New Insights on Solvent-Induced Changes in Refractivity and Specific Rotation of Poly(propylene oxide) Systems Extracted from Channeled Spectra.

Investigation of chiroptical polymers in the solution phase is paramount for designing supramolecular architectures for photonic or biomedical devices. This work is devoted to the case study of poly(propylene oxide) (PPO) optical activity in several solvents: benzonitrile, carbon disulfide, chloroform, ethyl acetate, and p-dioxane. To attain information on the interactions in these systems, rheological testing was undertaken, showing distinct variations of the rheological parameters as a function of the solvent type. These aspects are also reflected in the refractive index dispersive behavior, from which linear and non-linear optical properties are extracted. To determine the circular birefringence and specific rotation of the PPO solutions, the alternative method of the channeled spectra was employed. The spectral data were correlated with the molecular modeling of the PPO structural unit in the selected solvents. Density functional theory (DFT) computational data indicated that the torsional potential energy-related to the O1-C2-C3-O4 dihedral angle from the polymer repeating unit-was hindered in solvation environments characterized by high polarity and the ability to interact via hydrogen bonding. This was in agreement with the optical characterization of the samples, which indicated a lower circular birefringence and specific rotation for the solutions of PPO in ethyl acetate and p-dioxane. Also, the shape of optical rotatory dispersion curves was slightly modified for PPO in these solvents compared with the other ones.

Radiobiological approach to treatment gaps in locally advanced head and neck cancers radical radiotherapy arising from the COVID-19 pandemic.

Gaps of radiotherapy treatment are one of the factors recognized as unfavorable in terms of tumor control and disease prognosis. All strategies for compensating the negative effect of radiotherapy treatment gaps are based on radiobiological models. Using the modified square linear formalism (Dale`s equation) it is possible to calculate the additional dose in order to compensate the accelerated tumor repopulation effect. SARS-CoV-2 infection is an important factor that can lead to an interruption of irradiation for medium and long- term intervals. We aim to present the radiobiological data underlying the recalculation of radiotherapy treatment and exemplification for different clinical scenarios in the case of head and neck cancers (Ref. 17). Keywords: adiobiology, treatment gaps, locally advanced head and neck cancers, radical radiotherapy, COVID-19 pandemic.