Transcript Lecture_30.Carbohydrates.Tannins

Lecture №30
General characteristic of the carbohydrates,
their sources of getting, properties,
qualitative and quantitative analysis,
storage and usage. Tannins.
prepared: assist. Logoyda L.S.
Carbohydrates are carbon compounds that contain large quantities of
hydroxyl groups . The presence of the hydroxyl groups allows
carbohydrates to interact with the aqueous environment and to
participate in hydrogen bonding. Carbohydrates can combine with
lipid to form glycolipids or with protein to form glycoproteins.
They have a wide range of functions including providing a significant
fraction of the energy in the diet of most organism , acting as a
storage form of energy in the body and serving as cell membrane
components.
Also carbohydrates serve as a structural component of many
organisms including cell walls of bacteria.
Carbohydrates serve as metabolic intermediate ( e.g Glucose 6
phosphate, fructose 1,6 diphosphate).
Ribose ,deoxyribose play a major role in the synthesis DNA and RNA.
all life activities are dependent upon carbohydrates. When insufficient
carbohydrates are available from the diet, the body converts fat
reserves to carbohydrates for its use, and amino acids are utilized as
carbohydrates instead of being used to make body protein.
Carbohydrates, along with proteins and fats, comprise the major
components of living matter and are used for maintenance of cellular
functional activities and as reserve and structural materials for cells
• Carbohydrates with an aldehyde group are called aldoses where
those with a keto group are called ketoses. For example ,
glyceraldehyde is an aldose, whereas, dihydroxyacetone is a
ketose.
• Disaccharides: contain two monosaccharides units. Maltose ,
sucrose
• Oligosaccharides : contain from three to about 12 monosaccharides
units. For example, Blood group antigens.
• Polysaccharides : contain more than 12 monosaccharides units and
can be hundreds of sugar units in length. Starch , cellulose
• All carbohydrates can be hydrolyzed (broken down) into two or
more monosaccharides.
• For further understanding of these different classifications of
carbohydrates, the monosaccharides and disaccharides can be
grouped together and compared with the polysaccharides. This can
be done because monosaccharides and disaccharides have certain
things in common.
• They are both water soluble. In addition, they have a sweet taste
and a crystalline structure.
Simple sugars, starches and cellulose are
organic compounds that have the
approximate formula C(H2O)n, which
accounts for the name carbohydrate (or
hydrate of carbon) that is usually applied
to this group of compounds They are not
truly hydrates of carbon but are
polyhydroxy (alcohol) compounds that
contai an aldehyde or ketone functional
group. These functional groups give the
carbohydrates some of their chemical
properties that will be studied in this lab.
Monosaccharides
Simple sugars & cannot be hydrolysed
further. They are further classified on
the basis of number of carbon atoms
present as well as on the presence of
functional groups.
Carbon atoms
Examples
Functional groups
Trioses (3 carbon)
Glyceraldehyde
Dihydroxy acetone
Aldehyde (aldotriose)
Ketone (Ketotriose)
Tetroses (4 carbon)
Erythrose
Aldehyde (aldotetrose)
Pentoses (5 carbon
Ribose
Xylose
Xylulose
Aldehyde(Aldopentose)
Aldehyde(Aldopentose)
Ketone (Ketopentose)
Hexoses (6 carbons)
Glucose
Galactose
Fructose
Aldehyde (Aldohexose)
Aldehyde (Aldohexose)
Ketone (Ketohexose)
Disaccharides.
• Contain two molecules of same or
different monosaccharide units. On
hydrolysis they give two
monosaccharide units.
Monosaccharide units are joined by
glycosidic bond.
Examples
Product formed
Upon hydrolysis
Glycosidic
Linkage
Sources
Maltose
glucose + glucose
α 1-4
Malt
Lactose
galactose +
glucose
β 1-4
Milk
Sucrose
glucose +
Fructose
Isomaltose
glucose + glucose
β 1-2
α 1-6
Sugar cane
Digestion of
amylopectin
Oligosaccharides
Contain - molecules of monosaccharide
units.
E.g. Maltotriose. (Glucose + Glucose +
Glucose)
The D Aldose Family
Carbohydrates
Isomers and epimers
• Compounds that have the same chemical formula but have
different structures are called isomers. For example Fructose,
glucose , mannose and galactose are all isomers of each other
having the same chemical formula C6H12O6. If two
monosaccharides differ in configuration around only one specific
carbon atom , they are defined as epimers of each other. For
example, glucose and galactose are C4 epimers, their structures
differ only in the position of the hydroxyl group at C4 ( Note , the
carbons in sugar are numbered beginning at the end that contain
the aldehyde or ketone group.
• Glucose and mannose are C2 epimers. However, galactose and
mannose are not epimers they differ in the position of the hydroxyl
group at two carbon 2 and 4 and therefore, defined only as
isomers.
• Enantiomers: A special type of isomerism is found in the pairs
of structures that are mirror images of each other. These mirror
images are called enantiomers. The two members of the pair are
called as D and L sugars. The majority of the sugars in human are D
sugars.
Anomeric carbon
• Formation of a ring results in the creation of an
anomeric carbon at C1 of an aldose or C2 of a ketose.
These structures are called the α andβ configuration of
the sugar . For example α-D glucose and β-D-glucose.
These two sugars are both glucose but they are
anomers of each other. Enzymes are able to distinguish
between these two structures and use one or the other
preferentially. For example glycogen is synthesised
from α-D –glucosepyranose whereas, cellulose is
synthesised from β-D-glucopyranose. The cyclic α and β
anomers of a sugar in solution are in equilibrium with
each other and can be spontaneously interconverted in
a process called mutarotation.
Optical activity
The compounds having asymmetric carbon atoms
can rotate the beam of plane polarized light and
are said to be optically active. An isomer which
can rotate the plane of polarized light to the right
is called as dextrorotatory and is designated as
(d) or (+) Example: D- (d)-glucose or it is also
known as dextrose. While the isomer which
rotates the plane of polarized light to left is
known as levorotatory, and is identified as (l) or
(-). Example: D-(l)-fructose.
A levorotatory (–) substance rotates polarized light to
the left. [E.g., l-glucose; (-)-glucose] A dextrorotatory
(+) substanc rotates polarized light to the right. [E.g., dglucose; (+)-glucose]
Molecules which rotate the plane of of polarized light are
optically active. Most biologically important molecules
are chiral, and hence are optically active. Often, living
systems contain only one of all of the possible
stereochemical forms of a compound. In some cases,
one form of a molecule is beneficial, and the enantiomer
is a poison (e.g., thalidomide).
Polarimetry
monochromator
light source polarizer
sample cell
Glucose cyclic formed by reaction
of CHO with -OH on C5.
Glucose
• Ribose and deoxyribose
Anomers
=>
Mutarotation
Reducing Sugars
• If the oxygen on the anomeric carbon of a sugar is not
attached to any other structure that sugar is a reducing
sugar .A reducing sugar can react with chemical
reagents ( Benedicts solution ) and reducing the
reactive component with the anomeric carbon
becoming oxidized ( Note only oxygen on the anomeric
carbon determines if the sugar is reducing or nonreducing .
• Glucose :
• This monosaccharide is the most important carbohydrate in human
nutrition because it is the one that the body fuses directly to supply
its energy needs. Glucose is formed from the hydrolysis of di- and
polysaccharides, including starch, dextrin, maltose, sucrose and
lactose; from the monosaccharide fructose largely during
absorption; and from both fructose and galactose in the liver
during metabolism.
• Glucose is the carbohydrate found in the bloodstream, and it
provides an immediate source of energy for the body's cells and
tissues. Glucose is also formed when stored body carbohydrate
(glycogen) is broken down for use.
• Fructose :
• Fructose, a monosaccharide, is very similar to another
monosaccharide, galactose. These two simple sugars share the
same chemical formula; however, the arrangements of their
chemical groups along the chemical chain differ. Fructose is the
sweetest of all the sugars and is found in fruits, vegetables and the
nectar of flowers, as well as molasses and honey. In humans,
fructose is produced during the hydrolysis of the disaccharide,
sucrose.
• Galactose
• Galactose differs from the other simple sugars, glucose and
fructose, in that it does not occur free in nature. It is produced in
the body in the digestion of lactose, a disaccharide.
Disaccharides
. The linkage of two monosaccharides to form disaccharides involves
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a glycosidic bond by dehydration . Several physiogically important
disaccharides are sucrose, lactose and maltose.
Sucrose
prevalent in sugar cane and sugar beets, is composed of glucose
and fructose through an a-(1,2)β -glycosidic bond.
Lactose
is found exclusively in the milk of mammals and consists of
galactose and glucose in a β -(1,4) glycosidic bond.
This disaccharide is found only in milk. Human milk contains about
4.8 g per 100 ml and cow's milk contains approximately 6.8 g per
100 ml. When lactose is hydrolyzed it yields one unit of the
monosaccharide glucose and one unit of the monosaccharide
galactose. The enzyme lactase is needed to digest lactose.
• Maltose : This involved C1 and C4 , this special bond is called 1-4
glycosidic bond. Maltose occurs in the body as an intermediate
product of starch digestion. (Starch is a polysaccharide.) When
maltose is hydrolyzed, it yields two molecules of glucose.
Sucrose
=>
Lactose
=>
Maltose
=>
Polysaccharides
• Most of the carbohydrates found in nature occur in the
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form of high molecular weight polymers called
polysaccharides . The building blocks used to generate
polysaccharides can be varied; however, the
predominant monosaccharide found in polysaccharides
is D-glucose. When polysaccharides are composed of a
single monosaccharide building block, they are termed
homopolysaccharides. Polysaccharides composed of
more than one type of monosaccharide are termed
heteropolysaccharides. Many polysaccharides unlike
sugars are insoluble in water. Dietary fiber include
polysacchaides and oligosaccharides that are resistant
to digestion and absorption in the human small
intestine but which are completely or partially
fermented by microorganisms in the large intestine.
• Glycogen :
• Glycogen is the major form of stored carbohydrate in animals. This
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molecule is a homopolymer of glucose in a-(1,4) linkage; it is also highly
branched, with a-(1,6) branch linkages occurring every 8-10 residues.
Glycogen is a very compact. This compactness allows large amounts of
carbon energy to be stored in a small volume. Glycogen is the reserve
carbohydrate in humans. Glycogen is very similar to amylopectin, having a
high molecular weight and branched-chain structures made up of
thousands of glucose molecules. The main difference between glycogen
and amylopectin is that glycogen has more and shorter branches, resulting
in a more compact shape.
Glycogen is stored primarily in the liver and muscles of animals. About
two-thirds of total body glycogen is stored in the muscles and about onethird is stored in the liver.
Starch is the major form of stored carbohydrate in plant cells. Its structure
is identical to glycogen, except for a much lower degree of branching
(about every 20-30 residues). Unbranched starch is called amylose;
branched starch is called amylopectin
• Amylose : Molecules consist of 200- 20,000 glucose units which
form helix as a result of the bond angles between the glucose
units.( α- 1,4 glycosidic linkage).
• Amylopectin : Differs from amylose is being highly branched. Short
side chains of about 30 glucose units are attached with α 1-6
linkage approximately every 20- 30 glucose unit along the chain .
Amylopectin molecules may contain up to 2 million glucose units.
• Dextran : Is a polysaccharides similar to amylopectin but the main
chains are formed by α1-6 glucosidic linkages and the side
branches are attached by α1-3 or α 1-4 linkages. Dextran is an oral
bacterial product that adheres to the teeth , creating a film called
plague. It is used commercially as food additives .
• Cellulose : Is composed of chains of D-glucose unit joined by β 1-4
glycosidic linkages. The chains are linear unbranched .It is a
structural polysaccharides of plant cells. Like starch and glycogen,
cellulose is composed of thousands of glucose molecules. It is the
structural constituent of the cell walls of plants. Cellulose is,
therefore, the most abundant naturally-occurring organic
substance. It is characterized by its insolubility and its physical
rigidity. This polysaccharide can be digested by cows, sheep,
horses, etc., as these animals have bacteria in their rumens
(stomachs) whose enzyme systems break down cellulose
molecules. Humans do not have the enzyme needed to digest
cellulose, so it is passed through the digestive tract unchanged.
Amylose
=>
Amylopectin
Cellulose
=>
• Amino sugars
• Sugar acids
• Sugar alcohol
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Glucosamine, Galactosamine
Ascorbic acid, Glucuronic acid
D-Sorbitol from D-glucose
D- Mannitol from D- Mannose
D-Dulcitol from D- Galactose
• Glycoprotein Component of cell wall and membrane
• Blood group antigens: Specific oligosaccharides bound
to proteins , lipids on membrane surfaces.
• Disease Conditions Related To Carbohydrate Consumption
1. Lactose intolerance
2. Galactosemia
3. Dental caries
4. Diabetes mellitus
5. Hypoglycemia.
Functions of carbohydrates
• 1. Most abundant dietary source of energy
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(4Cal/g)
2. They are precursors for many organic
compounds (fats, amino acids)
3. Carbohydrates (glycoprotein, glycolipids)
participate in the structure of cell membrane and
cellular functions
4. Structural components of many organisms.
These include the fibers (cellulose) of plant,
exoskeleton of some insects and the cell wall of
microorganisms.
5. Serve as the storage form of energy (glycogen)
to meet the immediate energy demands of the
body.
Qualitative Tests for
Carbohydrates
Reducing sugars are usually detected with
Benedict's reagent, which contains Cu2+ ions
in alkaline solution with sodium citrate added to
keep the cupric ions in solution. The alkaline
conditions of this test causes isomeric
transformation of ketoses to aldoses, resulting in
all monosaccharides and most disaccharides
reducing the blue Cu2+ ion to cuprous oxide
(Cu2O), a brick red-orange precipitate. This
solution has been used in clinical laboratories for
testing urine.
Barfoed's solution contains cupric ions in an
acidic medium. The milder condition allows
oxidation of monosaccharides but does not
oxidize disaccharides. If the time of heating is
carefully controlled, disaccharides do not react
while reducing monosaccharides give the
positive result (red Cu2O precipitate). Ketoses do
not isomerize with this reagent. Carbohydrates
are dehydrated in the presence of nonoxidizing
acids to form furfural and hydroxymethylfurfural.
Seliwanoff's reagent contains resorcinol in 6
M hydrochloric acid. Hexoses undergo
dehydration when heated in this reagent to form
hydroxymethylfurfural, that condenses with
resorcinol to give a red product. Ketohexoses
(such as fructose) and disaccharides containing
a ketohexose (such as sucrose) form a cherryred condensation product. Other sugars may
produce yellow to faint pink colors.
Bial's reagent contains orcinol (5-
methylresorcinol) in concentrated HCl
with a small amount of FeCl3 catalyst.
Pentoses are converted to furfural by
this reagent, which form a bluegreen
color with orcinol. This test is used to
distinguish pentoses from hexoses.
Iodine forms a deep blue color in the
presence of starch. Potassium iodide
is added to the reagent solution in
order to make the iodine more
soluble in water. Some forms of
starch may yield a greenish color.
Simple carbohydrates (mono- and
disaccharides) and cellulose do not
cause any change in the orangebrown color of the iodine reagent.
Glucose anhydrous
Appearance. The crystalline powder of white color with sweet taste.
Solubility. Easily soluble in water R, moderately soluble in 96%
alcohol R.
IDENTIFICATION
1.
2.
TLC
Reaction with reagents Feling. 0.1 g of the substance is dissolved in 10 ml of
water R, 3 ml solution of copper tartratic R is added and it is heated; red sediment
is formed:
To the 0,02 g of the substance are added
a few crystals of resorcinol R, 1-2 ml of
dilute hydrochloric acid R and it is heated
till boiling; there appears pink color.
4. To 0,01 g of the substance is added 0.01
g thymol R, 5-6 drops of sulphate acid R
and R 1-2 drops of water R; there appears
dark red color.
3.
TEST ON PURITY
• Irrelevant sugars, soluble starch,
dextrins. 1.0 g of the substance is
dissolved by boiling in 30 ml of alcohol
(90% v / v) R then it is cooled; the
solution must remain transparent.
QUANTITATIVE
DETERMINATION
• State Pharmacopoeia of Ukraine does not provide
quantitative determination of glucose in the
substance.
• Iodometry, the reverse titration
Approximately 0.1 g of substance (exact batch), is
placed in a flask capacity 250 ml, it is dissolved in 10 ml
of water R. It is added 20.0 ml of 0.05 M solution of
iodine, 10.0 ml of 1% solution of sodium hydroxide R
and left for 15 min. Then the solution is acidified by 10
ml dilute acid sulphate R and titrated by 0.1 M solution
of sodium thiosulfate (indicator - starch solution R). In
parallels a control experiment is conducted.
• I2 + 2NaOH → NaI + NaIO + H2O;
• NaIO + NaI + H2SO4 → I2 + Na2SO4 +
H2O;
• I2 + 2Na2S2O3 → 2NaI + Na2S4O6.
• Em = М. м./2
STORAGE
In tightly closed container.
APPLICATION
During various diseases of heart, liver, at
shock treatment, collapse, as a source of
nutrition, which is easily assimilated by
organism and improves the functions of
different organs.
• Tannins can be modified to change their
solubility properties or to eliminate the reactive
phenolic functional groups. The modified tannins
do not retain the characteristic chemical or
biological reactivities of native tannins.
Acetylation
• Puts an acetyl group on each hydroxyl group of the
starting material. Polarity of the tannin is diminished,
and it is insoluble in aqueous solvents. Slowly drip a
mixture of 5 mL pyridine and 5 mL fresh acetic
anhydride into a flask containing 2 g tannic acid. Pour
the solution into water; a solid should form. The solid is
washed with dilute acetic acid (to remove the pyridine)
and then with water. It can be freeze dried. Its IR
spectrum shows loss of the phenolic OH group.
Methylation
• Converts each hydroxyl group to its methyl
ester. Polarity of the tannin is diminished and its
solubility altered. We have not attempted this
procedure. To methylate tannin, mix it with
excess methyl iodide, reagent acetone and solid
potassium carbonate. Reflux the mixture
overnight and purify the product.
Thank you for attention!