Dipolar Photosystems: Engineering Oriented Push–Pull Components into Double‐ and Triple‐Channel Surface Architectures

Push–pull aromatics are not popular as optoelectronic materials because their supramolecular organization is difficult to control. However, recent progress with synthetic methods has suggested that the directional integration of push–pull components into multicomponent photosystems should become possible. In this study, we report the design, synthesis, and evaluation of double‐ or triple‐channel architectures that contain π stacks with push–pull components in parallel or mixed orientation. Moreover, the parallel push–pull stacks were uniformly oriented with regard to co‐axial stacks, either with inward or outward oriented push–pull dipoles. Hole‐transporting (p) aminoperylenemonoimides (APIs) and aminonaphthalimides (ANIs) are explored for ordered push–pull stacks. For the co‐axial electron‐transporting (n) stacks, naphthalenediimides (NDIs) are used. In double‐channel photosystems, mixed push–pull stacks are overall less active than parallel push–pull stacks. The orientation of the parallel push–pull stacks with regard to the co‐axial NDI stacks has little influence on activity. In triple‐channel photosystems, outward‐directed dipoles in bridging stacks between peripheral p and central n channels show higher activity than inward‐directed dipolar stacks. Higher activities in response to direct irradiation of outward‐directed parallel stacks reveal the occurrence of quite remarkable optical gating.     

Bidirectional switching of near IR emitting boradiazaindacene fluorophores

Two novel distyryl-boradiazaindacene dyes with dimethylaminostyryl and pyridylethenyl substituents display opposite spectral shifts on protonation with TFA in organic solvents. This bidirectional switching of the dyes can be shown to be directly related to ICT donor and acceptor characteristics of the substituents attached to the BODIPY core. The observed spectral response of these dyes could be very useful in the design of novel NIR fluorescent ratiometric probes for pH.     

Simultaneous determination of retinol,retinyl palmitate and β-carotene in rat serum treated with 7,12-dimethylbenz[a]anthracene and <Emphasis Type="Italic">Hypericum Perforatum</Emphasis> L. by high-performance liquid chromatography with diode-array detection

A new and simple high-performance liquid chromatography method was developed and validated for the simultaneous determination of retinol, retinyl palmitate and β-carotene in rat serum treated with Hypericum Perforatum L. and 7,12-dimethylbenz[a]anthracene. Furthermore, vitamin C was determined spectrophotometrically. High-performance liquid chromatography analysis was performed utilizing an Inertsil ODS3 reversed phase column with methanol-acetonitrile-tetrahydrofuran (65:30:5, v/v/v) as mobile phase, at a flow rate of 1.5 mL min⁻¹ and 40°C. Diode-array detection was conducted at 325 and 450 nm for retinol and retinyl palmitate, and β-carotene, respectively with a running time of 26 min. The high-performance liquid chromatography assay and extraction procedure proposed are simple, rapid, sensitive and accurate. This method was then applied to determine the amounts of retinol, retinyl palmitate and β-carotene in rat serum. Results of this study demonstrated that at 60^th day in the 7,12-dimethylbenz[a]anthracene-treated group there was a significant decrease (p<0.001), (p<0,01), (p<0.05) in levels of retinol, retinyl palmitate and vitamin C, respectively compared to the control group levels. A significant decrease (p<0.01) in retinyl palimitate was observed in the 7,12 dimethylbenz[a] anthracene + Hypericum Perforatum L. treated group compared to the control group..     

Structurally sophisticated octahedral metal complexes as highly selective protein kinase inhibitors

The generation of synthetic compounds with exclusive target specificity is an extraordinary challenge of molecular recognition and demands novel design strategies, in particular for large and homologous protein families such as protein kinases with more than 500 members. Simple organic molecules often do not reach the necessary sophistication to fulfill this task. Here, we present six carefully tailored, stable metal-containing compounds in which unique and defined molecular geometries with natural-product-like structural complexity are constructed around octahedral ruthenium(II) or iridium(III) metal centers. Each of the six reported metal compounds displays high selectivity for an individual protein kinase, namely GSK3α, PAK1, PIM1, DAPK1, MLCK, and FLT4. Although being conventional ATP-competitive inhibitors, the combination of the unusual globular shape and rigidity characteristics, of these compounds facilitates the design of highly selective protein kinase inhibitors. Unique structural features of the octahedral coordination geometry allow novel interactions with the glycine-rich loop, which contribute significantly to binding potencies and selectivities. The sensitive correlation between metal coordination sphere and inhibition properties suggests that in this design, the metal is located at a "hot spot" within the ATP binding pocket, not too close to the hinge region where globular space is unavailable, and at the same time not too far out toward the solvent where the octahedral coordination sphere would not have a significant impact on potency and selectivity. This study thus demonstrates that inert (stable) octahedral metal complexes are sophisticated structural scaffolds for the design of highly selective chemical probes.     

Effect of surface modification on magnetization of iron oxide nanoparticle colloids

Magnetic iron oxide nanoparticles have numerous applications in the biomedical field, some more mature, such as contrast agents in magnetic resonance imaging (MRI), and some emerging, such as heating agents in hyperthermia for cancer therapy. In all of these applications, the magnetic particles are coated with surfactants and polymers to enhance biocompatibility, prevent agglomeration, and add functionality. However, the coatings may interact with the surface atoms of the magnetic core and form a magnetically disordered layer, reducing the total amount of the magnetic phase, which is the key parameter in many applications. In the current study, amine and carboxyl functionalized and bare iron oxide nanoparticles, all suspended in water, were purchased and characterized. The presence of the coatings in commercial samples was verified with X-ray photoelectron spectroscopy (XPS). The class of iron oxide (magnetite) was verified via Raman spectroscopy and X-ray diffraction. In addition to these, in-house prepared iron oxide nanoparticles coated with oleic acid and suspended in heptane and hexane were also investigated. The saturation magnetization obtained from vibrating sample magnetometry (VSM) measurements was used to determine the effective concentration of magnetic phase in all samples. The Tiron chelation test was then utilized to check the real concentration of the iron oxide in the suspension. The difference between the concentration results from VSM and the Tiron test confirmed the reduction of magnetic phase of magnetic core in the presence of coatings and different suspension media. For the biocompatible coatings, the largest reduction was experienced by amine particles, where the ratio of the effective weight of magnetic phase reported to the real weight was 0.5. Carboxyl-coated samples experienced smaller reduction with a ratio of 0.64. Uncoated sample also exhibits a reduction with a ratio of 0.6. Oleic acid covered samples show a solvent-depended reduction with a ratio of 0.5 in heptane and 0.4 in hexane. The corresponding effective thickness of the nonmagnetic layer between magnetic core and surface coating was calculated by fitting experimentally measured magnetization to the modified Langevin equation.     

Linear analysis of an axially grooved rectangular gyrotron for harmonic operation

In an axially grooved rectangular waveguide the linearized Vlasov equation is solved to find the perturbed distribution function resulting from the electromagnetic forces on the electrons. The resulting beam current and the propagating electromagnetic waves of the cold tube are used in the inhomogeneous Maxwell's equation to derive the general dispersion equation. This equation is then transformed into the electron beam frame and the resulting linear growth rate of amplification is calculated. By maximizing the linear growth rate, the operational parameters of the gyrotron are then optimized.Work supported in part by NASA Lewis Research Center, Cleveland, Ohio     

Library synthesis and characterization of 3‐aminopropyl‐terminated poly(dimethylsiloxane)s and poly(ϵ‐caprolactone)‐b‐poly(dimethylsiloxane)s

Libraries of 3‐aminopropyl‐terminated poly(dimethylsiloxane) (APT–PDMS) and poly(?‐caprolactone)–poly(dimethylsiloxane)–poly(?‐caprolactone) (PCL—PDMS–PCL) triblock copolymers were synthesized. Preliminary experiments were carried out to select an appropriate catalyst and route for the poly(dimethylsiloxane) synthesis, and trial experiments were conducted to verify the successful synthesis of the intended polymer compositions. Then, a series of APT–PDMS oligomers were synthesized with an automated combinatorial high‐throughput synthesis system to cover a molecular weight range of 2500–50,000 g/mol. Trial PCL—PDMS–PCL triblock copolymers were synthesized with the automated reactor system and characterized in detail with rapid gel permeation chromatography, high‐throughput Fourier transform infrared, nuclear magnetic resonance, and differential scanning calorimetry. Finally, two library synthesis experiments were carried out in which the lengths of both the poly(dimethylsiloxane) and poly(?‐caprolactone) blocks in the PCL—PDMS–PCL triblock copolymers were varied. The results obtained from these experiments demonstrated that it was possible to synthesize libraries of well‐defined APT–PDMS oligomers and PCL—PDMS–PCL triblock copolymers with an automated high‐throughput system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4880–4894, 2006     

Performance of glass woven fabric composites with admicellar-coated thin elastomeric interphase

Adequate stress transfer between the inorganic reinforcement and surrounding polymeric matrix is essential for achieving enhanced structural integrity and extended lifetime performance of fiber-reinforced composites. The insertion of an elastomeric interlayer helps increase the stress-transfer capabilities across the fiber/matrix interface and considerably reduces crack initiation phenomena at the fiber ends. In this study, admicellar polymerization is used to modify the fiber/matrix interface in glass woven fabric composites by forming thickness-controlled poly(styrene-co-isoprene) coatings. These admicellar interphases have distinct characteristics (e.g. topology and surface coverage) depending on the surfactant/monomer ratios used during the polymerization reaction. Overall, the admicellar coatings have a positive effect on the mechanical response of resin transfer molded, E-glass/epoxy parts. For instance, ultimate tensile strength of composites with admicellar sizings improved 50–55% over the control-desized samples. Interlaminar shear strength also showed increases ranging from 18 to 38% over the same control group. Interestingly, the flexural properties of these composites proved sensitive to the type of interphase formed for various admicellar polymerization conditions. Higher surface coverage and film connectedness in admicellar polymeric sizings are observed to enhance stress transfer at the interfacial region.     

Observations associated with non-linear voltage-current characteristics of type II superconductors

Independent currents at right angles were sent through type II superconducting alumnum films in the flux-flow state, and the voltage measured along one of the current directions. The voltage was found to increase with increasing perpendicular current, due to the non-linear voltage characteristics of the specimens.