X‐ray investigations of bicyclic α‐methylene‐δ‐valerolactones. V. (4aS,7R,8aR)‐7‐Isopropenyl‐4a‐methyl‐3‐methyleneperhydrochromen‐2‐one

The title compound, C₁₄H₂₀O₂, adopts a conformation in which the δ‐valerolactone and cyclohexane rings are almost coplanar with one another. The γ‐methyl substituent occupies an axial position with respect to the cyclohexane ring. The δ‐valerolactone moiety adopts an envelope arrangement, while the cyclohexane ring exists in a chair conformation.     

Oxidative reactivity of Cu-TESHHK- and its alanine analogues

Redox properties of Cu(II) complexes of the terminally blocked hexapeptide -TESHHK- and a series of its alanine substituted analogs: -TASHHK-, -TEAHHK-, -TESAHK-, -TESHAK-, were investigated in their reactions with hydrogen peroxide in solution and by cyclic voltammetry in a broad range of pH. The formation of reactive oxygen species was followed with the use of spectrophotometric indicators, NDMA and NBT. The results indicate that the ability of these complexes to generate hydroxyl-like radicals correlates with the formation of active Cu(III) complexes resulting from the oxidation of Cu(II) by H2O2, which interact with further H2O2 molecules specifically.     

Spatial dependence of meson correlation functions at high temperature

The spatial dependence of meson correlation functions at high temperature is studied in perturbative QCD, keeping only the lowest order term. We obtain analytic results for the static correlation function in this approximation. Problems connected with the regularization of the divergent expressions are discussed in detail. The meson screening mass is determined from the form of the correlation function at large distances. We obtain , which agrees with the results of Eletskii and Ioffe, for massless quarks (M=0). Finally, the correlation function in the temporal direction is briefly discussed. For massless quarks, we find the corresponding screening massm _scr=2T.Research supported in part by the Polish State Committee for Scientific Research under Grant No. 2.0204.91.01     

Analytical possibilities of square-wave amperometry

The application of improved electronic equipment for square-wave amperometry (SWA) is described. This equipment has better resolution between waiting and sampling times and a simple, low-noise logic part. Titrations with electrogenerated bromine, iodine, iron(II) and silver ions were investigated as examples to compare SWA with d.c. amperometry (DCA). The sensitivity of SWA in titrations of < 10^?5 moll^?1 concentrations with iodine or silver(I) is more than 100 times greater than that of DCA. For measurements of higher concentations, DCA is preferred because of its better linear response. The change in current near the end-point of titrations with silver ions is sharper with SWA than with DCA.     

A Convenient Synthesis of Vinyl Sulfides

tert-Alkyl sulfides, with an α-(1H-benzotriazol-1-yl) group 6 and 13 , are readily prepared from N-[(aryl-thio)methyl]-1H-benzotriazoles 3 and N-( 11 ), respectively, by reaction with BuLi and then with the appropriate electrophile. The tert-alkyl sulfides 6 and 13 are smoothly converted by BF₃. OEt₂ into vinyl sulfides 5, 7 or 12 , respectively, in satisfactory yields.     

Oxathiaphospholane approach to the synthesis of oligodeoxyribonucleotides containing stereodefined internucleotide phosphoroselenoate function

5'-O-DMT-deoxyribonucleoside-3'-O-(2-selena-4,4-pentamethylene-1,3,2-oxathiaphospholane) monomers, derivatives of dA, dC, dG, and T, can be resolved into pure P-diastereomers by silica gel column chromatography. They have been used for DBU-promoted, either solution- or solid-phase synthesis of P-stereodefined phosphoroselenoate analogues of oligodeoxyribonucleotides. Fast- and slow-eluting monomers are precursors of phosphoroselenoate internucleotide linkage of R(P) and S(P) absolute configuration, respectively. [reaction: see text]     

An improved synthesis of 1-phenylpentafluoropropenes

1-Phenylpentafluoropropene and a number of its para- and ortho-substituted derivatives were prepared in high yields by reaction of hexafluoropropene with etheral solutions of corresponding phenylmagnesium bromides in sealed glass tubes under autogenous pressure. The products were obtained as mixtures of the Z and E isomers, which ratios varied from 1/2 to 1/6 in favour of the E forms. ¹⁹F n.m.r. and i.r. spectra and b.p. of the 1-phenylpentafluoropropenes are reported.     

Flow-injection single-point titration of acids with biamperometric detection at polarized platinum electrodes

Flow-injection single-point titration of acids is based on biamperometric measurement of iodine formed quantitatively in the reaction of iodide with iodate. Results are presented for determination of sulphuric, hydrofluoric, monochloroacetic, formic and acetic acids. The slopes of the calibration plots, which are linear for about 1–10 rum acid, depend on the strength of the acid, decreasing from sulphuric acid to acetic acid. With microcomputer on-line data processing, relative standard deviations were about 0.2%.     

Spontaneous Nef reaction of 3-aryl-2-(diethoxyphosphoryl)-4-nitroalkanoic acids

Spontaneous Nef reaction of primary and secondary 3-aryl-2-(diethoxyphosphoryl)-4-nitroalkanoic acids has been observed for the first time. The reaction provides a general and effective, highly diastereoselective synthesis of 3-(diethoxyphosphoryl)-1-hydroxysuccinimides and 2-(diethoxyphosphoryl)-4-oxoalkanoic acids.