1. LECTURE 4 -CARBOHYDRATES
Carbohydrates and their classification. Determine the carbohydrates, quantitative and qualitative analysis.

14. D- and L- enantiomers

15. Mutarotation –
alfa and beta forms of sugars are readily interconverted when dissolved in water
Mutarotation is the change in the optical rotation because of the change in the equilibrium between two anomers, when the corresponding stereocenters interconvert. Cyclic sugars show mutarotation as α and β anomeric forms interconvert.[1] The optical rotation of the solution depends on the optical rotation of each anomer and their ratio in the solution.
Mutarotation was discovered by French chemist Dubrunfaut in 1846, when he noticed that the specific rotation of aqueous sugar solution changes with time

16. FISHER AND HAWORTH FORMS OF SUGAR

17. 2.3 Cyclic structure of monosacharides
in aqueous solution, monosaccharides with five or more carbon atoms in the backbone occur predominantly as cyclic (ring) structures in which the carbonyl group has formed a covalent bond with the oxygen of a hydroxyl group along the chain.
The new chiral center in cyclic (c1) is called anomeric carbon

18. SUMMARY OF SUGAR STRUCTURES
ISOMERS- compounds that have the same chemical formula e.g. fructose, glucose, mannose, and galactose are isomers of each other having formula C6H12O6.
EPIMERS- refer to sugars whose configuration differ around one specific carbon atom e.g. glucose and galactose are C-4 epimers and glucose and mannose are C-2 epimers.
ENANTIOMERS- a special type of isomerism found in pairs of structures that are mirror images of each other. The mirror images are termed as enantiomers and the two members are designated as D- and L- sugar. The vast majority of sugars in humans are D-sugars.
CYCLIZATION OF SUGARS- most monosaccharides with 5 or more carbon atoms are predominately found in a ring form, where the aldehyde or ketone group has reacted with an alcoholic group on the same sugar group to form a hemiacetal or hemiketal ring.
Pyranose ring- if the ring has 5 carbons and 1 oxygen.
Furanose ring- if the ring is 5-membered (4 carbons and 1 oxygen

19. Pyranoses: six-membered ring compounds ( resemble pyran )
Furanoses : fivemembered rings, (resemble furan)
The structure systematic names glucose & fructose become
HAWORTH STRUCTURES
Pyranoses& Furanoses
An English chemist W.N. Haworth gave a more accurate picture of carbohydrate structure. (Ref. P.205 of textbook)

20. IMPORTANT REACTIONS (Cont)
ISOMERIZATION
Monosaccharides undergo several types of isomerization e.g. D-glucose in alkaline solution for several hours containn D-mannose and D-fructose. The conversion of glucose to mannose is termed s epimerization. (p of Textbook).
ESTERIFICATION
Free OH groups of carbohydrates react with acids to form esters. This reaction an change the physical and chemical propteries of sugar.
GLYCOSIDE FORMATION-
Hemiacetals and hemiketals reaction with alcohols to form the corressponding aceta or ketal (p.210 of Text).On the contrary when a cyclic hemiacetal or hemiketal form of monosaccharide reacts with alcohol, the new linkage is called glycosidic linkage and the compound glycoside.

21. Alfa & beta GLYCOCIDIC BOND

22. Section 4.1 DISACCHARIDES AND OLIGOSACCHARIDES

23. DISACCHARIDES AND OLIGOSACCHARIDES
Cnfigurations: alfa or beta ( 1,4, glycosidic bonds or linkages; other linkages 1,1; 1,2; 1,3; 1,6)
Digestion aided by enzymes. Defficiency of any one enzyme causes unpleasant symptoms (fermentation) in colon produces gas [bloating of cramps].
Most common defficiency, an ancestoral disorder, lactose intolerance caused by reduced synthesis of lactase

24. Important sugars of Disaccharides
LACTOSE
(milk sugar) disaccharide found in milk; composed of one molecule of galactose and glucose linked through beta(1,4) glycosidic linkage; because of the hemiacetal group of the glucose component, lactose is a reducing sugar

25. OLIGOSACCHARIDE SUGARS
Oligosaccharides are small polymers often found attached to polypeptides in glycoproteins and some glycolipids.
They are attached to membrane and secretory proteins found in endoplasmic reticulum and Golgi complex of various cells
Two classes: N-linked and O-linked

26. Section 4.2 POLYSACCHARIDES

27. 4.2. Classification of Polisacharides

28. 4.2.1.HOMOSACCHARIDES Found in abundance in nature
Important examples: starch, glycogen, cellulose, and chitin
Starch, glycogen, and cellulose all yield D- glucose when they are hydrolyzed
Cellulose - primary component of plant cells
Chitin – principal structural component of exoskeletons of arthropods and cell walls of many fungi; yield glucose derivative N-acetyl glucosamine when it is hydrolyzed.
4.2.1.HOMOSACCHARIDES

29. 4.2.1.HOMOSACCHARIDES Found in abundance in nature
Important examples: starch, glycogen, cellulose, and chitin
Starch, glycogen, and cellulose all yield D- glucose when they are hydrolyzed
Cellulose - primary component of plant cells
Chitin – principal structural component of exoskeletons of arthropods and cell walls of many fungi; yield glucose derivative N-acetyl glucosamine when it is hydrolyzed.

30. STARCH (Homosaccharide)
A naturally abundant nutrient carbohydrate, (C6H10O5)n, found chiefly in the seeds, fruits, tubers, roots, and stem pith of plants, notably in corn, potatoes, wheat, and rice, and varying widely in appearance according to source but commonly prepared as a white amorphous tasteless powder.
Any of various substances, such as natural starch, used to stiffen cloth, as in laundering.
Two polysaccharides occur together in starch: amylose and amylopectin
Amylose – unbranched chains of D-glucose residues linked with alfa(1,4,)glycosidic bonds
Amylopectin – a branched polymer containing both alfa(1,4,) and alfa(1,6) glcosidic linkages; the alfa(1,6) branch points may occur every glucose residues to prevent helix formation
Starch digestion begins in the mouth; alfa-amylase in the saliva initiates hydrolysis of the gycosidic linkages

31. GLYCOGEN (Homosaccharide)
Glycogen is the storage form of glucose in animals and humans which is analogous to the starch in plants.
Glycogen is synthesized and stored mainly in the liver and the muscles.
Structurally, glycogen is very similar to amylopectin with alpha acetal linkages, however, it has even more branching and more glucose units are present than in amylopectin.
Various samples of glycogen have been measured at 1, ,000 units of glucose.
The structure of glycogen consists of long polymer chains of glucose units connected by an alpha acetal linkage.
The branches are formed by linking C # 1 to a C # 6 through an acetal linkages.
In glycogen, the branches occur at intervals of 8-10 glucose units, while in amylopectin the branches are separated by glucose units.

32. STRUCTURE OF GLYCOGEN

33. CELLULOSE (Homosaccharide)
Cellulose is found in plants as microfibrils (2-20 nm diameter and nm long). These form the structurally strong  framework in the cell walls.
Cellulose is mostly prepared from wood pulp
Cellulose is a linear polymer of β-(1 4)-D-glucopyranose units in 4C1 conformation. The fully equatorial conformation of β-linked glucopyranose residues stabilizes the chair structure, minimizing its flexibility
Cellulose has many uses as an anticake agent, emulsifier, stabilizer, dispersing agent, thickener, and gelling agent but these are generally subsidiary to its most important use of holding on to water.
Water cannot penetrate crystalline cellulose but dry amorphous cellulose absorbs water becoming soft and flexible.
Purified cellulose is used as the base material for a number of water-soluble derivatives e.g. Methyl cellulose, carbomethycellulose

38. Chromatographic Separation of Sugar
*Chromatography:
is the collective term for a family of laboratory techniques for the separation of mixtures.
It involves passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the analyte to be measured from other molecules in the mixture and allows it to be isolated.
The analyte is the substance that is to be separated during chromatography

39. Chromatographic Separation of Sugar
The term chromatography comes from the earlier times when the technique was used for the separation of colored plants pigments.
Chromatography is a technique for separation of closely related groups of compounds. The separation is brought about by differential migration along a porous medium and the migration is caused by the flow of solvent.

40. Chromatographic Separation of Sugar
Within limits chromatography can be divided into two types : partition and adsorption chromatography .Paper chromatography is an example of liquid-liquid chromatography .

43. Chromatographic Separation of Sugar
In this type of chromatography separation is due to differential partition of solutes between two liquid phases .One liquid phase is bound to the porous medium for example, the water bound in the cellulose paper, this phase is referred to as, the stationary phase. The other liquid phase, the mobile phase flows along the porous medium .As the mobile phase flows over the solute mixture, the individual solutes partition themselves between the aqueous stationary phase and the organic mobile phase relative to their solubilities in the two phases. The more soluble a solute

44. Chromatographic Separation of Sugar
in the mobile phase, the faster it will travel along the paper, and conversely, the mobile phase must be a mixture in which the compounds to be separated are soluble or partially soluble .In paper chromatography solute or solute mixture is spotted in solution along a base line on a sheet of filter paper(whatman No. 1).The mobile phase(solvent) is allowed to flow over the spots either ascending the paper by capillary action or descending the paper by gravity.

45. Chromatographic Separation of Sugar
The separation is measured in terms of a unit called Rf (relative rates of flow) with respect to the solvent front.
The figure below explains how to calculate this value.

47. Chromatographic Separation of Sugar
The Rf value of a compound in a particular solvent system is constant under identical conditions of the experiment, e.g. temperature, pH, etc.
Because most compound are colorless the spots are visualized after separation by specific reagent. The location reagent is applied by spraying the paper or rapidly dipping it in a solution of the reagent in a volatile solvent. Viewing under ultraviolet light is also useful since some compound which absorb it strongly show up as dark spots against the florescent background of the paper.

48. glucose
Fructose
Maltose
Lactose
mixture 1 2 3 4 5

49. General summary of the behavior of the various sugars to these reagents are given below:
d c b a Sugars
pink Aldohexoses
red Ketohexoses
Blue,green Aldopentoses
Ketopentoses
Deoxy sugars
Glycosides
Amino sugars

50. Materials:
Paper: usally whatman No. 1 filter paper is used because of its known.
Solvents:
[a] water-sturated phenol + 1% ammonia
[b] n-butanol-acetic acid-water (4:1:5 v/v)
[c] isopropanol- pyridine- water- acetic acid (8:8:4:1 v/v)

51. Materials: Spray reagent A. Ammoniacal silver nitrate:
add equal volumes of NH4OH to a saturated solution of AgNO3 and dilute the methanol to give a final concentration of 0.3M.After spraying the developed chromatograms,place them in an oven for 5-10 minutes, when the reducing sugars appear as brown spots.
B. Alkaline permanganate:
Prepare aqueous solution of KMNO4 (1%) containing 2 % NaCO3.After spraying with this mixture, the chromatograms are kept at 100C for a few minutes, when the sugar spots appear as yellow spots in purple background.

52. Materials: Spray reagent C. Aniline diphenylamine reagent:
Mix 5 volumes of 1% aniline and 5 volumes of 1% diphenylamine in acetone with 1 volume of 85% phosphoric acid .after spraying the dried chromatograms with this solution the spots are visualized by heating the paper at 100C for a few minutes.
D.Resorcinol reagent:
Mix 1% ethanolic solution of resorcinol and 0.2N HCl (1:1 v/v).Spray the dried chromatograms and visualize spots by heating at 90C.

53. Rf: Solvent c Solvent b Solvent a Sugar 0.64 0.18 0.39 Glucose
Galactose
Fructose
Ribose
Deoxy ribose
Lactose
Maltose
Sucrose