Carbohydrate Chemistry (5/13) Flashcards
Anomers
Carbohydrate isomers that differ in their orientation of their substituents at the anomeric carbon (mainly the hydroxyl group)
The anomeric carbon
The carbon with the double bond to oxygen in its linear form. It is a solid electrophile making it a promising site for nucleophilic attack
When aldose cyclizes
Forms a hemiacetal
When a ketose cyclizes
Forms a hemikatal (instead of a second bound to oxygen, it forms a bond with another R-group
If hydroxyl attacks from carbon 4
Intermolecular attack to form a furanose
If hydroxyl attacks from carbon 5
Intermolecular attack to form a pyranose
When hydroxyl group points up
beta
When hydroxyl group points downwards
alpha
Mutarotation
alpha and beta can rapidly convert back and fourth
Glycosidic bonds
dehydration reaction
Glycosidic bond hydrolysis
Hydration event. Water comes in and attaches, then is deprotonated to restore hydroxyl group
Maillard reaction
occurs between 140-165 degrees C
amino acids in foods are reacting with certain carbohydrates
happens faster under basic conditions
Reducing sugars
undergo a redox reactions and therefore lose electrons to become oxidized
EX)
aldehydes, non-aldose sugars that can be converted into aldoses, maltose and lactose (because they have a free anomeric carbon)
If apart of a glycosidic bond…
Cannot participate in a redox reaction
Metals that usually carry out redox reactions
Act as oxidizing agents:
Cu, Ag, Fe
Tollen’s test
When aqueous silver is added to a sugar and then forms a solid. Once it precipitates from a solution, it produces a visible silver film that looks like a mirror
Benedict’s test
When aqueous copper is added to sugar the solution start blue and if aldehyde is present, turns solution red
Fehling’s test
Adding aqueous copper to sugar and measured the amount of oxidizing agent (CuO)
Sugar chemistry for the Maillard reaction
All monosaccharides are reducing agents
All ketoses tautomerize to aldoses and all aldoses are reducing agents
Disaccharides are reducing agents if they have a free anomeric carbon
Polysaccharides are usually non-reducing agents