A theoretical insight into the photophysics of psoralen

Thio and Seleno Derivatives of Angelicin as Efficient Triplet Harvesting Photosensitizers: Implications in Photodynamic Therapy

Photodynamic therapy (PDT) is widely accepted in medical practice for its targeted induction of apoptosis in cancerous cells. Angelicin (Ang) has traditionally been known for its efficacy in cancer treatment and its capability to enter a photoexcited triplet state. This study has comprehensively assessed the effects of substituting individual chalcogen atoms at three specific positions in Angelicin, with the objective of facilitating access to this elusive triplet state to enhance its role as a photosensitizer in PDT. The study scrutinizes various enhancements and factors that are crucial for efficient triplet harvesting. The decrease in singlet-triplet energy gap (ΔEST) and increased spin-orbit coupling (SOC) values present numerous viable pathways for intersystem crossing (ISC), leading to the triplet manifold. The lifetime of ISC, thus, decreases from 10-5 s-1 in Ang to 10-8 s-1 in thioangelicin (TAng) and finally to 10-9 s-1 in selenoangelicin (SeAng). Additionally, this study investigates the two-photon absorption properties of thio and seleno-substituted Angelicin for their potentialities as non-UV photosensitizers. The interplay between electron-withdrawing and electron-donating substitutions in these derivatives significantly enhances the two-photon absorption cross-sections (σ) to as high as 49.3 GM while shifting the absorption wavelengths towards the infrared region enabling them as efficient PDT photosensitizers.

Thio and Seleno-Psoralens as Efficient Triplet Harvesting Photosensitizers for Photodynamic Therapy

The Psoralen (Pso) molecule finds extensive applications in photo-chemotherapy, courtesy of its triplet state forming ability. Sulfur and selenium replacement of exocyclic carbonyl oxygen of organic chromophores foster efficient triplet harvesting with near unity triplet quantum yield. These triplet-forming photosensitizers are useful in Photodynamic Therapy (PDT) applications for selective apoptosis of cancer cells. In this work, we have critically assessed the effect of the sulfur and selenium substitution at the exocyclic carbonyl (TPso and SePso, respectively) and endocyclic oxygen positions of Psoralen. It resulted in a significant redshifted absorption spectrum to access the PDT therapeutic window with increased oscillator strength. The reduction in singlet-triplet energy gap and enhancement in the spin-orbit coupling values increase the number of intersystem crossing (ISC) pathways to the triplet manifold, which shortens the ISC lifetime from 10-5 s for Pso to 10-8 s for TPso and 10-9 s for SePso. The intramolecular photo-induced electron transfer process, a competitive pathway to ISC, is also considerably curbed by exocyclic functionalizations. In addition, a maximum of 115 GM of two-photon absorption (2PA) with IR absorption (660-1050 nm) confirms that the Psoralen skeleton can be effectively tweaked via single chalcogen atom replacement to design a suitable PDT photosensitizer.

Microbial efflux systems and inhibitors: approaches to drug discovery and the challenge of clinical implementation

Conventional antimicrobials are increasingly ineffective due to the emergence of multidrug-resistance among pathogenic microorganisms. The need to overcome these deficiencies has triggered exploration for novel and unconventional approaches to controlling microbial infections. Multidrug efflux systems (MES) have been a profound obstacle in the successful deployment of antimicrobials. The discovery of small molecule efflux system blockers has been an active and rapidly expanding research discipline. A major theme in this platform involves efflux pump inhibitors (EPIs) from natural sources. The discovery methodologies and the available number of natural EPI-chemotypes are increasing. Advances in our understanding of microbial physiology have shed light on a series of pathways and phenotypes where the role of efflux systems is pivotal. Complementing existing antimicrobial discovery platforms such as photodynamic therapy (PDT) with efflux inhibition is a subject under investigation. This core information is a stepping stone in the challenge of highlighting an effective drug development path for EPIs since the puzzle of clinical implementation remains unsolved. This review summarizes advances in the path of EPI discovery, discusses potential avenues of EPI implementation and development, and underlines the need for highly informative and comprehensive translational approaches.

Multiconfigurational Second-Order Perturbation Theory Restricted Active Space (RASPT2) Method for Electronic Excited States: A Benchmark Study

The recently developed second-order perturbation theory restricted active space (RASPT2) method has been benchmarked versus the well-established complete active space (CASPT2) approach. Vertical excitation energies for valence and Rydberg excited states of different groups of organic (polyenes, acenes, heterocycles, azabenzenes, nucleobases, and free base porphin) and inorganic (nickel atom and copper tetrachloride dianion) molecules have been computed at the RASPT2 and multistate (MS) RASPT2 levels using different reference spaces and compared with CASPT2, CCSD, and experimental data in order to set the accuracy of the approach, which extends the applicability of multiconfigurational perturbation theory to much larger and complex systems than previously. Relevant aspects in multiconfigurational excited state quantum chemistry such as the valence-Rydberg mixing problem in organic molecules or the double d-shell effect for first-row transition metals have also been addressed.