Some solutions to obtain very efficient separations in isocratic and gradient modes using small particles size and ultra-high pressure.

The UHPLC strategy which combines sub-2 microm porous particles and ultra-high pressure (>1000 bar) was investigated considering very high resolution criteria in both isocratic and gradient modes, with mobile phase temperatures between 30 and 90 degrees C. In isocratic mode, experimental conditions to reach the maximal efficiency were determined using the kinetic plot representation for DeltaP(max)=1000 bar. It has been first confirmed that the molecular weight of the compounds (MW) was a critical parameter which should be considered in the construction of such curves. With a MW around 1000 g mol(-1), efficiencies as high as 300,000 plates could be theoretically attained using UHPLC at 30 degrees C. By limiting the column length to 450 mm, the maximal plate count was around 100,000. In gradient mode, the longest column does not provide the maximal peak capacity for a given analysis time in UHPLC. This was attributed to the fact that peak capacity is not only related to the plate number but also to column dead time. Therefore, a compromise should be found and a 150 mm column should be preferentially selected for gradient lengths up to 60 min at 30 degrees C, while the columns coupled in series (3x 150 mm) were attractive only for t(grad)>250 min. Compared to 30 degrees C, peak capacities were increased by about 20-30% for a constant gradient length at 90 degrees C and gradient time decreased by 2-fold for an identical peak capacity.

Oscillation modes of microtubules.

Microtubules are long, filamentous protein complexes which play a central role in several cellular physiological processes, such as cell division transport and locomotion. Their mechanical properties are extremely important since they determine the biological function. In a recently published experiment [Phys. Rev. Lett. 89 (2002) 248101], microtubule's Young's and shear moduli were simultaneously measured, proving that they are highly anisotropic. Together with the known structure, this finding opens the way to better understand and predict their mechanical behavior under a particular set of conditions. In the present study, we modeled microtubules by using the finite elements method and analyzed their oscillation modes. The analysis revealed that oscillation modes involving a change in the diameter of the microtubules strongly depend on the shear modulus. In these modes, the correlation times of the movements are just slightly shorter than diffusion times of free molecules surrounding the microtubule. It could be therefore speculated that the matching of the two timescales could play a role in facilitating the interactions between microtubules and MT associated proteins, and between microtubules and tubulins themselves.

Dispersal modes and fruiting periods in hyperseasonal and seasonal savannas, central Brazil

Seasonal savannas are characterized by an intense drought that influences their functioning. Hyperseasonal savannas experience additionally a waterlogging during the rainy season. In South America, the largest savanna environment is the Brazilian cerrado. To assess whether a particular dispersal mode or fruiting period is associated to the waterlogging, we examined dispersal and phenological groups in hyperseasonal and seasonal cerrado plant species. We compared the proportion of species and individuals in these groups with G-tests for independence in contingency tables. We did not find differences in the proportion of species; however, based on the proportion of individuals, the main dispersal strategy was anemochory in the hyperseasonal cerrado and zoochory in the seasonal cerrado. Phenological strategies of fruiting in safe periods of the year were differently selected in both cerrados. In the hyperseasonal cerrado, most individuals fruited in non-waterlogged periods, whereas in the seasonal cerrado, most individuals fruited in wetter periods. Thus, waterlogging may drive important modifications in the efficiency of the dispersal and phenological strategies of hyperseasonal savannas plants.

Investigation of the composition of linear alkylbenzenes with emphasis on the identification and quantitation of some trace compounds using GS/MS system in both electron impact and chemical ionization modes

Linear alkylbenzenes, LAB, formed by the Alel3 or HF catalyzed alkylation of benzene are common raw materials for surfactant manufacture. Normally they are sulphonated using S03 or oleum to give the corresponding linear alkylbenzene sulphonates In >95 % yield. As concern has grown about the environmental impact of surfactants,' questions have been raised about the trace levels of unreacted raw materials, linear alkylbenzenes and minor impurities present in them. With the advent of modem analytical instruments and techniques, namely GCIMS, the opportunity has arisen to identify the exact nature of these impurities and to determine the actual levels of them present in the commercial linear ,alkylbenzenes. The object of the proposed study was to separate, identify and quantify major and minor components (1-10%) in commercial linear alkylbenzenes. The focus of this study was on the structure elucidation and determination of impurities and on the qualitative determination of them in all analyzed linear alkylbenzene samples. A gas chromatography/mass spectrometry, (GCIMS) study was performed o~ five samples from the same manufacturer (different production dates) and then it was followed by the analyses of ten commercial linear alkylbenzenes from four different suppliers. All the major components, namely linear alkylbenzene isomers, followed the same elution pattern with the 2-phenyl isomer eluting last. The individual isomers were identified by interpretation of their electron impact and chemical ionization mass spectra. The percent isomer distribution was found to be different from sample to sample. Average molecular weights were calculated using two methods, GC and GCIMS, and compared with the results reported on the Certificate of Analyses (C.O.A.) provided by the manufacturers of commercial linear alkylbenzenes. The GC results in most cases agreed with the reported values, whereas GC/MS results were significantly lower, between 0.41 and 3.29 amu. The minor components, impurities such as branched alkylbenzenes and dialkyltetralins eluted according to their molecular weights. Their fragmentation patterns were studied using electron impact ionization mode and their molecular weight ions confirmed by a 'soft ionization technique', chemical ionization. The level of impurities present i~ the analyzed commercial linear alkylbenzenes was expressed as the percent of the total sample weight, as well as, in mg/g. The percent of impurities was observed to vary between 4.5 % and 16.8 % with the highest being in sample "I". Quantitation (mg/g) of impurities such as branched alkylbenzenes and dialkyltetralins was done using cis/trans-l,4,6,7-tetramethyltetralin as an internal standard. Samples were analyzed using .GC/MS system operating under full scan and single ion monitoring data acquisition modes. The latter data acquisition mode, which offers higher sensitivity, was used to analyze all samples under investigation for presence of linear dialkyltetralins. Dialkyltetralins were reported quantitatively, whereas branched alkylbenzenes were reported semi-qualitatively. The GC/MS method that was developed during the course of this study allowed identification of some other trace impurities present in commercial LABs. Compounds such as non-linear dialkyltetralins, dialkylindanes, diphenylalkanes and alkylnaphthalenes were identified but their detailed structure elucidation and the quantitation was beyond the scope of this study. However, further investigation of these compounds will be the subject of a future study.

Analyse comparee des modes d'adjudication appliques aux bons du tresor.

Rapport de recherche

On the relationship of normal modes to local modes in molecular vibrations

A simple model for the effective vibrational hamiltonian of the XH stretching vibrations in H2O, NH3 and CH4 is considered, based on a morse potential function for the bond stretches plus potential and kinetic energy coupling between pairs of bond oscillators. It is shown that this model can be set up as a matrix in local mode basis functions, or as a matrix in normal mode basis functions, leading to identical results. The energy levels obtained exhibit normal mode patterns at low vibrational excitation, and local mode patterns at high excitation. When the hamiltonian is set up in the normal mode basis it is shown that Darling-Dennison resonances must be included, and simple relations are found to exist between the xrs, gtt, and Krrss anharmonic constants (where the Darling-Dennison coefficients are denoted K) due to their contributions from morse anharmonicity in the bond stretches. The importance of the Darling-Dennison resonances is stressed. The relationship of the two alternative representations of this local mode/normal mode model are investigated, and the potential uses and limitations of the model are discussed.

Coordination modes of 3-aminosalicylic and 3-hydroxyanthranilic acids in palladium(II), platinum(II) and rhenium(V) complexes. The crystal structure of cis-[Pt(HsalNH)(PPh3)(2)] (.) 0.25C(2)H(5)OH

New Pd(II), Pt(II) and Re(V) complexes of 3-aminosalicylic acid (H(2)salNH(2)) and 3-hydroxyantranilic acid (HantOH) have been prepared, cis-[Pt (HsalNH)(PPh3)(2)] center dot 0.25C(2)H(5)OH (1), trans-[PdCl(salNH(2))(PPh3)(2)](2), trans-[ReOI2(HsalNH(2))(PPh3)] center dot (CH3)(2)CO (3), cis-[Pt(HantO)(PPh3)(2)] (4), trans-[PdCl(antOH)(PPh3)(2)] center dot 4H(2)O (5), [PdCl(antOH)(bipy)] center dot C2H5OH (6), [PdCl2(HantOH)(2)] (7) and trans-[ReOI(HantO)(PPh3)(2)] center dot (CH3)(2)CO (8). The crystal structure of complex I was determined showing chelation of HsalNH(2-) through the adjacent nitrogen and oxygen atoms of the amino and phenolate groups. Infrared and H-1 NMR spectroscopic data for the complexes are presented. (c) 2005 Elsevier Ltd. All rights reserved.

Consequences of N,C,N '- and C,N,N '-coordination modes on electronic and photophysical properties of cyclometalated aryl ruthenium(II) complexes

The effects of isoelectronic replacement of a neutral nitrogen donor atom by an anionic carbon atom in terpyridine ruthenium(II) complexes on the electronic and photophysical properties of the resulting N,C,N'- and C,N,N'-cyclometalated aryl ruthenium(II) complexes were investigated. To this end, a series of complexes was prepared either with ligands containing exclusively nitrogen donor atoms, that is, [Ru(R-1-tpy)(R-2-tpy)](2+) (R-1, R-2 = H, CO2Et), or bearing either one N,C,N'- or C,N,N'-cyclometalated ligand and one tpy ligand, that is, [Ru(R-1-(NCN)-C-Lambda-N-Lambda)(R-2-tpy)](+) and [Ru(R-1-(CNN)-N-Lambda-N-Lambda)(R-2-tpy)](+), respectively. Single-crystal X-ray structure determinations showed that cyclometalation does not significantly alter the overall geometry of the complexes but does change the bond lengths around the ruthenium(II) center, especially the nitrogen-to-ruthenium bond length trans to the carbanion. Substitution of either of the ligands with electron-withdrawing ester functionalities fine-tuned the electronic properties and resulted in the presence of an IR probe. Using trends obtained from redox potentials, emission energies, IR spectroelectrochemical responses, and the character of the lowest unoccupied molecular orbitals from DFT studies, it is shown that the first reduction process and luminescence are associated with the ester-substituted C,N,N'-cyclometalated ligand in [Ru(EtO2C-(CNN)-N-Lambda-N-Lambda)(tpy)](+). Cyclometalation in an N,C,N'-bonding motif changed the energetic order of the ruthenium d(zx), d(yz), and d(xy) orbitals. The red-shifted absorption in the N,C,N'-cyclometalated complexes is assigned to MLCT transitions to the tpy ligand. The red shift observed upon introduction of the ester moiety is associated with an increase in intensity of low-energy transitions, rather than a red shift of the main transition. Cyclometalation in the C,N,N'-binding motif also red-shifts the absorption, but the corresponding transition is associated with both ligand types. Luminescence of the cyclometalated complexes is relatively independent of the mode of cyclometalation, obeying the energy gap law within each individual series.

Classification of instability modes in a model of aluminium reduction cells with a uniform magnetic field

A unified view on the interfacial instability in a model of aluminium reduction cells in the presence of a uniform, vertical, background magnetic field is presented. The classification of instability modes is based on the asymptotic theory for high values of parameter β, which characterises the ratio of the Lorentz force based on the disturbance current, and gravity. It is shown that the spectrum of the travelling waves consists of two parts independent of the horizontal cross-section of the cell: highly unstable wall modes and stable or weakly unstable centre, or Sele’s modes. The wall modes with the disturbance of the interface being localised at the sidewalls of the cell dominate the dynamics of instability. Sele’s modes are characterised by a distributed disturbance over the whole horizontal extent of the cell. As β increases these modes are stabilized by the field.

Molecular modelling studies of binding of DACD derivatives into G-Quadruplex DNA: comparison of force field and quantum polarized ligand docking methods

The DNA G-qadruplexes are one of the targets being actively explored for anti-cancer therapy by inhibiting them through small molecules. This computational study was conducted to predict the binding strengths and orientations of a set of novel dimethyl-amino-ethyl-acridine (DACA) analogues that are designed and synthesized in our laboratory, but did not diffract in Synchrotron light.Thecrystal structure of DNA G-Quadruplex(TGGGGT)4(PDB: 1O0K) was used as target for their binding properties in our studies.We used both the force field (FF) and QM/MM derived atomic charge schemes simultaneously for comparing the predictions of drug binding modes and their energetics. This study evaluates the comparative performance of fixed point charge based Glide XP docking and the quantum polarized ligand docking schemes. These results will provide insights on the effects of including or ignoring the drug-receptor interfacial polarization events in molecular docking simulations, which in turn, will aid the rational selection of computational methods at different levels of theory in future drug design programs. Plenty of molecular modelling tools and methods currently exist for modelling drug-receptor or protein-protein, or DNA-protein interactionssat different levels of complexities.Yet, the capasity of such tools to describevarious physico-chemical propertiesmore accuratelyis the next step ahead in currentresearch.Especially, the usage of most accurate methods in quantum mechanics(QM) is severely restricted by theirtedious nature. Though the usage of massively parallel super computing environments resulted in a tremendous improvement in molecular mechanics (MM) calculations like molecular dynamics,they are still capable of dealing with only a couple of tens to hundreds of atoms for QM methods. One such efficient strategy that utilizes thepowers of both MM and QM are the QM/MM hybrid methods. Lately, attempts have been directed towards the goal of deploying several different QM methods for betterment of force field based simulations, but with practical restrictions in place. One of such methods utilizes the inclusion of charge polarization events at the drug-receptor interface, that is not explicitly present in the MM FF.

Crystal structures of Λ-[Ru(phen)2dppz]2+ with oligonucleotides containing TA/TA and AT/AT steps show two intercalation modes

The ruthenium complex [Ru(phen)2(dppz)] (where phen is a phenanthroline and dppz a dipyridyl–phenazine ligand) is known as a ‘light switch’ complex because its luminescence in solution is significantly enhanced in the presence of DNA. This property is poised to serve in diagnostic and therapeutic applications, but its binding mode with DNA needs to be elucidated further. Here, we describe the crystal structures of the L enantiomer bound to two oligonucleotide duplexes. The dppz ligand intercalates symmetrically and perpendicularly from the minor groove of the d(CCGGTACCGG)2 duplex at the central TA/TA step, but not at the central AT/AT step of d(CCGGATCCGG)2. In both structures, however, a second ruthenium complex links the duplexes through the combination of a shallower angled intercalation into the C1C2/G9G10 step at the end of the duplex, and semi-intercalation into the G3G4 step of an adjacent duplex. The TA/TA specificity of the perpendicular intercalation arises from the packing of phenanthroline ligands against the adenosine residue.

Response of the North Atlantic wave climate to atmospheric modes of variability

This study investigates the relationship between the wind wave climate and the main climate modes of atmospheric variability in the North Atlantic Ocean. The modes considered are the North Atlantic Oscillation (NAO), the East Atlantic (EA) pattern, the East Atlantic Western Russian (EA/WR) pattern and the Scandinavian (SCAN) pattern. The wave dataset consists of buoys records, remote sensing altimetry observations and a numerical hindcast providing significant wave height (SWH), mean wave period (MWP) and mean wave direction (MWD) for the period 1989–2009. After evaluating the reliability of the hindcast, we focus on the impact of each mode on seasonal wave parameters and on the relative importance of wind-sea and swell components. Results demonstrate that the NAO and EA patterns are the most relevant, whereas EA/WR and SCAN patterns have a weaker impact on the North Atlantic wave climate variability. During their positive phases, both NAO and EA patterns are related to winter SWH at a rate that reaches 1 m per unit index along the Scottish coast (NAO) and Iberian coast (EA) patterns. In terms of winter MWD, the two modes induce a counterclockwise shift of up to 65° per negative NAO (positive EA) unit over west European coasts. They also increase the winter MWP in the North Sea and in the Bay of Biscay (up to 1 s per unit NAO) and along the western coasts of Europe and North Africa (1 s per unit EA). The impact of winter EA pattern on all wave parameters is mostly caused through the swell wave component.

Annular modes and apparent eddy feedbacks in the Southern Hemisphere

Lagged correlation analysis is often used to infer intraseasonal dynamical effects but is known to be affected by non-stationarity. We highlight a pronounced quasi-two-year peak in the anomalous zonal wind and eddy momentum flux convergence power spectra in the Southern Hemisphere, which is prima facie evidence for non-stationarity. We then investigate the consequences of this non-stationarity for the Southern Annular Mode and for eddy momentum flux convergence. We argue that positive lagged correlations previously attributed to the existence of an eddy feedback are more plausibly attributed to non-stationary interannual variability external to any potential feedback process in the mid-latitude troposphere. The findings have implications for the diagnosis of feedbacks in both models and re-analysis data as well as for understanding the mechanisms underlying variations in the zonal wind.