Heterometallic Uranyl (Hydroxyethyl)iminodiacetic Acid (Heidi) Complexes: Molecular Models for U(VI) Uptake in Complex Media

Amidoximated absorbents (AO-PAN) effectively remove U(VI) from aqueous solution, but previous studies reported more variability for complex natural waters that contain additional confounding ions and molecules. Ternary phases containing U(VI), M(III) (M=Fe(III), Al(III), Ga(III)), and organic molecules exist under these conditions and cause heterogeneous U(VI) uptake on AO-PAN. The goal of the current study is to provide additional insights into the structural features ternary complexes using N-(2-hydroxyethyl)-iminodiacetic acid (HEIDI) as the model organic chelator and explore the relevance of these species on U(VI) capture. Three model compounds ([(UO₂)(Fe)₂(μ₃-O)(C₆NO₅H₈)₂(H₂O)₄] ( UFe₂ ), ([(UO₂)(Al)₂(μ₂-OH)(C₆NO₅H₈)₂(H₂O)₃] ( UAl₂ ) and [(UO₂)(Ga)₂(μ₂-OH)(C₆NO₅H₈)₂(H₂O)₃] ( UGa₂ )) were characterized by single-crystal X-ray diffraction. Raman spectra of the model compounds were compared with solution data and the ternary phases were noted in the case of Al(III) and Ga(III), but not in the Fe(III) system. U(VI) adsorption onto AO-PAN was not impacted by the presence of HEIDI or the trivalent metal species.     

Controlling Topology within Halogen-Bonded Networks by Varying the Regiochemistry of the Cyclobutane-Based Nodes

The formation of a pair of extended networks sustained by halogen bonds based upon two regioisomers of a photoproduct, namely rctt-1,3-bis(4-pyridyl)-2,4-bis(phenyl)cyclobutane (ht-PP) and rctt-1,2-bis(4-pyridyl)-3,4-bis(phenyl)cyclobutane (hh-PP), that have varied topology is reported. These networks are held together via I⋯N halogen bonds between the photoproduct and the halogen-bond donor 1,4-diiodoperchlorobenzene (C₆I₂Cl₄). The observed topology in each solid is controlled by the regiochemical position of the halogen-bond accepting 4-pyridyl group. This paper demonstrates the ability to vary the topology of molecular networks by altering the position of the halogen bond acceptor within the cyclobutane-based node.     

Isotope Effects during Metabolism of (+)- and (−)- Trans Tramadol Isotopomers by Human Liver Microsomes

Abstract

As for the unlabelled (±)-1(e)-(m-methoxyphenyl)-2(e)-(dimethylaminomethyl)cyclohexane 1(a)-ol, tramadol, (T), pronounced stereochemical effects were observed for the isotopomers with regard to the extent of formation of O- and N-demethylated metabolites. The pharmacological active O-demethylated metabolite M1 was formed from the unlabelled as well as from the labelled (+)-tramadols about 6 times less than from the corresponding (?)-T. In contrast, the N-demethylated metabolite M2 was formed from the (+)-tramadols about 1.5 times more than from the corresponding (?)-T. These steric effects were modulated by the smaller apparent isotope effects for the isotopomers. Isotope effects were expressed as k_H/k_D (calculated from concentrations) and as ^DV, ^DV/K and ^HK_m/^DK_m (from Eadie-Hofstee plots).     

An introduction to the multi-grid method for numerical relativists

The multi-grid method, which has made a considerable impact on both theoretical and applied numerical analysis in the past decade, is reviewed within the context of the solution of boundary value problems in 3 + 1 numerical relativity. The basic principles of operation of a multi-grid algorithm are discussed and, with the aid of numerical experiments on exactly soluble model problems, the method is compared to more traditional techniques such as SOR. The results of application of the method to a set of axisymmetric problems for black hole initial data, previously determined by relaxation techniques, are presented.     

The stereochemistry of the thermal cheletropic decarbonylation of 3-cyclopentenone as determined by multiphoton infrared photolysis/thermolysis

There are two allowed pathways for the thermal cheletropic decarbonylation of 3-cyclopentenone. The stereochemistry of decarbonylation of an unconstrained derivative (trans,trans-2,5-dimethyl-3-cyclopentenone, 4) has been determined for the first time. Under conventional pyrolysis conditions, thermal rearrangements of the initial product (trans,trans-2,4-hexadiene, 5) occur at the high temperatures required for the decarbonylation. However, by using multiphoton infrared photolysis/thermolysis to initiate decarbonylation, it was shown that the initial products from thermal decarbonylation of 4 are solely carbon monoxide and stereospecifically 5. The stereochemistry of decarbonylation is thus disrotatory, in accord with prior theoretical studies. A survey of crystal structures reveals ground-state distortions along this reaction coordinate as well.     

Theory of lithium ordering in LixTiS2

Real space renormalization group and Monte Carlo techniques are used to study the statistical mechanics of a lattice gas model of Li ordering in an intercalation battery. The dependence of the voltage on the state of charge of the battery is related to the number and types of sites available to the Li ions and to the strength and distance dependence of the Li-Li interaction. Several models are discussed and compared with the observed behaviour of Li_xTiS₂.     

The measurement of quantum noise reduction in squeezed states

The use of a photomultiplier to measure the reduction in counting statistics noise (from the usual N^1/2 form) which is expected to occur for squeezed coherent light is shown to lead to no reduction or to an increase of the noise unless the number of photons in a fundamental measuring time of the photomultiplier is very large. This fundamental time is estimated to be less than 10^–13 sec for ordinary detectors. A technique for using squeezed states for determining the time a photomultiplier takes to detect the presence of a photon is presented.