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Reactive oxygen species (ROS), including superoxide anion, are involved in regulating various signaling pathways and are also responsible for oxidative stress. Sensing superoxide anion is of particular importance due to its biological significance. One potential approach is to use Coelenterazine as a chemiluminescent probe for the dynamic sensing of this ROS. In this study, we investigated the superoxide anion-triggered chemiluminescence of native Coelenterazine and two halogenated analogs and found that they showed a ~100-fold enhancement of light emission in aqueous solution, which was significantly reduced in methanol and nonexistent in aprotic solvents. In fact, Coelenterazine showed more intense light emission in aprotic solvents and, interestingly, although the light emission of the analogs seemed relatively unaffected by the solvents, their chemiluminescence was significantly quenched in water compared to methanol and, especially, to aprotic media. This suggests that the quenching effect observed for Coelenterazine is responsible for the differences in aqueous media, rather than an intrinsic enhanced emission by the analogs. In summary, we present Coelenterazine analogs that could serve as a basis for enhanced sensing of superoxide anion, providing information that could further our understanding of this chemiluminescent system.

Cancer is a very challenging disease to treat, both in terms of therapeutic efficiency and harmful side effects, which continues to motivate the pursuit for novel molecules with potential anticancer activity. Herein, we have designed, synthesized, and evaluated the cytotoxicity of different brominated coelenteramines, which are metabolic products and synthesis precursors of the chemi-/bioluminescent system of marine coelenterazine. The evaluation of the anticancer potential of these molecules was carried out for both prostate and breast cancer, while also exploring their potential for use in combination therapy. Our results provided further insight into the structure–activity relationship of this type of molecule, such as their high structural specificity, as well highlighting the 4-bromophenyl moiety as essential for the anticancer activity. The obtained data also indicated that, despite their similarity, the anticancer activity displayed by both brominated coelenteramines and coelenterazines should arise from independent mechanisms of action. Finally, one of the studied coelenteramines was able to improve the profile of a known chemotherapeutic agent, even at concentrations in which its anticancer activity was not relevant. Thus, our work showed the potential of different components of marine chemi-/bioluminescent systems as novel anticancer molecules, while providing useful information for future optimizations.

Brown carbon is a type of carbonaceous aerosol with strong light absorption in the ultraviolet and visible wavelengths that leads to radiative forcing. However, it is difficult to correlate the chemical composition of brown carbon with its atmospheric light absorption properties, which translates into significant uncertainty. Thus, a time-dependent density functional theory (TD-DFT) approach was used to model the real-world absorption properties of 14 polycyclic aromatic hydrocarbons (PAHs) over three regions of the Basque Country (Spain): Bilbao, Urretxu, and Azpeitia. The data were corrected for atmospheric concentration. The results show that the absorption spectra over each region are qualitatively identical, with the absorption intensities being significantly higher over Bilbao than over Azpeitia and Urretxu. Furthermore, it was found that the light absorption by PAHs should be more relevant for radiative forcing when it occurs at UVA and (sub)visible wavelengths. Finally, among the 14 studied PAHs, benzo[b]fluoranthene, pyrene, fluoranthene, benzo[a]pyrene, and benzo[k]fluoranthene and benzoperylene were identified as the molecules with larger contributions to radiative forcing.

Application of light in chemistry presents an active field of research with a very promising outlook, particularly in technology and medicine. Molecules which mediate the transfer of light to another molecule (photosensitizers) are the cornerstone of exploitation of light. The current state of research and recent progress in applications of photosensitizers in diverse fields are documented in twelve chapters written by scientists from around the world. Chapter 1 gives a general overview on the applications of photosensitizers in synthetic organic chemistry. This review is followed by Chapters 2-7, which deal with the various applications of photosensitizers in medicine, in particular for photodynamic cancer therapy. The subsequent Chapters 8-12 cover different aspects of applications of photosensitizers in material science, such as for dye-sensitized solar cells and photo-responsive materials.

Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/ijms23158271/s1., Cancer is still a challenging disease to treat, both in terms of harmful side effects and therapeutic efficiency of the available treatments. Herein, to develop new therapeutic molecules, we have investigated the anticancer activity of halogenated derivatives of different components of the bioluminescent system of marine Coelenterazine: Coelenterazine (Clz) itself, Coelenteramide (Clmd), and Coelenteramine (Clm). We have found that Clz derivatives possess variable anticancer activity toward gastric and lung cancer. Interestingly, we also found that both brominated Clmd (Br-Clmd) and Clm (Br-Clm) were the most potent anticancer compounds toward these cell lines, with this being the first report of the anticancer potential of these types of molecules. Interestingly, Br-Clm possessed some safety profile towards noncancer cells. Further evaluation revealed that the latter compound induced cell death via apoptosis, with evidence for crosstalk between intrinsic and extrinsic pathways. Finally, a thorough exploration of the chemical space of the studied Br-Clm helped identify the structural features responsible for its observed anticancer activity. In conclusion, a new type of compounds with anticancer activity toward gastric and lung cancer was reported and characterized, which showed interesting properties to be considered as a starting point for future optimizations towards obtaining suitable chemotherapeutic agents., The Portuguese “Fundação para a Ciência e Tecnologia“ (FCT) is acknowledged for funding project PTDC/QUI-QFI/2870/2020, the R&D Units CIQUP (UIDB/00081/2020), GreenUPorto (UIDB/05748/2020), LAQV/REQUIMTE (UIDB/50006/2020), and the Associated Laboratory IMS (LA/P/0056/2020). L. Pinto da Silva acknowledges funding from FCT under the Scientific Employ ment Stimulus (2021.00768.CEECIND). Patricia González-Berdullas acknowledges funding for her postdoctoral position in the framework of project PTDC/QUI/QFI/2870/2020. Carla Magalhães acknowledges FCT for her PhD grant (SRFH/BD/143211/2019). Renato B. Pereira acknowledges PRIMA Foundation (H2020- PRIMA 2018—Section 2, Project MILKQUA) and FCT (PTDC/QUI QFI/2870/2020) for the funding.

Dioxetanone is one of the prototypical cyclic peroxide intermediates in several chemiluminescent and bioluminescent systems, in which thermolysis reactions allow efficient singlet chemiexcitation. While the chemiexcitation mechanism of dioxetanone and peroxide intermediates is still far from understood, the presence of a peroxide bond that undergoes bond breaking has been found to be a constant. Here we have addressed the following questions: can other non-peroxide bonds lead to chemiexcitation and, if not, can the differences between dioxetanone and non-peroxide derivatives help to elucidate their chemiexcitation mechanism? To this end, we have used a reliable TD-DFT approach to model the thermolysis and chemiexcitation of a model dioxetanone and its three other non-peroxide derivatives. The results showed that only the dioxetanone molecule could lead to chemiluminescence as it is the only one for which thermolysis is energetically favorable and provides a pathway for singlet chemiexcitation. Finally, the chemiexcitation of the model dioxetanone is explained by its access, during thermolysis, to a biradical region where the ground and excited states are degenerate. This occurs due to an increased interaction between the reaction fragments, which extends the biradical regions and delays the rupture of the peroxide ring.

Chemi- and bioluminescence are remarkable light-emitting phenomena, in which thermal energy is converted into excitation energy due to a (bio)chemical reaction. Among a wide variety of chemi-/bioluminescent systems, one of the most well-known and studied systems is that of marine imidazopyrazinones, such as Coelenterazine and Cypridina luciferin. Due to the increasing usefulness of their chemi-/bioluminescent reactions in terms of imaging and sensing applications, among others, significant effort has been made over the years by researchers to develop new derivatives with enhanced properties. Herein, we report the synthesis and chemiluminescent characterization of a novel dibrominated Coelenterazine analog. This novel compound consistently showed superior luminescence, in terms of total light output and emission lifetime, to natural imidazopyrazinones and commercially available analogs in aprotic media, while being capable of yellow light emission. Finally, this new compound showed enhanced chemiluminescence in an aqueous solution when triggered by superoxide anion, showing potential to be used as a basis for optimized probes for reactive oxygen species. In conclusion, bromination of the imidazopyrazinone scaffold appears to be a suitable strategy for obtaining Coelenterazines with enhanced properties.

Superoxide anion is a reactive oxygen species (ROS) of biological interest. More specifically, it plays a role in intra- and intercellular signaling, besides being associated with conditions such as inflammation and cancer. Given this, efforts have been made by the research community to devise new sensing strategies for this ROS species. Among them, the chemiluminescent reaction of marine Coelenterazine has been employed as a sensitive and dynamic probing approach. Nevertheless, chemiluminescent reactions are typically associated with lower emissions in aqueous solutions. Herein, here we report the synthesis of a new Coelenterazine derivative with the potential for superoxide anion sensing. Namely, this novel compound is capable of chemiluminescence in a dose-dependent manner when triggered by this ROS species. More importantly, the light-emission intensities provided by this derivative were relevantly enhanced (intensities 2.13 × 101 to 1.11 × 104 times higher) in aqueous solutions at different pH conditions when compared to native Coelenterazine. The half-life of the chemiluminescent signal is also greatly increased for the derivative. Thus, a new chemiluminescence molecule with significant potential for superoxide anion sensing was discovered and reported for the first time.

As part of our program on synthesis of labeled vitamin D metabolites and analogs, we describe here an efficient and versatile synthetic approach to 28,28,28-trideutero- 25-hydroxydihydrotachysterol2 where isotopic labeling was incorporated stereoselectively in the last step of the synthesis. This deuterated compound will allow the study this analog in vitro or in vivo and to measure AT10-like compounds in serum by LC-MS/MS.

A convergent approach to 25S,26-dihydroxyvitamin D3 (1) has been developed in our laboratories. The A-ring and the CD-fragment are constructed from ergocalciferol and Inhoffen-Lythgoe diol, respectively. The triene system is assembled by a Wittig-Horner coupling. With this convergent synthesis, a novel hydroxylated vitamin D metabolite in our laboratory is available for biological testing.

A new approach to 19-nor-A-ring phosphine oxide 5 together with a convergent synthesis of the vitamin D3 analogue 1α,25-dihydroxy-19-norvitamin D3 (3) have been developed. The 19-nor-A-ring is constructed from (S)-carvone. The triene system is assembled by a Wittig-Horner coupling.

As part of our program on synthesis of labeled vitamin D metabolites and analogs, we describe here an efficient and versatile synthetic approach to 28,28,28-trideutero- 25-hydroxydihydrotachysterol

A convergent approach to 25S,26-dihydroxyvitamin D

While photodynamic therapy is known for significant advantages over conventional cancer therapies, its dependence on light has limited it to treating tumors on or just under the skin or on the outer lining of organs/cavities. Herein, we have developed a single-molecule photosensitizer capable of intracellular self-activation and with potential tumor-selectivity due to a chemiluminescent reaction involving only a cancer marker. Thus, the photosensitizer is directly chemiexcited to a triplet excited state capable of generating singlet oxygen, without requiring either a light source or any catalyst/co-factor. Cytotoxicity assays involving the photosensitizer show significant toxicity toward tumor cells, even better than reference drugs, while not inducing toxicity toward normal cells. This work provides a proof-of-concept for a novel type of photosensitizer that eliminates the current restrictions that photodynamic therapy presents regarding tumor size and localization.

The first synthesis of 1α,25-dihydroxy-3-epi-vitamin D2 is described. Key steps of the synthesis entail the construction of the triene unit by a Pd-catalyzed ring closure of an enol-triflate (A-ring fragment) followed by a Suzuki–Miyaura coupling with a boronate (upper fragment), and the installation of the methyl group at C-24 by an SN2′-syn displacement of an allylic carbamate. This article is part of a Special Issue entitled ‘SI:17th Vitamin D Workshop’.

An efficient convergent synthesis of nonadeuterated 1α,25-dihydroxyvitamin D2 (1) by Pd(0)-catalyzed coupling between the boronate ester (upper fragment) and the enol triflate (A-ring fragment) is described. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

The first synthesis of 1α,25-dihydroxy-3-epi-vitamin D2 is described. Key steps of the synthesis entail the construction of the triene unit by a Pd-catalyzed ring closure of an enol-triflate (A-ring fragment) followed by a Suzuki–Miyaura coupling with a boronate (upper fragment), and the installation of the methyl group at C-24 by an SN2′-syn displacement of an allylic carbamate. This article is part of a Special Issue entitled ‘SI:17th Vitamin D Workshop’.