Dedicated t o P r o f . Dr. K a r l K r a t e l ABSTRACT C h a r g e -t r a n s f e r complexes were found t o o c c u r between k r a f t l i g n i n and a n added model quinone, 3 , 5 -d i -~-b u t y 1 -1 , 2 -b e n z o q u i n o n e . The o c c u r r e n c e of c h a r g e -t r a n s f e r i n t e r a c t i o n s was a l s o a p p a r e n t i n an o x i d i z e d k r a f t l i g n i n w i t h a n i n c r e a s e d quinone c o n t e n t . I n t h e s e systems, f r e e p h e n o l i c groups w i t h i n t h e l i g n i n were cons i d e r e d t h e donor s p e c i e s and ortho-quinones t h e complementary a c c e p t o r m o i e t i e s . Carbon-I4 l a b e l i n g r e v e a l e d t h a t t h e quinone c o n t e n t of t h e i n v e s t i g a t e d k r a f t l i g n i n averaged 3%. These q u i n o n e s were determined t o have a molar a b s o r p t i v i t y of 528 L/mol-cm. Upon sodium borohydride r e d u c t i o n of t h i s l i g n i n , o n l y o n e -t h i r d of t h e absorbance d e c r e a s e c o u l d be accounted f o r by t h i s number of quinones. The remaining t w o -t h i r d s of t h e d e c r e a s e i n absorbance was a s s i g n e d t o t h e d i s r u p t i o n of c h a r g e -t r a n s f e r complexes. The quinones, t h e r e f o r e , played a d u a
Chelation and removal of transition metals from the kraft lignin employed in this study did not reduce the lignin's visible absorbance.Likewise, hydrogenation of carbon-carbon double bonds in this lignin also had no effect on its visible spectrum. This indicated that extended conjugated systems were not a significant contributor to the color of this lignin. Of the structures investigated, quinones were found to be the major visible-light absorbing chromophores. Since a large component of the quinone's absorption results 1 from their participation in charge-transfer complexes (CTC's), CTC's were a significant contributor to the color of this lignin.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.