ACS Physical Chemistry Au最新文献

C₆₀ has been regarded as a suitable photosensitizer for photodynamic therapy due to its excitation in the phototherapeutic window (650–900 nm), high quantum yields of ¹O₂ generation, and low dark toxicity. However, the use of this molecule in biomedical applications has been limited by its high aggregation tendency in polar solvents (e.g., water), resulting in quenching of its excited states. In this study, a C₆₀-peptide conjugate, C₆₀-oligo-Lys, with a lower aggregation tendency was investigated by chemical, physical, and photophysical methods in comparison to a previously reported water-soluble C₆₀-PEG conjugate. Photoinduced ¹O₂ generation was evaluated by both phosphorescence at 1274 nm and the electron spin resonance method in an aqueous solution, with comparison to the control C₆₀-PEG, revealing the superior capacity of the C₆₀-oligo-Lys conjugate. Importantly, the photoinduced type I electron transfer reaction is occurring in C60-oligo-Lys very efficiently, even in the absence of an e^– donor, presumably due to the partially unprotonated amines in the peptide, to form O₂^•– and ^•OH, which are generated in a further enhanced way by the addition of a physiological concentration of NADH. These species are more harmful to the target cells, including hypoxic tissues with limited oxygen concentration. Femtosecond transient absorption spectroscopy revealed different excited state dynamics for C₆₀-oligo-Lys and C₆₀-PEG at short time scales in water. By an in vitro cellular assay, significant cytotoxicity of C₆₀-oligo-Lys was observed (IC₅₀ < 1 μM) on HeLa cells under visible light irradiation (527, 630, and 660 nm), while very limited cytotoxicity was observed for C₆₀-PEG (IC₅₀ > 25 μM) under the same conditions. The strongly enhanced photocytotoxicity of C₆₀-oligo-Lys can be ascribed to the higher generation of both type I and type II ROS in addition to the potential affinity of the positively charged oligo-Lys moiety for the negatively charged cell membrane. The C₆₀-oligo-Lys conjugate reported in this study therefore shows high potential as a core photosensitizer for photodynamic therapy.

The electronic transition dipole moment 4-point time correlation function for a dimeric photosynthetic complex, from which nonlinear optical time-domain signals may be obtained. This 4-point time correlation function draws on an experimentally fit spectral density of the surrounding phonons of the photosynthetic protein. The spectral density of the photosynthetic phonons renders a phonon-sideband characterized by its asymmetry, caused by the unequal contribution from the photosynthetic phonons (bath) to the low- and high-energy sides of the optical signals. This spectral density manifests its asymmetry explicitly in the 1-phonon profile, due to the intimate spectral connection between them, which will in turn reflect in the entire phononic part of the absorption spectrum. The asymmetry plays an important role in characterizing the exciton–phonon coupling strength and the phonon relaxation mechanism, thereby providing flexibility in modeling the degree of symmetry needed for the bath and imparting the capability of fine-tuning the nature of electron–phonon coupling caused by pigment–protein interaction. To this end, the obtained nonlinear optical electronic transition dipole moment time correlation functions (Liouville space pathways) whereby both excitonic and exciton–phonon couplings are accounted for are deemed convenient, more tractable, and computationally expedient, a unique advantageous feature in the case of a multimode system, which is often the case in photosynthetic complexes. Linear spectra and photon echo signals to probe pigment–protein complexes, in which pure electronic dephasing, vibrational relaxation effects, 1-phonon profile asymmetry, exciton–exciton coupling, and exciton–phonon coupling in bacterial reaction centers and photosynthetic complexes are provided.