A new strategy of tandem transetherification-intramolecular hetero Diels-Alder reaction with (E,Z)-mixture of ethyl 2-nitro-3-ethoxyacrylate and δ,ε-unsaturated alcohols leading to functionalized trans-fused bicyclic nitronates

Tandem reaction of (E,Z)-ethyl 2-nitro-3-ethoxyacrylate (E:Z=25:75) with δ,ε-unsaturated alcohols leading to functionalized trans-fused bicyclic nitronates as single stereoisomers in high yields has been developed under thermal condition and in the presence of a catalytic amount of a Lewis acid catalyst such as Yb(OTf)₃. This process involves the configurational control of transetherified intermediates under a rapid, reversible transetherification reaction pathway for affording stereoselective trans-fused cyclic nitronates as single stereoisomers in intramolecular hetero Diels-Alder reaction.     

π-cyclopentadienyls of nickel(II) : XV. Insertion reaction of RNCS into the nickel—carbon bond

η⁵-C₅H₅NiPBu₃CH(CN)₂ (I) readily undergoes ethyl- or phenyl-isothiocyanate insertion, producing the stable products η⁵-C₅H₅NiPBu₃SC(NRH) = C(CN)₂ (IIIa; R = C₂H₅, IIIb; R = C₆H₅. η⁵-C₅H₅NiPPh₃CH(CN)₂ (II) reacts with RNCS (R = C₂H₅ and C₆H₅) to undergo two types of insertion reaction; with C₂H₅NCS, η⁵C₅H₅NiPPh₃SC[N(C₂H₅)H] = C(CN)₂ (IVa) is obtained, with C₆H₅NCS, on the other hand, η⁵-C₅H₅NiPPh₃SC(NC₆H₅)CH(CN)₂ (IVb) is produced. p ]IIIa and IIIb react with PBu₃ to give ionic complexes [η⁵-C₅H₅Ni(PBu₃)₂]⁺ [SC(NC₂H₅H)C(CN)₂]^? (Va) and [η⁵-C₅H₅Ni(PBu₃)₂]⁺ [SC(NC₆H₅)CH(CN)₂]^?(Vb), respectively.     

Simultaneous determination of iron and copper ions by low-injection analysis with a multichannel photodiode-array detector

Iron(II) and copper(II) ions are determined simultaneously in a simple manifold by using a multichannel photodiode-array detector. 1-(2-Pyridlazo)-2-hydroxy-7-sulfonaphthalene (PAN-7S) is used as the sole chromogenic reagent. The absorbance at 550 nm is related to the PAN-7S chelates of iron(II) and copper(II)and that at 764 nm to the iron(II) chelate alone. Calibrations are linear over the range 0–8.0 x 10^?6 M for each metal. Interference from zinc is avoided by addition of nitrilotriacetic acid; nickel interferes. Appliation to the determination of iron and copper ions in blood serum is discussed.     

A quantum chemical method for rapid optimization of protein structures

A quantum chemical method for rapid optimization of protein structures is proposed. In this method, a protein structure is treated as an assembly of amino acid units, and the geometry optimization of each unit is performed with taking the effect of its surrounding environment into account. The optimized geometry of a whole protein is obtained by repeated application of such a local optimization procedure over the entire part of the protein. Here, we implemented this method in the MOPAC program and performed geometry optimization for three different sizes of proteins. Consequently, these results demonstrate that the total energies of the proteins are much efficiently minimized compared with the use of conventional optimization methods, including the MOZYME algorithm (a representative linear-scaling method) with the BFGS routine. The proposed method is superior to the conventional methods in both CPU time and memory requirements.     

Kinetic analysis of hydrolytic reaction of homo- and heterochiral adenylyl(3'-5')adenosine isomers: breaking homochirality reduces hydrolytic stability of RNA

The hydrolytic stability of the diastereomeric isomers of ApA was compared and the results show that heterochiral ApAs are more rapidly hydrolyzed than homochiral ApAs at low temperatures, suggesting that hydrolytic selection in cold environments in conjunction with selective polymerization may have been effective in enriching the homochirality of RNA.     

Initiation and propagation in γ-radiation-induced polymerization of ethylene

The initiation and propagation reaction in γ-ray-induced polymerization of ethylene was studied by the two-stage irradiation method, i.e., a first stage in which initiation and propagation occur at a high dose rate, and a second stage where only the growth of polymer radical occurs. The rate of initiation is calculated from the amount of polymerized monomer and the degree of polymerization as the rate of increase in the number of polymer chains. The initiation rate is shown to be proportional to the ethylene density in the reactor and dose rate. G_R of radical formation is found to be about 1.6 at 30°C. at a dose rate of 2.5 × 10⁴ rad/hr. and is almost independent of ethylene density but decreases slightly with increasing irradiation dose rate. The lifetime of the growing polymer chain radical is shown to be long at normal temperature. The absolute propagation rate is proportional to the square of ethylene fugacity and depends on dose rate to some extent. For chain growth, irradiation of low dose rate is necessary. The apparent activation energy for the propagation reaction is ?9 kcal./mole.     

Cyclic acetal-photosensitized polymerization. I. Photopolymerization of styrene in the presence of 1,3-dioxolanes

Styrene(St) was polymerized in benzene solution in the presence of substituted 1,3-dioxolane(DO) compounds by means of photoirradiation of the system at 40°C. The subtraction of the square of the polymerization rate in the absence of DO compounds (R_pab) from the square of the rate in the presence of DO compounds (R_ppr) was found to follow the equation: The effect of substituents in the 2-position on the polymerization rate increased in the order of methyl < hydrogen < ethyl < n-propyl < phenyl, as shown by the rate constant k_d′ of decomposition of DO compounds.     

Rhodium-catalyzed reductive coupling of disulfides and diselenides with alkyl halides, using hydrogen as a reducing agent

[reaction: see text] We have established that RhCl(PPh3)3 catalyzes a reductive coupling of disulfides and diselenides with alkyl halides in the presence of triethylamine using hydrogen as a reducing agent. This reaction serves as a convenient new method to produce unsymmetrical sulfides and selenides from disulfides and diselenides instead of unstable and odoriferous thiols and selenols.     

Kinetics of monolayer growth

The kinetics of a monolayer growth is studied using the two-dimensional lattice gas model by means of the path-probability method (PPM) for nonequilibrium phenomena. Kinetic equations for the combined processes of relaxation (adsorption and desorption) and diffusion are derived analytically and solved for the first time in the square approximation of the PPM. Comparison of the square approximation with the point and pair approximations along with Monte Carlo simulation shows the effect of using a larger basic cluster than in the previous studies. When the square approximation is used, the growth rate results are much improved in both cases with and without diffusion and agree well with the Monte Carlo simulations results, except for very small values of the driving forceL=/k _b T where is the chemical potential difference between the vapor and the solid phase. In the range where the agreement is good, there exists a region where the growth rateR is proportional to exp(–c/L with a constantc. This is the feature which is characteristic of two-dimensional nucleation-limited growth.