Density functional theory for strongly-interacting electrons: perspectives for physics and chemistry

Improving the accuracy and thus broadening the applicability of electronic density functional theory (DFT) is crucial to many research areas, from material science, to theoretical chemistry, biophysics and biochemistry. In the last three years, the mathematical structure of the strong-interaction limit of density functional theory has been uncovered, and exact information on this limit has started to become available. The aim of this paper is to give a perspective on how this new piece of exact information can be used to treat situations that are problematic for standard Kohn-Sham DFT. One way to use the strong-interaction limit, more relevant for solid-state physical devices, is to define a new framework to do practical, non-conventional, DFT calculations in which a strong-interacting reference system is used instead of the traditional non-interacting one of Kohn and Sham. Another way to proceed, more related to chemical applications, is to include the exact treatment of the strong-interaction limit into approximate exchange-correlation energy density functionals in order to describe difficult situations such as the breaking of the chemical bond.     

Binding of H+ and Zn(II) ions with a new fluorescent macrocyclic phenanthrolinophane

The new macrocyclic ligand 1,9(4,7)-diphenanthroline-3,7,11,15-tetraazacyclohexadecaphane (L) was synthesized by a 2?:?2 reaction of 1,10-phenanthroline-4,7-dialdehyde with 1,3-diaminopropane, followed by reduction with NaBH(4). L contains two phenanthroline groups linked together by two 1,3-diaminopropane chains in such a way that the heteroaromatic nitrogen atoms point outside the ligand cavity. The ligand structure defines two pairs of identical compartments displaying a specific ability in the binding of protons (1,3-diaminopropane) and metal ions (phenanthroline). Protonation and Zn(II) coordination were studied by means of potentiometric and spectroscopic ((1)H NMR, UV-vis, fluorescence) techniques. Both protonation and Zn(II) coordination consistently affect the fluorescence emission properties of L, giving rise to enhancement or quenching of the emission, depending on the species involved. L becomes emissive upon protonation, but the formation of the highly protonated species, in particular the fully protonated [H(6)L](6+), quenches the emission. The mono- and dinuclear Zn(II) complexes of the unprotonated ligand are non-emissive, like free L, while Zn(II) binding to [HL](+) activates the emission. The most interesting aspect, however, is the chelation enhancement of quenching (CHEQ) observed upon Zn(II) binding to [H(2)L](2+) and [H(4)L](4+), being among the few examples of CHEQ effect observed for Zn(II) complexes. Hydrogen bonding between a metal coordinated water molecule and a phenanthroline group seems to be responsible for the CHEQ observed for [ZnH(2)L](4+).     

Essential oil composition of leaves of Stachys yemenensis obtained by supercritical CO₂

This article reports the composition of the essential oil from the leaves of Stachys yemenensis. The essential oil was extracted by supercritical CO? (90 bar; 40 °C) and its chemical composition was determined by gas chromatography and gas chromatography-mass spectrometry. The major components of the sample were α-phellandrene (13.9%), β-phellandrene (11.7%), elemol (12.0%), spathulenol (6.7%), β-eudesmol (5.0%), α-eudesmol (4.75%) and squalene (4.8%). On the exhausted matrix, deprived of the volatiles, we carried out a high-pressure (250 bar) treatment for the extraction of squalene (49.7%). The antimicrobial activity of the essential oils has been assayed by using the broth dilution method on two American Type Culture Collection (ATCC) strains, Escherichia coli ATCC 35218 and Staphylococcus aureus ATCC 43300, and two clinical strains, Candida albicans and Candida glabrata.     

Iodine determination in food by inductively coupled plasma mass spectrometry after digestion by microwave-induced combustion

Iodine determination in food samples was performed by inductively coupled plasma mass spectrometry (ICP-MS) after digestion by microwave-induced combustion (MIC). Sample masses up to 500 mg of bovine liver, corn starch, milk powder, or wheat flour were completely combusted using the MIC system. Ammonium nitrate (6 mol l⁻¹ solution, 50 μl) was used as an aid for ignition and vessels were charged with 15 bar of O₂. The use of H₂O, 0.9 mmol l⁻¹ H₂O₂, 10 to 50 mmol l⁻¹ (NH₄)₂CO₃ and 56 mmol l⁻¹ tetramethylammonium hydroxide was investigated as absorbing solutions, as well as the suitability of performing a reflux step after the combustion process. Digestion of food samples by pressurized microwave-assisted acid digestion, microwave-assisted extraction and conventional extraction of iodine in alkaline solution were also evaluated. Iodine recoveries higher than 99% were obtained using MIC and 50 mmol l⁻¹ (NH₄)₂CO₃ or 56 mmol l⁻¹ tetramethylammonium hydroxide as absorbing solution and with 5 min for the reflux step. Accuracy was evaluated using certified reference materials (bovine muscle, corn bran, and milk powder) and agreement better than 97% was obtained. The limit of quantification by MIC and further ICP-MS determination was 0.002 μg g⁻¹. Blanks were always low and no memory effects were observed. Digestion by MIC allowed the processing of up to eight samples by each run in 25 min with high efficiency of digestion (residual carbon content lower than 1%) providing a suitable medium for further iodine determination by ICP-MS.     

Multidimensional liquid chromatography for the determination of chiral coumarins and furocoumarins in Citrus essential oils

In this work the enantiomeric distribution of chiral coumarins (meranzin and epoxyaurapten), and furocoumarins (oxypeucedanin, byakangelicol, and epoxybergamottin) in different Citrus essential oils (lemon, lime, grapefruit, and bitter orange) was determined by means of a heart-cutting multidimensional-liquid chromatography (MD-LC) system, equipped with a microsilica column in the first dimension in a combination to a cellulosic-based chiral column used in the second dimension. The normal phase-liquid chromatography-liquid chromatography (NP-LC-LC) instrumentation was equipped with a photodiode array detector and a multiport valve as interface. For method optimization and the determination of absolute configuration, natural compounds were isolated and racemic mixture was synthesized. The NP-LC-LC/PDA (where PDA is photodiode array) method provided a good baseline separation of chiral coumarins (meranzin and epoxyaurapten) and furocoumarins (epoxybergamottin and byakangelicol) present in cold-pressed Citrus essential oils without any sample pretreatment. Results obtained showed that for all the chiral compounds present in Citrus essential oils analyzed, there is always a clear prevalence of one of the two enantiomers, and do not appear influenced by the different geographical origin of the oils.     

Fast and reversible CO2 quartz crystal microbalance response of vinylimidazolium‐based poly(ionic liquid)s

A series of poly(ionic liquid)s (pILs) based on the 1‐vinyl‐3‐hexylimidazolium polymerizable cation and on the bis(trifluoromethylsulfonyl)imide, nonafluoro‐1‐butanesulfonate, dodecylbenzenesulfonate, heptadecafluorooctanesulfonate, and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11‐heptadecafluoroundecanoate anions have been synthesized and characterized. Their sorption/desorption response towards CO₂ has been tested through quartz crystal microbalance investigations. The obtained results show that all of the pILs here reported are featured by peculiar CO₂ sorption properties as they display fast and linear response, reversibility without any memory effect, and reproducibility, suggesting that anion plays a key role in determining sensitivity. Copyright © 2011 John Wiley & Sons, Ltd.     

The interrelation between acoustic context effects and available response categories in speech sound categorization

In an investigation of contextual influences on sound categorization, 64 Peruvian Spanish listeners categorized vowels on an /i/ to /e/ continuum. First, to measure the influence of the stimulus range (broad acoustic context) and the preceding stimuli (local acoustic context), listeners were presented with different subsets of the Spanish /i/-/e/ continuum in separate blocks. Second, the influence of the number of response categories was measured by presenting half of the participants with /i/ and /e/ as responses, and the other half with /i/, /e/, /a/, /o/, and /u/. The results showed that the perceptual category boundary between /i/ and /e/ shifted depending on the stimulus range and that the formant values of locally preceding items had a contrastive influence. Categorization was less susceptible to broad and local acoustic context effects, however, when listeners were presented with five rather than two response options. Vowel categorization depends not only on the acoustic properties of the target stimulus, but also on its broad and local acoustic context. The influence of such context is in turn affected by the number of internal referents that are available to the listener in a task.     

Analysis of breath by proton transfer reaction time of flight mass spectrometry in rats with steatohepatitis induced by high-fat diet

Breath testing has been largely used as a diagnostic tool, but the difficulties in data interpretation and sample collection have limited its application. We developed a fast (< 20?s), on-line, non-invasive method for the collection and analysis of exhaled breath in awake rats based on proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) and applied it to investigate possible relationships between pathologies induced by dietary regime and breath composition. As a case study, we investigated rats with dietary induced non-alcoholic steatohepatitis (NASH) and modifications induced by coffee addition to the diet. We considered two different diets (standard and high fat) complemented with two different drinking possibilities (water or decaffeinated coffee) for a total of four groups with four rats each. Several spectrometric peaks were reliable markers for both dietary fat content and coffee supplementation. The high resolution and accuracy of PTR-ToF-MS allowed the identification of related compounds such as methanol, dimethyl sulphide, dimethyl sulphone and ammonia. In conclusion, the rapid and minimally invasive breath analysis of awake rats permitted the identification of markers related to diet and specific pathologic conditions and provided a useful tool for broader metabolic investigations. Copyright ? 2012 John Wiley & Sons, Ltd.     

Design,Synthesis and Antiparasitic Evaluation of Click Phospholipids

A library of seventeen novel ether phospholipid analogues, containing 5-membered heterocyclic rings (1,2,3-triazolyl, isoxazolyl, 1,3,4-oxadiazolyl and 1,2,4-oxadiazolyl) in the lipid portion were designed and synthesized aiming to identify optimised miltefosine analogues. The compounds were evaluated for their in vitro antiparasitic activity against Leishmania infantum and Leishmania donovani intracellular amastigotes, against Trypanosoma brucei brucei and against different developmental stages of Trypanosoma cruzi. The nature of the substituents of the heterocyclic ring (tail) and the oligomethylene spacer between the head group and the heterocyclic ring was found to affect the activity and toxicity of these compounds leading to a significantly improved understanding of their structure–activity relationships. The early ADMET profile of the new derivatives did not reveal major liabilities for the potent compounds. The 1,2,3-triazole derivative 27 substituted by a decyl tail, an undecyl spacer and a choline head group exhibited broad spectrum antiparasitic activity. It possessed low micromolar activity against the intracellular amastigotes of two L. infantum strains and T. cruzi Y strain epimastigotes, intracellular amastigotes and trypomastigotes, while its cytotoxicity concentration (CC₅₀) against THP-1 macrophages ranged between 50 and 100 μM. Altogether, our work paves the way for the development of improved ether phospholipid derivatives to control neglected tropical diseases.