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Time-domain evaluation of drug–solvent interactions of the photosensitizers TPCS2a and TPPS2a as part of physicochemical characterization

Paper ID Volume ID Publish Year Pages File Format Full-Text
27517 44028 2010 8 PDF Available
Title
Time-domain evaluation of drug–solvent interactions of the photosensitizers TPCS2a and TPPS2a as part of physicochemical characterization
Abstract

The patented photosensitizer meso-tetraphenyl chlorin disulphonate (TPCS2a) is intended for use in the technology of photochemical internalization (PCI). The compound is advantageous with respect to the related meso-tetraphenyl porphyrin disulphonate (TPPS2a), due to its high absorption in the red part of the absorption spectrum (λabs ≈ 650 nm). We report a time-resolved fluorescence study of TPCS2a aimed to elucidate the susceptibility of the photosensitizer's excited state dynamics to properties of its environment, such as polarity and hydrogen bond formation. TPPS2a is used as a reference compound. Fluorescence decays with <30 ps temporal resolution of TPCS2a and TPPS2a in 14 organic solvents of varying polarity and amphiprotic properties were measured by time-correlated single-photon counting (TCSPC). Both compounds show triple exponential fluorescence decays in non-polar environment, i.e. τL ∼ 7 ns, τI ∼ 2 ns and τS ∼ 0.5 ns. The two shorter decay components, τI and τS, which we associated with two different intramolecular charge transfer mechanisms, readily disappear when the solvent polarity is slightly increased. The fluorescence decays of both compounds in any solvent of dielectric constant ɛ > 7.58 are well fitted by a single exponential model, with decay time roughly constant, τL ∼ 10 ns, and independent of the amphiprotic properties of the solvents. The present results allow concluding that the fluorescence decay pathways of TPCS2a and TPPS2a are only slightly affected by the environmental properties under consideration, as previously probed by steady-state measurements (Lilletvedt et al. [1]). Singlet oxygen (1O2) generation of the two photosensitizers were measured indirectly in water by applying the singlet oxygen sensor green (SOSG) reagent. Both photosensitizers generate 1O2 to some extent upon excitation in vitro.

Keywords
α, solvent proton donor parameter; API, active pharmaceutical ingredient; β, solvent proton acceptor parameter; DMF, dimethyl formamide; DMSO, dimethyl sulfoxide; ɛ, solvent dielectric constant; ESICT, excited state intramolecular charge transfer; ESIET,
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Time-domain evaluation of drug–solvent interactions of the photosensitizers TPCS2a and TPPS2a as part of physicochemical characterization
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 214, Issue 1, 5 July 2010, Pages 40–47
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us