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

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 βCs and their biological role in living systems are discussed.

Distribution of photoactive β-carboline alkaloids across Passiflora caerulea floral organs

This study reports valuable information regarding the presence and concentration of a series of photoactive β-carboline (βCs) 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 βCs' content ranged from 1 to 110 μg kg-1 , depending on the floral organ and age. In certain physiologically relevant organs, such as anthers, βCs' content was one order of magnitude higher than in other organs, suggesting a special role for βCs in this specific organ. βCs' content also varied in a structure-dependent manner. Alkaloids bearing a hydroxyl group at position C(7) of the main βC ring were present at concentrations one order of magnitude higher than other βC 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 βCs in floral organs may have several (photo)biological implications that are further discussed.

Synthesis of Fluorescent, DNA-Binding Benzo[b]indolonaphthyridinium Derivatives by a Misguided Westphal Condensation

A novel type of azoniahetarene, namely, benzo[b]indolonaphthyridinium, was unexpectedly formed by the reaction of N-alkylated β-carbolinium derivatives and the enolizable 1,2-cyclohexadione under typical conditions of a Westphal reaction. The products exhibit high fluorescence intensities in polar solvents (Φ_fl = 0.52-0.67) and bind to DNA by intercalation with high affinity (K_b = 1.5 × 10⁶ M^-1). Furthermore, under the same conditions, DNA-binding sempervirine derivatives were synthesized in a Westphal reaction from 1,2-diketones that have at least one non-enolizable α-carbon atom, which shows that the reaction pathway is determined by the substrate structure.