Exploring potooxidative degradation pathways of harmol and harmalol alkaloids in water: effects of pH, excitation sources and atmospheric conditions.

This work explores the photochemical degradation of cationic species of 7-hydroxy-1-methyl-2H-pyrido[3,4-b]indole or harmol (1C) and the corresponding partially hydrogenated derivative 7-hydroxy-1-methyl-3,4-dihydro-2H-pyrido[3,4-b]indole or harmalol (2C) in aqueous solution. UV-visible absorption and fluorescence emission spectroscopy coupled with multivariate data analysis (MCR-ALS and PARAFAC), HPLC and HRESI-MS techniques were used for both quantitative and qualitative analysis. The formation of hydrogen peroxide reactive oxygen species (ROS) was quantified, and the influence of pH, oxygen partial pressure and photoexcitation source on the photochemical degradation of both compounds was assessed. The potential implications on the biosynthesis of ßCs and their biological role in living systems are discussed.

Distribution of photoactive ß-carboline alkaloids across Passiflora caerulea floral organs.

This study reports valuable information regarding the presence and concentration of a series of photoactive ß-carboline (ßCs) alkaloids (norharmane, harmane, harmine, harmol, harmaline, and harmalol) and their distribution across the floral age and organs of Passiflora caerulea. UHPLC-MS/MS data reported herein reveal that the ßCs' content ranged from 1 to 110 µg kg-1 , depending on the floral organ and age. In certain physiologically relevant organs, such as anthers, ßCs' content was one order of magnitude higher than in other organs, suggesting a special role for ßCs in this specific organ. ßCs' content also varied in a structure-dependent manner. Alkaloids bearing a hydroxyl group at position C(7) of the main ßC ring were present at concentrations one order of magnitude higher than other ßC derivatives investigated. UV-visible and fluorescence spectroscopy of the flower extracts provided complementary information regarding other biologically relevant groups of chromophores (phenolic/indolic derivatives, flavonoids/carotenes, and chlorophylls). Since flowers are constantly exposed to solar radiation, the presence of photoactive ßCs in floral organs may have several (photo)biological implications that are further discussed.

Spectroscopic and quantum chemical characterization of the ground and lowest electronically excited singlet and triplet states of halo- and nitro-harmines in aqueous media.

Halogenated and nitro ß-carboline (ßCs) alkaloids have garnered increasing interest for their role in a broad range of biological, pharmacological and biotechnological processes. Addressing their spectroscopic and photophysical properties provide tools to further explore the presence of these alkaloids in complex biological matrices. In addition, these studies help to elucidate processes where these alkaloids are involved. The UV-visible and steady-state room temperature fluorescence of bromo- and nitro-harmines in an aqueous environment at different pHs, low-temperature phosphorescence (at 77 K) and quantum yields of singlet oxygen production are reported herein. Singlet (S0 and S1) and triplet (T1) electronic states are further analyzed using density functional theory (DFT) and the results compared with experimental data. Data are discussed in the framework of potential biotechnological applications of these ßC alkaloids.

Photophysical and spectroscopic features of 3,4-dihydro-ß-carbolines: a combined experimental and theoretical approach.

3,4-Dihydro-ß-carbolines (DHßCs) are a set of endogenously synthesized alkaloids spread over a great variety of living species (e.g., plants, animals and microorganisms), playing a broad spectrum of biological, biochemical and/or pharmacological roles, in a structure-dependent manner. Addressing unresolved fundamental aspects related to the photophysical properties of DHßCs might help to gain further insights into the molecular basis of the mechanisms of the biological processes where these alkaloids are involved. In this work, the UV-visible spectroscopic features of DHßCs are revisited and they are further analyzed by calculations at the Density Functional Theory (DFT) level. In addition, steady-state and time-resolved fluorescence spectroscopy, as well as quantitative singlet oxygen production analysis is reported. Data obtained herein are discussed in the framework of the potential biological role of these alkaloids.

Photophysics and photochemistry of carminic acid and related natural pigments.

Carminic acid (CA) and other related compounds have been widely used as dyes in cultural heritage, cosmetics and the food industry. Therefore, the study of their properties upon photoexcitation is particularly important. In this work, the photophysical and photochemical properties of CA, carminic lake and other related pigments in aqueous solutions are revisited. Novel quantitative information regarding the fate of the photoexcited states is provided including the efficiency of reactive oxygen species (ROS) photosensitized production (i.e., singlet oxygen and hydrogen peroxide) as well as the efficiency of nonradiative deactivation pathways. Laser-induced optoacoustic spectroscopy (LIOAS) data revealed that for all the investigated compounds, almost all the absorbed energy is released as prompt heat to the media. This is in agreement with the fact that other deactivation pathways, including fluorescence (ΦF ∼ 10-3-10-5), photochemical degradation (ΦR ∼ 10-4) and/or photosensitized ROS formation (ΦH2O2 < 10-5 and ΦΔ âˆ¼ 0), are negligible or null. In addition, a comprehensive investigation of the photodegradation of CA and lake is herein reported. The influence of different experimental parameters such as irradiation wavelength and oxygen partial pressure was evaluated. UV-vis absorption and fluorescence emission spectroscopy in combination with chemometric data analysis were used to elucidate the relevant aspects of the photodegradation mechanism involved and the spectroscopic features of the photoproducts generated. In aqueous media, CA follows an O2-dependent photochemical degradation when subject to elapsed photoexcitation in the UVB, UVA and visible regions. The photoproduct profile depends on the excitation wavelength giving rise to quite distinctive spectroscopic profiles. With respect to lake, our data suggest that upon photoexcitation, this pigment releases a CA-like chromophore that follows a similar fate to CA.

DNA damage photo-induced by chloroharmine isomers: hydrolysis versus oxidation of nucleobases.

Photodynamic therapy (PDT) is an emerging clinical treatment currently being used against a wide range of both cancerous and noncancerous diseases. The search for new active photosensitizers as well as the development of novel selective delivery systems are the major challenges faced in the application of PDT. We investigated herein three chloroharmine derivatives (6-, 8- and 6,8-dichloroharmines) with quite promising intrinsic photochemical tunable properties and their ability to photoinduce DNA damage in order to elucidate the underlying photochemical mechanisms. Data revealed that the three compounds are quite efficient photosensitizers. The overall extent of photo-oxidative DNA damage induced by both 8-chloro-substituted ß-carbolines is higher than that induced by 6-chloro-harmine. The predominant type of lesion generated also depends on the position of the chlorine atom in the ß-carboline ring. Both 8-chloro-substituted ß-carbolines mostly oxidize purines via type I mechanism, whereas 6-chloro-harmine mainly behaves as a "clean" artificial photonuclease inducing single-strand breaks and site of base loss via proton transfer and concerted (HO--mediated) hydrolytic attack. The latter finding represents an exception to the general photosensitizing reactions and, to the best of our knowledge, this is the first time that this process is well documented. The controlled and selective production of different oxygen-independent lesions could be fine-tuned by simply changing the substituent groups in the ß-carboline ring. This could be a promising tool for the design and development of novel photo-therapeutic agents aimed to tackle hypoxic conditions shown in certain types of tumours.