Energetics of Intermolecular Hydrogen Bonds in a Hydrophobic Protein Cavity

This work explores the energetics of intermolecular H-bonds inside a hydrophobic protein cavity. Kinetic measurements were performed on the gaseous deprotonated ions (at the ?7 charge state) of complexes of bovine β-lactoglobulin (Lg) and three monohydroxylated analogs of palmitic acid (PA): 3-hydroxypalmitic acid (3-OHPA), 7-hydroxypalmitic acid (7-OHPA), and 16-hydroxypalmitic acid (16-OHPA). From the increase in the activation energy for the dissociation of the (Lg + X-OHPA)^7– ions, compared with that of the (Lg + PA)^7– ion, it is concluded that the –OH groups of the X-OHPA ligands participate in strong (5 – 11 kcal mol^–1) intermolecular H-bonds in the hydrophobic cavity of Lg. The results of molecular dynamics (MD) simulations suggest that the –OH groups of 3-OHPA and 16-OHPA act as H-bond donors and interact with backbone carbonyl oxygens, whereas the –OH group of 7-OHPA acts as both H-bond donor and acceptor with nearby side chains. The capacity for intermolecular H-bonds within the Lg cavity, as suggested by the gas-phase measurements, does not necessarily lead to enhanced binding in aqueous solution. The association constant (K_a) measured for 7-OHPA [(2.3 ± 0.2) × 10⁵ M^–1] is similar to the value for the PA [(3.8 ± 0.1) × 10⁵ M^–1]; K_a for 3-OHPA [(1.1 ± 0.3) × 10⁶ M^–1] is approximately three-times larger, whereas K_a for 16-OHPA [(2.3 ± 0.2) × 10⁴ M^–1] is an order of magnitude smaller. Taken together, the results of this study suggest that the energetic penalty to desolvating the ligand –OH groups, which is necessary for complex formation, is similar in magnitude to the energetic contribution of the intermolecular H-bonds.

Conformational properties of 1-methyl-1-germacyclohexane: low-temperature NMR and quantum chemical calculations

The conformational preference of the methyl group of 1-methyl-1-germacyclohexane was studied experimentally in solution (low-temperature ¹³C NMR) and by quantum chemical calculations (CCSD(T), MP2 and DFT methods). The NMR experiment resulted in an axial/equatorial ratio of 44/56 mol% at 114 K corresponding to an A value (A = G _ax ? G _eq) of 0.06 kcal mol^?1. An average value for ΔG _e→a ^#  = 5.0 ± 0.1 kcal mol^?1 was obtained for the temperature range 106–134 K. The experimental results are very well reproduced by the calculations. CCSD(T)/CBS calculations + thermal corrections resulted in an A value of 0.02 kcal mol^?1, whereas a ΔE value of ?0.01 kcal mol^?1 at 0 K was obtained.     

Quantum chemical investigation on the influence of amino substitution on proton affinity of oxazolidin-2-one

The scenarios of preferred protonation sites and the absolute gas-phase proton affinities of C5- and N4-amino derivatives of oxazolidinone (OXA) molecules possessing two oxygen and two nitrogen atoms, are studied to investigate the effect of substitution of amino group on geometry, electronic structure, and proton affinities of these molecules. The natural bond orbital analysis is invoked to obtain the second-order delocalization energies, occupations of lone pairs, charge distribution, and bond orders to rationalize the obtained results. Our findings reveal a strong nucleophilicity of O1 site in C5-amino and N4-amino-substituted OXA isomers just as in un-substituted OXA. The substituent nitrogen in N4-amino-substituted OXA has comparable electrophilicity to O1 site while lesser than acyl oxygen and higher than nitrogen of OXA ring in C5-amino-substituted OXA. The PA values of C5- and N4-amino-substituted OXA isomers span in the range 172.06–205.77 kcal mol^?1 (at CBS-Q). The PA values for the potential sites increase in the range 1.96–27.08 kcal mol^?1 as a result of the amino substitution at C5 and N4 in orientation (b) while exceptionally they decrease by 0.57–2.95 kcal mol^?1 as a result of the amino substitution at N4 in orientation (a). The results for the order of PA values of potential sites have been supported by molecular electrostatic potential maps. Our findings indicate that the factors such as geometrical rearrangements, variations in atomic charge densities and electron delocalization, effect of substituent, intramolecular hydrogen bonding, and electronic changes direct the relative stabilities and proton affinities of N, C5-substituted amino OXA isomers.     

The SAMPL5 challenge for embedded-cluster integral equation theory: solvation free energies,aqueous p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript>, and cyclohexane–water log <Emphasis Type="Italic">D</Emphasis>

We predict cyclohexane–water distribution coefficients (log D _7.4) for drug-like molecules taken from the SAMPL5 blind prediction challenge by the “embedded cluster reference interaction site model” (EC-RISM) integral equation theory. This task involves the coupled problem of predicting both partition coefficients (log P) of neutral species between the solvents and aqueous acidity constants (pK _a) in order to account for a change of protonation states. The first issue is addressed by calibrating an EC-RISM-based model for solvation free energies derived from the “Minnesota Solvation Database” (MNSOL) for both water and cyclohexane utilizing a correction based on the partial molar volume, yielding a root mean square error (RMSE) of 2.4 kcal mol^?1 for water and 0.8–0.9 kcal mol^?1 for cyclohexane depending on the parametrization. The second one is treated by employing on one hand an empirical pK _a model (MoKa) and, on the other hand, an EC-RISM-derived regression of published acidity constants (RMSE of 1.5 for a single model covering acids and bases). In total, at most 8 adjustable parameters are necessary (2–3 for each solvent and two for the pK _a) for training solvation and acidity models. Applying the final models to the log D _7.4 dataset corresponds to evaluating an independent test set comprising other, composite observables, yielding, for different cyclohexane parametrizations, 2.0–2.1 for the RMSE with the first and 2.2–2.8 with the combined first and second SAMPL5 data set batches. Notably, a pure log P model (assuming neutral species only) performs statistically similarly for these particular compounds. The nature of the approximations and possible perspectives for future developments are discussed.     

Ab initio study of dehalohydrogenation reaction of 2-halo-2,3-dihydrophosphinine

Decomposition of 2-fluoro-2,3-dihydrophosphinine (1), 2-chloro-2,3-dihydrophosphinine (3), 2-bromo-2,3-dihydrophosphinine (5) to phosphinine was investigated using Molecular orbital and density functional theory. Study on the B3LYP/6-311+G** level of theory revealed that the required energy for the decomposition of compounds 1, 3, and 5 to phosphinine is 30.56 kcal·mol^?1, 28.23 kcal·mol^?1, and 24.03 kcal·mol^?1, respectively. HF/6-311+G**//B3LYP/6-311+G** calculated barrier height for the decomposition of compound 1, 3, and 5 to phosphinine is 57.56 kcal·mol^?1, 37.26 kcal·mol^?1, and 30.77 kcal·mol^?1, respectively. Also, MP2/6-311+G**//B3LYP/6-311+G** results indicated that the barrier height for the decomposition of compound 1, 3, and 5 to phosphinine is 46.59 kcal·mol^?1, 47.28 kcal·mol^?1, and 42.57 kcal·mol^?1, respectively. Natural bond orbital (NBO) population analysis and nuclear independent chemical shift (NICS) results showed that, reactants are non-aromatic but products of elimination reaction are aromatic, C-H and C-X bonds are broken and H-X bond is appear.     

Binding of cyclic carboxylates to octa-acid deep-cavity cavitand

As part of the fourth statistical assessment of modeling of proteins and ligands (sampl.eyesopen.com) prediction challenge, the strength of association of nine guests (1–9) binding to octa-acid host was determined by a combination of ¹H NMR and isothermal titration calorimetry. Association constants in sodium tetraborate buffered (pH 9.2) aqueous solution ranged from 5.39 × 10² M^?1 in the case of benzoate 1, up to 3.82 × 10⁵ M^?1 for trans-4-methylcyclohexanoate 7. Overall, the free energy difference between the free energies of complexation of these weakest and strongest binding guests was ΔΔG° = 3.88 kcal mol^?1. Based on a multitude of previous studies, the anticipated order of strength of binding was close to that which was actually obtained. However, the binding of guest 3 (4-ethylbenzoate) was considerably stronger than initially estimated.     

Theoretical study of spin–orbit coupling and kinetics in spin-forbidden reaction between Ta(NH2)3 and N2O

The activation mechanism of the nitrous oxide (N₂O) with the Ta(NH₂)₃ complex on the singlet and triplet potential energy surfaces has been investigated using the hybrid exchange correlation functional B3LYP. The minimum energy crossing point (MECP) is located by using the methods of Harvey et al. The rate-determining step of the N–O activation reaction is the intersystem crossing from ¹ 2 to ³ 2. The reacting system will change its spin multiplicities from the singlet state to the triplet state near MECP-1, which takes place with a spin crossing barrier of 32.5 kcal mol^?1, and then move on the triplet potential energy surface as the reaction proceeds. Analysis of spin–orbit coupling (SOC) using localized orbitals shows that MECP-1 will produce the significant SOC matrix element, the value of SOC is 272.46 cm^?1, due to the electron shift between two perpendicular π orbitals with the same rotation direction and the contribution from heavy atom Ta. The rate coefficients are calculated using Non-adiabatic Rice-Ramsperger-Kassel-Marcus (RRKM). Results indicate that the coefficients, k(E), are exceedingly high, k(E) > 10¹² s^?1, for energies above the intersystem crossing barrier (32.5 kcal mol^?1); however, in the lower temperature range of 200–600 K, the intersystem crossing is very slow, k(T) < 10^?6 s^?1.     

Photochemical synthesis and electronic spectra of fulminene ([6]phenacene)

Facile synthesis of fulminene ([6]phenacene) was achieved through the Mallory reaction of 1-(1-naphthyl)-2-(1-phenanthryl)ethene or the 9-fluorenone-sensitized photo-ring-closure of 1-(1-naphthyl)-2-(1-phenanthryl)ethane. The electronic spectral properties of fulminene were investigated for the first time using photoluminescence as well as transient absorption spectroscopy. The spectral features were compared with those of a series of lower phenacene homologs such as phenanthrene ([3]phenacene), chrysene ([4]phenacene), and picene ([5]phenacene). For the [n]phenacene series, both the fluorescence and phosphorescence bands linearly red-shifted with an increase in the number of the benzene rings (n). Trends in the energy levels of the excited singlet (E _S) and the triplet (E _T) states were expressed as E _s = ?2.6n + 89.1 (kcal mol^?1) and E _T = ?1.8n + 66.2 (kcal mol^?1), respectively. In the case of fulminene, laser flash photolysis displayed a transient spectrum with an absorption maximum (λ _max ^T–T ) at 675 nm, which was assigned as the triplet fulminene excited state. The λ _max ^T–T values for the [n]phenacene series showed a linear correlation as a function of the ring number n, given by an equation, λ _max ^T–T  = 60n + 318 (nm).     

Monoclonal antibodies with group specificity toward sulfonamides: selection of hapten and antibody selectivity

Immunoassays based on the current available antibodies for large multi-sulfonamide screening programs have suffered from high selectivity for individual sulfonamides and a wide range of selectivities for different sulfonamides. In this study, five synthesized haptens, HS, BS, CS, SA10, and TS and two sulfonamides, SG and SMX were used as haptens, which may or may not contain a ring structure at the N1 position of the sulfonamides, were selected to evaluate the effectiveness for producing group-specific monoclonal antibodies (MAbs). Mice immunized with three different two-ring haptens were used for hybridoma production, which resulted in three unique MAbs recognizing 10, 13, and 15 sulfonamides showing 50 % inhibition (IC₅₀) at concentrations below 100 ng?mL^–1. MAb 4D11 derived from one novel immunizing hapten could recognize 12 sulfonamides with IC₅₀ values ranging from 1.2 to 12.4 ng?mL^–1, almost within 1 order of magnitude. These produced MAbs show lower IC₅₀ values in addition to significantly improved group specificity compared with previously generated MAbs. This study clearly indicates that the careful selection of the immunizing hapten has an important effect on the specificity of the generated antibodies.

Reinvestigation of the Structure of Protonated Lysine Dimer

To better understand inconsistencies between the predicted infrared (IR) spectra of previously suggested isomers of Lys₂H⁺ reported by Wu et al. (J. Am. Soc. Mass Spectrom. 22:1651–1659, 18) and the experimental IR photon dissociation (IRPD) spectrum obtained by Oh et al. (J. Am. Chem. Soc. 127:4076–4083, 4), the structure of Lys₂H⁺ was reinvestigated using IRPD spectroscopy in the extended region 2700–3700 cm^?1 and theoretical calculations. The new experimental IRPD spectrum is in good agreement with Oh’s spectrum in the corresponding wavelength range. Based on calculations at the MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) and MP2/6-31?+?G(d,p)//MP2/6-31?+?G(d,p) levels, a new salt-bridged isomer, ZW1, was found to be the most stable isomer; it is more energetically favored than the previously suggested charge-solvated isomer LL-CS01 by 10 or 26 kJ mol^?1. Although the calculated IR spectrum of ZW1 is in good agreement with the experimental one in the range 2700–3700 cm^?1, it is in poor agreement with the previous IRPD spectrum in the range 1000–1900 cm^?1. This investigation shows that the intermolecular interactions inside the dimer are more complex than previously supposed. It is possible that both salt-bridged and charge-solvated isomers of Lys₂H⁺ are stable in the gas phase, and the isomers generated during ionization are sensitive to the experimental conditions.

Activation Energies of Fragmentations of Disaccharides by Tandem Mass Spectrometry

A simple multiple collision model for collision induced dissociation (CID) in quadrupole was applied for the estimation of the activation energy (E_o) of the fragmentation processes for lithiated and trifluoroacetated disaccharides, such as maltose, cellobiose, isomaltose, gentiobiose, and trehalose. The internal energy-dependent rate constants k(E_int) were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM) or the Rice-Ramsperger-Kassel (RRK) theory. The E_o values were estimated by fitting the calculated survival yield (SY) curves to the experimental ones. The calculated E_o values of the fragmentation processes for lithiated disaccharides were in the range of 1.4–1.7 eV, and were found to increase in the order trehalose < maltose < isomaltose < cellobiose < gentiobiose.

Synthesis, crystal structures and electrochemical properties of CoIII complexes with hexadentate ligand containing thioether-amidopyridyl donor set

Two new cobalt(III) complexes of the hexadentate ligand [1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane] (H₂bpctb) with N₄S₂ donor set atoms have been synthesized. A reaction of Co(CH₃COO)₂·4H₂O with (H₂bpctb) leads to the formation of [Co^III(bpctb)]PF₆ (1) having a CoN₂(pyridine)N′₂(amide)S₂(thioether) coordination by symmetric bpctb^2? ligand. A similar reaction under slightly different conditions, however, gives [Co^III(L ^a )(L ^b )] (2), resulting from a C–S bond cleavage reaction triggered by an acetate ion as a base, having CoN₂(pyridine)N′₂(amide)S(thioether)S′(thiolate) coordination. These two Co(III) complexes have been characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structures of [Co^III(bpctb)]PF₆ (1) in the form of the solvate (1·MeOH·H₂O) and of [Co^III(L ^a )(L ^b )] (2) have been determined by X-ray crystallography. The Co atoms of both complexes exhibit distorted octahedral geometry. The electrochemical investigation of [Co(bpctb)]PF₆·MeOH·H₂O (1·MeOH·H₂O) and [Co^III(L ^a )(L ^b )] (2) by cyclic voltammetry reveals a reversible Co^III–Co^II redox process at E _1/2 = ?0.32 V (ΔE _p = 80 mV); for 1, and E _1/2 = ?0. 87 V (ΔE _p = 70 mV) for 2.     

Experimental and theoretical evidence suggests carbamate intermediates play a key role in CO2 sequestration catalysed by sterically hindered amines

The chemisorption of CO₂ by aqueous-hindered amines has been investigated experimentally and theoretically. Negative-ion ESI–MS analysis of solutions containing a sterically hindered amine and a source of ¹³CO₂ reveals peaks corresponding to [M–H + 45]^?. These ions readily lose 45 Da when subjected to collisional activation, and together with other key fragments confirms the generation of the ¹³C-labelled carbamate derivatives. The thermochemistry of the two key capture reactions: $$2.{\text{amine }} + {\text{ CO}}_{ 2} { \leftrightarrows }{\text{amine}} - {\text{CO}}_{ 2}^{ - } + {\text{ amine}} - {\text{H}}^{ + } {\kern 1pt} \quad 1:{\text{carbam}}$$ $${\text{amine }} + {\text{ CO}}_{ 2} + {\text{ H}}_{ 2} {\text{O}}{ \leftrightarrows }{\text{HCO}}_{ 3}^{ - } + {\text{ amine}} - {\text{H}}^{ + } \quad 2:{\text{ bicarb}}$$ at 298 K was modelled using composite chemistry methods, CCSD(T), DFT, and SM8 free energies of solvation. The aqueous reaction free energies (ΔG ₂₉₈) for reaction 1 are predicted to be more negative than ΔG ₂₉₈ for reaction 2 when amine = ammonia, 2-aminoethanol (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-hydroxymethyl-propane-1,3-diol (tris), and 2-piperidinemethanol (2-PM). For AMP, tris, and 2-PM, activation free energies ΔG ₂₉₈ ^? for reaction 1 (SM8 + CCSD(T)/6-311 ++G(d,p)//M08-HX/MG3S: 38–67 kJ mol^?1) are smaller than the corresponding values for 2 (109–113 kJ mol^?1). For 2-PM, the computed carbamate ΔG ₂₉₈ ^? (38 kJ mol^?1) is comparable to the MEA value (45 kJ mol^?1), whereas the primary amines with tertiary alpha carbons have slightly larger values (60–70 kJ mol^?1). The organic amine values are much lower than the value for ammonia (93 kJ mol^?1). The results indicate CO₂ chemisorption proceeds via a carbamate intermediate for all aqueous primary and secondary amines. Hindered carbamates are susceptible to further chemical transformations following their formation.     

Reagentless d-sorbitol biosensor based on d-sorbitol dehydrogenase immobilized in a sol–gel carbon nanotubes–poly(methylene green) composite

A reagentless d-sorbitol biosensor based on NAD-dependent d-sorbitol dehydrogenase (DSDH) immobilized in a sol–gel carbon nanotubes–poly(methylene green) composite has been developed. It was prepared by durably immobilizing the NAD⁺ cofactor with DSDH in a sol–gel thin film on the surface of carbon nanotubes functionalized with poly(methylene green). This device enables selective determination of d-sorbitol at 0.2 V with a sensitivity of 8.7?μA?mmol^?1?L?cm^?2 and a detection limit of 0.11 mmol?L^?1. Moreover, this biosensor has excellent operational stability upon continuous use in hydrodynamic conditions.

Fragmentation Reactions of Methionine-Containing Protonated Octapeptides and Fragment Ions Therefrom: An Energy-Resolved Study

The fragmentation reactions of the MH⁺ ions as well as the b₇, a₇, and a₇* ions derived therefrom have been studied in detail for the octapeptides MAAAAAAA, AAMAAAAA, AAAAMAAA, and AAAAAAMA. Ionization was by electrospray using a QqToF mass spectrometer, which allowed a study of the evolution of the fragmentation channels as a function of the collision energy. Not surprisingly, the product ion mass spectra for the b₇ ions are independent of the original precursor sequence, indicating macrocyclization and reopening to the same mixture of protonated oxazolones prior to fragmentation. The results show that this sequence scrambling results in a distinct preference to place the Met residue in the C-terminal position of the protonated oxazolones. The a₇ and a₇* ions also produce product ion mass spectra independent of the original peptide sequence. The results for the a₇ ions indicate that fragmentation occurs primarily from an amide structure analogous to that observed for a₄ ions (Bythell et al. in J Am Chem Soc 132:14766–14779, 2010). Clearly, the rearrangement reaction they have proposed applies equally well to a_n ions as large as a₇. The major fragmentation modes of the MH⁺ ions at low collision energies produce b₇, b_6, and b₅ ions. As the collision energy is increased further fragmentation of these primary products produces, in part, non-direct sequence ions, which become prominent at lower m/z values, particularly for the peptides with the Met residue near the N-terminus.

Inclusion Complexes of Ionic Liquids and Cyclodextrins: Are They Formed in the Gas Phase?

The interaction of imidazolium-based ionic liquids with α- and β-cyclodextrins was investigated by electrospray ionization mass spectrometry with variable collision induced dissociation energy and quantum chemical gas-phase calculations. The center-of-mass energy at which 50 % of a precursor ion decomposes (E_cm,1/2) was determined for the isolated [cyclodextrin + cation]⁺ or [cyclodextrin + anion]^– adduct ions of imidazolium-based ionic liquids with different alkyl chain lengths combined with a large set of anions, such as chloride, bromide, bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, trifluoromethanesulfonate, methanesulfonate, dicyanamide, and hydrogensulfate. Moreover, both symmetric and asymmetric imidazolium cationic cores were evaluated. The relative interaction energies in the adduct ions were interpreted in terms of the influence of cation/anion structures and their inherent properties, such as hydrophobicity and hydrogen bond accepting ability, in the complexation process with the cyclodextrins. The trends observed in the mass spectral data together with quantum-chemical calculations suggest that in the gas phase, cations and anions will preferentially interact with the lower or upper rim of the cyclodextrin, respectively, as opposed to what has been reported in condensed phase where the formation of an inclusion complex between ionic liquid and cyclodextrin is assumed.

Detection of trace nitrite in waters using a QDs-based chemiluminescence analysis system

In the present work, a novel flow-injection chemiluminescence method based on CdTe quantum dots (QDs) was developed for the determination of nitrite. Weak chemiluminescence (CL) signals were observed from a CdTe QDs–H₂O₂ system under basic conditions. The addition of a trace amount of hemoglobin (Hb) caused the CL from the CdTe QDs–H₂O₂ system to increase substantially. In the presence of nitrite, the ferrous Hb reacted with the nitrate to form ferric Hb and NO. The NO then bound to ferrous Hb to generate iron nitrosyl Hb. As a result, the CL signal from the CdTe QDs–H₂O₂–Hb system was quenched. Thus, a flow-injection CL analytical system for the determination of trace nitrite was established. Under optimum conditions, there was a good linear relationship between CL intensity and the concentration of nitrite in the range 1.0?×?10^?9 to 8.0?×?10^?7 mol L^?1 (R ²?=?0.9957). The limit of detection for nitrite using this system was 3.0?×?10^?10 mol L^?1 (S/N?=?3). This method was successfully applied to detect nitrite in water samples.

Mononuclear copper(II) complexes of bis-triazole-based macrocyclic Schiff base hydrazones: direct synthesis,EPR studies,magnetic and thermal properties

Mononuclear copper(II) complexes of 1,2,4-triazole-based Schiff base macrocyclic hydrazones, III and IV, have been reported. The prepared amorphous complexes have been characterized by spectroscopic methods, electron spray ionization mass spectrometry, and elemental analysis data. Electrochemical studies of the complexes in DMSO show only one quasi-reversible reduction wave at +0.43 V (ΔE = 70 mV) and +0.42 V (ΔE = 310 mV) for III and IV, respectively, which is assigned to the Cu(II) → Cu(I) reduction process. Temperature dependence of magnetic susceptibilities of III and IV has been measured within an interval of 2–290 K. The values of χ_M at 290 K are 1.72 × 10^?3 cm³ mol^?1 and 1.71 × 10^?3 for III and IV, respectively, which increases continuously upon cooling to 2 K. EPR spectra of III and IV in frozen DMSO and DMF were also reported. The trend g_|| > g⊥ > g_e suggests the presence of an unpaired electron in the d_x2?y2 orbital of the Cu(II) in both complexes. Furthermore, spectral and antimicrobial properties of the prepared complexes were also investigated.     

Determination of phthalate esters in edible oils by use of QuEChERS coupled with ionic-liquid-based dispersive liquid–liquid microextraction before high-performance liquid chromatography

A selective and low organic-solvent-consuming method of sample preparation combined with high-performance liquid chromatography with diode-array detection is introduced for analysis of phthalic acid esters in edible oils. Sample treatment involves initial liquid–liquid partitioning with acetonitrile, then QuEChERS cleanup by dispersive solid-phase extraction with primary secondary amine as sorbent. Preconcentration of the analytes is performed by ionic-liquid-based dispersive liquid–liquid microextraction, with the cleaned-up extract as disperser solvent and 1-hexyl-3-methylimidazolium hexafluorophosphate as extraction solvent. Under the optimized conditions, correlation coefficients (r) were 0.998–0.999 and standard errors (S _y/x ) were 2.67–3.37?×?10³ for calibration curves in the range 50–1000 ng g^?1. Detection limits, at a signal-to-noise ratio of 3, ranged from 6 to 9 ng g^?1. Intra-day and inter-day repeatability, expressed as relative standard deviation, were in the ranges 1.0–6.9 % and 2.4–9.4 %, respectively. Recovery varied between 84 % and 106 %. The developed method was successfully used for analysis of the analytes in 28 edible oils. The dibutyl phthalate content of four of the 28 samples (14 %) exceeded the specific migration limit established by domestic and international regulations.

On-line species-unspecific isotope dilution analysis in the picomolar range reveals the time- and species-depending mercury uptake in human astrocytes

In order to reveal the time-depending mercury species uptake by human astrocytes, a novel approach for total mercury analysis is presented, which uses an accelerated sample introduction system combined on-line with an inductively coupled plasma mass spectrometer equipped with a collision/reaction cell. Human astrocyte samples were incubated with inorganic mercury (HgCl₂), methylmercury chloride (MeHgCl), and thimerosal. After 1-h incubation with Hg²⁺, cellular concentrations of 3 μM were obtained, whereas for organic species, concentrations of 14–18 μM could be found. After 24 h, a cellular accumulation factor of 0.3 was observed for the cells incubated with Hg²⁺, whereas the organic species both showed values of about 5. Due to the obtained steady-state signals, reliable results with relative standard deviations of well below 5 % and limits of detection in the concentration range of 1 ng L^?1 were obtained using external calibration and species-unspecific isotope dilution analysis approaches. The results were further validated using atomic fluorescence spectrometry.