Asymmetric total synthesis of dibenzocyclooctadiene lignan natural products

[structure: see text] Full details of the asymmetric total syntheses of the dibenzocyclooctadiene lignans interiotherin A, angeloylgomisin R, gomisin O, and gomisin E (epigomisin O) are presented. The syntheses were based on a unified synthetic strategy involving a novel crotylation using the Leighton auxiliary that occurred with excellent asymmetric induction (>98:2 enantiomeric ratio), a diastereoselective hydroboration/Suzuki-Miyaura coupling reaction sequence, and an atropdiastereoselective biarylcuprate coupling, both of which occurred with total (>20:1) stereocontrol. The syntheses were achieved in six to eight steps from simple aromatic precursors.     

Antibacterial Activity and Synergistic Effect of Biosynthesized AgNPs with Antibiotics Against Multidrug-Resistant Biofilm-Forming Coagulase-Negative Staphylococci Isolated from Clinical Samples

Silver nanoparticles form promising template for designing antimicrobial agents against drug resistant pathogenic microorganisms. Thus, the development of a reliable green approach for the synthesis of nanoparticles is an important aspect of current nanotechnology research. In the present investigation, silver nanoparticles synthesized by a soil Bacillus sp. were characterized using UV–vis spectroscopy, FTIR, SEM, and EDS. The antibacterial potential of biosynthesized silver nanoparticles, standard antibiotics, and their conjugates were evaluated against multidrug-resistant biofilm-forming coagulase-negative S. epidermidis strains, S. aureus, Salmonella Typhi, Salmonella Paratyphi, and V. cholerae. Interestingly, silver nanoparticles (AgNPs) showed remarkable antibacterial activity against all the test strains with the highest activity against S. epidermidis strains 145 and 152. In addition, the highest synergistic effect of AgNPs was observed with chloramphenicol against Salmonella typhi. The results of the study clearly indicate the promising biomedical applications of biosynthesized AgNPs.     

Surface Functionalization of Green-synthesized Reduced Graphene Oxide with PPIX Enhances Photosensitization of Cancer Cells

Photosensitizer-functionalized reduced graphene oxide (rGO) nanoparticles are promising materials for photodynamic therapy in cancer management. In this study, rGO is synthesized by a green route employing glucose as the reducing agent and functionalized with photosensitizer, protoporphyrin IX (PPIX) in a convenient, single-step procedure. PPIX-functionalized rGO exhibits photodynamic effect against cancer cells (HeLa) at 0.001 mg mL⁻¹ under visible light illumination (635 nm). A 50% elimination of HeLa cells after 5 min irradiation is observed while very low phototoxicity (80% cell viability) is noted against normal dermal fibroblast cells. A positive correlation with ROS accumulation and increased expression of caspase-3 in PPIX-functionalized rGO-treated cancer cells is also established. The results evidence a simple and cost-effective route for developing photosensitizer-functionalized rGO for effective and selective killing of cancer cells.     

Multi-Material Inkjet Printing of Self-Assembling and Reacting Coatings

Inkjet printing was used to deposit alternating 100 nm layers of anionic and cationic polymers in order to form self-assembled ionic complexes on flat and fabric substrates. The layers formed are characterized by elemental analysis, microscopy and solubility. As initially deposited, layers are soluble but form insoluble complexes when they are heated and annealed. This approach has been applied to polypeptides, polymer dyes, polymers with nanoparticulate pigments and also to epoxy adhesives.     

A molecular simulation study of a cyclic siloxane with attached biphehylyl 4-allyloxybenzoate mesogens

Abstract

A molecular simulation study of a cyclic siloxane macromolecule based on a pentamethylcyclosiloxane core and biphenylyl 4-allyloxybenzoate mesogenic units is reported. Molecular dynamics and semi-empirical calculations were used to provide insight into the conformation and the dielectric properties of the material. Out of three proposed conformations of the molecules, a cylindrical conformation was found to be the most probable. The intermolecular interactions were found to be optimized for the case where the mesogenic groups were planar and parallel to each other. The calculated mesogen length and inter-mesogen distances were consistent with available X-ray data. Electrostatic interactions were found to make a very significant contribution to the total energy. For the cylindrical model, the major component of the dipole was calculated to be along the long axis of the molecules. This is consistent with the alignment of the molecules parallel to a low frequency applied electric field as found experimentally.     

Self-assembled monolayers of Aβ peptides on Au electrodes: an artificial platform for probing the reactivity of redox active metals and cofactors relevant to Alzheimer's disease

The water-soluble hydrophilic part of human Aβ peptide has been extended to include a C-terminal cysteine residue. Utilizing the thiol functionality of this cysteine residue, self-assembled monolayers (SAM) of these peptides are formed on Au electrodes. Atomic force microscopy imaging confirms formation of small Aβ aggregates on the surface of the electrode. These aggregates bind redox active metals like Cu and cofactors like heme, both of which are proposed to generate toxic partially reduced oxygen species (PROS) and play a vital role in Alzheimer's disease. The spectroscopic and electrochemical properties of these Cu and heme bound Aβ SAM are similar to those reported for the soluble Cu and heme bound Aβ peptide. Experiments performed on these Aβ-SAM electrodes clearly demonstrate that (1) heme bound Aβ is kinetically more competent in reducing O(2) than Cu bound Aβ, (2) under physiological conditions the reduced Cu site produces twice as much PROS (measured in situ) than the reduced heme site, and (3) chelators like clioquinol remove Cu from these aggregates, while drugs like methylene blue inhibit O(2) reactivity of the heme cofactor. This artificial construct provides a very easy platform for investigating potential drugs affecting aggregation of human Aβ peptides and PROS generation by its complexes with redox active metals and cofactors.     

Modelling a nematic liquid crystal

The bulk phase liquid crystalline behaviour of a cyclic siloxane with a pentamethylcyclosiloxane core and biphenyl-4-allyloxybenzoate mesogens (BCS) was studied using molecular dynamics (MD) and wide angle X-ray analysis. This material exhibits partial crystallinity at room temperature and liquid crystalline behaviour above 120° C. For the MD simulations an ensemble of 27 molecules with 135 mesogenic units was simulated and a molecular mechanics force field was used to model the structural anisotropy of the siloxane molecules. Simulations were carried out both at room temperature and at an elevated temperature (425 K). Room temperature simulations showed that, contrary to our initial assumptions, the low energy molecular conformations were not cylindrical but splayed in shape. During the simulation a smectic-like, tilted layer structure was found to evolve for the cluster when full atom potentials were used, while no such development was observed when electrostatic interactions were neglected. The presence of a tilted layered structure was also suggested by the X-ray data. These results indicate that long range electrostatic interactions are significant for the molecular system under study. In order to calculate the orientational order parameter, the orientation of the molecular axis had to be determined. This was achieved by describing the mesogen shapes to be ellipsoidal and defining the principal axis of the ellipsoids to be the molecular directors. By sampling over 200 ps of simulation at 425 K, the time averaged order parameter (S) was calculated. The calculated S of 0.36 was comparable to the value of 0.4-0.45 found from the experimental data. Apart from providing insight into the relative importance of the various competing forces in the formation of the liquid crystalline phase, these simulations are also expected to be useful in predicting the mesophase behaviour of liquid crystalline systems.     

1,3-Dipolar cycloaddition between a metal-azide (Ph3PAuN3) and a metal-acetylide (Ph3PAuC≡CPh): an inorganic version of a click reaction

This report describes the synthesis and characterization of 1,5-bis-triphenylphosphinegold(I) 1,2,3-triazolate (3((1,5))). The synthesis of the dinuclear complex 3((1,5)) is achieved via an unprecedented inorganic click (iClick) reaction between the metal-azide PPh(3)AuN(3) (1) and the metal-acetylide PPh(3)Au-C≡CPh (2). Characterization of 3((1,5)) includes multinuclear NMR spectroscopy, combustion analysis, and single crystal X-ray crystallography. Experimental characterization is complemented with density-functional-theory (DFT) calculations which indicate the 1,4-isomer 3((1,4)) is less stable by 3.3 kcal mol(-1). The energetic difference lies primarily in the ability of the phenyl group in the 4-position of 3((1,5)) to lie coplanar with the triazolate to create a delocalized π-bonding HOMO orbital.