Short chain acyclic crown ethers

A series of short chain acyclic crown ethers such as (1,2), (1,3), (1,4)-phenylenediethers and some symmetric or assymmetrico-substituted phenyl ethers were prepared. The complexation studies of these compounds were carried out by a) direct UV titration method, b) picrate extraction method and c) isolation of crystalline complex.Taken in part from the master's thesis ofMaria Cecilia Bastos Vieira de Souza, Instituto Militar de Engenharia, 1978.     

Luminescence lifetime distributions analysis in heterogeneous systems by the use of Excel's Solver

A detailed study of the luminescence decay curves of pyrene included within p-tert-butylcalix[4]arene cavities and benzophenone into silicalite channels is reported. A new methodology for a lifetime distribution analysis of the decay curve of probes onto heterogeneous surfaces is presented, which allows for asymmetric distributions and uses Voigt profiles (Gaussian and Lorentzian mixture) instead of pure Gaussian or Lorentzian distributions. Our approach uses a very simple and widely available tool for fitting, the Microsoft Excel Solver. In the case of the pyrene/tert-butylcalix[4]arene sample, the room temperature luminescence detected in the microsecond time scale was not only the phosphorescence of pyrene but also monomer delayed fluorescence, crystal phosphorescence, and excimer delayed fluorescence. In the benzophenone/silicalite case, three emissive forms of benzophenone could be assigned, one of benzophenone included into the silicalite circular zigzag channels, another for emplacement into the elliptical straight channels and finally when benzophenone is placed at the crossing points of those silicalite channels, where smaller spatial restrictions for benzophenone exist.     

Neutron activation analysis of atmospheric biomonitors from the Azores: A comparative study of lower and higher plants

Summary Within an extensive survey of lower and higher plants in the Azores' Terceira and Santa Maria islands, this study is focused on the evaluation of ectohydric bryophytes and bark from Cryptomeria japonica as an alternative to epiphytic lichens for air-monitoring purposes. Neutron activation analysis (k₀-NAA) has been applied to all field samples for elemental determinations. Judging from the present results, and since the islands embody most features of the whole archipelago, bryophytes do not appear as an option for further campaigns in the Azores, due to scanty supply and relatively poor performance as biomonitors. On the other hand, comparisons of bark with lichens collected at the same sites seem fairly good, and elements are enriched in bark to an even greater extent than in lichens. All things considered - including material availability and ecological concern - bark stands for a sensible choice for biomonitoring in the Azores.     

Supported stereospecific metallocene binary catalyst for propylene polymerization

In this work, propylene was polymerized with isospecific and syndiospecific catalysts in homogeneous and heterogeneous systems. The binary metallocene system of both isospecific and syndiospecific catalysts in the heterogeneous system was also used. Besides the type of catalyst, parameters such as polymerization temperature and pressure were varied to achieve the better conditions for the polymerization. The objective of this work is to investigate the influence of these parameters on the characteristics of the produced polymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2979–2986, 2002     

Experimental thermochemical study of two polymethylpyrazine N,N′-dioxide derivatives

The standard (p° = 0.1 MPa) molar enthalpies of formation of crystalline 2,3,5-trimethylpyrazine-1,4-dioxide and 2,3,5,6-tetramethylpyrazine-1,4-dioxide were measured, at T = 298.15 K, by static bomb calorimetry and the standard molar enthalpies of sublimation, at T = 298.15 K, were obtained from Calvet microcalorimetric measurements. These values were used to derive the respective standard molar enthalpies of formation in gaseous phase. The mean N–O bond dissociation enthalpy has been calculated for both compounds.     

Adsorption of Cu(II) on porous chitosan membranes functionalized with histidine

The ability of chitosan to form complexes with bivalent metal ions has been broadly explored in the literature. The present work investigates the influence of functionalization of macroporous chitosan membranes with histidine on their ability to remove copper ions from aqueous solution in the range of pH 4–6. The maximum adsorption capacity for Cu(II) ion was 2.5 mmol metal/g pristine chitosan membranes. Under this condition, no influence of membrane porosity was observed. However, for membranes with immobilized histidine, the porosity was shown to be a factor that affects the maximum adsorption capacity, with values ranging from 2.0 to 3.0 mmol metal/g chitosan. These results indicate that the immobilization of histidine on porous chitosan membranes presents synergy with porosity in the ability to complex Cu(II) ions. This synergy may be negative or positive, depending on the initial membrane porosity.     

Preparation of thin arsenic and radioarsenic targets for neutron capture studies

A simple method for the electrodeposition of elemental arsenic (As) on a metal backing from aqueous solutions has been developed. The method was successfully applied to stable As (⁷⁵As). Thin (2.5 mg cm⁻²) coherent, smooth layers of the metalloid on Ti foils (2.5 μm thickness) were obtained. Electrodeposits served as targets for ⁷⁵As(n,γ) ⁷⁶As neutron capture experiments at Los Alamos Neutron Science Center (LANSCE). Respective ⁷³As(n,γ) ⁷⁴As experiments are planned for the near future, and ⁷³As targets will be prepared in a similar fashion utilizing the new electrodeposition method. The preparation of an ⁷³As (half-life 80.3 days) plating bath solution from proton irradiated germanium has been demonstrated. Germanium target irradiation was performed at the Los Alamos Isotope Production Facility (IPF).     

A tool for predicting the integrity of Y zeolite crystalline structure

The purpose of this work was to employ the differential thermal analysis technique (DTA) to compare variations in the collapse energy of the Y zeolite crystalline structure in a fresh sample and in the sample after temperature treatment and impregnated with 3,000 ppm of vanadium and nickel. A small exothermic signal in the DTA curve at 950–1,150 °C indicated the collapse of the crystalline structure. The areas of the exothermic signals in the DTA curves of the samples indicated a 20% reduction in the exothermic area peak of sample treated 600 °C for 3 h and 25% reduction in same peak in the metal impregnated Y zeolite. These results were compared with X-ray data leading to the conclusion that metal impregnation affects the Y zeolite crystalline structure and that the DTA technique is a potentially useful tool for measuring the integrity of Y zeolite in catalysts.     

Kinetic study of crystallization of PHB in presence of hydroxy acids

Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid (TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear fitting to obtain the estimation for activation energy (E _a ) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the average activation energy, 73 ± 9 kJ mol⁻¹ and 63 ± 1 kJ mol⁻¹, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain. PHB/TA show increase in the medium value of E _a, 119 ± 2 kJ mol⁻¹ and T _c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E _a=73 ± 9 kJ mol⁻¹, T _c = 44.8 °C at 5 °C/min).