Phase behavior and rheological properties of polyelectrolyte inks for direct-write assembly

Three-dimensional (3-D) structures with micron-sized features have been fabricated via the direct-write assembly of polyelectrolyte inks. By mixing oppositely charged species under solution conditions that promote polyelectrolyte exchange reactions, we have created concentrated fluids capable of flowing through microscale deposition nozzles. Ink deposition into an alcohol/water coagulation reservoir yielded polyelectrolyte filaments that rapidly solidify to enable three-dimensional patterning of microperiodic structures with self-supporting features. The influence of ink and reservoir chemistry on the phase behavior, rheological properties, and assembly of concentrated polyelectrolyte complexes is reported with an emphasis on the optimal conditions for 3-D writing.     

Facile homogeneous hydrogenations of hindered olefins with [Ir(cod)py(PCy3)]PF6

The title complex readily hydrogenates a number of hindered steroidal olefin groups from the α face, without reducing ketone carbonyl groups, carbon—halogen bonds or cyclopropane rings.     

Ultrasonic and Raman Scattering Spectroscopy of Zinc Thiocyanate Complexes in Water at 25<Superscript>∘</Superscript>C: Kinetics of Complex Formation Determined by Multivariate Analysis

Advances have been made recently in broadening the accessible ultrasonic absorption frequency range and improving the detectability of minor species present in solution using Raman spectroscopy. Development of chemometric techniques in these areas needs to keep pace with the improvement of these experimental methods. Refinements in the analysis of ultrasonic and Raman data based on multivariable least squares and factor analysis, respectively, are examined to investigate the kinetics of zinc thiocyanate complex formation in water. Analysis of ultrasonic absorption relaxation spectra verified that the observed process in aqueous Zn(SCN)₂ involves substitution of water from the first coordination shell of Zn²⁺. Use of a multivariable least-squares error surface is described that enhances the reliability of assigned frequencies of ultrasonic absorption maxima. Factor analysis of Raman scattering data provided direct evidence that at least four complex species, such as Zn(SCN)⁺ and Zn(SCN)₂, are simultaneously present in the aqueous zinc thiocyanate solutions.     

Study of the chromonic liquid-crystalline phases of bis-(N,N-diethylaminoethyl)perylene-3,4,9,10-tetracarboxylic diimide dihydrochloride by polarized optical microscopy and 2H NMR spectroscopy

The chromonic liquid-crystalline properties of bis-(N,N-diethylaminoethyl)perylene-3,4,9,10-tetracarboxylic diimide dihydrochloride in an aqueous solution were investigated by polarized light microscopy and 2H NMR spectroscopy. Both techniques indicate a narrow I + N biphasic region and a broad N phase region at concentrations ranging from approximately 6.9 to approximately 30 wt % at room temperature. Optical microscopy indicates that a hexagonal M phase exists at higher concentrations. The variation of the I --> N + I and N + I --> N transition temperatures with concentration was studied by 2H NMR spectroscopy. Finally, the effects of temperature and concentration on the order parameter of the N phase were investigated by 2H NMR using a tetra-deuterated derivative. A value of 0.97 was obtained for the N phase at its upper concentration limit.     

An in situ atomic force microscopy study of uric acid crystal growth

Kidney stones are heterogeneous polycrystalline aggregates that can consist of several different building blocks. A significant number of human stones contain uric acid crystals as a crystalline component, though the molecular-level growth of this important biomaterial has not been previously well-characterized. In the present study, in situ atomic force microscopy (AFM) is used to investigate the real-time growth on the (100) surface of uric acid (UA) single crystals as a function of fundamental solution parameters. Layer-by-layer growth on UA (100) was found to be initiated at screw dislocation sites and to proceed via highly anisotropic rates which depend on the crystallographic direction. The smallest b-steps exhibited minimum heights corresponding to two molecular layers, while fast-moving c-steps more commonly showed monolayer heights. Growth kinetics measured under a range of flow rates, supersaturation levels, and pH values reveal linear trends in the growth kinetics, with faster growth attained in solutions with higher supersaturation and/or pH. The calculated kinetic parameters for UA growth derived from these experiments are in good agreement with the values reported for other crystal systems.     

Microfabrication of three-dimensional bioelectronic architectures

The functionality and structural diversity of biological macromolecules has motivated efforts to exploit proteins and DNA as templates for synthesis of electronic architectures. Although such materials offer promise for numerous applications in the fabrication of cellular interfaces, biosensors, and nanoelectronics, identification of techniques for positioning and ordering bioelectronic components into useful patterns capable of sophisticated function has presented a major challenge. Here, we describe the fabrication of electronic materials using biomolecular scaffolds that can be constructed with precisely defined topographies. In this approach, a tightly focused pulsed laser beam capable of promoting protein photo-cross-linking in specified femtoliter volume elements is scanned within a protein solution, creating biomolecular matrices that either remain in integral contact with a support surface or extend as free-standing structures through solution, tethered at their ends. Once fabricated, specific protein scaffolds can be selectively metallized via targeted deposition and growth of metal nanoparticles, yielding high-conductivity bioelectronic materials. This aqueous fabrication strategy opens new opportunities for creating electronic materials in chemically sensitive environments and may offer a general approach for creating microscopically defined inorganic landscapes.     

Chemical and Structural Changes in Blood Undergoing Laser Photocoagulation¶

The treatment of cutaneous vascular lesions (port wine stains etc.) using lasers has been guided by theories based on the “cold” or room‐temperature optical properties of the hemoglobin target chromophore. We have recently presented evidence showing that under the influence of laser irradiation, the optical properties of blood in vitro are time and temperature dependent. Such complications are not currently subsumed into the in vivo theory. Here, we study the time‐domain optical properties of blood undergoing photocoagulation in vitro using two newly developed time‐resolved techniques. We also study the asymptotic effect of laser photocoagulation on the chemical and structural properties of the components of the blood matrix. We present evidence showing that the photocoagulation process involves significant changes in the optical absorption and scattering properties of blood, coupled with photothermally induced chemical and structural changes. We demonstrate the first use of a laser to deliberately generate magnetic resonance imaging contrast in vitro. We show that this technique offers significant potential advantages to in vivo intravenous chemical contrast agent injection.     

Synthesis of crystalline skutterudite superlattices using the modulated elemental reactant method

A series of samples ((AB)(x)(CD)(y))(z) were prepared containing both short repeat units (AB and CD) and long repeat units ((AB)(x)(CD)(y)), where the short repeat units were designed to have the composition appropriate to form square M(4)Sb(12) skutterudites (M = Fe, Co, or Ir; square = vacancy, La, or Y). X-ray diffraction and reflectivity were used to follow the evolution of the films from amorphous, layered materials to crystalline skutterudite superlattices as a function of annealing temperature and time. In all cases, the short repeat units interdiffused and crystallized the expected skutterudite, while the long repeat period persisted after annealing. The skutterudites crystallize with random crystallographic orientation with respect to the substrate. The observed splitting of the peaks in the high-angle diffraction data from the IrSb(3)/CoSb(3) sample indicates the formation of a novel superlattice structure with each grain having a random crystallographic orientation of the skutterudite lattice with respect to the superlattice direction.     

Esmodil: an acetylcholine mimetic resurfaces in a Southern Australian marine sponge Raspailia (Raspailia) sp

Bioassay directed fractionation of a Raspailia (Raspailia) sp. (Order Poecilosclerida; Family Raspailiidae) collected during scientific trawling operations off the Northern Rottnest Shelf yielded as nematocidal agents the known metabolites, phorboxazoles A (1) and B (2). Further examination revealed the new natural product but known synthetic compound, esmodil (3). The structure for 3 was confirmed by spectroscopic analysis and total synthesis.     

Total Synthesis of (+)-okaramine J featuring an exceptionally facile N-reverse-prenyl to C-prenyl aza-Claisen rearrangement

[reaction: see text] The convergent total synthesis of (+)-okaramine J was achieved in a longest linear sequence of 12 steps from l-tryptophan tert-butyl ester. A key reaction was the acid-catalyzed room-temperature aza-Claisen rearrangement of a N-reverse-prenylated hexahydro[2,3-b]pyrroloindole to a C-prenylated derivative.