Synthesis and characterization of semi- and full-interpenetrating polymer networks of poly(2,6-dimethyl-1,4-phenylene oxide) and polydimethylsiloxane

The synthesis and characterization of pseudo or semi- and full-interpenetrating polymer networks (IPNs) of poly(2,6-dimethyl-1,4-phenylene oxide) and polydimethylsiloxane were performed. We observed that in full IPNs, the elasticity of the IPN samples increased very drastically, as the composition of polydimethylsiloxane increased (i.e. 0–60%) while the tensile strength (TS) and the glass transition temperature (T_g) decreases. The pseudo IPNs appeared to consist of two phases while the full IPNs of lower siloxane content were miscible.     

Photopatterning in poly-L-lysine thin films using UV-enhanced hydrophilicity

Deep UV lithography on poly-L-lysine thin films was used to generate microarrays with enhanced hydrophilicity. This was manifested as adsorption of ambient humidity from air by areas exposed to UV fluence around 5 J/cm2 and was made visible by phase-contrast microscopy. Kinetics of adsorption was investigated by a novel technique involving fabrication of submicrometer hydrophilicity grating by two-beam UV interferometry. In an aqueous colloidal medium, gold and polystyrene microspheres preferentially attach to areas that are relatively less hydrophilic, i.e., those areas not exposed to UV light. This observation provides a method for fabricating micro- and nanoporous arrays with controlled porosity. The technique is demonstrated with microspheres of sizes between 250 nm and 10 microm.     

The convergent total synthesis and antibacterial profile of the natural product streptothricin F

A convergent, diversity-enabling total synthesis of the natural product streptothricin F has been achieved. Herein, we describe the potent antimicrobial activity of streptothricin F and highlight the importance of a total synthesis that allows for the installation of practical divergent steps for medicinal chemistry exploits. Key features of our synthesis include a Burgess reagent-mediated 1,2-anti-diamine installation, diastereoselective azidation of a lactam enolate, and a mercury(ii) chloride-mediated desulfurization-guanidination. The development of this chemistry enables the synthesis and structure–activity studies of streptothricin F analogs.

The second ever total synthesis of streptothricin F and the first achieved through a diversity-enabling convergent route. The synthesis is achieved in 35 total steps, with a longest linear sequence of 19 steps, and 0.40% overall yield.     

Photoinduced grating formation in azo-dye-labeled phospholipid thin films by 244-nm light

Holographic gratings are recorded in azo-dye nitrobenzoxazole-labeled phospholipid thin films by use of 244-nm UV light. The gratings continue to grow for more than 1 h, even after the recording light is removed. The diffraction efficiency of these gratings shows extreme sensitivity to humidity and can increase reversibly by 2 orders of magnitude in air that is saturated with water vapor. This effect is related to the unique characteristics of phospholipid molecules that undergo hydration-dependent structural reorganization and self-assembly.     

Photochemically deposited surface relief gratings of an azo-dye-labeled phospholipid from the aqueous phase

Surface relief holographic gratings are fabricated on the polybutadiene-coated walls of a cell filled with an aqueous solution of an azo-dye-labeled phospholipid. A low power (2 mW) 488 nm argon ion laser wavelength is used. Laser-excited azo dye reacts to produce a permanent surface-relief pattern on the polybutadiene substrate. Gratings are recorded for varying concentrations of the phospholipid solution as well as laser intensity. Lithographic masks are used to show that the photochemical pattern on the substrate is an exact replica of the light intensity distribution, and so the technique can be used for holographic recording as well as for biomolecular applications.     

α-haloalkanesulfonyl bromides in organic synthesis. 4. Regioselective γ-deprotonation of α,β-unsaturated sulfones. A simple synthesis of 2-alkyl-1,3-butadienes.

A simple method for converting 2-methyl-1-alkenes into 2-alkyl-1,3-butadienes is described. Evidence for complexation of lithium cations by sulfonyl groups in the course of reactions of α,β-unsaturated sulfones with LiOt-Bu is presented.     

Photodegradation of melanin by an interferometric technique

Photodegradation of melanin thin films is investigated for a UVA wavelength of 355 nm and a UVC wavelength of 244 nm. The technique involves interferometric exposure of melanin with two coherent beams from a low-power UV laser. The periodic photodegradation-grating pattern is monitored by diffraction of a second low-power He-Ne laser. Dependence of the photodegradation rate on UV intensity as well as the effect of ambient humidity is investigated and explained with a simple model. The technique has promise for investigating photo-induced effects in other biomolecular substrates as well.     

Study of a molybdenum dithiocarboxylato complex. Chemical characterization,crystal and molecular structure of tetrakis(α-dithionaphthoato)molybdenum(IV)

Summary The complex Mo(-C₁₀H₇CS₂)₄ has been prepared from several starting materials: [Mo(NNHPh)₂(butane-2,3-diolate)₂] · H₂NNHPh, [MoCl(NNMe₂)₂(PPh₃)₂]⁺Cl^–, [MoO₂ (MeCHOCHOHMe)₂] · 2MeCHOHCHOHMe or [(C₄H₉)₄N]₆Mo₇O₂₄, reacted with-C₁₀H₇CS₂H. The complex Mo(-C₁₀H₇CS₂)₄ crystallizes from CH₂Cl₂-Et₂O in the orthorhombic space group Pbca,a=13.655(3)Å,b=21.707(5)Å,c= 26.365(2)Å, V=7814.81ų, Z=8; 5075 reflections collected, 2723 used in solution to give R=0.0517, R_w=0.0564. The molybdenum is eight coordinate with geometry approximating to aD _2d dodecahedron. The average Mo-S bond lengths are 2.526(3)Å and 2.479(3)Å for the dodecahedrala andb sites, respectively.