Light-induced full aromatization and hydroxylation of 7-methoxy-1-methyl-3,4-dihydro-2H-pyrido[3,4-b]indole alkaloid: Oxygen partial pressure as a key modulator of the photoproducts distribution.

Full-aromatic and partially hydrogenated ß-carboline (ßC) derivatives constitute a group of alkaloids widely distributed in a great variety of living systems. In plants and bacteria, tetrahydro-ßCs are the primary product of the Pictet-Spengler enzymatically catalyzed condensation. Tetrahydro-ßC skeleton is further modified giving rise to the formation of a vast set of derivatives including dihydro- and full-aromatic ßCs. However, in most of the cases, the later processes still remain unclear and other sources, such as photo-triggered reactions, deserve to be explored. In this context, the photophysic and photochemistry of 7-methoxy-1-methyl-3,4-dihydro-2H-pyrido[3,4-b]indole or harmaline (Hlina) in aqueous solution is reported herein. UV-visible absorption and fluorescence emission spectroscopy coupled with multivariate data analysis (PARAFAC), HPLC and HRESI-MS techniques were used for both quantitative and qualitative analysis. The formation singlet oxygen and hydrogen peroxide reactive oxygen species (ROS) was quantified and their role together with the influence of pH and oxygen partial pressure on the photochemical degradation of HlinaH+ was assessed. We report herein the first study on photochemical full-aromatization of a dihydro-ßC derivative. These results can shed some light on the ßCs biosynthesis and role in living systems.

norHarmane containing ionic liquid matrices for low molecular weight MALDI-MS carbohydrate analysis: The perfect couple with α-cyano-4-hydroxycinnamic acid.

Cinnamic acid derivatives, particularly α-cyano-4-hydroxycinnamic acid (E-α-cyano-4-hydroxycinnamic acid or (E)-2-cyano-3-(4-hydroxyphenyl)prop-2-enoate; CHCA), have been extensively used especially for protein and peptide analysis. Together with the introduction of ionic liquid MALDI matrix (ILM) started the study of applications of IL prepared with CHCA and a counter organic base (ie, aliphatic amines) in which CHCA moiety is the chromophore responsible of UV-laser absorption. Despite the extensive studies of norharmane (9H-pyrido[3,4-b]indole; nHo) applications as matrix and its peculiar basic properties in the ground and electronic excited state, nHo containing ILM was never tested in MALDI-MS experiments. This pyrido-indole compound was introduced as MALDI matrix 22 years ago for different applications including low molecular weight (LMW) carbohydrates (neutral, acidic, and basic carbohydrates). These facts encouraged us to use it as a base, for the first time, for ILM preparation. As a rational design of new IL MALDI matrices, E-α-cyanocinnamic acid.nHo and E-cinnamic acid.nHo were prepared and their properties as matrices studied. Their performance was compared with that of (a) the corresponding IL prepared with butylamine as basic component, (b) the corresponding crystalline E-α-cyanocinnamic and E-cinnamic acid, and (c) the classical crystalline matrices (2,5-dihydroxybenzoic acid, DHB; nHo) used in the analysis of neutral/sulfated carbohydrates. The IL DHB.nHo was tested, too. Herein, we demonstrate the outstanding performance for the IL CHCA.nHo for LMW carbohydrate in positive and negative ion mode (linear and reflectron modes). Sulfated oligosaccharides were detected in negative ion mode, and although the dissociation of sulfate groups was not completely suppressed the relative intensity (RI) of [M - Na]- peak was quite high. Additionally, to better understand the quite different performance of each IL tested as matrix, the physical and morphological properties in solid state were studied (optical image; MS image).

Photophysical and Photochemical Properties of Naturally Occurring normelinonine F and Melinonine F Alkaloids and Structurally Related N(2)- and/or N(9)-methyl-ß-carboline Derivatives.

In the present work, we have synthesized and fully characterized the photophysical and photochemical properties of a selected group of N-methyl-ß-carboline derivatives (9-methyl-ß-carbolines and iodine salts of 2-methyl- and 2,9-dimethyl-ß-carbolinium) in aqueous solutions, in the pH range 4.0-14.5. Moreover, despite the quite extensive studies reported in the literature regarding the overall photophysical behavior of N-unsubstituted ßCs, this work constitutes the first full and unambiguous characterization of anionic species of N-unsubstituted ßCs (norharmane, harmane and harmine), present in aqueous solution under highly alkaline conditions (pH > 13.0). Acid dissociation constants (Ka ), thermal stabilities, room temperature UV-visible absorption and fluorescence emission and excitation spectra, fluorescence quantum yields (ФF ) and fluorescence lifetimes (τF ), as well as quantum yields of singlet oxygen production (Ð¤Δ ) have been measured for all the studied compounds. Furthermore, for the first time to our knowledge, chemometric techniques (MCR-ALS and PARAFAC) were applied on these systems, providing relevant information about the equilibria and species involved. The impact of all the foregoing observations on the biological role, as well as the potential biotechnological applications of these compounds, is discussed.