Generation of new landomycins by combinatorial biosynthetic manipulation of the LndGT4 gene of the landomycin E cluster in S. globisporus

A 3 kb DNA fragment from the Streptomyces globisporus 1912 landomycin E (LaE) biosynthetic gene cluster (lnd) was completely sequenced. Three open reading frames were identified, lndGT4, lndZ4, and lndZ5, whose probable translation products resemble a glycosyltransferase, a reductase, and a hydroxylase, respectively. Studies of generated mutants from disruption and complementation experiments involving the lndGT4 gene allowed us to determine that LndGT4 controls the terminal L-rhodinose sugar attachment during LaE biosynthesis and that LndZ4/LndZ5 are responsible for the unique C11-hydroxylation of the landomycins. Generation of the novel landomycins F, G, and H in the course of these studies provided evidence for the flexibility of lnd glycosyltransferases toward their acceptor substrates and a basis for initial structure-activity relationships within the landomycin family of antibiotics.     

Reaction of 1,2,4-triazole-3-thione with acetylene

A mixture of 1,2,4-triazol-3-yl vinyl sulfide and N,S-divinyl derivatives is formed in the reaction of 1,2,4-triazole-3-thione with acetylene under pressure. The mixture of N,S-divinyl derivatives was separated into two isomers by gas-liquid chromatography. The hydrogenation, polymerization, and complexing of 1,2,4-triazol-3-yl vinyl sulfide were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1561–1563, November, 1977.     

Electrochemical fluorination of N,N-dimethylperfluoroacylamides

The electrochemical fluorination (ECF) of N,N-dimethylperfluoroacylamides gives the corresponding perfluoro-N,N-dimethylacylamides in low yield. With increase of the number of carbon atoms in the perfluoroacyl radical the yield of the required perfluoro-N,N-dimethylacylamides is slightly increased.     

15N NMR spectra and specific intramolecular interactions in N-vinylazoles

The factors that affect the chemical shifts in the ¹⁵N NMR spectra of N-vinylazoles were investigated. It was shown that an additional positive contribution to the shielding constant of the pyridine nitrogen atom occurs in the s-cis-(N₍₂₎) conformation of N-vinylpyrazoles due to overlapping of the electron cloud of its unshared electron pair and the s-orbital of the vinyl group hydrogen -cis-atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1055–1059, August, 1991.     

NMR spectra of paramagnetic complexes of 1-vinylimidazole with iron group metals

The high-resolution ¹H and ¹³C NMR spectra of 1-vinylimidazole complexes with iron group metals were recorded. The contact coupling in these systems was established in the ¹H and ¹³C NMR spectra. The applicability of the NMR spectra transformed by long-range hyperfine coupling for elucidating the molecular structure of the ligand was shown. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1430–1433, June, 2005.     

Synthesis and structure of ternary transition-metal silicides Zr3Mn4Si6 and Hf3Mn4Si6

The isostructural ternary transition-metal silicides Zr₃Mn₄Si₆ and Hf₃Mn₄Si₆ can be prepared by direct reaction of the elemental components or by arc-melting. The single-crystal structure of Zr₃Mn₄Si₆ was determined by X-ray diffraction (Pearson symbol tP104, tetragonal, space group P4₂/mbc, Z=8, , ). Zr₃Mn₄Si₆ is isostructural to Nb₃Fe₃CrSi₆ and contains an essentially ordered arrangement of the transition-metal atoms. Square antiprismatic clusters with Zr and Mn atoms at the corners and Si atoms at the center share opposite faces to form one-dimensional columns extending along the c direction. These columns occupy channels that are outlined by a framework of edge- and face-sharing MnSi₆ octahedra. The extensive metal-metal interactions in the structure are complemented by Si-Si bonding in the form of dumbbells, linear chains, and zigzag chains.     

Generalized oscillator representations for generalized Calogero Hamiltonians

We construct generalized oscillator representations for all generalized Calogero Hamiltonians with the potential V (x) = g ₁ /x ² + g ₂ x ² , g ₁ ≥ ?1/4, g ₂ > 0. These representations are generically nonunique, but for each Hamiltonian, there exists an optimum representation explicitly determining the ground state and its energy. For generalized Calogero Hamiltonians with coupling constants g ₁ < ?1/4 or g ₂ < 0, generalized oscillator representations do not exist, which agrees with the fact that the corresponding Hamiltonians are not bounded from below.     

A raman study of hydrostatic pressure induced phase transitions in Rb2KInF6 crystals

The Raman spectra of the elpasolite (Rb₂KInF₆) crystal have been studied in the pressure range from 0 to 5.3 GPa at a temperature of 295 K. A phase transition at a pressure of approximately 0.9 GPa has been found. An analysis of the variations in the spectral parameters has led to the conclusion that the phase transition to a distorted phase is accompanied by the doubling of the volume of the primitive cell of the initial cubic phase. Numerical calculations of the lattice dynamics in the Rb₂KInF₆ crystal have been performed. The numerical simulation has established that the phase transition at a pressure of 0.9 GPa is associated with condensation of the F _lg mode. A probable high-pressure phase is the phase with space group C2/m.     

Asymptotic behavior of functionals of cyclic long-range dependent random fields

Long-range dependent random fields with spectral densities, which are unbounded at some frequencies, are investigated. We demonstrate new examples of covariance functions, which do not exhibit a regular varying asymptotic behavior at infinity. However, the variances of averaged functionals of these fields are regularly varying. The limit theorems for weighted functionals of cyclic long-range dependent fields are obtained. The order of normalizing constants and relations between the weight functions and singularities in non-degenerative asymptotics are discussed.     

Crotonic,cynnamic, and propiolic acids motifs in the synthesis of thiopyrano[2,3-d][1,3]thiazoles via hetero-Diels–Alder reaction and related tandem processes

Various novel thiopyrano[2,3-d][1,3]thiazol-2-one-6-carboxylic acids derivatives were synthesized in 54–86% yields via hetero-Diels–Alder reactions and related acylation-based tandem processes of 5-arylidene-4-thioxo-2-thiazolidinones with crotonic, propiolic, and cynnamic acids derivatives. Stereo- and regioselectivity of cycloaddition were investigated.