Help with a Problem Involving Polysaccharides

[zerobladex]

There’s a question in my textbook that goes: "In the 1800’s German scientists added hydrochloric acid to a heated starch solution to in order to artificially create sugar. However this only broke half of the glycosidic bonds in the starch. Why do you think this happened?"

First of all, how does Hydrochloric acid work in breaking glycosidic bonds? Does it have to do with the fact that some starches like amylopectin have lots of branches?

[david23]

yeah you are on the right track, starch has the normal 1-4 link and also the branch 1-6 links. The HCl here works like a catalyst that breaks down the bonds with hydrolysis. Have you had Orgo yet? if not, then ignore how HCl really works. But nevertheless, the HCl here works like an enzyme, and like enzymes, amylases for example, 1-4 bonds are easy, while 1-6 branch bounds are slight more protected.

[JackBean]

quote david23:

yeah you are on the right track, starch has the normal 1-4 link and also the branch 1-6 links. The HCl here works like a catalyst that breaks down the bonds with hydrolysis. Have you had Orgo yet? if not, then ignore how HCl really works. But nevertheless, the HCl here works like an enzyme, and like enzymes, amylases for example, 1-4 bonds are easy, while 1-6 branch bounds are slight more protected.

No way, HCl is definitely not like enzymes. It misses the specificity. To my knowledge, HCl should work by acid catalysis, by providing protons it accelerates the hydrolysis.

[MrMistery]

i think he meant that like an enzyme, it is a catalyst. Yes it definitely is not an enzyme, but when trying to explain to someone you simplify things.

[david23]

Yeah i should have made it clear, sorry for the confusion Jack, and thanks Mistery. Enzymes are catalysts, but catalysts include a broader range of things.

[JackBean]

OK 🙂 but it sounded, like, that it’s the reason, that there are some sterical obstackels as well

[monthir]

A sample of starch was exposed to HCl vapours in a closed dessicator for 48 hr. The acid starch was then heated for 30 min at 100°C. It has been found that transglucosidation occurs in both acid and heated starch samples.

[JackBean]

quote monthir:

A sample of starch was exposed to HCl vapours in a closed dessicator for 48 hr. The acid starch was then heated for 30 min at 100°C. It has been found that transglucosidation occurs in both acid and heated starch samples.

Yeah, acid and heat both work as catalysts. Heat accelerates "all" reactions by giving higher kinetic energy (I think its van’t Hoff’s law? That it speeds up 2-4-times when increasing temperature by 10°C) and acid is catalyst, as has been mentioned before (The hydrogen binds to hemiacetal oxygen… blablabla…)

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