The Polyphenols α-Mangostin and Nordihydroguaiaretic Acid Induce Oxidative Stress,Cell Cycle Arrest,and Apoptosis in a Cellular Model of Medulloblastoma

Medulloblastoma is a common malignant brain tumor in the pediatric age. The current therapeutics present serious collateral effects. Polyphenols α-mangostin and nordihydroguaiaretic acid (NDGA) exert potent antitumoral activity in different cancer models, although their antitumoral effects have not been described in medulloblastoma cells yet. This study aimed to examine the proapoptotic effects of these polyphenols on human medulloblastoma cells. Medulloblastoma cell line Daoy was incubated with increasing concentrations of α-mangostin or NDGA for 24 h. The cell viability was analyzed using crystal violet and trypan blue dyes. Determination of the glutathione (GSH)/glutathione disulfide (GSSG) ratio and levels of carbonylated proteins was performed to evaluate the oxidative stress. Cell cycle progression and induction of cell death by fluorochrome-couple and TUNEL assays were evaluated using flow cytometry assays. Individual treatments with α-mangostin or NDGA decreased the viability of Daoy cells in a dose-dependent manner, inducing G2/M and S-G2/M cell cycle arrest, respectively. Both polyphenols induced cell death and increased oxidative stress. Very interestingly, α-mangostin showed more potent effects than NDGA. Our results indicate that α-mangostin and NDGA exert important cytostatic and cytotoxic effects in the Daoy cell line. These data highlight the potential usefulness of these compounds as an alternative strategy in medulloblastoma treatment.     

Unification of Spins and Charges

Polynomials in Grassmann algebra can be used to describe the internal degrees, spins and charges of spinors, scalars, and vectors. It was shown by Manko Bortnik and Nielsen that Kähler spinors can be generalized to describe spins of vectors as well as spins and charges of scalars, vectors, and spinors. In dimensions 14 and higher, the spontaneous breaking of symmetry leads gravity in d dimensions to manifest in 4-dimensional subspace as ordinary gravity and all needed gauge fields as well as the Yukawa couplings. Both approaches, Kähler's one (if generalized) and ours, manifest four generations of massless fermions, which are left-handed SU(2) doublets and right-handed SU(2) singlets. A possible way of spontaneously breaking symmetries is pointed out at the level of canonical momentum.     

Multielectron photoreduction of a bridged ruthenium dimer, [(phen)2Ru(tatpp)Ru(phen)2][PF6]4: aqueous reactivity and chemical and spectroelectrochemical identification of the photoproducts

The dinuclear ruthenium(II) complex [(phen)(2)Ru(tatpp)Ru(phen)(2)][PF(6)](4) (P) (where phen is 1,10-phenanthroline and tatpp is 9,11,20,22-tetraazatetrapyrido[3,2-a:2'3'-c:3' ',2' '-l:2' ",3' "]pentacene) is shown to accept up to four electrons and two protons on the central tatpp bridging ligand via a combination of stoichiometric chemical reductions and protonations and spectroelectrochemistry (SEC) in acetonitrile. The absorption spectra of seven distinct species related by reduction and/or protonation of the central tatpp ligand were obtained and the two sequential photoproducts obtained from visible irradiation of P in acetonitrile (with 0.25 M triethylamine (TEA)) thus identified as P(-) (singly reduced, nonprotonated P) and HP(-) (doubly reduced, monoprotonated P), respectively. Importantly, the photochemical activity is maintained in mixed water-acetonitrile (1:4) solutions under basic conditions, and the protonation state of the photoproducts is readily controlled by varying the solution pH between 8 and 12. Absorption spectra obtained by SEC under similar solvent conditions were virtually identical to those obtained photochemically, and thus the doubly reduced photoproducts were identified as P(2)(-) (pH 12), HP(-) (pH 10), and H(2)()P (pH 8). This last photoproduct, H(2)()P, is particularly promising with respect to solar hydrogen production in that it can be produced in the presence of water and its dehydrogenation under appropriate conditions could yield H(2) and regenerate P. A qualitative MO diagram is presented as a framework for understanding the observed optical transitions as a function of oxidation and protonation state.     

Polymer/Laponite Composite Latexes: Particle Morphology,Film Microstructure,and Properties

Transparent film materials with excellent mechanical and thermal properties were elaborated by drying a latex suspension of armored polymer/Laponite composite particles. Low‐temperature TEM observation of ultrathin cross‐sections of the films indicated a unique network morphology characterized by a “honeycomb” distribution of the Laponite platelets remindful of the original particles morphology.

     

Flavin Derivatives with Tailored Redox Properties: Synthesis,Characterization, and Electrochemical Behavior

This study establishes structure–property relationships for four synthetic flavin molecules as bioinspired redox mediators in electro‐ and photocatalysis applications. The studied flavin compounds were disubstituted with polar substituents at the N1 and N3 positions (alloxazine) or at the N3 and N10 positions (isoalloxazines). The electrochemical behavior of one such synthetic flavin analogue was examined in detail in aqueous solutions of varying pH in the range from 1 to 10. Cyclic voltammetry, used in conjunction with hydrodynamic (rotating disk electrode) voltammetry, showed quasi‐reversible behavior consistent with freely diffusing molecules and an overall global 2e^?, 2H⁺ proton‐coupled electron transfer scheme. UV/Vis spectroelectrochemical data was also employed to study the pH‐dependent electrochemical behavior of this derivative. Substituent effects on the redox behavior were compared and contrasted for all the four compounds, and visualized within a scatter plot framework to afford comparison with prior knowledge on mostly natural flavins in aqueous media. Finally, a preliminary assessment of one of the synthetic flavins was performed of its electrocatalytic activity toward dioxygen reduction as a prelude to further (quantitative) studies of both freely diffusing and tethered molecules on various electrode surfaces.     

Quantum chemical study of a new class of sensitisers: influence of the substitution of aromatic rings on the properties of copper complexes

We present a computational study of new copper complexes with potential applications as sensitisers for solar cells. The applied methodology for this study is based on the density functional theory (DFT) and time-dependent DFT, using the B3LYP, PBE0 and M06 functionals with the LANL2DZ (D95V on first row), 6-31G(d,p), 6-311G(d,p) and DZVP basis sets. Optimised molecular structure, the absorption spectra, the molecular orbitals energies and the chemical reactivity parameters that arise from conceptual DFT were calculated. Solvent effects have been taken into account by an implicit approach, namely, the polarisable continuum model (PCM), using the non-equilibrium version of the integral equation formalism of the PCM model. Interesting work for experimentalists in the dye sensitised solar cells’ field.     

Catalyst and substituent effects on the rhodium(II)-catalysed intramolecular Buchner reaction

Intramolecular rhodium(II)-catalysed aromatic addition (Buchner) reactions of a range of α- and β-substituted α-diazoketones are reported. Both steric and electronic effects are evident for the aromatic additions investigated. In general, highly efficient aromatic addition is achieved through use of rhodium carboxylates bearing electronegative ligands, such as rhodium trifluoroacetate, while aromatic addition employing rhodium catalysts with more electron-donating ligands, such as rhodium caprolactam, is less efficient. Excellent levels of diastereoselectivity are possible for this process in the presence of rhodium acetate and rhodium caprolactam, however, a reduction in diastereocontrol is generally associated with use of the more reactive, electronegative catalysts. Interestingly, these catalyst effects can be overcome through the steric effects of the substituents on the α-diazoketone substrates, with the presence of sterically bulky substituents at the 2- or 3-position rendering the aromatic addition essentially catalyst independent in terms of efficiency and diastereocontrol.