A new reaction of sulfur ylides. Imination of dimethylsulfonium ketoylides with tosyl isocyanate

Russian Chemical Bulletin -     

DNA-hydrolyzing autoantibodies

Catalysis by antibodies could be a frequent phenomenon if the immune system generates a sufficiently diverse number of antibodyactive sites, some of which may possess catalytic activity. A catalytic antibody can be expected to do more damage than one that simply binds antigen. The best biochemical marker of systemic lupus erythematosus (SLE) is presence of autoantibodies to DNA. In the present article, we describe the DNA-hydrolyzing activity of DNA-binding autoantibodies purified from SLE patients. The substrates employed were supercoiled plasmid, radiolabeled plasmid fragments, and oligonucleotides. Hydrolysis of DNA by the antibodies was indicated by the appearance of fragments visualized by ethidium bromide staining of agarose gels or autoradiography of polyacrylamide gels. Changes in linear dichroism values were also indicative of DNA hydrolysis. The antibody activity was purified by protein A-sepharose chromatography, high-performance liquid chromatography gel filtration, and DNA-affinity chromatography. Scrupulous control studies were done to demonstrate that DNA-hydrolyzing activity really belongs to the antibodies. Purified Fab fragments showed hydrolyzing activity, whereas the Fc fragment was inactive. The specificity of DNA cleavage was investigated, and the rate parameters of hydrolysis by antibodies and conventional nucleases were compared.     

Silicon-containing esters of α-cyanoacrylic acid: synthesis and properties

A number of cyanoacetates have been synthesized: cyanoacetoxymethyitrimethylsilane (1), cyanoacetoxymethylpentamethyldisiloxane (2), cyanoacetoxyetoxymethylpentamethyldisiloxane (3). They were converted by the Knoevenagel reaction to novel esters of a-cyanoacrylic acid (4–13) containing silicon atoms in the ester groups and having the general formula RCH=C(CN)COOCH₂X (where R=H, 4-MeOC₆H₄, MeCH=CH, 2-furyl; X=SiMe₃, SiMe₂OSiMe₃, CH₂OCH₂SiMe₂OSiMe₃). These compounds are capable of copolymerization with esters of cyanoacrylic acid which are the precursors to adhesives for cold curing.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 949–952, May, 1993.     

C-N migration of allyl-and propargyloxycarbonyl groups

Reactions of triisopropylphosphine with allyl-and propargyl-2-cyanoacrylates give corresponding 1,3-zwitterions. Under the action of phenyl-or 1-naphthylisocyanates the zwitterions exert C-N migration of allyl-or propargyloxycarbonyl groups affording carbamates. Atropisomerism at room temperature was established for the carbamate formed from 1-naphthylisocyanate.     

Stability and error estimates for the $\theta$-method for strongly monotone and infinitely stiff evolution equations

Summary.   For evolution equations with a strongly monotone operator we derive unconditional stability and discretization error estimates valid for all . For the -method, with , we prove an error estimate , if , where is the maximal integration step for an arbitrary choice of sequence of steps and with no assumptions about the existence of the Jacobian as well as other derivatives of the operator , and an optimal estimate under some additional relation between neighboring steps. The first result is an improvement over the implicit midpoint method , for which an order reduction to sometimes may occur for infinitely stiff problems. Numerical tests illustrate the results. Received March 10, 1999 / Revised version received April 3, 2000 / Published online February 5, 2001     

Influence of polytypism on structural phase transformations in TlGaSe2 crystals

The polytypism is found to have a significant influence on the structural transformation of the crystal lattice of the TlGaSe₂ ferroelectric with variations in temperature. In the 2C-polytype, unlike the C-polytype, a first-order structural phase transition, which leads to a change in the translational symmetry along the C axis, is not observed in the temperature range T = 90–300 K and a second-order phase transition due to the formation of an incommensurate phase occurs at a higher temperature.