Biosynthetic studies of marine lipids—3 : Experimental demonstration of the course of side chain extension in marine sterols

The Pacific sponge Aplysina fistularis was fed cholesterol-[4-¹⁴C],(24R)-methyl-25-dehydrocholesterol-[26-¹⁴C] (epicodisterol[26-¹⁴C]), (24S)-methyl-25-dehydrocholesterol-[26-¹⁴C] (codisterol-[26-¹⁴C]), and 24-methylenecholesterol-[28-¹⁴C]. Only epicodisterol, which has the same stereochemistry at C-24 as (24R,25S)-24,26-dimethylcholesterol (aplysterol), was converted with high efficiency into (24R)-24,27-dimethyl-25-dehydrocholesterol (25-dehydroaplysterol). Further side chain extension [to E-(24R)-24,26,27-trimethyl-25-dehydrocholesterol (verongulasterol)] could also be demonstrated.     

Supramolecular Cationic Tetraruthenated Porphyrin Induces Single-Strand Breaks and 8-Oxo-7,8-dihydro-2'-deoxyguanosine Formation in DNA in the Presence of Light

Abstract— The aim of this investigation is the evaluation of DNA interaction of with tetraruthenated porphyrin (TRP) and of DNA damage in the presence of light. Direct-fluorescence and electronic absorption measurements after incubation of DNA with TRP indicate strong binding between pBR322 DNA or calf thymus DNA with the modified porphyrin. Exposure of pBR322 DNA to TRP (up to 3 μ M ) and light leads to single-strand break formation as determined by the conversion of the supercoiled form (form I) of the plasmid into the nicked circular form (form II). Oxidative DNA base damage was evaluated by the detection of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) after irradiation of calf thymus DNA in the presence of the TRP. The data demonstrated a dose and time dependence with each type of DNA damage. These data indicate (1) a specificity of the binding mode and (2) type I and II photoinduced mechanisms leading to strand scission activity and 8-oxodGuo formation. Accordingly, singlet molecular oxygen formation, after TRP excitation, was confirmed by near-infrared emission. From these investigations a potential application of TRP in photodynamic therapy is proposed.     

Protein‐free ligand screening: simplification of chiral chromatographic development via novel adaptation of NMR screening methodologies

We demonstrate here a promising NMR method that provides evidence for chiral compound selector interaction as a first‐pass screening method. A novel adaptation of commonly used protein‐based screening technologies, this approach relies upon ligand‐to‐stationary phase interaction wherein the stationary phase is tethered to sepharose beads. At only minutes per experiment, this methodology significantly reduces the time required for chiral separation methodology development and complements currently available chromatographic purity technologies.Copyright © 2009 John Wiley & Sons, Ltd.     

Scanning tunneling microscopy and spectroscopy on cracked surfaces of superconducting CeRu2

Scanning tunneling microscopy and scanning tunneling spectroscopy measurements have been performed on a single crystal of CeRu₂ down to 2.2 K under a magnetic field up to 2.0 T. The sample surfaces for the measurements are prepared by cutting or cracking the single crystal at 4.2 K. The vortex lattice has been imaged by mapping the quasiparticle density of states at the Fermi energy on the surface. We have observed that the surface has been covered with microstructures a few nm in diameter. These microstructures are characteristic of the surface when the sample is cut or cracked at low temperature.     

Chemical modification of cellulose nanocrystals and their application in thermoplastic starch (TPS) and poly(3‐hydroxybutyrate) (P3HB) nanocomposites

The effect of sulfated (original), carboxylated (oxidized), and Jeffamines M2005‐grafted cellulose nanocrystals (CNCs) on the barrier and mechanical properties of thermoplastic starch (TPS) and poly(3‐hydroxybutyrate) (P(3HB)) matrices was investigated. CNCs were first oxidized via a catalytic reaction using NaClO as an oxidant and then grafted with an amine‐terminated ethylene oxide (EO)/propylene oxide (PO) copolymer (Jeffamine) by an amine‐acid coupling reaction. A degree of oxidation (DO) of 0.108 (mol/mol of anhydroglucose) was attempted for the carboxylated CNCs, whereas a degree of substitution (DS) of 0.04 (mol/mol of anhydroglucose) was determined for the M2005‐grafted CNCs. These values indicated satisfactory reactive process, with yields of 68% and 47.3% for the carboxylation and peptide coupling reactions, respectively. Fourier‐transform infrared spectroscopy (FTIR) analysis showed bands at 1643 cm^?1 and 1550 cm^?1 in the spectrum of M2005‐grafted CNCs, which qualitatively indicated the amide bond formation. In addition, the morphology and the zeta potential of modified CNCs ensured their homogeneity, stability, and surface degree of charge. In spite of a decrease in the solubility in water of the modified crystals, the procedure of chemical modification used avoided any variation in their crystalline structure and thermal stability. Then, the incorporation of sulfated, oxidized, or M2005‐grafted CNCs in matrices of TPS and P(3HB) allowed to produce reinforced nanocomposite films, with excellent barrier properties. Therefore, the chemical compatibility between CNCs and the polymer matrices is essential to produce attractive nanocomposites with improved mechanical properties for industrial applications.     

Electron-positron pair production by photons in nonuniform strong fields

A probability of electron-positron pair production by photons in strong nonuniform fields is derived by applying a model trajectory method in the frame of a semiclassical approach. In addition to the well known invariant field parameter chi, a new invariant parameter nu is introduced to characterize the nonuniformity of the field. For nu>1, the obtained expression is reduced to the uniform-field approximation while it approaches the Bethe-Heitler formula for nu<1. The pair production is predicted for relatively weak external fields where the uniform-field approximation gives no effect. The theory agrees well with the experimental results of crystal-assisted pair production.     

Membrane trafficking and mitochondrial abnormalities precede subunit c deposition in a cerebellar cell model of juvenile neuronal ceroid lipofuscinosis

Background  

JNCL is a recessively inherited, childhood-onset neurodegenerative disease most-commonly caused by a ~1 kb CLN3 mutation. The resulting loss of battenin activity leads to deposition of mitochondrial ATP synthase, subunit c and a specific loss of CNS neurons. We previously generated Cln3 ^Δex7/8 knock-in mice, which replicate the common JNCL mutation, express mutant battenin and display JNCL-like pathology.     

Improved synthesis of beta-D-6-methylpurine riboside and antitumor effects of the beta-D- and alpha-D-anomers

6-Methylpurine-beta-D-riboside (beta-D-MPR) has been synthesized by coupling 6-methylpurine and 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribose using conditions that produce the beta-D-anomer exclusively. The in vitro antitumor effects of beta-D-MPR and 6-methyl-purine-alpha-D-riboside (alpha-D-MPR) in five human tumor cell lines showed that beta-D-MPR was highly active (IC(50) values ranging from 6 to 34 nM). alpha-D-MPR, although less active than beta-D-MPR, also exhibited significant antitumor effects (IC50 values ranging from 1.47 to 4.83 microM).