Polyfurfuryl alcohol (PFA) is one of the most intriguing polymers because, despite its easy polymerization in acid environment, its molecular structure is definitely not obvious. Many studies have been performed in recent decades, and every time, surprising aspects came out. With the present study, we aim to take advantage of all of the findings of previous investigations and exploit them for the interpretation of the completely cured PFA spectra registered with three of the most powerful techniques for the characterization of solid, insoluble polymers: Solid-State ¹³C-NMR, Attenuated Total Reflectance (ATR), Fourier Transform Infrared (FTIR) spectroscopy, and UV-resonant Raman spectroscopy at different excitation wavelengths, using both an UV laser source and UV synchrotron radiation. In addition, the foreseen structures were modeled and the corresponding ¹³C-NMR and FTIR spectra were simulated with first-principles and semi-empiric methods to evaluate their matching with experimental ones. Thanks to this multi-technique approach, based on complementary analytical tools and computational support, it was possible to conclude that, in addition to the major linear unconjugated polymerization, the PFA structure consists of Diels-Alder rearrangements occurring after the opening of some furanic units, while the terminal moieties of the chain involves γ-lactone arrangements. The occurrence of head-head methylene ether bridges and free hydroxyl groups (from unreacted furfuryl alcohol, FA, or terminal chains) could be excluded, while the conjugated systems could be considered rather limited.

We report on the use of the UV Raman technique to monitor the oxidative damage of deoxynucleotide triphosphates (dATP, dGTP, dCTP and dTTP) and DNA (plasmid vector) solutions. Nucleotide and DNA aqueous solutions were exposed to hydrogen peroxide (H₂O₂) and iron containing carbon nanotubes (CNTs) to produce Fenton's reaction and induce oxidative damage. UV Raman spectroscopy is shown to be maximally efficient to reveal changes in the nitrogenous bases during the oxidative mechanisms occurring on these molecules. The analysis of Raman spectra, supported by numerical computations, revealed that the Fenton's reaction causes an oxidation of the nitrogenous bases in dATP, dGTP and dCTP solutions leading to the production of 2-hydroxyadenine, 8-hydroxyguanine and 5-hydroxycytosine. No thymine change was revealed in the dTTP solution under the same conditions. Compared to single nucleotide solutions, plasmid DNA oxidation has resulted in more radical damage that causes the breaking of the adenine and guanine aromatic rings. Our study demonstrates the advantage of using UV Raman spectroscopy for rapidly monitoring the oxidation changes in DNA aqueous solutions that can be assigned to specific nitrogenous bases.

The actual chemical structure of polyfurfuryl alcohol (PFA) is still uncertain in spite of several studies on the topic, variations during the polymerization processes being one reason that must be addressed. The use of a limited set of analytical techniques is often insufficient to provide an exhaustive chemical characterization. Moreover, it is still not possible to exactly determine presence and amount of each specific functional group in the polymeric structure. We employed both Fourier Transform Infrared Spectroscopy (FTIR) and Resonant Raman spectroscopy (RR), corroborated by quantum mechanically aided analysis of the experimental spectra, to infer about the chemical structure of two samples of PFAs, synthetized in different ways and appearing macroscopically different, the first one being a liquid and viscous commercial sample, the second one being a self-prepared solid and rigid sample produced following a thermosetting procedure. The vibrational spectroscopic analysis confirms the presence of differences in their chemical structures. The viscous form of PFA is mainly composed by short polymeric chains, and is characterized by the presence of isolated furfuryl alcohol and furfural residues similar to 5-hydroxymethylfurfural; the thermosetted PFA is formed by more cross-linked structures, characterized by several ketones and alkene double bonds, as well as a significant presence of Diels-Alder structures. In summary, the present study evidences how the use of both FTIR and RR spectroscopy, the latter carried out at several laser excitation wavelengths, indicates an accurate way to spectroscopically investigate complex polymers enabling to satisfactorily infer about their peculiar chemical structure.