Structural Phase Transition and the Dielectric Permittivity of the Model Lipid Bilayer [(CH2)12(NH3)2]CuCl4

Structural phase transitions in the lipid-like bilayer material [(CH₂)₁₂(NH₃)₂]CuCl₄ have been observed using differential thermal scanning. The compound shows an irreversible thermochromic transition at ? 465 K and three reversible transitions at T ₁ = 433 ± 4 K and T ₂ = 411 ± 2 K and T ₃ = 358 K. The transition at 350 K is ascribed to chain melting. The other two correspond to crystalline phase transformation.

Phase (IV) T₃ = 358 ± 2K Phase (III) T₂ = 411 ± 2K Phase (II) T₁ = 433 ± 4K Phase (I)

Dielectric permittivity is studied as a function of temperature in the range 300-440 K and frequency, range (60 Hz-100 kHz). It confirms the observed transitions. The dielectric permittivity reflects rotational and conformational transitions for the compound. The variation of the real part of the conductivity with temperature is thermally activated in the temperature range above 350 K, with frequency-dependent activation energy, the values of activation energy lie in the range of ionic hopping. The dependence of the conductivity on frequency follows the universal power law σ = σ₀ + A(T) ω ^{s ( T )} with 0<s<1. Comparison of this material with other members of the series is discussed     

Unified reciprocity of dithiophosphate by dichalcogenophosph(in)ate ligands on copper hydride nanoclusters via ligand exchange reaction

A structural study of ligand exchange on chalcogen‐passivated copper nanoclusters is far less developed. Herein, we report the synthesis of polyhydrido copper nanoclusters [Cu₂₀H₁₁{Se₂P(O ⁱBu)₂}₉] ( 2 ) passivated by Se‐donor ligands via ligand replacement reaction on [Cu₂₀H₁₁{S₂P(O ⁱPr)₂}₉] ( 1 ) with NH₄[Se₂P(O ⁱBu)₂]. In parallel to the synthesis of 2 , cluster [Cu₂₀H₁₁{S₂P(CH₂CH₂Ph)₂}₉] ( 4 ) was produced by the ligand exchange reaction on a new derivative of 1 , that is [Cu₂₀H₁₁{S₂P(O ⁿPr)₂}₉] ( 3 ). Solid state structures of both clusters 2 and 4 were unequivocally established by single‐crystal X‐ray diffraction studies and cluster 4 epitomizes exceptional case to preserve both the shape and size of the nanocluster during the course of ligand exchange. Structurally precise cluster 2 is the second example where the copper hydride nanocluster is stabilized by Se‐donor ligands. The anatomy of 2 can be visualized as a twisted cuboctahedral Cu₁₃ core, two triangular faces of which are capped by a Cu₆ cupola and a single Cu atom along the C₃ rotational axis.     

New pyrazinoquinazoline alkaloids Isolated from a culture of Stenotrophomonas maltophilia QB-77

Two new pyrazinoquinazoline alkaloids, epi-fiscalin D (1) and epi-fiscalin E (2), as well as three known analogues, norquinadoline A (3), quinadoline A (4), and fiscalin C (5), were isolated from ethyl acetate extract of the fermentation broth of Stentrophomonas maltophilia QB-77. The structures of new compounds were elucidated on the basis of extensive spectroscopic data analysis including UV, HRESIMS, and 1D and 2D NMR experiments. All the isolated compounds were tested for their in vitro cytotoxicity against five human cancer cell lines (SMMC-7721, MCF-7, HL-60, SW480, and A-549) and antibacterial activities against Bacillus subtilis, Escherichia coli, and Staphylococcus aureus.     

Frequency-dependent linear and non-linear response properties of single carrier quantum dots: Role of effective mass and anharmonicity in the confinement potential

We explore the pattern of frequency-dependent linear and non-linear optical (NLO) response of one electron quantum dots harmonically confined in two dimensions. For some fixed values of transverse magnetic field strength (ω_c), and harmonic confinement potential (ω₀), the influence of effective mass (m^*) of the system and the symmetry breaking anharmonic interaction on the frequency-dependent linear (α), and the first (β), and second (γ) NLO responses of the dot is computed through linear variational route. The investigation reveals interesting roles played by the anharmonic interaction and effective mass in modulating the response properties.     

A natural abundance Se solid-state NMR study of inorganic compounds

Various inorganic selenium-based compounds were analysed by ⁷⁷Se solid-state NMR, and a distinct difference in chemical shift ranges for compounds where selenium is present as selenide (Se²⁻) ionically and covalently bonded systems was observed. The selenides exhibit a shift range of approximately −700 to −100 ppm, as opposed to 700 to 1600 ppm for the compounds where there tends to be more direct covalent bonding to the selenium. The anisotropic hyperfine shift observed in NbSe₂ is shown to be axially symmetric, where the H₁₁ component is found to be normal to the Se3-trigonal plane.     

Some properties of rapidly varying sequences

We investigate the class R∞,s of rapidly varying sequences from different points of view. It is shown: (1) a sequence (cn)_n∈N of positive real numbers is rapidly varying if and only if the corresponding function x→c[x], x?1, is rapidly varying; (2) the class R∞,s satisfies some selection properties, as well as game-theoretical and Ramsey-theoretical conditions.     

Synthetic studies for the preparation of phosphorus carbonyl rhenacycles with the selenoimidodiphosphinate ligand [N(SePPh2)2]

The synthesis of the rhenacycles [Re(CO)₃(PR₃){Ph₂P(Se)NP(Se)Ph₂-κ²Se}], PR₃ = PPh₃ (1), PMePh₂ (2), and PMe₂Ph (3) by a straightforward high yield procedure is described. Attempts at the preparation of the spiro [Re(CO)₂(Ph₂PCH₂CH₂PPh₂-κ²P){Ph₂P(Se)NP(Se)Ph₂-κ²Se}] resulted in the formation of complexes [Re₂(CO)₆{Ph₂P(Se)NP(Se)Ph₂-κ²Se}₂(μ-Ph₂PCH₂CH₂PPh₂)] (4) and [Re(CO)₃(Ph₂PCH₂CH₂PPh₂-κ²P){Ph₂P(Se)NP(Se)Ph₂-κSe}] (5). All new inorganic rhenacycles 1-5 were characterized in solution and in solid state. The X-ray diffraction analysis of [Re(CO)₃PPh₃{Ph₂P(Se)NP(Se)Ph₂-κ²Se}] showed that its MnSePNPSe ring conformation is sensitive to temperature.     

Synthese und spektroskopische Charakterisierung von [Rh(SeCN)6]3– und trans‐[Rh(CN)2(SeCN)4]3–, Kristallstruktur von (Me4N)3[Rh(SeCN)6]

Synthesis and Spectroscopic Characterization of [Rh(SeCN)₆]^3– and trans ‐[Rh(CN)₂(SeCN)₄]^3–, Crystal Structure of (Me₄N)₃[Rh(SeCN)₆] Treatment of RhCl₃ with KSeCN in acetone yields a mixture of selenocyanato‐rhodates(III), from which [Rh(SeCN)₆]^3– and trans‐[Rh(CN)₂(SeCN)₄]^3– have been isolated by ion exchange chromatography on diethylaminoethyl cellulose. The X‐ray structure determination on a single crystal of (Me₄N)₃[Rh(SeCN)₆] (trigonal, space group R3, a = 14.997(2), c = 24.437(3) Å, Z = 6) reveals, that the compound crystallizes isotypically to (Me₄N)₃[Ir(SCN)₆]. The exclusively via Se coordinated selenocyanato ligands are bonded with the average Rh–Se distance of 2.490 Å and the Rh–Se–C angle of 104.6°. In the low temperature IR and Raman spectra the metal ligand stretching modes ν(RhSe) of (n‐Bu₄N)₃[Rh(SeCN)₆] ( 1 ) and trans‐(n‐Bu₄N)₃[Rh(CN)₂(SeCN)₄] ( 2 ) are in the range of 170–250 cm^–1. In 2 ν_as(CRhC) is observed at 479 cm^–1. The vibrational spectra are assigned by normal coordinate analysis based on the molecular parameters of the X‐ray determination. The valence force constants are f_d(RhSe) = 1.08 ( 1 ), 1.10 ( 2 ) and f_d(RhC) = 3.14 mdyn/Å ( 2 ). f_d(RhS) = 1.32 mdyn/Å is determined for [Rh(SCN)₆]^3–, which has not been calculated so far. The ¹⁰³Rh NMR resonances are 2287 ( 1 ), 1680 ppm ( 2 ) and the ⁷⁷Se NMR resonances are –32.7 ( 1 ) and –110.7 ppm ( 2 ). The Rh–C bonding of the cyano ligand in 2 is confirmed by a dublett in the ¹³C NMR spectrum at 136.3 ppm.     

Improved synthesis of polyfluorinated l-lysine for 19F NMR-based screening

Polyfluorinated N-α-Fmoc--Boc-l-lysine represents the best-in-class among a set of polyfluorinated amino acids (PFAs) which are useful tools for ¹⁹F NMR-Based Screening. In this communication, optimized reaction conditions that allowed for the multi-gram preparation of this unnatural amino acid are reported.     

A finite volume method for approximating 3D diffusion operators on general meshes

A finite volume method is presented for discretizing 3D diffusion operators with variable full tensor coefficients. This method handles anisotropic, non-symmetric or discontinuous variable tensor coefficients while distorted, non-matching or non-convex n-faced polyhedron meshes can be used. For meshes of polyhedra whose faces have not more than four edges, the associated matrix is positive definite (and symmetric if the diffusion tensor is symmetric). A second-order (resp. first-order) accuracy is numerically observed for the solution (resp. gradient of the solution).