MNK
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Can refrigeration lesson the life of an alkaloid?
i know this may seem like a stupid question, but i found a backwater site that suggested that certain alkaloids may actually last longer at room
temperature than at refrigerator temperatures. This seems ilogical to me, could anyone simply confirm or deny the validity of this information. thank
you kindly
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stateofhack
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I guess it really comes down to the type of Alkaloid  It would help to know which
one your talking about or providing us with the "backwater site" (What does it mean?).
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Saerynide
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It could be that they mean the process of freezing and thawing could decrease it's life span if you're not careful. For example, opening the
container before it has thawed will cause water vapor from the atmosphere to condense inside. If you do this enough times, you'll definately end up
with a lot more water in the container.
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Nicodem
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This question is so incredibly vague and the original poster does not appear interested in providing not even the minimal information needed. I'm
moving it to Beginnings.
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JeffAMX
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How much longer of a life-span do you think a chemical would have if it was kept in a refrigerator?
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The_Davster
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Depends on the chemical, some which are supposed to be kept cold have data out there for the length of time they can be stored at various temps.
Others last essentially forever at any common storage temp.
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JeffAMX
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Oh ok, yeah, i was just wondering about preserving chemicals from breaking down. How much room temperature heat causes them to break down and how
fast, how much longer of a life span it would get if it was kept in a fridge or if its best to freeze.
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JeffAMX
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ya know what i mean? for example Ib profen, with a current expiration date of 2010, if kept in a refrigerator would that substantially increase the
life of the chemical?
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Nicodem
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You mean ibuprofen? But it does not deteriorate with time. If protected from light it should be stable for several dozens of years. Where did you hear that
is not stable? The most it can occur with it is enolization, but since it is most comonly sold as racemate this is irrelevant. Its oxidation with
oxygen from air is possible but probably extremely slow and besides if stored airtight sooner or later the oxygen present gets consumed and the
oxidation stops (talking about 50 years or longer periods). In practice hermetically closed light protected ibuprofen should be useful for centuries
either stored at room temperature or freezer. And besides, what does an "expiration date" have to do with compounds stability?
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MNK
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Alkaloid Degredation - how to minimise it
I know im speaking generally here but any help would be appreciated. Im looking to know what factors result in the degredation of alkaloids. I know
light, moisture and heat all tend to decay alkaloids, but i'd like to know what periods of time i would be dealing with as well as which of the above
mentioned factors have the greatest influence on degredation. Ive also heard that alkaloids are generally more stable when stored out of solution than
in.
My main concerns are the inevitable temperature change that the alkaloid experiences after or during extraction - in order to evaporate the solvent
(methanol, ethanol) one would usually elevate the solvents temperature, or earlier, in order to increase its ability to extract the alkaloids. Once
all of the solvent has been evaporated would it be advisable to store them in a closed container in a refrigerator (and suffer the temperature change
from evaporation to refrigeration) or rather place it in the same container but leave it at room temperature (which would minimise the change in
temperature that the alkaloid is exposed to between extraction and storage)
Any information on the subject (be it general or specific) would be appreciated
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Sauron
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You can greatly reduce the required temperature by using vacuum pump to lower the bp. Methanol you ought to be able to get to come off in a rotavap at
room temperature at about 20 torr. Ethanol, you might need a water bath at 30-40 C. The literature should tell you how labile these alkaloids are to
heat, light and atmosphere. You might need a N2 or Ar atmosphere.
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ScienceSquirrel
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It is very hard to generalise as there are so many alkaloids.
Some of them are as tough as old boots while others degrade quite quickly.
I have seen a bottle of quinine sulphate that had one of the old BDH labels on it sitting on an open laboratory shelf in the early eighties and it was
a white crystalline powder, bottles of tonic water that are years old still fluoresce blue under UV light and have the characteristic bitter taste so
I would say that it is stable for decades at room temperature.
On the other hand ergotamine degrades quite rapidly and extraction from the fungus requires care to obtain optimum yields.
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Ritter
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| Quote: | Originally posted by JeffAMX
How much longer of a life-span do you think a chemical would have if it was kept in a refrigerator? |
Alkaloid degradation, especially in solution, occurs via a variety of different mechanisms: air oxidation, photolysis, etc. Some alkaloids, such as
the highly basic mescaline, even react with atmospheric CO2 to form an inactive urea. But these mechanisms are all chemical in nature. In general, the
rate of any chemical reaction doubles with each 10 degree (C) increase in temperature. So the reverse is also true: the rate of the reaction decreases
by the same factor for every 10 degree decrease in temperature. Assuming we are talking about a refrigerator, this would be in the dark when the door
is closed.
Very sensitive molecules such as insulin are stored in refrigerators in order to extend their shelf lives. In general, refrigeration is almost
universally used to extend the shelf life of sensitive molecules such as alkaloids. Research chemical catalogs such as the Sigma-Aldrich state the
reccomended storage temperature for each product.
I have had consistently satisfactory results with storing aqueous extracts of plant alkaloids in a refrigerator overnight. For longer term storage you
would need to remove the water & replace the oxygen with nitrogen or another inert gas.
Non-aqueous solutions of alkaloids should be stored in refrigerators only when proper care is taken to avoid flammable solvents that could result in a
serious explosion once the door is opened. Household refrigerators are not designed to be explosion-proof. The microswitch that turns the interior
light on when the door is opened can generate a spark that could trigger a solvent-air mixture detonation.
This thread might be better placed in Biochemistry as alkaloids are natural products.
[Edited on 22-8-2008 by Ritter]
Ritter
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