title: The time-dependent behaviour of hematoporphyrin-derivative in saline: a study of spectral modifications.
abstract: Hematoporphyrin-Derivative (HpD), a widely-used tumor-specific photosensitizer, is a complex mixture of porphyrins whose composition has yet to be clarified. This paper reports on the behaviour of HpD in saline. From a spectroscopic point of view, the fresh solution is characterized by two main absorption peaks, attributable to monomeric and dimeric forms. With aging, a new porphyrin species (NPS) appears. To define the NPS, absorption, excitation and emission spectra were measured in different conditions and time-resolved fluorescence measurements were also performed. This species exhibits an absorption/excitation peak at 405 nm, an emission peak at 575 nm and a fluorescence decay time of approximately 3.5 ns. Its formation is strongly influenced by many environmental factors: in particular, gases diluted in the solution, temperature, pH and concentration. The presence of Oxygen and a pH value outside the 6-8 range may be considered inhibiting factors. The NPS seems to be quite important in the understanding of HpD tumor-specificity, since the presence of an emission band similar to the NPS one seems to be favoured in tumor cells as compared with normal cells.
mesh_terms: D017324:Hematoporphyrin Derivative; D006415:Hematoporphyrins; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D012965:Sodium Chloride; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry
chemical_list: D006415:Hematoporphyrins; D046911:Macromolecular Substances; D012996:Solutions; D012965:Sodium Chloride; D017324:Hematoporphyrin Derivative