A hydrolysable 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 Precipitation (chemistry), precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' is widel ...
that, on heating with
hydrochloric or
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
s, 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 backward because it can be o ...
s.
At the center of a hydrolysable tannin
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
, there is a
carbohydrate
A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...
(usually
D-glucose but also
cyclitol
In organic chemistry, a cyclitol is a cycloalkane containing at least three hydroxyl, each attached to a different ring carbon atom. The general formula for an unsubstituted cyclitol is or where 3 ≤ ''x'' ≤ ''n''.
The name is also used for ...
s like
quinic or
shikimic acids). The hydroxyl groups of the carbohydrate are partially or totally
esterified 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 plant ...
in
gallotannins 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 backward because it can be o ...
in
ellagitannin
image:Castalagin.svg, 130px, Castalagin is a representative ellagitannin, characterized by coupled gallic acid substituents
The ellagitannins are a diverse class of hydrolyzable tannins, a type of polyphenol formed primarily from the oxidative link ...
s. Hydrolysable tannins are mixtures of polygalloyl glucoses and/or poly-galloyl
quinic acid derivatives containing in between 3 up to 12 gallic acid residues per molecule.
Hydrolysable tannins are hydrolysed by weak acids or weak bases to produce carbohydrate and
phenolic acid
Phenolic acids or phenolcarboxylic acids ? are phenolic compounds and 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 nat ...
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 plant ...
ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s of
glucose
Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...
in
tannic acid
Tannic acid is a specific form of tannin, a type of polyphenol. Its weak acidity (Acid dissociation constant, pKa around 6) is due to the numerous phenol groups in the structure. The chemical formula for commercial tannic acid is often given as ...
(C
76H
52O
46), found in the
leaves
A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...
and
bark
Bark may refer to:
Common meanings
* Bark (botany), an outer layer of a woody plant such as a tree or stick
* Bark (sound), a vocalization of some animals (which is commonly the dog)
Arts and entertainment
* ''Bark'' (Jefferson Airplane album), ...
of many
plant
Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
species.
Hydrolysable tannins can be extracted from different vegetable
plants
Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars f ...
, such as
chestnut
The chestnuts are the deciduous trees and shrubs in the genus ''Castanea'', in the beech family Fagaceae. The name also refers to the edible nuts they produce. They are native to temperate regions of the Northern Hemisphere.
Description
...
wood (''
Castanea sativa
The sweet chestnut (''Castanea sativa''), also known as the Spanish chestnut or European chestnut, is a species of tree in the family Fagaceae, native to Southern Europe and Asia Minor, and widely cultivated throughout the Temperate climate, te ...
''),
oak
An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...
wood (''
Quercus robur
''Quercus robur'', the pedunculate oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native plant, native to most of Europe and western Asia, and is widely cultivated in other temperate regions. It ...
'', ''
Quercus petraea
''Quercus petraea'', commonly known as the sessile oak, Welsh 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 un ...
'' and ''
Quercus alba
''Quercus alba'', the white oak, is one of the preeminent hardwoods of eastern and central North America. It is a long-lived oak, native to eastern and central North America and found from Minnesota, Ontario, Quebec, and southern Maine south as ...
''), tara pods (''
Caesalpinia spinosa''),
gall
Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or war ...
nuts (''
Quercus infectoria'' and ''
Rhus semialata''), myrobalan (''
Terminalia chebula''),
sumac (''
Rhus coriaria'') and Aleppo gallnuts (''
Andricus kollari'').
[''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 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 (chemistry), basic heterocyclic compound, 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, weak ...
. 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 backward because it can be o ...
(epigallitannins), are inhibitors of
HIV 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 ...
,
punicalagin
Punicalagin (''Pyuni-cala-jen'') 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 ...
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 T cells (for cell-mediated and cytotoxic adaptive immunity), B cells (for humoral, antibody-driven adaptive immunity), an ...
s with little cytotoxicity. Two compounds, punicalin and
punicacortein C, inhibited purified HIV
reverse transcriptase
A reverse transcriptase (RT) is an enzyme used to convert RNA genome to DNA, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobi ...
.
Hydrolysable tannins have shown also potential antibacterial effects against ''
Helicobacter pylori
''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...
''.
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