478—Theory of Brdička current and the dependence of the current on cobalt ion concentration

An equation of Brdi?ka current and its experimental verification are presented, in which Brdi?ka current is expressed by a function of the surface concentration of protein, the bulk concentration of cobalt ion and two parameters, n_ck_c and k_f/k_d, characterizing the protein-zero-valent cobalt complex which is to catalize the hydrogen evolution, where n_c is the total number of sites on which the complex can be formed in a protein molecule, and k_c and k_d are the (average) constants representing the intrinsic catalytic activity and the lifetime respectively, of the complex.     

The synthesis of (4S,5S)-(−)-isocytoxazone

(4S,5S)-(?)-Isocytoxazone, which is needed for a configurational study, was synthesized from the commercially available (1S,2S)-(+)-2-amino-1-(4-nitrophenyl)-1,3-propanediol in which the p-nitro substituent was replaced by a p-methoxyl group; the thus prepared p-methoxyphenyl amino diol was cyclized via an N-Boc derivative.     

Representation T-V-X d'une monotexie dans les systemes binaires a tension de vapeur non negligeable

Binary systems with non-negligible vapour pressure in which a monotectic equilibrium takes place are described in aT-V-x diagram. Two kinds of equilibrium may occur, which correspond to the following reactions:S+L ₁ ? L ₂+V, andS+L ₁ +V?L ₂, when the temperature rises. The first generates a quadrilateral monotectic invariant. The second generates a triangular monotectic invariant. These two invariants are described in theT-V-x diagram and discussed.     

Configuration interaction in the 6s n d 1 D 2 and 6s n s 1 S 0 states of Yb probed by lifetime measurements

Radiative lifetimes in the even parity 6s n d ¹ D ₂ (n=6?13) and 6s n s ¹ S ₀ (n=8?14) level series of neutral Yb have been measured. In contrast to a monotonicn*³ behaviour which is expected in the absence of configuration interaction a drastic decrease of the lifetime data was observed in the vicinity of multiply excited states. In addition, for certain levels a strong increase of the lifetime values has been found which may be ascribed to destructive interference due to configuration mixing which can also affect the branching ratios of the radiative decay of these levels.     

Cellulose synthase (CesA) genes in algae and seedless plants

Microfibril structure is determined largely by the organization of arrays of integral plasma membrane protein particles known as “terminal complexes”, which include cellulose synthase catalytic subunits encoded by CesA genes. Although the CesA genes of plants and bacteria share conserved regions, variations in terminal complex and microfibril structure presumably result from sequence differences. Thus, the CesA domains that influence terminal complex assembly may be revealed by examining the differences between CesA genes from green algae in which terminal complex structure ranges from rosettes (plant-like) to linear (bacteria-like). This report describes a second CesA gene that has been cloned from Mesotaenium caldariorum, a unicellular green alga from the order Zygnematales, which have rosette terminal complexes. Both McCesA1 and McCesA2 are similar to seed plant CesAs in domain structure and intron position. Seed plants have multiple CesAs and CesA-like (Csl) genes, some of which appear to be expressed specifically during cell expansion, secondary cell wall deposition in vascular tissue, or tip growth. Diversification of the CesA and Csl gene families can be explored by comparing these genes in mosses, which lack vascular tissue with secondary cell walls, and early divergent vascular plants such as ferns. Degenerate primers were used to amplify and clone five unique CesA and Csl fragments from genomic DNA isolated from Physcomitrella patens. Probes derived from the cloned fragments were used to isolate several clones from a Physcomitrella genomic library. One Csl fragment was amplified from genomic DNA isolated from the fern Ceratopteris richardii. Phylogenetic analysis supports the presence of CslD genes in both mosses and ferns, but does not support the presence of secondary cell wall specific CesA orthologs in mosses.     

Time-dependent perturbation: a recursive generation of the transition amplitudes between bound states

We present a new expansion of the solution to the time-dependent Schrödinger equation it ∂U/∂t = {H₀ + V(t)}U. A complete set of eigenvectors of H₀ spanning the Hilbert space in which H₀ and V operate is partitioned in two subsets. Transition amplitudes from the first subspace to the second one are calculated by building an adequate series of intermediate representations with respect to the couplings which produce the transition from the model space into its orthogonal complement. These expansions yield a coupling matrix series V⁽ⁿ⁾ for which an iterative solution V⁽ⁿ⁾ → V⁽ⁿ⁺¹⁾ is derived. This solution leads to a recursive numerical treatment of the calculation of transition amplitudes. A simple example, concerning a harmonic oscillator under an intense laser field, is considered using a Fourier analysis of the perturbation.     

Influence of composition on the structural and superconducting properties of the two polymorphic forms of iridium- or silicon-substituted YIr2Si2

The structural and superconducting properties of the low and high temperature forms of YIr₂−xSi_2+x compounds, which have structures of the ThCr₂Si₂ and CaBe₂Ge₂ types respectively, were studied. Each modification exhibits a narrow homogeneity range spreading over the silicon-poor and silicon-rich sides. The materials were obtained as pure phases only for 0⩽ x < 0.075. The critical temperature increases slightly with increasing silicon content. Whereas the compounds with the low temperature structure show a broad transition which disappears in silicon-poor samples (x< 0), those with the high temperature structure exhibit a sharp transition corresponding to a critical temperature which increases with x. A new superconducting silicide Y₂Ir₃Si₅, which is isostructural with U₂Co₃Si₅, was prepared (T_cr = 2.8–3.05K). The occurrence of superconductivity is related to the crystal structure of the materials, and structural relations which take account of the variation in T_cr are established.     

The nπ* states of the thiocarbonyl halides: The ā3A ← X̄1A' electronic transition in thiocarbonyl chlorofluoride

The visible absorption spectrum of thiocarbonyl chlorofluoride, C1FCS in the 495-nm region has been observed in the vapour phase under conditions of high resolution and pressure x path-length and has been assigned to the ā³A'' (n, π^*) ← X?¹A' electronic transition. Three of the six fundamental modes have been assigned for the upper electronic state. Prom a fit of the observed levels in v¹_o (the out-of-plane wagging mode) to the eigenvalues obtained from a quadratic-gaussian potential, the barrier to inversion in the ā³A state has been evaluated to be 1622 cm^?1 The electronic effects of replacing a sulphur by an oxygen atom on the height of the barrier to inversion in the nπ^* carbonyl and thiocarbonyl halides have been explored by the CNDO/2 method. The much lower barriers in the thiocarbonyl compounds has been attributed to the sulphur d_xz AO which is not present in the carbonyl compounds. This AO, which has relatively high weight in the LCAOs which form the π^* MO, has the effect of relieving some of the antibonding density which resides on the carbon atom and thereby reduces the barrier to inversion.     

Infrared and Mössbauer spectroscopic study of the metal-insulator transition in some oxides of perovskite structure

The IR spectra of some LaNi_1−xB_xO₃ (B = Cr, Fe, and Co) compounds having perovskite structure have been studied in the range 1000−300 cm⁻¹. An investigation of the changes in the metal-oxygen stretching frequency as x → x_c from the insulating side has been carried out. An important feature is that as x → x_c the vibrational features in the infrared spectra disappear when the resistivity is ∼10⁻¹ Ω cm which is of two orders of magnitude more than the value of ϱ₀ at which the temperature coefficient of resistance changes sign. Mössbauer studies on Fe-containing samples with various conductivities show that the isomer shift decreases as conductivity increases which is indicative of larger FeO overlap.     

Direct N- and C-alkenylation of nitrogen-containing heterocycles with magnesium alkylidene carbenoids

Treatment of magnesium alkylidene carbenoids, which were generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with N-lithio nitrogen-containing heterocycles gave N-alkenylated products in moderate to good yields. Also, the reaction of C-lithio indoles, which were generated from N-protected indoles, with magnesium alkylidene carbenoids gave C-2 or C-3 alkenylated products, corresponding to the protective group. The intermediate of these reactions were found to be the alkenyl anion, which could be trapped with electrophiles to give the heterocycles having fully substituted alkenes.     

Preparation and structure of fluorite-type (Sr,Y)Cl2.05

Anion excess colorless fluorite-type strontium-yttrium chloride has been prepared. Single crystals of the SrY compound exhibit a primitive cubic lattice with a = 6.967(1)Å. Two mutually exclusive structural models for solutions, neither of which is exact, are discussed. The first is a vacancy model in which the extra charge which results from substitution of Y³⁺ for Sr²⁺ is balanced by the simultaneous removal of a Sr²⁺Cl^? ion pair. This model requires individual ion sites to be partially occupied and nonequivalent and is strongly suggestive of vacancy ordering. Refinement in space group P1, with sites refined independenty, led to R = 0.1096. The second model describes the structure in terms of a Willis cluster of defects and includes both anion vacancies and interstitial anions. Full-matrix least squares refinement in space group Fm3m, with positions analogous to those in UO_2.12 and (Ca,Y)F_2.10, converged at R = 0.0633 for the 114 face-centered parent structure reflections whose |F|;² > σ(F²). This second model is discussed in relation to a probable true solution which involves longrange order.     

Amber suppressors of Erwinia chrysanthemi

Mutations trpl and thyA1, both of a polyauxotrophic derivative of the Erwinia chrysanthemi strain B374, were characterized as amber mutations with an Escherichia coli suppressor, supA1P2, which inserts a glutamine in response to UAG. Simultaneous reversion of both mutations allowed us to isolate amber suppressor mutants of E. chrysanthemi. These suppressors were tested with a set of amber mutants of bacteriophage Mu which had been previously characterized on E. coli. The two independently isolated suppressors behaved as supD and supE mutants, respectively, of E. coli.     

Predictability of properties in ternary n-alkane/butanone/poly(dimethylsiloxane) systems from flory-huggins binary interaction parameters and inversion point in preferential solvation

An empirical procedure has been developed, based on the Flory-Huggins theory as generalized by Pouchlý, which permits the calculation of preferential sorption coefficient, λ, and the total sorption term, Y, from previous information on the binary interaction parameters, χ_13′⁰, χ₂₃⁰ and g₁₂(φ₁₀) and of the mixture composition at which the sign of λ inverts. The obtained expressions were applied to seven cosolvent polymer systems, n-alkane/butanone/poly(dimethylsiloxane), for which experimental values of λ and Y are known. In all the studied systems, the theoretical predictions are in fair accord with the experimental data.     

Efficient and practical synthesis of both enantiomers of 6-silyloxy-3-pyranone derivatives

Lipase catalyzed kinetic resolution of racemic cis-6-(tert-butyldimethylsilyloxy)-3,6-dihydro-2H-pyran-3-ol (rac)-1 was achieved in high enantiomeric excess. Transesterification of (rac)-1 with vinylacetate in ^tBuOMe yielded the alcohol (3S,6R)-1 in 99.0% ee, whereas (3R,6S)-1 was obtained, in 99.0% ee, by the lipase catalyzed ester hydrolysis of acetate (3R,6S)-2, which was obtained along with the transesterification. Both (3S,6R)-1 and (3R,6S)-1 were subjected to oxidation to provide the corresponding 6-silyloxy-3-pyranone (6R)-3 and (6S)-3, respectively. Application to the synthesis of 7, which is the key intermediate of asymmetric synthesis of pseudomonic acid A 9 is also described.     

Xanthone. I. optical detection of an extremely large sublevel splitting the lowest triplet state

The phosphorescence spectrum of xanthone in n-hexane is resolved into three components, one of which is due to thermally activated emission from a n_π* origin. The other two emissions originate from extremely widely split sublevels of the lowest triplet state, which is of ³ππ* origin. higher energy of T_Lx, and T_1y, and thus below 4K there is thermal depletion of T_1z which has the largest radiative strength. Th consequence of spin-orbit coupling between the T_x and T_y sublevels of the-two very close-lying, lowest triplet states. There are signif mixing of orbital character, a mixing which is governed by spin-orbit coupling rather than vibronic coupling.     

Multidimensional Magic Mountains and Matrix Art for the generalized repeat space theory

The Asymptotic Linearity Theorem (ALT), which proves the Fukui conjecture in a broader context, plays a significant role in the repeat space theory (RST), which is the central unifying theory in the First and the Second Generation Fukui Project. Proving the Asymptotic Linearity Theorem Extension Conjecture (ALTEC) is a fundamental problem in the repeat space theory. The present paper constructs a class of functions MagicMtθ, which serves as a powerful tool for proving the Asymptotic Linearity Theorem Extension Conjecture and related propositions. The d-dimensional generalization?μ _d,n,θ of MagicMt _θ , which is given in the present paper and is called a ‘d-dimensional Magic Mountain’, provides inwardly repeating fractals in multidimensional spaces useful for interdisciplinary research that uses the generalized repeat space theory.     

Etude structurale et magnétique de pérovskites de formule Ba3Fe2−xHoxUO9

The compounds crystallize in cubic perovskite-type system. The space group is Fm3m and the cell is entirely ordered. 4a positions (Wyckoff's notation) contain iron and uranium, 4b positions, barium and iron, 8c positions, barium and any holmium, which therefore fills coordinance-12 crystallographic sites. For iron-rich compounds (0 < x ? 0.8), interactions between Fe³⁺ ions from two magnetic sublattices 4a and 4b are antiferromagnetic. The interactions between the third magnetic sublattice, which corresponds to Ho³⁺ ions filling 8c positions, and the resultant of the first two, are slightly ferromagnetic. Such data have been obtained with all the other compounds for which the formula is Ba₃Fe_2?xLn_xUO₉, where Ln is Yb, Tm, Er, Dy, Tb, and Gd.     

Skipped diynes—VII : Stereospecific thermal isomerization of a tetraethynyldimethylenecyclobutane

1,1-Bis(t-butylethynyl)-3-t-butylchloroallene (1) dimerizes stereospecifically at ca 25° to give Z - 1 - (t - butylchloromethylene) - 2- bis(t - butylethynylmethylene) - 3 - t - butyl - 3 - chloro - 4,4 -bis(t - butylethynyl)cyclob Z-I in the solvent bis(2 - ethoxyethyl) ether. Rate data for 100° are k = 111 × 10^?6 sec^?1, ΔH^≠ = 30·8 ± 1 kcal/mole and ΔS^≠ = 15 ± 3 eu. It is proposed that the dimerization of 1 produces a bisallyl diradical in an orthogonal conformation from which conrotatory paths lead to Z-I or trans-II. The observations on this system are used to construct a useful, if simplistic, approach to rationalize or predict product distributions in reactions such as allene dimerizations, 1, 2 - dimethylenecyclobutane rearrangements, etc, which proceed through the bisallyl diradical. On the graph which connects all of the species (or on the energy surface which contains all of the species) the first products should be those which are one allowed reaction step away from a given diradical. Applications and exceptions to this concept of favored kinetic control are discussed.     

Thermally-reversible photoisomerization of trans-dinitrobis(tri-N-propylphosphine)palladium(II)

UV irradiation of trans-dinitrobis(tri-n-propylphosphine)palladium(II) in MeOH yields a photostationary trans-cis mixture which reverts quantitatively in the dark to the trans-form. The cis-isomer, which can be isolated in crystalline form by irradiation of trans-species in n-hexane, has been characterized by UV, IR ¹H and ³¹P NMR spectroscopy. Irradiation of a 1/1 mixture of trans-[(PBu₃ⁿ)₂Pd(NO₂)₂] and trans-[(PPr₃ⁿ)₂Pd(NO₂)₂] gives almost entirely a 1/1 mixture of the corresponding cis-isomer, indicating an intramolecular process.