Coordination of diatomic ligands to heme: simply CO

The synthesis and molecular structures of three iron(II) porphyrinates with only CO as the axial ligand(s) are reported. Two five-coordinate [Fe(OEP)(CO)] derivatives have Fe-C = 1.7077(13) and 1.7140(10) A, much shorter than those of six-coordinate [Fe(OEP)(Im)(CO)], although nu(C-O) is 1944-1948 cm(-1). The six-coordinate species [Fe(OEP)(CO)2] has also been studied. The competition for pi-back-bonding of two CO ligands leads to Fe-C distance of 1.8558(10) A and nu(C-O) being increased to 2021 cm(-1). The M?ssbauer spectrum has a quadrupole splitting constant of 0 mm/s at 4.2 K, indicating high electronic symmetry.     

Carbon monoxide promoted reductive elimination of hydrogen from Tp' platinum complexes

Acid-assisted reductive elimination of hydrogen from Tp'PtH(3) and of methane and hydrogen from Tp'PtMeH(2) (Tp' = hydridotris(3,5-dimethylpyrazolyl)borate) is examined herein. Loss of H(2) is observed from solutions containing platinum(IV) complexes of the type Tp'Pt(R)(H)(2) (R = Me, H) upon protonation and addition of a ligand such as CO. Results of kinetic studies on reductive elimination of H(2) and formation of [kappa(2)-(HTp')Pt(R)(L)][BAr'(4)] products from intermediates derived from Tp'Pt(R)(H)(2) precursors are described. Elimination appears to occur from cationic 6-coordinate [kappa(2)-(HTp')Pt(R)(H)(2)(L)][BAr'(4)] species.     

Perfect polar stacking of parallel beloamphiphile layers. Synthesis, structure and solid-state optical properties of the unsymmetrical acetophenone azine DCA

Extraordinary high degrees of polar order can be achieved by a rational design that involves the polar stacking of parallel beloamphiphile monolayers (PBAM). This strategy is exemplified by the acetophenone azines MCA (4-methoxy-4'-chloroacetophenone azine) and DCA (4-decoxy-4'-chloroacetophenone azine). The beloamphiphile design aims to achieve strong lateral interactions by way of arene-arene, azine-azine, arene-azine and halogen-bonding interactions. Dipole-induced interactions and halogen bonding dominate interlayer interactions and halogen bonding is shown to effect the layer stacking. Crystals of DCA contain PBAMs with perfect polar order and perfect polar layer stacking, while crystals of MCA features perfect polar order only in one of two layers and layer stacking is polar but not entirely perfect. We report the synthesis of the beloamphiphile DCA, its crystal structure, and we present a comparative discussion of the structures and intermolecular interactions of MCA and DCA. Absorbance and photoluminescence measurements have been carried out for solutions of DCA and for DCA crystals. DCA exhibits a broad emission centered at 2.5 eV when excited with UV radiation. The nonlinear optical response was studied by measuring second harmonic generation (SHG). Strong SHG signals have been observed due to the polar alignment and the DCA crystal's NLO response is 34 times larger than that of urea. Optimization of the beloamphiphile and systematic SAR studies of the polar organic crystals, which are now possible for the very first time, will further improve the performance of this new class of functional organic materials. The materials are organic semiconductors and show promise as blue emitters, as nonlinear optical materials and as OLED materials.     

Pyridinyloxazolidines: versatile scaffolds for chiral catalyst construction

Pyridinyloxazolidines are structurally versatile chiral ligand frameworks that are easily made and coordinated to Pd(II); the resulting complexes, which show significant steric and electronic differences from their oxazoline counterparts, as well as intermolecular H-bonding in the solid state, can be isolated in diastereomerically pure form and are remarkably resistant to hydrolysis.     

Epimerization reaction of a substituted vinylcyclopropane catalyzed by ruthenium carbenes: mechanistic analysis

A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine or nitrogen ligand is added. NMR and kinetic studies suggest that the isomerization reaction occurs through the intermediacy of a ruthenacyclopentene. The observation suggests that cyclopropylmethylidene ruthenium carbenes of synthetic utility may be accessible via ruthenacyclopentenes obtained via other routes.     

Scotopic and photopic visual thresholds and spatial and temporal discrimination evaluated by behavior of mice in a water maze

Methods that allow specific manipulations of the mouse genome have made it possible to alter specific aspects of photoreceptor function within the mouse retina. Mice with photoreceptors that have altered photosensitivities and altered photoresponse kinetics are now available. Methods are needed that can show how those perturbations in photoreceptor response characteristics translate into perturbations in visual sensitivity and perception. We have adapted a previously described method to evaluate visual threshold, spatial discrimination and temporal discrimination in mice swimming in a water maze. In this report we describe the sensitivities of rod-mediated and cone-mediated vision using GNAT1-/-and GNAT2-/- mice. Cone-mediated vision is approximately 10,000 times less sensitive than rod-mediated vision in mice. We also demonstrate that mice can distinguish striped from solid objects in the water maze and that they can distinguish flickering from continuous illumination.     

Conversion of Chromium(III) Propionate to Chromate/dichromate(VI) by the Advanced Oxidation Process. Pretreatment of a Biomimetic Complex for Metal Analysis

The use of H₂O₂ and UV irradiation to remove organic ligands in a chromium(III) complex for the subsequent chromium analysis is reported. The Advanced Oxidation Process (AOP) using a 5.5-W UV lamp, H₂O₂ and Fe²⁺/Fe³⁺ as catalyst (photo Fenton process) was found to give complete and quantitative Cr(III) → Cr(VI) conversion and removal of ligands in chromium(III) propionate [Cr₃O(O₂CCH₂CH₃)₆(H₂O)₃]NO₃, a biomimetic chromium species, as subsequent chromium analyses by the 1,5-diphenylcarbazide method and atomic absorption revealed. The current process eliminates the need for mineralization and/or dissolution of the matrix in order to remove the organic ligand, the traditional pretreatments of a sample for metal analysis. Studies to optimize the conditions for the oxidation processes, including the use of Fe²⁺/Fe³⁺ catalyst, length of UV irradiation, H₂O₂ concentration, pH, power of UV lamp, and reactor size, are reported.     

Visualization method to predict the nucleophilic asymmetric induction of prochiral electrophiles

[reaction: see text] This work focuses on the development of a simple technique to accurately predict and visualize the diastereoselectivity of ketone, aldehyde, and allyl chloride reductions by mapping electrostatic potential onto the frontier molecular orbital involved in the reduction. A distinct difference of electrostatic potential on the faces of the carbonyl can be used to predict the face of nucleophilic attack with a high level of accuracy.     

Surface engineering of microchannel walls for protein separation and directed microfluidic flow

The preparation of surfaces in microfluidic devices that selectively retain proteins may be difficult to implement due to the incompatibility of derivatization methods with microdevice fabrication techniques. This review describes recently reported developments in simple and rapid methods for engineering the surface chemistries of microchannels based on construction of press-fit microdevices. These devices are fabricated by placing a glass fiber on a PDMS film and pressing the film on a silicon wafer or a microscope slide that has been derivatized with octadecyltrichlorosilane (ODS). The film adheres to the slide and forms an elliptically shaped channel around the fiber. The combination of surface wettability of a hydrophilic glass microfiber and the surrounding hydrophobic microchannel surfaces directs a narrow boundary layer of liquid next to the fiber in order to bring the sample in contact with the separation media and results in selective retention of proteins. This phenomenon may be exploited to enable microscale separation applications since there are a wide variety of fibers available with different chemistries. These may be used to rapidly fabricate microchannels that serve as stationary phases for separation at a microscale. The fundamental properties of such devices are discussed.