Evaluating the spectral sensitivity of the nonlinear-optical terahertz wave radiation detecors via spontaneous parametric down-conversion spectra

Principal parameters of the nonlinear-optical crystals are analyzed, which govern the spectral sensitivity of the terahertz wave detectors based on the frequency conversion from terahertz to optical range. A method is developed and experimentally demonstrated for characterizing these parameters. The method is founded on the spontaneous parametric down-conversion spectra observation without external terahertz wave radiation.     

Biochemical and Structural Studies of Conserved Maf Proteins Revealed Nucleotide Pyrophosphatases with a Preference for Modified Nucleotides

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New Luminescent Lanthanide Tetrakis-Complexes NEt4[LnL4] Based on Dimethyl-N-Benzoylamidophosphate

New lanthanide dimethyl-N-benzoylamidophosphate (HL) based tetrakis-complexes NEt₄[LnL₄] (Ln³⁺=La, Nd, Sm, Eu, Gd, Tb, Dy) are reported. The complexes are characterized by means of NMR, IR, absorption, and luminescent spectroscopy as well as by elemental, X-Ray, and thermal gravimetric analyses. The phenyl groups of the four ligands of the complex anion are directed towards one side, while the methoxy groups are directed in the opposite side, which makes the complexes under consideration structurally similar to calixarenes. The effect of changing the alkali metal counterion to the organic cation NEt₄⁺ on the structure and properties of the tetrakis-complex [LnL4]^- is analyzed. The complexes exhibit bright characteristic for respective lanthanides luminescence. Rather high intensity of the band of ⁵D₀→⁷F₄ transition, observed in the luminescence spectrum of NEt₄[EuL₄], is discussed based on theoretical calculations.     

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.     

Facile one-pot synthesis of 5-aryl/heterylidene-2-(2-hydroxyethyl- and 3-hydroxypropylamino)-thiazol-4-ones via catalytic aminolysis

A multicomponent synthetic approach for 5-aryl/heterylidene-2-(2-hydroxyethylamino)- and 2-(3-hydroxypropylamino)-thiazol-4-ones starting from 2-thioxothiazolidin-4-one or 2-methylsulfanylthiazol-4-one was developed. The proposed method involves simultaneous aminolysis of 2-thioxo- or 2-methylsulfanyl groups and Knoevenagel condensation with (hetero)aromatic aldehydes using 2-aminoethanol or 3-aminopropan-1-ol as catalysts. Side-chain prototropic amino–imino tautomerism was observed for target 5-ylidene-2-alkylaminothiazol-4-ones.     

Synthesis of chromeno[3,4-b]pyrrol-4(3H)-ones by cyclocondensation of 1,3-dicarbonyl compounds with 4-chloro-3-nitrocoumarin

The base-mediated cyclocondensation of 1,3-dicarbonyl compounds with 4-chloro-3-nitrocoumarin provides a convenient approach to various chromeno[3,4-b]pyrrol-4(3H)-ones.     

An optimized protocol for the multigram synthesis of 3-(trifluoromethyl)bicyclo[1.1.1]pent-1-ylglycine (CF3-Bpg)

An optimized procedure for the multigram synthesis of 3-(trifluoromethyl)bicyclo[1.1.1]pent-1-ylglycine (CF₃-Bpg) has been developed. The overall yield of the synthesis for the optimized up-scaling was increased from 35% to 53%. Moreover, conditions for separating the key isomeric aminonitriles 7 and 8 by crystallization were found, which greatly facilitated the isolation of 8 on a multigram scale. Following this optimized protocol, 100 g of optically pure CF₃-Bpg have been synthesized.     

Synthesis of 3-cyano-5-ethoxycarbonyl-6-hydroxypyridine-2-thiol derivatives

Ethyl ethoxymethylenemalonate reacts with cyanothioacetamide andN-methylmorpholine to giveN-methylmorpholinium 3-cyano-5-ethoxycarbonyl-6-oxopyridine-2-thiolate. Alkylation of the latter yieldsS-alkyl derivatives. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 196–197, January, 1999.