A single crystal study of eight-layer barium managanese oxide,BaMnO3

A single crystal study of hydrothermally prepared eight-layer BaMnO₃ has been carried out which confirms the (Zhdanov notation) 121121 layer stacking scheme for the BaO₃ layers. The MnO₆ octahedra share faces in strings of four, and these strings are connected to each other by corner sharing. The compound has an hexagonal unit cell of dimensions a = 5.667 ± 0.003 and c = 18.738 ± 0.009 Å, probable space group $\text{P6}{}_3\text{mmc}\text{, Z = 8}$. Its structure has been determined from 352 independent reflections, of which 242 were considered observed, collected manually by a counter technique and refined to a conventional R value of 0.079.     

Photochemical reactions of Ru3(CO)12 involving metalmetal bond fission

Photolysis of Ru₃(CO)₁₂ in the presence of donor ligands rapidly produces monomeric ruthenium species.     

Photoproteins as luminescent labels in binding assays

Certain marine organisms produce calcium-activated photoproteins that allow them to emit light for a variety of purposes, such as defense, feeding, breeding, etc. Even though there are many bioluminescent organisms in nature, only a few photoproteins have been isolated and characterized. The mechanism of emission of light in the blue region is the result of an internal chemical reaction. Because there is no need for excitation through external irradiation for the emission of bioluminescence, the signal produced has virtually no background. This allows for the detection of the proteins at extremely low levels, making these photoproteins attractive labels for analytical applications. In that regard, the use of certain photoproteins, namely, aequorin, obelin, and the green fluorescent protein as labels in the design and development of binding assays for biomolecules has been reviewed. In addition, a related fluorescent photoprotein, the green fluorescent protein (GFP), has been recently employed in bioanalysis. The use of GFP in binding assays is also discussed in this review.     

Sequence distribution and intramolecular excimer formation in styrene-acrylonitrile copolymers

Styrene-acrylonitrile copolymers, like many other copolymers containing styrene, exhibit both normal and excimer fluorescence. We have shown that the ratio of the excimer to monomer fluorescence intensities in random styrene-acrylonitrile copolymers is linearly dependent upon the concentration of styrene-styrene bonds in the copolymer. This observation is consistent with a photophysical model which allows the energy absorbed by styrene units to migrate freely along the copolymer chain. Some of the energy is emitted in the form of normal fluorescence; some of the energy, trapped by neighbouring styrene-styrene pairs suitably oriented to allow excimer formation, is emitted as excimer fluorescence. The fluorescence characteristics of acrylonitrile-styrene copolymers are contrasted with those of methyl methacrylate-styrene copolymers, in which the methylmethacrylate sequences are believed to present partial barriers to energy migration along the copolymer chains.     

Rotational diffusion effects on absorbance measurements: limitations to the magic-angle approach.

Optical absorbance changes are commonly used to characterize intermediates which appear in the bleaching sequence of rhodopsin and in the photocycle of bacteriorhodopsin. Absorbance changes can be caused by an intermediate's rotational diffusion, and when this occurs it can distort absorbance changes due to the structural evolution of intermediates. Linear polarization of an optical probe source at 54.7 degrees (the magic angle) relative to the polarization direction of a linearly polarized actinic source has often been used to eliminate signals due to rotational diffusion. We used Jones calculus to investigate the validity of the magic-angle strategy. Taylor expansion of the result in powers of the absorbances of the bleached ground state and of the intermediates leads to a relatively simple expression which can be used to determine whether rotational contributions are likely under various experimental conditions. This expression shows that in first order no dichroism-dependent term appears in the absorbance measured at magic angle. In second order, however, linear dichroism contributes to signals. For the sequence of rhodopsin intermediates: rhodopsin hv----bathorhodopsin in equilibrium BSI----lumirhodopsin, where BSI is a recently discovered blue-shifted intermediate, we determined the magnitude of the dichroism signals to be, on average, less than 2% of the true absorbance change due to the intermediates themselves (and hence undetectable). Freedom from dichroism artifacts in this case results from the fact that the transition dipoles of these intermediates are similar to that of rhodopsin. Larger and certainly detectable dichroism signals are predicted to occur, even at the magic angle, for later intermediates which have transition dipole moments which differ significantly from that of rhodopsin.(ABSTRACT TRUNCATED AT 250 WORDS)     

The incorporation of heavy metals into diazo-type electron beam resists

Metals may be chemically incorporated into organic lithographic resists that contain or can be functionalized with ? OH groups. A wide range of metal incorporation (0.04–12% of total solids by weight) has been demonstrated for AZ-1370 (Shipley), a diazo-type photo- and electron resist. The novolac component of the resist is reacted with an organometallic halide, R_yMX (R = alkyl, aryl; M = transition or main group metal; X = CI, Br; 1 ≤ y ≤ 4, depending on M) to introduce the corresponding organometallic function into the resist.     

Mass spectra of benzotriazinones and the first loss of 28 mass units

Mass spectra of five benzotriazinone derivatives are reported and the fragmentation mechanisms are discussed. That the first loss of 28 mass units is a nitrogen molecule appears to be characteristic of the molecules.     

The different steric environments of the 5-exo- and 5-endo- substituent for a pair of isomeric tricarbonyl(methoxycyclohexa-1,-diene)irons

A shift reagent has been employed to demonstrate the sterically-hindered environment of the methoxy group in tricarbonyl(5-endo-methoxycyclohexa-1,-diene)iron relative to that of the methoxy group in the 5-exo analogue.