Spectral-luminescent study of interaction of squaraine dyes with biological substances

The spectral-luminescent and photo-physical characteristics of some squaraine dyes, which fluoresce in red spectral range—most suitable for medical-biological investigation, were studied. The charge distribution and structural parameters of these dyes were calculated by semi-empirical AM1 method.It was found that the absorption and fluorescence spectra of water soluble dyes I–III solutions remain invariable over wide concentrations range (10−4–10−6 M). This testifies that dyes' molecules in solution exist in monomer form; the wavelength maxima of absorption and fluorescence bands, extinction coefficients, strength of oscillators, radiational lifetimes of excited state, quantum yield of fluorescence and frequencies of 0–0 transitions were determined for them. The interaction of these water soluble dyes with biological objects was studied. It was found, that the addition of enzyme gialuronidaze (64 units) to water solution of dye II, at constant concentration (2×10−6 M) of dye, leads to the drop of absorptive and fluorescent abilities of solution and to the broadening of absorption spectrum. The addition of this enzyme to water solution of dye III leads to the appearance of a new emission band at λmax=702 nm in fluorescence spectrum and to the intensification of emission on this band at further increase of enzyme concentration in the solution. The binding parameters of dye molecules with bovine serum albumin were determined as well.