3-D-electron microscopy configuration of TMOS wet silica gels prepared by the quick-freeze,deep-etching-rotary-replication technique

Silica gel provides a useful medium for crystal growth; solution growth is confined to pores left free by the polymer during its development. All growth steps depend on the gel structure, which is not completely known for crystal growth conditions. Therefore, a three-dimensional (3-D) visualization has been performed for two TMOS aqueous gels, which are rather fragile: the quick-freeze, deep-etching, rotary-replication method has been applied for sample preparation. An original surface labeling technique has been used for surface recognition. The results concern the distribution of macropores that are responsible for crystal nucleation; micropores whose total volume is larger have not been visualized due to the limits of the method. These results are discussed in comparison with previous data performed by light scattering.     

Buffer layer effect in nanostructured tin electrodeposition on insulating and conducting substrates

The electroplating techniques for metal aggregates and films deposition commonly use an electric current to reduce metal ions in solution, but are restricted to conducting substrate. This new electrochemical technique permits coating of insulating or conducting substrates with metals having controlled aggregate size and growth speed. The basis of our approach is the progressive outward growth of the metal from an electrode in contact with the substrate, with the cell geometry chosen in such a way that the electron current providing the reduction passes through the growing deposit. The nanostructured deposit is composed of branched nanoaggregates from a quasi-continuous film to a more dendritic morphology dependant on current conditions. This approach has been used to elaborate tin electrodeposited thin films composed of a homogeneous distribution of nanoparticles on conducting or insulating substrates. In our works, when a non-continuous buffer gold coating is used, spontaneous mixing of tin atoms into AuSn nanoparticles takes place even at room temperature forming a nanostructured fractal film, if the substrate is conducting or insulating. Without a gold buffer layer, the deposit is composed of large pure tin micro-crystals with a large size distribution, less adapted to tin oxide nanoparticle formation. Indeed, from these tin metal deposits, the final goal is to elaborate functional nanostructured tin oxide films by oxidation for gas sensor applications.     

Diagnostic di‐ and triphosphate cyclisation in the negative ion electrospray mass spectra of phosphoSer peptides

It has been shown previously that [M–H]^– anions of small peptides containing two phosphate residues undergo cyclisation of the phosphate groups, following collision‐induced dissociation (CID), to form a characteristic singly charged anion A (H₃P₂O₇^–, m/z 177). In the present study it is shown that the precursor anions derived from the diphosphopeptides of caerin 1.1 [GLLSVLGSVAKHVLPHVVPVIAEHL(NH₂)] and frenatin 3 [GLMSVLGHAVGNVLGGLFKPKS(OH)] also form the characteristic product anion A (m/z 177). Both of the precursor peptides show random structures in water, but partial helices in membrane‐mimicking solvents [e.g. in d₃‐trifluoroethanol/water (1:1)]. In both cases the diphosphopeptide precursor anions must have flexible conformations in order to allow approach of the phosphate groups with consequent formation of A: for example, the two pSer groups of 4,22‐diphosphofrenatin 3 are seventeen residues apart. Finally, CID tandem mass spectrometric (MS/MS) data from the [M–H]^– anion of the model triphosphoSer‐containing peptide GpSGLGpSGLGpSGL(OH) show the presence of both product anions A (m/z 177) and D (m/z 257, H₄P₃O₁₀^–). Ab initio calculations at the HF/6‐31+G(d)//AM1 level of theory suggest that cyclisation of the three phosphate groups occurs by a stepwise cascade mechanism in an energetically favourable reaction (ΔG = ?245 kJ mol^–1) with a maximum barrier of +123 kJ mol^–1. Copyright © 2011 John Wiley & Sons, Ltd.     

Bioactivity and chemical composition of the essential oil from the leaves of Guatteria australis A.St.-Hil

Essential oil from the leaves of Guatteria australis was obtained by hydrodistillation, analyzed by Gas Chromatography coupled to Mass Spectromery (GC–MS) and their antiproliferative, antileishmanial, antibacterial, antifungal and antioxidant activities were also evaluated. Twenty-three compounds were identified among which germacrene B (50.66%), germacrene D (22.22%) and (E)-caryophyllene (8.99%) were the main compounds. The highest antiproliferative activity was observed against NCI-ADR/RES (TGI = 31.08 μg/ml) and HT-29 (TGI = 32.81 μg/ml) cell lines. It also showed good antileishmanial activity against Leishmania infantum (IC₅₀ = 30.71 μg/ml). On the other hand, the oil exhibited a small effect against Staphylococcus aureus ATCC 6538, S. aureus ATCC 14458 and Escherichia coli ATCC 10799 (MIC = 250 μg/ml), as well as small antioxidant activity (457 μmol TE/g) assessed through ORAC_FL assay. These results represent the first report regarding chemical composition and bioactivity of G. australis essential oil.     

Negative ion fragmentations of deprotonated peptides containing post‐translational modifications. An unusual cyclisation/rearrangement involving phosphotyrosine; a joint experimental and theoretical study

The characteristic fragmentations of a pTyr group in the negative ion electrospray mass spectrum of the [M–H]^? anion of a peptide or protein involve the formation of PO (m/z 79) and the corresponding [(M‐H)^?–HPO₃]^? species. In some tetrapeptides where pTyr is the third residue, these characteristic anion fragmentations are accompanied by ions corresponding to H₂PO and [(M‐H)^?–H₃PO₄]^? (these are fragmentations normally indicating the presence of pSer or pThr). These product ions are formed by rearrangement processes which involve initial nucleophilic attack of a C‐terminal ‐CO [or ‐C(?NH)O^?] group at the phosphorus of the Tyr side chain [an S_N2(P) reaction]. The rearrangement reactions have been studied by ab initio calculations at the HF/6‐31+G(d)//AM1 level of theory. The study suggests the possibility of two processes following the initial S_N2(P) reaction. In the rearrangement (involving a C‐terminal carboxylate anion) with the lower energy reaction profile, the formation of the H₂PO and [(M‐H)^?–H₃PO₄]^? anions is endothermic by 180 and 318 kJ mol^?1, respectively, with a maximum barrier (to a transition state) of 229 kJ mol^?1. The energy required to form H₂PO by this rearrangement process is (i) more than that necessary to effect the characteristic formation of PO from pTyr, but (ii) comparable with that required to effect the characteristic α, β and γ backbone cleavages of peptide negative ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Stress distribution in L-shaped butt joint: Welded or bonded

The stresses in L-shaped butt joint, welded or bonded, are obtained by the finite element method. Correction for kinematic nonlinearity is made by including an upward movement of the joint. The local stress field behavior depends on the bead dimension, applied load and the governing material properties. The ways with which these parameters affect the joint behavior are investigated by comparing results obtained from a linear and nonlinear analysis.     

Characteristic negative ion fragmentations of deprotonated peptides containing post-translational modifications: mono-phosphorylated Ser, Thr and Tyr. A joint experimental and theoretical study

Peptides and proteins may contain post-translationally modified phosphorylated amino acid residues, in particular phosphorylated serine (pSer), threonine (pThr) and tyrosine (pTyr). Following earlier work by Lehmann et al., the [M-H]- anions of peptides containing pSer and pThr functionality show loss of the elements of H3PO4. This process, illustrated for Ser (and using a model system), is CH3CONH-C(CH2OPO3H2)CONHCH(3) --> [CH3CONHC(==CH2)CONHCH3 (-OPO3H2)] (a) --> [CH3CONHC(==CH2)CONHCH3-H]- + H3PO4, a process endothermic by 83 kJ mol(-1) at the MP2/6-31++G(d,p)//HF/6-31++G(d,p) level of theory. In addition, intermediate (a) may decompose to yield CH3CONHC(==CH2)CONHCH3 + H2PO4 - in a process exothermic by 3 kJ mol(-1). The barrier to the transition state for these two processes is 49 kJ mol(-1). Characteristic cleavages of pSer and pThr are more energetically favourable than the negative ion backbone cleavages of peptides described previously. In contrast, loss of HPO3 from [M-H]- is characteristic of pTyr. The cleavage [NH2CH(CH2-C6H4-OPO3H-)CO2H] --> [NH2C(CH2-C6H4-O-)CO2H (HPO3)] (b) --> NH2CH(CH2-C6H4-O-)CO2H + HPO3 is endothermic by 318 kJ mol(-1) at the HF/6-31+G(d)//AM1 level of theory. In addition, intermediate (b) also yields NH2CH(CH2-C6H4-OH)CO2H + PO3 - (reaction endothermic by 137 kJ mol(-1)). The two negative ion cleavages of pTyr have a barrier to the transition state of 198 kJ mol(-1) (at the HF/6-31+G(d)//AM1 level of theory) comparable with those already reported for negative ion backbone cleavages.     

Plasma sputtering of an alloyed target for the synthesis of Zr-based metallic glass thin films

ZrTiAlCuNi films are deposited by plasma sputtering from an alloyed target prepared by induction – cold crucible melting method. The films are found to be amorphous and exhibit a composition very similar to the target one. It is shown that the amorphous character of the deposits is rather due to the high glass forming ability (GFA) of the Zr-based alloy system, than to the deposition method used. The sputtering process of the alloyed target, composed of mixed Zr-containing phases, has been studied. It appears to be a global process leading to a quasi-congruent transfer of the target elements into the film. PACS 81.15.Cd; 61.43.Dq; 52.40.Hf