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"Photosensitization"
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Fear nothing : a novel
While investigating the death of his mother who was a scientist, Chris Snow discovers she was engaged in secret experiments on a nearby military base, experiments which went wrong and which produced monsters. The next he knows, the monsters come visiting and they are not friendly.
Book
Photosensitized, energy transfer-mediated organometallic catalysis through electronically excited nickel(II)
Transition metal catalysis has traditionally relied on organometallic complexes that can cycle through a series of ground-state oxidation levels to achieve a series of discrete yet fundamental fragment-coupling steps. The viability of excited-state organometallic catalysis via direct photoexcitation has been demonstrated. Although the utility of triplet sensitization by energy transfer has long been known as a powerful activation mode in organic photochemistry, it is surprising to recognize that photosensitization mechanisms to access excited-state organometallic catalysts have lagged far behind. Here, we demonstrate excited-state organometallic catalysis via such an activation pathway: Energy transfer from an iridium sensitizer produces an excited-state nickel complex that couples aryl halides with carboxylic acids. Detailed mechanistic studies confirm the role of photosensitization via energy transfer.
Journal Article
Seize the night
Poet Christopher Snow, a man who cannot stand daylight, teams up with his genetically engineered dog, Orson, to investigate the abduction of children in Moonlight Bay, California. The children are believed to be prisoners in an army base populated by intelligent animals, produced by scientific experiments. Snow and Orson penetrate the base to search for them. A sequel to Fear Nothing.
Oxygen-independent organic photosensitizer with ultralow-power NIR photoexcitation for tumor-specific photodynamic therapy
Photodynamic therapy (PDT) is a promising cancer treatment but has limitations due to its dependence on oxygen and high-power-density photoexcitation. Here, we report polymer-based organic photosensitizers (PSs) through rational PS skeleton design and precise side-chain engineering to generate •O
2
−
and •OH under oxygen-free conditions using ultralow-power 808 nm photoexcitation for tumor-specific photodynamic ablation. The designed organic PS skeletons can generate electron-hole pairs to sensitize H
2
O into •O
2
−
and •OH under oxygen-free conditions with 808 nm photoexcitation, achieving NIR-photoexcited and oxygen-independent •O
2
−
and •OH production. Further, compared with commonly used alkyl side chains, glycol oligomer as the PS side chain mitigates electron-hole recombination and offers more H
2
O molecules around the electron-hole pairs generated from the hydrophobic PS skeletons, which can yield 4-fold stronger •O
2
−
and •OH production, thus allowing an ultralow-power photoexcitation to yield high PDT effect. Finally, the feasibility of developing activatable PSs for tumor-specific photodynamic therapy in female mice is further demonstrated under 808 nm irradiation with an ultralow-power of 15 mW cm
−2
. The study not only provides further insights into the PDT mechanism but also offers a general design guideline to develop an oxygen-independent organic PS using ultralow-power NIR photoexcitation for tumor-specific PDT.
Conventional photodynamic therapy (PDT) is hindered by oxygen-dependent photosensitization pathways and high-power-density photoexcitation. Here, the authors develop polymer-based organic photosensitizers (PSs) through PS skeleton design and side-chain engineering to allow tumor-specific PDT under oxygen-free conditions using ultralow-power 808 nm photoexcitation.
Journal Article
Boron-enabled geometric isomerization of alkenes via selective energy-transfer catalysis
Isomerization-based strategies to enable the stereodivergent construction of complex polyenes from geometrically defined alkene linchpins remain conspicuously underdeveloped. Mitigating the thermodynamic constraints inherent to isomerization is further frustrated by the considerations of atom efficiency in idealized low–molecular weight precursors. In this work, we report a general ambiphilic C3 scaffold that can be isomerized and bidirectionally extended. Predicated on highly efficient triplet energy transfer, the selective isomerization of β-borylacrylates is contingent on the participation of the boron p orbital in the substrate chromophore. Rotation of the C(sp²)–B bond by 90° in the product renders re-excitation inefficient and endows directionality. This subtle stereoelectronic gating mechanism enables the stereocontrolled syntheses of well-defined retinoic acid derivatives.
Journal Article
Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis
The importance of fluorinated products in pharmaceutical and medicinal chemistry has necessitated the development of synthetic fluorination methods, of which direct C–H fluorination is among the most powerful. Despite the challenges and limitations associated with the direct fluorination of unactivated C–H bonds, appreciable advancements in manipulating the selectivity and reactivity have been made, especially via transition metal catalysis and photochemistry. Where transition metal catalysis provides one strategy for C–H bond activation, transition-metal-free photochemical C–H fluorination can provide a complementary selectivity via a radical mechanism that proceeds under milder conditions than thermal radical activation methods. One exciting development in C–F bond formation is the use of small-molecule photosensitizers, allowing the reactions i) to proceed under mild conditions, ii) to be user-friendly, iii) to be cost-effective and iv) to be more amenable to scalability than typical photoredox-catalyzed methods. In this review, we highlight photosensitized C–H fluorination as a recent strategy for the direct and remote activation of C–H (especially C(sp 3 )–H) bonds. To guide the readers, we present the developing mechanistic understandings of these reactions and exemplify concepts to assist the future planning of reactions.
Journal Article
X-ray induced photodynamic therapy with copper-cysteamine nanoparticles in mice tumors
Photodynamic therapy (PDT), a treatment that uses a photosensitizer, molecular oxygen, and light to kill target cells, is a promising cancer treatment method. However, a limitation of PDT is its dependence on light that is not highly penetrating, precluding the treatment of tumors located deep in the body. Copper-cysteamine nanoparticles are a new type of photosensitizer that can generate cytotoxic singlet oxygen molecules upon activation by X-rays. In this paper, we report on the use of copper-cysteamine nanoparticles, designed to be targeted to tumors, for X-ray–induced PDT. In an in vivo study, results show a statistically significant reduction in tumor size under X-ray activation of pH-low insertion peptide–conjugated, copper-cysteamine nanoparticles in mouse tumors. This work confirms the effectiveness of copper-cysteamine nanoparticles as a photosensitizer when activated by radiation and suggests that these Cu-Cy nanoparticles may be good candidates for PDT in deeply seated tumors when combined with X-rays and conjugated to a tumor-targeting molecule.
Journal Article
5-aminolevulinic acid photodynamic therapy for the treatment of high-grade gliomas
Introduction
Photodynamic therapy (PDT) is a two-step treatment involving the administration of a photosensitive agent followed by its activation at a specific light wavelength for targeting of tumor cells.
Materials/Methods
A comprehensive review of the literature was performed to analyze the indications for PDT, mechanisms of action, use of different photosensitizers, the immunomodulatory effects of PDT, and both preclinical and clinical studies for use in high-grade gliomas (HGGs).
Results
PDT has been approved by the United States Food and Drug Administration (FDA) for the treatment of premalignant and malignant diseases, such as actinic keratoses, Barrett’s esophagus, esophageal cancers, and endobronchial non-small cell lung cancers, as well as for the treatment of choroidal neovascularization. In neuro-oncology, clinical trials are currently underway to demonstrate PDT efficacy against a number of malignancies that include HGGs and other brain tumors. Both photosensitizers and photosensitizing precursors have been used for PDT. 5-aminolevulinic acid (5-ALA), an intermediate in the heme synthesis pathway, is a photosensitizing precursor with FDA approval for PDT of actinic keratosis and as an intraoperative imaging agent for fluorescence-guided visualization of malignant tissue during glioma surgery. New trials are underway to utilize 5-ALA as a therapeutic agent for PDT of the intraoperative resection cavity and interstitial PDT for inoperable HGGs.
Conclusion
PDT remains a promising therapeutic approach that requires further study in HGGs. Use of 5-ALA PDT permits selective tumor targeting due to the intracellular metabolism of 5-ALA. The immunomodulatory effects of PDT further strengthen its use for treatment of HGGs and requires a better understanding. The combination of PDT with adjuvant therapies for HGGs will need to be studied in randomized, controlled studies.
Journal Article
Photodynamic Efficiency: From Molecular Photochemistry to Cell Death
Photodynamic therapy (PDT) is a clinical modality used to treat cancer and infectious diseases. The main agent is the photosensitizer (PS), which is excited by light and converted to a triplet excited state. This latter species leads to the formation of singlet oxygen and radicals that oxidize biomolecules. The main motivation for this review is to suggest alternatives for achieving high-efficiency PDT protocols, by taking advantage of knowledge on the chemical and biological processes taking place during and after photosensitization. We defend that in order to obtain specific mechanisms of cell death and maximize PDT efficiency, PSes should oxidize specific molecular targets. We consider the role of subcellular localization, how PS photochemistry and photophysics can change according to its nanoenvironment, and how can all these trigger specific cell death mechanisms. We propose that in order to develop PSes that will cause a breakthrough enhancement in the efficiency of PDT, researchers should first consider tissue and intracellular localization, instead of trying to maximize singlet oxygen quantum yields in in vitro tests. In addition to this, we also indicate many open questions and challenges remaining in this field, hoping to encourage future research.
Journal Article
Structural basis for enzymatic photocatalysis in chlorophyll biosynthesis
The enzyme protochlorophyllide oxidoreductase (POR) catalyses a light-dependent step in chlorophyll biosynthesis that is essential to photosynthesis and, ultimately, all life on Earth
1
–
3
. POR, which is one of three known light-dependent enzymes
4
,
5
, catalyses reduction of the photosensitizer and substrate protochlorophyllide to form the pigment chlorophyllide. Despite its biological importance, the structural basis for POR photocatalysis has remained unknown. Here we report crystal structures of cyanobacterial PORs from
Thermosynechococcus elongatus
and
Synechocystis
sp. in their free forms, and in complex with the nicotinamide coenzyme. Our structural models and simulations of the ternary protochlorophyllide–NADPH–POR complex identify multiple interactions in the POR active site that are important for protochlorophyllide binding, photosensitization and photochemical conversion to chlorophyllide. We demonstrate the importance of active-site architecture and protochlorophyllide structure in driving POR photochemistry in experiments using POR variants and protochlorophyllide analogues. These studies reveal how the POR active site facilitates light-driven reduction of protochlorophyllide by localized hydride transfer from NADPH and long-range proton transfer along structurally defined proton-transfer pathways.
Crystal structures of cyanobacterial protochlorophyllide oxidoreductases reveal the basis of the photocatalytic activities of this enzyme, through the role of its active site in enabling the light-driven reduction of protochlorophyllide.
Journal Article