Tannins relationship with

The apparent source materials for forming such a hypothetical humic polymer would be lignin degradation products or plant polyphenols such as flavonoids. Because it has little relationship with the physical or chemical characteristics of actual humic materials, this type of model has fallen out of favor almost completely, except for ambiguous statements, still occasionally encountered, that the color of natural waters is due to tannins. ... 

Tannins. Collective name, derived from French ta-nin=to tan hides, for a group of natural polyphenols with widely varying composition, more frequently known as gallotannins on account of the relationship with gallic acid. The so-called tannin (gallotannic... 

Contradictory opinions have been referred to in the literature particularly on the nature of the iron-tarmate and its interaction with the rusted steel due to the diversity of the material used in different studies. Studies have included the use of tannic acid [7-10], gallic acid [11], oak tannin [12, 13], pine tannin [14] and mimosa tannin [15]. In order to establish the correlation between the ferric-taimate formation and the low inhibition efficiency observed at high pH from the electrochemical studies, phase transformations of pre-rusted steels in the presence of tannins were evaluated. In this work the quantum chemical calculations are conducted to analyse the relationship between the molecular stracture and properties of ferric-taimate complex and its inhibitory mechanism. 

Okuda, T., Mori, K., and Hatano, T., Relationships of the structures of tannins to the binding activities with hemoglobin and methylene blue. Chem. Pharm. Bull. 33, 1424, 1985. 

It is obvious that such a definition will include molecules which are not tannins in the commercial sense of being economically important in the tanning of hides, but will exclude a large number of substances whose only relationship to the tannins is their capacity to reduce alkaline permanganate or give colors with ferric salts. 

Singleton and Esau (I) reviewed the methods for phenol analysis of wine. They pointed out that study would be greatly advanced if one could determine the total content of phenolic substances and express it in such a way that analysis of subclasses of phenols could be related to the original total and a balance sheet could be obtained. One could then say, for example, this wine has a total phenolic content of 1200 mg/liter calculated as gallic acid, and of that total, cinnamic acid derivatives account for 200 mg/liter, anthocyanins for 300 mg/liter, other small flavonoids for 200 mg/liter, and condensed tannins complete the total with 500 mg/liter of gallic acid equivalent. To accomplish this, the total phenol analysis not only must meet ordinary criteria of reproducibility and precision, but it also must be based on chemical relationships such that fractions determined separately can be converted to units of the total. Of course when clearcut fractionation can be accomplished by... 

Protocatechuic Acid.—One of the di-hydroxy benzoic acids is related to vanillin, which we have already studied. The acid is known as protocatechuic acid, and derives its name from the fact that it may be obtained from a gum or resin, known as gum catechin by fusion with potash, i.e. by heat and oxidation in presence of an alkali. A large variety of plant products including alkaloids essential oils, gums, resins and tannins yield this acid. The following may be mentioned gum catechin, gum benzoin, guaiac resin, myrrh, piperine or piperic acid, vanillin, cafe-tannic acid. These natural sources at once suggest a relationship to vanillin (p. 661) and heliotropin (p. 662). It is the acid corresponding to protocatechuic aldehyde, 3-4-di-hydroxy benzal-dehyde (p. 661), which explains the relationship just mentioned. Its constitution, is then ... 

There appears to be a close relationship between color and flavor. Deeply colored samples generally have an unpleasant taste. The color may result from l annins which have an astringent taste. At least part of the color in inferior grades is associated with tannins contained in the bark-contaminated product, but even gums free from bark are often colored. Some hold that tannin is derived from bark in contact with the exudation, others that it is formed in the gum by chemical changes. 

The biosynthetic pathway for isoflavonoids in soybean and the relationship of the isoflavonoids to several other classes of phenylpropanoids is presented in Fig. 8.2. Production of /i-coumaryl-CoA from phenylalanine requires phenylalanine ammonia lyase to convert phenylalanine to cinnamate, cinnamic acid hydroxylase to convert cinnamate to /7-coumarate, and coumaraterCoA ligase to convert jt -coumarate to -coumaroyl-CoA. Lignins may be produced from j3-coumaroyl-CoA or from />-coumarate. Chalcone synthase catalyzes the condensation of three molecules of malonyl CoA with p-coumaroyl-CoA to form 4, 2 , 4 , 6 -tetrahydroxychalcone, which is subsequently isomerized in a reaction catalyzed by chalcone isomerase to naringenin, the precursor to genistein, flavones, flavonols, condensed tannins, anthocyanins, and others. 

In the TMA plot in Fig. 7 it is possible to note the interactive nature of the substrate on the curing of the PF adhesive. For example, the modulus of elasticity (MOE) increase curve shows two sections (and a two peak first derivative curve). This indicates formation of entanglement networks of the resin in wood which is not possible on noninteractive substrates such as glass as in Fig. 6. Of course DMA and TMA give equally good results when used on the same wood substrate [379,380]. The ABES technique is also linearly correlated with TMA and DMA results as has been demonstrated by the linear relationship that has been found for both MUF and tannin formaldehyde adhesives in the results of TMA and ABES [381]. 

Deshpande et al., 1982 Price et al., 1980). It appears from these reports that white-seeded strains contain no detectable tannins compared to colored seeds. Ma and Bliss (1978) reported that tannins were mostly associated with the testa layer of common dry beans, and that black seeds were usually higher than other seeds in tannin content. Although black seeds contained more tannin, few plants with colored, non-black seeds had high tannin contents. These observations were later supported by Deshpande et al. (1982). Similarly, several researchers (Thayer et al., 1957 Blessin et al., 1963 Stephenson et al., 1968 Harris, 1969 Damron et al., 1968 Mabbayad and Tipton, 1975 Nelson et al., 1975) reported no direct relationship between pericarp colors and tannin contents of grain sorghums. 

One of the first published preparations of gallic acid, however, is that of Sir Humphrey Davy (79) in the Journal of the Royal Institute (1803) he followed a directive from the trustees and governors to present a series of lectures on the chemical principles of the art of tanning. This incident vividly illustrates the intimate relationship, for both scientific and historical reasons, that studies of the chemistry and biochemistry of gallic acid and its derivatives have with those of the vegetable tannins and ultimately the proanthocyanidins (142). 

---