Conformational analysis of synthetic neolignans active against leishmaniasis,using the molecular mechanics method (MM2)

Conformational analysis of 20 neolignans was performed to determine the most probable conformer that may fit the receptor. The molecular mechanics method (MM2) was employed to construct conformational maps in both a vacuum and a biological environment. Boltzmann's distribution among several local minima was calculated. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 712–721, 1997     

Trends in anomalous small-angle X-ray scattering in grazing incidence for supported nanoalloyed and core-shell metallic nanoparticles

As atomic structure and morphology of particles are directly correlated to their functional properties, experimental methods probing local and average features of particles at the nanoscale elicit a growing interest. Anomalous small-angle X-ray scattering (ASAXS) is a very attractive technique to investigate the size, shape and spatial distribution of nanoobjects embedded in a homogeneous matrix or in porous media. The anomalous variation of the scattering factor close to an absorption edge enables element specific investigations. In the case of supported nano-objects, the use of grazing incidence is necessary to limit the probed depth. The combination of grazing incidence with the anomalous technique provides a powerful new method, anomalous grazing incidence small-angle X-ray scattering (AGISAXS), to disentangle complex chemical patterns in supported multi-component nano-structures. Nevertheless, a proper data analysis requires accurate quantitative measurements associated to an adapted theoretical framework. This paper presents anomalous methods applied to nanoalloys phase separation in the 1–10 nm size range, and focuses on the application of AGISAXS in bimetallic systems: nanocomposite films and core-shell supported nanoparticles.     

垂直氧化锌纳米线中的激射现象

通过水热的方法以退火0.5 h的ZnO薄膜作为籽晶,得到垂直的ZnO纳米线.在X射线衍射谱中,除了Si的(400)衍射峰以外,只观察到了ZnO的(002)衍射峰.室温光致发光谱中出现了强的紫外发射峰,同时也伴随着弱的缺陷相关的发射.这些数据表明垂直的ZnO纳米线序列有着较好的晶体质量.同时,通过光泵浦也观察到了ZnO纳...     

Negative ion fragmentations of deprotonated peptides. The unusual case of isoAsp: a joint experimental and theoretical study. Comparison with positive ion cleavages

The following peptides have been examined in this study: GLDFG(OH), caeridin 1.1 [GLLDGLLGLGGL(NH₂)], 11 Ala citropin 1.1 [GLFDVIKKVAAVIGGL(NH₂)], Crinia angiotensin [APGDRIYVHPF(OH)] and their isoAsp isomers. It is not possible to differentiate between Asp‐ and isoAsp‐containing peptides (used in this study) using negative ion electrospray mass spectrometry. This is because the isoAsp residue cleaves to give the same fragment anions as those formed by δ and γ backbone cleavage of Asp. The isoAsp fragmentations are as follows: RNHCH(CO₂H)^?CHCONHR′ → [RNH^?(HO₂CCH?CHCONHR′)] → RNH^?+HO₂CCH?CHCONHR′ and RNHCH(CO₂H)^?CHCONHR′ → [RNH^?(HO₂CCH?CHCONHR′] → ^?O₂CCH?CHCONHR′+RNH₂. Calculations at the HF/6‐31+G(d)//AM1 level of theory indicate that the first of these isoAsp cleavage processes is endothermic (by +115 kJ mol^?1), while the second is exothermic (?85 kJ mol^?1). The barrier to the highest transition state is 42 kJ mol^?1. No diagnostic cleavage cations were observed in the electrospray mass spectra of the MH⁺ ion of the Asp‐ and isoAsp‐containing peptides (used in this study) to allow differentiation between these two amino acid residues. Copyright © 2009 John Wiley & Sons, Ltd.     

The formation of the stable radicals .CH2CN, CH3.CHCN and .CH2CH2CN from the anions -CH2CN, CH3-CHCN and -CH2CH2CN in the gas phase. A joint experimental and theoretical study

Franck-Condon one-electron oxidation of the stable anions -CH2CN, CH3-CHCN and -CH2CH2CN (in the collision cell of a reverse-sector mass spectrometer) produce the radicals .CH2CN, CH3.CHCN and .CH2CH2CN, which neither rearrange nor decompose during the microsecond duration of the neutralisation-reionisation experiment. Acetonitrile (CH3CN) and propionitrile (CH3CH2CN) are known interstellar molecules and radical abstraction of these could produce energised .CH2CN and CH3.CHCN, which might react with NH2. (a known interstellar radical) on interstellar dust or ice surfaces to form NH2CH2CN and NH2CH(CH3)CN, precursors of the amino acids glycine and alanine.     

Controlling structure and morphology of CoPt nanoparticles through dynamical or static coalescence effects

The structure and morphology of 1 to 3 nm size CoPt nanoparticles have been investigated in situ and in real time under different conditions: growth at 500 degrees C or at room temperature (RT) followed by annealing at 500 degrees C. The small-angle x-ray scattering measurements show size and temperature dependent growth mode with particle motions on the surface, while wide-angle scattering results, supported by Monte Carlo simulations, allow structure identification. If icosahedra are systematically detected at the first growth stages at RT, annealing at 500 degrees C yields the decahedral structure from the quasistatic coalescence of icosahedral morphology. Meanwhile, growth at 500 degrees C proceeds by a dynamical coalescence mechanism at the early stage, yielding truncated octahedral cubic structures.     

Modelling of extreme wave heights and periods through copulas

Optimal design of coastal or offshore structures requires the estimation of extreme quantiles of oceanographic data such as wave heights and wave periods. Since there are strong correlations between oceanographic variables, it is necessary to use multivariate models in order to capture its dependencies. To achieve this, an approach based on copulas is proposed and is compared to a model based on the physical behaviour of waves.     

Real-time icosahedral to fcc structure transition during CoPt nanoparticles formation

Nucleation and growth of supported CoPt nanoparticles were studied in situ and in real time by combined grazing incidence small-angle x-ray scattering (GISAXS) and grazing incidence x-ray diffraction (GIXD). GISAXS provides morphological features of nanoparticles as a function of size, shape and correlation distance between particles, while GIXD allows the determination of the atomic structure. We focus on the formation of ultrasmall CoPt nanoparticles, in the 1–4 nm size range at 500^○C. The structural analysis method based on the Debye equation is coupled with cluster model calculations performed by Monte Carlo simulations using a semi-empirical tight-binding potential to interpret diffraction spectra and structural transitions. Our results show that the cluster structure evolution during the growth is size-dependent and composition-dependent, yielding an icosahedral to fcc structure transition.     

Physical–chemical characterization studies of ketoprofen for orodispersible tablets

The objective of this work was to investigate the thermal, morphological, spectroscopic and cytotoxicity of hydroxyapatite–wollastonite powders obtained via sol–gel synthesis and of biocomposites chitosan–hydroxyapatite–wollastonite. A mixture of wollastonite, calcium nitrate tetrahydrate and ammonium dihydrogen phosphate with a ratio of 1:2:1.2 or 2:2:1.2, respectively, was produced following drying and heat treatment where the final composite was macerated. These powders were added to a chitosan solution where it was further dried and neutralized. The ceramic loads were used in various ratios. The materials were characterized by TG, DSC, DRX, MEV, FTIR and cytotoxicity. Based on the studied properties, it can be said that the sol–gel process proved to be effective in obtaining hydroxyapatite–wollastonite powders. By TG, it was verified that the thermal stability of the powders increased when a greater percentage of wollastonite was used. For biocomposites with higher percentages of load, there was increase in thermal stability, probably attributed to the higher compaction of the biocomposites when compared to the pure. By DSC, there was a tendency of displacement of the endothermic and exothermic peaks, suggesting that the biocomposite with higher load has greater capacity of retention and interaction stronger with molecules of water, but also has greater thermal stability. The samples present biomaterial potential with prospects of endodontic use, which showed cell viability in L929 fibroblast cell culture above 70.00%.