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47-1122: They are called proanthocyanidins as they yield anthocyanidins when depolymerized under oxidative conditions. Different types of condensed tannins exist, such as the procyanidins , propelargonidins , prodelphinidins , profisetinidins , proteracacinidins , proguibourtinidins or prorobinetidins . All of the above are formed from flavan-3-ols , but flavan-3,4-diols, called ( leucoanthocyanidin ) also form condensed tannin oligomers, e.g. leuco-fisetinidin form profisetinidin , and flavan-4-ols form condensed tannins, e.g. 3',4',5,7-flavan-4-ol form proluteolinidin (luteoforolor). One particular type of condensed tannin, found in grape, are procyanidins , which are polymers of 2 to 50 (or more) catechin units joined by carbon-carbon bonds. These are not susceptible to being cleaved by hydrolysis . While many hydrolyzable tannins and most condensed tannins are water-soluble, several tannins are also highly octanol -soluble. Some large condensed tannins are insoluble. Differences in solubilities are likely to affect their biological functions. Tannins of tropical woods tend to be of

94-440: A nucleophile is a chemical species that forms bonds by donating an electron pair . All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases . Nucleophilic describes the affinity of a nucleophile to bond with positively charged atomic nuclei . Nucleophilicity, sometimes referred to as nucleophile strength, refers to

141-497: A nucleophilic displacement on benzyl chloride , the azide anion reacts 3000 times faster than water. The Ritchie equation, derived in 1972, is another free-energy relationship: where N is the nucleophile dependent parameter and k 0 the reaction rate constant for water. In this equation, a substrate-dependent parameter like s in the Swain–Scott equation is absent. The equation states that two nucleophiles react with

188-527: A 2014 scientific opinion by the European Food Safety Authority rejected physiological evidence that cranberry PACs have a role in inhibiting bacterial pathogens involved in UTIs; 2) an updated 2023 Cochrane Collaboration review supported the use of cranberry products for the prevention of UTIs for certain groups. A 2017 systematic review concluded that cranberry products significantly reduced

235-688: A catechin nature rather than of the gallic type present in temperate woods . Condensed tannins can be recovered from Lithocarpus glaber or can be found in Prunus sp. The bark of Commiphora angolensis contains condensed tannins. Commercial sources of condensed tannins are plants such as quebracho wood ( Schinopsis lorentzii ), mimosa bark ( Acacia mollissima ), grape seeds ( Vitis vinifera ), pine barks and spruce barks. Condensed tannins are formed in tannosomes , specialized organelles, in Tracheophytes, i.e. vascular plants . Pycnogenol

282-449: A class of polyphenols found in many plants, such as cranberry , blueberry , and grape seeds . Chemically, they are oligomeric flavonoids . Many are oligomers of catechin and epicatechin and their gallic acid esters . More complex polyphenols, having the same polymeric building block, form the group of condensed tannins . Proanthocyanidins were discovered in 1947 by Jacques Masquelier, who developed and patented techniques for

329-455: A database of botanical and food sources of proanthocyanidins. In nature, proanthocyanidins serve among other chemical and induced defense mechanisms against plant pathogens and predators , such as occurs in strawberries . Proanthocyanidin has low bioavailability, with 90% remaining unabsorbed from the intestines until metabolized by gut flora to the more bioavailable metabolites. Condensed tannins can undergo acid-catalyzed cleavage in

376-459: A five US fluid ounces (150 ml) serving of red wine averages 91 milligrams ( i.e. , 145.6 milligrams per 8 fl. oz. or 240 mL). Many other foods and beverages may also contain proanthocyanidins, but few attain the levels found in red grape seeds and skins, with a notable exception being aronia , which has the highest recorded level of proanthocyanidins among fruits assessed to date (664 milligrams per 100 g). Nucleophile In chemistry ,

423-561: A given nucleophile and a substrate constant s that depends on the sensitivity of a substrate to nucleophilic attack (defined as 1 for methyl bromide ). This treatment results in the following values for typical nucleophilic anions: acetate 2.7, chloride 3.0, azide 4.0, hydroxide 4.2, aniline 4.5, iodide 5.0, and thiosulfate 6.4. Typical substrate constants are 0.66 for ethyl tosylate , 0.77 for β-propiolactone , 1.00 for 2,3-epoxypropanol , 0.87 for benzyl chloride , and 1.43 for benzoyl chloride . The equation predicts that, in

470-571: A low oxidation state and/or carrying a negative charge) are among the strongest recorded nucleophiles and are sometimes referred to as "supernucleophiles." For instance, using methyl iodide as the reference electrophile, Ph 3 Sn is about 10000 times more nucleophilic than I , while the Co(I) form of vitamin B 12 (vitamin B 12s ) is about 10 times more nucleophilic. Other supernucleophilic metal centers include low oxidation state carbonyl metalate anions (e.g., CpFe(CO) 2 ). The following table shows

517-613: A low solubility in water. They involve a moderate (50 to 90 °C) heating for a few minutes. Epimerisation may happen. Phloroglucinolysis can be used for instance for proanthocyanidins characterisation in wine or in grape seeds and skin. Thioglycolysis can be used to study proanthocyanidins or the oxidation of condensed tannins. It is also used for lignin quantitation . Reaction on condensed tannins from Douglas fir bark produces epicatechin and catechin thioglycolates . Condensed tannins from Lithocarpus glaber leaves have been analysed through acid-catalyzed degradation in

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564-560: A mass spectrometer with an electrospray ionization source, only able to form ions with smaller molecules. The butanol– hydrochloric acid –iron assay (Porter assay) is a colorimetric assay. It is based on acid catalysed oxidative depolymerization of condensed tannins into corresponding anthocyanidins . The method has also been used for determination of bound condensed tannins, but has limitations. This reagent has recently been improved considerably by inclusion of acetone. The condensed tannins can nevertheless undergo acid-catalyzed cleavage in

611-402: A new chemical bond with the carbon at the end of the bromopropane molecule. The bond between the carbon and the bromine then undergoes heterolytic fission , with the bromine atom taking the donated electron and becoming the bromide ion (Br ), because a S N 2 reaction occurs by backside attack. This means that the hydroxide ion attacks the carbon atom from the other side, exactly opposite

658-931: A nucleophilicity parameter N , an electrophilicity parameter E , and a nucleophile-dependent slope parameter s . The constant s is defined as 1 with 2-methyl-1-pentene as the nucleophile. Many of the constants have been derived from reaction of so-called benzhydrylium ions as the electrophiles : and a diverse collection of π-nucleophiles: Typical E values are +6.2 for R = chlorine , +5.90 for R = hydrogen , 0 for R = methoxy and −7.02 for R = dimethylamine . Typical N values with s in parentheses are −4.47 (1.32) for electrophilic aromatic substitution to toluene (1), −0.41 (1.12) for electrophilic addition to 1-phenyl-2-propene (2), and 0.96 (1) for addition to 2-methyl-1-pentene (3), −0.13 (1.21) for reaction with triphenylallylsilane (4), 3.61 (1.11) for reaction with 2-methylfuran (5), +7.48 (0.89) for reaction with isobutenyltributylstannane (6) and +13.36 (0.81) for reaction with

705-429: A substance's nucleophilic character and is often used to compare the affinity of atoms . Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis . Nucleophiles may take part in nucleophilic substitution , whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition . Nucleophilicity is closely related to basicity . The difference between

752-507: A type of substitution reaction in organic chemistry , involving a carbocation intermediate under strongly acidic conditions in polar protic solvents like methanol. The reaction leads to the formation of free and derived monomers that can be further analyzed or used to enhance procyanidin absorption and bioavailability . The free monomers correspond to the terminal units of the condensed tannins chains. In general, reactions are made in methanol, especially thiolysis, as benzyl mercaptan has

799-517: A type of substitution reaction in organic chemistry, involving a carbocation intermediate under strongly acidic conditions in polar protic solvents like methanol . The reaction leads to the formation of free and derived monomers that can be further analyzed. The free monomers correspond to the terminal units of the condensed tannins chains. If thiolysis is done directly on plant material (rather than on purified tannins), it is, however, important to subtract naturally occurring free flavanol monomers from

846-647: Is a dietary supplement derived from extracts from maritime pine bark, is standardised to contain 70% procyanidin and is marketed with claims it can treat many conditions; however, according to a 2020 Cochrane review , the evidence is insufficient to support its use for the treatment of any chronic disorder. Condensed tannins can be characterised by a number of modern techniques including depolymerisation, asymmetric flow field flow fractionation , small-angle X-ray scattering and MALDI-TOF mass spectrometry. Their interactions with proteins can be studied by isothermal titration calorimetry and this provides information on

893-550: Is a testing method that measures the change in color when the product is mixed with certain chemicals. The greater the color changes, the higher the PCOs content is. However, the Procyanidolic Index is a relative value that can measure well over 100. Unfortunately, a Procyanidolic Index of 95 was erroneously taken to mean 95% PCO by some and began appearing on the labels of finished products. All current methods of analysis suggest that

940-809: Is catalyzed by acid or base . Enols are ambident nucleophiles, but, in general, nucleophilic at the alpha carbon atom. Enols are commonly used in condensation reactions , including the Claisen condensation and the aldol condensation reactions. Examples of oxygen nucleophiles are water (H 2 O), hydroxide anion, alcohols , alkoxide anions, hydrogen peroxide , and carboxylate anions . Nucleophilic attack does not take place during intermolecular hydrogen bonding. Of sulfur nucleophiles, hydrogen sulfide and its salts, thiols (RSH), thiolate anions (RS ), anions of thiolcarboxylic acids (RC(O)-S ), and anions of dithiocarbonates (RO-C(S)-S ) and dithiocarbamates (R 2 N-C(S)-S ) are used most often. In general, sulfur

987-733: Is derived from nucleus and the Greek word φιλος, philos , meaning friend. In general, in a group across the periodic table, the more basic the ion (the higher the pK a of the conjugate acid) the more reactive it is as a nucleophile. Within a series of nucleophiles with the same attacking element (e.g. oxygen), the order of nucleophilicity will follow basicity. Sulfur is in general a better nucleophile than oxygen. Many schemes attempting to quantify relative nucleophilic strength have been devised. The following empirical data have been obtained by measuring reaction rates for many reactions involving many nucleophiles and electrophiles. Nucleophiles displaying

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1034-522: Is the weakest nucleophile, and I the strongest; this order is reversed in polar, aprotic solvents. Carbon nucleophiles are often organometallic reagents such as those found in the Grignard reaction , Blaise reaction , Reformatsky reaction , and Barbier reaction or reactions involving organolithium reagents and acetylides . These reagents are often used to perform nucleophilic additions . Enols are also carbon nucleophiles. The formation of an enol

1081-474: Is very nucleophilic because of its large size , which makes it readily polarizable, and its lone pairs of electrons are readily accessible. Nitrogen nucleophiles include ammonia , azide , amines , nitrites , hydroxylamine , hydrazine , carbazide , phenylhydrazine , semicarbazide , and amide . Although metal centers (e.g., Li , Zn , Sc , etc.) are most commonly cationic and electrophilic (Lewis acidic) in nature, certain metal centers (particularly ones in

1128-473: The Red Delicious and Granny Smith varieties. An extract of maritime pine bark called Pycnogenol bears 65–75 percent proanthocyanidins (procyanidins). Thus a 100 mg serving would contain 65 to 75 mg of proanthocyanidins (procyanidins). Proanthocyanidin glycosides can be isolated from cocoa liquor . The seed testas of field beans ( Vicia faba ) contain proanthocyanidins that affect

1175-463: The cyanide anion, 7.5 for the methoxide anion, 8.5 for the azide anion, and 10.7 for the thiophenol anion. The values for the relative cation reactivities are −0.4 for the malachite green cation, +2.6 for the benzenediazonium cation , and +4.5 for the tropylium cation . In the Mayr–Patz equation (1994): The second order reaction rate constant k at 20 °C for a reaction is related to

1222-467: The digestibility in piglets and could have an inhibitory activity on enzymes. Cistus salviifolius also contains oligomeric proanthocyanidins. (mg/100g) Condensed tannins may be characterised by a number of techniques including depolymerisation , asymmetric flow field flow fractionation or small-angle X-ray scattering . DMACA is a dye that is particularly useful for localization of proanthocyanidin compounds in plant histology. The use of

1269-475: The enamine 7. The range of organic reactions also include SN2 reactions : With E = −9.15 for the S-methyldibenzothiophenium ion , typical nucleophile values N (s) are 15.63 (0.64) for piperidine , 10.49 (0.68) for methoxide , and 5.20 (0.89) for water. In short, nucleophilicities towards sp 2 or sp 3 centers follow the same pattern. In an effort to unify the above described equations

1316-523: The thiocyanate ion (SCN ) may attack from either the sulfur or the nitrogen. For this reason, the S N 2 reaction of an alkyl halide with SCN often leads to a mixture of an alkyl thiocyanate (R-SCN) and an alkyl isothiocyanate (R-NCS). Similar considerations apply in the Kolbe nitrile synthesis . While the halogens are not nucleophilic in their diatomic form (e.g. I 2 is not a nucleophile), their anions are good nucleophiles. In polar, protic solvents, F

1363-471: The Mayr equation is rewritten as: with s E the electrophile-dependent slope parameter and s N the nucleophile-dependent slope parameter. This equation can be rewritten in several ways: Examples of nucleophiles are anions such as Cl , or a compound with a lone pair of electrons such as NH 3 ( ammonia ) and PR 3 . In the example below, the oxygen of the hydroxide ion donates an electron pair to form

1410-555: The actual PCO content of these products is much lower than 95%. Gel permeation chromatography (GPC) analysis allows separation of monomers from larger proanthocyanidin molecules. Monomers of proanthocyanidins can be characterized by analysis with HPLC and mass spectrometry . Condensed tannins can undergo acid-catalyzed cleavage in the presence of a nucleophile like phloroglucinol (reaction called phloroglucinolysis), thioglycolic acid (thioglycolysis), benzyl mercaptan or cysteamine (processes called thiolysis ) leading to

1457-533: The affinity constant, enthalpy and stoichiometry in the tannin-protein complex. Depolymerisation reactions are mainly analytical techniques but it is envisaged to use them as means to produce molecules for the chemical industry derived from waste products, such as bark from the wood industry or pomaces from the wine industry. Depolymerisation is an indirect method of analysis allowing to gain information such as average degree of polymerisation , percentage of galloylation, etc. The depolymerised sample can be injected on

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1504-858: The aroma, flavor, mouth-feel and astringency of red wines. In red wines, total OPC content, including flavan-3-ols ( catechins ), was substantially higher (177  mg/L) than that in white wines (9  mg/L). Proanthocyanidins found in the proprietary extract of maritime pine bark called Pycnogenol were not found (in 2012) to be effective as a treatment for any disease: Proanthocyanidins are present in fresh grapes, juice, red wine , and other darkly pigmented fruits such as cranberry , blackcurrant , elderberry , and aronia . Although red wine may contain more proanthocyanidins by mass per unit of volume than does red grape juice, red grape juice contains more proanthocyanidins per average serving size. An eight US fluid ounces (240 ml) serving of grape juice averages 124 milligrams proanthocyanidins, whereas

1551-444: The bromine ion. Because of this backside attack, S N 2 reactions result in a inversion of the configuration of the electrophile. If the electrophile is chiral , it typically maintains its chirality, though the S N 2 product's absolute configuration is flipped as compared to that of the original electrophile. An ambident nucleophile is one that can attack from two or more places, resulting in two or more products. For example,

1598-415: The concentration of terminal units that are released during depolymerisation. Reactions are generally made in methanol , especially thiolysis, as benzyl mercaptan has a low solubility in water. They involve a moderate (40 to 90 °C (104 to 194 °F)) heating for a few minutes. Epimerisation may happen. Phloroglucinolysis can be used for instance for proanthocyanidins characterisation in wine or in

1645-953: The extraction of oligomeric proanthocyanidins from pine bark and grape seeds . Proanthocyanidins are under preliminary research for the potential to reduce the risk of urinary tract infections (UTIs) by consuming cranberries, grape seeds or red wine . Proanthocyanidins, including the lesser bioactive and bioavailable polymers (four or more catechins), represent a group of condensed flavan-3-ols, such as procyanidins , prodelphinidins and propelargonidins. They can be found in many plants, most notably apples , maritime pine bark and that of most other pine species, cinnamon , aronia fruit, cocoa beans , grape seed, grape skin (procyanidins and prodelphinidins ), and red wines of Vitis vinifera (the European wine grape). However, bilberry , cranberry , black currant , green tea , black tea , and other plants also contain these flavonoids. Cocoa beans contain

1692-570: The formation of oligomers that can be further analyzed. Tandem mass spectrometry can be used to sequence proanthocyanidins. Oligomeric proanthocyanidins (OPC) strictly refer to dimer and trimer polymerizations of catechins. OPCs are found in most plants and thus are common in the human diet. Especially the skin , seeds, and seed coats of purple or red pigmented plants contain large amounts of OPCs. They are dense in grape seeds and skin, and therefore in red wine and grape seed extract, cocoa, nuts and all Prunus fruits (most concentrated in

1739-534: The grape seed and skin tissues. Thioglycolysis can be used to study proanthocyanidins or the oxidation of condensed tannins. It is also used for lignin quantitation . Reaction on condensed tannins from Douglas fir bark produces epicatechin and catechin thioglycolates . Condensed tannins from Lithocarpus glaber leaves have been analysed through acid-catalyzed degradation in the presence of cysteamine . Proanthocyanidin Proanthocyanidins are

1786-407: The highest concentrations. Proanthocyanidins also may be isolated from Quercus petraea and Q. robur heartwood (wine barrel oaks ). Açaí oil , obtained from the fruit of the açaí palm ( Euterpe oleracea ), is rich in numerous procyanidin oligomers. Apples contain on average per serving about eight times the amount of proanthocyanidin found in wine, with some of the highest amounts found in

1833-609: The incidence of UTIs, indicating that cranberry products may be effective particularly for individuals with recurrent infections. In 2019, the American Urological Association released guidelines stating that a moderate level of evidence supports the use of cranberry products containing PACs for possible prevention from recurrent UTIs. Proanthocyanidins are the principal polyphenols in red wine that are under research to assess risk of coronary heart disease and lower overall mortality. With tannins , they also influence

1880-484: The presence of cysteamine . Cranberries have A2-type proanthocyanidins (PACs) which may be important for the ability of PACs to bind to proteins, such as the adhesins present on E. coli fimbriae and were thought to inhibit bacterial infections, such as urinary tract infections (UTIs). Clinical trials have produced mixed results when asking the question to confirm that PACs, particularly from cranberries, were an alternative to antibiotic prophylaxis for UTIs: 1)

1927-405: The presence of (an excess of) a nucleophile like phloroglucinol (reaction called phloroglucinolysis), benzyl mercaptan (reaction called thiolysis ), thioglycolic acid (reaction called thioglycolysis) or cysteamine . These techniques are generally called depolymerisation and give information such as average degree of polymerisation or percentage of galloylation. These are SN1 reactions ,

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1974-552: The presence of (or an excess of) a nucleophile like phloroglucinol (reaction called phloroglucinolysis), benzyl mercaptan (reaction called thiolysis ), thioglycolic acid (reaction called thioglycolysis) or cysteamine . Flavan-3-ol compounds used with methanol produce short-chain procyanidin dimers , trimers , or tetramers which are more absorbable. These techniques are generally called depolymerisation and give information such as average degree of polymerisation or percentage of galloylation. These are SN1 reactions ,

2021-530: The reagent results in blue staining. It can also be used to titrate proanthocyanidins. Proanthocyanidins from field beans ( Vicia faba ) or barley have been estimated using the vanillin-HCl method , resulting in a red color of the test in the presence of catechins or proanthocyanidins. Proanthocyanidins can be titrated using the Procyanidolic Index (also called the Bates-Smith Assay ). It

2068-590: The same relative reactivity regardless of the nature of the electrophile, which is in violation of the reactivity–selectivity principle . For this reason, this equation is also called the constant selectivity relationship . In the original publication the data were obtained by reactions of selected nucleophiles with selected electrophilic carbocations such as tropylium or diazonium cations: or (not displayed) ions based on malachite green . Many other reaction types have since been described. Typical Ritchie N values (in methanol ) are: 0.5 for methanol , 5.9 for

2115-501: The skin), and in the bark of Cinnamomum ( cinnamon ) and Pinus pinaster (pine bark; formerly known as Pinus maritima ), along with many other pine species. OPCs also can be found in blueberries , cranberries (notably procyanidin A2 ), aronia , hawthorn , rosehip , and sea buckthorn . Oligomeric proanthocyanidins can be extracted via Vaccinium pahalae from in vitro cell culture. The US Department of Agriculture maintains

2162-427: The so-called alpha effect are usually omitted in this type of treatment. The first such attempt is found in the Swain–Scott equation derived in 1953: This free-energy relationship relates the pseudo first order reaction rate constant (in water at 25 °C), k , of a reaction, normalized to the reaction rate, k 0 , of a standard reaction with water as the nucleophile, to a nucleophilic constant n for

2209-414: The two is, that basicity is a thermodynamic property (i.e. relates to an equilibrium state), but nucleophilicity is a kinetic property, which relates to rates of certain chemical reactions. The terms nucleophile and electrophile were introduced by Christopher Kelk Ingold in 1933, replacing the terms anionoid and cationoid proposed earlier by A. J. Lapworth in 1925. The word nucleophile

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