Mechanism of the initial stages of nitrogen-doped single-walled carbon nanotube growth

We have studied the mechanism of the initial stages of nitrogen-doped single-walled carbon nanotube growth illustrated for the case of a floating catalyst chemical vapor deposition system, which uses carbon monoxide (CO) and ammonia (NH(3)) as precursors and iron as a catalyst. We performed first-principles electronic-structure calculations, fully incorporating the effects of spin polarization and magnetic moments, to investigate the bonding and chemistry of CO, NH(3), and their fragments on a model Fe(55) icosahedral cluster. A possible dissociation path for NH(3) to atomic nitrogen and hydrogen was identified, with a reaction barrier consistent with an experimentally determined value we measured by tandem infrared and mass spectrometry. Both C-C and C-N bond formation reactions were found to be barrierless and exothermic, while a parasitic reaction of HCN formation had a barrier of over 1 eV.     

Are electrophilicity and electrofugality related concepts? A density functional theory study

It is proposed that the electrofugality of a fragment within a molecule is determined by its group nucleophilicity. The variation of electrofugality should be tightly related to the electron releasing ability of the substituent attached to the electrofuge moiety. This contribution closes the set of relationships between philicity and fugality quantities: while nucleofugality appears related to the group electrophilicity of the leaving group, electrofugality is related to the group nucleophilicity of the permanent group.     

Reliable identification and quantification of volatile components of sage essential oil using ultra HRGC

Salvia officinalis (common sage) essential oil was chemically characterized by means of GC-MS, using 100 meter capillary columns with two different stationary phases. Identification of the analytes was carried out by means of the FFNSC mass spectrum library and the use of the Linear Retention Index (LRI) as an extra criterion of library searching. Quantitative analysis was also carried out by means of GC-FID with the internal standard method and the use of relative response factors determined for each chemical class of components. A total of 45 compounds were identified and quantified and reported with their experimental LRI values.     

Analysis of native carotenoid composition of sweet bell peppers by serially coupled C30 columns

Serial coupled columns reversed-phase separations in high-performance liquid chromatography can be a useful tool for the analysis of complex real samples. The great difficulties found when analyzing complex carotenoid samples, due to the high natural variability of these compounds, as well as to the presence of carotenoid esters, are well documented. In the present contribution, the applicability of connecting two C30 columns to increase significantly the separation power, resolution and peak capacity for the analysis of carotenoids in a complex carotenoid sample, like sweet bell peppers, has been shown for the first time. By using LC coupled to PDA/APCI-MS detectors, 56 different carotenoids have been detected in red sweet bell peppers. By using two serial coupled C30 columns a peak capacity of 95.4 was obtained, compared with 73 achieved using a single column. Moreover, resolution greatly improved between different critical peaks when using two serial coupled C30 columns, compared with a single column. Interestingly, free carotenoids, mono-esters and diesters were quantitatively equally represented (around 33% for each different class) in red sweet bell pepper, showing, therefore, a value for the ratio of mono-esters/diesters of around 1, which could be considered a parameter of typicality. Free beta-carotene (12.6%), capsanthin-C14:0 (8.4%), and capsanthin-C12:0-C14:0 (8.9%) were the most abundant carotenoids in the three different classes of red sweet bell pepper. No carotenoid esters were detected in either yellow or green sweet bell peppers. The application of such methodology in the analysis of other complex carotenoid matrices could be a future objective of research.     

Nonlocal cauchy problems and their controllability for semilinear differential inclusions with lower Scorza-Dragoni nonlinearities

In this paper we prove the existence of mild solutions and the controllability for semilinear differential inclusions with nonlocal conditions. Our results extend some recent theorems.     

A new family of regular semivalues and applications

We define a new family of values for cooperative games, including as a particular case the Shapley value. They are defined on the collection of the unanimity games, then extended by linearity. Our most relevant result shows that the family of the weighting coefficients characterizing the values so defined is an open curve on the simplex of the regular semivalues. We give an explicit formula for the values when the parameter characterizing the family is a natural number and we offer an algorithm to calculate them in weighted majority games, slightly extending previous results (see Bilbao et al., TOP, 8:191–213, 2000). The paper ends with two applications. The first one is classical, and serves to see how the indices behave with respect to the Shapley and Banzhaf values in the case of the EU parliament and in the UN Security Council. The second one is much more recent: it deals with the microarray games, introduced in Moretti et al. (TOP, 15:256–280, 2007), which are average of unanimity games. The idea is to rank genes taken from DNA of patients affected by a specific disease, with the aim of singling out a group of genes potentially responsible of the disease. In this last case we consider some microarray data available on the net and concerning some specific diseases and we show that several genes mentioned in the medical literature as potentially responsible for the onset of the disease are present in the first places according to our rankings.     

CE analysis and molecular characterisation of depurinated DNA samples

A DNA sample was partially degraded by scalar heat-acid treatments to study the extent of apurinic-apyrimidinic (A-P) lesions produced along the molecule. A CE-UV method allowed us to measure the rate of depurination at pH 5.0 and 70°C which was calculated to be 5.41×10(-6) s(-1) for adenine and 6.27×10(-6) s(-1) for guanine. CE identified depurination on treated samples when it occurred with a loss of >4% of the basic moieties. The molecular features of the A-P enriched samples were investigated by using molecular assays (agarose gel electrophoresis, UV spectrophotometry and quantitative PCR) and the consistency of the results of the STR typing were compared with the degree of depurination of the PCR template. The treated DNA samples showed molecular features such as fragmentation, altered OD(260) /OD(280) ratios and decreased ability of the quantitative PCR to synthesise the human target, related to the severity of depurination. A satisfactory correlation between the degree of damage and the amount of residual PCR-sensitive target sequences was also demonstrated (r(2) =0.9717). The conventional and mini-STR typing of the samples showed that the genetic outcome was influenced by a depurination damage that exceeded 4% when locus drop-outs and artefactual PCR results were evident. As the success of STR typing depends on the integrity of the DNA recovered from the samples, the CE-UV, physical and molecular assays described here are proposed as a set of useful methods in the analysis of certain forensic and clinical samples, for a critical evaluation of the outcome of the genetic testing.     

IBIsCO: a molecular dynamics simulation package for coarse-grained simulation

IBIsCO is a parallel molecular dynamics simulation package developed specially for coarse-grained simulations with numerical potentials derived by the iterative Boltzmann inversion (IBI) method (Reith et al., J Comput Chem 2003, 24, 1624). In addition to common features of molecular dynamics programs, the techniques of dissipative particle dynamics (Groot and Warren, J Chem Phys 1997, 107, 4423) and Lowe-Andersen dynamics (Lowe, Europhys Lett 1999, 47, 145) are implemented, which can be used both as thermostats and as sources of friction to compensate the loss of degrees of freedom by coarse-graining. The reverse nonequilibrium molecular dynamics simulation method (Müller-Plathe, Phys Rev E 1999, 59, 4894) for the calculation of viscosities is also implemented. Details of the algorithms, functionalities, implementation, user interfaces, and file formats are described. The code is parallelized using PE_MPI on PowerPC architecture. The execution time scales satisfactorily with the number of processors.     

Development and validation of a solid-phase extraction method coupled to high-performance liquid chromatography with ultraviolet-diode array detection for the determination of sulfonylurea herbicide residues in bovine milk samples

This study proposes a fast, simple and sensitive liquid chromatography diode array detector (LC/UV-DAD)-based method for the simultaneous determination of eight sulfonylurea herbicides (bensulfuron methyl, chlorsulfuron, metsulfuron methyl, primisulfuron methyl, rimsulfuron, thifensulfuron methyl, triasulfuron and tribenuron methyl) in bovine whole milk at concentrations lower than the default limit of 0.01 mg kg(-1) allowed by current legislation (Regulation EC/396/2005 and following Annexes). An effective one-step solid phase extraction (SPE) and clean up procedure was defined with use of Chem Elut cartridges, providing good recoveries for all the analytes tested and with no matrix effects affecting method accuracy. Separation of herbicides was obtained on a C(18) column by acetonitrile- water gradient elution. Method validation has been performed according to European Commission Decision 2002/657/EC criteria, in terms of linearity, recovery, precision, specificity, decision limit (CC(α)) and detection capability (CC(β)). Typical recoveries ranged between 78.4% and 99.7%, at the maximum residue limits (MRLs) levels established by Regulation EC/396/2005, with relative standard deviations (RSD) no larger than 10%.