Dynamics of water molecules in the active-site cavity of human cytochromes P450

We have studied the dynamics of water molecules in six crystal structures of four human cytochromes P450, 2A6, 2C8, 2C9, and 3A4, with molecular dynamics simulations. In the crystal structures, only a few water molecules are seen and the reported sizes of the active-site cavity vary a lot. In the simulations, the cavities are completely filled with water molecules, although with approximately 20% lower density than in bulk water. The 2A6 protein differs from the other three in that it has a very small cavity with only two water molecules and no exchange with the surroundings. The other three proteins have quite big cavities, with 41 water molecules on average in 2C8 and 54-58 in 2C9 and 3A4, giving a water volume of 1500-2100 A3. The two crystal structures of 2C9 differ quite appreciably, whereas those of 3A4 are quite similar. The active-site cavity is connected to the surroundings by three to six channels, through which there is a quite frequent exchange of water molecules (one molecule is exchanged every 30-200 ps), except in 2A6. Most of the channels are observed also in the crystal structures, but two to three channels in each protein open only during the simulations. There are no water molecules close to the heme iron ion in these simulations of the high-spin ferric state (the average distance to the closest water molecule is 3.3-5 A), and there are few ordered water molecules in the active sites, none of which is conserved in all proteins.     

Weyl product algebras and modulation spaces

We discuss algebraic properties of the Weyl product acting on modulation spaces. For a certain class of weight functions ω we prove that is an algebra under the Weyl product if p∈[1,∞] and 1?q?min(p,p^′). For the remaining cases p∈[1,∞] and min(p,p^′)<q?∞ we show that the unweighted spaces Mp,q are not algebras under the Weyl product.     

Continuous full filling capillary electrochromatography: nanoparticle synthesis and evaluation

Reversed phase continuous full filling capillary electrochromatography with electrospray ionisation mass spectrometric detection was performed with highly sulphated poly[styrene-co-(lauryl methacrylate)-co-(divinylbenzene)] nanoparticles. The nanoparticles that contained a hydrophobic core and a hydrophilic surface were prepared in a one step synthesis using soap free emulsion polymerisation. By changing the concentration of monomers, the polymerisation temperature, and the polarity of the dispersive phase, the size of the nanoparticles could be controlled. With the optimised conditions, nanoparticles with an average size of 157 nm were obtained. These nanoparticles were dispersed in the background electrolyte and used for reversed phase continuous full filling. An orthogonal electrospray ionisation interface was used to separate the eluting nanoparticles from the eluting analytes prior to mass spectrometry detection. Compared to previous studies on reversed phase continuous full filling, the retention, the separation efficiency, and the resolution of a homologous series of dialkyl phthalates were greatly improved.     

Continuous full filling capillary electrochromatography: chromatographic performance and reproducibility

Continuous full filling capillary electrochromatography with nanoparticles as pseudostationary phase interfaced with electrospray ionisation mass spectrometric detection was used for reversed phase separations with very high separation efficiency. Several batches of nanoparticles were synthesised and their electrochromatographic performance were evaluated. Different parameters, such as repeatability, reproducibility, limit of detection, and peak asymmetry, were investigated yielding excellent results. The stability of the system over wide pH ranges and over time was found to be excellent. Very high separation efficiencies with over 1.1 million theoretical plates per metre were obtained. The limit of detection for the investigated dialkyl phthalates was approximately 1.0 micromol L(-1), corresponding to 3-5 fmol injected. After preparation, nanoparticle suspensions could be used without further treatment for at least an entire working day with maintained chromatographic qualities.     

Tilted two-fluid Bianchi type I models

In this paper we investigate expanding Bianchi type I models with two tilted fluids with the same linear equation of state, characterized by the equation of state parameter w. Individually the fluids have non-zero energy fluxes w.r.t. the symmetry surfaces, but these cancel each other because of the Codazzi constraint. We prove that when w = 0 the model isotropizes to the future. Using numerical simulations and a linear analysis we also find the asymptotic states of models with w > 0. We find that future isotropization occurs if and only if w ￡ \frac13{w\leq \frac{1}{3}} . The results are compared to similar models investigated previously where the two fluids have different equation of state parameters.     

The quantification of carbon dioxide in humid air and exhaled breath by selected ion flow tube mass spectrometry

The reactions of carbon dioxide, CO₂, with the precursor ions used for selected ion flow tube mass spectrometry, SIFT‐MS, analyses, viz. H₃O⁺, NO⁺ and O, are so slow that the presence of CO₂ in exhaled breath has, until recently, not had to be accounted for in SIFT‐MS analyses of breath. This has, however, to be accounted for in the analysis of acetaldehyde in breath, because an overlap occurs of the monohydrate of protonated acetaldehyde and the weakly bound adduct ion, H₃O⁺CO₂, formed by the slow association reaction of the precursor ion H₃O⁺ with CO₂ molecules. The understanding of the kinetics of formation and the loss rates of the relevant ions gained from experimentation using the new generation of more sensitive SIFT‐MS instruments now allows accurate quantification of CO₂ in breath using the level of the H₃O⁺CO₂ adduct ion. However, this is complicated by the rapid reaction of H₃O⁺CO₂ with water vapour molecules, H₂O, that are in abundance in exhaled breath. Thus, a study has been carried out of the formation of this adduct ion by the slow three‐body association reaction of H₃O⁺ with CO₂ and its rapid loss in the two‐body reaction with H₂O molecules. It is seen that the signal level of the H₃O⁺CO₂ adduct ion is sensitively dependent on the humidity (H₂O concentration) of the sample to be analysed and a functional form of this dependence has been obtained. This has resulted in an appropriate extension of the SIFT‐MS software and kinetics library that allows accurate measurement of CO₂ levels in air samples, ranging from very low percentage levels (0.03% typical of tropospheric air) to the 6% level that is about the upper limit in exhaled breath. Thus, the level of CO₂ can be traced through single time exhalation cycles along with that of water vapour, also close to the 6% level, and of trace gas metabolites that are present at only a few parts‐per‐billion. This has added a further dimension to the analysis of major and trace compounds in breath using SIFT‐MS. Copyright © 2009 John Wiley & Sons, Ltd.     

X-ray induced photocatalysis on TiO2 and TiO2 nanotubes: Degradation of organics and drug release

The photocatalytic activity of titanium dioxide under X-ray radiation is of great interest for biomedical applications. In the present work we explore the use of compact TiO₂ layers and TiO₂ nanotubes for X-ray induced photocatalysis, in particular the degradation of organics and monolayer chain scission for drug release. The radiation was done with a conventional X-ray source and doses up to 50 × 10^?3 J/kg. The results show the feasibility of X-ray catalysis on TiO₂ and X-ray induced monolayer chain scission by the release of surface attached Zn–porphyrin molecules. Furthermore, a higher efficiency for anatase films and nanotubes is obtained than for amorphous morphologies.     

The importance of alkali cations in the [{RuCl2(p-cymene)}2]-pseudo-dipeptide-catalyzed enantioselective transfer hydrogenation of ketones

We studied the role of alkali cations in the [{RuCl2(p-cymene)}2]-pseudo-dipeptide-catalyzed enantioselective transfer hydrogenation of ketones with isopropanol. Lithium salts were shown to increase the enantioselectivity of the reaction when iPrONa or iPrOK was used as the base. Similar transfer-hydrogenation systems that employ chiral amino alcohol or monotosylated diamine ligands are not affected by the addition of lithium salts. These observations have led us to propose that an alternative reaction mechanism operates in pseudo-dipeptide-based systems, in which the alkali cation is an important player in the ligand-assisted hydrogen-transfer step. DFT calculations of the proposed transition-state (TS) models involving different cations (Li+, Na+, and K+) confirm a considerable loosening of the TS with larger cations. This loosening may be responsible for the fewer interactions between the substrate and the catalytic complex, leading to lower enantiodifferentiation. This mechanistic hypothesis has found additional experimental support; the low ee obtained with [BnNMe3]OH (a large cation) as base can be dramatically improved by introducing lithium cations into the system. Also, the complexation of Na+, K+, and Li+ cations by the addition of [15]crown-5 and [18]crown-6 ethers and cryptand 2.1.1 (which selectively bind to these cations and, thus, increase their bulkiness), respectively, to the reaction mixture led to a significant drop in the enantioselectivity of the reaction. The lithium effect has proved useful for enhancing the reduction of different aromatic and heteroaromatic ketones.     

Study of synthesis of 2‐(2‐alkoxyphenyl)‐1H‐imidazoles. Comparison of oxidative aromatization reactions of imidazolines

The reaction of methyl salicylate with ethane‐1,2‐diamine has been used to prepare 2‐(2‐hydroxyphenyl)‐1H‐imidazoline. This compound was alkylated with alkyl halides to give five new 2‐(2‐alkoxyphenyl)‐1H‐imidazolines (alkyl = propyl, isopropyl, isobutyl, sec‐butyl, benzyl). Seven types of transformation reactions of imidazolines into the respective imidazoles were tested. Out of them successful were the dehydrogenation on palladium in toluene (several‐day refluxing), oxidation with activated manganese dioxide in toluene (several‐hour heating at 60 °C), and the oxidation with potassium nitrosodisulfonate (Fremy's salt) at room temperature. Seven new 2‐(2‐alkoxyphenyl)‐1H‐imidazoles were synthesized (alkyl = ethyl, propyl, isopropyl, butyl, isobutyl, sec‐butyl, benzyl) via mentioned methods. Comparison of individual oxidative aromatization reactions is discussed from the point of view of experimental arrangement, reaction time and conditions, purity of the products obtained, and yields.     

Validation of the extended Tanaka column characterization protocol by multivariate analysis of chromatographic retention of low‐molecular‐weight analytes on reversed phase columns using methanol and acetonitrile as organic modifiers

The validity of the extended Tanaka column characterization procedure against the retention behavior of 101 analytes of widely differing properties chromatographed on five differing stationary phase chemistries has been established using a chemometric technique called principal component analysis (PCA). It was concluded that the simple and conveniently determined column characterization parameters covered the same space in the PCA loading plot as the retention times for the 101 differing analytes. This confirms that the ten column characterization parameters of the extended Tanaka protocol encode the same information as the retention times of the 101 analytes. Significant selectivity differences were observed between stationary phases and the mobile‐phase modifiers – MeOH and MeCN. PCA contribution plots served as a convenient way to highlight specific selectivity differences between stationary phases. logD values exhibited a poor correlation with retention indicating that retention in RP‐LC is not solely dictated by the analyte's hydrophobicity. The use of MeOH was found to generate greater selectivity differences with the five stationary phases than when MeCN is used.