Condensed tannins. 1. A study of complex leuco-anthocyanins present in condensed tannins

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Abstract
Examination of the heartwood extractives of 144 "hardwood" spp. by methods developed by Roux Nature (180: 93. 1957) show that 33% give strongly positive reactions for leuco-anthocyanins. Lower RF polymeric forms predominate, and in only 12%, mainly amongst the Leguminosae, is evidence found of the presence of monomeric leuco-anthocyanins. Black-wattle and quebracho tannins have been shown to be relatively rich in complex leuco-robinetinidins and leuco-fisetinidins (Roux, 1957b). Comparison of the yields of anthocyanidins from complex naturally occurring leuco-anthocyanins and from synthetic monomeric leuco-anthocyanins indicates that about 25% of the "fundamental units" present in these complex tannins are of the leuco-anthocyanin type. For each tannin mixture, a gradational increase of molecular weight with decrease of RF value of the tannins was found, when separated on paper chromatograms in 2% acetic acid. Molecular weights of wattle tannins fall mainly in the range 550-1630, although a small fraction of much higher (3240) molecular weight is also present. Values for quebracho tannins fall in the range 800-2350. Similar proportions of leuco-anthocyanins are present throughout the whole molecular-weight range of both tannins, indicating the presence of leuco-anthocyanins (e.g., leuco-robinetinidins and leuco-fisetinidins) of increasing complexity from the higher RF (0.5-0.6) to the lower RF (0) regions. With increase in molecular weight condensed tannins show a parallel increase in "affinity" for cellulose, and also for collagen (Roux, Jour. Soc. Leath. Tr. Chem. 39: 80. 1955).