Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₃₈Mo₄B₁₈ metallic glass ribbons. 90 MeV ¹²⁷I beam was used for the irradiations. Irradiation doses were 5×10¹³ and 7.5×10¹³ ions/cm². The relative intensity ratios D ₂₃ of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.     

Study of CO chemisorption on polycrystalline Pt

The chemisorption of CO on a sputtered and annealed polycrystalline Pt surface has been examined using ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). Data obtained from an isotopic TPD experiment indicate that adsorption is molecular with no detectable CO dissociation. ISS data demonstrate that the CO bonds to the Pt through the C with the O pointing away from the surface and that about 80% of the Pt surface is covered at saturation based on the relative sizes of the ISS Pt peak heights obtained from the clean and CO-saturated surfaces. Coverage versus exposure plots have been determined from both the ISS and TPD data, and the agreement is generally good. The sticking coefficient is close to 1 up to =0.5 and than falls rapidly with increasing exposure to the saturation exposure of 90 L. The Kisliuk adsorption model, which assumes adsorption at a single type of site, is able to provide a good fit of the ISS uptake data but is not as successful in fitting the TPD uptake data.     

Analysis of B3LYP and MP2 conformational population distributions in trans‐nicotine,acetylcholine, and ABT‐594

This work presents an analysis of the equivalence of MP2 and DFT (B3LYP functional) conformational populations. As a test case, we select three cholinergic agents (trans‐nicotine, acetylcholine, and the nicotinic analgesic ABT‐594), where the minima on the conformational energy hypersurfaces expand a large range of energies (～0–30 kJ mol^?1). From energetic and structural data obtained in vacuo at the MP2 and B3LYP/cc‐pVDZ levels, we build conformational partition functions, including the effect of the conformational kinetic energy and the rotovibrational coupling. Our results at a physiological temperature (37°C) show qualitative agreement in all cases. Quantitative agreement, however, is only found for trans‐nicotine and ABT‐594. In the first case, energy minima differ by <0.2 kJ mol^?1. Therefore, the equivalence of structural results translates in the equivalence of the conformational distribution. For ABT‐594, the minima are separated by as much as 8.0 kJ mol^?1, and the conformational energy determines the conformational distribution. In this case, the slight relative variation of conformational energy, between B3LYP and MP2, does not affect the population, since the secondary minima are high in energy and very low in population. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Characterization of a New Bacteriocin from Lactobacillus plantarum LE5 and LE27 Isolated from Ensiled Corn

Bacteriocins are low molecular peptides with antimicrobial activity, which are of great interest as food bio-preservatives and for treating diseases caused by pathogenic bacteria. In this study, we present the characterization of bacteriocins produced by Lactobacillus plantarum LE5 and LE27 isolated from ensiled corn. Bacteriocins were purified through ammonium sulfate precipitation and double dialysis by using 12- and 1-kDa membranes. Bacteriocins showed activity against Listeria innocua, Listeria monocytogenes, and Enteroccocus faecalis. Molecular weight was estimated through Tricine-SDS-PAGE and overloading the gel onto Mueller-Hinton agar seeded with L. monocytogenes, showing an inhibition zone between 5 and 10 kDa. NanoLC-MS/MS analysis allowed the identification of UPF0291 protein (UniProtKB/Swiss-Prot Q88VI7), which is also presented in other lactic acid bacteria without assigned function. Ab initio modeling showed it has an α-helix-rich structure and a large positive-charged region. Bacteriocins were stable between 4 and 121 °C and pH 2 and 12, and the activity was inhibited by SDS and proteases. Mode of action assay suggests that the bacteriocin causes of target microorganism. Taken together, these results describe a possible new class IIa bacteriocin produced by L. plantarum, which has a wide stability to physicochemical conditions, and that could be used as an alternative for the control of foodborne diseases.     

A theoretical study on three conformational structures of 2,6‐distyrylpyridine

Ab initio methods at the levels HF/cc‐pVDZ, HF/6‐31G(d,p), MP2/cc‐pVDZ, and MP2/6‐31G(d,p), as well as methods based on density functional theory (DFT) employing the hybrid functional B3LYP with the basis sets cc‐pVDZ and 6‐31G(d,p), have been applied to study the conformers of 2,6‐distyrylpyridine. Bond distances, bond angles, and dihedral angles have been calculated at the B3LYP level. The calculated values were in good agreement with those measured by X‐ray diffraction analysis of 2,6‐distyrylpyridine. The values calculated using the Hartree‐Fock method and second‐order perturbation theory (MP2) were inconsistent. The optimized lowest‐energy geometries were calculated from the reported X‐ray structural data by the B3LYP/cc‐pVDZ method. Three conformations, A, B, and C, were proposed for 2,6‐distyrylpyridine. Calculations at the three levels of theory indicated that conformation A was the most stable structure, with conformations C and B being higher in energy by 1.10 and 2.57 kcal/mol, respectively, using the same method and basis function. The same trend in the relative energies of the three possible conformations was observed at the two levels of theory and with the different basis sets employed. The reported X‐ray data were utilized to optimize total molecular energy of conformation A at the different calculation levels. The bond lengths, bond angles, and dihedral angles were then obtained from the optimized geometries by ab initio methods and by applying DFT using the two basis functions cc‐pVDZ and 6‐31G(d,p). The values were analyzed and compared. The calculated total energies, the relative energies of the molecular orbitals, the gap between them, and the dipole moment for each conformational structure proposed for 2,6‐distyrylpyridine are also reported. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Host-Guest Interactions between Calixarenes and Cp(2)NbCl(2)

The possible inclusion complexes of Cp₂NbCl₂ into calixarenes hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed by a combination of NMR, ab-initio calculations, thermogravimetric analysis, FTIR, Raman and PXRD. Ab-initio calculations, ¹H NMR solution and solid state ¹³C CP-MAS NMR results demonstrated that p-sulfonic calix[6]arene does form an inclusion complex with Cp₂NbCl₂. Raman spectroscopy showed, for the inclusion compound of p-sulfonic calix[6]arene-Cp₂NbCl₂, a band between 500 and 850 cm⁻¹ characteristic of Nb-O vibration. This result suggests that Nb(V) may engage in coordination with the oxygen of the sulfonate group, as part of the host-guest interaction. However, it is important to mention that the niobocene dichloride (Cp₂NbCl₂) dissolves in water and undergoes oxidation and hydrolysis processes to yield Cp₂NbCl₂(OH) species. For that reason this band does not exclude that the Nb-O band belongs to Cp₂NbCl₂(OH). Solid State ¹³C CP-MAS NMR and solution ¹H NMR spectroscopies together with ab-initio results showed that Cp₂NbCl₂ is included in the p-sulfonic calix[6]arene cavity, with both Cp rings inside the cavity. In contrast, the solution ¹H NMR results demonstrated that calix[6]arene does not form inclusion complex with Cp₂NbCl₂ in CDCl₃ solution. Cp₂NbCl₂ is not included in the calix[6]arene cavity, possibly due to the lack of sulfonate heads which promote Nb-O interactions and assist the inclusion of Cp₂NbCl₂ into the cavity.     

Glass/PDMS hybrid microfluidic device integrating vertically aligned SWCNTs to ultrasensitive electrochemical determinations

This communication reports a promising platform for rapid, simple, direct, and ultrasensitive determination of serotonin. The method is related to integration of vertically aligned single-walled carbon nanotubes (SWCNTs) in electrochemical microfluidic devices. The required microfabrication protocol is simple and fast. In addition, the nanomaterial influenced remarkably the obtained limit-of-detection (LOD) values. Our system achieved a LOD of 0.2 nmol L(-1) for serotonin, to the best of our knowledge one of the lowest values reported in the literature.     

Asymmetric hydrogenation of tryptophan precursors catalyzed by rhodium-DIOP complexes

Z-2-benzamido(acetamido)-3-(3-indolyl)-2-propenoic acids were hydrogenated with neutral and cationic rhodium(I) complexes containing the chiral diphosphine (–) or (+)–2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)-butane [(–) or (+)–DIOP].

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Z-2- ()-3-(3-)-2- () (I), (–) (+)-2,3--2,3--1,4- ()-.

     

6-n-Alkoxy-3-Pyridinecarboxaldehydes: New Intermediates to Liquid Crystals. Properties of Some Derivatives

The synthesis of new intermediates to liquid crystals, a series of 6-n-alkoxy-3-pyridinecarboxaldehydes is described. The mesomorphic properties of their precursors, the 6-n-alkoxy-3-pyridinecarboxylic acids are reported. Some derivatives of the carboxaldehydes, the 6,6′-di-n-alkoxy-3,3′-dipyridylmethylenehydrazines and the 6′,6”- di-n-n-alkoxy-3′,3”-dipyridylmethylene-l,4-phenylenediamines, are described and their mesomorphic properties reported. The 1,4-phenylenediamine derivatives show greater mesomorphic stability than the azines, most of the azines being non-mesomorphic while the 1,4-phenylenediamine derivatives show smectic polymorphism with wide mesophase ranges.     

Hydrogen Bonding Aggregation of a Series of Bis-Amidinium Halide Salts in the Solid State

A series of bis-amidinium derivatives has been prepared and shown to form ordered aggregates in the solid state. The primary organizing interactions are bidentate hydrogen bonds between the syn-hydrogen atoms of the amidinium ions and the halide counter anion.