Potential Application In Photodynamic Therapy Research Articles

Fabrication of Carbon Dots with Singlet Oxygen Generation and Their Potential Photodynamic Therapy Applications.

Due to the unique chemical and biomedical properties of carbon dots (CDs), they have increasingly obtained the attention in many research fields, for example, bioimaging, fluorescence sensing, and drug delivery, etc. Recently, it was found that, under light excitation, CDs can also be exploited as a novel photosensitizer to prepare reactive oxygen species (ROS), which expand their applications in the field of photodynamic therapy for cancer treatment. Nevertheless, the high cost and complex fabrication approach of CDs significantly limit their applications. To address this issue, bottom-up routes usually utilize sustainable and inexpensive carbon precursor as starting materials, employed N,N-dimethylformamide (DMF) or ethanol as an environmental-friendly solvent. Bottom-up approach was energy efficient, and the purification process was relatively simple by dialysis. Therefore, carbon dots (CDs) were facilely fabricated in a one-pot solvothermal process using 1-aminoanthraquinone as a precursor, and their application as photosensitizers for in vitro antitumor cells, especially photodynamic therapy (PDT) was established. Then the photophysical and nanoscale dimensions properties of the fabricated CDs were characterized via TEM, UV-visible, fluorescence, and FT-IR spectroscopy. The synthesized N-doped CDs can easily dissolve in water, possess very low biotoxicity, yellow-light emission (maximum peak at 587nm). More importantly, PDT studies demonstrated that the obtained CDs possess a high singlet oxygen yield of 35%, and exhibit significant phototoxicity to cancer cells upon 635nm laser irradiation. These studies highlight that N-doped CDs can be facilely synthesized from only one precursor, and are a potentially novel theranostic agent for in vivo PDT.

Engineering Metal Halide Perovskite Nanocrystals with BODIPY Dyes for Photosensitization and Photocatalytic Applications.

The sensitization of surface-anchored organic dyes on semiconductor nanocrystals through energy transfer mechanisms has received increasing attention owing to their potential applications in photodynamic therapy, photocatalysis, and photon upconversion. Here, we investigate the sensitization mechanisms through visible-light excitation of two nanohybrids based on CsPbBr3 perovskite nanocrystals (NC) functionalized with borondipyrromethene (BODIPY) dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP), named as NC@BDP and NC@I2-BDP, respectively. The ability of I2-BDP dyes to extract hot hole carriers from the perovskite nanocrystals is comprehensively investigated by combining steady-state and time-resolved fluorescence as well as femtosecond transient absorption spectroscopy with spectroelectrochemistry and quantum chemical theoretical calculations, which together provide a complete overview of the phenomena that take place in the nanohybrid. Förster resonance energy transfer (FRET) dominates (82%) the photosensitization of the singlet excited state of BDP in the NC@BDP nanohybrid with a rate constant of 3.8 ± 0.2 × 1010 s-1, while charge transfer (64%) mediated by an ultrafast charge transfer rate constant of 1.00 ± 0.08 × 1012 s-1 from hot states and hole transfer from the band edge is found to be mainly responsible for the photosensitization of the triplet excited state of I2-BDP in the NC@I2-BDP nanohybrid. These findings suggest that the NC@I2-BDP nanohybrid is a unique energy transfer photocatalyst for oxidizing α-terpinene to ascaridole through singlet oxygen formation.

The evaluation of four nano-formulations loaded-Elsinochrome A on characteristics and in vitro cytotoxicity effect.

Elsinochrome A (EA) is a naturally occurring photosensitizer with potential applications in photodynamic therapy (PDT) for various malignancies. Despite its promising therapeutic properties, the poor solubility of EA hampers its effective utilization in clinical settings. To circumvent this limitation, we engineered four distinct nano-formulations: PLGA/EA nanoparticles (NPs), CMC-PLGA/EA NPs, mPEG-PCL/EA nanomicelles (NMs), and LHP-CHOL/EA nanoliposomes (NLs), all designed to enhance the solubility of EA. A comparative evaluation of these formulations, based on metrics such as particle size, Zeta potential, drug loading efficiency, and encapsulation efficiency, identified PLGA/EA NPs and mPEG-PCL/EA NMs as the most efficacious candidates. Subsequent in vitro investigations into the drug release kinetics under varying pH conditions and the impact on cell viability and apoptosis in A549 and MCF-7 cell lines were conducted. Remarkably, the maximum drug release for PLGA/EA NPs and mPEG-PCL/EA NMs was recorded at 62.5% and 70.8% in an acidic environment (pH 5.7), respectively. Upon exposure to 460nm light, PLGA/EA NPs induced a significant reduction in A549 cell viability to 13.8% and an apoptosis rate of 93.8%, whereas mPEG-PCL/EA NMs elicited a decrease in MCF-7 cell viability to 12.8% and an apoptosis rate of 73.0%.

Cyclometalated Ir(III) Complexes as Lysosome-Targeted Photodynamic Anticancer Agents.

We have designed and synthesized two Ir(III) complexes (Ir1 and Ir2) coordinated with an 8-sulfonamidoquinoline derivative ligand as photosensitizers, which exhibit strong red phosphorescence emission and a long phosphorescence lifetime. The Ir(III) complexes exhibit a high population of triplet states, which enable red phosphorescence and efficient singlet oxygen generation. Ir1 and Ir2 rapidly enter the cancer cells and accumulate in lysosomes, producing large amounts of intracellular singlet oxygen when exposed to light irradiation, eventually leading to cancer cell death, and the phototoxic indexes of complexes Ir1 and Ir2 against cancer cells are in the range of 76-228. Overall, our studies indicate that the synthesized Ir(III) complexes with quinoline ligands exhibit photosensitizing properties, effectively inducing cancer cell death when exposed to light. These promising results suggest their potential application in photodynamic therapy.

Antitumoral photoinduced effects of crude extract, fractions, and naphthoquinones from Sinningia magnifica (Otto & A. Dietr.) Wiehler (Gesneriaceae) in a bioguided study.

Photodynamic therapy (PDT) has been used for various purposes, including as an antitumor resource in a noninvasive therapy with minimal side effects. Sinningia magnifica (Otto & A. Dietr.) Wiehler is a rupicolous plant found in rock crevices in Brazilian tropical forests. Initial studies indicate the presence of phenolic glycosides and anthraquinones in species of the genus Sinningia (Generiaceae family). It is known that anthraquinones are natural photosensitizers with potential PDT applications. This led us to investigate the potential compounds of S. magnifica for use as a natural photosensitizer against the melanoma (SK-MEL-103) and the prostate cancer (PC-3) cell lines in a bioguided study. Our results showed that singlet oxygen production by the 1,3-DPBF photodegradation assay greatly increased in the presence of crude extract and fractions. The biological activity evaluation showed photodynamic action against melanoma cell line SK-MEL-103 and prostate cell line PC-3. These results suggest the presence of potential photosensitizing substances, as demonstrated in this in vitro antitumor PDT study by the naphthoquinones Dunniol and 7-hydroxy-6-methoxy-α-dunnione for the first time. Naphthoquinones, anthraquinones and phenolic compounds were identified in the crude extract by UHPLC-MS/MS analysis, motivating us to continue with the bioguided phytochemical study aiming to discover more photochemically bioactive substances in Gesneriaceae plants.

Shallow- and Deep-Water Ophiura Species Produce a Panel of Chlorin Compounds with Potent Photodynamic Anticancer Activities.

A Pacific brittle star Ophiura sarsii has previously been shown to produce a chlorin (3S,4S)-14-Ethyl-9-(hydroxymethyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (ETPA) (1) with potent phototoxic activities, making it applicable to photodynamic therapy. Using extensive LC-MS metabolite profiling, molecular network analysis, and targeted isolation with de novo NMR structure elucidation, we herein identify five additional chlorin compounds from O. sarsii and its deep-sea relative O. ooplax: 10S-Hydroxypheophorbide a (2), Pheophorbide a (3), Pyropheophorbide a (4), (3S,4S,21R)-14-Ethyl-9-(hydroxymethyl)-21-(methoxycarbonyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (5), and (3S,4S,21R)-14-Ethyl-21-hydroxy-9-(hydroxymethyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (6). Chlorins 5 and 6 have not been previously reported in natural sources. Interestingly, low amounts of chlorins 1-4 and 6 could also be identified in a distant species, the basket star Gorgonocephalus cf. eucnemis, demonstrating that chlorins are produced by a wide spectrum of marine invertebrates of the class Ophiuroidea. Following the purification of these major Ophiura chlorin metabolites, we discovered the significant singlet oxygen quantum yield upon their photoinduction and the resulting phototoxicity against triple-negative breast cancer BT-20 cells. These studies identify an arsenal of brittle star chlorins as natural photosensitizers with potential photodynamic therapy applications.

Adsorption of singlet and triplet oxygen on B-doped graphene: adsorption and electronic characteristics.

The density functional calculations of electronic and structural properties of the adsorption of dioxygen on boron-doped graphene surfaces are conducted using spin-polarized density functional theory methods, including van der Waals correction. The results show significant differences in the adsorption characteristics of singlet and triplet oxygen on boron-doped graphene surfaces. Both triplet and singlet show only weak attraction to intrinsic and singly doped graphene. The singlet oxygen adsorption on doped graphene shows fascinating features involving chemisorption with dioxetane ring formation with appreciable charge transfer. In contrast, the triplet oxygen is only weakly physisorbed on the boron-doped surfaces. Chemisorption of singlet oxygen occurs with noticeable charge transfer and leads to almost featureless band structures, while the triplet oxygen physisorption proceeds with a well-defined band structure. Chemisorption of the singlet oxygen is attributed to the enormous mixing of π* of dioxygen and the p-orbitals of dopant and carbon. Because of the difference in adsorption characteristics, chemically modified graphene can find use in detecting and trapping singlet oxygen, which has potential applications in photodynamic therapy.

Synergistic effect of ultrasound and light to efficient singlet oxygen formation for photodynamic purposes

As cancer is one of the leading causes of death globally, it is highly desirable to explore the therapeutic potential of new sensitizers in photodynamic therapy (PDT). In recent years, PDT applications performed with the help of ultrasound have attracted attention. Also, the importance of phthalocyanines, which are used as sensitizers in photodynamic and/or sonodynamic therapy (SDT), is increasing. The most important properties of phthalocyanines for therapeutic applications are their ability to generate reactive oxygen species (ROS) at the appropriate wavelength. To improve ROS production by phthalocyanines applying ultrasounds seems to be the reasonable pathway of development for this treatment method. In this context, to evaluate potentials for sonophotodynamic therapy (SPDT), the syntheses of highly soluble non-peripherally substituted metal-free (2), gallium (3), and indium (4) phthalocyanines were completed by substituting 3-methoxybenzyloxy groups. All prepared compounds were elucidated using many different spectroscopic approaches encompassing Fourier transform infrared (FT-IR), ultraviolet–visible (UV–Vis), 1H NMR, and matrix-assisted laser deionization/ionization time-of-flight mass spectroscopy (MALDI-TOF MS) techniques. Additionally, photophysical, photochemical, and sono-photochemical evaluations of the novel phthalocyanines are presented. The combination of ultrasound and light had an enhancing effect on singlet oxygen production in all phthalocyanine derivatives (2–4). Singlet oxygen quantum yields increased between 50% and 80% for metal-free, gallium, and indium phthalocyanines. Density Functional Theory (DFT) and time-dependent (TD-DFT) were used for the description of optical and electronic properties of metal-free, gallium, and indium phthalocyanines. The Spin Orbital Coupling Constant (SOCC) for these molecules was also calculated through the quasi-degenerate perturbation theory method. Considering the singlet and triplet states of lower energy, we have calculated the most probable intersystem spin crossing (ISC) pathways. Our results suggest that all the phthalocyanines have potential application in PDT, however, indium phthalocyanine has greater applicability in PDT.

Porphyrins and Metalloporphyrins Combined with N-Heterocyclic Carbene (NHC) Gold(I) Complexes for Photodynamic Therapy Application: What Is the Weight of the Heavy Atom Effect?

The photophysical properties of two classes of porphyrins and metalloporphyrins linked to N-heterocyclic carbene (NHC) Au(I) complexes have been investigated by means of density functional theory and its time-dependent extension for their potential application in photodynamic therapy. For this purpose, the absorption spectra, the singlet–triplet energy gaps, and the spin–orbit coupling (SOC) constants have been determined. The obtained results show that all the studied compounds possess the appropriate properties to generate cytotoxic singlet molecular oxygen, and consequently, they can be employed as photosensitizers in photodynamic therapy. Nevertheless, on the basis of the computed SOCs and the analysis of the metal contribution to the involved molecular orbitals, a different influence in terms of the heavy atom effect in promoting the intersystem crossing process has been found as a function of the identity of the metal center and its position in the center of the porphyrin core or linked to the peripheral NHC.

An Effective Supramolecular Approach to Boost the Photodynamic Therapy Efficacy of a Near-Infrared Activating Perylene Diimide-Based Photosensitizer

Perylene diimide (PDI) derivatives with outstanding photo-physicochemical properties hold significant promise for application in solar energy conversion, pollutant degradation, and disease diagnosis. However, the inherent characteristics of PDI molecules, including poor water solubility, short-wavelength absorption, and negligible singlet oxygen (1O2) generation capabilities, severely limit their application in photodynamic therapy (PDT). Here, a novel PDI-based photosensitizer was deliberately designed with the potential to solve these limitations. By facile modifications of a PDI molecule, we constructed an amphiphilic PDI-based compound (PDIPa) that can be self-assembled into a functional supramolecular photosensitizer (NanoPDIPa) with excellent water dispersity and intense near-infrared (NIR) absorbance. Remarkably, the intermolecular electronic coupling and interaction in NanoPDIPa can induce efficiency intersystem crossing (ISC) through the minimization of singlet–triplet energy gap (ΔEST), a characteristic that is not possessed by the monomer, thus resulting in significant 1O2 production. The successful development of NanoPDIPa not only can enlarge the family of NIR-absorbing photosensitizers for potential PDT applications but also can provide a solution to overcome the limitations of clinically used photosensitizers.

Study of the utility of Fe2O3-Au nanocomposite in photodynamic therapy

A novel multifunctional nanofluid composite of Iron oxide/Gold (Fe2O3-Au) was prepared using simple wet chemical method by reducing Chloroauric acid using trisodium citrate in the presence of Fe2O3 stock solution. The optical and morphological characterization confirmed the formation of hybrid structure of Iron Oxide with Gold nanoparticles. In-vitro cytoprotective studies of the sample was carried out in L929 cells. The study showed an increase up to 15% in the cell viability by the co-administration of 25 μL of Fe2O3-Au nanofluid in the L929 cells, which suffered significant reduction in cell viability due to laser irradiation. Thus, the sample is found to possess potential application in Photodynamic therapy.

Dissecting conjugation and electronic effects on the linear and non-linear optical properties of rhenium(I) carbonyl complexes.

Herein, we report a theoretical and experimental analysis of the conjugation and electronic effects on the one-photon (1PA) and two-photon absorption (2PA) properties of a series of Re(I) carbonyl complexes with terpyridine-based ligands. An excellent agreement was obtained between the calculated and experimental 2PA spectra of the κ2N-terpyridine tricarbonyl complexes (1a-b), with 2PA cross sections reaching up to ca. 40 GM in DMF. By stepwise lowering the conjugation length in the terpy ligand and changing the local symmetry around the metal centre, we show that conjugation and delocalisation play a major role in increasing 2PA cross sections, and that the character of the excited states does not directly enhance the non-linear properties of these complexes-contrary to the results observed in 1PA. Altogether, these results give valuable guidelines towards more efficient two-photon-absorbing coordination complexes of Re(I), with potential applications in photodynamic therapy and two-photon imaging.

Bovine Serum Albumin-Encapsulated Ultrasmall Gold Nanoclusters for Photodynamic Therapy of Tumors

Gold nanoclusters (AuNCs) with an ultrasmall size showed potential application in photodynamic therapy (PDT), but short circulation and weak tumor retention restricted their PDT performance. Herein, bovine serum albumin (BSA) nanospheres with good biocompatibility were used to encapsulate AuNCs, by which the stable and biocompatible AuNCs@BSA nanoprobes were synthesized to boost PDT performance. The results showed that ultrasmall AuNCs with a size of 1.5 nm were encapsulated in BSA nanospheres, and the prepared AuNCs@BSA nanoparticles with an average size of 120 nm have high colloid stability and enhanced fluorescence emission. Compared with single AuNCs, AuNCs@BSA possessed higher singlet oxygen yield, which increased from 34.5% to 45.5%. Moreover, AuNCs@BSA showed lower cytotoxicity and stronger cellular uptake, by which the cell viability was reduced to 20.6% and 4T1 tumor completely disappeared, compared with 47.5% cell viability and tumor recurrence of single AuNCs. The results demonstrated that the prepared AuNCs@BSA nanoprobes possessed good biocompatibility and boosted PDT performance and will be potential highly efficient PDT nanoprobes owing to their safety and reliability.

Interactions of chlorophyll-derived photosensitizers with human serum albumin are determined by the central metal ion

Two structurally similar derivatives of chlorophyll a, chlorophyllide a (Chlide) and zinc-pheophorbide a (Zn-Pheide), differing only in central metal ion (Mg2+ or Zn2+, respectively) substituting the tetrapyrrole ring, were investigated with regard to their binding to human serum albumin (HSA). Chlide and Zn-Pheide are very promising photosensitizers with potential application in photodynamic therapy, therefore it is desirable to investigate their interactions with serum proteins. The studies included absorption and steady-state fluorescence spectroscopy, as well as molecular docking. It was found that both investigated compounds form complexes with HSA. Experimental data revealed two classes of binding sites for each compound. The affinities (Ka) for the first class were in the range of 105 and 106 M−1 for Chlide and Zn-Pheide, respectively, while the second class was characterized by the affinities of the order of 104 M−1 for both derivatives. Molecular docking simulations together with displacement studies revealed that the primary binding site of the studied compounds is the heme site, localized in the subdomain IB, however the best characterized binding sites of HSA, namely the Sudlow’s sites I and II are also involved. The interactions between the derivatives of chlorophyll and HSA were found to be predominantly hydrophobic and to a lesser extent hydrogen bonding. Our results demonstrate that the centrally bound metal ion determines both the affinity and mode of binding to HSA, which may be a feature differentiating these compounds in terms of their pharmacokinetics. Communicated by Ramaswamy H. Sarma

Biocompatible Nanocarriers for Enhanced Cancer Photodynamic Therapy Applications.

In recent years, the role of nanotechnology in drug delivery has become increasingly important, and this field of research holds many potential benefits for cancer treatment, particularly, in achieving cancer cell targeting and reducing the side effects of anticancer drugs. Biocompatible and biodegradable properties have been essential for using a novel material as a carrier molecule in drug delivery applications. Biocompatible nanocarriers are easy to synthesize, and their surface chemistry often enables them to load different types of photosensitizers (PS) to use targeted photodynamic therapy (PDT) for cancer treatment. This review article explores recent studies on the use of different biocompatible nanocarriers, their potential applications in PDT, including PS-loaded biocompatible nanocarriers, and the effective targeting therapy of PS-loaded biocompatible nanocarriers in PDT for cancer treatment. Furthermore, the review briefly recaps the global clinical trials of PDT and its applications in cancer treatment.

Lactose-conjugated porphyrin: synthesis and photobiological evaluation as potential agents for photodynamic therapy

Porphyrin-based photosensitizers are conventional photodynamic agents that are used clinically. However, their clinical applications have been overshadowed by poor water solubility. In addition, they have weak tumor selectivity, which may cause undesirable side effects. The preparation of novel porphyrin derivatives has been explored for potential applications in photodynamic therapy (PDT). To achieve this goal, lactose-conjugated porphyrin nanoparticles (Lac-Por NPs) have been synthesized and characterized. PDT with Lac-Por NPs exhibited tumor-specific cytotoxicity in lactose receptor-overexpressing HepG2 cells in vitro and in vivo. In summary, we designed and synthesized lactose conjugate porphyrins with enhanced water solubility and tumor selectivity. This work expands the application range of porphyrin-based photosensitizers for cancer treatment.

Synthesis and Characterization of Polyvinylpyrrolidone-Modified ZnO Quantum Dots and Their In Vitro Photodynamic Tumor Suppressive Action.

Despite the numerous available treatments for cancer, many patients succumb to side effects and reoccurrence. Zinc oxide (ZnO) quantum dots (QDs) are inexpensive inorganic nanomaterials with potential applications in photodynamic therapy. To verify the photoluminescence of ZnO QDs and determine their inhibitory effect on tumors, we synthesized and characterized ZnO QDs modified with polyvinylpyrrolidone. The photoluminescent properties and reactive oxygen species levels of these ZnO/PVP QDs were also measured. Finally, in vitro and in vivo experiments were performed to test their photodynamic therapeutic effects in SW480 cancer cells and female nude mice. Our results indicate that the ZnO QDs had good photoluminescence and exerted an obvious inhibitory effect on SW480 tumor cells. These findings illustrate the potential applications of ZnO QDs in the fields of photoluminescence and photodynamic therapy.

Air-Filled Bubbles Stabilized by Gold Nanoparticle/Photodynamic Dye Hybrid Structures for Theranostics.

Microbubbles have already reached clinical practice as ultrasound contrast agents for angiography. However, modification of the bubbles’ shell is needed to produce probes for ultrasound and multimodal (fluorescence/photoacoustic) imaging methods in combination with theranostics (diagnostics and therapeutics). In the present work, hybrid structures based on microbubbles with an air core and a shell composed of bovine serum albumin, albumin-coated gold nanoparticles, and clinically available photodynamic dyes (zinc phthalocyanine, indocyanine green) were shown to achieve multimodal imaging for potential applications in photodynamic therapy. Microbubbles with an average size of 1.5 ± 0.3 μm and concentration up to 1.2 × 109 microbubbles/mL were obtained and characterized. The introduction of the dye into the system reduced the solution’s surface tension, leading to an increase in the concentration and stability of bubbles. The combination of gold nanoparticles and photodynamic dyes’ influence on the fluorescent signal and probes’ stability is described. The potential use of the obtained probes in biomedical applications was evaluated using fluorescence tomography, raster-scanning optoacoustic microscopy and ultrasound response measurements using a medical ultrasound device at the frequency of 33 MHz. The results demonstrate the impact of microbubbles’ stabilization using gold nanoparticle/photodynamic dye hybrid structures to achieve probe applications in theranostics.

A near-infrared and lysosomal targeting thiophene-BODIPY photosensitizer: Synthesis and its imaging guided photodynamic therapy of cancer cells

In this study, a novel NIR and lysosomal targeting thiophene-BODIPY photosensitizer SBOP-Lyso was synthesized to explore its potential applications in photodynamic therapy of A549 cells. In the strategy of designing SBOP-Lyso, S atom in thiophene as well as heavy atom I were introduced to promote ISC efficiency to ensure high singlet oxygen yield. A common lysosome targeted group (M1: 1-(2-morpholinoethyl)-1H-indole-3-carbaldehyde) was linked to SBOP to extend its wavelength to the NIR region. Its absorption peak was at 660 nm (εmax = 5.2 × 104 cm−1 M−1) and its corresponding emission peak was located at 705 nm. Singlet oxygen could be quickly generated by SBOP-Lyso in the presence of 660 nm LED irradiation and the singlet oxygen yield was up to 44.1%. In addition, it also had good biocompatibility and could enter cells or zebrafish in a short time. SBOP-Lyso had negligible dark cytotoxicity (cell survival rate > 80%) and excellent phototoxicity (IC50 = 0.2 μM). DCFH-DA (ROS indicator) proved that SBOP-Lyso could generate singlet oxygen with 660 nm LED irradiation. Singlet oxygen produced by SBOP-Lyso could kill cancer cells in PDT process and it had the ability to effectively inhibit A549 cells migration. Besides that, lysosomal colocalization assay showed that it had good lysosomal localization ability (Pearson colocation coefficient, R = 0.93). Considering the above results, SBOP-Lyso as a unique lysosome-targeted photosensitizer with excellent properties would exhibit positive results in PDT process of cancer cells.

Comparative singlet oxygen photosensitizer efficiency of berberine, rose bengal, and methylene blue by time course nuclear magnetic resonance (NMR) monitoring of a photochemical 4+2 cycloaddition endoperoxide formation

Berberine, a natural product alkaloid, has been shown to exert biological activity via in situ production of singlet oxygen when photo irradiated. Berberine utilizes singlet oxygen in its putative mechanism of action, wherein it forms an activated complex with DNA and photosensitizes triplet oxygen to singlet oxygen to specifically oxidize guanine residues, thereby halting cell replication and leading to cell death. This has potential application in photodynamic therapy, alongside other such compounds which also act as photosensitizers and produce singlet oxygen in situ. The quantification of singlet oxygen in various photosensitizers, including berberine, is essential for determining their photosensitizer efficiencies. We postulated that the singlet oxygen produced by photoirradiation of berberine would be superior in terms of singlet oxygen production to the aforementioned photosensitizers when irradiated with UV light, but inferior under visible light conditions, due to its strong absorbance of UV wavelengths. Here, we report the usage of time course 1H nuclear magnetic resonance (NMR) spectroscopy to trap singlet oxygen via a 4+2 cycloaddition with terpinene, as well as theoretical calculations by time-dependent density functional theory (TD-DFT) towards quantification of berberine's singlet oxygen production against two known photosensitizers, methylene blue and rose bengal, to determine berberine’s efficacy as a singlet oxygen photosensitizer. We envision that similar processes can be utilized for the evaluation of berberine analogs or other photosensitizing agents and the identification of other potential medicinally significant singlet oxygen photosensitizers.