ShadowWarrior4444
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Rosocyanine Analogs
Rosocyanine is the deep red complex formed from Curcumin and Boron, though recently I’ve been having some...odd results synthesizing the complex.
Firstly, the control went awry. Cucrumin, extracted from Turmeric via ethanol(denat. with methanol) exhibited the right coloring, and absorption into
cellulose. I then added Boric acid 99.9%, and! Orange. Yes, slightly orange, no deep red, which I found interesting because Rosocyanine is said to
form very easily under acidic conditions, only hydrolyzing in alkaline environment. So, it was time for another borate, specifically Borax; this time
the deep red complex did form, though on drying, no green crystals were observed, only a vaguely red powder. On drying the Boric acid test, likewise,
only an orange powder. Curcumin alone dried to a yellow powder, all three exhibited slightly interesting diffraction effects against the plastic petri
dish (very small wave-like rainbows.)
In addition, Sodium Metasilicate added to Curcumin provided a much deeper red than any of the boron compounds, and as I don't suspect rampant
borate impurities in the silicate, I was wondering if Curcumin formed a complex with Silicon analogous to Rosocyanine?
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pantone159
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Curcumin does form a deep red color with base, e.g. NaHCO3, acting as a pH indicator.
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ShadowWarrior4444
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| Quote: | Originally posted by pantone159
Curcumin does form a deep red color with base, e.g. NaHCO3, acting as a pH indicator. |
Yes I had suspected this might be the case from furthur research on Curcumin--do you know if this color is stable after the solution has dried?
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pantone159
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| Quote: | Originally posted by ShadowWarrior4444
do you know if this color is stable after the solution has dried? |
Don't know yet, but I just dumped some of this red solution into a dish to dry out, so we will see.
EDIT - Upon drying out, the basic solution is a similar dark red/brown color as the liquid was, definitely different than dried curcumin solution. No
sign of anything green.
[Edited on 9-5-2008 by pantone159]
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JohnWW
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I think that that intense red complex formed by reaction of curcumin with aqueous borates is the basis for a colorimetric or spectrophotometric method
for determination of the concentration of B in water, which I once used. Sea-water, in particular, has an appreciable B content, and this is liable to
be retained in soils that come into contact with sea-water. It should be in Standard Methods For The Examination Of Water & Wastewater, for which
I have posted downloading links in the references section.
[Edited on 11-5-08 by JohnWW]
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ShadowWarrior4444
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| Quote: | Originally posted by JohnWW
I think that that the intense red complex formed by reaction of curcumin with aqueous borates is the basis for a colorimetric or spectrophotometric
method for determination of the concentration of B in water. It should be in Standard Methods For The Examination Of Water & Wastewater, for which
I have posted downloading links in the references section. |
It appears that I will need to request access to the references section from a moderator. Though, I was aware of its use to determine the amount of
boron in water, I am curious now as to whether this complex will form in an organic solvent as well as an aqueous one.
The most interesting result of my cursory testing that that boric acid did not from a red complex with curcumin in ethanol, rather it was vaguely
orange. If it requires water to form the complex, the 5% water in the denatured alch may have provided just enough to form a slight bit of
rosocyanine, which combined with the rest of the curcumin appeared orange. Solubility reports for rosocyanine seem to indicate that it is much more
soluble in alcohol, though. Water sol="Very slightly sol" 0.01, Alcohol, acetic acid, etc= 0.1
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woelen
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Curcuma (a.k.a. turmeric) already gives the red color on itself when it is boiled. I sometimes make yellow rice by boiling a pan of water with a pinch
of curcuma in it. When the water boils, the liquid is red instead of yellow. Then I add the rice and let it simmer in the water. After this treatment,
the rice is yellow though (and has the typical taste of curcuma), not red, nor orange. So, it seems that there also is a temperature dependence.
[Edited on 10-5-08 by woelen]
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pantone159
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I just tried the following:
I put in three test tubes small amounts of:
a) H2O
b) NaHSO4 aq solution
c) borax aq solution, acidified with HCl to a similar pH as b)
To each of these I added a solution of curcumin in 95% EtOH.
I got a yellow-orange ppt in all three, very similar in appearance. (Presumably the curcumin is insoluble in water.)
No sign of anything different in the borax containing mixture.
In the past, I do remember a dark red color formed with (non acidified) borax solution and curcumin, but this did not seem any different than that
formed with high pH and curcumin, so I concluded that this was not any special complex.
[Edited on 10-5-2008 by pantone159]
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pantone159
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Now I tried this:
I added c. 1-2 ml of curcumin/EtOH solution to a container, and added c. 30-40 ml of H2O to that. A cloudy yellow (slightly orange) suspension
formed. I brought that to a gentle boil. No color change was observed.
Woelen - Is is possible that boiling your tap water is driving off dissolved CO2 and raising the pH to the point that the dark red color change
occurs?
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unionised
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Here's a cheap and cheerful version of that coourimetric procedure.
http://www.macherey-nagel.com/tabid/10434/default.aspx
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pantone159
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| Quote: | Originally posted by pantone159
I put in three test tubes small amounts of:
a) H2O
b) NaHSO4 aq solution
c) borax aq solution, acidified with HCl to a similar pH as b)
To each of these I added a solution of curcumin in 95% EtOH.
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After standing there does seem to be a some difference between the acidified borax solution c) and the plain acid solution b).
The borax one has a hint of red color, and this is most pronounced in the stains/evaporated residue on the sides of the test tube, these have a
distinct red tint in c). It isn't a huge difference, though.
I haven't tried making the papers yet, perhaps that is the next step.
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pantone159
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Some more tests... I made up some turmeric paper. I have had the tincture for some time, I followed mostly the procedure in my CRC (71st):
Digest ground turmeric root with several quantities of water which are discarded. Dry the residue and digest it several days with six times its
weight of alcohol. Filter.
To make the papers, I cut a filter paper into strips, put them in a test tube, and added the tincture, and let the paper soak. When I took out the
papers, they seemed to be unevenly colored, so I put them back in the tube and added more tincture, and let them sit for a couple of days. The
resulting papers were still unevenly colored. I think my test tube was too cramped for them all, but I think the result is ok.
To test the papers: I put a small amount of B(OH)3 solution in a cup, and added a little HCl. I then wetted the test paper with this. The paper
acquired an orange color, which is distinct from the yellow/brown that the plain papers have. A similar paper put into a solution of HCl in water
showed no color change.
The color change does not seem all that dramatic to me. Yellow and orange are not so different in color, and since the turmeric ranges from yellow to
brown (due to concentration) this is not as clear as I initially expected for a good test.
My previous tries to get a color change in aqueous solution were confused by precipitates formed, as curcumin is poorly soluble in water. So today I
tried doing this in 95% EtOH solution. In one 150 ml beaker, I added some B(OH)3 powder (amount not measured), then c. 60 ml EtOH, some HCl, and
about a full eyedropper of turmeric tincture. To another beaker, I added the EtOH, HCl and turmeric, but no boric acid. The first beaker turned
distinctly orange, while the second is yellow, only very slightly tinted orange. The two are distinctly different. The resulting solutions are much
cleaner than I ever got with aqueous solutions.
Again, this is not as dramatic as I would like. (And I shouldn't have used as much as 120 ml of EtOH when I wasn't bothering to measure everything!
Silly waste.) But there is definitely a difference.
http://en.wikipedia.org/wiki/Rosocyanine
The above wikipedia article suggests that the complex formed has two curcumin molecules per boron atom, I surely have much less curcumin in my
mixtures, rather I have comparable masses of solid boric acid and turmeric tincture.
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