Have you watched Erin Brokovich? The movie is based on a true story of a real person and real litigation over water contaminated with Chromium (VI).
Chromium (VI) is chromium in a +6 oxidation state, as it is in CrO3 and K2Cr2O7, and other heavy-weight chromium oxidizing agents. It's both toxic and carcinogenic. There aren't a lot of other heavyweight oxidizers out there, so this stuff is used frequently. One alternative that gets some use is KMnO4, potassium permanganate.
Oxygen gas (O2) and ozone (O3) also are used to oxidize stuff, although O2 is pretty slow for laboratory chemistry. However it is cheap and readily available, and on longer timescales it reacts readily with a lot of stuff, including things we don't want it to react with.....like the surface of a cut avocado or apple, or the metal surface of a shovel left out in the elements over the winter.
Tuesday, November 25, 2008
Diabetic ketoacidosis and bicarbonate
Diabetics have a lot to worry about. Living with the disease surely isn't easy, and poor control of serum glucose levels can cause a wide variety of ugly, debilitating problems like blindness and circulatory problems leading to gangrene and amputations.
The seriousness of the disease was made real to me years ago by an experience I had in a hospital, where a previously perfectly lucid and cheerful old guy was admitted incoherent and super-sick. The doc ordered a bunch of diagnostic tests, but it was an easy diagnosis once the chem screen results were back: the guy's blood sugar was something like 400. His blood pH was like 6.9.
In situations like this there are a number of ways a person can end up dead. But one thing that causes concern is lowered blood pH. What can be done? Well, in addition to giving insulin when needed, sometimes lowly old bicarbonate (HCO3-) is also used to add buffer capacity to the blood and stabilize pH. At least, this is what I have heard. I don't have a good citation for this info.
Audience--especially those of you who have clinical or veterinary experience (pets get diabetic, too!)--can you help?
The old guy lived for a while longer, by the way. His ability to make sense was rapidly regained once his blood sugar returned to normal.
The seriousness of the disease was made real to me years ago by an experience I had in a hospital, where a previously perfectly lucid and cheerful old guy was admitted incoherent and super-sick. The doc ordered a bunch of diagnostic tests, but it was an easy diagnosis once the chem screen results were back: the guy's blood sugar was something like 400. His blood pH was like 6.9.
In situations like this there are a number of ways a person can end up dead. But one thing that causes concern is lowered blood pH. What can be done? Well, in addition to giving insulin when needed, sometimes lowly old bicarbonate (HCO3-) is also used to add buffer capacity to the blood and stabilize pH. At least, this is what I have heard. I don't have a good citation for this info.
Audience--especially those of you who have clinical or veterinary experience (pets get diabetic, too!)--can you help?
The old guy lived for a while longer, by the way. His ability to make sense was rapidly regained once his blood sugar returned to normal.
Sunday, November 23, 2008
seein' fluoroscein
The other day it came up that the dye making Mountain Dew yellow might be one and the same as the stuff that is used to color antifreeze. Seemed possible to me. I just happened to be familiar with this particular compound, called fluorescein, since I used it in grad school as a fluorescent tag on some molecules I was interested in.
As usual I searched Wikipedia, and I found a nice article about fluorescein. And according to my completely unverifiable web research, Mountain Dew is dyed with yellow number 5, and fluorescein dyes include yellow numbers 7 and 8.
The list of uses Wikipedia has for fluorescein is pretty amazing, though. In addition to its use as a dye and as a flluorescent chemical marker, it is also used in forensics to detect latent blood stains, in hydrology (dump it in at point A and look for it at point B, where you think the water flows), and medically to detect problems in the eyes and vascular system.
As to its use as a colorant in auto radiator fluid, I found an article posted on MedLine that suggests this was at least true in 1990, when the article was published. The gist of the article is that when given a dose of fluorescein similar to that which one would get from ingesting a toxic amount of antifreeze, men passed enough fluorescein in their urine that it could be detected with something called a Wood's lamp, which must be a uv lamp.
That's pretty weird but I think it's also pretty cool!
As usual I searched Wikipedia, and I found a nice article about fluorescein. And according to my completely unverifiable web research, Mountain Dew is dyed with yellow number 5, and fluorescein dyes include yellow numbers 7 and 8.
The list of uses Wikipedia has for fluorescein is pretty amazing, though. In addition to its use as a dye and as a flluorescent chemical marker, it is also used in forensics to detect latent blood stains, in hydrology (dump it in at point A and look for it at point B, where you think the water flows), and medically to detect problems in the eyes and vascular system.
As to its use as a colorant in auto radiator fluid, I found an article posted on MedLine that suggests this was at least true in 1990, when the article was published. The gist of the article is that when given a dose of fluorescein similar to that which one would get from ingesting a toxic amount of antifreeze, men passed enough fluorescein in their urine that it could be detected with something called a Wood's lamp, which must be a uv lamp.
That's pretty weird but I think it's also pretty cool!
Wednesday, November 19, 2008
more on cholinesterase inhibitors
Organophosphate pesticides are in the news again this morning.
A quick Wikipedia search left me sighing and unsurpised to see that all the culprits in the Oregonian's article--diazinon, malathion, and chlorpyrifos--are organophosphates and acetylcholine esterase inhibitors. My, oh my, I thought we'd finished on that topic.
Incidentally, I remember as a little girl getting my first garden and soon after buying my first cardboard can of Sevin. I also remember television ads for Lorsban and Dursban. It's an Iowa thing, seeing ag chemicals advertised during the evening news.
A quick Wikipedia search left me sighing and unsurpised to see that all the culprits in the Oregonian's article--diazinon, malathion, and chlorpyrifos--are organophosphates and acetylcholine esterase inhibitors. My, oh my, I thought we'd finished on that topic.
Incidentally, I remember as a little girl getting my first garden and soon after buying my first cardboard can of Sevin. I also remember television ads for Lorsban and Dursban. It's an Iowa thing, seeing ag chemicals advertised during the evening news.
Tuesday, November 18, 2008
Gulf War Syndrome in the news
Many of you may not remember how much fuss there was about a strange affliction that veterans of the first Gulf War reported soon after they returned from the Middle East. But in the early 1990s it was big news: Gulf War Syndrome. The synmptoms were of the sort it would be easy to dismiss because they aren't "threshhold" types of things where a person knows something is wrong. Instead they are vague and could conceivably be assigned to all sorts of causes: stress, PTSD, depression, etc.. Now--about what, 18 years later?--we have a report that suggests the syndrome is real and that the cause could perhaps be one of two things: pesticide exposure or exposure to substances used to protect against nerve gases.
As is usually the case the news didn't get super-specific about the names of things. So I checked Wikipedia to see what's there and was delighted to see they've got a nice description of the report contents on the site. To see it just search Gulf War Syndrome.
The pesticides were probably used to protect our soldiers from communicable diseases or simple irritation associated with insects, including sand flies. They were likely organophosphates or carbamates. These substances are acetylcholine esterase inhibitors. Aceetylcholine is a neurotransmitter that is removed from the synapse by acetylcholine esterase. The inhibitors block the enzyme, causing a buildup of acetylcholine in the synapse and altered nerve function. Hence the insects get screwed up and croak. Hence, perhaps with lots of exposure, people get symptoms related to nerve function. Such a syndrome is described for farm workers who get accidental poisoning, although symptoms of massive exposure don't sound quite the same as those described for the Gulf War Syndrome.
The other possible source of the problem are agents used to protect against nerve gases that could have been used as chemical warfare. These agents include Soman (mentioned in the Wikipedia article) and also more familiar agents like Sarin and VX....which we have manufactured in the U.S. and which are now being destroyed at places like the Umatilla Chemical Depot in Umatilla. Just like the pesticides, these substances are all acetylcholine esterase inhibitors. They act via a very similar biochemical mechanism.
Interestingly, the protection against such agents that may be implicated in the Syndrome is again an acetylcholine esterase inhibitor. It is called pyridostigmine. I'm not sure how it works but my guess is that it competes for binding to the acetylcholine esterase but does so reversibly, so it can block the nerve agent without causing severe or long-term effects. .....or maybe it does. ....maybe in combination with exposure to other acetylcholine esterase inhibitors.
Check out the structures for pyridostigmine and for the pesticide sevin on Wikipedia. See the similarity?
It's a fascinating and sad story that continues to unfold.
As is usually the case the news didn't get super-specific about the names of things. So I checked Wikipedia to see what's there and was delighted to see they've got a nice description of the report contents on the site. To see it just search Gulf War Syndrome.
The pesticides were probably used to protect our soldiers from communicable diseases or simple irritation associated with insects, including sand flies. They were likely organophosphates or carbamates. These substances are acetylcholine esterase inhibitors. Aceetylcholine is a neurotransmitter that is removed from the synapse by acetylcholine esterase. The inhibitors block the enzyme, causing a buildup of acetylcholine in the synapse and altered nerve function. Hence the insects get screwed up and croak. Hence, perhaps with lots of exposure, people get symptoms related to nerve function. Such a syndrome is described for farm workers who get accidental poisoning, although symptoms of massive exposure don't sound quite the same as those described for the Gulf War Syndrome.
The other possible source of the problem are agents used to protect against nerve gases that could have been used as chemical warfare. These agents include Soman (mentioned in the Wikipedia article) and also more familiar agents like Sarin and VX....which we have manufactured in the U.S. and which are now being destroyed at places like the Umatilla Chemical Depot in Umatilla. Just like the pesticides, these substances are all acetylcholine esterase inhibitors. They act via a very similar biochemical mechanism.
Interestingly, the protection against such agents that may be implicated in the Syndrome is again an acetylcholine esterase inhibitor. It is called pyridostigmine. I'm not sure how it works but my guess is that it competes for binding to the acetylcholine esterase but does so reversibly, so it can block the nerve agent without causing severe or long-term effects. .....or maybe it does. ....maybe in combination with exposure to other acetylcholine esterase inhibitors.
Check out the structures for pyridostigmine and for the pesticide sevin on Wikipedia. See the similarity?
It's a fascinating and sad story that continues to unfold.
Markovnikov: theme and variations
I did some scouting around about how addition reactions involving a cyclic intermediate can lead to Markovnikov products (products that you would predict would form from Markovnikov's rule, based on a carbocation intermediate). The explanation as I understand it goes like this:
Fact: cyclic alkenes that undergo addition of halogens like Br2 end up with the halogen atoms trans in the product. Similarly halohydrin formation results in trans configurations.
Fact: a carbocation mechanism does not agree with the statement above, so it does not explain the reaction.
Fact: cyclic intermediates such as the bromonium ion can be appealed to, and provide an adequate explanation for the trans stereochemistry. So we use this mechanism.
Fact: these reactions yield Markovnikov products.
It's these last two facts that seem contradictory, unless you take a more nuanced view of the cyclic intermediates. Imagine that these intermediates are not exactly symmetrical. If they are shifted a bit so that there is some carbocation character in the cyclic intermediate, then we could explain both the trans orientation of the added groups and also the Markovnikov product formation. Which is the best explanation there is.
Fact: cyclic alkenes that undergo addition of halogens like Br2 end up with the halogen atoms trans in the product. Similarly halohydrin formation results in trans configurations.
Fact: a carbocation mechanism does not agree with the statement above, so it does not explain the reaction.
Fact: cyclic intermediates such as the bromonium ion can be appealed to, and provide an adequate explanation for the trans stereochemistry. So we use this mechanism.
Fact: these reactions yield Markovnikov products.
It's these last two facts that seem contradictory, unless you take a more nuanced view of the cyclic intermediates. Imagine that these intermediates are not exactly symmetrical. If they are shifted a bit so that there is some carbocation character in the cyclic intermediate, then we could explain both the trans orientation of the added groups and also the Markovnikov product formation. Which is the best explanation there is.
Thursday, November 13, 2008
the white zombie
Want an electric car? You don't have to compromise when it comes to acceleration:
http://www.youtube.com/watch?v=zp_jwE0KdOk&feature=related
That would be 103 mph. Check out Oregon Field Guide's rebroadcast on Sunday evening (6:30) if you want to see more.
http://www.youtube.com/watch?v=zp_jwE0KdOk&feature=related
That would be 103 mph. Check out Oregon Field Guide's rebroadcast on Sunday evening (6:30) if you want to see more.
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