Two-dimensional codistribution spectroscopy applied to UVRR and ROA investigations of biomolecular transitions

• 2DCOS identifies sequential orders of spectral intensity variations.
• 2DCDS identifies the distributed presence of species along the perturbation axis.
• For biomolecular studies 2DCOS and 2DCDS provide complimentary information.
• 2DCDS can be successfully applied to Raman optical activity.

The first Raman optical activity (ROA) two-dimensional correlation spectroscopy (2DCOS) study in 2006, monitoring the temperature-induced α-helix-to-β-sheet transition in poly(l-lysine), demonstrated the versatility of 2DCOS. The combination of ROA and 2DCOS provided new ROA band assignments, enabled a direct comparison between the simultaneously collected Raman and ROA data using heterocorrelations and probed sequential information. This study also confirmed that 2DCOS can be successfully used with bisignate data, although specific care is needed when interpreting the results. However, as time has passed, doubts have been raised about not only the sequential orders reported in the study but also the general reliability of sequential data. This issue has now been addressed with the introduction of 2D codistribution (2DCDS) which is specifically designed to provide the sequence of the distributed presence of species along the perturbation variable axis. In light of these new developments in 2D correlation techniques we have revisited the original ROA data and we present our updated results. Furthermore, we demonstrate how 2DCDS can be successfully applied to bisignate data using new spectral data sets of perturbation-induced transitions in polynucleotides.