3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) sensitizes mammalian cells to UV radiation by causing the S-phase arrest, not by inhibiting the repair of DNA damage as observed in Escherichia coli

The order of multiple excited state proton transfer in ternary complex of norharmane and acetic acids

Dolores Reyman et al. found the norharmane (9H-pyrido [3,4-b] indole) (NHM) and two acetic acid molecules can form the ternary complex (NHM-2A) in component solvent of dichloromethane and acetic acid via the hydrogen bond chain (J. Lumin. 2014, 148, 64). But the specific reaction details during this process were rarely reported. In this study, we will give an insight into the reasons which promote the occurrence of this reaction as well as its reaction order. The hydrogen bond enhancing behavior in first excited state (S₁) is verified through the analysis of geometric configurations, infrared spectra, frontier molecular orbitals and potential energy curves. The absorption and fluorescence spectra we calculated are well coincident with the experimental results. Meanwhile, it is obvious that the hydrogen bond intensity is gradually enhanced from N₁H₂⋯O₃, O₄H₅⋯O₆ to O₇H₈⋯N₉ by analyzing the reduced density gradient (RDG) isosurface. The hydrogen bond strengthening mechanism has been confirmed in which the hydrogen bond interaction acts as driving force for excited state proton transfer (ESPT) reaction. In order to provide a reliable description of the reaction energy profiles, we compare the barrier differences obtained by m062x and B3LYP methods. We might safely draw the conclusion that the multiple ESPT is a gradual process initiated by the proton transfer of O₇H₈⋯N₉. And we further proof the ESPT process can be completed via the NHM-2A → NHM-2AS → NHM-2AD → NHM-2AT in S₁ state. Theoretical research of NHM-2A has been carried out by density functional theory (DFT) and time-dependent density functional theory (TDDFT). It is worth noting that we predicted that the fluorescence at 400 nm observed in experiment is more likely to be emitted by NHM-2AS in S₁ state.

Shipment of a photodynamic therapy agent into model membrane and its controlled release: A photophysical approach

Harmine, an efficient cancer cell photosensitizer (PS), emits intense violet color when it is incorporated in well established self assembly based drug carrier formed by cationic surfactants of identical positive charge of head group but varying chain length, namely, dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB). Micelle entrapped drug emits in the UV region when it interacts with non-toxic β-cyclodextrin (β-CD). Inspired by these unique fluorescence/structural switching properties of the anticancer drug, in the present work we have monitored the interplay of the drug between micelles and non-toxic β-CDs. We have observed that the model membranes formed by micelles differing in their hydrophobic chain length interact with the drug differently. Variation in the surfactant chain length plays an important role for structural switching i.e. in choosing a particular structural form of the drug that will be finally presented to their targets. The present study shows that in case of necessity, the bound drug molecule can be removed from its binding site in a controlled manner by the use of non-toxic β-CD and it is exploited to serve a significant purpose for the removal of excess/unused adsorbed drugs from the model cell membranes. We believe this kind of β-CD driven translocation of drugs monitored by fluorescence switching may find possible applications in controlled release of the drug inside cells.

UVA Photoactivation of Harmol Enhances Its Antifungal Activity against the Phytopathogens Penicillium digitatum and Botrytis cinerea

Phytopathogenic fungi responsible for post-harvest diseases on fruit and vegetables cause important economic losses. We have previously reported that harmol (1-methyl-9H-pyrido[3,4-b]indol-7-ol) is active against the causal agents of green and gray molds Penicillium digitatum and Botrytis cinerea, respectively. Here, antifungal activity of harmol was characterized in terms of pH dependency and conidial targets; also photodynamic effects of UVA irradiation on the antimicrobial action were evaluated. Harmol was able to inhibit the growth of both post-harvest fungal disease agents only in acidic conditions (pH 5), when it was found in its protonated form. Conidia treated with harmol exhibited membrane integrity loss, cell wall disruption, and cytoplasm disorganization. All these deleterious effects were more evident for B. cinerea in comparison to P. digitatum. When conidial suspensions were irradiated with UVA in the presence of harmol, antimicrobial activity against both pathogens was enhanced, compared to non-irradiated conditions. B. cinerea exhibited a high intracellular production of reactive oxygen species (ROS) when was incubated with harmol in irradiated and non-irradiated treatments. P. digitatum showed a significant increase in ROS accumulation only when treated with photoexcited harmol. The present work contributes to unravel the antifungal activity of harmol and its photoexcited counterpart against phytopathogenic conidia, focusing on ROS accumulation which could account for damage on different cellular targets.

Determining the molecular basis for the pH-dependent interaction between 2'-deoxynucleotides and 9H-pyrido[3,4-b]indole in its ground and electronic excited states

Interaction between norharmane and three different 2'-deoxynucleotides (dNMP) (2'-deoxyguanosine 5'-monophosphate (dGMP), 2'-deoxyadenosine 5'-monophosphate (dAMP) and 2'-deoxycytidine 5'-monophosphate (dCMP)), in aqueous solution, was studied in the ground state by means of UV-vis and (1)H-NMR spectroscopy and in the first electronic excited state using steady-state and time-resolved fluorescence spectroscopy. In all cases, the norharmane-dNMP interaction dependence on the pH was examined. Possible mechanisms for the interaction of both ground and electronic excited states of norharmane with nucleotides are discussed. Spectroscopic, molecular modeling and chemometric analysis were performed to further characterize the chemical structure of the complexes formed and to get additional information concerning the interaction between dNMPs and norharmane.

Photosensitized electron transfer within a self-assembled norharmane-2'-deoxyadenosine 5'-monophosphate (dAMP) complex

Norharmane is a compound that belongs to a family of alkaloids called β-carbolines (βCs). These alkaloids are present in a wide range of biological systems, playing a variety of significant photo-dependent roles. Upon UV-A irradiation, βCs are able to act as efficient photosensitizers. In this work, we have investigated the photosensitized oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) by norharmane in an aqueous phase, upon UV-A (350 nm) irradiation. The effect of the pH was evaluated on both the interactions between norharmane and dAMP in the ground and electronic excited states, and on the dAMP photosensitized oxidation. A quite strong static interaction between norharmane and dAMP was observed, especially under those pH conditions where the protonated form of the alkaloid is present (pH < 7). Theoretical studies were performed to further characterize the static complex structure. The participation of reactive oxygen species (ROS) in the photosensitized reaction was also investigated and the photoproducts were characterized by means of UV-LDI-MS and ESI-MS. All the data provided herein indicate that electron transfer (Type I) within a self-assembled norharmane-dAMP complex is the operative mechanism in the dAMP photosensitization.

Effect of electrolytes, nucleotides and DNA on the fluorescence of flavopereirine natural alkaloid

The absorption and fluorescence characteristics of flavopereirine, a pharmaceutically important natural alkaloid, were studied to reveal how the complex formation and the change of the microenvironment affect the deactivation kinetics from the singlet-excited state. The fluorescence lifetime was not influenced by the ionic strength, but a significant deuterium effect was observed showing that hydrogen bonding in the singlet-excited state promoted energy dissipation. Nucleotides caused both static and dynamic quenching. The rate constant of the latter process increased when the nucleobase was capable of donating electron to the excited flavopereirine. The spectrophotometric measurements provided evidence for non-cooperative binding to double-stranded DNA with an equilibrium constant of 4.6 × 10(5) M(-1). Time-resolved fluorescence signals showed that three kinds of complexes are formed with distinct fluorescence lifetimes. Flavopereirine binding to chondroitin sulfate was also found, which led to different fluorescence characteristics at pH 2 and 6.