Reactions of 3-cyclopropyl-3-oxopropionitrile anion generated by electroreduction of 5-cyclopropylisoxazole

3-Cyclopropyl-3-oxopropionitrile anion obtained by cathodic reduction of 5-cyclopropylisoxazole in an aprotic medium was used as an example to demonstrate that cyano ketone anions show a dual reactivity. The reaction of acetyl chloride with the electrogenerated tetrabutylammonium salt of 3-cyclopropyl-3-oxopropionitrile gave O-acylation products, whereas the reaction with its sodium salt gives C-acylation products. The reactions of these salts with hydroxylamine hydrochloride follow a different route: in the case of the tetrabutylammonium salt, resinification takes place, while in the case of the sodium salt, 5-amino-3-cyclopropylisoxazole is formed. The condensation of this product with 4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione in glacial AcOH affords 3-cyclopropyl-6-(2-thienyl)-4-(trifluoromethyl)isoxazolo[5,4-b]pyridine in 85% yield. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2110–2114, November, 2007.     

Billion-fold acceleration of the methanolysis of paraoxon promoted by La(OTf)3 in methanol

The methanolysis of the insecticide paraoxon (2) was investigated in methanol solution containing varying [La(OTf)(3)] (OTf = (-)OS(O)(2)CF(3)) as a function of at 25 degrees C. Plots of the pseudo-first-order rate constants (k(obs)) for methanolysis as a function of [La(OTf)(3)](total) were obtained under buffered conditions from 5.15 to 10.97, and the slopes of the linear parts of these were used to determine the second-order rate constants (k(2)(obs)) for the La(3+)-catalyzed methanolysis of 2. Detailed analysis of the potentiometric titration data of La(OTf)(3) in methanol through fits to a multicomponent equilibrium mixture of dimers of general stoichiometry La(3+)(2)((-)OCH3)n, where n assumes values of 1-5, gives the equilibrium distribution of each as a function of. These data, when fit to a second expression describing k(2)(obs) in terms of a linear combination of individual rate constants k(2)(2:1), k(2)(2:2).k(2)(2:)n for the dimers, allow one to describe the overall catalytic profile in terms of the individual contributions. The most catalytically important species are the three dimers La(3+)(2)((-)OCH3)1, La(3+)(2)((-)OCH3)2, and La(3+)(2)((-)OCH3)3. The catalysis of the methanolysis of 2 is spectacular: a 2 x 10(-3) M solution of [La(3+)](total), at neutral, affords a 10(9)-fold acceleration relative to the base reaction (t(1/2) approximately 20 s at 8.2) with excellent turnover. A mechanism of the catalyzed reaction involving the La(3+)(2)((-)OCH3)2 species is proposed.     

Galvanomagnetic study of the quantum-well valence band of germanium in the Ge<Subscript>1−x</Subscript>Si<Subscript>x</Subscript>/Ge/Ge<Subscript>1−x</Subscript>Si<Subscript>x</Subscript> potential well

The structure of the quantum-well valence band in a Ge(111) two-dimensional layer is calculated by the self-consistent method. It is shown that the effective mass characterizing the motion of holes along the germanium layer is almost one order of magnitude smaller than the mass for the motion of heavy holes along the [111] direction in a bulk material (this mass is responsible for the formation of quantum-well levels). This creates a unique situation in which a large number of subbands appear to be populated at moderate values of the layer thickness d _w and the hole concentration p _s . The depopulation of two or more upper subbands in a 38-nm-thick germanium layer at a hole concentration p _s = 5 × 10¹⁵ m^?2 is revealed from the results of measuring the magnetoresistance in a strong magnetic field aligned parallel to the germanium layers. The destruction of the quantum Hall state at a filling factor ν = 1 indicates that the two lower subbands merge together in a self-formed potential profile of the double quantum well. It is demonstrated that, in a quasi-two-dimensional hole gas, the latter effect should be sensitive to the layer strain.     

Formation of high pressure domains during plastic deformation

A synergetic macrostructure characterized by an inhomogeneous material and pressure density distribution is formed in plastically deformable specimens. The kinetics of macrostructure formation and partially the parameters are determined by two processes: autostimulated redistribution of the density and diffusion relaxation. Domains with elevated density perform primarily rotational motion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 85–90, June, 1990.     

Study on the transesterification of methyl aryl phosphorothioates in methanol promoted by Cd(II), Mn(II), and a synthetic Pd(II) complex

Methanol solutions containing Cd(II), Mn(II), and a palladacycle, (dimethanol bis(N,N-dimethylbenzylamine-2C,N)palladium(II) (3), are shown to promote the methanolytic transesterification of O-methyl O-4-nitrophenyl phosphorothioate (2b) at 25 °C with impressive rate accelerations of 10(6)-10(11) over the background methoxide promoted reaction. A detailed mechanistic investigation of the methanolytic cleavage of 2a-d having various leaving group aryl substitutions, and particularly the 4-nitrophenyl derivative (2b), catalyzed by Pd-complex 3 is presented. Plots of k(obs) versus palladacycle [3] demonstrate strong saturation binding to form 2b:3. Numerical fits of the kinetic data to a universal binding equation provide binding constants, K(b), and first order catalytic rate constants for the methanolysis reaction of the 2b:3 complex (k(cat)) which, when corrected for buffer effects, give corrected (k(cat)(corr)) rate constants. A sigmoidal shaped plot of log(k(cat)(corr)) versus (s)(s)pH (in methanol) for the cleavage of 2b displays a broad (s)(s)pH independent region from 5.6 ≤ (s)(s)pH ≤ 10 with a k(minimum) = (1.45 ± 0.24) × 10(-2) s(-1) and a [lyoxide] dependent wing plateauing above a kinetically determined (s)(s)pK(a) of 12.71 ± 0.17 to give a k(maximum) = 7.1 ± 1.7 s(-1). Br?nsted plots were constructed for reaction of 2a-d at (s)(s)pH 8.7 and 14.1, corresponding to reaction in the midpoints of the low and high (s)(s)pH plateaus. The Br?nsted coefficients (β(LG)) are computed as -0.01 ± 0.03 and -0.86 ± 0.004 at low and high (s)(s)pH, respectively. In the low (s)(s)pH plateau, and under conditions of saturating 3, a solvent deuterium kinetic isotope effect of k(H)/k(D) = 1.17 ± 0.08 is observed; activation parameters (ΔH(Pd)(++) = 14.0 ± 0.6 kcal/mol and ΔS(Pd)(++)= -20 ± 2 cal/mol·K) were obtained for the 3-catalyzed cleavage reaction of 2b. Possible mechanisms are discussed for the reactions catalyzed by 3 at low and high sspH. This catalytic system is shown to promote the methanolytic cleavage of O,O-dimethyl phosphorothioate in CD3OD, producing (CD3O)2P═O(S(-)) with a half time for reaction of 34 min.     

Study of the physicomechanical properties of various types of biotissues for the purpose of selecting alloprosthetic material

The results of in vitro tests to determine the physicomechanical properties of muscle and fatty tissues, myofascial composite tissues, and the structural soft tissues of the living organism are compared with similar data for unfilled SKTN silicone rubber vulcanizates with different degrees of cross-linking. It is shown that the properties of encapsulated silicone materials are similar to those of myofascial composite tissues tested in vitro. It is proposed to use vulcanizates with a relatively dense vulcanization network, selected on the basis of the modulus of elasticity, for the cosmetic correlation of defects of muscle tissues.     

Dinuclear Zn(II) catalysts as biomimics of RNA and DNA phosphoryl transfer enzymes: changing the medium from water to alcohol provides enzyme‐like rate enhancements

Phosphodiesters are notoriously hydrolytically inert compounds that are demonstrated to have large accelerations of P‐OR cleavage promoted by transition and lanthanide metal ions in methanol and ethanol media. This review commentary describes recent findings of how a simple mononuclear and a dinuclear Zn(II) complex promote the cleavage of a series of RNA models and DNA models in alcohol media. The discussion centers on the analysis of the mechanisms of cleavage, energetics of the catalytic process, on recent findings of electrophilic assistance of leaving group departure, and the observation of a rapid hydrolytic reaction of a DNA model promoted by the dinuclear Zn(II) complex in ethanol containing less than 2% water. Copyright © 2009 John Wiley & Sons, Ltd.     

A Study of the Influence of Nanoparticles on the Properties of Drilling Fluids

The effect of nanoparticles with different compositions and sizes on the rheological properties, filtration losses, and lubricating ability of drilling fluids has been experimentally studied. Nanoparticles of silicon, aluminum, and titanium oxides have been examined, while an aqueous bentonite suspension with a solid phase mass fraction of 5% has been used as a basic model of a drilling fluid. The concentrations and sizes of nanoparticles in the drilling fluids have been varied from 0.25 to 2 wt % and from 5 to 100 nm, respectively. It has been shown that the addition of nanoparticles substantially changes the properties of the drilling fluids. In contrast to suspensions of particles with macro- and microscopic sizes, the rheological parameters, filtration losses, and lubricating and sticking abilities of the suspensions containing nanoparticles depend on the size and nature of the latter and vary markedly already at low nanoparticle concentrations.     

A simple DNase model system comprising a dinuclear Zn(II) complex in methanol accelerates the cleavage of a series of methyl aryl phosphate diesters by 10(11)-10(13)

The di-Zn(II) complex of 1,3-bis[ N1, N1'-(1,5,9-triazacyclododecyl)]propane with an associated methoxide ( 3:Zn(II) 2: (-)OCH 3) was prepared and its catalysis of the methanolysis of a series of fourteen methyl aryl phosphate diesters ( 6) was studied at s (s)pH 9.8 in methanol at 25.0 +/- 0.1 degrees C. Plots of k obs vs [ 3:Zn(II) 2: (-)OCH 3] free for all members of 6 show saturation behavior from which K(M) and kcat (max) were determined. The second order rate constants for the catalyzed reactions (kcat (max)/K(M)) for each substrate are larger than the corresponding methoxide catalyzed reaction (k 2 (-OMe)) by 1.4 x 10(8) to 3 x 10 (9)-fold. The values of k cat (max) for all members of 6 are between 4 x 10(11) and 3 x 10(13) times larger than the solution reaction at s (s)pH 9.8, with the largest accelerations being given for substrates where the departing aryloxy unit contains ortho-NO 2 or C(O)OCH 3 groups. Based on the linear Br?nsted plots of k cat (max) vs s (s)pKa of the phenol, beta lg values of -0.57 and -0.34 are determined respectively for the catalyzed methanolysis of "regular" substrates that do not contain the ortho-NO 2 or C(O)OCH 3 groups, and those substrates that do. The data are consistent with a two step mechanism for the catalyzed reaction with rate limiting formation of a catalyst-coordinated phosphorane intermediate, followed by fast loss of the aryloxy leaving group. A detailed energetics calculation indicates that the catalyst binds the transition state comprising [CH 3O (-): 6], giving a hypothetical [ 3:Zn(II) 2:CH 3O (-): 6] complex, by -21.4 to -24.5 kcal/mol, with the strongest binding being for those substrates having the ortho-NO 2 or C(O)OCH 3 groups.     

Rapid three-step cleavage of RNA and DNA model systems promoted by a dinuclear Cu(II) complex in methanol. energetic origins of the catalytic efficacy

A dinuclear Cu(II) complex of 1,3-bis-N(1)-(1,5,9-triazacyclododecyl)propane with an associated methoxide (2-Cu(II)(2):(-OCH(3))) was prepared, and its kinetics of reaction with an RNA model (2-hydroxypropyl-p-nitrophenyl phosphate (1, HPNPP)) and two DNA models (methyl p-nitrophenyl phosphate (3) and iso-butyl p-chlorophenyl phosphate (4)) were studied in methanol solution at (s)(s)pH 7.2 +/- 0.2. X-ray diffraction structures of 2-Cu(II)(2):(-OH)(H(2)O)(CF(3)SO(3)-)(3):0.5CH(3)CH(2)OCH(2)CH(3) and 2-Cu(II)(2):(-OH)((C(6)H(5)CH(2)O)(2)PO(2)-)(CF(3)SO(3)-)2 show the mode of coordination of the bridging -OH and H(2)O between the two Cu(II) ions in the first complex and bridging -OH and phosphate groups in the second. The kinetic studies with 1 and 3 reveal some common preliminary steps prior to the chemical one of the catalyzed formation of p-nitrophenol. With 3, and also with the far less reactive substrate (4), two relatively fast events are cleanly observed via stopped-flow kinetics. The first of these is interpreted as a binding step which is linearly dependent on [catalyst] while the second is a unimolecular step independent of [catalyst] proposed to be a rearrangement that forms a doubly Cu(II)-coordinated phosphate. The catalysis of the cleavage of 1 and 3 is very strong, the first-order rate constants for formation of p-nitrophenol from the complex being approximately 0.7 s(-1) and 2.4 x 10(-3) s(-1), respectively. With substrate 3, 2-Cu(II)(2):(-OCH(3)) exhibits Michaelis-Mentin kinetics with a k(cat)/K(M) value of 30 M(-1) s(-1) which is 3.8 x 10(7)-fold greater than the methoxide promoted reaction of 3 (7.9 x 10(-7) M(-1) s(-1)). A free energy calculation indicates that the binding of 2-Cu(II)(2):(-OCH(3)) to the transition states for 1 and 3 cleavage stabilizes them by -21 and -24 kcal/mol, respectively, relative to that of the methoxide promoted reactions. The results are compared with a literature example where the cleavage of 1 in water is promoted by a dinuclear Zn(II) catalyst, and the energetic origins of the exalted catalysis of the 2-Cu(II)(2) and 2-Zn(II)(2) methanol systems are discussed.