THEME: Heterofunctional THEME: Heterofunctional carboxylic acidscarboxylic acids..

LECTURE № 9

associate. prof. Ye. B. Dmukhalska, assistant. I.I. Medvid

OutlineOutline1.1. Physical and chemical properties of oxoacids. Physical and chemical properties of oxoacids.

Acetoacetic ester.Acetoacetic ester.2.2. Physical and chemical properties of halogenacidsPhysical and chemical properties of halogenacids3.3. Physical and chemical properties of hydroxyacids.Physical and chemical properties of hydroxyacids.4.4. Physical and chemical properties of phenolacids.Physical and chemical properties of phenolacids.5.5. Physical and chemical properties of aminoacids.Physical and chemical properties of aminoacids.6.6. Chloranhydrides of Chloranhydrides of carboncarbonicic acid acida) Physical and chemical properties of aa) Physical and chemical properties of a phosgenephosgene7. Amides of carbonic acid7. Amides of carbonic acida)a) Physical and chemical properties of an ureaPhysical and chemical properties of an ureab)b) Physical and chemical properties of a guanidinePhysical and chemical properties of a guanidine8. 8. Sulfoacids: Sulfoacids: aliphatic and aromatic.aliphatic and aromatic.9. Aminoacids. 9. Aminoacids. Peptides.Peptides.

1. Oxoacids1. OxoacidsTo oxoacids include aldehydo- and ketonoacids. To oxoacids include aldehydo- and ketonoacids. These compounds include in the structure of the These compounds include in the structure of the carboxyl group, aldehyde functional group or ketone carboxyl group, aldehyde functional group or ketone functional group.functional group.

γ-ketovaleric acid,4-oxopentanoic acid,levulinic acid

acetoacetic acid,3-oxobutanoic acid,β-ketobutyric acid

oxalacetic acid,oxobutanedioic acid,ketosuccinic acid

glyoxylic acid,oxoethanoic acid

pyroracemic acid,2-oxopropanoic acid

Methods of extraction of oxoacidsMethods of extraction of oxoacids::1.1. Oxidation of hydroxyacids:Oxidation of hydroxyacids:

2.2. Hydrolysis dihalogenocarboxylic acidsHydrolysis dihalogenocarboxylic acids

+ H2OCH2C CH2

O

OH

[O]

OH

CHC CH2

O

OHO

lactic acid pyroracemic acidlactic acid pyroracemic acid

2,2-dichlorpropanoic acid pyroracemic acid (pyruvic acid) 2,2-dichlorpropanoic acid pyroracemic acid (pyruvic acid)

Chemical properties of oxoacidsChemical properties of oxoacids1.1. Decarboxylation of Decarboxylation of αα-oxoacids-oxoacids

2.2. Decarboxylation of Decarboxylation of ββ-oxoacids-oxoacids

CH3 C

O

COOHconc. H2SO4, t

CH3 C + CO2

O

Hpyroracemic acid acetaldehyd

CH3 C

O

t

acetoacetic acid

CH2 COOH CH3 C CH3

Oacetone

- CO2

Acetoacetic esterAcetoacetic ester

Acetoacetic ester synthesisAcetoacetic ester synthesis is a chemical reaction where is a chemical reaction where ethylacetate is alkylated at the α-carbon to both carbonyl ethylacetate is alkylated at the α-carbon to both carbonyl groups and then converted into a ketone, or more groups and then converted into a ketone, or more specifically an α-substituted acetone.specifically an α-substituted acetone.

Acetoacetic ester Acetoacetic ester is a is a tautomeric substance. He tautomeric substance. He characterized keto-enol tautomery. characterized keto-enol tautomery.

CH3 C

O

OC2H5

ethylacetat

C2H5O-

Na+

CH3 C

O

CH2 COOC2H5

+ C2H5OH

acetoacetic aster

2

H3C-C-CH2-C

O

O

OC2H5

H3C-C=CH -C

OH

O

OC2H5

Acetoacetic ester ketone form ( 92,5% )

Acetoacetic ester enol form ( 7,5% )

Chemical properties of acetoacetic ester:Chemical properties of acetoacetic ester:1.1. Reactions of ketone form:Reactions of ketone form:

2. Reactions to enol form:2. Reactions to enol form:a)a) interaction of “acetoacetic ester” with metallic interaction of “acetoacetic ester” with metallic

sodiumsodium

b)b) interaction of “acetoacetic ester” with NaOHinteraction of “acetoacetic ester” with NaOH

c) interaction “acetoacetic ester” with PCLc) interaction “acetoacetic ester” with PCL55

H3C-C=CH-C + 2Na

OH

O

OC2H5

H3C-C=CH -C

ONa

O

OC2H5

+H22 2

H3C-C=CH-C + NaOH

OH

O

OC2H5

H3C-C=CH -C

ONa

O

OC2H5

+H2O

Sodiumacetoacetic ester

ethyl-3-chlorbutene-2-oate

d) interaction of “acetoacetic ester” with bromine water.

The discoloration of bromine water, that explained unsaturated of "acetoacetic ester”.

e) interaction of “acetoacetic ester” with FeCl FeCl33

H3C-C-CH-C + Br2

OH

O

OC2H5

H3C-C- CH -C

OH

O

OC2H5

Br

Br-HBr

H3C-C-CH -C

O Br

O

OC2H5

Bromacetoacetic ester

H3C-C=CH-C

OH

O

OC2H5

H3C-C=CH -C

O-Fe

O

OC2H5

Fe3+

violetcolour

The characteristic feature of The characteristic feature of “acetoacetic ester” is is the ability to the ability to ketone decompositionketone decomposition and acid and acid decompositiondecomposition . .

Ketone decompositionKetone decomposition occurs when heated in the occurs when heated in the presence of the dilute solutions of acids or alkalis.presence of the dilute solutions of acids or alkalis.

Acid Acid decomposition of decomposition of “acetoacetic ester”

H3C-C-CH2 -CO

OC2H5

H2O; t, H+

+ C2H5OH

O

+ CO2H3C-C-CH3

O

CH3 C

O

CH2 COOC2H5

NaOH (conc.)CH3COONa + C2H5OH2

An “acetoacetic ester” used in the organic synthesis for the extraction used in the organic synthesis for the extraction of difference ketones and carboxylic acids.of difference ketones and carboxylic acids.

CH3 C

O

CH2 COOC2H5

C2H5O-Na+

CH3 C

O

CH COOC2H5

-

CH3 C

O

CH COOC2H5

- Na+

CH3I

- NaI

CH3 C

O

CH

CH3

COOC2H5

sodium acetoacetic ester

methylacetoacetic ester

acid decomposition

ketone decomposition

NaOH (conc.)

H or OH (H2O)-+

CH3 C

O

CH2 CH3 + C2H5OH + CO2

butanon

CH3COONasodium acetate

+ CH3 CH2 COONa + C2H5OH

sodium propionate

2. Halogenoacids2. HalogenoacidsHalogenoacidsHalogenoacids are the derivatives of carboxyl acids are the derivatives of carboxyl acids

that contain halogen radical (1 or more).that contain halogen radical (1 or more).

α-bromopropanoic acidα-bromopropanoic acid

2-bromopropanoic acid2-bromopropanoic acid

H3C CH C

Br

O

OH

3 2 1

2-bromo-3-methylbutanoic acid,α - bromoisovaleric acid

Cl

COOH

o-chlorobenzoic acid2-chlorobenzoic acid

Methods of extraction of hMethods of extraction of halogenalogenoocarboxylic acidcarboxylic acid ::

1.1. Halogenation of saturated carboxylic acids:Halogenation of saturated carboxylic acids:

2.2. Hydrohalogenation of unsaturated carboxylic acidsHydrohalogenation of unsaturated carboxylic acids

3.3. Halogenation of aromatic carboxylic acids:Halogenation of aromatic carboxylic acids:

H3C CH2 CO

OHCl2

PH3C CH C

Cl

O

OHHCl+ +

H2C CH2 CO

OHH2C CH C

O

OH+ HCl

Clacrylic acid acrylic acid ββ-chloropropanoic acid-chloropropanoic acid

CO

OH

Cl2AlCl3

CO

OH

Cl

HCl+ +

m-chlorobenzoic acidm-chlorobenzoic acid

I. Carboxyl group can react with formation of:I. Carboxyl group can react with formation of:

a)a) SaltsSalts

H2C CH2 CO

OHCl

NaOH H2C CH2 CO

ONaCl

H2O+ +

2 H2C CH2 CO

OHCl

2 Na 2 H2C CH2 CO

ONaCl

H2+ +

2 H2C CH2 CO

OHCl

MgO

H2C CH2 CO

OMg

O

CO

H2C CH2

Cl

Cl

H2O+ +

H2C CH2 CO

OHCl

NaHCO3 H2C CH2 CO

ONaCl

H2CO3

H2O CO2

++

chloroacetate sodiumchloroacetate sodium

b) complex ethers:b) complex ethers:

c) amides:c) amides:

H2C CH2 CO

OH++

Cl

H2OHO CH3 H2C CH2 CO

OCl

CH3

methyl ether of methyl ether of ββ-chloropropanoic acid-chloropropanoic acid

H2C CH2 CO

OH+NH3+

Cl

H2C CH2 CO

NH2Cl

H2Ot=200o

amide amide ββ-chloropropanoic acid-chloropropanoic acid

II. Halogen radical can react with:II. Halogen radical can react with:a)a) ammonium:ammonium:

b) b) NaOH (water solution):NaOH (water solution): 1) for α-halogenoacids1) for α-halogenoacids

H2C CH2 CO

OHCl

2NH3 H2C CH2 CO

ONH2

NH4++ + HCl

ammonium salt of ammonium salt of ββ-aminopropanoic acid-aminopropanoic acid

CH3C CH

O

OHCl

NaOHH2O

CH3C CH

O

OHOH

NaCl+ +

lactic acid

2) for β-halogenoacids2) for β-halogenoacids

3) for γ,σ-halogenoacids3) for γ,σ-halogenoacids

CH2C CH2

Cl

O

OHNaOH

H2O

-NaClCH2C CH

OH

O

OHH

H2C CH CO

OH+

to

ββ-chloropropanoic acid -chloropropanoic acid ββ-hydroxypropanoic acid acrylic acid-hydroxypropanoic acid acrylic acid

CH2 CO

OHH2C CH2

Cl

NaOHH2O

-NaCl

CH2

CH2C

CH2

OO

+

γγ-butyrolactone-butyrolactone

Representatives of hRepresentatives of halogenalogenoocarboxylic acid carboxylic acid ::

Monochloroacetic acid Dichloroacetic acid Trichloroacetic acid

CCH2

O

OHCl

CCH

O

OHCl

ClCC

O

OHCl

Cl

Cl

These acids are used in organic synthesis

Ureide of α-bromoisovaleric acid (bromisoval) used in medical practice as a hypnotic.

CH3 CH

CH3

CHBr

O

NH

O

C NH2

C

3. 3. HydroxyacidsHydroxyacids HydroxyacidsHydroxyacids are the derivatives of carboxyl acids that are the derivatives of carboxyl acids that

contain –OH group (1 or more).contain –OH group (1 or more).

3 2 1CH3C CH

O

OHOH

β α

2-hydroxypropanoic acidα-hydroxypropanoic acid

tartaric acidα,α’-dihydroxysuccinic acid,2,3-dihydroxybutandioic acid,

lactic acid,α- hydroxypropanoic acid,2- hydroxypropanoic acid

malic acid,hydroxysuccinic acidhydroxybutanedioic acid

citric acid,2-hydroxy-1,2,3-propantricarboxylic acid

glycolic acid,hydroxyacetic acid,hydroxyethanoic acid

In a row of hydroxyacids often found the optical In a row of hydroxyacids often found the optical isomery.isomery.

D-, or (R,R)-tartaric acid

L-, or (S,S)-tartaric acid

mezo-, or (R,S)-tartaric acid

Methods of peparetion of hydroxyacids:Methods of peparetion of hydroxyacids:1.1. Hydrolysis of α-halogenoacidsHydrolysis of α-halogenoacids

2.2. Oxidations of diols and hydroxyaldehydesOxidations of diols and hydroxyaldehydes

3.3. Hydration of α,β-unsaturated carboxylic acidsHydration of α,β-unsaturated carboxylic acids

4.4. Hydrolysis of hydroxynitriles (cyanohydrins)Hydrolysis of hydroxynitriles (cyanohydrins)

CH3C CH

O

OHCl

NaOHH2O CH3C CH

O

OHOH

NaCl+ +

lactic acidlactic acid

CH3C CH

O

HOH

CH2H3C CH

OHOH

CH3C CH

O

OHOH

[O] [O]

CH CO

OHH2O+CH2 CH2C CH2

O

OH

H+

OH

ββ-hydroxypropanoic acid-hydroxypropanoic acid

Physical and chemical properties of Physical and chemical properties of

hydroxyhydroxycarboxylic acidcarboxylic acid For For physical propertiesphysical properties of hydroxycarboxylic acids are of hydroxycarboxylic acids are

colorless liquids or crystalline substance, soluble in water.colorless liquids or crystalline substance, soluble in water.

Chemical properties:Chemical properties: in the molecule of hydroxyacids ether – in the molecule of hydroxyacids ether –OH group or carboxyl group can react.OH group or carboxyl group can react.

Carboxyl group can react forming:Carboxyl group can react forming:

a) salts:a) salts:

H2C CH2 CO

OHOH

NaOH H2C CH2 CO

ONaOH

H2O+ +

sodium sodium ββ-hydroxypropanoic acid-hydroxypropanoic acid

2 H2C CH2 CO

OHOH

2 Na 2 H2C CH2 CO

ONaOH

H2+ +

b) complex ethers:b) complex ethers:

2 H2C CH2 CO

OHOH

MgO

H2C CH2 CO

OMg

O

CO

H2C CH2

OH

OH

H2O+ +

H2C CH2 CO

OHOH

NaHCO3 H2C CH2 CO

ONaOH

H2CO3

H2O CO2

++

H2C CH2 CO

OH++

OH

H2OHO CH3 H2C CH2 CO

OOH

CH3

methyl ether of methyl ether of ββ-hydroxypropanoic acid-hydroxypropanoic acid

c) amides:c) amides:

II. –OH group can react with:II. –OH group can react with:

a)a) hydrohalogens (HCl, HBr, HI, HF)hydrohalogens (HCl, HBr, HI, HF)

b) can oxidizeb) can oxidize

H2C CH2 CO

OH+NH3+

OH

H2C CH2 CO

NH2OH

H2Ot=200o

amide of amide of ββ-hydroxypropanoic acid-hydroxypropanoic acid

HCl ++ H2OH2C CH2 CO

OHCl

CH2C CH2

O

OHOH

+ H2OCH2C CH2

O

OH

[O]

OH

CHC CH2

O

OHO

ββ-oxopropanoic acid-oxopropanoic acid

lactic acid lactide

3-hydroxybutanoic acid

butene-2-onic (crotonic) acid

Related to heat of:

1. α-hydroxyacids

2. β-hydroxyacids

heating

3. γ-hydroxyacids

γ-butyrolacton 4-hydroxybutanic acid

heating

H

O

C

O H

C H 3

O

C

H

+

O

O H

CС H 3 С

O H

H

H 2S O 4к .

t

HCOOH CO + H2Oк. Н2SO4, t

Ñ ÑH2COOHHOOCH2C

OH

COOH

H CO

OHC CH2COOH

O

HOOCH2C

C CH3CH3

O

ê. H2SO4 +

CO H2O 2 CO2

t acetidicarbonic acid

Decomposition of α-hydroxyacids

acetic acid formic acid

Phenolacids.Phenolacids.

o-hydroxycinnamic acid salicylic acid,2-hydroxybenzoic acid

4-hydroxybenzoic acid

3,4,5-trihydroxybenzoic acid,gallic acid

PhenolacidsPhenolacids are the derivatives of aromatic carboxyl acids that are the derivatives of aromatic carboxyl acids that contain –OH group (1 or more).contain –OH group (1 or more).

Methods of phenolacids extraction:Methods of phenolacids extraction:

1.1. Carboxylation of Carboxylation of phenolsphenols by by carbon oxidecarbon oxide (IV): (IV): In the Kolbe synthesis, also known as the Kolbe–Schmitt reaction, In the Kolbe synthesis, also known as the Kolbe–Schmitt reaction,

sodium phenoxide is heated with carbon dioxide under pressure, and sodium phenoxide is heated with carbon dioxide under pressure, and

the reaction mixture is subsequently acidified to yield salicylic acidthe reaction mixture is subsequently acidified to yield salicylic acid::

2. Hydroxylation of arenecarboxylic acids2. Hydroxylation of arenecarboxylic acids

C

O

O-Na+ Cu(OH)2

- NaOH

CO

Cu

OH

O

t

- Cu

COOH

OH

KCOOH

SO3H

+ KOHalloying +

COO

K2SO3 + H2O

OH

- +

3 2

3. Alloying of sulphobenzoic acid with alkalis3. Alloying of sulphobenzoic acid with alkalis

m-sulphobenzoic acid potassium salt of m-sulphobenzoic acid potassium salt of 3-hydroxybenzoic acid3-hydroxybenzoic acid

COOH

OH OH

COONa+ CO2+ NaHCO3 + H2O

salicylic acid

Chemical properties of phenoloacids: Chemical properties of phenoloacids: Chemical properties of Chemical properties of phenoloacids due to the presence phenoloacids due to the presence

in their structure of carboxyl group, phenolic hydroxyl and the in their structure of carboxyl group, phenolic hydroxyl and the aromatic nucleus.aromatic nucleus.

DecarboxylationDecarboxylation

COOH

OH

COOH

OH

Br

Br+ Br22 + HBr2

3, 5-dibromsalicylic acidwhite precipitate

1

23

4

5

6

Br

OH

Br

BrCOOH

OH

Br

Br+ Br2 + HBr + CO2

yellow precipitate

OH

COOH

NaHCO3

-CO2, -H2O

OH

COONa POCl3, C 6H5ONa

-NaCl, -NaPO3

OH

OC 6H5

O

CH3OH

(H2SO4)-H2O

OH

COOCH3NH3

OH

NH2

O

(CH3CO)2O

- CH3COOH

O

COOH

CH3

O

NH2

OH

-C 6H5OH

OHO

NH

OH

Salicylic acid

Sodium salicylate

C

Phenylsalicylate, salol

Methylsalicylate

C

Salicylamide

C

Acetylsalicylic acid,aspirin

C

Oxaphenamide

The best known aryl ester is O-acetylsalicylic acid, better The best known aryl ester is O-acetylsalicylic acid, better known as aspirin. It is prepared by acetylation of the phenolic known as aspirin. It is prepared by acetylation of the phenolic hydroxyl group of salicylic acid:hydroxyl group of salicylic acid:

5. Aminoacids5. Aminoacids An An aminoacidaminoacid is an organic compound that is an organic compound that

contains both a amino (–NНcontains both a amino (–NН22) group and a ) group and a

carboxyl (-СООН) group. The amino acids carboxyl (-СООН) group. The amino acids found in proteins are always α-amino acids.found in proteins are always α-amino acids.

Methods of aminoacids extraction:Methods of aminoacids extraction:

1.1. Effects of ammonia on halogencarboxylic acids :Effects of ammonia on halogencarboxylic acids :

2.2. Effects of ammonia and HCN on aldehydesEffects of ammonia and HCN on aldehydes

CH3 CH

Cl

COOH + NH3CH3 CH

NH2

COOH + NH4Cl2

CH3 CH

NH2

C N

H2O; H+

- NH3

CH3 CH COOH

NH2

2CH3 C

H

NHHCN

CH3 C

O

H

NH3

- H2O

αα-chlorpropanoic acid -chlorpropanoic acid αα-aminopropanoic acid-aminopropanoic acid

acetalaldehydeacetalaldehyde aldiminealdimineαα-aminopropanonitrile-aminopropanonitrile

αα-aminopropanoic acid-aminopropanoic acid

[ H ]

- H2O

COOH

NO2

COOH

NH2

CH2 CH COOH + : NH3 CH2

NH2

CH2 COOH

3. Accession of ammonia to the α, β–unsatured acids

acrylic acid

β-aminopropanoic acid

4. Reduce of nitrobenzoic acid

n-nitrobenzoic acid n-aminobenzoic acid

Optical propertiesOptical properties

Physical and chemical properties of aminoacidsPhysical and chemical properties of aminoacids

Both an acidic group (-СООН) and а basic group (-NНBoth an acidic group (-СООН) and а basic group (-NН22) are ) are

present on the same carbon in an α-amino acid.present on the same carbon in an α-amino acid.

The net result is that in neutral solution, amino acid molecules The net result is that in neutral solution, amino acid molecules have the structure:have the structure:

А А zwitter-ion zwitter-ion is а molecule that has а positive charge on one is а molecule that has а positive charge on one atom and а negative charge on another atom. atom and а negative charge on another atom.

Reactions on amino-group:Reactions on amino-group:

R CH COOH

NH2

HClR CH COOH

NH3Cl+ -

chlorhydrolic salt

RIR CH COOH

NHR- HI

N-alkilderivate

R CH COOH

NHCOR

RCOCl

- HCl

N-acylderivate

HNO2

-N2, - H2O

R CH COOH

OH

hydroxyacid

Reactions on carboxylic group:Reactions on carboxylic group:

R CH COOH

NH2

NaOHR CH COONa

NH2

sodium salt

ROH, HR CH COOR

NH2

- H2O

ester

R CH CONHR

NH2

RNH2

- H2O

amide

PCl5

- POCl3, - HCl

R CH COCl

NH2

chloranhydrid

- H2O

+

Heating of: Heating of:

1.1. αα-aminoacids-aminoacids

2.2. ββ-aminoacids-aminoacids

CH COOH

NH2

CH3

tN

C CH

CH

N

CO

O

H

H

CH3

CH3

+ H2O2

2

CH COOHCHCH3 + NH3CH2COOHCH

tCH3

NH2

αα-aminopropanoic acid-aminopropanoic acid

3,6-dimethyl-2,5-diketopiperazine3,6-dimethyl-2,5-diketopiperazine

ββ-aminooil acid crotonic acid-aminooil acid crotonic acid

N O + H2OCH2COOHCH2

tCH2

NH2H

3. 3. γγ-aminoacids-aminoacids

γγ-aminooil acid -aminooil acid γγ-lactam -lactam

React React αα-aminoacids with ninhydrin-aminoacids with ninhydrin

OH

OH

O

O

+ H3N-CH-COO-

R

+

O

O

N-CH-COOH+H2O

R

Ninhydrin

O

O

N-CH-C

R

H

O

O

N=C-C

R

H2OH

NH2

O

O

2-aminoindandion

O

OHO

OH

H

H2N

O

O

OH

OH

O

O

+

O

O

N

H

O

O

O

O

N

O

O

H+

Âlue - violet dye-stuff

HO C

Omonoethyl ester of carbonic acid, monoethyl carbonate

OC2H5

C

Odiethyl ester of carbonic acid, diethyl carbonate

OC2H5C2H5O

OHCl C

Omonochoranhydride carbonic acid ,chlorcarbonic acid

Cl C

Odichoranhydride carbonic acid , phosgene

Cl

HO C

Omonoamide carbonic acid,carbamic acid

NH2 C

Odiamide carbonic acid, carbamide, urea

NH2H2N

C

O ethyl ester of chlorcarbonic acid

OC2H5Cl C

Oethyl ester of carbamic acid, urethane

C2H5O NH2

Functional dFunctional derivates of carbonerivates of carbonicic acid. acid.

Cl C

Odichoranhydride carbonic acid , phosgene

ClCO + Cl2

hv

6. Chloranhydrides of 6. Chloranhydrides of carboncarbonicic acid acid

OHCl C

Omonochoranhydride carbonic acid ,chlorcarbonic acid

Cl C

Odichoranhydride carbonic acid , phosgene

Cl

Produces phosgene by interaction of carbon oxide (II) Produces phosgene by interaction of carbon oxide (II) with chlorine on the light.with chlorine on the light.

HO C

Omonoamide carbonic acid,carbamic acid

NH2

+ NH3 + HClC

O

methyl ester of carbamic acid

H2N OCH3C

O

methyl ester of chlorcarbonic acid

OCH3Cl

C

Odiethyl ester of carbonic acid, diethyl carbonate

OC2H5C2H5O C

Oethyl ester of carbamic acid, urethane

C2H5O NH2+ NH3+ C2H5OH

7. Amides of carbonic acidC

Odiamide carbonic acid, carbamide, urea

NH2H2N

Esters of carbamic acid are named urethanes

CH2

H2N C

O

O CH2 C

CH3

CH2 CH3

CH2 O C

O

NH2

meprothan (meprobamate),dicarbamate 2-methyl-2-propylpropandiol-1,3

Meprothan used in a medicine as a medicament, which has tranquilization and hypnotic effects.

C

Odiamide carbonic acid, carbamide, urea

NH2H2NNH3 + CO2

p, t + H2O2

Urea or carbamide is an organic compound with the chemical formula (NH2)2CO. The molecule has two amine (-NH2) residues joined by a carbonyl (-CO-) functional group. Urea was first discovered from urine in 1773 by the French chemist Hilaire Rouelle.In 1828, the German chemist Friedrich Wöhler obtained urea by treating of silver isocyanate with ammonium chloride in a failed attempt to prepare ammonium cyanate:

AgNCO + NH4Cl → (NH2)2CO + AgCl

In the industry urea produces by interaction of an ammonia with carbon oxide (IV)

C

O

urea

NH2H2N + HNO3 C

nitrate urea

NH2H2N

OH

+NO3

-

C

O

urea

NH2H2N + H2O NH3

+H or OH

-

CO2 + 2

Physical and chemical properties of ureaPhysical and chemical properties of ureaThe urea molecule is planar. Each carbonyl oxygen atom accepts four N-H-O hydrogen The urea molecule is planar. Each carbonyl oxygen atom accepts four N-H-O hydrogen bonds. This dense and energetically favourable hydrogen-bond network is probably bonds. This dense and energetically favourable hydrogen-bond network is probably established at the cost of efficient molecular packingestablished at the cost of efficient molecular packing.. The structure is quite open, the The structure is quite open, the ribbons forming tunnels with square cross-section. The carbon in urea is described as ribbons forming tunnels with square cross-section. The carbon in urea is described as spsp²² hybridized, the C-N bonds have significant double bond character, and the carbonyl hybridized, the C-N bonds have significant double bond character, and the carbonyl oxygen is basic compared to formaldehyde. Its high solubility is due to extensive oxygen is basic compared to formaldehyde. Its high solubility is due to extensive hydrogen bonding with water: up to eight hydrogen bonds may form - two from the hydrogen bonding with water: up to eight hydrogen bonds may form - two from the oxygen atom, one from each hydrogen atom and one from each nitrogen atom.oxygen atom, one from each hydrogen atom and one from each nitrogen atom.

1. 1. Interaction of an urea with strong acidsInteraction of an urea with strong acids

2. 2. Hydrolysis of an urea during the heatingHydrolysis of an urea during the heating

C

O

urea

NH2H2N + +C2H5I C2H5NH C

O

NH2 HI

ethylurea

C

O

urea

NH2H2N + +CH3 C NH C

O

NH2 HCl

acetylurea

C

O

Cl O

CH3

44. . Interaction of an urea with halogen anhydrides of carboxylic Interaction of an urea with halogen anhydrides of carboxylic acids (acylation)acids (acylation)

3. 3. Interaction of an urea with halogen alkanes (alkylation)Interaction of an urea with halogen alkanes (alkylation)

Dicarboxylic acids can form with an urea cycle ureides. For example,barbituric acid or malonylurea or 6-hydroxyuracil is an organic compound based on a pyrimidine heterocyclic skeleton. It is an odorless powder soluble in hot water. Barbituric acid is the parent compound of barbiturate medicine, although barbituric acid itself is not pharmacologically active.

C

O

urea

NH2H2N + +HNO2 CO2 N2 + H2O2 2 3

C

O

urea

NH2H2N + +NaOBr CO2 N2 + H2O3 2 + NaBr3

55. . Interaction of an urea with HNOInteraction of an urea with HNO22

66. . Interaction of an urea with water solution of Interaction of an urea with water solution of hypobromides. Thishypobromides. This reaction as the previous can be used toreaction as the previous can be used to quantitative determination of an ureaquantitative determination of an urea..

5. 5. Biuret reaction. Used for qualitative determination of an urea Biuret reaction. Used for qualitative determination of an urea and proteins, as containing in its structure of a groupand proteins, as containing in its structure of a group–С–СO-NH-.O-NH-.

COH2N

H2N +

+NH2

C O

NH2+

H2N C NH2

O

3NH3 +C

N

NO C O

H

N HH

C

O

isocyanuric acid

C

N

NO C OH

N

H

H

C

Ocyanuric acid

By-product of a biuret reaction is the isocyanuric acid, which By-product of a biuret reaction is the isocyanuric acid, which forms as a result of trimerazation of cyanuric acidforms as a result of trimerazation of cyanuric acid..

C

guanidine

NH2H2N + HCl C

guanidinium chloride

NH2H2N+

Cl-

NH NH2

C

guanidine

NH2H2N

NH

C

guanidine

NH2H2N

NH+

C2H5O C

O

CH2

C

O

C2H5O

H2SO4; POCl3; H2

H2N

N

N

2-aminopyrimidine

Physical and chemical properties of a guanidinePhysical and chemical properties of a guanidine

1. 1. Interaction a guanidine with acidsInteraction a guanidine with acids

2. 2. Interaction a guanidine with bifunctional compoundsInteraction a guanidine with bifunctional compounds(diesters, diketones)(diesters, diketones)

Arginine Arginine plays an important plays an important role in cell division, the healing of role in cell division, the healing of

wounds, removing ammonia wounds, removing ammonia from the from the body,body, immune function, and immune function, and ththee release release of hormonesof hormones..

The remain of guanidine is the structural components of The remain of guanidine is the structural components of many compounds. For example:many compounds. For example:

Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA.

SulfoacidsSulfoacids called the derivatives of organic called the derivatives of organic compounds in which an atom of hydrogen compounds in which an atom of hydrogen replaced by the residue of sulfuric acid – replaced by the residue of sulfuric acid – sulfogroup sulfogroup – – SOSO33H.H.

Aliphatic sulfoacidsAliphatic sulfoacids

ССHH33-SO-SO22OHOH С СHH33--ССHH22-SO-SO22OHOH methanesulfonic acid ethanesulfonicmethanesulfonic acid ethanesulfonic acid acid

((methanesulfoacidmethanesulfoacid)) ((ethanesulfoacidethanesulfoacid))

Functional derivatives of sulfoacidsFunctional derivatives of sulfoacids

CHCH33-SO-SO22Cl - choranhydride of methanesulfoacid (methane Cl - choranhydride of methanesulfoacid (methane sulfonylchloride) sulfonylchloride)

CHCH33-SO-SO22ONa – sodium salt of methanesulfoacid ONa – sodium salt of methanesulfoacid (methanesulfate sodium) (methanesulfate sodium)

CHCH33-SO-SO22NHNH22 – amide of methanesulfoacid – amide of methanesulfoacid (methanesulfonamide) (methanesulfonamide)

CHCH33-SO-SO22-OC-OC22HH55 – ethyl ester of methanesulfoacid – ethyl ester of methanesulfoacid (ethylmetanesulfonate) (ethylmetanesulfonate)

EExtractionxtraction of aliphatic sulfoacids : of aliphatic sulfoacids :

1.1. Sulfochlorination:Sulfochlorination:

2.2. Sulfooxidation:Sulfooxidation:

2R-H + 2SO2R-H + 2SO22 + O + O22 = 2R-SO = 2R-SO22OHOH

alkanesulfonic acidalkanesulfonic acid

3. Oxidation of thiols:3. Oxidation of thiols:

CH3 CH3 + SO2 + Cl2hv

CH3 CH2 SO2Cl + HCl

ethanesulfonylchloride

C2H5SH

KMnO4 or HNO3C2H5 SO2 + H2O

ethanethiol ethanesulfoacid

4. Sulfonation of alkanes by conc. H4. Sulfonation of alkanes by conc. H22SOSO4 4 ::

5. 5. AAccessionccession of hydrosulfites to alkenes: of hydrosulfites to alkenes:

CH

CH3

CH3

H3C + SO3

H2SO4C

CH3

CH3

H3C SO2OH

isobutane2-methyl-2-propanesulfoacid

R CH CH2 + NaHSO3

R OORR CH2 CH2

SO2ONa

alkanesulfonate sodium

Chemical properties of aliphatic sulfoacidsChemical properties of aliphatic sulfoacids1. Formation salts of sulfoacids:1. Formation salts of sulfoacids:

CC22HH55-SO-SO22-OH + NaOH = C-OH + NaOH = C22HH55-SO-SO22-ONa + H-ONa + H22OO

2 C2 C22HH55-SO-SO22-OH + 2 Na = 2 C-OH + 2 Na = 2 C22HH55-SO-SO22-ONa + H-ONa + H22

2. Formation of sulfonylchlorides2. Formation of sulfonylchlorides

R-SOR-SO22-OH + PCl-OH + PCl55 = R-SO = R-SO22Cl + POClCl + POCl33 + HCl + HCl

3. Formation of sulfonamides3. Formation of sulfonamides

R-SOR-SO22-Cl + 2 NH-Cl + 2 NH33 = R-SO = R-SO22-NH-NH22 + NH + NH44ClCl

4. Formation esters of sulfoacids4. Formation esters of sulfoacids

R-SOR-SO22-Cl + 2 NaO-R-Cl + 2 NaO-R′′ = R-SO = R-SO22-O-R-O-R′′ + NaCl + NaCl

C2H5 SO2OH + Ca

C2H5 SO2O

C2H5 SO2 OCa + H22

Aromatic sulfoacidsAromatic sulfoacids

SO3H

benzol sulfoacid

SO3H

p-toluol sulfoacid

CH3

SO3H

m-benzoldisulfoacid

SO3H

SO3H

1,3,5-benzoltrisulfoacid

SO3HH3OS

OH

SO3H

H2SO4

OH

H2SO4

OH

HO3St=-20 t=+100

o-hydroxybenzylsulphoacid p-hydroxybenzylsulphoacid

EExtractionxtraction of aromaric sulfoacids: of aromaric sulfoacids:

H2SO4

SO3H

H2O+ +

1. Sulfonation of aromatic ring1. Sulfonation of aromatic ring

CH3

+ H2SO4

25 C

+

CH3 CH3

SO2OH

SO2OH

p-toluol sulfoacid 65%

p-toluol sulfoacid 32%

+ H2O2 2 2

SO3H

+ SO3

210 C

H2SO4

SO3, 275C

Hg

SO3H

SO3H SO3HSO3H

SO3H

Chemical properties of aromatic sulfoacidsChemical properties of aromatic sulfoacids

I.I. Reactions of the sulfogroup:Reactions of the sulfogroup:a) formation salts of sulfoacids:a) formation salts of sulfoacids:

CC66HH55SOSO22OH + NaOH = COH + NaOH = C66HH55SOSO22Na + HNa + H22OO

b) formation of sulfonylchlorides:b) formation of sulfonylchlorides:

CC66HH55SOSO22OH + PClOH + PCl55 = C = C66HH55-SO-SO22-Cl + POCl-Cl + POCl33 + HCl + HCl

CC66HH55 + 2 HO-SO + 2 HO-SO22Cl = CCl = C66HH55-SO-SO22Cl + HCl + H22SOSO44 + HCl + HCl

c) formation of sulfonamides:c) formation of sulfonamides:

CC66HH55SOSO22Cl + 2 NHCl + 2 NH33 = C = C66HH55-SO-SO22-NH-NH22 + NH + NH44ClCl

d) formation esters:d) formation esters:

CC66HH55SOSO22Cl + HO-CCl + HO-C22HH55 = C = C66HH55-SO-SO22-O-C-O-C22HH55 + HCl + HCl

e) reduced of the sulfogroup:e) reduced of the sulfogroup:

C6H5 SO2OH6 H

Zn+ H2SO4

C6H5 SH + 3 H2O

f) sf) synthesisynthesis of saccharin of saccharin

O

CH3

+ HOSO2ClCH3

SO2Cl

-

CH3

SO2Cl -NH4Cl

+ 2 NH3

CH3

SO2NH2

KMnO4

SO2NH2

COOH t

- H2O

o-toluolsulfonamide o-toluolsulfonamide of benzoic acid

o-toluolsulfonimide of benzoic acid

SO2

CN H

+ NaOH, H2O

SO2

C

O

N Na * 2 H20

saccharin

2

II. Reactions of SII. Reactions of SEE, S, SNN of sulfo-group: of sulfo-group:

C6H5 SO2OH C6H6 + H2SO4

t

HCl+ H2O

C6H5 SO2OH + NaOH C6H5SO2ONa + H2O

C6H5 SO2ONa+ NaOH C6H5ONa + H2O2 Na2SO4 +t

C6H5 ONa + H2CO4C6H5OH + NaHCO3

H+

C6H5 SO2ONa + NaCN C6H5CN + Na2SO3t, Sn

b) a reaction of alkali floatingb) a reaction of alkali floating

a) desulfonationa) desulfonation

Sulphanylamidic preparations. All sulphanylamidic Sulphanylamidic preparations. All sulphanylamidic

medicines contain the next fragment:medicines contain the next fragment:

Albucyde (sulphacyl)Albucyde (sulphacyl) – is an antibacterial mean, is a part of – is an antibacterial mean, is a part of eye-drops.eye-drops.

UrosulphaneUrosulphane – is an antibacterial mean by infection of urinal – is an antibacterial mean by infection of urinal canals.canals.

NorsulphazolNorsulphazol – is used by pneumonia, meningitis, – is used by pneumonia, meningitis, staphylococcal and streptococcal sepsis, infectious diseases.staphylococcal and streptococcal sepsis, infectious diseases.

BucarbaneBucarbane – is a hypoglycemic mean. – is a hypoglycemic mean.

NH2

O2SNH

CH3

O

NH2

O2SNH

NH2

O

S

N

NH2

O2SNH

NH2

O2SNH

NH

C4H9

O

C

Альбуцил,сульфацил

C

Уросульфан Норсульфазол

C

БукарбанAlbucyde Urosulphane Norsulphazol Bucarbane(sulphacyl)

According to the chemical origin of the residue According to the chemical origin of the residue connected with connected with αα-aminoacid fragment – -aminoacid fragment – CH(NH2)COOH, CH(NH2)COOH, αα-aminoacids divided on aliphatic, -aminoacids divided on aliphatic, aromatic and heterocyclic. aromatic and heterocyclic.

In heterocyclic In heterocyclic αα-aminoacids proline and oxyproline -aminoacids proline and oxyproline αα--aminoacid’s fragment presents in hetecyclic structure. aminoacid’s fragment presents in hetecyclic structure.

According to the quantity of –NH2 and –COOH groups in According to the quantity of –NH2 and –COOH groups in molecule molecule αα-aminoacids-aminoacids divided on monoaminocarbonic, divided on monoaminocarbonic, monoaminodicarbonic and diaminomonocarbonic.monoaminodicarbonic and diaminomonocarbonic.

5). Chemical properties of 5). Chemical properties of αα--aminoacidsaminoacidsA.A. Reaction on amino-groupReaction on amino-group

1) Formation of N-acylderivatives. This reaction use for blocking 1) Formation of N-acylderivatives. This reaction use for blocking (protection) of aminogroup at the synthesis of peptides. As (protection) of aminogroup at the synthesis of peptides. As acylation agents use benzoxycarbonylchloride (a) or tret-acylation agents use benzoxycarbonylchloride (a) or tret-butoxycarboxazide (b)butoxycarboxazide (b)

Blocked carbobenzoxygroup removed by catalytic hydrogenolysis or by action of HBr in acetic acid in cold.

Tret-butoxycarbonyl group destroyed by action of Tret-butoxycarbonyl group destroyed by action of triftoracetic acid:triftoracetic acid:

2) Deamination:2) Deamination:

a)a) oxidation deaminationoxidation deamination – important pathway for the – important pathway for the biodegradation of α-aminoacids:biodegradation of α-aminoacids:

b)b) hydrolytic deaminationhydrolytic deamination – reaction with nitrous acid. – reaction with nitrous acid. Aminoacids react with nitrous acid to give hydroxyacid Aminoacids react with nitrous acid to give hydroxyacid along with the evolution of nitrogen.along with the evolution of nitrogen.

The nitrogen can be collected and The nitrogen can be collected and measured. Thus this reaction constitutes one of the measured. Thus this reaction constitutes one of the methods for the estimation of amino acids.methods for the estimation of amino acids.

c) intramolecular deamination - unsaturated acids c) intramolecular deamination - unsaturated acids are formed:are formed:

d) redaction deamination – saturated carboxylic d) redaction deamination – saturated carboxylic acid formation:acid formation:

3) Tranceamination. Reaction goes under the 3) Tranceamination. Reaction goes under the present of enzymes tranceaminases and present of enzymes tranceaminases and coenzyme pyridoxalphosphate:coenzyme pyridoxalphosphate:

4) Interaction with carbonyl compounds:

5) Reaction with phenylisothiocyanate (Edmane 5) Reaction with phenylisothiocyanate (Edmane reaction). Form derivatives of 3-phenyl-2-reaction). Form derivatives of 3-phenyl-2-thiohydantoine (derivatives of thiohydantoine (derivatives of phenylthiohydantoine): phenylthiohydantoine):

6) Interaction with 2,4-dinitroftorbenzol (Senher’s 6) Interaction with 2,4-dinitroftorbenzol (Senher’s reagent):reagent):

B. Reaction on carboxyl groupB. Reaction on carboxyl group1) Formation of helate compounds ( complex 1) Formation of helate compounds ( complex

salts with ions of heard metals) salts with ions of heard metals)

2) Reaction with alcohols – difficult esters formation:2) Reaction with alcohols – difficult esters formation:

3) Reaction with ammonia – amides formation. The amides of 3) Reaction with ammonia – amides formation. The amides of aspartic and glutamic acid acids, asparagine and glutamine, play aspartic and glutamic acid acids, asparagine and glutamine, play important role in the transport of ammonia in the body.important role in the transport of ammonia in the body.

4) Formation of halogenanhydrides and anhydrides ( like carbonyl acids). Before these reaction blocked aminogroup by formation of N-acylderivatives.

5) 5) Decarboxylation.Decarboxylation. Aminoacids may be decarboxylated by heat, acids, bases or Aminoacids may be decarboxylated by heat, acids, bases or specific enzymes to the primary amines:specific enzymes to the primary amines:

Some of the decarboxylation reaction are of great importance in the body, Some of the decarboxylation reaction are of great importance in the body, decarboxylation of histidine to histaminedecarboxylation of histidine to histamine::

In the presence of foreign protein introduced into the body, very large In the presence of foreign protein introduced into the body, very large quantities of histamine are produced in the body and allergic reactions quantities of histamine are produced in the body and allergic reactions become evident. In extreme cases shock may result. The physiological become evident. In extreme cases shock may result. The physiological effects of histamine may be neutralized or minimized by the use of effects of histamine may be neutralized or minimized by the use of chemical compounds known as antihistamines.chemical compounds known as antihistamines.

C. Formation of salts. All aminoacids can react C. Formation of salts. All aminoacids can react with some inorganic acids and bases and with some inorganic acids and bases and form two kind of sold: form two kind of sold:

D. Peptide formation.D. Peptide formation. Two aminoacids can react in а Two aminoacids can react in а similar way - the carboxyl group of one aminoacid similar way - the carboxyl group of one aminoacid reacts with the amino group of the other aminoacid. reacts with the amino group of the other aminoacid.

In aminoacid chemistry, amide bonds that link aminoacids together are given the specific name of peptide bond. А peptide bond is а bond between the carboxyl group of one aminoacid and the amino group of another aminoacid. Under proper conditions, many aminoacids can bond together to give chains of aminoacids containing numerous peptide bonds. For example, four peptide bonds are present in а chain of five aminoacids.

The structural formula for а polypeptide may be The structural formula for а polypeptide may be written out in full, or the sequence of aminoacids present may written out in full, or the sequence of aminoacids present may be indicated by using the standard three-letter aminoacid be indicated by using the standard three-letter aminoacid abbreviations. The abbreviated formula for the tripeptide:abbreviations. The abbreviated formula for the tripeptide:

which contains the aminoacids glycine, which contains the aminoacids glycine, alanine, and serine, is Gly – Ala – Ser. When alanine, and serine, is Gly – Ala – Ser. When we use this abbreviated notation, by we use this abbreviated notation, by convention, the aminoacid at the N-terminal convention, the aminoacid at the N-terminal end of the peptide is always written on the left.end of the peptide is always written on the left.

The repeating chain of peptide bonds and α-carbon The repeating chain of peptide bonds and α-carbon atoms in а peptide is referred to as the backbone of the atoms in а peptide is referred to as the backbone of the peptide. The R group side chains are substituents on the peptide. The R group side chains are substituents on the backbone. Peptides that contain the same aminoacids but in backbone. Peptides that contain the same aminoacids but in different order are different molecules (structural isomers) different order are different molecules (structural isomers) with different properties. For example, two different with different properties. For example, two different dipeptides can be formed from one molecule of alanine and dipeptides can be formed from one molecule of alanine and one molecule of glycine.one molecule of glycine.

In the first dipeptide, the alanine is the N-terminal In the first dipeptide, the alanine is the N-terminal residue, and in the second molecule, it is the С-terminal residue, and in the second molecule, it is the С-terminal residue. These two compounds are isomers with different residue. These two compounds are isomers with different chemical and physical properties.chemical and physical properties.

Two important hormones produced by the pituitary gland Two important hormones produced by the pituitary gland are oxytocin and vasopressin, Each hormone is а nonapeptide are oxytocin and vasopressin, Each hormone is а nonapeptide (nine amino acid residues) with six of the residues hells in the (nine amino acid residues) with six of the residues hells in the form of а loop by а disulfide bond formed from the interaction of form of а loop by а disulfide bond formed from the interaction of two cysteine residues.two cysteine residues.

Oxytocin regulates uterine contractions and lactation. Vasopressin Oxytocin regulates uterine contractions and lactation. Vasopressin regulates the excretion of water by the kidneys; it also affects blood pressure. regulates the excretion of water by the kidneys; it also affects blood pressure. The structure of vasopressin differs from that of oxytocin at only two The structure of vasopressin differs from that of oxytocin at only two aminoacid positions: the third and eighth aminoacid residues. The result of aminoacid positions: the third and eighth aminoacid residues. The result of these variations is а significant difference in physiological action.these variations is а significant difference in physiological action.

Xanthoprotein test. On treatment with concentrated nitric acid, certain proteins give yellow color. This yellow color is the same that is formed on the skin when the latter comes in contact with the concentrated nitric acid. The test is given only by the proteins having at least one mole of aromatic aminoacid, such as tryptophan, phenylalanine, and tyrosine which are actually nitrated during treatment with concentrated nitric acid. When you add after conc. HNO3 conc. NaOH forms light orange color (hynoid structure).

The The primary structure of а proteinprimary structure of а protein is the sequence of aminoacids present in its is the sequence of aminoacids present in its peptide chain or chains. Knowledge of primary structure tells us which peptide chain or chains. Knowledge of primary structure tells us which aminoacids are present, the number of each, their sequence, and the length aminoacids are present, the number of each, their sequence, and the length and number of polypeptide chains.and number of polypeptide chains.

The first protein whose primary structure was determined was insulin, the The first protein whose primary structure was determined was insulin, the hormone that regulates blood-glucose level; а deficiency of insulin leads to hormone that regulates blood-glucose level; а deficiency of insulin leads to diabetes. The sequencing of insulin, which took over 8 years, was completed diabetes. The sequencing of insulin, which took over 8 years, was completed in 1953. Today, thousands of proteins have been sequenced; that is, in 1953. Today, thousands of proteins have been sequenced; that is, researchers have determined the order of amino acids within the polypeptide researchers have determined the order of amino acids within the polypeptide chain or chains.chain or chains.

The The secondary structure of а proteinsecondary structure of а protein is the arrangement in is the arrangement in space of the atoms in the backbone of the protein. Three major space of the atoms in the backbone of the protein. Three major types of protein secondary structure are known; the alpha types of protein secondary structure are known; the alpha helix, the beta pleated sheet, and the triple helix. The major helix, the beta pleated sheet, and the triple helix. The major force responsible for all three types of secondary structure is force responsible for all three types of secondary structure is hydrogen bonding between а carbonyl oxygen atom of а hydrogen bonding between а carbonyl oxygen atom of а peptide linkage and the hydrogen atom of an amino group (-peptide linkage and the hydrogen atom of an amino group (-NH) of another peptide linkage farther along the backbone. NH) of another peptide linkage farther along the backbone. This hydrogen-bonding interaction may be diagrammed as This hydrogen-bonding interaction may be diagrammed as follows:follows:

The The Alpha HelixAlpha Helix The alpha helix (α-helix) structure resembles а The alpha helix (α-helix) structure resembles а coiled helical spring, with the coil configuration maintained by hydrogen coiled helical spring, with the coil configuration maintained by hydrogen bonds between N – Н and С= О groups of every fourth aminoacid, as is bonds between N – Н and С= О groups of every fourth aminoacid, as is shown diagrammatically in Figure.2.shown diagrammatically in Figure.2.

Figure. Three representations of (а) the а helix protein structure. Figure. Three representations of (а) the а helix protein structure. Hydrogen bonds between amide groups (peptide linkages) are shown in (b) Hydrogen bonds between amide groups (peptide linkages) are shown in (b) and (с). (d) The top view of an а helix shows that amino acid side chains (R and (с). (d) The top view of an а helix shows that amino acid side chains (R groups) point away from the long axis of the helix.groups) point away from the long axis of the helix.

Figure. Two representations of the p pleated sheet protein structure. (а) А Figure. Two representations of the p pleated sheet protein structure. (а) А representation emphasizing the hydrogen bonds between protein chains. (b) А representation emphasizing the hydrogen bonds between protein chains. (b) А representation emphasizing the pleats and the location of the R groups. representation emphasizing the pleats and the location of the R groups. Proteins have varying amounts of α-helical secondary structure, ranging from Proteins have varying amounts of α-helical secondary structure, ranging from а few percent to nearly 100 %. In an α-helix, all of the aminoacid side chains а few percent to nearly 100 %. In an α-helix, all of the aminoacid side chains (R groups) lie outside the helix; there is not enough room for them in the (R groups) lie outside the helix; there is not enough room for them in the interior. Figure.3d illustrates this situation. This structural feature of the α-interior. Figure.3d illustrates this situation. This structural feature of the α-helix is the basis for protein tertiary structure.helix is the basis for protein tertiary structure.

Collagen, the structural protein of Collagen, the structural protein of connective tissue (cartilage, tendon, and skin), connective tissue (cartilage, tendon, and skin), has а triple-helix structure. Collagen molecules has а triple-helix structure. Collagen molecules are very long, thin, and rigid. Many such are very long, thin, and rigid. Many such molecules, lined up alongside each other, molecules, lined up alongside each other, combine to make collagen fibers. Cross-combine to make collagen fibers. Cross-linking gives the fibers extra strength. linking gives the fibers extra strength.

Figure. Four types of interactions between aminoacid R Figure. Four types of interactions between aminoacid R groups produce thetertiary structure of а protein. (а) Disulfide groups produce thetertiary structure of а protein. (а) Disulfide bonds. (b) Electrostatic interactions (salt bridges). (с) Hydrogen bonds. (b) Electrostatic interactions (salt bridges). (с) Hydrogen bonds. (d) Hydrophobic interactions. Electrostatic interactions, bonds. (d) Hydrophobic interactions. Electrostatic interactions, also called salt bridges, always involve aminoacids with charged also called salt bridges, always involve aminoacids with charged side chains. These aminoacids are the acidic and basic side chains. These aminoacids are the acidic and basic aminoacids. The two R groups, one acidic and one basic, interact aminoacids. The two R groups, one acidic and one basic, interact through ion — ion attractions. Figure.b shows an electrostatic through ion — ion attractions. Figure.b shows an electrostatic interaction.interaction.

Table. 1 Some common fibrous and globular proteinsTable. 1 Some common fibrous and globular proteins

Table.2. Types of conjugated proteinsTable.2. Types of conjugated proteins

Thank you for attention!