Flavin-Helicene Amphiphilic Hybrids: Synthesis, Characterization, and Preparation of Surface-Supported Films

This work reports on the preparation and structural characterization of flavo[7]helicene 1 (flavin-[7]helicene conjugate), which was subsequently characterized at the molecular level in either an aqueous environment or an organic phase, at the supramolecular level in the form of polymeric layers, and also embedded in a lipidic mesophase environment to study the resulting properties of such a hybrid relative to its parent molecules. The flavin benzo[g]pteridin-2,4-dione (isoalloxazine) was selected for conjugation because of its photoactivity and reversible redox behavior. Compound 1 was prepared from 2-nitroso[6]helicene and 6-methylamino-3-methyluracil, and characterized using common structural and spectroscopic tools: circular dichroism (CD), circularly polarized luminescence (CPL) spectroscopy, cyclic voltammetry (CV), and DFT quantum calculations. In addition, a methodology that allows the loading of 1 enantiomers into an internally nanostructured lipid (1-monoolein) matrix was developed.

Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings

The first racemization-stable helicene derivatives fluorinated at terminal rings, 1,2,3,4-tetrafluoro[6]helicene (6) and 1,2,3,4,13,14,15,16-octafluoro[6]helicene (15), were synthesized via the Wittig reaction followed by oxidative photocyclization in an overall yield of 41% of 6 and 76% of 15. The changed electronic structure in fluorinated helicenes was reflected in a slight shift of UV-vis absorption, fluorescence excitation, and emission spectra maxima when compared to unsubstituted [6]helicene. Cyclic voltammetry revealed a moderate decrease in the HOMO-LUMO gap with increasing fluorination. The specific rotation of tetrafluoro[6]helicene 6 enantiomers was found to be approximately 25% lower than that of unsubstituted [6]helicene. The theoretical study of the racemization barrier suggested a reasonable shift toward higher energy with increasing fluorination. The increasing fluorination also significantly affected the intermolecular interactions in the crystal lattice. The observed CH···F interactions led to the formation of 1D-molecular chains in the crystal structures of both fluorinated helicenes.

Novel insights into the electrochemical detection of nitric oxide in biological systems

In recent years, microsensor technologies have made a rapid expansion into different fields of physical sciences, engineering, and biomedicine. For analyses of various biomolecules, novel sensors and detection platforms in the electrochemical field have been reported recently. The most important applications based on microelectromechanical systems dramatically reduce the need of manipulation steps with samples, while improving data quality and quantitative capabilities. This is also the case of a special class of electrochemical sensors that allow direct, real-time and non-invasive measurements of nitric oxide, whose determination is crucial for the purposes of basic research, as well as of preclinical and clinical studies. Therefore, this minireview will focus on the description of recent discoveries in the electrochemical determination of nitric oxide, released in different in vitro systems.

[Regional migrating osteoporosis - a case report]

Regional migrating osteoporosis (RMO) was observed in young man with episodes of bone pain in bearing joints, which migrated from hip to leg and subsequently to knee on the unilateral side. Dynamic scintigraphy (SPECT) carried out during relapse of pain demonstrated increased accumulation of radioizotope in Lisfrank joint, distal epiphysis of femur and proximal epiphysis of tibia on the unilateral side due to hyperperfusion and high metabolic turnover in these regions of the skeleton. Dia-gnosis of RMO was confirmed by magnetic resonance (MRI), which showed bone marrow edema of corresponding regions. Although RMO is relatively benign disease with spontaneous remissions, infection etiology or the more serious avascular necrosis should be taken into account.

Antioxidant, metal-binding and DNA-damaging properties of flavonolignans: a joint experimental and computational highlight based on 7-O-galloylsilybin

Besides the well-known chemoprotective effects of polyphenols, their prooxidant activities via interactions with biomacromolecules as DNA and proteins are of the utmost importance. Current research focuses not only on natural polyphenols but also on synthetically prepared analogs with promising biological activities. In the present study, the antioxidant and prooxidant properties of a semi-synthetic flavonolignan 7-O-galloylsilybin (7-GSB) are described. The presence of the galloyl moiety significantly enhances the antioxidant capacity of 7-GSB compared to that of silybin (SB). These findings were supported by electrochemistry, DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activity, total antioxidant capacity (CL-TAC) and DFT (density functional theory) calculations. A three-step oxidation mechanism of 7-GSB is proposed at pH 7.4, in which the galloyl moiety is first oxidized at Ep,1=+0.20V (vs. Ag/AgCl3M KCl) followed by oxidation of the 20-OH (Ep,2=+0.55V) and most probably 5-OH (Ep,3=+0.95V) group of SB moiety. The molecular orbital analysis and the calculation of O-H bond dissociation enthalpies (BDE) fully rationalize the electrooxidation processes. The metal (Cu(2+)) complexation of 7-GSB was studied, which appeared to involve both the galloyl moiety and the 5-OH group. The prooxidant effects of the metal-complexes were then studied according to their capacity to oxidatively induce DNA modification and cleavage. These results paved the way towards the conclusion that 7-O-galloyl substitution to SB concomitantly (i) enhances antioxidant (ROS scavenging) capacity and (ii) decreases prooxidant effect/DNA damage after Cu complexation. This multidisciplinary approach provides a comprehensive mechanistic picture of the antioxidant vs. metal-induced prooxidant effects of flavonolignans at the molecular level, under ex vivo conditions.

Cytotoxicity and Pro-Apoptotic Activity of 2,2´-Bis[4,5-bis(4-hydroxybenzyl)-2-(4-hydroxyphenyl)cyclopent-4-en-1,3-dione], a Phenolic Cyclopentenedione Isolated from the Cyanobacterium Strain Nostoc sp. str. Lukešová 27/97

The cytotoxicity of the polyphenol 2,2´-bis[4,5-bis(4-hydroxybenzyl)-2-(4-hydroxyphenyl)cyclopent-4-en-1,3-dione], nostotrebin 6 (NOS-6), was tested under in vitro conditions using mouse fibroblasts (BALB/c cells). Identification of NOS-6 and its uptake into fibroblasts was examined by multi-stage mass spectrometry analysis with the following fragmentation pattern: MS (m/z) [M+H]⁺ 799.1 → MS² 399.1 → MS³ 305.1 → MS⁴ 277.1. Using several cell viability assays, the IC₅₀ of NOS-6 after 24 h incubation was found to be 8.48 ± 0.16/12.15 ± 1.96 µM (neutral red/MTT assay) which was higher than that of doxorubicin. It was found that NOS-6 is capable of inducing both types of cell death, apoptosis and necrosis in a dose-dependent manner. The biological activities of the cyclopentenediones and preliminary data on NOS-6 cytotoxicity are discussed.