Introduction of Marinelli effective solid angles for correcting the calibration of NaI(Tl) field gamma-ray spectrometry in TL/OSL dating

A study is made of the corrections that are needed in the evaluation of the annual radiation dose, for use in TL/OSL-dating, via NaI(Tl) field gamma-ray spectrometry (monitoring of K, Th and U), calibrated via voluminous blocks that are simulating the Auger hole measuring conditions. Two cases are considered: the Heidelberg granite calibration block, which was found to be quasi-infinite, and the Oxford concrete calibration blocks, for which effective concentrations of elements are reported so as to account for their non-infiniteness. The calculations, via the software package ANGLE, are based on the concept of effective solid angles for Marinelli geometries.     

Synthesis and properties of a new family of cyclodextrin analogues

The chemical synthesis of a series of cyclic oligosaccharides built up from (14)-linked alternatingD– andl-pyranosidic units is described for the first time. Key intermediates employed were disaccharides representing minimal repeating units. These disaccharides (monomers) have been prepared in specifically modified forms so that they bear both glycosyl donor (cyanoethylidene group) and glycosyl acceptor (trityloxy group) functions. Polycondensation-cyclisation of these disaccharide monomers, catalysed by TrC1O₄ under normal conditions of dilution, has led to series of homologous cyclic oligosaccharides with an even number of sugar residues (6, 8, 10, 12,etc.) in each case. Cyclic hexa- and octa-saccharides, based onl-rhamnose andD-mannose as the alternating monosaccharides units, have been deprotected to produce analogues of - and -cyclodextrins (CDs) and the X-ray crystal structure of the cyclic octasaccharide has been determined.     

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXXVI Structural Studies in the Copper(I) Halide : Norbornadiene System

The structural characterizations of some copper(I) halide (CuX) adducts with norbornadiene (nbd) are recorded. CuCl : nbd (1:1)₄ (a redetermination), (2:1)_2(|), are systems both based around Cu₄Cl₄ cubane-type cluster arrays. CuBr : nbd (7:3)_(|)( 0.5 MeOH), a complex polymer with 3-symmetry, is believed to be the complex previously described as an adduct of 2:1 stoichiometry. Attempts to obtain an iodide counterpart have resulted in the definition of an ephemeral adduct CuI : MeCN (3:2)_(|). 0.5 C₇H₈ in which, remarkably, the nbd is uncoordinated; the complex is a polymer, related to the [AgX(quinoline)]_(|) (X = Cl, Br) saddle polymer.     

Effect of hydrothermal treatment on the gelatinisation properties of potato starch as measured by differential scanning calorimetry

Gelatinisation temperatures as a function of moisture content were determined for potato starch. The native starch was then hydrothermally treated at a temperature 3% (Kelvin degrees) below the gelatinisation peak temperature and at moisture levels varying from 20 to 67% (by weight). Gelatinisation temperatures, temperature ranges and enthalpy values were affected for all treated samples. However, two sample populations could be distinguished: those samples treated under limited moisture conditions and other samples treated in the presence of extragranular moisture. A two-step hydrothermal treatment further increased the gelatinisation temperature, but the effect of the second step was small in comparison to that of the first.We thank the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek for research positions as aspirant (H. Jacobs) and post-doctoraal onderzoeker (R. C. Eerlingen).     

Topics in calixarene chemistry

Several facets of calixarene chemistry have been investigated including the mechanism of their formation by the base-induced condensation of phenols and formaldehyde, procedures for introducing functional groups onto the upper rim and lower rim of calixarenes, the conformational behavior of calixarene oxyanions, the formation of complexes in aqueous and nonaqueous systems, and the application of calixarenes as catalysts.     

Symmetry and other properties of second-order phenomenological coefficients and thier significance in a chemical system

Using a second-order phenomenological equationJ _i = _j L _ij X_j + _{j, k} L _ijk X_j X_kand assuming that the system is at a state near equilibrium, it has been shown that the symmetry ofL _ijk is retained with respect to the permutations of suffices i j and k Furthermore, using the second-order flux equations, the thermodynamic stability criterion is expressed. The symmetry is shown to be retained in a reaction scheme representing the emplate model. The significance of the stability criterion as expressed by the higher-order phenomenological coefficients is discussed.     

Thermal behaviour of perovskite ceramics as a matrix for encapsulation of hazardous elements

Summary Emanation thermal analysis (ETA) was used to characterize thermal behaviour of the perovskite ceramics designed as a matrix for the encapsulation of high level radioactive waste. The perovskite ceramics (composition CaTiO₃ where small admixtures of Nd and Ce simulated the radioactive elements Cm and Pu, respectively) was prepared from sol-gel precursors by hot pressing at 1250°C/29 MPa for 2 h. The chemical durability of the ceramics was tested by leaching in the solution with pH 2 at 90°C/2 months. ETA results of as-leached and as-prepared perovskite ceramics samples were compared and evaluated by means of a mathematical model. Three temperature ranges of the annealing of structure defects in the as-prepared sample were determined from the decrease of radon release rate in the ranges 280-560, 800-960 and 960-1200°C, respectively. One annealing step was determined for the as-leached sample from the decrease of radon release rate in the range of 800-950°C.     

Preparation and characterization of Mg(II)-, Ca(II) and Cd(II) complexes of 1,2-ethanediol and water

Mixed ligand complexes of different compositions were prepared with water, sulfate ion and 1,2-ethanediol as ligand. IR spectra and the thermoanalytical curves of the complexes were recorded. Oxygen atoms bound by one or two coordinate bonds to the metal ion, or by hydrogen-bonds in the crystal, were observed. As for the water molecule, 1,2-ethanediol molecules of crystal and monohydrate type were found, depending on the type of binding of the oxygen atoms.This revised version was published online in November 2005 with corrections to the Cover Date.     

On the selection of the optimal plasticizer for calix[n]arene-based ion-selective electrodes: Possible correlation between the ion selectivity and the ‘softness’ of the plasticizer

A criterion for the selection of a suitable plasticizer for calix[n]arene-based ion-selective electrodes is discussed. The cation selectivity of plasticized membranes without the ligand was first measured as a reference. The membranes can be roughly classified into two groups. The first group shows cation selectivity in the order Cs⁺+>K⁺>Na⁺>Li⁺. The membranes in the second group are made of phosphorus plasticizers, which show a selectivity in the reverse order. The plasticizers in the first group featured a linear relationship between the dipole moment of the plasticizer (calculated by a PM3 method) and the ratio of cesium selectivity to lithium selectivity. The linear relationship supports the view that the polar membrane which includes a soft plasticizer with a large dipole moment shows selectivity for Cs⁺, whereas the nonpolar membrane including the soft plasticizer with the small dipole moment shows much lower selectivity for Cs⁺. Next, 2-fluorphenyl-2-nitrophenyl ether (FPNPE) which showed the highest Cs⁺ selectivity and tris(2-ethylhexyl)phosphate (TEHP) which showed the highest Li⁺ selectivity were mixed in an appropriate ratio to make membranes with a different affinity for hard ions. The metal selectivities of several crown-based and calixarene-based ionophores were examined in these membranes. Although a few exceptions exist, the polar soft membrane is favorable when the interfering metal ion is hard, whereas the hard membrane is favorable when the interfering metal ion is soft.     

Periodic precipitation of mercury sulphide

Summary In the gelatin medium Revert types of rings of mercuric sulphide are obtained. A system containing both Revert types of rings and Direct types of rings in the same test tube is obtained in the agar agar and starch gels.

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Zusammenfassung In Gelatine als Medium erhält man Ringe von Quecksilbersulfid vom Revert-Typus. Ein System, das beiderlei Ringe, Revert-Typus und Direkt-Typus im gleichen Proberohr aufweist, wird in Agar-Agar- und Stärke-Gelen erhalten.

     

Automated molecular design: A new fragment-joining algorithm

Summary A popular first step in the problem of structure-based, de novo molecule design is to identify regions where specific functional groups or chemical entities would be expected to interact strongly. When the three-dimensional structure of the receptor is not available, it may be possible to derive a pharmacophore giving the three-dimensional relationships between such chemical groups. The task then is to design synthetically feasible molecules which not only contain the required groups, but which can also position them in the desired relative orientation. One way to do this is to first link the groups using an acyclic chain. We have investigated the application of the tweak algorithm [Shenkin, P.S. et al., Biopolymers, 26 (1987) 2053] for generating families of acyclic linkers. These linking structures can subsequently be braced using a ring-joining algorithm [Leach, A.R. and Lewis, R.A., J. Comput. Chem., 15 (1994) 233], giving rise to an even wider variety of molecular skeletons for further studies.     

A microcalorimetric study of the different states of argon and nitrogen adsorbed AT 77 K on silicalite-I and ZSM-5

The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16相似文献   

Distance geometry analysis of ligand binding to drug receptor sites

Summary The method known as distance geometry approach for receptor mapping procedures is discussed. In this method a ligand binding to a certain receptor is considered as a collection of ligand points. Binding sites of the receptor are either empty or filled site points; a ligand point might bind to an empty site point; filled site points indicate that at that point no binding is possible. A binding mode of a ligand is a list of which ligand points coincide with which empty binding sites. The applicability of the method for QSAR studies is discussed; as examples are mentioned the dihydrofolate reductase, ₁- and ₂-receptors. Finally, some ideas on future developments in receptor mapping are discussed.DEDICATION This article is dedicated to the late Dr. Teake Bultsma who introduced the distance geometry approach into our department.     

Plutonium-244 and strange xenon components in the solar system

A number of strange xenon components have been reported in the literature during the past three decades; for example, AVCC (average carbonaceous chondrite), CCF (carbonaceous chondrite fission) xenon, xenon-X, xenon-H, xenon-L, xenon-S, xenon-U, SUCOR (surface correlated xenon), BEOC (Bern Oberflächen-Correliert) xenon, and so on. It is often assumed that they reprsent the isotopic compositions of more or less pure or primordial components of xenon. If one attempts to interpret the existing xenon isotope data for meteorites and lunar samples, assuming that they are pure or primordial, however, one encounters all sorts of problems and no coherent theory concerning the variation of the isotopic composition of xenon in the solar system emerges. We have therefore re-examined over 4,000 sets of existing xenon isotope data for meteorites and lunar samples. The results indicate that these strange xenon components are mixtures of²⁴⁴Pu fission xenon and atmospheric xenon, whose isotopic compositions have been altered by the processes of a) mass-fractionation, b) spallation and c) neutron-capture reactions.     

Conformation of receptor-associated PGI2: An investigation by molecular modeling

Summary To elucidate the conformation of receptor-associated prostacyclin (PGI₂), we first performed structure-activity correlation analysis of over 200 PGI₂ analogues and derived from this analysis several crucial features pertaining to structural requirements for PGI₂ activity [Ah-lim Tsai and Kenneth K. Wu, Eicosanoids, 2 (1989) 131–143]. These structural features proved to be useful guidelines for selecting model molecules for further investigations by molecular mechanics. By properly selecting four analogues with either rigid or uniquely oriented -side chain structure for geometric fitting, we succeeded in maximally minimizing the degree of freedom of the carboxylate terminus of PGI₂. We were able to define the spatial relationship among the four critical functional groups, i.e., C1-COOH, C6a-O, C11-OH and C15-OH. More information is needed, however, to define the geometry of the -side chain, particularly for the moiety beyond C15. Nevertheless, results from structure-activity correlation analysis and molecular modeling provide useful information regarding the conformation of receptor-associated PGI₂, which assumes an elongated conformation instead of the traditional hairpin structure.     

The application of modulated differential scanning calorimetry to the glass transition

The modulated differential scanning calorimetry (MDSC) technique superimposes upon the conventional DSC heating rate a sinusoidally varying modulation. The result of this modulation of the heating rate is a periodically varying heat flow, which can be analysed in various ways. In particular, MDSC yields two components (reversing and non reversing) of the heat flow, and a phase angle. These each show a characteristic behaviour in the glass transition region, but their interpretation has hitherto been unclear. The present work clarifies this situation by a theoretical analysis of the technique of MDSC, which introduces a kinetic response of the glass in the transition region. This analysis is able to describe all the usual features observed by MDSC in the glass transition region. In addition, the model is also able to predict the effects of the modulation variables, and some of these are discussed briefly.Financial support has been provided by the DGICYT (Project no.PB93/1241). J.M.H. wishes to acknowledge financial assistance for a sabbatical period from the Generalitat de Catalunya.     

Metrologically based procedures for the temperature, heat and heat flow rate calibration of DSC

Metrologically based measuring procedures and evaluation methods are recommended as guidance for practical temperature, heat and heat flow rate calibration of DSC instruments which are largely independent of instrumental, test and sample parameters. The relevant terms are defined, the measuring procedures and evaluation methods described, calibration materials and their characteristic data stated and guidance for the sample handling provided. Reference is made to three extended papers on calibration. The recommendations were developed by the working group Calibration of Scanning Calorimeters of the German Society of Thermal Analysis (GEFTA).Recommendation of the working group Calibration of scanning calorimeters of the Gesellschaft für Thermische Analyse e.V. (GEFTA)     

The importance of the geometrical factor in nuclear activation analysis

When a beam of radiation is used as a probe in order to study the elemental composition of an object, the factors involved in obtaining maximum detection sensitivity include target homogeneity, beam uniformity and the solid angle subtended between target and detector. Here we have investigated, both theoretically and experimentally, the significance of these factors in an experimental facility for in-vitro prompt gamma-ray neutron activation analysis and an arrangement used in in-vivo activation analysis. The correction factor to the solid angle, to account for non-uniformity, and the optimisation of reaction rate and solid angle are considered.     

Synthesis of a Calix[4]arene Containing 'Hard' and 'Soft' Metal Ion Binding Sites

Co-receptor 1,3-calix[4]-di(aza-benzo)crown-crown-6 (1-H) designed with one calix[4]arene in a 1,3-alternate conformation and hard and soft metal ion binding sites has been prepared according to three pathways (A-C). Pathway B, consisting of two different 1 + 1 condensations with ditosylate derivatives, was shown to be the most efficient.     

Determination of Particle Size and Shape during the Hydrolysis of Pb(Zr0.3Ti0.7)O3 Precursor Solutions

The formation and growth of polymeric particles during the hydrolysis and condensation of PbZr_0.3Ti_0.7 O₃ (PZT 30/70) sol-gel precursor solutions have been investigated by using photon correlation spectroscopy (PCS), small angle X-ray scattering (SAXS) and by measuring their rheological properties. The measurements showed that the growth of the particles in the transition of PZT sol to gel followed a simple polymerisation process. Solution A (containing by-products) and Solution B (by-products removed) displayed a similar plot of logarithmic viscosity against logarithmic time, indicating that the particles in both solutions have similar structures after hydrolysis. The changes in viscosity and particle size with time were described by single logarithmic growth models. However, the increasing rate of logarithmic particle size in Solution B is higher than that in Solution A. A model for the form of the aggregates is discussed which is applicable to PZT organometal-particle aggregation process in systems with acetic acid as a modifier.