resumo
Dioxane and milled wood Lignins were isolated from the core and bark of kenaf (Hibiscus cannabinus), variety Salvador. These lignins were characterized by C-13 and H-1 NMR, FTIR, and UV spectroscopies, permanganate oxidation, and alkaline hydrolysis followed by GC and GC-MS analysis of the released products and by functional groups analysis. The permanganate oxidation and alkaline hydrolysis was also applied to "in situ" lignins. Isolated and "in situ" lignins showed significant differences in composition and structure. Strong structural differences were observed between bark and core lignins, suggesting their different biosynthetic routes. The beta-O-4 type linkages are the main interunit linkages and are more abundant in bark than in core lignin. The core lignin is more "condensed" and shows higher contents of beta-beta plus beta-5 Linkages than those in the bark lignin. Permanganate oxidation showed that both core and bark "in situ" lignins are HGS-type lignins with HGS proportions of 15:66:19 and 12:56:32, respectively (H including coumarate structures in the case of core lignin). Coumarates represent about 50% of the H units of core lignin and are absent in bark lignins. The presence of suberin-like aliphatic chains covalently bound to lignin was suggested for bark lignin.
palavras-chave
MILLED WOOD LIGNIN; MACROMOLECULAR COMPONENTS; CHEMICAL-COMPOSITION; HYDROXYL-GROUPS; ARUNDO-DONAX; SPECTROSCOPY; POLYMER; WHEAT; PULP
categoria
Agriculture; Chemistry; Food Science & Technology
autores
Seca, AML; Cavaleiro, JAS; Domingues, FMJ; Silvestre, AJD; Evtuguin, D; Neto, CP
nossos autores
Armando Jorge Domingues Silvestre
Professor Catedrático
Carlos Pascoal Neto
Diretor do Raiz