Chemical modifications for intensity variation and spectrum extension of brazilein extract from sappanwood (Caesalpinia sappan L.)

Abstract

Aqueous extract of sappanwood (Caesalpinia sappan L.) was treated using acid-base and mordant additions in order to expand the intensity and spectra of the colors. The colorant molecule of sappanwood was brazilein, which gained its color characteristics through its double bonds. The results of this study confirmed three basic mechanisms which formed the fundamental for systematic optimization of natural dye applications. Acid addition induced protonation of the hydroxyl groups in the brazilein structure so that the electrons were distributed in the molecule more evenly. Therefore, the color intensity was reduced. Basic treatment created deprotonation of the hydroxyl groups and hence localized the electron on several spots. This made the color of the extract shifted to deeper tones. The addition of mordant created more significant change in color spectrum through the mechanism of chelation to form coordinated complexes. Transitional metals from group 1 and 2 did not chelate strongly so that the spectrum shift was not very obvious. However, transitional metals from group 3 had strong chelating character and consequently they could strongly bind the dye molecules to increase its intensity and shift the spectrum towards deeper colors.