title: Design, synthesis, and photophysical characterization of water-soluble chlorins.
abstract: The use of chlorins as photosensitizers or fluorophores in a range of biological applications requires facile provisions for imparting high water solubility. Two free base chlorins have been prepared wherein each chlorin bears a geminal dimethyl group in the reduced ring and a water-solubilizing unit at the chlorin 10-position. In one design (FbC1-PO3H2), the water-solubilizing unit is a 1,5-diphosphonopent-3-yl ("swallowtail") unit, which has previously been used to good effect with porphyrins. In the other design (FbC2-PO3H2), the water-solubilizing unit is a 2,6-bis(phosphonomethoxy)phenyl unit. Two complementary routes were developed for preparing FbC2-PO3H2 that entail introduction of the protected phosphonate moieties either in the Eastern-half precursor to the chlorin or by derivatization of an intact chlorin. Water-solubilization is achieved in the last step of each synthesis upon removal of the phosphonate protecting groups. The chlorins FbC1-PO3H2 and FbC2-PO3H2 are highly water-soluble (>10 mM) as shown by 1H NMR spectroscopy (D2O) and UV-vis absorption spectroscopy. The photophysical properties of the water-soluble chlorins in phosphate-buffered saline solution (pH 7.4) at room temperature were investigated using static and time-resolved absorption and fluorescence spectroscopic techniques. Each chlorin exhibits dominant absorption bands in the blue and the red region (lambda = 398, 626 nm), a modest fluorescence yield (Phi f approximately 0.11), a long singlet excited-state lifetime (tau = 7.5 ns), and a high yield of intersystem crossing to give the triplet state (Phi isc = 0.9). The properties of the water-soluble chlorins in aqueous media are comparable to those of hydrophobic chlorins in toluene. The high aqueous solubility combined with the attractive photophysical properties make these compounds suitable for a wide range of biomedical applications.
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
authors.forename: K Eszter
authors.initials: KE
authors.lastname: Borbas
authors.forename: Vanampally
authors.initials: V
authors.lastname: Chandrashaker
authors.forename: Chinnasamy
authors.initials: C
authors.lastname: Muthiah
authors.forename: Hooi Ling
authors.initials: HL
authors.lastname: Kee
authors.forename: Dewey
authors.initials: D
authors.lastname: Holten
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Lindsey
mesh_terms: D015394:Molecular Structure; D010777:Photochemistry; D011166:Porphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D012995:Solubility; D013053:Spectrophotometry; D014867:Water / Q000737:chemistry*
chemical_list: D011166:Porphyrins; D014867:Water; C006969:chlorin