Search results for "ORBIT"
showing 10 items of 1104 documents
Improving the local vertex invariants in alkane graphs through a standard molecular orbital approach
2007
Abstract In this work, novel topological indices are introduced by the application of algorithms based on molecular orbital theory. Actually, the novel indices are obtained by computing new values of the local vertex invariants (LOVIs) in alkane graphs. The most significant result is the dramatic increase in the predictive capability achieved with the topological charge indices weighted according the new LOVIs’ values in the prediction of four key properties in the set of octane isomers, namely heat of atomization, molar refraction, heat of vaporization and boiling point.
Cu–Cu interactions in the transparent p-type conductors: CuAlO2 and SrCu2O2
2003
Abstract Electronic structures of the p-type Transparent Conducting Oxides (TCO): CuAlO2 and SrCu2O2 are calculated using the Tight Binding Linearized Muffin Tin Orbital within the Atomic Sphere Approximation method (TB-LMTO-ASA). The band structures indicate two gaps for CuAlO2 (an indirect one with ΔE≈0.45 eV and a direct one with ΔE≈1.25 eV) and one direct gap for SrCu2O2 (with ΔE≈2 eV). In both oxides the Cu states are dominant at the top of the valence band, close to the Fermi level and the existence of weak Cu–Cu bonding interactions is revealed through the Integrated Crystal Orbital Hamiltonian Population (ICOHP). The presence of such interactions suggests that for the hole doped oxi…
Ab initio molecular orbital study of the substituent effect on ammonia and phosphine–borane complexes
2004
Abstract The complexation energies of H 3 BXH 3− n F n ( X =N, P; n =0–3) and the proton affinities of XH 3– n F n compounds have been investigated at the G2(MP2) level of theory. The G2(MP2) results show that the phosphine complexes are more stable than the corresponding ammonia ones. Increasing fluorine substitution on nitrogen atom reduces both the basicity of NH 3− n F n and the stability of ammonia complexes. For the phosphine complexes, the successive fluorine substitution on the phosphine increase the stability of H 3 BPH 3− n F n complexes although the reduction of the basicity of the PH 3– n F n ligands with this substitution. The NBO partitioning scheme shows that the stability of…
Substituent effect on ammonia–borane donor–acceptor complexes: a G2(MP2) molecular orbital study
1998
Abstract H3BNHnMe3−n and Me3−nHnBNH3 (n=0–3) donor–acceptor complexes have been studied using the G2(MP2) method. Predicted equilibrium structures and dissociation energies have been correlated to the degree of substitution on the donor and the acceptor separately. It is found that successive methyl substitutions on boron reduce the dissociation energies of the complexes, contrary to the successive substitutions on nitrogen. The NBO partitioning scheme suggests that there is no correlation between the charge transfer and the dissociation energies. These results are interpreted in terms of the changes in the HOMO−LUMO gap, the type of acceptor and donor involved, and distortion of the accept…
Analytical capabilities of high performance liquid chromatography – Atmospheric pressure photoionization – Orbitrap mass spectrometry (HPLC-APPI-Orbi…
2015
A new analytical method was established and validated for the analysis of 27 brominated flame retardants (BFRs), including so called "emerging" and "novel" BFRs (EBFRs and NBFRs) in fish samples. High performance liquid chromatography (HPLC) coupled to Orbitrap mass spectrometry (Orbitrap-MS) employing atmospheric pressure photoionization (APPI) interface operated in negative mode was used for the identification/quantitation of contaminants. HPLC-Orbitrap-MS analysis provided a fast separation of selected analytes within 14 min, thus demonstrating a high throughput processing of samples. The developed methodology was tested by intralaboratory validation in terms of recovery, repeatability, …
Development of a Rapid Method for the Determination of Phenolic Antioxidants in Dark Chocolate Using Ultra Performance Liquid Chromatography Coupled …
2017
Development of a new comprehensive method based on one-step liquid-liquid extraction (LLE) combined with ultra-high-performance liquid chromatography-Orbitrap high resolution mass spectrometry (UHPLC-Orbitrap-HRMS) for the determination of eight phenolic compounds in dark chocolate is demonstrated. The study focuses on the optimization of sample preparation, chromatographic separation and Orbitrap-HRMS detection parameters to adjust selectivity and sensitivity of the method. The LLE mixture of formic acid-water-acetonitrile (2:58:40, v/v) and hexane at the component ratio of 1:1 (v/v) was applied for sample preparation. The inter-day and intra-day precision expressed from the relative stand…
Application of ultra-high pressure liquid chromatography linear ion-trap orbitrap to qualitative and quantitative assessment of pesticide residues
2014
Abstract The analysis of pesticides residues using a last generation high resolution and high mass accuracy hybrid linear ion trap-Orbitrap mass spectrometer (LTQ-Orbitrap-MS) was explored. Pesticides were extracted from fruits, fish, bees and sediments by QuEChERS and from water by solid-phase with Oasis HLB cartridges. Ultra-high pressure liquid chromatography (UHPLC)–LTQ-Orbitrap mass spectrometer acquired full scan MS data for quantification, and data dependent (dd) MS 2 and MS 3 product ion spectra for identification and/or confirmation. The regression coefficients ( r 2 ) for the calibration curves (two order of magnitude up to the lowest calibration level) in the study were ≥0.99. Th…
Target analysis and retrospective screening of mycotoxins and pharmacologically active substances in milk using an ultra-high-performance liquid chro…
2020
Milk is a nutritious food suitable for infants and adults, and it plays an important role in the human diet. However, it may also be a vehicle for food contaminants. In this report, we developed a method using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-Q-Exactive Orbitrap HRMS; Thermo Fisher Scientific, Waltham, MA) for simultaneous identification of target pharmacologically active substances and mycotoxins in milk. We also used the Q-Orbitrap operating in full scan mode to identify other possible drugs and microbial metabolites that occurred in samples. Fifty-six commercially available milk samples from the Italian market were analyze…
Wide-range screening of banned veterinary drugs in urine by ultra high liquid chromatography coupled to high-resolution mass spectrometry
2012
In this work, an ultra high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) methodology is proposed for the multi-class multi-residue screening of banned and unauthorized veterinary drugs in bovine urine, using an Orbitrap Exactive™ analyzer working at a resolving power of 50,000 FWHM in full scan, both in positive and negative mode. The method currently covers 87 analytes belonging to different families such as steroid hormones, β-agonists, resorcylic acid lactones (RAL), stilbens, tranquillizers, nitroimidazoles, corticosteroids, NSAIDs, amphenicoles, thyreostatics and other substances such as dapsone. A database including the elemental composition, the po…
Applicability of hybrid linear ion trap-high resolution mass spectrometry and quadrupole-linear ion trap-mass spectrometry for mycotoxin analysis in …
2012
Abstract Recent developments in mass spectrometers have created a paradoxical situation; different mass spectrometers are available, each of them with their specific strengths and drawbacks. Hybrid instruments try to unify several advantages in one instrument. In this study two of wide-used hybrid instruments were compared: hybrid quadrupole-linear ion trap-mass spectrometry (QTRAP ® ) and the hybrid linear ion trap-high resolution mass spectrometry (LTQ-Orbitrap ® ). Both instruments were applied to detect the presence of 18 selected mycotoxins in baby food. Analytical parameters were validated according to 2002/657/CE. Limits of quantification (LOQs) obtained by QTRAP ® instrument ranged …