Carbohydrates

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victor
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Carbohydrates

Post by victor » Fri Sep 22, 2006 10:32 am

Um..actually I got confused whether I have to post it in biology forum or in chemistry forum. But, since I've joined both forum, so I'll post this in both forum.... :mrgreen:

Um, my question is about qualitative tests on monosaccharides glucose, fructose and arabinose.

1. For Benedict test which is tested on those three samples, I got the results that all of them form a red sediment (which means as positive result). What I wanna ask is, during the formation of red sediment, which is a reduction of Cu2+ as CuSO4 into Cu+ as Cu2O, meand thst the sugar is oxydized. I got confused about the reaction mechanism, which in the book is said that this reduction of Cu is related with enol forms of each sugar.
Now, let's see for fructose, it has a ketone group in C-2. What makes me confused is that a ketone group is not as easy as an aldehyde group when it comes to an oxydation (so supposed that ketone sugar wouldn't reduce that Cu), but the fact said a different thing....I think that it's due to formation of enol tautomer of fructose. But, do anyone know about the reaction mechanism? oh, also if you may, please give a link about this....

2. About Seliwanoff and Bial test, actually this is a silly question.. Grin When I was in the Biochemistry lab yesterday, I did the Bial test in acid room (kinda room to place concentrated acid), maybe because Bial reagent is made of Orcynol, conc. HCl and FeCl3. But, when it comes to do the Seliwanoff test (Seliwanoff reagent is made of Resorcynol (m-dihydroxybenzene) and conc. H2SO4 ), I do it not in the acid room (because the Seliwanoff reagent is placed on the desk just like that). Well, considering that both of the reagents contain concentrated acid, how come that Seliwanoff reagent is placeed outside the acid room? Or is it just an error in placing that reagent?

3. Then, for Mollisch reaction. When I did this reaction, I put 3 samples of sugars (glucose, fructose and arabinose) and slowly drops a few drops of alpha-naphtol towards three of them. After that I slowly put conc. H2SO4 into the reaction tube. The result it there's a purple ring formed in the middle of the solution, which is said that the acid get reacted with the sugar and formed a furfural which then condensed with alpha-naphtol to form a purple ring as a middle layer. My question is why did the acid won't get react with all the sugar (so it form a three-layer solution) ? and then, do you know what are the substance in that three-layer solution? My guess ia that, the bottom layer is acid ; middle layer is a furfural-alpha naphtol complex ; and the top layer is the remaining sugar (not in furfural state).

And another favor, could anyone please give me a link about mechanisms in Seliwanoff, Benedict, Bial, Mollisch, and Osazone reaction? any help would be appreciated... :D
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mada-vet
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Post by mada-vet » Thu Oct 12, 2006 8:39 am

i need information on the medical imprtance of monosaccharides derivatives

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