A hydrolyzable tannin or
pyrogallol
Pyrogallol is an organic compound with the formula C6H3(OH)3. It is a water-soluble, white solid although samples are typically brownish because of its sensitivity toward oxygen. It is one of three isomers of benzenetriols.
Production and reac ...
-type tannin is a type of
tannin
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'' ...
that, on heating with
hydrochloric
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestiv ...
or
sulfuric acids, yields
gallic or
ellagic acid
Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid.
Name
The name comes from the French term ''acide ellagique'', from the word ''galle'' spelled backwards because it can be ...
s.
At the center of a hydrolyzable tannin
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
, there is a
carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or m ...
(usually
D-glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usin ...
but also
cyclitols like
quinic or
shikimic acid
Shikimic acid, more commonly known as its anionic form shikimate, is a cyclohexene, a cyclitol and a cyclohexanecarboxylic acid. It is an important biochemical metabolite in plants and microorganisms. Its name comes from the Japanese flower ''shik ...
s). The hydroxyl groups of the carbohydrate are partially or totally
esterified
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
with phenolic groups such as
gallic acid
Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. I ...
in
gallotannin A gallotannin is any of a class of molecules belonging to the hydrolysable tannins. Gallotannins are polymers formed when gallic acid, a polyphenol monomer, esterifies and binds with the hydroxyl group of a polyol carbohydrate such as glucose.
Meta ...
s or
ellagic acid
Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid.
Name
The name comes from the French term ''acide ellagique'', from the word ''galle'' spelled backwards because it can be ...
in
ellagitannin
The ellagitannins are a diverse class of hydrolyzable tannins, a type of polyphenol formed primarily from the oxidative linkage of galloyl groups in 1,2,3,4,6-pentagalloyl glucose. Ellagitannins differ from gallotannins, in that their galloyl ...
s. Hydrolysable tannins are mixtures of polygalloyl glucoses and/or poly-galloyl
quinic acid
Quinic acid is a cyclitol, a cyclic polyol, and a cyclohexanecarboxylic acid. It is a colorless solid that can be extracted from plant sources. Quinic acid is implicated in the perceived acidity of coffee.
Occurrence and preparation
The compound ...
derivatives containing in between 3 up to 12 gallic acid residues per molecule.
Hydrolyzable tannins are hydrolyzed by weak acids or weak bases to produce carbohydrate and
phenolic acid
Phenolic acids or phenolcarboxylic acids are types of aromatic acid compounds. Included in that class are substances containing a phenolic ring and an organic carboxylic acid function (C6-C1 skeleton). Two important naturally occurring types of ph ...
s.
Examples of gallotannins are the
gallic acid
Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. I ...
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...
s of
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
in
tannic acid
Tannic acid is a specific form of tannin, a type of polyphenol. Its weak acidity ( pKa around 6) is due to the numerous phenol groups in the structure. The chemical formula for commercial tannic acid is often given as C76H52O46, which corresp ...
(C
76H
52O
46), found in the
leaves and
bark of many
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
species.
Hydrolysable tannins can be extracted from different vegetable
plants
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
, such as
chestnut wood (''
Castanea sativa
''Castanea sativa'', the sweet chestnut, Spanish chestnut or just chestnut, is a species of tree in the family Fagaceae, native to Southern Europe and Asia Minor, and widely cultivated throughout the Temperate climate, temperate world. A substa ...
''),
oak
An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
wood (''
Quercus robur
''Quercus robur'', commonly known as common oak, pedunculate oak, European oak or English oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native to most of Europe west of the Caucasus. It is widel ...
'', ''
Quercus petraea
''Quercus petraea'', commonly known as the sessile oak, Cornish oak, Irish Oak or durmast oak, is a species of oak tree native to most of Europe and into Anatolia and Iran. The sessile oak is the national tree of Ireland, and an unofficial embl ...
'' and ''
Quercus alba
An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ...
''), tara pods (''
Caesalpinia spinosa
''Tara spinosa'', commonly known as ''tara'' (Quechua), also known as Peruvian carob or spiny holdback, is a small leguminous tree or thorny shrub native to Peru. ''T. spinosa'' is cultivated as a source of tannins based on a galloylated quin ...
''),
gallnuts (''
Quercus infectoria
''Quercus infectoria'' or the Aleppo oak is a species of oak well known for producing galls (called manjakani in Malaysia, majuphal in India) that have been traditionally used for centuries in Asia medicinally while also used in softening leathe ...
'' and ''
Rhus semialata''), myrobalan (''
Terminalia chebula
''Terminalia chebula'', commonly known as black- or chebulic myrobalan, is a species of '' Terminalia'', native to South Asia from India and Nepal east to southwest China (Yunnan), and south to Sri Lanka, Malaysia, and Vietnam.Flora of China''Te ...
''),
sumac
Sumac ( or ), also spelled sumach, is any of about 35 species of flowering plants in the genus ''Rhus'' and related genera in the cashew family (Anacardiaceae). Sumacs grow in subtropical and temperate regions throughout the world, including Eas ...
(''
Rhus coriaria
''Rhus coriaria'', commonly called Sicilian sumac, tanner's sumach, or elm-leaved sumach, is a deciduous shrub to small tree in the cashew family Anacardiaceae. It is native to southern Europe and western Asia. The dried fruits are used as a spi ...
'') and Aleppo gallnuts (''
Andricus kollari
''Andricus kollari'', also known as the marble gall wasp, is a parthenogenetic species of wasp which causes the formation of marble galls on oak trees. Synonyms for the species include ''Cynips kollari'', ''Andricus quercusgemmae'', ''A. minor ...
'').
[''Haslam E. Plant Polyphenols, Vegetable Tannins Revisited. Cambridge University Press, Cambridge, UK (1989)''](_blank)
[Hemingway RW, Laks PE. Plant polyphenols Plant Polyphenols: Synthesis, Properties and Significance. Springer (1992).]
Analysis
;
; Gallic acid determination
50 mg of sample tannin in 5 ml 2N H
2SO
4 are put into constricted test tubes and frozen. The tubes are vacuum-sealed and heated for 24 hours at 100 °C. The tubes are cooled, opened and the contents made up to 50 ml with water. Then 1.5 ml of freshly prepared 0.667% w/v
rhodanine
Rhodanine is a 5-membered heterocyclic organic compound possessing a thiazolidine core. It was discovered in 1877 by Marceli Nencki who named it ''"Rhodaninsaure"'' in reference to its synthesis from ammonium rhodanide (known as ammonium thiocya ...
in methanol and 1 ml of sample are mixed. After exactly 5 min 1 ml of 0.5 N KOH solution is added. After 2.5 min the mixture is diluted to 25 ml with distilled water and 5–10 min later the absorbance at 520 nm is measured. The measured absorbance obeys the relationship:
A520=
.13 × (mg of gallic acid) +0.03
Gallic acid is used as a standard and the data are based on experiments carried out in triplicate.
;Ellagic acid determination
10 mg of samples tannin in 1 ml 2N H
2SO
4 are put into constricted test tubes and frozen. The tubes are vacuum-waled and heated for 24 hours at 100 °C. Tubes were cooled, opened and the filtered content made up to 10 ml with
pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a ...
. Then 1.1 ml of pyridine and l ml of sample are mixed in a dry test tube. After adding 0.10 ml of concentrated HCl and mixing, the sample is brought to 30 °C. The sample is quickly mixed after 0.10 ml of 1% (w/v) NaNO
2 in water and the absorbance 538 nm is immediately recorded. After a 36 min incubating period at 30 °C, the absorbance is again recorded. The difference between the initial absorbance and the absorbance at 36 min (D A538) is proportional to the ellagic acid concentration. The measured absorbance obeys the relationship:
A538 =
.03 × (mg of ellagic acid)– 0.04
Ellagic acid is used as a standard and the data were based on experiments carried out in triplicate.
;Alkaline hydrolysis
4.8 g sample tannin in 9 ml water are refluxed in 4.2 ml 40% NaOH for 6h at pH 12 - 13. Neutralization to pH = 6.8 - 7 is performed with 62% H
2SO
4.
;HPLC determination
Uses
Tannins, including gallo and
ellagic acid
Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid.
Name
The name comes from the French term ''acide ellagique'', from the word ''galle'' spelled backwards because it can be ...
(epigallitannins), are inhibitors of
HIV
The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
replication.
1,3,4-Tri-O-galloylquinic acid,
3,5-di-O-galloyl-shikimic acid,
3,4,5-tri-O-galloylshikimic acid,
punicalin
Punicalin is an ellagitannin. It can be found in ''Punica granatum'' (pomegranate) or in the leaves of ''Terminalia catappa'', a plant used to treat dermatitis and hepatitis. It is also reported in '' Combretum glutinosum'', all three species bein ...
,
punicalagin
Punicalagin is an ellagitannin, a type of phenolic compound. It is found as alpha and beta isomers in pomegranates (''Punica granatum''), ''Terminalia catappa'', ''Terminalia myriocarpa'', and in ''Combretum molle'', the velvet bushwillow, a plant ...
inhibited HIV replication in infected H9
lymphocyte
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...
s with little cytotoxicity. Two compounds, punicalin and
punicacortein C, inhibited purified HIV
reverse transcriptase.
Hydrolysable tannins have shown also potential antibacterial effects against ''
Helicobacter pylori
''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...
''.
In the past few years, hydrolysable tannins have also been studied for their potential effects against cancer through different mechanisms.
References
{{DEFAULTSORT:Hydrolysable Tannin
Hydrolysable tannins