Parallelization of a multiconfigurational perturbation theory

In this work, we present a parallel approach to complete and restricted active space second‐order perturbation theory, (CASPT2/RASPT2). We also make an assessment of the performance characteristics of its particular implementation in the Molcas quantum chemistry programming package. Parallel scaling is limited by memory and I/O bandwidth instead of available cores. Significant time savings for calculations on large and complex systems can be achieved by increasing the number of processes on a single machine, as long as memory bandwidth allows, or by using multiple nodes with a fast, low‐latency interconnect. We found that parallel efficiency drops below 50% when using 8–16 cores on the shared‐memory architecture, or 16–32 nodes on the distributed‐memory architecture, depending on the calculation. This limits the scalability of the implementation to a moderate amount of processes. Nonetheless, calculations that took more than 3 days on a serial machine could be performed in less than 5 h on an InfiniBand cluster, where the individual nodes were not even capable of running the calculation because of memory and I/O requirements. This ensures the continuing study of larger molecular systems by means of CASPT2/RASPT2 through the use of the aggregated computational resources offered by distributed computing systems. © 2013 Wiley Periodicals, Inc.     

Ethyl Pyrogall[6]arene and Pyrogall[4]arene: Synthesis,Structural Analysis and Derivatization

In the acid-catalyzed synthesis of ethyl pyrogallarene, a novel hexamer, ethyl pyrogall arene, is obtained as a readily isolable minor product. Pyrogallarene can be isolated from the reaction mixture in three different ways yielding the hexamer in different forms and stabilities. Crystallization from DMSO and then recrystallization from acetone gives a stable crystalline solid, recrystallization directly from acetone yields an unstable white powder, while direct recrystallization from THF gives a stable white powder. Both pyrogallarene and pyrogallarene crystallize readily with DMSO filling the voids in the crystal lattice. Co-crystallization studies of the hexamer isolated by recrystallization from acetone resulted in a novel directly hydrogen-bonded capsule formed by two pyrogallarenes and an included TMA cation, while the DMSO/acetone isolated product yielded the intact hexamer with clathrate-type TMA inclusion.     

Modification of crystallinity and pore size distribution in coagulated cellulose films

In this study the effects of altering the coagulation medium during regeneration of cellulose dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate, were investigated using solid-state NMR spectroscopy and NMR cryoporometry. In addition, the influence of drying procedure on the structure of regenerated cellulose was studied. Complete conversion of the starting material into regenerated cellulose was seen regardless of the choice of coagulation medium. Coagulation in water predominantly formed cellulose II, whereas coagulation in alcohols mainly generated non-crystalline structures. Subsequent drying of the regenerated cellulose films, induced hornification effects in the form of irreversible aggregation. This was indicated by solid-state NMR as an increase in signal intensity originating from crystalline structures accompanied by a decrease of signal intensity originating from cellulose surfaces. This phenomenon was observed for all used coagulants in this study, but to various degrees with regard to the polarity of the coagulant. From NMR cryoporometry, it was concluded that drying induced hornification generates an increase of nano-sized pores. A bimodal pore size distribution with pore radius maxima of a few nanometers was observed, and this pattern increased as a function of drying. Additionally, cyclic drying and rewetting generated a narrow monomodal pore size pattern. This study implies that the porosity and crystallinity of regenerated cellulose can be manipulated by the choice of drying condition.     

Two-Photon Solvatochromism II: Experimental and Theoretical Study of Solvent Effects on the Two-Photon Absorption Spectrum of Reichardt’s Dye

In this study, we report on the influence of solvent on the two-photon absorption (2PA) spectra of Reichardt’s dye (RD). The measurement of 2PA cross-sections is performed for three solvents (chloroform, dimethyl formamide, and dimethyl sulfoxide) using the Z-scan technique. The key finding of this study is the observation that the cross-section, corresponding to the 2PA of the intramolecular charge-transfer state, diminishes substantially upon increasing the solvent polarity. To unravel the solvent dependence of the 2PA cross-section, the electronic structure of RD is determined using a hybrid quantum mechanics/molecular mechanics (QM/MM) approach, in which polarization between the solute and solvent is taken into account by using a self-consistent scheme in the solvent polarization. The two-state approximation proves to be adequate for the studied system, and allowed the observed solvent-polarity-induced decrease of the 2PA cross-section to be related to the decrease of the transition moment and the increase in the excitation energy.     

A concept study on non-targeted screening for chemical contaminants in food using liquid chromatography–mass spectrometry in combination with a metabolomics approach

A generic method to screen for new or unexpected contaminants at ppm levels in food has been developed. The method comprises an acidic acetonitrile extraction, detection with ultra-high-pressure liquid chromatography coupled to electrospray ionisation time-of-flight mass spectrometry and statistical evaluation using a metabolomics approach comparing suspected contaminated food with uncontaminated foods. The method was tested for 26 model contaminants from 100 μg/g down to 0.4 μg/g in three brands of fresh orange juice. Blinded statistical evaluation revealed signals from all added contaminants detectable by liquid chromatography–electrospray ionisation using positive ionisation mode, while only two false-positive signals were reported. The method is primarily intended to be used for investigation of food samples suspected to be contaminated with unknown substances. Additionally it could be used to continuously monitor for appearance of new food contaminants as a complement to the specific targeted analysis that is today’s foundation of food safety analysis.     

Strategy for quantifying trace levels of BMAA in cyanobacteria by LC/MS/MS

The cyanobacterial neurotoxin β-N-methylamino-l-alanine (BMAA) is an amino acid that is putatively associated with the pathology of amyotrophic lateral sclerosis/Parkinsonism–dementia complex (ALS-PDC) disease. It raises serious health risk concerns since cyanobacteria are ubiquitous thus making human exposure almost inevitable. The identification and quantification of BMAA in cyanobacteria is challenging because it is present only in trace amounts and occurs alongside structurally similar compounds such as BMAA isomers. This work describes an enhanced liquid chromatography/tandem mass spectrometry platform that can distinguish BMAA from its isomers β-amino-N-methyl-alanine, N-(2-aminoethyl) glycine (AEG), and 2,4-diaminobutyric acid, thus ensuring confident identification of BMAA. The method's sensitivity was improved fourfold by a post-column addition of acetonitrile. The instrument and method limits of detection were shown to be 4.2 fmol/injection (or 0.5 pg/one column) and 0.1 μg/g dry weight of cyanobacteria, respectively. The quantification method uses synthesized deuterated BMAA as an internal standard and exhibits good linearity, accuracy, and precision. Matrix effects were also investigated, revealing an ion enhancement of around 18 %. A lab-cultured cyanobacterial sample (Leptolyngbya PCC73110) was analyzed and shown to contain about 0.73 μg/g dry weight BMAA. The isomer AEG, whose chromatographic properties closely resemble those of BMAA, was also detected. These results highlight the importance of distinguishing BMAA from its isomers for reliable identification as well as providing a sensitive and accurate quantification method for measuring trace levels of BMAA in cyanobacterial samples.     

Acid/Base Switching of the Tautomerism and Conformation of a Dioxoporphyrin for Integrated Binary Subtraction

Compared with most of the reported logic devices based on the supramolecular approach, systems based on individual molecules can avoid challenging construction requirements. Herein, a novel dioxoporphyrin DPH₂₂ was synthesized and two of its tautomers were characterized by single‐crystal X‐ray diffraction studies. Compound DPH₂₂ exhibits multichannel controllable stepwise tautomerization, protonation, and deprotonation processes through interactions with H⁺ and F^? ions. By using the addition of H⁺ and F^? ions as inputs and UV/Vis absorption values at λ=412, 510, 562, and 603 nm as outputs, the controlled tautomerism of DPH₂₂ has been successfully used for the construction of an integrated molecular level half‐subtractor and comparator. In addition, this acid/base‐switched tautomerism is reversible, thus endowing the system with ease of reset and recycling; consequently, there is no need to modulate complicated intermolecular interactions and electron‐/charge‐transfer processes.     

Iron(III)‐Quantity‐Dependent Aggregation–Dispersion Conversion of Functionalized Gold Nanoparticles

Developing gold nanoparticles (AuNPs) with well‐designed functionality is highly desirable for boosting the performance and versatility of inorganic–organic hybrid materials. In an attempt to achieve ion recognition with specific signal expressions, we present here 4‐piperazinyl‐1,8‐naphthalimide‐functionalized AuNPs for the realization of quantitative recognition of Fe^III ions with dual (colorimetric and fluorescent) output. The research takes advantage of 1) quantity‐controlled chelation‐mode transformation of the piperazinyl moiety on the AuNPs towards Fe^III, thereby resulting in an aggregation–dispersion conversion of the AuNPs in solution, and 2) photoinduced electron transfer of a naphthaimide fluorophore on the AuNPs, thus leading to reversible absorption and emission changes. The functional AuNPs are also responsive to pH variations. This strategy for realizing the aggregation–dispersion conversion of AuNPs with returnable signal output might exhibit application potential for advanced nanoscale chemosensors.     

On χ2-test of goodness-of-fit for a class of discrete multivariate models

A model for an n-dimensional random vector which is the sum of v i.i.d. random variables with an exponential family distribution is considered. It is shown that the exact test can be approximated by a χ²-test as v → ∞. As an example a goodness-of-fit test for Poisson-distribution based on observed frequencies is derived.