Photostability of Bacteriochlorophyll a and Derivatives: Potential Sensitizers for Photodynamic Tumor Therapy

Abstract

The photostabilities of bacteriochlorophyll a and several of its derivatives, which are of interest as potential sensitizers in photodynamic tumor therapy, were investigated. The pigments were irradiated with light >630 nm in organic solvents (acetone, tetrahydrofuran, pyridine, methanol, ethanol, n-propanol, 2-propanol and toluene) and in aqueous detergent solutions (cetyl-trimethyl-ammonium bromide [CTAB], lauryldimethyl-aminoxide [LDAO] or sodium dodecyl-sulfate [SDS] and Triton X-100 [TX100]). Their stabilities in these different solvents were determined in the presence and absence of an external sensitizer (pyromethyl-pheophorbide a), oxygen, sodium ascorbate and inert gas (Ar) or vacuum. The photodegradation products of bacteriochlorophyll a in acetone solution were isolated, purified by HPLC and analyzed by their absorption spectra and mass spectroscopy. Besides the well-known dehydrogenation products, such as [3-acetyl]-chlorophyll a, which were obtained as by-products, the major products had low absorption in the visible-near infrared spectral range. The spectral signature of the major component of these products was characteristic of linear open-chain tetrapyrroles, but they lacked the characteristic protonation-deprotonation behavior and reactivity of bilins with Zn(++).

Molecular Electronic Tuning of Photosensitizers to Enhance Photodynamic Therapy: Synthetic Dicyanobacteriochlorins as a Case Study

“…Prior studies of the photodegradation of bacteriochlorophyll a and derivatives show that the process is highly solvent‐dependent and requires O 2 . Typical photoproducts include chlorins such as 2‐acetylchlorophyll a and other derivatives formed by two‐electron oxidation of the macrocycle, bilin‐like open‐chain tetrapyrroles likely formed via addition of singlet oxygen and ring opening, and other species that have no featured absorption in the visible region . The geminal dimethyl groups in the synthetic bacteriochlorins are incorporated to avoid dehydrogenation to form chlorins and porphyrins , which when observed are produced in such low yield that the expected features are cleanly resolved only via fluorescence.…”

An unusual role for the phytyl chains in the photoprotection of the chlorophylls bound to Water-Soluble Chlorophyll-binding Proteins

“…The phytyls are also in close contact with the central Mg ions of the Chls and shield the Mg from the solvent. In a study conducted on bacteriochlorophylls (BChl) it has been proposed that interactions between oxygen and Mg increase the residence time of singlet oxygen near the BChls and, thus, lowers the photostability of the pigments 66 . Consequently, phytyls in WSCP may exert their photoprotective role also by masking the Mg ions rather than methine 20.…”

Characterisation of uniformly 13C, 15N labelled bacteriochlorophyll a and bacteriopheophytin a in solution and in solid state: complete assignment of the 13C, 1H and 15N chemical shifts

“…The characterisation of pigments is important for fundamental research, for the study ligand-protein interactions [1] and functional diversity, [2] for medical applications of porphyrin derivatives as drugs [3] and for food industry. [4] It demonstrates characterisation of natural products in the context of the growing importance of natural products in new medical technologies, in food and feed ingredients and as biofuels.…”