Mass number dependence of activation capture cross sections for 14 MeV neutrons

Radiative capture cross sections of 14.5 MeV neutrons have been measured for several nuclei with an essentially improved activation method. The results agree with those from the spectrum method, which confirms that “shell effects” exhibited by earlier activation data are due to experimental errors.     

Crystal Structure,Dielectric Characteristics and Conduction Mechanism of a New Hybrid Material,Tetra(Phenylpiperazinium) Decachlorotriplumbate(II)

Monocrystalline (C₁₀H₁₅N₂)₄Pb₃Cl₁₀ was obtained via an aqueous solution reaction and characterized by single-crystal X-ray diffraction technique, elemental analyses, IR spectroscopy, UV–Vis spectrum, photoluminescence properties and thermal analysis. Structural characterization reveals that the title compound is built from [Pb₃Cl₁₀]^4? units sharing Cl2 atom to form 2-D [Pb₃Cl₁₀] _n ^4n? layers, these anions are linked to the organic cations via N–H···Cl and C–H···Cl hydrogen bonding. Moreover, dielectric relaxation spectroscopy has also been determined to show different molecular motions. Measurements of AC conductivity as a function of frequency at different temperatures indicated the hopping conduction mechanism.     

Statistical Physics of Evolving Systems

Evolution is customarily perceived as a biological process. However, when formulated in terms of physics, evolution is understood to entail everything. Based on the axiom of everything comprising quanta of actions (e.g., quanta of light), statistical physics describes any system evolving toward thermodynamic balance with its surroundings systems. Fluxes of quanta naturally select those processes leveling out differences in energy as soon as possible. This least-time maxim results in ubiquitous patterns (i.e., power laws, approximating sigmoidal cumulative curves of skewed distributions, oscillations, and even the regularity of chaos). While the equation of evolution can be written exactly, it cannot be solved exactly. Variables are inseparable since motions consume driving forces that affect motions (and so on). Thus, evolution is inherently a non-deterministic process. Yet, the future is not all arbitrary but teleological, the final cause being the least-time free energy consumption itself. Eventually, trajectories are computable when the system has evolved into a state of balance where free energy is used up altogether.     

Conformations and energetics of sulfur and selenium diimides

The geometries and energetics of different conformations of sulfur and selenium diimides E(NR)(2) (E = S, Se; R = H, Me, (t)Bu, C(6)H(3)Me(2)-2,6, SiMe(3)) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH)(2), but in general, the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH)(2) the present calculations further confirm that syn,syn and syn,anti conformations lie energetically close to each other. From the three different theoretical methods used, B3PW91/6-31G proved to be the most suitable method for predicting the geometries of chalcogen diimides. The optimized geometrical parameters are in a good agreement with all available experimental data. While qualitative energy ordering of the different conformations is independent of the level of theory, the quantitative energy differences are dependent on the method used. The performance and reliability of higher level ab initio calculations and DFT methods using large basis sets were tested and compared with experimental information where available. All of the higher level ab inito methods give very similar results, but the use of large basis sets with the B3PW91 method does not increase the reliability of the results. The combination of CCSD(T)/cc-pVDZ with the B3PW91/6-31G-optimized geometries is found to be the method of choice to study energetic properties of chalcogen diimides.     

Comparison of calculated DFT/B3LYP and experimental C and O NMR chemical shifts, ab initio HF/6-31G* optimised structures, and single crystal X-ray structures of some substituted methyl 5β-cholan-24-oates

Single crystal X-ray structures (monoclinic space group P2₁) for methyl 3-oxo-5β-cholan-24-oate and methyl 3,12-dioxo-5β-cholan-24-oate have been solved and compared with HF/6-31G* optimised structures. In the crystalline packings the side chains are connected with weak OC(sp³)HO-type of interactions between C25–H and C24–O–C25 and the keto ends with weak C(sp³)HO=C-type of interactions between C4–H and O=C3. The orientations of the side chains, which steric configurations are of great importance to the biological activity of the molecules, are compared with the experimental structure of methyl 3-hydroxy-5β-cholan-24-oate. Probable reasons for the observed differences are discussed. In addition, ¹³C and ¹⁷O NMR chemical shifts of methyl 3-oxo-5β-cholan-24-oate and methyl 3,12-dioxo-5β-cholan-24-oate as well as the epimeric methyl 3-hydroxy-5β-cholan-24-oate and methyl 3β-hydroxy-5β-cholan-24-oate have been calculated (DFT/B3LYP/6-311G*) and compared with the experimental values by linear regression analyses. In general, the correspondence between the theoretical and experimental parameters is good or excellent.     

Scalable total synthesis of (-)-berkelic acid by using a protecting-group-free strategy

Supply chain: the polycyclic core of (-)-berkelic acid (1) was constructed in just one step from very simple starting materials. The total synthesis of 1 involves a seven-step linear sequence. Protection/deprotection steps were avoided and all but the last step were performed on a gram scale. This synthesis could solve the supply problem associated with the exhaustion of the natural source.     

Mukaiyama-Michael reactions with acrolein and methacrolein: a catalytic enantioselective synthesis of the C17-C28 fragment of pectenotoxins

Enantioselective iminium-catalyzed reactions with acrolein and methacrolein are rare. A catalytic enantioselective Mukaiyama-Michael reaction that readily accepts acrolein or methacrolein as substrates, affording the products in good yields and 91-97% ee, is presented. As an application of the methodology, an enantioselective route to the key C17-C28 segment of the pectenotoxin using the Mukaiyama-Michael reaction as the key step is described.     

Characterization of oil-free and oil-loaded liquid-crystalline particles stabilized by negatively charged stabilizer citrem

The present study was designed to evaluate the effect of the negatively charged food-grade emulsifier citrem on the internal nanostructures of oil-free and oil-loaded aqueous dispersions of phytantriol (PHYT) and glyceryl monooleate (GMO). To our knowledge, this is the first report in the literature on the utilization of this charged stabilizing agent in the formation of aqueous dispersions consisting of well-ordered interiors (either inverted-type hexagonal (H(2)) phases or inverted-type microemulsion systems). Synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) were used to characterize the dispersed and the corresponding nondispersed phases of inverted-type nonlamellar liquid-crystalline phases and microemulsions. The results suggest a transition between different internal nanostructures of the aqueous dispersions after the addition of the stabilizer. In addition to the main function of citrem as a stabilizer that adheres to the surface of the dispersed particles, it has a significant impact on the internal nanostructures, which is governed by the following factors: (1) its penetration between the hydrophobic tails of the lipid molecules and (2) its degree of incorporation into the lipid-water interfacial area. In the presence of citrem, the formation of aqueous dispersions with functionalized hydrophilic domains by the enlargement of the hydrophilic nanochannels of the internal H(2) phase in hexosomes and the hydrophilic core of the L(2) phase in emulsified microemulsions (EMEs) could be particularly attractive for solubilizing and controlling the release of positively charged drugs.     

Cooperativity of H-bonding and anion-π interaction in the binding of anions with neutral π-acceptors

A rare anion-π complex between bromide and a neutral receptor is reported and related receptor systems are studied with a series of anions. The interaction is observed in the solid state and in solution, and further evidence for it is obtained by a computational study.     

Synthesis of 2,5-dihydropyridine derivatives by gold-catalyzed reactions of β-ketoesters and propargylamines

The reaction of simple β-ketoesters and propargylamines under gold(III) catalysis leads to the formation of the elusive 2,5-dihydropyridine system. This new reaction provides the synthesis of potentially bioactive compounds in moderate to high yields.