Physical Properties of Carbohydrates carbohydrates are solid at room temperature monosaccharides and disaccharides are white crystalline substances and are soluble in water starches are amorphous and slightly soluble in water cellulose is fibrous and fibrous and insoluble in water

Chemical Properties of CarbohydratesReducing agents1. All aldoses can be reducing sugars because they contain free aldehyde group. (The aldehydes are oxidized by a mild oxidizing agent (Benedicts or Fehlings) to the corresponding carbohydratesR-CHO + 2Cu2+ R-COO-Na+ + Cu2OFehlingss Reagentppt2. All ketoses are reducing sugars because they have a ketone functional group next to an alcohol functional group.3. Carbohydrates with hemiacetal functional groups can reduce mild oxidizing agent because hemiacetals can form aldehydes through the following equilibrium equation:

Sucrose is a non-reducing sugar because it does not contain a hemiacetal functional group Starch is a non-reducing sugar because the hemiacetal function group is insignificant in a very large starch molecule

Hydrolysis of acetal groups1. Disaccharides and polysaccharides can be converted into monosaccharide by hydrolysis.

C12H22O11 + H2O C6H12O6 + C6H12O6Lactose Glucose Galactose

Isolation of Carbohydrates1. Glycogen from Chicken livera. Energy storage polysaccharide in plantsb. A branched-chain polysaccharide (homoglycan)c. Consists entirely of linear chains of glucose units connected by -1,4-glycosidic bonds and branched points every 1 in 10 glucose units linked by -1,6-glycosidic bondsi. Homogenization- disrupts membranesii. 0.1% acetic acid- removes protein via precipitationiii. Glycogen is insoluble in ethanoliv. Method: Protein denaturation and solubility of glycogen2. Starch from Potatoa. Energy storage polysaccharide in plantsb. A homoglycan mixture of amylase and amylopectini. Amylase- linear homoglycan of glucose connected by -1,4 linkageii. Amylopectin- -1,4 and -1,6 fashionc. Method: Selective dissolutionHydrolysis of Carbohydrates1. Acida. 2N HClb. Complete hydrolysisc. Efficient method to obtain monosaccharidesStarch/Glycogen

Glucose 2. Enzymatica. Salivary amylase (-amylase)b. Very specificc. An endoglycosidase hydrolyzing -1,4 linkages and random to yield a mixture of glucose, maltose, dextrin and hydrolysatesStarch/glycogen

Dextrins, amylodextrins, maltose, glucose

3. Dialysisa. Separation of particle sizeb. Sugar out, water in

Thin Layer Chromatography of Carbohydrates1. Spotting2. Development3. Visualizing Based on adsorption phenomenon Normal phase chromatography Stationary phase- silica gel G-250 Mobile phase- butanol:acetic acid:ether:water (9:6:3:1) Visualizing- p-anisaldehyde Appeared as dark-green spots Standards: dextrin, maltose, glucose Higher Rf, less polar

Quantitative Analysis Nelsons Reagent A- Na2CO3, NaKTartrate, NaHCO3, Na2SO4 B- CuSO5H2O, H2SO4 CuSO4- oxidizing agent Na2CO3 & NaHCO3- sugars more reactive NaKTartrate- prevent precipitation of Cu(OH)2; would tend to reduce Cu2+ in time Arsenomolybdate- dissolves Cu2O and is converted into molybdenum blue; color intensity of molybdenum in A480

Characterization of Carbohydrates

TestReagentPurposePositive ResultPrinciple InvolvedRemarks

1. Molisch Test

conc H2SO4, -napthol in 95% EtOHconfirms presence of Carbohydratesviolet interfacehydrolysis, dehydration forming either a furfural (pentose) or a 5-hydroxyfurfural (hexose) condensation with -napthol

H2SO4- hydrolysis, dehydration

Hexose- H2SO4 6-hydroxyfurfural purple colored

2. Anthrone TestCuSO4, Na3C6H5O7, Na2CO3(Benedeicts Reagent)Detection of reducing sugarBrick red pptOxidation in less basic media

3. Barfoeds TestCu(Ac)2 + acetic acid (Barfoeds reagent)Detect reducing sugar distinguishing reducing monosaccharide and reducing disaccharideBrick red pptOxidation of a reducing monosaccharide or disaccharide in acidic condition

4. Bials Orcinol TestOrcinol in conc HClFeCl3 (Bials Test)Detect presence of pentosesBlue green solutionDehydration and condensation with orcinol

5. Seliwanoffs TestResorcinolHClKetohexose vs aldohexoseCherry red solutionrapid dehydration and condensation reaction with resonance

6. Mucic Acid TestConc HNO3Detects galactoseRhombic crystals1,6 oxidation with sugars galactose-containing carbohydrates from meso compound (galactanic acid)

Osazone Test- Sucrose- doesnt form osazone unless hydrolyzed (-)- Glucosazone- needlelike/featherlike 4-5mm- Fructosazone- needlelike/featherlike 2mm- Mannosazone- needlike/featherlike 0.5mm- Lactosazone- fine-needle, grouped in balls, soluble in water- Galactosazone- broad flat crystals 15-20mm- Maltosazone- broad needlelike crystals, soluble in hot water- Xylosazone- long thin needlelike crystals-Starch- no osazone unless hydrolyzed

MolischIodineBenedictsBarfoedSeliwanoffBial Orcinol

Glucose+-++--

Fructose++++-

Xylose+-++-+

Lactose+-+---

Sucrose+---+-

Starch++----

Glycogen+-----

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