Synthesis of conformationally constrained adamantane imidazolines with trypanocidal activity

Aiming at the development of new adamantano building blocks for treating African trypanosomiasis, we report on the synthesis of spiro adamantane 2‐imidazolines 8a‐f and 9a‐c , and their congeneric 5‐(1‐adamantyl)imidazolines 14 and 15 . The potency of these compounds against Trypanosoma brucei was compared to that of rimantadine and found, in the case of compound 14e , to be three fold higher. Together with the other active compounds, 14b and 15b , which were equipotent to rimantadine, the new molecules illustrate the synergistic effect of the lipophilic character of adamantane and the C1 amidine functionality on trypanocidal activity.     

Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2O Vapor Sorption

In this work we report a strategy for generating porosity in hybrid metal halide materials using molecular cages that serve as both structure-directing agents and counter-cations. Reaction of the [2.2.2] cryptand (DHS) linker with Pb^II in acidic media gave rise to the first porous and water-stable 2D metal halide semiconductor (DHS)₂Pb₅Br₁₄. The corresponding material is stable in water for a year, while gas and vapor-sorption studies revealed that it can selectively and reversibly adsorb H₂O and D₂O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H₂O and D₂O in the organic linker cavities and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half-maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens new pathways towards unexplored applications (e.g. solid-state batteries) for this class of hybrid semiconductors.     

Theoretical study of gallium nitride molecules, GaN2 and GaN4

The electronic and geometric structures of gallium dinitride GaN 2, and gallium tetranitride molecules, GaN 4, were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4( (2)B 1) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2, while 37 structures were identified for GaN 4 corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4. The dissociation energy of the ground-state GaN 2 ( X (2)Pi) is 1.1 kcal/mol with respect to Ga( (2)P) + N 2( X (1)Sigma g (+)). The ground-state and the first two excited minima of GaN 4 are of (2)B 1( C 2 v ), (2)A 1( C 2 v , five member ring), and (4)Sigma g (-)( D infinityh ) symmetry, respectively. The dissociation energy ( D e) of the ground-state of GaN 4, X (2)B 1, with respect to Ga( (2)P) + 2 N 2( X (1)Sigma g (+)), is 2.4 kcal/mol, whereas the D e of (4)Sigma g (-) with respect to Ga( (4)P) + 2 N 2( X (1)Sigma g (+)) is 17.6 kcal/mol.     

A refined semilocal convergence analysis of an algorithm for solving the Ricatti equation

The semilocal convergence of a numerical algorithm for solving the algebraic Ricatti equation with multiparameter singularly perturbed systems is investigated here. We show that under weaker hypotheses and the some computational cost than in Mukaidani et al. (J. Math. Anal. Appl. 267:209–234, [2002]) finer estimates on the distances involved and a more precise information on the location of the solution can be obtained.     

Evaluating a Cumaean Sibyl: Domenichino or later? A multi analytical approach

The purpose of this study is to clarify important details about a Cumaean Sibyl painting that is preserved in a private collection. This work, bearing neither signature nor date, has never undergone conservation. It was executed after Domenichino's Cumaean Sibyl, a work known to have been used as a model by many 18th century painters.Investigation of the anonymous artist's painting technique and identification of its constituent materials were facilitated by employing optical microscopy (OM), scanning electron microscopy (SEM/EDS), FTIR and microRaman spectroscopies and high performance liquid chromatography with diode array detection (HPLC-DAD). The painter's palette comprised lead white, yellow ochre, lead-antimonate yellow (Naples yellow), cinnabar, cochineal lake, madder lake, haematite, Prussian blue and carbon black.The detection of Prussian blue (synthesized in 1704 and widely used as artist's pigment after 1750) was decisive in establishing the work's authenticity for, as such, it cannot be attributed either to Domenico Zampieri (1581-1641) or to his apprentices. In addition, the identification of Naples yellow, which prevailed in the period from 1750 to 1850, supports this statement. Nevertheless, its elaborate painting technique strongly suggests an artist greatly influenced by the Renaissance masters. A comparison of its stylistic features with those of the Cumaean Sibyl of Angelica Kauffmann (1741-1807), a prolific 18th century artist known to have studied and to have copied Domenichino's Sibyl, reveals significant similarities between the two in composition and palette. The unsigned Sibyl, therefore, could well be by Kauffmann.     

Disposable mercury-free cell-on-a-chip devices with integrated microfabricated electrodes for the determination of trace nickel(II) by adsorptive stripping voltammetry

This work reports the fabrication of disposable three-electrode cells with integrated sputtered metal-film electrodes. The working electrode was a bismuth-film electrode (BiFE) while the reference and counter electrodes were made of Ag and Pt, respectively. The deposition of the metal layers was carried out by sputtering of the respective metals on a silicon substrate while the exact geometry of the electrodes was defined via a metal mask placed on the substrate during the deposition process. Initially, the electrodes were characterised by cyclic voltammetry. The utility of these devices was tested for the trace determination of Ni(II) by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (the presence of oxygen, the DMG concentration, the preconcentration potential, the accumulation time and the SW parameters), as well as potential interferences, were investigated. Using the selected conditions, the 3sigma limit of detection was 100 ng L(-1) for Ni(II) (for 90 s of preconcentration) and the relative standard deviation for Ni(II) was 2.3% at the 10 microg L(-1) level (n=8). Finally, the method was applied to the determination of Ni(II) in a certified river water sample.     

Theoretical study on the electronic states of NaLi

Configuration interaction calculations have been carried out on electronic states of the NaLi molecule and the cation NaLi(+). Potential energy curves are presented for the lowest nine (1)Sigma(+), seven (1)Pi, four (1)Delta, eight (3)Sigma(+), seven (3)Pi, and four (3)Delta states of NaLi as well as for the lowest ten (2)Sigma(+), six (2)Pi, and two (2)Delta states of NaLi(+). The results of the present many-electron configuration interaction calculations on the cation are in support of previous core-polarization effective potential calculations. The present calculations on the NaLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously as well as an investigation of nonadiabatic effects leading to spectral perturbations. Furthermore, ab initio potential energy curves of the neutral and the ground state of the cation are employed to determine quantum defect that may be employed to generate potential energy curves for nd and (n+1)p (for n>3) Rydberg states of NaLi. The present results on the 3 (1)Pi and 4 (1)Pi states are in good agreement with recent experimental work, whereas on the basis of theoretical data, the recently observed state 5 (1)Pi is better described as 6 (1)Pi.     

Design of a field flow system for the on-line spectrophotometric determination of phosphate, nitrite and nitrate in natural water and wastewater

This study describes the design and optimisation of a field flow system for the in-situ collection and on-line determination of phosphate, nitrate and nitrite by flow injection analysis-spectrophotometry. The method is based on the initial determination of phosphate as its phosphoantimonylmolybdenum blue complex which is then oxidized on-line by nitrite and the decrease in absorbance is monitored at 880 nm. Nitrate is determined as the difference between total and initial nitrite content in a separate flow after reduction to nitrite in a cadmium reductive column. The calibration curves were linear in the range 0–2.00 mg L⁻¹ P-phosphate, 0–10.00 mg L⁻¹ nitrite and 0–7.00 mg L⁻¹ nitrate with correlation coefficients of 0.9979, 0.9993 and 0.9995, respectively. The detection limits, calculated as 3S/N, were 0.15 mg L⁻¹ for P-phosphate, 0.17 mg L⁻¹ for nitrite and 0.09 mg L⁻¹ for nitrate. The reproducibility was below 3.0% (n = 7). Method validation in the analysis of natural water and wastewater samples revealed that it can efficiently be applied to the determination of the target analytes, with recoveries in the range of 92–108%. Correspondence: Athanasios G. Vlessidis, Laboratory of Analytical Chemistry, Department of Chemistry, University of Ioannina, Ioannina 45110, Greece     

Molecular dynamics simulations of pure methane and carbon dioxide hydrates: lattice constants and derivative properties

ABSTRACT

We report extensive molecular dynamics simulation results of pure methane and carbon dioxide hydrates at pressure and temperature conditions that are of interest to various practical applications. We focus on the calculation of the lattice constants of the two pure hydrates and their dependence on pressure and temperature. The calculated lattice constants are correlated using second order polynomials which are functions of either temperature or pressure. Finally, the obtained correlations are used in order to calculate two derivative properties, namely the isothermal compressibility and the isobaric thermal expansion coefficient. The current simulation results are also compared against reported experimental measurements and other simulation studies and good agreement is found for the case of isothermal compressibility. On the other hand, for the case of isobaric thermal expansion coefficient good agreement is found only with other simulation studies, while the simulation studies are in disagreement with experiments, particularly at low temperatures.     

Development and validation of an HPLC method for the determination of penicillin antibiotics residues in bovine muscle according to the European Union Decision 2002/657/EC

A high-performance liquid chromatographic method was developed for the determination of five penicillins: penicillin G (PENG), penicillin V (PENV), oxacillin (OX), cloxacillin (CLO), and dicloxacillin (DICLO), in bovine muscle. Samples were macerated with a mixture of H(2)O/CH(3)CN (1:1) and purified using RP-8 Adsorbex SPE cartridges after centrifugation, with mean recovery from spiked samples higher than 89%. The separation of the examined penicillins was achieved on an analytical column, an Inertsil C8 5 microm, 250x4 mm(2), at ambient temperature. The mobile phase consisted of 0.1% TFA/ACN 50:50 v/v delivered isocratically at a flow rate of 1.1 mL/min. Analytes were monitored at 240 nm. The procedure was validated according to the European Union Decision 2002/657/EC by means of selectivity, stability, decision limit, detection capability, accuracy, and precision. Method's LOQ values achieved were 54 microg/kg for PENG and DICLO, 46 microg/kg for PENV, 16 microg/kg for OX, and 43 microg/kg for DICLO. The detection capabilities (CC(beta)) were 73.6 microg/kg for PENG, 29.1 microg/kg for PENV, 350.6 microg/kg for OX, 379.9 microg/kg for CLO, and 355.8 microg/kg for DICLO. The method was applied to various samples from the local market. Two penicillins were identified by photodiode array (PDA) detection and quantified.