Combining silica-based adsorbents and SPME fibers in the extraction of the volatiles of beer: an exploratory study

A series of silica-based materials were employed as sorbents within solid-phase microextraction vials. The aim of the study was to evaluate the effect of an additional phase on the distribution of the volatile and less volatile analytes. The adsorption of six probe molecules, namely isoamyl acetate, ethyl hexanoate (ethyl caproate), phenylethyl alcohol, ethyl octanoate (ethyl caprilate), 2-phenylethyl acetate, and ethyl decanoate, was monitored by detecting the desorbed amount on a DVD–CAR–PDMS fiber from Pilsen beer. The microextraction process involved the presence of different silica-based phases produced via different methods: xerogel produced by hydrolytic and non-hydrolytic routes, aerogel, pyrogenic, and precipitated silica. The resulting data are discussed in correlation with sorbent texture properties (specific area and pore diameter). The modification of silica with alkyl groups also affects the preconcentrated amount of the target molecules in the headspace. The presence of sorbents was shown to affect the analyte signal more than the addition of NaCl or the use of ultrasound. Analyte’s equilibrium between fiber and sorbent     

Capillary electrophoresis-mass spectrometry characterisation of secondary metabolites from the antihyperglycaemic plant Genista tenera

Genista tenera is endemic to the Portuguese island of Madeira, where an infusion of the aerial parts of the plant is used in folk medicine as an antidiabetic agent. Consequently the medicinal properties of the secondary metabolites of this plant have been the subject of an ongoing study. A recently reported LC-MS method using a 100 min separation allowed identification of five flavonoid components in an extract of the aerial parts of this plant. In order to obtain additional information on the range and complexity of the plant's secondary metabolite components a CE-MS method has been developed and applied for the analysis of an extract of G. tenera. Twenty-six different components are distinguished in an analysis time of only 10 min. Results demonstrate that CE-MS/MS rapidly generates data complementary to those obtainable by LC-MS/MS and is particularly suited to the analysis of plant metabolites where concentration is not limiting.     

Nitrogen and water adsorption in aluminum methylphosphonate alpha: a molecular simulation study

We present here Monte Carlo simulation and experimental results on the adsorption of nitrogen and water in aluminum methylphosphonate polymorph alpha (AlMePO-alpha). We have assumed a detailed atomic model for the material, using experimental information to construct the simulation cell. Nitrogen was modeled with two different approaches: as a simple Lennard-Jones (LJ) sphere with no charges, and as a diatomic molecule with charges explicitly included. Water was represented by the TIP4P model. Experimental adsorption isotherms were used to tune the proposed molecular model for the adsorbent. Simulated adsorption capacities were in agreement with the experimental results obtained for the studied systems. The influence of the surface model on the adsorption behavior was taken into account by considering different values of the surface methyl group size parameter. Our results corroborate the strong sensitivity of the simulation results to this parameter, as previously observed by Schumacher and co-workers. It is also observed that charged models are essential to accurately describe the low-pressure region of the adsorption isotherm, where the solid-fluid interaction rules the system behavior. However, a simple uncharged molecular model for nitrogen is able to describe the three loci arrangement at maximum loading. Experimental and simulation results presented here also confirm the low water affinity of AlMePO-alpha. These results enforce the application of this methodology to achieve quantitative predictions on similar systems, with the appropriate transferability of the molecular parameters.     

A starburst-shaped heterometallic compound incorporating six densely packed gd(3+) ions

The heterotritopic ligand [bpy(DTTA)2]8- has two diethylenediamine-tetraacetate units for selective lanthanide(III) coordination and one bipyridine function for selective Fe(II) coordination. In aqueous solution and in the presence of these metals, the ligand is capable of self-assembly to form a rigid supramolecular metallostar structure, [Fe[Gd2bpy(DTTA)2(H2O)4]3]4-. We report here the physicochemical characterization of the dinuclear complex [Gd2bpy(DTTA)2(H2O)4]2- and the metallostar [Fe[Gd2bpy(DTTA)2(H2O)4]3]4- with regard to potential MRI contrast agent applications. A combination of pH potentiometry and 1H NMR spectroscopy has been used to determine protonation constants for the ligand [bpy(DTTA)2]8- and for the complexes [Fe[bpy(DTTA)2]3]22- and [Y2bpy(DTTA)2]2-. In addition, stability constants have been measured for the dinuclear chelates [M2bpy(DTTA)2]n- formed with M = Gd3+ and Zn2+ (log K(GdL) = 18.2; log K(ZnL) = 18.0; log K(ZnHL) = 3.4). A multiple field, variable-temperature 17O NMR and proton relaxivity study on [Gd2bpy(DTTA)2(H2O)4]2- and [Fe[Gd2bpy(DTTA)2(H2O)4]3](4-) yielded the parameters for water exchange and the rotational dynamics. The 17O chemical shifts are indicative of bishydration of the lanthanide ion. The exchange rates of the two inner-sphere water molecules are very similar in the dinuclear [Gd2bpy(DTTA)2(H2O)(4)]2- and in the metallostar (k(ex)298 = 8.1 +/- 0.3 x 10(6) and 7.4 +/- 0.2 x 10(6) s(-1), respectively), and are comparable to k(ex)298 for similar Gd(III) poly(amino carboxylates). The rotational dynamics of the metallostar has been described by means of the Lipari-Szabo approach, which involves separating global and local motions. The difference between the local and global rotational correlation times, tau(lO)298 = 190 +/- 15 ps and tau(gO)298 = 930 +/- 50 ps, respectively, shows that the metallostar is not completely rigid. However, the relatively high value of S2 = 0.60 +/- 0.04, describing the restriction of the local motions with regard to the global one, points to a limited flexibility compared with previously reported macromolecules such as dendrimers. As a result of the two inner-sphere water molecules, with their near-optimal exchange rate, and the limited flexibility, the metallostar has a remarkable molar proton relaxivity, particularly at high magnetic fields (r1 = 33.2 and 16.4 mM(-1) s(-1) at 60 and 200 MHz, respectively, at 25 degrees C). It packs six efficiently relaxing Gd(III) ions into a small molecular space, which leads, to the best of our knowledge, to the highest relaxivity per molecular mass ever reported for a Gd(III) complex. The [bpy(DTTA)2]8- ligand is also a prime candidate as a terminal ligand for constructing larger sized, Fe(II) (or Ru(II))-based metallostars or metallodendrimers loaded with Gd(III) on the surface.     

Induction of apoptosis by photoexcited tetracyclic compounds derivatives of benzo[b]thiophenes and pyridines

The antiproliferative activity, upon UVA irradiation, of two tetracyclic derivatives of benzo[b]thiophenes and pyridines, a benzo[b]thienopyridopyrimidone (1) and a thienocarboline (2), has been investigated in a panel of human tumor cell lines. The two compounds present a remarkable cytotoxicity after UVA irradiation (365 nm), reaching an IC50 of 0.1 microM in the leukaemia cell lines and 0.3-0.5 microM in the solid tumour cell lines. Their effect on the cell cycle was measured by flow cytometry in Jurkat cells. The compounds induce cell cycle perturbations and trigger a massive apoptosis as revealed by the externalisation of Annexin V-targeted residues at the outer plasmatic membrane. Furthermore the drugs induce, upon UVA irradiation significant variations of the mitochondrial potential (Deltapsi(mt)) measured by flow cytometry using the fluorochrome JC-1. In addition we characterized the mitochondrial production of reactive oxygen species (ROS) using the probe dihydroethidine (HE) and the oxidations of the mitochondrial phospholipid cardiolipin using the interacting probe nonyl acridine orange (NAO). Both compounds stimulate the production of ROS, and remarkably induce oxidation of cardiolipin. We have investigated the DNA-binding properties of these two compounds by means of UV-Vis spectroscopy and fluorescence. The two compounds exhibit a low affinity toward the macromolecule. The mode of binding was also investigated by means of flow linear dichroism (LD) which has revealed that the two compounds do not efficiently intercalate into DNA. Finally, the DNA-photocleavaging properties of the test compounds were studied on pBR322 plasmid DNA as a model. Only compound 1 is able to induce a significant production of single strand breaks only after digestion with the base excision repair enzyme Endo III. Altogether these data suggest that DNA is not a preferential target of these molecules and other subcellular structures may be responsible for their high phototoxic activity.     

QTAIM charge-charge flux-dipole flux models for the infrared fundamental intensities of the fluorochloromethanes

The molecular dipole moments, their derivatives, and the fundamental IR intensities of the fluoro-, chloro-, and fluorochloromethanes are determined from QTAIM atomic charges and dipoles and their fluxes at the MP2/6-311++G(3d,3p) level. Root-mean-square (rms) errors of 0.01 D and 5.6 km mol(-1) are found for the dipole moments and fundamental IR intensities calculated using QTAIM parameters when compared with those obtained directly from the MP2/6-311++(3d,3p) calculations and 0.04 D and 23.1 km mol(-1) when compared with the experimental values. Charge, charge flux, and dipole flux contributions are calculated for all the normal vibrations of these molecules. A large negative correlation coefficient of -0.92 is calculated between the charge flux and dipole flux contributions and indicates that electron transfer from one side of the molecule to the other during vibrations is accompanied by relaxation with electron density polarization in the opposite direction. The CF, CCl, and CH stretching normal modes of these molecules are shown to have characteristic sets of charge, charge flux, and dipole flux contributions. Although the FCF and ClCCl deformation normal modes can also be discriminated from one another based on the sizes and signs of these contributions, some HCH deformations have contributions that are similar to those for some of the ClCCl deformations.     

Ground and lowest-lying electronic states of CoN. A multiconfigurational study

The lowest-lying X1Sigma+, a3Phi, b3II, c5Delta, A1Phi, and B1II electronic states of CoN have been investigated at the ab initio MRCI and MS-CASPT2 levels, with extended atomic basis sets and inclusion of scalar relativistic effects. Among the singlet states, the A1Phi and B1II states have been described for the first time. Potential energy curves, excitation energies, spectroscopic constants, and bonding character for all states are reported. Comparison with other early transition-metal nitrides (ScN, TiN, VN, and CrN), isoelectronic (NiC) and isovalent (RhN and IrN) species has been made, besides analyzing the B1II <=> X1+ electronic transition in terms of Franck-Condon factors, Einstein coefficients, and radiative lifetimes. At both levels of theory, the following energetic order has been obtained: X1Sigma+, a3Phi, b3II, c5Delta, A1Phi, and B1II, with good agreement with experimental results. In contrast, previous DFT and MRCI calculations predicted the ground state to be the 5Delta state.     

Enthalpy of formation of the cyclopentadienyl radical: photoacoustic calorimetry and ab initio studies

The gas-phase C-H bond dissociation enthalpy (BDE) in 1,3-cyclopentadiene has been determined by time-resolved photoacoustic calorimetry (TR-PAC) as 358 +/- 7 kJ mol(-1). Theoretical results from ab initio complete basis-set approaches, including the composite CBS-Q and CBS-QB3 procedures, and basis-set extrapolated coupled-cluster calculations (CCSD(T)) are reported. The CCSD(T) prediction for the C-H BDE of 1,3-cyclopentadiene (353.3 kJ mol(-1)) is in good agreement with the TR-PAC result. On the basis of the experimental and the theoretical values obtained, we recommend 355 +/- 8 kJ mol(-1) for the C-H BDE of 1,3-cyclopentadiene and 271 +/- 8 kJ mol(-1) for the enthalpy of formation of cyclopentadienyl radical.     

Photophysics of an indigo derivative (keto and leuco structures) with singular properties

Spectral and photophysical properties of the indigo derivative Cibalackrot in keto and reduced (leuco) forms were studied by absorption spectra, fluorescence and pulse radiolysis and compared with the structurally similar indigo. With the keto form of this dye, fluorescence (phiF = 0.76) and intersystem crossing (phiT = 0.11) are dominant, whereas with indigo, efficient internal conversion (phiIC = 0.99) is observed, probably involving proton transfer through intramolecular hydrogen bonds. With Cibalackrot, this pathway is blocked, supporting the above model for indigo. With the reduced form of Cibalackrot, more than 98% of the absorbed quanta are dissipated through S1 approximately --> S0 internal conversion, which contrasts with leuco-indigo, where fluorescence (phiF = 0.35), internal conversion (phiIC = 0.53) and intersystem crossing (phiT = 0.125) are found to be competitive. In addition, a synthetic precursor of Cibalackrot (preCiba) was also investigated. This has a rigid molecular structure (with a moiety identical to Cibalackrot and the other to indigo), but intra- or intermolecular proton transfer is allowed between adjacent carbonyl and N-H groups. With this precursor in its keto structure the photophysical parameters are generally very close to those of the keto form of indigo, and different from those of Cibalackrot. A more detailed investigation of the time-decay profiles of preCiba in dioxane (and with added water and D2O) has shown that these follow biexponential laws with a shorter component of 14-25 ps, which appears associated with a risetime at longer wavelength emissions (and to a positive preexponential at shorter emission wavelengths) and a longer lived (decay) component of 104-130 ps. In the steady-state spectra of preCiba, the variation with temperature reveals a blue shift of the emission maxima, which is interpreted as the presence (simultaneous emission) of two species (keto and enol) in the excited state. Indigo and deuterated indigo are also found to present a similar behavior. The overall data are interpreted as to be due to an excited-state process involving the proton transfer between keto and enol forms. Rate constants with values of 7 x 10(10) s-1 for preCiba and 1.6 x 10(11) s-1 for deuterated indigo were obtained. This inverse isotope effect is justified on the basis of the proposed model for proton-transfer excited-state deactivation.     

Proton transfer mediated by the vibronic coupling in oxygen core ionized states of glyoxalmonoxime studied by infrared-X-ray pump-probe spectroscopy

The theory of IR-X-ray pump-probe spectroscopy beyond the Born-Oppenheimer approximation is developed and applied to the study of the dynamics of intramolecular proton transfer in glyoxalmonoxime leading to the formation of the tautomer 2-nitrosoethenol. Due to the IR pump pulses the molecule gains sufficient energy to promote a proton to a weakly bound well. A femtosecond X-ray pulse snapshots the wave packet route and, hence, the dynamics of the proton transfer. The glyoxalmonoxime molecule contains two chemically nonequivalent oxygen atoms that possess distinct roles in the hydrogen bond, a hydrogen donor and an acceptor. Core ionizations of these form two intersecting core-ionized states, the vibronic coupling between which along the OH stretching mode partially delocalizes the core hole, resulting in a hopping of the core hole from one site to another. This, in turn, affects the dynamics of the proton transfer in the core-ionized state. The quantum dynamical simulations of X-ray photoelectron spectra of glyoxalmonoxime driven by strong IR pulses demonstrate the general applicability of the technique for studies of intramolecular proton transfer in systems with vibronic coupling.