Quercetin alone without metol provides developers like weak caffenol.
Qu-2
Water(room temp)...........................500 ml
Washing soda,Arm & Hammer (US).....4.5 tsp
or washing soda decahydrate (UK).......10 tsp
Iodized salt......................................0.5 tsp
Quercetin, 2 capsules contents,..........1.0 g
Stir 15 min,filter through cotton wool.
I semi-stand developed APX 100 in this 2hrs 70F, agitate every 30 min.
The negatives are much fogged but strongly stained and tanned.
Qu-3
As Qu-2 with addition of 1 tsp vitamin C.
I developed APX 100 in this 30 min 68F, agitate 10s/minute.
The negatives are somewhat fogged but produce sharp ,fairly fine grained prints.
There is only weak tanning, probably not enough to control highlight density.
Likely the reason why addition of vitamin C speeds up the development is that in Qu-3 it removes the oxidation products found with Qu-2 that tan the gelatin.
Quercetin is the best electron donor of all investigated flavonoids (measured E10.8= 0.09 V, and calculated E7= 0.33 V). The favourable electron-donating properties originate from the electron donating 0-3 hydroxy group in the C ring, which is conjugated to the catechol (B ring) radical through the 2,3-double bond
In neutral and slightly alkaline media (pH 7–9), all investigated flavonoids are inferior electron donors to ascorbate. Quercetin, E7= 0.33 V, and gallocatechins, E7= 0.43 V, can reduce vitamin E radicals (assuming the same reduction potential as Trolox C radicals, E7= 0.48 V).
Furthermore I forgot to post that this article https://pubs.rsc.org/en/content/articlelanding/1996/p2/p29960002497 says:
According to Haist, one measure of whether or not an agent will be good for development (aside from the other characteristics which Quercetin has) is if it can overcome the initial inertia required to start development. This requires a negative potential of something like 80 mV to be effective. D-76 with the full formula has a negative potential of 259 mV. D-72 has 407 mV. Too high will result in developing unexposed silver, so there is a Goldilocks region where the potential needs to be.
Quercetin, if I understand that article, is something like 330 mV. That theoretically puts Quercetin right in the range of being very effective on its own.
Reduction potential is just one factor, a necessary one but by itself not sufficient. Some capable reducers (e.g. Ascorbic Acid) are very effective together with a primary development agent, but are very weak developers on their own. There are strong reducers with no development activity at all (e.g. Sodium Sulfite). These 330mV are not a constant either: pH certainly has an effect, and most likely also its concentration.Quercetin, if I understand that article, is something like 330 mV. That theoretically puts Quercetin right in the range of being very effective on its own.
Reduction potential is just one factor, a necessary one but by itself not sufficient. Some capable reducers (e.g. Ascorbic Acid) are very effective together with a primary development agent, but are very weak developers on their own. There are strong reducers with no development activity at all (e.g. Sodium Sulfite). These 330mV are not a constant either: pH certainly has an effect, and most likely also its concentration.
It's complicated ...
Yeah thanks Rudi. I was focusing on reduction potential because we already knew it was capable of operating as a developing agent and has a ring that is a catechol. The link says that the reduction potential of 330 mV is between pH 7-9, meaning the sweet spot of 8-9 is covered. I was trying to suggest that given the right circumstances, it looks potentially promising as a primary agent.
Sorry for being a nitpick, but the article you quoted states, that this reduction potential of 330mV is the value for pH 7. As with most developers, there is a strong relationship between pH and reduction potential (see the public version of "Theory of the Photographic Process", pages 478ff). This number puts Quercetin right into the group of Catechol, Hydroquione and the likes.
HQ vs pH is here:
I see, I was misreading how the numbers worked from the statement about ph 7-9. Well, that's still of interest as a secondary agent. I didn't expect it to exceed catechol, but I don't have numbers for that that I can find so far.
It may work as primary or secondary development agent. If it is just a secondary development agent, then the search for the primary development agent in coffee continues. Something activates the ascorbate, which is an exceedingly poor developer on its own.
BTW don't get hung up on its precise reduction potential. Some adjustment of pH alleviates all these differences between developers.
I think the likely outcome is that there are several “primary” agents in caffenol, all appearing to be forms of catechol. But it would be nice if a more deterministic outcome were possible by isolating one or more of the agents. I think Alan has shown that the right formula of a Quercetin developer might be a starting point. That was my interest.
Catechol is not really known as primary developer, which would be superadditive with ascorbate. There have to be some other compounds in coffee, which serve this purpose.
Do you have any catechol? I don't but this would be interesting.Based on redox potential sulfite could reduce oxidized Phenidone as well, but it doesn't. It could reduce silver ions directly, but it doesn't. It could reduce Quinone back to Hydroquinone, but instead forms a sulfonate. From reading through investigated reactions of quinones in food stuff, most seem to happen in acidic environment, not where our developers typically operate.
It would be interesting, whether caffenol would also work, if we replaced the ascorbate with Catechol. This should answer in one set, whether the catechol derivatives in caffenol are reduced by the ascorbates, or whether some primary dev agent is hidden in coffee, which unleashes the ascorbate's development action.
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