The Bifurcation Study of 1:2 Resonance in a Delayed System of Two Coupled Neurons

In this paper, we consider a delayed system of differential equations modeling two neurons: one is excitatory, the other is inhibitory. We study the stability and bifurcations of the trivial equilibrium. Using center manifold theory for delay differential equations, we develop the universal unfolding of the system when the trivial equilibrium point has a double zero eigenvalue. In particular, we show a universal unfolding may be obtained by perturbing any two of the parameters in the system. Our study shows that the dynamics on the center manifold are characterized by a planar system whose vector field has the property of 1:2 resonance, also frequently referred as the Bogdanov–Takens bifurcation with $Z_2$ symmetry. We show that the unfolding of the singularity exhibits Hopf bifurcation, pitchfork bifurcation, homoclinic bifurcation, and fold bifurcation of limit cycles. The symmetry gives rise to a “figure-eight” homoclinic orbit.     

Conversion of Natural Narciclasine to Its C-1 and C-6 Derivatives and Their Antitumor Activity Evaluation: Some Unusual Chemistry of Narciclasine

During the search for a general, efficient route toward the synthesis of C-1 analogues of narciclasine, natural narciclasine was protected and converted to its C-1 enol derivative using a novel semi-synthetic route. Attempted conversion of this material to its triflate in order to conduct cross-coupling at C-1 resulted in a triflate at C-6 that was successfully coupled with several functionalities. Four novel compounds were fully deprotected after seven steps and subjected to evaluation for cytotoxic activity against three cancer cell lines. Only one derivative showed moderate activity compared to that of narciclasine. Spectral and physical data are provided for all new compounds.     

Green,Black and Rooibos Tea Inhibit Prostaglandin E2 Formation in Human Monocytes by Inhibiting Expression of Enzymes in the Prostaglandin E2 Pathway

The formation of prostaglandin E2 (PGE2) is associated with adverse inflammatory effects. However, long-term treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) comes with risk of severe side effects. Therefore, alternative ways to inhibit PGE2 are warranted. We have investigated the effects of tea extracts and the polyphenols epigallocatechin gallate (EGCG) and quercetin on PGE2 formation, determined by immunoassay, and protein expression, determined by immunoblotting, of cytosolic phospholipase A2 (cPLA2), cyclooxygenase 2 (COX-2) and microsomal PGE synthase-1 (mPGES-1) in human monocytes. Green and black tea extracts, and with a lower potency, Rooibos tea extract, inhibited lipopolysaccharide (LPS) and calcium ionophore-induced PGE2 formation. In addition, all tea extracts inhibited the LPS-induced expression of mPGES-1, and the green and black tea extracts also inhibited, to a lesser extent, COX-2 expression. The tea extracts only marginally reduced cPLA2 expression and had no effect on COX-1 expression. EGCG, present in green and black tea, and quercetin, present in all three teas, also inhibited PGE2 formation and expression of mPGES-1, COX-2 and cPLA2. Cell-based and cell-free assays were also performed to evaluate direct effects on the enzymatic activity of COX and PGE synthases. Mainly, the cell-free assay demonstrated partial inhibition by the tea extracts and polyphenols. However, the inhibition required higher doses compared to the effects demonstrated on protein expression. In conclusion, green and black tea, and to a lesser extent Rooibos tea, are potent inhibitors of PGE2 formation in human monocytes, and mediate their effects by inhibiting the expression of the enzymes responsible for PGE2 formation, especially mPGES-1.     

Spectral analysis of laser-induced ultraweak delayed luminescence in cultured normal and tumor human cells: temperature dependence

The emission spectrum of ultraviolet A laser induced ultraweak delayed luminescence in cell cultures of mammalian cells depended on the temperature during irradiation and photonic measurements. A new method using a sophisticated photomultiplier system was developed in order to find differences between normal and tumor cells. The maximal peak of the emitted light for cultures measured at low temperature of 10 degrees C was near 510 nm in the green visible region while following irradiation at 32 degrees C this maximum was shifted to yellow-orange at 570 nm both in normal and melanoma cells. Overall, this ultraweak photonic model of cultured cells provides to be a new and powerful non-invasive tool for developing new strategies in skin cancer detection.     

Determination of the REE content,geological age,and absorbed alpha dose of allanite mineral from Palawan,Philippines

Allanite is a common accessory mineral in igneous rocks that contains significant amounts of rare-earth elements (REEs), thorium (Th), and uranium (U). The presence of Th and U in the allanite exposes it to radiation resulting in radiation damage in its crystal structure and further leads to metamictization. Hence, allanite can be used as a natural analogue to assess the long-term radiation effects in materials for high-level nuclear waste disposal. It provides information on the effect of α-decay on the crystal structure including the stability and integrity of the material. In this study, the absorbed α-dose of allanite from Ombo, Palawan, Philippines, was estimated from the Th and U content and geological age of the mineral using X-ray fluorescence and gamma-ray spectrometry. The amount of Th and REE was measured to be around 1.37 and ~30.4 wt.%, respectively. Radiometric dating using gamma-ray spectrometry estimated the age of the allanite mineral to be around 24–35 million years. Having obtained the amount of radioactivity and the time of exposure, the corresponding absorbed α-dose was estimated to be at 2.84 × 10¹⁴ α-decays/mg. Results suggest that the allanite mineral studied has not accumulated significant radiation damage to cause amorphization and still exhibit a crystalline structure. This study may provide data on the properties of allanite or silicate matrices as part of the ongoing studies on silicate minerals as natural analogues.     

Cytotoxicity and photocytotoxicity of a dendritic C(60) mono-adduct and a malonic acid C(60) tris-adduct on Jurkat cells

The cytotoxic and photocytotoxic effects of two water-soluble fullerene derivatives, a dendritic C(60) mono-adduct and the malonic acid C(60) tris-adduct were tested on Jurkat cells. Cell growth and vitality were determined by a cell counting and staining technique. After 2 weeks cultivation in the presence of the fullerene derivatives, it was found that only the dendritic mono-adduct inhibits cell growth (within 2 weeks the cell number decreased to 19%), whereas the tris-malonic acid adduct has little effect. The growth inhibition is reversible; cultivating the same cells further in the absence of fullerene, the cell number increased to 106.4%. Other experiments showed that these fullerene derivatives become toxic when irradiated with UVA or UVB light. The cell death is mainly caused by membrane damage and it is UV dose-dependent. Tris-malonic acid fullerene was found to be more phototoxic than the dendritic derivative. This result is in contrast to the singlet oxygen quantum yields determined for the two compounds. We propose that the two fullerene derivatives may interact with the cell membrane in different ways thus causing the observed effects. Further experiments will be done to determine the location and concentration of the two compounds in and on the cells.     

Biodegradable Polymers from Renewable Sources. New Hemicellulose‐Based Hydrogels

Hemicellulose/poly(2‐hydroxyethyl methacrylate) (PHEMA)‐based hydrogels were prepared by the radical polymerization of HEMA with hemicellulose purposely modified with well‐defined amounts of methacrylic functions using a redox initiator system. Oligomeric hydrosoluble hemicelluloses produced from spruce chips were used for modification studies. The chemical modification of hemicellulose was performed with 2‐[(1‐imidazolyl)formyloxy]ethyl methacrylate as a modifying agent and triethylamine as the catalyst. The kinetics of the modification reaction was monitored by means of ¹H NMR spectroscopy. The resulting hydrogels obtained after a 30 min reaction were homogeneous, elastic, and transparent materials.