Spectral properties and chromophoric characterization of Lannea fulva and Terminalia brownii Dye Extracts

Abstract

Lannea fulva, and Terminalia brownii, have been used for decades not only in herbal medicine, but also as a major source of dye for traditional handwork, especially by Marakwet community in Kenya. However, as a source of dye, there exists wide gap in knowledge on the specific chromophores and spectral properties such as: molecular mass, molecular structure and dye disintegration pattern of individual dyestuff compounds responsible for dyeing capability. Similarly, the lack of individual dye components identification has hindered the exploitation of the dyes in modern textile industries in the face of the huge challenges posed by synthetic dyes such as their carcinogenicity to human health and toxicity to environment, more so when applied in textile and printing industries. The main purpose of this study was to assess the dyeing properties and to characterize the compounds responsible for the property in L. fulva and T. brownii dye extracts. Maceration and soxhlet method were used to extract dyes using both organic and aqueous solvents. Qualitative analysis of the extracts was done using UV-VIS, FT-IR, and LC-MS spectroscopic methods. UV-VIS analysis identified delocalization of different types of functional groups like carbon-carbon double bonds (C=C), carbon-oxygen double bonds (C=O) lone pairs electron on oxygen and benzene rings as the main chromophores responsible for colour. These were confirmed by FT-IR with characteristic absorption spectra displayed at 1598.31 cm -1 , attributed to C=C conjugated system common in benzene rings, absorption band at 1401.66 cm -1 due to C=O double bond of carboxylic acid and C- OH stretch from polysaccharides shown at frequency 1069.61cm -1 to 605.67 cm -1 confirmed by LC-MS to be water soluble sugars. L. fulva glycosides identified for the first time include: Rubiadin primeveroside, ruberythric acid, lucidin primeveroside. Rubiadin, alizarin, lucidin and xanthopurpurin were also identified in L. fulva as aglycones. In T. brownii for example, the chromophoric compounds identified include: Catechin, epiChatechin, genipin and baccatins. Gentianose, geniposide and genipin were reported for the first time to be present in T. brownii. The identification on T. brownii compounds were based on two peaks at UV-VIS λ max 258.5nm which was identified as C=C owing to delocalized electron from fluorescent aromatic compounds (benzene rings) confirmed by FT-IR by absorption band occurring at 1597.61 cm -1 and 1400.77 cm -1 which is attributed to stretching of C=C of aromatic/benzene rings. The second peak with absorbance at λ max 361 nm was attributed to C=O due to lone pairs electron on the oxygen atom causing absorbance to occurs at longer wavelength. This was further confirmed by FT-IR at frequency 3131.94 cm -1 due to stretching vibration of OH from carboxylic acid [COOH] and C-H stretch or CHO spectra displayed at frequency 2935.48 cm -1 vibration due to carbohydrates present in geniposide and gentianose which confirmed their decarboxylation in LC-MS. Maceration method of extraction was better in extracting natural dyes compounds from L. fulva and T. brownii dye extracts. The identification of chromophores and other functional groups was valuable in unlocking full chemical information embedded in the dye structure. The spectral properties, in particular degradation pattern, have bearing in determination of nature of dye dyestuff.