Hot nuclei — Effective shapes and entrance channel effect

The γ-decay of the Giant Dipole Resonance in hot rotating compound nuclei has provided valuable information on the nuclear structure at finite temperature. A number of experimental results showing that the nuclear shapes change with temperature and angular momentum are here reviewed. In particular we concentrate on the temperature interval from 1 to 2 MeV, rotational frequencies from 0.2 to 1.5 MeV and on nuclei in the mass regionsA≈160–170 andA≈110, characterized by the prolate-oblate and spherical-oblate phase transitions, respectively. The possibility to study the shapes involved in the compound nucleus formation is also discussed. For this purpose long formation times are required and the nucleus¹⁷⁰W formed with the reaction⁶⁰Ni+¹¹⁰Pd, here studied, seems to be a good candidate. The gamma and particle decays were compared to those of the reaction⁴⁸Ti+¹²²Te. The comparison shows that in average the energy of the α-particles is larger for the more symmetric reaction, consistent with longer formation times and larger deformations in the pre-equilibrium stage.     

Polymerization of vinyl chloride in the presence of modified Ziegler–Natta catalysts comprising long chain organoaluminum compounds

Polymerization of vinyl chloride in the presence of systems containing a transition metal compound/Lewis base and an organoaluminum compound of a different length of carbon chain have been carried out. The influence of the structure and the concentrations of particular components on the polymerization yield and molecular weight of the products has been determined. The polymerization of vinyl chloride proceeds according to the free radical mechanism, and the effectiveness of such types of initiators decreases with an increase in the length of the substituent chain in the organoaluminum chain. When using ethyl derivatives, the maximum degree of vinyl chloride conversion is about 75%, and for polystyryl or polyisoprenylaluminum of an average polymerization degree of 50–100, the conversion did not exceed 0.5%. The maximum polymerization degree of vinyl chloride in block copolymers containing polyisoprenyl or polystyryl units was 90–300.     

1,2-O-(1-Ethylpropylidene)-α-d-glucofuranose, a low molecular mass organogelator: benzene gel formation and their thermal stabilities

Fourier transform infrared spectroscopy has demonstrated that hydrogen bonds are responsible for the aggregation of 1,2-O-(1-ethylpropylidene)-α-d-glucofuranose molecules in solid and benzene gels. The thermal stability of the studied gel is described by its melting temperature T_GS and thermal parameters. The deduced value of the gel-sol transition enthalpy is 50 kJ/mol. Viscosity is the major factor which influences the dynamics of the benzene molecules in the gels, as proved by the relaxation measurements.     

Voltammetry of Undiluted Red‐Ox Systems. Electrochemical ESR‐ and Electrochemical Impedance Spectroscopy Evidence for Formation of Ionic Liquid at Microelectrode Surface

It is believed that voltammetry of undiluted red‐ox liquids can lead to the formation of stable thin layers of ionic liquids at the microelectrode surface. Such situation was postulated for several liquids (solvents), however, so far no hard evidence supporting this expectation was obtained. By using electron spin resonance in combination with voltammetric experiments and electrochemical impedance spectroscopy we have shown that the concentration of the cation radicals at the microelectrode surface may be high (nitrobenzene) and the overall resistance of the solution abruptly drops (methanol) when the potential at the microelectrode corresponds to the wave plateau of the undiluted organic liquid. Both facts constitute a good evidence for the formation of microlayers of ionic liquids at the microelectrode surface during electrolysis of undiluted red‐ox systems.     

Novel Aspects of a Convenient Synthesis and of Electroproperties of Derivatives Based on Diphenylamine

The substituted monomers 4a , c , d, 5a , b, 6a, 7a , b , and 8a of novel poly(diphenylamines), possessing the respective photochromic groups, were synthesized by the Stille cross‐coupling methodology (Scheme). The hyperbranched structures were characterized by ¹H‐ and ¹³C‐NMR spectroscopy. The obtained monomers show good stability in common organic solvents such as CHCl₃, toluene, and CH₂Cl₂, and exhibit excellent thermal stability. Electrochemical results and theoretical calculations suggest that oxidation and reduction of the monomers start from the side of the amine function and the five‐membered heterocyclic ring moieties, respectively.     

Benzotriazole-mediated alkoxyalkylation and acyloxyalkylation

Reactions of readily available and stable 1-(α-alkoxyalkyl)benzotriazoles type 9a,b and 10a-d with a variety of silyl enol ethers 11 or 1,3-dicarbonyl compounds 13 give the expected ketones 12a-l (60-92%), β-keto esters 14a,b (62-67%), and malonates 14c,d (79-88%) in which a tetrahydrofuran or tetrahydropyran moiety has been introduced at the α position. 1-(Benzotriazol-1-yl)alkyl esters 7 are converted by cyanide anion into cyanohydrin esters 15a-i (55-98%).     

Microbiological Study in Petrol-Spiked Soil

The pollution of arable lands and water with petroleum-derived products is still a valid problem, mainly due the extensive works aimed to improve their production technology to reduce fuel consumption and protect engines. An example of the upgraded fuels is the BP 98 unleaded petrol with Active technology. A pot experiment was carried out in which Eutric Cambisol soil was polluted with petrol to determine its effect on the microbiological and biochemical properties of this soil. Analyses were carried out to determine soil microbiome composition—with the incubation and metagenomic methods, the activity of seven enzymes, and cocksfoot effect on hydrocarbon degradation. The following indices were determined: colony development index (CD); ecophysiological diversity index (EP); index of cocksfoot effect on soil microorganisms and enzymes (IF_G); index of petrol effect on soil microorganisms and enzymes (IF_P); index of the resistance of microorganisms, enzymes, and cocksfoot to soil pollution with petrol (RS); Shannon–Weaver’s index of bacterial taxa diversity (H); and Shannon–Weaver’s index of hydrocarbon degradation (ID_H). The soil pollution with petrol was found to increase population numbers of bacteria and fungi, and Protebacteria phylum abundance as well as to decrease the abundance of Actinobacteria and Acidobacteria phyla. The cultivation of cocksfoot on the petrol-polluted soil had an especially beneficial effect mainly on the bacteria belonging to the Ramlibacter, Pseudoxanthomonas, Mycoplana, and Sphingobium genera. The least susceptible to the soil pollution with petrol and cocksfoot cultivation were the bacteria of the following genera: Kaistobacter, Rhodoplanes, Bacillus, Streptomyces, Paenibacillus, Phenylobacterium, and Terracoccus. Cocksfoot proved effective in the phytoremediation of petrol-polluted soil, as it accelerated hydrocarbon degradation and increased the genetic diversity of bacteria. It additionally enhanced the activities of soil enzymes.     

Reductive cleavage mechanism of methylcobalamin: elementary steps of Co-C bond breaking

Density functional theory has been applied to the investigation of the reductive cleavage mechanism of methylcobalamin (MeCbl). In the reductive cleavage of MeCbl, the Co-C bond is cleaved homolytically, and formation of the anion radical ([MeCbl]*-) reduces the dissociation energy by approximately 50%. Such dissociation energy lowering in [MeCbl]*- arises from the involvement of two electronic states: the initial state, which is formed upon electron addition, has dominant pi*corrin character, but when the Co-C bond is stretched the unpaired electron moves to the sigma*Co-C state, and the final cleavage involves the three-electron (sigma)2(sigma*)1 bond. The pi*corrin-sigma*Co-C states crossing does not take place at the equilibrium geometry of [MeCbl]*- but only when the Co-C bond is stretched to 2.3 A. In contrast to the neutral cofactor, the most energetically efficient cleavage of the Co-C bond is from the base-off form. The analysis of thermodynamic and kinetic data provides a rationale as to why Co-C cleavage in reduced form requires prior departure of the axial base. Finally, the possible connection of present work to B12 enzymatic catalysis and the involvement of anion-radical-like [MeCbl]*- species in relevant methyl transfer reactions is discussed.     

New chiral discotics with helical organization of the mesophase—liquid crystalline derivatives of dibenzotetraaza[14]annulene

Two optically pure derivatives of dibenzotetraaza[14]annulene, bearing four (S)- or (R)- 3,7-dimethyloctoxy peripheral chiral tails, respectively, and two hydroxybenzoyl meso substituents were synthesized using a convergent multi-step route. The structure of the products was determined by ¹H and ¹³C NMR spectroscopy, ESI-MS, and elemental analysis. The mesomorphic behavior of the two chiral compounds, deciphered by differential scanning calorimetry (DSC), small-angle X-ray diffractometry (SA-XRD), and polarizing optical microscopy (POM) investigations, revealed the induction of two lamello-columnar phases, i.e., columnar stacks confined in smectic layers, whose columns may be arranged either according to the pg rectangular planar symmetry (for the low-temperature phase) or without registry between vicinal layers (for the high-temperature mesophase). Evidence of a helical organization of the molecules in the mesophases was obtained using a combination of electronic circular dichroism (ECD) and SA-XRD results, Molecular Dynamics simulations and quantum-chemical calculations.     

Intercomparison measurements of Rn concentration in water samples in Poland

The paper presents the results of intercalibration measurements of ²²²Rn concentration in water samples. The aim of the experiments was to evaluate the different measurement methods of radon determination in water samples performed by eleven laboratories in Poland and to test these methods in field work. In the years 2001-2003 three national intercomparison experiments were organized. The results allowed the participating laboratories to improve their measurement methodologies and to achieve better, i.e. more convergent results of determining radon concentration in water samples. The results show that the use of liquid-scintillation technique seems to be the best measurement method. It should be emphasized that comparative experiments are essential for all laboratories and they should be carried out as often as possible, based both on prepared samples with known concentration values of ²²²Rn and natural water samples, the most commonly used in laboratory practice.