Propionic acid
Encyclopedia
Propanoic acid is a naturally occurring carboxylic acid
with chemical formula
C
H
3CH2CO
OH. It is a clear liquid with a pungent odor. The anion CH3CH2COO− as well as the salts and ester
s of propanoic acid are known as propanoates (or propionates).
, who found it among the degradation products of sugar
. Over the next few years, other chemists produced propanoic acid in various other ways, none of them realizing they were producing the same substance. In 1847, the French chemist Jean-Baptiste Dumas
established that all the acids were the same compound, which he called propionic acid, from the Greek
words protos = "first" and pion = "fat", because it was the smallest H(CH2)nCOOH acid that exhibited the properties of the other fatty acid
s, such as producing an oily layer when salted out of water and having a soap
y potassium
salt
.
and acetic
acids, and the larger fatty acid
s. It is miscible with water, but can be removed from water by adding salt. As with acetic and formic acids, it consists of hydrogen bond
ed pairs of molecules both as the liquid and vapor.
Propanoic acid displays the general properties of carboxylic acids: it can form amide
, ester
, anhydride, and chloride
derivatives. It can undergo alpha-halogenation
with bromine
in the presence of PBr3
as catalyst (the HVZ reaction
) to form CH3CHBrCOOH.
using nickel carbonyl
as the catalyst:
It is also produced by the aerobic oxidation of propionaldehyde
. In the presence of cobalt
or manganese
ion
s, this reaction proceeds rapidly at temperatures as mild as 40–50 °C:
Large amounts of propanoic acid were once produced as a byproduct of acetic acid manufacture. Currently the world's largest producer of propanoic acid is BASF
, with approximately 80 kt/a production capacity.
Propanoic acid is produced biologically as its coenzyme A ester, propionyl-CoA
, from the metabolic
breakdown of fatty acids containing odd numbers of carbon
atoms, and also from the breakdown of some amino acid
s. Bacteria
of the genus Propionibacterium
produce propanoic acid as the end product of their anaerobic
metabolism. This class of bacteria is commonly found in the stomachs of ruminant
s and the sweat glands of humans
, and their activity is partially responsible for the odor of both Swiss cheese
and sweat
.
and some bacteria
at the levels between 0.1 and 1% by weight. As a result, most propanoic acid produced is consumed as a preservative
for both animal feed and food for human consumption. For animal feed, it is used either directly or as its ammonium
salt. The antibiotic Monensin
is added to cattle feed to favor propionibacteria over acetic acid producers in the rumen; this produces less carbon dioxide and feed conversion is better. This application accounts for about half of the world production of propanoic acid. Another major application is as a preservative in baked goods, which use the sodium
and calcium
salts. As a food additive
it is approved for use in the EU, USA and Australia and New Zealand; it is listed by its INS number (280) or E number
E280.
Propanoic acid is also useful as an intermediate in the production of other chemicals, especially polymers. Cellulose
-acetate-propionate is a useful thermoplastic. Vinyl propionate is also used. In more specialized applications, it is also used to make pesticide
s and pharmaceuticals. The ester
s of propanoic acid have fruit-like odors and are sometimes used as solvent
s or artificial flavorings.
(propionyl-CoA), the usual first step in the metabolism of carboxylic acid
s. Since propanoic acid has three carbons, propionyl-CoA cannot directly enter either beta oxidation
or the citric acid cycle
s. In most vertebrate
s, propionyl-CoA is carboxylated
to D-methylmalonyl-CoA, which is isomerised
to L-methylmalonyl-CoA. A vitamin B12
-dependent enzyme catalyzes rearrangement of L-methylmalonyl-CoA to succinyl-CoA
, which is an intermediate of the citric acid cycle and can be readily incorporated there.
In propanoic acidemia
, a rare inherited genetic disorder, propionate acts as a metabolic toxin in liver cells by accumulating in mitochondria as propionyl-CoA and its derivative, methylcitrate, two tricarboxylic acid cycle inhibitors. Propanoate is metabolized oxidatively by glia, which suggests astrocytic vulnerability in propanoic acidemia when intramitochondrial propionyl-CoA may accumulate. Propanoic acidemia may alter both neuronal and glial gene expression by affecting histone acetylation. When propanoic acid is infused directly into rodents brains it produces reversible behavior (e.g., hyperactivity, dystonia
, social impairment, perseveration) and brain (e.g., innate neuroinflammation, glutathione depletion) changes that may be used as a means to model autism
in rats.
is host of several species of bacteria known as Propionibacteria, which are named after their ability to produce propanoic acid. The most notable one is the Propionibacterium acnes
, which lives mainly in the sebaceous gland
s of the skin and is one of the principal causes of acne
.
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
with chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
C
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
3CH2CO
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
OH. It is a clear liquid with a pungent odor. The anion CH3CH2COO− as well as the salts and ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s of propanoic acid are known as propanoates (or propionates).
History
Propanoic acid was first described in 1844 by Johann GottliebJohann Gottlieb
Johann Gottlieb was an Austrian chemist who first synthesized Propionic acid. Gottlieb was born in Brno, Bohemia in Austria . Since 1846 he was a professor at the University of Graz. He died of natural causes in Graz, Austria.- External links :*...
, who found it among the degradation products of sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
. Over the next few years, other chemists produced propanoic acid in various other ways, none of them realizing they were producing the same substance. In 1847, the French chemist Jean-Baptiste Dumas
Jean-Baptiste Dumas
Jean Baptiste André Dumas was a French chemist, best known for his works on organic analysis and synthesis, as well as the determination of atomic weights and molecular weights by measuring vapor densities...
established that all the acids were the same compound, which he called propionic acid, from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
words protos = "first" and pion = "fat", because it was the smallest H(CH2)nCOOH acid that exhibited the properties of the other fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s, such as producing an oily layer when salted out of water and having a soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
y potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
salt
Potassium propionate
Potassium propanoate or potassium propionate has formula K. Its melting point is 410 °C. It is the potassium salt of propanoic acid.-Use:...
.
Properties
Propanoic acid has physical properties intermediate between those of the smaller carboxylic acids, formicFormic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
and acetic
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
acids, and the larger fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s. It is miscible with water, but can be removed from water by adding salt. As with acetic and formic acids, it consists of hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
ed pairs of molecules both as the liquid and vapor.
Propanoic acid displays the general properties of carboxylic acids: it can form amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...
, ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
, anhydride, and chloride
Acyl chloride
In organic chemistry, an acyl chloride is an organic compound with the functional group -CO-Cl. Their formula is usually written RCOCl, where R is a side chain. They are usually considered to be reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride,...
derivatives. It can undergo alpha-halogenation
Halogenation
Halogenation is a chemical reaction that incorporates a halogen atom into a molecule in substitution of hydrogen atom. Halogenation takes place in the gas phase. There are four types of halogenation: fluorination, chlorination, bromination, and iodination...
with bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
in the presence of PBr3
Phosphorus tribromide
Phosphorus tribromide is a colourless liquid with the formula PBr3. It fumes in air due to hydrolysis and has a penetrating odour. It is widely used in the laboratory for the conversion of alcohols to alkyl bromides.-Preparation:...
as catalyst (the HVZ reaction
Hell-Volhard-Zelinsky halogenation
The Hell-Volhard-Zelinsky halogenation reaction halogenates carboxylic acids at the α carbon. The reaction is named after three chemists, the German chemists Carl Magnus von Hell and Jacob Volhard and the Russian chemist Nikolay Zelinsky .- Scheme :Unlike other halogenation reactions, this...
) to form CH3CHBrCOOH.
Production
In industry, propanoic acid is mainly produced by the hydrocarboxylation of ethyleneEthylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
using nickel carbonyl
Nickel carbonyl
Nickel carbonyl is the organonickel compound with the formula Ni4. This pale-yellow liquid is the principal carbonyl of nickel. It is an intermediate in the Mond process for the purification of nickel and a reagent in organometallic chemistry...
as the catalyst:
- H2C=CH2 + H2O + CO → CH3CH2CO2H
It is also produced by the aerobic oxidation of propionaldehyde
Propionaldehyde
Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturated 3-carbon aldehyde and is a structural isomer of acetone...
. In the presence of cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
or manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s, this reaction proceeds rapidly at temperatures as mild as 40–50 °C:
- CH3CH2CHOPropionaldehydePropionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturated 3-carbon aldehyde and is a structural isomer of acetone...
+ ½ O2OxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
→ CH3CH2COOH.
Large amounts of propanoic acid were once produced as a byproduct of acetic acid manufacture. Currently the world's largest producer of propanoic acid is BASF
BASF
BASF SE is the largest chemical company in the world and is headquartered in Germany. BASF originally stood for Badische Anilin- und Soda-Fabrik . Today, the four letters are a registered trademark and the company is listed on the Frankfurt Stock Exchange, London Stock Exchange, and Zurich Stock...
, with approximately 80 kt/a production capacity.
Propanoic acid is produced biologically as its coenzyme A ester, propionyl-CoA
Propionyl-CoA
Propionyl-CoA is a coenzyme A derivative of propionic acid.-Production:There are several different ways in which it is formed:* It is formed as a product of beta-oxidation of odd-chain fatty acids....
, from the metabolic
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
breakdown of fatty acids containing odd numbers of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atoms, and also from the breakdown of some amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s. Bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
of the genus Propionibacterium
Propionibacterium
Propionibacterium is a genus of bacteria named for their unique metabolism: They are able to synthesize propionic acid by using unusual transcarboxylase enzymes....
produce propanoic acid as the end product of their anaerobic
Anaerobic respiration
Anaerobic respiration is a form of respiration using electron acceptors other than oxygen. Although oxygen is not used as the final electron acceptor, the process still uses a respiratory electron transport chain; it is respiration without oxygen...
metabolism. This class of bacteria is commonly found in the stomachs of ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s and the sweat glands of humans
Propionibacterium acnes
Propionibacterium acnes is a relatively slow growing, typically aerotolerant anaerobic gram positive bacterium that is linked to the skin condition acne; it can also cause chronic blepharitis and endophthalmitis, the latter particularly following intraocular surgery...
, and their activity is partially responsible for the odor of both Swiss cheese
Swiss cheese
Swiss cheese is a generic name in North America for several related varieties of cheese which resemble the Swiss Emmental. Some types of Swiss cheese have a distinctive appearance, as the blocks of the cheese are riddled with holes known as "eyes". Swiss cheese has a piquant, but not very sharp,...
and sweat
SWEAT
SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...
.
Uses
Propanoic acid inhibits the growth of moldMold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...
and some bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
at the levels between 0.1 and 1% by weight. As a result, most propanoic acid produced is consumed as a preservative
Preservative
A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....
for both animal feed and food for human consumption. For animal feed, it is used either directly or as its ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
salt. The antibiotic Monensin
Monensin
Monensin is a polyether antibiotic isolated from Streptomyces cinnamonensis. It is widely used in animal feeds.The structure of monensin was first described by Agtarap et al. in 1967, and was the first polyether antibiotic to have its structure elucidated in this way...
is added to cattle feed to favor propionibacteria over acetic acid producers in the rumen; this produces less carbon dioxide and feed conversion is better. This application accounts for about half of the world production of propanoic acid. Another major application is as a preservative in baked goods, which use the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
salts. As a food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
it is approved for use in the EU, USA and Australia and New Zealand; it is listed by its INS number (280) or E number
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
E280.
Propanoic acid is also useful as an intermediate in the production of other chemicals, especially polymers. Cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
-acetate-propionate is a useful thermoplastic. Vinyl propionate is also used. In more specialized applications, it is also used to make pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s and pharmaceuticals. The ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s of propanoic acid have fruit-like odors and are sometimes used as solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s or artificial flavorings.
Metabolism
The metabolism of propanoic acid begins with its conversion to propionyl coenzyme ACoenzyme A
Coenzyme A is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All sequenced genomes encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it as a substrate...
(propionyl-CoA), the usual first step in the metabolism of carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
s. Since propanoic acid has three carbons, propionyl-CoA cannot directly enter either beta oxidation
Beta oxidation
Beta oxidation is the process by which fatty acids, in the form of Acyl-CoA molecules, are broken down in mitochondria and/or in peroxisomes to generate Acetyl-CoA, the entry molecule for the Citric Acid cycle....
or the citric acid cycle
Citric acid cycle
The citric acid cycle — also known as the tricarboxylic acid cycle , the Krebs cycle, or the Szent-Györgyi-Krebs cycle — is a series of chemical reactions which is used by all aerobic living organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats and...
s. In most vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, propionyl-CoA is carboxylated
Carboxylation
Carboxylation in chemistry is a chemical reaction in which a carboxylic acid group is introduced in a substrate. The opposite reaction is decarboxylation.-Carboxylation in organic chemistry:In organic chemistry many different protocols exist for carboxylation...
to D-methylmalonyl-CoA, which is isomerised
Isomerisation
In chemistry isomerisation is the process by which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g. A-B-C → B-A-C . In some molecules and under some conditions, isomerisation occurs spontaneously...
to L-methylmalonyl-CoA. A vitamin B12
Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
-dependent enzyme catalyzes rearrangement of L-methylmalonyl-CoA to succinyl-CoA
Succinyl-CoA
Succinyl-Coenzyme A, abbreviated as Succinyl-CoA or SucCoA, is a combination of succinic acid and coenzyme A.-Source:It is an important intermediate in the citric acid cycle, where it is synthesized from α-Ketoglutarate by α-ketoglutarate dehydrogenase through decarboxylation...
, which is an intermediate of the citric acid cycle and can be readily incorporated there.
In propanoic acidemia
Propionic acidemia
Propionic acidemia, also known as propionic aciduria, propionyl-CoA carboxylase deficiency and ketotic glycinemia, is an autosomal recessive metabolic disorder, classified as a branched-chain organic acidemia....
, a rare inherited genetic disorder, propionate acts as a metabolic toxin in liver cells by accumulating in mitochondria as propionyl-CoA and its derivative, methylcitrate, two tricarboxylic acid cycle inhibitors. Propanoate is metabolized oxidatively by glia, which suggests astrocytic vulnerability in propanoic acidemia when intramitochondrial propionyl-CoA may accumulate. Propanoic acidemia may alter both neuronal and glial gene expression by affecting histone acetylation. When propanoic acid is infused directly into rodents brains it produces reversible behavior (e.g., hyperactivity, dystonia
Dystonia
Dystonia is a neurological movement disorder, in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures. The disorder may be hereditary or caused by other factors such as birth-related or other physical trauma, infection, poisoning or reaction to...
, social impairment, perseveration) and brain (e.g., innate neuroinflammation, glutathione depletion) changes that may be used as a means to model autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
in rats.
Human occurrence
The human skinSkin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is host of several species of bacteria known as Propionibacteria, which are named after their ability to produce propanoic acid. The most notable one is the Propionibacterium acnes
Propionibacterium acnes
Propionibacterium acnes is a relatively slow growing, typically aerotolerant anaerobic gram positive bacterium that is linked to the skin condition acne; it can also cause chronic blepharitis and endophthalmitis, the latter particularly following intraocular surgery...
, which lives mainly in the sebaceous gland
Sebaceous gland
The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
s of the skin and is one of the principal causes of acne
Acne
Acne is a general term used for acneiform eruptions. It is usually used as a synonym for acne vulgaris, but may also refer to:*Acne aestivalis*Acne conglobata*Acne cosmetica*Acne fulminans*Acne keloidalis nuchae*Acne mechanica...
.