Role of the H-Bond Interactions in the Colloidal Mixtures of Pyrazole-Based Bioactive Dyes and Poly(vinyl alcohol)

Three pyrazole-based dyes that inhibit human carbonic anhydrase enzyme have been blended with poly(vinyl alcohol) (PVA), used as an organic molecule carrier. The dyes and the polymer backbone of PVA interact to each other via hydrogen bond formations, which are apparent from the present spectral data. The hydrogen bonding interactions (i) cause the appearance of new bands in the ultraviolet-visible (UV-vis) absorption spectra of the dye molecules; (ii) modify some isotropic chemical shifts in the one-dimensional proton nuclear magnetic resonance spectra typically by around 0.5 ppm; and (iii) shift the diffusion coefficients in the two-dimensional proton diffusion ordered spectroscopy spectra, which correlates with the size of the colloidal polymer matrix. The measured changes in the diffusion rates of the dyes upon interacting with the PVA polymer open an arena for experimentalists to study PVA as a drug delivery agent. The sensitivity of electronic absorption bands of the dyes to the H-bond environment and their assignments to the frontier orbitals have been examined in terms of the time-dependent density functional calculations.