Configuration space partitioning and matrix buildup scaling for the vibrational configuration interaction method

The accurate computation of anharmonic vibrational states for medium to large molecules is a requirement for the detailed understanding of nonlinear multidimensional infrared spectra and the dynamical information encoded in them. The vibrational configuration interaction (VCI) method constitutes a particularly promising tool in this respect. It is generally hampered though by its unfavorable scaling with respect to system size. We analyze the scaling behavior of several well‐known as well as some new approximate VCI schemes in detail, which are complementary to the class of configuration selection schemes developed recently. We find that the combination of a configuration space partitioning, possibly based on configuration selection, with energetic thresholding and resonance screening provides an efficient scheme for the reduction of computational effort involved in VCI calculations while at the same time maintaining sufficient accuracy for the vibrational energies. © 2012 Wiley Periodicals, Inc.     

The adaptive hierarchical expansion of the kinetic energy operator

The hierarchical expansion of the kinetic energy (HEKE) operator in curvilinear coordinates presented recently (Strobusch and Scheurer, J. Chem. Phys. 2011a, 135, 124102; Strobusch and Scheurer, J. Chem. Phys. 2011b, 135, 144101) relies on a many‐body expansion of the metric tensor. It is shown how this expansion can be adapted to a specific system. An analytic formula is derived, which yields an estimate of the impact of a certain expansion term on the spectrum. In combination with the hierarchical structure of the many‐body expansion and interpolation techniques, the memory consumption and evaluation time of the HEKE operator as well as the computational costs for subsequent vibrational self‐consistent field and vibrational configuration interaction calculations are reduced significantly, which is demonstrated by studies on two small test systems H₂O₂ and formaldehyde (H₂CO). © 2013 Wiley Periodicals, Inc.     

Enantiospecific syntheses of copper cubanes, double-stranded copper/palladium helicates, and a (dilithium)-dinickel coronate from enantiomerically pure bis-1,3-diketones--solid-state self-organization towards wirelike copper/palladium strands

Enantiomerically pure, vicinal diols 1 afforded in a two-step synthesis (etherification and subsequent Claisen condensation) chiral bis-1,3-diketones H(2)L((S,S)) (3 a-c) with different substitution patterns. Reaction of these C(2)-symmetric ligands with various transition-metal acetates in the presence of alkali ions generated distinct polynuclear aggregates 4-8 by diastereoselective self-assembly. Starting from copper(II) acetate monohydrate and depending on the ratio of transition-metal ion to alkali ion to ligand, chiral tetranuclear copper(II) cubanes (C,C,C,C)-[Cu(4)(L((S,S)))(2)(OMe)(4)] (4 a-c) or dinuclear copper(II) helicates (P)-[Cu(2)(L((S,S)))(2)] (5) could be synthesized with square-pyramidal and square-planar coordination geometry at the metal center. In analogy to the last case, with palladium(II) acetate double-stranded helical systems (P)-[Pd(2)(L((S,S)))(2)] (6,7) were accessible exhibiting a linear self-organization of ligand-isolated palladium filaments in the solid state with short inter- and intramolecular metal distances. Finally, the introduction of hexacoordinate nickel(II) in combination with lithium hydroxide monohydrate and chiral ligand H(2)L((S,S)) (3 a) allowed the isolation of enantiomerically pure dinuclear nickel(II) coronate [(LiMeOH)(2) subset{(Delta,Lambda)-Ni(2)(L((S,S)))(2)(OMe)(2)}] (8) with two lithium ions in the voids, defined by the oxygen donors in the ligand backbone. The high diastereoselectivity, induced by the chiral ligands, during the self-assembly process in the systems 4-8 could be exemplarily proven by circular dichroism spectroscopy for the synthesized enantiomers of the chiral copper(II) cubane 4 a and palladium(II) helicate 6.     

Artificial sweeteners—a recently recognized class of emerging environmental contaminants: a review

An overview is given of existing trace analytical methods for the determination of seven popular artificial sweeteners [acesulfame (ACE), aspartame, cyclamate (CYC), neotame, neohesperidine dihydrochalcone, saccharin (SAC), and sucralose (SUC)] from aqueous environmental samples. Liquid chromatography-electrospray ionization tandem mass spectrometry and liquid chromatography-electrospray ionization high-resolution mass spectrometry are the methods most widely applied, either directly or after solid-phase extraction. Limits of detection and limits of quantification down to the low nanogram per liter range can be achieved. ACE, CYC, SAC, and SUC were detected in wastewater treatment plants in high microgram per liter concentrations. Per capita loads of individual sweeteners can vary within a wide range depending on their use in different countries. Whereas CYC and SAC are usually degraded by more than 90% during wastewater treatment, ACE and SUC pass through wastewater treatment plants mainly unchanged. This suggests their use as virtually perfect markers for the study of the impact of wastewater on source waters and drinking waters. In finished water of drinking water treatment plants using surface-water-influenced source water, ACE and SUC were detected in concentrations up to 7 and 2.4 μg/L, respectively. ACE was identified as a precursor of oxidation byproducts during ozonation, resulting in an aldehyde intermediate and acetic acid. Although the concentrations of ACE and SUC are among the highest measured for anthropogenic trace pollutants found in surface water, groundwater, and drinking water, the levels are at least three orders of magnitude lower than organoleptic threshold values. However, ecotoxicology studies are scarce and have focused on SUC. Thus, further research is needed both on identification of transformation products and on the ecotoxicological impact of artificial sweeteners and their transformation products.     

Analysis and occurrence of seven artificial sweeteners in German waste water and surface water and in soil aquifer treatment (SAT)

A method for the simultaneous determination of seven commonly used artificial sweeteners in water is presented. The analytes were extracted by solid phase extraction using Bakerbond SDB 1 cartridges at pH 3 and analyzed by liquid chromatography electrospray ionization tandem mass spectrometry in negative ionization mode. Ionization was enhanced by post-column addition of the alkaline modifier Tris(hydroxymethyl)amino methane. Except for aspartame and neohesperidin dihydrochalcone, recoveries were higher than 75% in potable water with comparable results for surface water. Matrix effects due to reduced extraction yields in undiluted waste water were negligible for aspartame and neotame but considerable for the other compounds. The widespread distribution of acesulfame, saccharin, cyclamate, and sucralose in the aquatic environment could be proven. Concentrations in two influents of German sewage treatment plants (STPs) were up to 190 μg/L for cyclamate, about 40 μg/L for acesulfame and saccharin, and less than 1 μg/L for sucralose. Removal in the STPs was limited for acesulfame and sucralose and >94% for saccharin and cyclamate. The persistence of some artificial sweeteners during soil aquifer treatment was demonstrated and confirmed their environmental relevance. The use of sucralose and acesulfame as tracers for anthropogenic contamination is conceivable. In German surface waters, acesulfame was the predominant artificial sweetener with concentrations exceeding 2 μg/L. Other sweeteners were detected up to several hundred nanograms per liter in the order saccharin ≈ cyclamate > sucralose. Figure Some artificial sweeteners are excreted unchanged and in particular acesulfame is a perfect tracer for municipal waste water Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.