions but there is data showing a nearly 4x reduction in diffusion coefficient in pure anionic surfactant vs clean water, see table 2 here:

https://core.ac.uk/download/pdf/12043274.pdf

Very interesting. Thanks Alan. So there might be a useful item in that patent. I guess the only way to test at home would be to make a developer, divide it in half in identical bottles, but one has one of these amino acids and the other doesn't. And see how oxidation proceeds.

 

[Alan Johnson]

Very interesting. Thanks Alan. So there might be a useful item in that patent. I guess the only way to test at home would be to make a developer, divide it in half in identical bottles, but one has one of these amino acids and the other doesn't. And see how oxidation proceeds.

Yes, that would be a good test.
Another accidental discovery from the link noting that diffusion is reduced in anionic surfactant is that sodium benzene sulfonate is an anionic surfactant so there might have been some point in using/testing it with Rodinal if that is exposed to air a lot.

 

[Nikola Dulgiarov]

The simple aliphatic amino acids aren't good reducing agents, and I can't think of a mechanism whereby they can prevent developing agent decomposition. Example 3 of the patent mentioned is perhaps telling - it compares the developing agent stability in varying sequestering agent compositions (removing TEA, HEDPA, or both). Glycin does form chelates with transition metals (see here and here), so we're probably back to Fenton-like degradation pathways. Note that a derivative of hydroxylamine (which acts as a 'proper' antioxidant, reducing agent) is also included as a test.

Veering off-topic a little, but I sometimes think about trying other common over-the-counter chelating agents with high affinity for copper and iron. For iron, there is a range of medication for iron overdose, such as deferoxamine and deferiprone, which have Fe3+ and Fe2+ binding constants orders of magnitude hiher than DTPA and I recall reading through a paper which studied the autoxidation of ascorbic acid and it inhibition by the aforementioned.

An even more easily obtainable sequestrant would be tannic acid. IIRC R. Suzuki had tested tannins to good results but abandoned them because of staining and the general brown color they have in solutions, certainly not desirable in a developer, but potentially mitigable. Some promising results in ascorbate systems are posted here and here. It is noteworthy that tannic acid can break EDTA and NTA iron complexes due to its higher bonding affinity and can essentially prevent sequestering agent mitigated Fenton reactions. I wonder if anyone has followed up on tannins and polyphenols as preservatives.

 

[relistan]

The simple aliphatic amino acids aren't good reducing agents, and I can't think of a mechanism whereby they can prevent developing agent decomposition. Example 3 of the patent mentioned is perhaps telling - it compares the developing agent stability in varying sequestering agent compositions (removing TEA, HEDPA, or both). Glycin does form chelates with transition metals (see here and here), so we're probably back to Fenton-like degradation pathways. Note that a derivative of hydroxylamine (which acts as a 'proper' antioxidant, reducing agent) is also included as a test.

Once my initial confusion of the two compounds was out of the way, the discussion above was not that they are reducing agents, it was that they may provide a route to reduction of rate of oxygen absorption into the developer. The Kodak patent was about "retard[ing] the aerial oxidation of the developing agent."

An even more easily obtainable sequestrant would be tannic acid. IIRC R. Suzuki had tested tannins to good results but abandoned them because of staining and the general brown color they have in solutions, certainly not desirable in a developer, but potentially mitigable. Some promising results in ascorbate systems are posted here and here. It is noteworthy that tannic acid can break EDTA and NTA iron complexes due to its higher bonding affinity and can essentially prevent sequestering agent mitigated Fenton reactions. I wonder if anyone has followed up on tannins and polyphenols as preservatives.

He was primarily using salicylic acid for this purpose as far as I know. See link above from @Alan Johnson . The published formulas of his mostly use that. I think I will play with it if I do a water-based ascorbic acid developer. But that is also interesting information, thanks.

 

[Rudeofus]

He was primarily using salicylic acid for this purpose as far as I know. See link above from @Alan Johnson . The published formulas of his mostly use that. I think I will play with it if I do a water-based ascorbic acid developer. But that is also interesting information, thanks.

To my best knowledge, Ryuji used Salicylic Acid together with TEA as comprehensive transition metal sequestrants. TEA binds Copper, Salicylic Acid binds Iron ions AFAIK.

 

[relistan]

To my best knowledge, Ryuji used Salicylic Acid together with TEA as comprehensive transition metal sequestrants. TEA binds Copper, Salicylic Acid binds Iron ions AFAIK.

Ah, interesting. I had seen he was using TEA but did not recognize that it was serving more than one purpose. Yes, he did mention only iron ions for salicylic acid.

 

[Nikola Dulgiarov]

To my best knowledge, Ryuji used Salicylic Acid together with TEA as comprehensive transition metal sequestrants. TEA binds Copper, Salicylic Acid binds Iron ions AFAIK.

Ryuji's posted DS-series of developers do indeed use the TEA/Salicylic acid sequestrant system, but IIRC even he eventually did not recommend storing these developers past several weeks since mixing.

On the archived silvergrain website, Suzuki lists experimental substances he was looking into as Fenton-like reactions inhibitors. He lists tannins and polyphenols.

In a post here, he refers to tannic acid and why he chose to move on to other sequestering agents. The most recent posts indicate some complex nitrogen heterocycles, which are outside the scope of amateur photographic chemistry. Suzuki's reasons to move away from tannins seem more related to their practicality in a commercial product. I do believe there's merit to testing out tannic acid derivatives as preservatives for ascorbate. Polyphenols can act as developers in and of themselves at high pH, but for the alkalinity of fine-grain developers like Xtol and DS-10, I think tannin will have a minimal contribution and if it does, it might act in an ETA secondary agent sense. I might get around to some tests in the near future..

 

[relistan]

I might get around to some tests in the near future..

That would be great. We won’t move the field forward without pushing around the borders of what is known.

 

[Rudeofus]

I cannot find any data for diffusion of oxygen in amino acid solutions but there is data showing a nearly 4x reduction in diffusion coefficient in pure anionic surfactant vs clean water, see table 2 here:

https://core.ac.uk/download/pdf/12043274.pdf

Looking through this document: surfactants aggregate on the liquid surfaces and allow less Oxygen to diffuse through them. This method may work well in an open tank, but I am not sure, whether it helps shelf life in a glass bottle, where diffusion through the bottle cap is the main limiting factor.

I would assume from that, that devs stored in glass bottles are helped more by reducers (HAS, sulfites, Mannitol) than by diffusion inhibitors.