Ynamide‐Mediated Thiopeptide Synthesis

Exploration of the full potential of thioamide substitution as a tool in the chemical biology of peptides and proteins has been hampered by insufficient synthetic strategies for the site‐specific introduction of a thioamide bond into a peptide backbone. A novel ynamide‐mediated two‐step strategy for thiopeptide bond formation with readily available monothiocarboxylic acids as thioacyl donors is described. The α‐thioacyloxyenamide intermediates formed from the ynamides and monothiocarboxylic acids can be purified, characterized, and stored. The balance between their activity and stability enables them to act as effective thioacylating reagents to afford thiopeptide bonds under mild reaction conditions. Amino acid functional groups such as OH, CONH₂, and indole NH groups need not be protected during thiopeptide synthesis. The modular nature of this strategy enables the site‐specific incorporation of a thioamide bond into peptide backbones in both solution and the solid phase.     

Application of electromodulated fluorescence to the study of the dynamics of single-strand oligonucleotides at modified gold surfaces

Single-strand oligonucleotides with fluorescein labels were immobilized on modified gold electrodes and the surface fluorescence intensity was measured as a function of the potential applied to the electrode. The potential consisted of a constant and sinusoidal parts. The fluorescence was detected synchronously with the sinusoidal component of the potential. Large variation in the electromodulated fluorescence (EmF) was observed as a function of the constant component of the applied potential. In the potential range -0.2 to +0.2 V (vs Ag/AgCl) the EmF signal was quasi-reversible. A model for surface fluorescence was applied to the analysis of the EmF in this potential range. The model assumed that the adsorption-desorption process and quenching by the metal were the dominant mechanisms responsible for the observed EmF. For constant potential more negative than -0.5 V, the observed EmF response appeared to have a contribution from ssDNA in solution. This interpretation was suggested by comparison to EmF from solutions containing free fluorescein or labeled ssDNA. Large variation in the EmF response was observed for electrodes modified with amine and carboxyl groups. This suggests that electrostatic interactions play a dominant role.     

STUDY ON THE UNIQUENESS OF LIMIT CYCLE OF THE QUADRATIC SYSTEM BY USING THE QUADRATIC CURVE WITHOUT CONTACT(CONTINUED 1)

１ＩｎｔｒｏｄｕｃｔｉｏｎａｎｄＲｅｓｕｌｔｓＣｏｎｓｉｄｅｒｔｈｅｑｕａｄｒａｔｉｃｓｙｓｔｅｍ［１］ｄｘｄｔ＝－ｙ＋δｘ＋ｌｘ２＋ｍｘｙ＋ｎｙ２＝Ｐ２（ｘ，ｙ），ｄｙｄｔ＝ｘ（１＋ａｘ＋ｂｙ）＝Ｑ２（ｘ，ｙ），（ｎ≥０，ａｂ≠０）Ｅ２ｗｉｔｈｏｕ...     

Origin of Bragg-Coulomb high-Tc superconductivity Green''s function and diagram method for umklapp e-e scattering

The Green's function method and diagram technique for umklapp electron-electron scattering mediated by the screened Coulomb interaction in layered anisotropic conductors are examined. Gor'kov-type equations and their general solution for anomalous and normal temperature Green's functions are derived taking into account umklapp scattering of all orders. Explicit equations for dielectric and superconducting order parameters, including coexistent Bragg and BCS pairing, are found. The possibility of the first-order phase transition to the superconducting state is discussed. The theory elucidates the origin of Bragg-Coulomb high-T_c superconductivity, proposed by the authors.     

Weibel instability associated with inverse bremsstrahlung absorption of intense electromagnetic radiation

We investigate the Weibel instability in a plasma with a nonstationary three-temperature electron distribution generated by inverse bremsstrahlung of an intense elliptically polarized electromagnetic wave. We show that electron-ion collisions in this strong high frequency field are simultaneously the cause of the development of the instability and the reason it is suppressed. We find plasma and radiation parameters for which spontaneous quasistationary solenoidal electromagnetic fields can increase by many times. Zh. éksp. Teor. Fiz. 111, 1245–1257 (April 1997)     

Typical property of convex sets

Translated from Matematicheskie Zametki, Vol. 49, No. 2, pp. 107–112, February, 1991.     

Boundary conditions for narrow-gap heterostructures described by the Dirac equation

Boundary conditions are obtained for narrow-gap heterostructures formed by semiconductors whose energy spectrum is described by the Dirac equation. The case where the carrier mass exhibits axial anisotropy is analyzed. A helicity operator whose eigenvalue is conserved over the entire heterostructure is generalized for anisotropic heterostructures. Fiz. Tverd. Tela (St. Petersburg) 40, 1345–1346 (July 1998)     

Polarization of the high harmonics of radiation in a laser plasma

The polarization of the high harmonics generated in plasmas by the bremsstrahlung of electrons oscillating under the influence of high-power plasma-heating electromagnetic radiation is described on the basis of a simple model of a cold plasma. It is shown that when the polarization of the heating radiation differs from plane polarization by a small but finite amount, the high harmonics are generated with almost perpendicular polarization, and the degree of circular polarization of the harmonics increases with the number of the harmonic. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 313–316 (10 March 1998)