Combined Raman spectroscopic and theoretical investigation of fundamental vibrational bands of furfuryl alcohol (2-furanmethanol).

Furfuryl alcohol (FA) is a promising reactive precursor for new materials. FA reaction mechanisms, that is, self-reactions or cross reactions with other substances, can be studied by vibrational spectroscopy. We present a necessary prerequisite for such studies by a Raman spectroscopic and theoretical study of FA in weakly interacting environments. It is the first study of FA vibrational properties based on density functional theory (DFT/B3LYP), and a recently proposed hybrid approach to the calculation of fundamental frequencies, which also includes an anharmonic contribution. FA occupies five different conformational states, each with more than 5% probability, and two of these dominate at T = 298 K. Excluding one frequency, the remaining ones are predicted as a weighted average over the two dominant conformers to a best RMS error of 8 cm(-1) and are qualitatively assigned. The excluded CH stretching mode is underestimated by 65 cm(-1). This may be due to a combination of an insufficient level of theory and the neglect of Fermi interactions for properly describing this type of mode.

Spectroscopic properties of oxidation species generated in the lignin of wood fibers by a laccase catalyzed treatment: electronic hole state migration and stabilization in the lignin matrix.

A laccase catalyzed oxidative treatment of wood pulp fibers has been found to induce unusual modifications of these fibers that are qualitatively different from those encountered when more severely degraded fibers are subjected to similar enzymatically catalyzed oxidative treatments. These results suggest that the physical/conformational state of the lignin of wood fibers determines which oxidation pathways dominate in a given oxidative treatment, leading to different lignin modifications depending on both the chemical and the physical structure of the lignin polymer. Spectroscopic measurements (ESR, IR, UV-Vis and fluorescence) show that the laccase treatment results in the formation of two different species in the dried fibers: one is interpreted as chemically transformed (via oxygen) lignin products, and the other as initial oxidation radicals which have gained stabilization against transformation into the first mentioned products via a migration mechanism. It is argued that these initial radicals may likely be cation radical (or hole state) parts in lignin. The migration mechanism is identified with site-to-site transfer or 'hopping' via electron transfer and it is postulated that this mechanism 'carries' cation radical parts of the lignin, produced at the surface of the fiber, into parts of the lignin where chemical transformation pathways are suppressed due to the lignin conformational state. The possible existence of such a migration mechanism, the relative dominance of which should depend sensitively on the polymer conformational state, may have implications for the biogeneration and biodegradation of lignin as well as for oxidative treatments of non-natural conjugated polymers.