Search

Liquids for electronic cigarettes and the vapor generated from them were examined by chemical and biological methods in order to reveal potential risk factors and their acceptability for consumers. Although the majority of the liquids on the market appear to be safe, some aroma compositions have been identified as possibly toxic for human vein epithelial cells, similar to tobacco smoke, thus indicating potential health risks and suggesting suitable test procedures before marketing the liquids.

Electronic cigarettes (e-cigarettes) have gained increasing popularity in recent years, mostly because they are supposed to be less harmful than regular cigarettes. Therefore, it is highly imperative to investigate possible noxious effects to protect the consumers. E-liquids consist of propylene glycol, glycerol, aroma compounds and sweeteners. One of these sweeteners is a chlorinated version of sucrose, namely sucralose. The aim of this work was to investigate degradation products of sucralose in the presence of propylene glycol and glycerol at different temperatures of commercially available e-cigarettes. Chemical analysis and biological tests were simultaneously performed on e-liquid aerosol condensates. The results of the chemical analysis, which was executed by employing GC‐MS/GC-FID, demonstrated high amounts of various chloropropanols. The most abundant one is extremely toxic, namely 3-chloropropane-1,2-diol, which can be detected at concentrations ranging up to 10,000 mg/kg. Furthermore, a cytotoxicity investigation of the condensates was performed on HUVEC/Tert2 cells in which metabolic activity was determined by means of resazurin assay. The cellular metabolic activity significantly decreased by treatment with e-liquid aerosol condensate. Due to the results of this study, we advise against the use of sucralose as sweetener in e-liquids.

QMCF-MD simulations have been carried out for Pr(III), Nd(III), Pm(III) and Sm(III) ions in aqueous environment, employing ab initio quantum mechanical treatment for ion, first and second hydration shell. Interchanging prismatic structures are found for all ions, the main coordination number being 9, in good agreement with EXAFS experimental data. The ligand dynamics are characterized by first-shell mean residence times in the range of 50 to ∼200 ps and by force constants for the Ln(III)–O(water) bond between 75 and 100 Nm −1 .

Hydration properties of trivalent thulium and ytterbium ions in aqueous solution are investigated via quantum mechanical charge field molecular dynamics (QMCF-MD) simulations. The QMCF-MD formalism is a special type of QM/MM simulation, where the chemically most relevant part of the system – in this case the ion with its first and second hydration shells – is treated by quantum mechanics. The mean ion O distances and the average coordination numbers of the first hydration shells are compared with experimental EXAFS data. Mean ligand residence times, vibrational frequencies and force constants were evaluated to characterise the dynamics of the systems.

A theoretical study of dysprosium(III) and holmium(III) in aqueous solution based on a quantum mechanical charge field-molecular dynamics (QMCF-MD) simulation is presented. The obtained structural and dynamical data were found to be in good agreement with several experimental and theoretical data. It is shown that the coordination number is constantly switching between eight and nine adopting square antiprismatic and tricapped trigonal prismatic configurations, thus supporting the interpretation of experimental data.

A comparison of the hydration characteristics of di- and trivalent europium ions in aqueous solution is presented. The established quantum mechanical charge-field molecular dynamics (QMCF-MD) approach yielded two 30 ps simulations. Significant differences among the two species were found in the Eu–O radial distribution functions, both in good agreement with experiments. The first shell coordination numbers of 8.1 and 8.9 were observed for Eu(II) and Eu(III), respectively. The mean residence time of first shell ligands differ by more than one order of magnitude, the divalent ion's hydration shell being more flexible, which is underlined by a weak ion-water bond strength.

MP2 energy evaluations required for the potential energy surface underlying a perturbation theory corrected vibrational self-consistent field (PT2-VSCF) calculation may be safely approximated with the RI-MP2 method. The wavenumbers of the 32 probed open- and closed shell systems differ on average from their MP2 references by 0.0 ± 0.1 cm−1. An up to 70 fold decrease in CPU time compared to standard MP2 calculations was observed while the overall energy surface scan underlying a PT2-VSCF calculation is sped up by a factor of two. Limitations of the approach are discussed and a comparison with B3LYP based PT2-VSCF calculations is made.

Immobilized metal ion affinity chromatography (IMAC) is an important chromatographic technique for biomolecules. In order to get a detailed understanding of the hydration of immobilized Fe(III), complexes of Fe(III) with methyl substituted iminodiacetate ([Fe(MSIDA)(H2O)3](+)) as well as with methyl substituted nitrilotriacetate ([Fe(MSNTA)(H2O)2]) were simulated in aqueous solutions with the quantum mechanical charge field molecular dynamics (QMCF MD) approach. The simulations were carried out at the Hartree-Fock (HF) level of theory, since cluster calculations at the HF, MP2, and B3LYP levels of theory showed that this method results in a good compromise between computational effort and accuracy. None of the coordinating water molecules were exchanged during the simulation period of 15 ps. The Fe-OH2O bond distances as well as the Fe-OH2O stretching motions differed among the coordinating water molecules, indicating different bond strengths. For the water molecules in the second hydration layer, mean residence times of 2.7 and 1.9 ps were obtained for [Fe(MSIDA)(H2O)3](+) and [Fe(MSNTA)(H2O)2], respectively. Furthermore, infrared measurements were carried out to characterize the most prominent bond features of aqueous Fe(III)-NTA and to discuss these results in conjunction with the computationally derived frequencies.

Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) simulations were performed for CO 2 + and SO 2 + in water at the restricted open-shell Hartree–Fock (ROHF) level of theory employing Dunning DZP basis sets for solute and solvent molecules. Simulation data of these hydrated ionic species were compared to their corresponding neutral precursors, CO 2 and SO 2 illustrating contrasting structures and dynamical behavior. Hydrated CO 2 + is subject to weaker hydration than CO 2 whereas SO 2 + associates with water molecules via stronger H-bonds than SO 2 , CO 2 + and CO 2 molecules. Ionization of both gases also leads to a different relative influence on the hydration behavior in aqueous environment reflected by C O wat and S O wat mean distances of ∼3.1 A and ∼2.7 A in hydrated CO 2 + and SO 2 + , respectively. In a cloudy atmosphere hydrated CO 2 + and SO 2 + can produce other oxidized species, which are thought to be partly implicated in earth’s temperature activity.

In this study a new type of immobilized metal ion affinity chromatography resin for the enrichment of carbohydrates and polyols was synthesized by radical polymerization reaction of vinyl phosphonic acid and 1,4-butandiole dimethacrylate using azo-bis-isobutyronitrile as radical initiator. Interaction between the chelated trivalent lanthanide ions and negatively charged hydroxyl groups of carbohydrates and polyols was observed by applying high pH values. The new method was evaluated by single standard solutions, mixtures of standards, honey and a more complex extract of Cynara scolymus. The washing step was accomplished by acetonitrile in excess volumes. Elution of enriched carbohydrates was successfully performed with deionized water. The subsequent analysis was carried out with matrix-free laser desorption/ionization-time of flight mass spectrometry involving a TiO2 -coated steel target, especially suitable for the measurement of low-molecular-weight substances. Quantitative analysis of the sugar alcohol xylitol as well as the determination of the maximal loading capacity was performed by gas chromatography in conjunction with mass spectrometric detection after chemical derivatization. In a parallel approach quantum mechanical geometry optimizations were performed in order to compare the coordination behavior of various trivalent lanthanide ions.

An ab initio quantum mechanical charge-field molecular dynamics simulation of the tetravalent thorium ion in aqueous environment is presented. Including the first and second hydration shell in the quantum mechanical treatment to enhance accuracy, this study yields very good results for a wide range of characteristics, as compared to experimental data. 20 ps of simulation time were used to investigate structural and dynamical properties of the hydrate by numerous methods, including radial and angular distribution functions, three-body distribution functions, ligand exchange analysis and vibrational spectra. The hydrate proved stable during the simulation and did not show hydrolysis. The first solvation shell was found to be a very flexible one, with a number of intrashell ligand rearrangements occurring along the simulation. The data of the simulation also indicated the existence of a third hydration layer. Vibrational analysis yielded an average ion–oxygen frequency of 420 cm−1, which is in excellent agreement with experimental data.

The cis- and trans-bis(glycinato)copper(II) complexes in aqueous solution have been investigated by means of a combined theoretical and experimental approach. The conducted quantum mechanical charge field molecular dynamics (QMCF-MD) studies, being the first quantum mechanical simulations of organometallic complexes by this method, yielded accurate structural details of the investigated isomers as well as novel dynamic data, which has successfully been confirmed and extended by subsequent mid-infrared measurements. The spectroscopic results, critically assessed by adjacent multivariate data analysis, indicate an isomeric stability at ambient conditions, vanishing at elevated temperatures.

We report a highly enantioselective oligomerization of isoleucine stereomers in the salt-induced peptide formation reaction under plausibly prebiotic earth conditions. Up to 6.5-fold superiority in reactivity of L-isoleucine was observed, compared to its D-enantiomer, after 14 evaporation cycles in the presence of Cu(2+) and NaCl. Since isoleucine is among the proteinogenic amino acids that were found enantioenriched in meteorites, this present work may further correlate the extraterrestrial delivery and endogenous production of biological homochirality by virtue of a protein constituent rather than the rarely occurring α-methylated amino acids.

The aqueous solutions of bisulfite (SO(3)H(-)) and sulfonate (HSO(3)(-)) were simulated by the ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism. All superimposed trajectories for the atomic coordinates of solutes with three-dimensional alignment here illustrated the reactivities of the ions. Power spectra were evaluated on the basis of the velocity autocorrelation functions (VACFs) with the normal-mode analysis, presenting a higher frequency of the symmetric SO(3) deformation (δ(s)(SO(3))) than the asymmetric SO(3) deformation (δ(as)(SO(3))) modes for the sulfonate ion. The different influence of solvent on the frequency of the O-H and S-H stretching suggests a higher stability of hydrated sulfonate ion. The bisulfite shows a slightly stronger molecular hydration shell than the sulfonate ion with the average number of ion-solvent hydrogen bonds (H-bonds) of 5.3 and 5.0, respectively. Extra water molecules within the molecular hydration shell are found for bisulfite (1.2) and for sulfonate (1.6). The mean residence times for the water ligands classify each ion as a structure maker, while the S-H bond within the sulfonate ion displays a hydrophobic behavior. No tautomerization was observed within the simulation period.

The hydration of the Bi(III) ion was determined via an ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) simulation. Ten picosecond sampling was carried out to determine structural and dynamical properties of the Bi(III) ion in aqueous solution. In the first hydration shell, the ion is 9-fold coordinated with a maximum probability of the Bi-O distance at 2.51 Å. In total, 11 exchanges were observed in the first-shell showing associative, dissociative, and interexchange character. As with the dominant existence of 9-fold coordination, the geometry of the Bi(III) ion is in between the tricapped trigonal prism and the capped square antiprism.

The previously investigated La3+-hydrate has been re-evaluated by means of the quantum mechanical charge field (QMCF) molecular dynamics (MD) approach. Improved description of the hydration characteristics has been realised by including the full second hydration shell into the quantum mechanically treated region and by introducing the influence of the surrounding bulk via an electrostatic embedding technique. Analytical tools such as the ligand angular radial distribution analysis have been employed to gain deeper insight into the structural features of the hydrate. La3+ simultaneously forms nona- and decahydrates with capped trigonal and quadratic prismatic structure, besides small amounts of an octahydrate.

An ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation has been carried out in order to obtain detailed insight into the hydration properties of Mg2+. The ion, being a ‘kosmotrope’, considerably influences the water hydrogen bond network in its vicinity. Certain types of hydrogen bonds are strengthened at the cost of weakening others. The cationic influence on the water hydrogen bonding network have been investigated primarily employing time correlation functions of H-bond dynamics. The frequencies of the MgO6 skeletal normal modes calculated using the normal coordinate analysis shows a close resemblance to the experimental data, thus validating the accuracy of ab initio quantum chemical simulations.

An ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation was performed on a single molecule of hydrogen peroxide immersed in water to investigate its stability in aqueous solution, since pure hydrogen peroxide is very unstable. The structural parameters such as radial distribution functions (RDFs), coordination number distributions (CNDs) and angular distribution functions (ADFs) indicate the existence of ∼4 hydrogen bonds between hydrogen peroxide and water molecules, with both molecules acting as hydrogen bond donors and hydrogen bond acceptors. The overall hydration shell consists of ∼6 water molecules surrounding the hydrogen peroxide molecule. The analysis of the hydrogen bond dynamics verified the presence of strong hydrogen bonds compared to pure water, thus confirming the stabilization of hydrogen peroxide in aqueous solution.

The ab initio quantum mechanical charge field molecular dynamics simulation technique was applied for the first time to an electronically excited system, namely hydrated Li(I). This approach does not only provide data for the influence of electronic excitation on structure and composition of the hydrate, but also leads to a spectrum for the excitation band including rotational, translational and vibrational energy transfers. The first excitation band for Li(I) in water peaks at 13.1 eV. The excitation leads to reduced coordination numbers of first and second hydration shell and stabilises the first and labilises the second shell.

Graphical abstract Highlights ►Concise treatment of highly charged ions with very different properties. ► Performed by ab initio simulations with the recent QMCF-MD methodology. ► Treating hydrates with extreme stability, labile hydrates and instable systems with (sub-)picosecond proton transfer reactions., Based on a series of ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulations, the broad spectrum of structural and dynamical properties of hydrates of trivalent and tetravalent ions is presented, ranging from extreme inertness to immediate hydrolysis. Main group and transition metal ions representative for different parts of the periodic system are treated, as are 2 threefold negatively charged anions. The results show that simple predictions of the properties of the hydrates appear impossible and that an accurate quantum mechanical simulation in cooperation with sophisticated experimental investigations seems the only way to obtain conclusive results.

Structure and dynamics of a carbon dioxide molecule in water were studied by an ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) simulation. Radial distribution functions, angular distribution functions, and coordination number distributions as well as dynamical data such as mean ligand residence time and vibrational spectra were utilized for the evaluation of physico–chemical properties of hydrated CO2. These data served for an assessment of hydrogen bonding between solute and solvent molecules. All the results evaluated were compared with available experimental results leading to a good agreement between theoretical and experimental data. The average lifetime of hydrogen bonding between H2 O and CO2 resulted as 0.61 ps, which is higher than the hydrogen bonding lifetime of pure water. The vibrational frequencies were also calculated for all the modes of hydrated CO2 to demonstrate the influence of solvent molecules on the IR spectrum of the solute. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

An ab initio Quantum Mechanical Charge Field Molecular Dynamics Simulation (QMCF MD) was performed to investigate structure and dynamics behavior of hydrated sulfur dioxide (SO(2)) at the Hartree-Fock level of theory employing Dunning DZP basis sets for solute and solvent molecules. The intramolecular structural characteristics of SO(2), such as S═O bond lengths and O═S═O bond angle, are in good agreement with the data available from a number of different experiments. The structural features of the hydrated SO(2) were primarily evaluated in the form of S-O(wat) and O(SO(2))-H(wat) radial distribution functions (RDFs) which gave mean distances of 2.9 and 2.2 Å, respectively. The dynamical behavior characterizes the solute molecule to have structure making properties in aqueous solution or water aerosols, where the hydrated SO(2) can easily get oxidized to form a number of sulfur(VI) species, which are believed to play an important role in the atmospheric processes.

The ab initio quantum mechanical charge field (QMCF) molecular dynamics (MD) formalism was used to evaluate structure and dynamics of the monomeric hydrated tetravalent hafnium. The ion forms three hydration shells and no hydrolysis reaction occurred during the simulation time of 7 ps. Eight water molecules coordinate in a more or less well-defined square antiprismatic geometry at the hafnium ion, as visible from the O–Hf–O angular distribution function, with a Hf (IV)–O bond length of 2.26 A and a bond force constant of 212 N/m, which classifies this bond as the strongest ion–water bond known so far.

The ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism was applied to simulate the bisulfate ion, HSO4-, in aqueous solution. The averaged geometry of bisulfate ion supports the separation of six normal modes of the O*-SO3 unit with C3v symmetry from three modes of the OH group in the evaluation of vibrational spectra obtained from the velocity autocorrelation functions (VACFs) with subsequent normal coordinate analyses. The calculated frequencies are in good agreement with the observations in Raman and IR experiments. The difference of the averaged coordination number obtained for the whole molecule (8.0) and the summation over coordinating sites (10.9) indicates some water molecules to be located in the overlapping volumes of individual hydration spheres. The averaged number of hydrogen bonds (H-bonds) during the simulation period (5.8) indicates that some water molecules are situated in the molecular hydration shell with an unsuitable orientation to form a hydrogen bond with the ion. The mean residence time in the surroundings of the bisulfate ion classify it generally as a weak structure-making ion, but the analysis of the individual sites reveals a more complex behavior of them, in particular a strong interaction with a water molecule at the hydrogen site.

Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) simulations have been performed for aqueous solutions of Fe(2+) and Fe(3+) ions at the Hartree-Fock level of theory to describe and compare their structural and dynamical behavior. The structural features of both hydrated ions are characterized by radial distribution functions that give the maximum probability of the ion-O distance for Fe(2+) and Fe(3+) ions at 2.15 and 2.03 A, respectively. The angular distribution functions of both ions prove the octahedral arrangement of six water ligands, whereas the second shells of these ions differ. Both ions show influence on the water molecules beyond the second shells. The structure-forming abilities of both ions are visible from the ligand mean residence times and ion-O stretching frequencies evaluated for both ions. The substantially improved data obtained from these QMCF-MD simulations show better correlation with available experimental results than the conventional quantum mechanics/molecular mechanics molecular dynamics (QM/MM MD) approaches with one hydration shell treated by quantum mechanics.

The ambiguous assignments of the CO–H stretching ( ν 1 ) mode of bicarbonate ion in Raman and IR spectra were clarified based on a careful investigation of hydrogen bonding and its influence on the power spectra evaluated from the velocity autocorrelation functions obtained by an ab initio QMCF MD simulation. The ν 1 spectrum includes inter- and intra-molecular OH stretching modes of hydrated bicarbonate ion and is presented together with the other vibrations, namely the symmetric CO stretching ( ν 3 ), the C–OH stretching ( ν 5 ) and the CO 3 out-of-plane deformation ( ν 8 ), modes.

The structure and dynamics of the stable four-times positively charged uranium(IV) cation in aqueous solution have been investigated by ab initio quantum mechanical charge field (QMCF) molecular dynamics (MD) simulation at the Hartree-Fock double-zeta quantum mechanical level. The QMCF-MD approach enables investigations with the accuracy of a quantum mechanics/molecular mechanics approach without the need for the construction of solute-solvent potentials. Angular distribution functions; radial distribution functions; coordination numbers of the first, second, and third shell (9, 19, and 44, respectively); coordination number distribution functions; tilt- and Theta-angle distribution functions; as well as local density corrected triangle distribution functions have been employed for the evaluation of the hydrated ion's structure. Special attention was paid to the determination of the geometry of the first hydration layer, and the results were compared to experimental large-angle X-ray scattering and extended X-ray absorption fine structure data. The solvent dynamics around the ion were also investigated using mean ligand residence times and related data and, resulting from the unavailability of any experimental data, were compared to ions with similar properties.

Quantum mechanical/molecular mechanical (QM/MM) and quantum mechanical charge field (QMCF) molecular (MD) simulations have been performed to describe structural and dynamical properties of Na(I) and K(I) in water and to compare the two approaches. The first and second hydration shells were treated by ab initio quantum mechanics at the restricted Hartree-Fock (RHF) level. The structural data are in good agreement with previously published experimental and theoretical results. A considerable number of water exchange reactions were observed within the first shell during the simulation time of 12 ps. The number of exchange events in both shells is higher in the case of K(I) than Na(I) reflecting the weaker ion-ligand bond strength of K(I). Comparison of the "conventional" QM/MM framework with the QMCF method clearly indicates the latter to be advantageous, as ambiguities arising from the coupling of the subregions occurring in the QM/MM MD simulations did not evolve when the QMCF ansatz was applied.

Quantum mechanical charge field (QMCF) molecular dynamics (MD) simulations including first and second hydration shell in the QM region have been performed to describe structural and dynamical properties of Ge(II) in water. The first and second hydration shells were treated by ab initio quantum mechanics at restricted Hartree-Fock (RHF) level. The radial distribution function (RDF) showed the maximum probability of the Ge–O bond length at 2.04 A, accompanied by an extended first shell located at ∼2.8 A. A uniquely distorted hydration structure with two tri-pyramidal substructures provides a new basis for the interpretation of the kinetic properties of germanium(II) complexes.