Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: cuso4 on 23/05/2003 07:55:49
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Type of alcohols can be distinguished using acidified potassium dichromate solution. Primary alcohols oxidise to aldehydes if distil, and carboxylic acids if reflux; secondary alcohols oxidise to ketones and don not oxidise further. Tertiary alcohols cannot be oxidised because it involves breaking a C-C bond and potassium dichromate is not a strong enough oxidising agent.
So which oxidising agent can oxidise tertiary alcohols? And what is the oxidation product?
Angel
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I am afraid you can't oxidise tertiary alcohols. Schoolboy chemistry says that oxidation is addition of oxygen or the removal of hydrogen or an electron. This definition (if primitive) tells us that a teriary alcohol can't be oxidised because there are no hydrogens on the carbon to be removed (unlike primary and secondary alcohols). The carbon is in it's highest oxidation state (+4)
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Hi Martin, welcome to the forum.
TNS
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How can I make solid alcohol?
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Stick it in the deep freezer [:)]
Am I dead? Am I alive? I'm both!
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Moshi, do you mean solid ethanol (freezing is about your only option) or an alcohol that happens to be a solid?
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quote:
Originally posted by cannabinoid
......or an alcohol that happens to be a solid?
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cannabinoid, does such alcohol exist? Must be a pretty big molecule.
Angel
"The people who will succeed are those who see the invisible and do the impossible."
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Yeah, very large alcohols tend to be solids, especially if they have benzene rings in the structure. (But the OH group can't be ON the benzene ring or it would be a phenol, not an alcohol)
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Once they start containing ring structures don't they become "steroid" alcohols, like oestrogen, testosterone etc.
chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Steroids are a particular class of multi-ringed compunds. You can be an alchol with a ring and not be a steroid. Steroids are classified by 3 linked 6-membered rings and a 5 membered ring (shared linkage) The functional groups are primarily alcohols, but can be carboxyl as well.
You might be thinking of the word "sterol" which literally means solid alcohol, and sterols are indeed alcohols, but they're usually classified as some sort of biomolecule. (for instance, cholesterol is a lipid) In fact, it's the extra hydroxl groups that makes certain cholesterol so prone to arterial adhesion. (due to added hydrogen bonding)
There are a lot of non-biomolecular solid alchols, even with rings....they're still generally quite large or have halogen substitions though. o-chlorobenzyl alcohol, for instance. Or lauryl alcohol, which isn't a ring, but is just really big, is solid at room temp.
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CAnnabinoid, thanks for clearing up the nomenclature and digging me out of the hole I excavated for myself !
One point to pick you up on though, in relation to arterial disease the cholesterol that becomes deposited within the vascular wall is, at least initially, intracellular. Samples of atheroma viewed beneath a microscope reveal macrophages (a kind of white blood cell) crammed with fats and cholesterol. In this condition these lardaceous cells are referred to as "foam cells".
A consistent feature of the cholesterol found in these lesions is that the side chain has been oxidised. This oxidation enables it to bond to a receptor on the foam cells and hence become internalised.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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I like that word. I think I'll stop saying obese and use lardaceous instead.
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Lardaceous...that's a great word.
Thanks for clearing up how cholesterol clogs up...I thought it was less complex than that. =)
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Vote #3 for lardaceous being a great word.
What are plant sterols then?
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Plant sterols are just that...sterols that are made by plants. They're chemically similar to cholesterol in that they have similiar structure and functional groups. It's believed that plant sterols ingested by humans can reduce the uptake of cholesterol because they compete for the same enzymes in the digestive tract.
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I'm glad I entreated to you a new word - lardaceous is my 'mot de choix' for lipidaceous individuals who clearly exhibit a deficit of prandial restraint. [;)]
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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quote:
Originally posted by cannabinoid
It's believed that plant sterols ingested by humans can reduce the uptake of cholesterol because they compete for the same enzymes in the digestive tract.
It's actually worth bearing in mind, however, that total body cholesterol is barely influenced by dietary cholesterol. Every cell in your body expresses a family of proteins called SRE's or "Steroid response elements" which are sensitive to cholesterol levels.
These SRE's switch on and off the metabolic pathway that enables your cells to make their own cholesterol. Once the levels of cholesterol entering the cell fall below certain limits the SRE's withdraw suppression of the rate-limiting step in the pathway (HMG-CoA Reductase) and cholesterol biosynthesis occurs de-novo within the cell.
HMG-CoA-Reductase is also the target of the statin class of cholesterol-lowering drugs.
chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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quote:
Originally posted by chris
I'm glad I entreated to you a new word - lardaceous is my 'mot de choix' for lipidaceous individuals who clearly exhibit a deficit of prandial restraint. [;)]
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
Hahahaha, you crack me up Chris. You'd be fun at a writer's group meeting.
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So what's the point of limiting cholesterol in your diet? Other than to ward off getting too lardaceous?
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I'm with bezoar on this one....if most cholesterol is made by the body, and the body will lower its production to meet with dietary intake of cholesterol, why limit cholesterol intake at all? Do your cells make both LDL and HDL cholesterols, or is one only obtained by ingesting "bad" foods? (I forget which of the two cholesterols is the "bad" one)
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That's precisely the point - people get terribly hung up about dietry cholesterol when in reality that is a minor contribution to total body cholesterol. The major determinant of serum cholesterol is dietary FAT, particularly saturated fat, and overall body weight.
Dietary fat is absorbed from the gut and forms cholesterol-rich chylomicrons in intestinal lacteals. These end up in circulation and are emptied of lipids by lipoprotein lipases expressed in adipose tissue (which is how fat cells pick up fat). The cholesterol-rich CM remnants are scavenged by the liver via Apo-B mediated uptake. In people with a deficiency in Apo-B receptors the fats spend much longer in the bloodstream before the liver removes them all and hence overall lipid levels are higher, increasing the liklihood of 'feeding' a vascular lesion - during their increased circulation times the cholesterol may become oxidised, increasing its atherogenicity.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Wow, there is a whole pot full of new words. I don't understand most of them, but I think I get the gist: Don't eat too much saturated fats.
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John
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So, essentially, lardaciousness would prove to have a greater tendency toward higher cholesterol levels.. I guess the queation I'd like to pose is, does an elevated cholesterol necessarily len ditself to increased arterial build-up, or are there some secondary effects that promote that?
Also, I'll have to add lardaceous to my vocabulary list!
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I just read my previous post and I must apologise for its content. I must have been in a dream or something and seem to have regurgitated the contents of a medical dictionary. Sorry for the baffling medical avalanche !
What the post essentially says is that the amount of choesterol in your diet makes virtually no contribution to serum (blood) cholesterol levels since cells make their own cholesterol if you reduce your oral intake.
But what does make a huge difference to blood cholesterol levels is total dietary fat because this is absorbed from the gut following emulsification with cholesterol-rich bile (from the liver). In the wall of the intestine the absorbed fats form small fat and cholesterol-rich particles called chylomicrons.
Obviously fats don't dissolve in water on their own and so specialised structures called apolipoproteins (APO- for short) are added. These proteins have a fat-loving part and a water-loving part. They surround the fatty molecules with their fat-loving regions on the inside and their water-loving region on the outside. In this way they can enable the chylomicron to be carried in the bloodstream without forming globules of fat that would otherwise immediately coalesce into one huge blob of oil and block up blood vessels.
One of the apolipoproteins can activate an enzyme expressed in certain tissues called lipoprotein-lipase. This enzyme breaks up oils and fats into fatty acids that can be picked up by cells. Tissues that like fat e.g. adipose tissue and breast tissue express high levels of lipoprotein-lipase and so when a chylomicron comes floating by, crammed with lipids, its apolipo-proteins switch on the lipoprotein-lipase which essentially unloads the fats into the target tissue. Once a chylomicron has unloaded its cargo of fat it becomes a cholesterol-rich chylomicron remnant which gets scavenged from the bloodstream by the liver. The cholesterol it contains ends up in bile and so the process begins again.
All of the time that fats are circulating in the bloodstream they can, and do, end up in the wrong place. Most blood vessels (except the smallest ones) have an inner lining called the endothelium which forms a barrier between the muscular wall of the vessel and the blood. If this layer is damaged (by high blood pressure, or by cigarette smoking) the wall of the blood vessel can become temporarily more permeable to fats from blood. Furthermore, other cells flock to the site of the injury to help repair the damage and in the process release growth factors to encourage the cells to regrow. Unfortunately these growth factors and inflammatory agents also encourage other cells to grow, including muscle cells from the muscle layer. These changes give rise to a 'bump' in the wall of the vessel containing fats, cells, and the foam cells we spoke of earlier which migrate in and soak up oxidised cholesterol that also gets into the lesion.
Because the vessel wall is now no longer smooth, and instead has a bump projecting into the vessel lumen, blood flow becomes turbulent which damages the endothelium even more, making the whole process above occur to an even greater extent. The evolving bump is an atheromatous plaque.
This is a basic overview of how fats traffic from the gut to their target tissue, sometimes ending up in the wrong place, and how vascular injury might explain some aspects of the process of atherogenesis.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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So, exercise would obviously be more effective combined with the diet, because it reduces your overall lardaceousness.
Chris, I've drawn blood on some of my patients, and you can actually see these yellow globules in it that appear to be fat. What's the story on that?
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That was a great explanation Chris! Thanks!
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John
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alcohols with large structure are most of the time solids, especially if they have benzene rings in the structure.