J. P. Ryall

Infrared and Raman Spectroscopy of Eugenol, Isoeugenol, and Methyl Eugenol: Conformational Analysis and Vibrational Assignments from Density Functional Theory Calculations of the Anharmonic Fundamentals.

IR and Raman spectra of eugenol, isoeugenol and methyl eugenol have been obtained in the liquid phase. Vibrational spectroscopic results are discussed in relation to computed structures and spectra of the low energy conformations of these molecules obtained from DFT calculations at the B3LYP/cc-pVTZ level. Although computed differences in vibrational spectra for the different conformers were generally small, close examination, in conjunction with the experimental spectra, enabled conformational analysis of all three molecules. Anharmonic contributions to computed vibrational spectra were obtained from calculations of cubic and quartic force constants at the B3LYP/DZ level. This permitted the determination of the anharmonic fundamentals for comparison with the experimental IR and Raman band positions, leading to an excellent fit between calculated and experimental spectra. Band assignments were obtained in terms of potential energy distributions (peds).

Vibrational spectra and structures of the anions of urazole and 4-methylurazole: DFT calculations of the normal modes and the influence of hydrogen bonding

Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the anions of urazole and 4-methylurazole, and their N-deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVTZ level, established that the structures and vibrational spectra of both anions can be interpreted using a model that incorporates hydrogen-bonded water molecules, in conjunction with the polarizable continuum solvation method. In the case of the urazole anion it is shown that deprotonation occurs primarily at N1 rather than N4, but there is also evidence for the second tautomer both in the solid state and in aqueous solution. The vibrational spectra were computed at the optimised molecular geometry in each case, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments.

Raman spectroscopic studies of chemically modified pullulans

In the studies reported herein pullulan has been structurally modified by chemical incorporation of various functional moieties and analysed by Raman spectroscopy. One reason for conducting such an investigation is to compare and contrast the usefulness of Raman compared to NMR [2] techniques for the analysis of the structural composition of the derivatized pullulans. Raman spectroscopy has proved to be particularly useful in identifying different chemical functionalities and assessing the degree of polymer modification.

A novel use of Raman spectroscopy: analysis of the structural composition of comonomer microgels

Co-monomer microgels, which have molecular weights of tens of millions of Daltons, present scientific challenges in attempts to analyse their monomer composition both qualitatively and quantitatively. However, uniquely, Raman spectroscopy may be a potentially useful technique for such purposes. Colloidal polymeric microgel systems [1] are particularly appealing from a research perspective because they provide an opportunity to investigate conformational changes in cross-linked polymeric systems. Microgels composed of co-monomers are currently of significant academic and industrial interest [2] due to their potential uses in diverse interdisciplinary areas of scientific interest [3] including drug delivery and as scaffolds for catalysis [4]. However the analysis of the structural composition of microgels is a non-trivial experimental problem. It is proposed that in the case of co-monomer microgels, Raman spectroscopy can be used as a quick and easy method to ensure that co-polymerization has occurred and also to determine, semi-quantitatively, the percentage incorporation of the monomers. Poly(N-isopropylacrylamide/methylenebisacrylamide) [poly(NIPAM/BA)] and poly(4vinylpyridine/methylenethylenebisacrylamide) [poly(4-VP/BA)] as well as poly(Nisopropylacrylamide/methylenebisacrylamide/4vinylpyridine) [poly(NIPAM/BA/4-VP)] microgels (the latter synthesized using 0.15 0.55 mole fraction of 4-VP) were prepared by surfactant-free emulsion polymerization followed by purification and characterization as described previously [2]. Freeze-dried samples of the microgels were subjected to analysis by Raman spectroscopy, at room temperature, using 632.8 nm exciting radiation from a helium-neon laser. Freeze-dried microgels differing in co-monomer composition (with constant mole fraction of BA) differ substantially in their Raman spectral profiles. An example (Fig. 1) shows the difference in Raman spectroscopic output between poly(NIPAM/BA) and poly(4-VP/BA) homopolymer microgels in the 2600-3200 cm region. Note the clear presence of the Raman band at ~3050 cm due to aromatic C-H stretching vibrational modes of 4-VP. In addition it is noteworthy that there are two low intensity (weak) bands at 2723 and 2766 cm (tentatively assigned to overtones of C-H bending vibrations in the 1300-1400 cm region) present in the Raman spectrum of poly(NIPAM/BA), but absent in the spectrum of poly(4-VP/BA) microgels.