Quercetin Chalcone develops like Pyrogallol

Rudeofus

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Yes, I do have a small stash of Catechol here. I am not a caffenol enthusiast, but assuming, that espresso drawn from a 6 servings Bialetti will do the job, I can do some quick experiments with photographic paper. One batch with roughly 30 g/l Potassium Carbonate (still have some stock solution sitting around here), some amount of coffee and either nothing (dev 1) or 5 g/l either Ascorbic Acid (dev 2) or Catechol (dev 3).

If Quercetin were indeed superadditive with Ascorbic Acid, then it should not be superadditive with Catechol, and there should be a profound difference between dev 2 vs. dev 1&3. If some other compound in coffee works as primary dev agent, then dev 2 and 3 should work more or less the same. Cross your fingers that I get dark room time on Wednesday.

I shall report here.
 

relistan

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The

Thanks Rudi, that will be very interesting! Fingers crossed you get time on Wednesday. I suggest that you use 16g/L of ascorbic acid because only the stand development version of caffenol uses less. If that abstract I linked to is applicable, 1.5% or more solutions change the nature of the relationship between catechol-related compounds and ascorbic acid.
 
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Alan Johnson

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Rudeofus

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The reason I wanted to go easy on the ascorbate/Catechol was pH: with 30 g/l Potassium Carbonate, 5 g/l of whatever won't change pH all that much, but 16 g/l certainly will. What I will probably do is adjust the amount of Ascorbic Acid to match the molar amount of the Catechol version. With some luck I'll haul my pH meter along and do a proper job.
 

relistan

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Alan Johnson said:
I added the line for the first oxidation product of ascorbate [light blue]
It is taken from here:
Click to expand...

Interesting how much lower the potential is all the way up the pH scale. That makes it clear why it doesn’t work by itself well.


That makes sense.
 

Rudeofus

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relistan said:
Interesting how much lower the potential is all the way up the pH scale. That makes it clear why it doesn’t work by itself well.
Click to expand...
You may be misreading the chart: lower value means stronger reducing agent. See, how the value drops as pH goes up. In theory Ascorbic Acid should be a powerful developer on the edge to becoming a fogging agent. In practice it is a very weak developer unless you unleash it through some primary development agent. As I said before: there are more aspects to silver halide development than pure reducing power.
 
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Alan Johnson

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Just to note that the oxidation product of quercetin is denoted by Q-BZF, see section 5:

Revisiting the Oxidation of Flavonoids: Loss, Conservation or Enhancement of Their Antioxidant Properties

Flavonoids display a broad range of health-promoting bioactivities. Among these, their capacity to act as antioxidants has remained most prominent. The canonical reactive oxygen species (ROS)-scavenging mode of the antioxidant action of flavonoids relies on the high susceptibility of their...
www.mdpi.com

 

Rudeofus

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The stage from p-Quinone Methide towards Flavylium Cation would require H+, which is not exactly abundant in caffenol. Would that reaction still happen?
 

relistan

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I see, Ok, my mistake.

As I said before: there are more aspects to silver halide development than pure reducing power.
Click to expand...

Yes, I know that. Because you keep saying that, I think you have some idea that I am focused entirely on redox potential. That is not true. I was initially going through all the ingredients in coffee, looking at their structure, and then looking for any known photographic use of those chemicals where they had a structure that looked potentially promising. I was then only looking at the redox potential to see if any of them were in the range that Haist suggested was the right region for them to possibly be good developers. It's not the only thing, but if the numbers are wildly off here then it wouldn't make sense to look at it. I do also know that this is affected by pH. I misunderstood the chart, which I think is normal considering I'm learning here.

Also, I have two interests here:
  1. Is quercetin a decent developer that could be used to make reliable developer formulations?
  2. Is it likely that it's one of the active ingredients in caffenol?
 

relistan

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Alan Johnson said:
Might get an answer from ref 53 for alkaline conditions as indicated in section 4 but I don't have free access.
Click to expand...

I can't quite understand what's going on here, but maybe you or @Rudeofus can. Here's a PDF from the same authors on a quite similar topic: http://schlegelgroup.wayne.edu/Pub_folder/434.pdf

This is the part that most stuck out to me:


But my chemistry is not good enough to understand exactly what is happening there. But I do see a free hydrogen ion as part of the process.
 

relistan

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Alan Johnson said:
It seems to be that Fenton like chemistry for quinones is possible.
They don't specify a particular quinone or a rate, so no guidance on the practical significance in a film developer.
Click to expand...
Ok, from my much less knowledgable reading I thought maybe it was also indicating a mechanism by which ascorbate could be interacting here.
 
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Alan Johnson

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I made a better sketch for potential-pH with hydroquinone [ from Electrochemistry of Quinones , James Chambers 1988] and added ascorbate as before.
At the pH of interest, something over 10, the line for the first oxidation product of ascorbate A-' is lower than those for HQ and all its ions showing that A-' is the most powerful reducer.
Since most of these food extracts seem to get a boost from ascorbate, some at least may contain quinones which are reduced by A-'
 

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relistan

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Ah OK, thanks for the chart. Now that I better understand how to read these I see what you mean.

Please correct me if I'm wrong, but to summarize what I think you said: I think you are confirming that it appears possible that at this pH level (sodium carbonate solution, so greater than 10), we may see what I quoted from that article happening, to quinones of the right potential, if they are present. We think that some of them are present—maybe quercetin is one, maybe it's not—because we can observe the boost in activity from ascorbate for all of these food-based developers (potatoes, coffee, tea, beer, etc) and this mechanism appears to be a possible route for that to work.
 
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Alan Johnson

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We don't have the equations for the proposed reaction of developer, eg quercetin or coffee ,possibly regenerated by A-', in the development of exposed silver bromide grains.
Likely quercetin is adsorbed on the silver grains. It may pass electrons from the ascorbate or it could also donate electrons to the silver bromide itself. Coffee may be similar and the experiment of Rudi may throw some light on this.

Your equations in post 61 would be for the decomposition of developer in air, nothing to do with the development of exposed silver bromide grains. On Photrio this decomposition is often abbreviated as Fenton Reaction.
 
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relistan

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Thanks for the clarification.
 

Rudeofus

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Yesterday's dark room tests yielded the following results:
  1. at pH 11.6 Italian style coffee shows no appreciable development
  2. at pH 9 Ascorbic Acid shows no appreciable development
  3. at pH 9 coffee plus Ascorbic Acid turns Fomaspeed 312 dark gray after 20 minutes
  4. at pH 9 Catechol with or without coffee turns Fomaspeed 312 dark gray (but not black! ) after 20 minutes
This tells me, that there is super additivity between coffee and Ascorbic Acid, but not between coffee and Catechol. This would support the "Quercetin is the driving force in Caffenol" theory. A primary development agent like Metol or Phenidone would have made Catechol go medieval on the paper after 20 minutes.
 

relistan

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Rudeofus said:
This tells me, that there is super additivity between coffee and Ascorbic Acid, but not between coffee and Catechol. This would support the "Quercetin is the driving force in Caffenol" theory.
Click to expand...
Excellent @Rudeofus ! This is a good outcome in the sense that it means we have a direction to continue investigating. Appreciate your work on this.

Rudeofus said:
A primary development agent like Metol or Phenidone would have made Catechol go medieval on the paper after 20 minutes.
Click to expand...
LOL. It would have been the dark ages for sure.

In the meantime I have secured another source of quercetin, albeit not as good or as cheap as the Oxford Vitality stuff: I will have to crush tablets with a mortar and pestle. There will be some non-quercetin crap in the there. But it should be here tomorrow or Saturday.
 
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Alan Johnson

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Thanks Rudi, a few comments, with regards to your good work:

1.Just to clarify, this is different from [4], coffee does not contain catechol:

The content of polyphenols in coffee beans as roasting, origin and storage effect - European Food Research and Technology

Coffee, one of the most popular beverages in the world, contains many bioactive compounds. The aim of this study was a comparative evaluation of the content of bioactive compounds in organic and conventional coffee (Coffea arabica) originating from Brazil during 12 months storage. The content of...
link.springer.com
2. OK
3. Yes, superadditivity, coffee/ascorbate. Although the presence of a small quantity of primary developing agent not listed in the table is not excluded it seems likely that this is superadditvity between ascorbate and one or several of the ingredients in the linked table.
4. No superadditvity , coffee/catechol. In theory A-' is a better reducing agent than HQ-' and probably catechol as well, post 64.
Not really known but it seems unlikely that the ingredients of coffee are superadditive amongst themselves since they show no sign of reacting with catechol. Each acts alone if at all.

5.I think it would be needed to test each of the constituents of coffee listed in the linked table for their contribution to activity before any one of them could be singled out. Here is my method for one of them:

Caffeic Acid-fill of beans

Caffeic acid is often mentioned as the possible developing agent in the instant coffee based developer Caffenol: http://caffenol.blogspot.de/2010/03/caffenol-c-m-recipe.html I compared the activity of Caffenol-C-M with that of a similar solution in which the 40g/L instant coffee (Lidl Arabica)...
www.photrio.com
Its unlikely anyone will do this in the forseeable future.
 

Rudeofus

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Well the idea was to search for a primary development agent, or to accept, that some variant of Catechol is the active ingredient in Caffenol. A while back I made the suggestion, that there are some wetting agents in coffee, which could also activate the ascorbate in Caffenol.

My tests suggests, that typical primary development agents do not play a significant role in Caffenol. There are some Catechol variants in coffee, which can develop film (but are too weakly diluted to actually do this in quantity), and which can be turned into a superadditive couple with Ascorbic Acid.

This was an interesting result for me, because until now most superadditive couples had one type of phenylenediamine or Aminophenol together with some di- or tri-hydroxy-benzene. This one it new to me, and it makes sense.
 

relistan

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To summarize my understanding: given
  1. the evidence from Rudi's experiment
  2. the abstracts and papers that show that ascorbate can reduce the first oxidation product of catechol in the right conditions
  3. the pourbaix charts from Alan showing that ascorbate is a more powerful reducer at the pH in question and should be able to do that
it sounds like this is the likely mechanism by which one or more of the compounds in coffee that have a catechol moiety could be superadditive with ascorbic acid and form the main development activity. Is that right?
 
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Alan Johnson

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I don't think we have [2] yet although it seems possible as a guess by comparison with hydroquinone.
TH James in The Theory of The Photographic Process 1966 has 4 lines on the reduction of HQ by ascorbate. Maybe Kodak were not interested or wished to keep quiet about it.
TOTPP p335 "Highly purified hydroquinone alone or in the presence of agents, such as sulfite and ascorbic acid , which can readily react with its initial oxidation product, can initiate development." It is not entirely clear if they mean ascorbate will work with HQ without sulfite. Likewise the ascorbate version of Sandy King's Pyrocat has sulfite in it.
Anyhow, WFH here, I will run a check on development by catechol alone and by a catechol ascorbate mixture at the pH of caffenol/ascorbate type.
 

relistan

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Thanks Alan. I had found and read this, which seemed to indicate that [2] was maybe true (and I saw it somewhere else I can't now find). Here's the relevant reaction (I think):



I understand this is oxidation of catechol by oxygen and not reduction of silver bromide. Maybe what we get from that reaction is not o-benzoquinone. But doesn't it indicate that ascorbic acid can reduce oxidized catechol-derived quinones back to catechol? I also read this interesting paper (the whole paper is there, below the abstract) about reduction of silver bromide by ascorbic acid in the presence of light. What I see there looks quite similar (to my untrained understanding) in that it is donating two hydrogens. It also seems to indicate that some level of activity is happening by ascorbic acid at pH around 10.

While writing that up, interestingly I also found this nice diagram (the whole paper is there also) showing the reduction of silver nitrate by quercetin! It appers that it is indeed the catechol moiety interacting with the silver nitrate. The intermediary product looks like it has donated two hydrogens. As I understand it, ascorbate should regenerate that because it is a stronger reducing agent, right?

Alan Johnson said:
Anyhow, WFH here, I will run a check on development by catechol alone and by a catechol ascorbate mixture at the pH of caffenol/ascorbate type.
Click to expand...

Excellent, look forward to seeing your results!
 
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