Rheological characterization of complex fluids in electro-magnetic fields

The paper is focused on the experimental investigations and rheological characterisations in magnetic and electric fields of liquids based on water in crude oils emulsions, added with ferrofluids (two types of crude oils are used in experiments: asphaltic and paraffinic, respectively). The final samples disclose weakly effects in the presence of magnetic field (saturated magnetization: M_n < 300 [G]) and behave almost as isolators in electric field (conductivity: σ < 10⁻⁵ [S/m]). The main goal of the study is to explore to what extent rheometry of complex fluids in electric and magnetic fields is able to offer value information about the internal structure of the samples. The experimental results prove that anomalous rheological behaviour (thixotropy, non-monotonic flow curve or viscosity function) of a complex fluid (in our case, emulsions based on paraffinic oil) generate also thixotropic properties and non-monotonic answers in the presence ferrofluids, under low magnetic and/or electric fields intensity. Our prospective study suggests that novel experimental procedures based on interaction: electro-magnetic field–complex fluids can be developed, in order to determine indirectly some relevant rheological properties of the complex fluids with internal network structure.     

Are liquid chromatography/electrospray tandem quadrupole fragmentation ratios unequivocal confirmation criteria?

Multiple reaction monitoring (MRM) ratios as provided by tandem mass spectrometers are used to confirm positive residue findings (e.g. veterinary drugs or pesticides). The Commission Decision 2002/657/EEC defines tolerance levels for MRM ratios, which are intended to prevent the reporting of false positives. This paper reports findings where blank sample extracts have been spiked by a drug (difloxacin) and the corresponding measured MRM ratios significantly deviated from MRM ratios observed in matrix‐free solution. The observation was explained by the formation of two different [M+H]⁺ analyte ions within the electrospray ionization (ESI) interface. These two ions vary only by the site of analyte protonation. Since they are isobaric, they are equally transmitted through the first quadrupole, but are differently fragmented in the collision chamber. The existence of two isobaric ions was deduced by statistical data and the observation of a doubly charged analyte ion. It was hypothesized that the combined presence of [M+H]⁺ and [M+2H]²⁺ implies the existence of two different singly charged ion species differing only by the site of protonation. Low‐ and high‐energy interface‐induced fragmentation was performed on the samples. The surviving precursor ion population was mass selected and again fragmented in the collision chamber. Equal product ion spectra would be expected. However, very different product ion spectra were observed for the two interface regimes. This is consistent with the assumption that the two postulated isobaric precursor ions show different stability in the interface. Hence the abundance ratio among the two types of surviving precursor ions will shift and change the resulting product ion spectra. The existence of the postulated singly charged ions with multiple chargeable sites was finally confirmed by successful ion mobility separation. Copyright © 2009 John Wiley & Sons, Ltd.     

Nb and Ta Adducts: Connecting d0 Metal Chlorides and Phosphorus Sulfide Cages

Phosphorus sulfide cages α‐P₄S₄, α‐P₄S₅, β‐P₄S₅, and β‐P₄S₆ and transition‐metal chlorides TaCl₅ and NbCl₅ form molecular adducts in CS₂/n‐hexane. The crystal structures of the adducts (TaCl₅)(α‐P₄S₄), (TaCl₅)(α‐P₄S₅), (TaCl₅)(β‐P₄S₅), (NbCl₅)(β‐P₄S₅), and (TaCl₅)(β‐P₄S₆) are reported and their conformation and energetic stability are discussed on the basis of ab initio electronic structure calculations. Furthermore bond lengths of coordinated and noncoordinated phosphorus sulfide cages obtained from experiment and theory are compared, emphasizing the changes within the cages that emerge upon coordination.     

On an evolution equation with acoustic boundary conditions

In this paper, we analyze from the mathematical point of view a model for small vertical vibrations of an elastic string with weak internal damping and quadratic term, coupled with mixed boundary conditions of Dirichlet type and acoustic type. Our goal is to extend some of the results of Frota‐Goldstein work in the sense of considering a weaker internal damping and one more quadratic nonlinearity in the elastic string equation. Copyright © 2011 John Wiley & Sons, Ltd.     

The Solid-State Cultivation of Streptococcus zooepidemicus in Polyurethane Foam as a Strategy for the Production of Hyaluronic Acid

Hyaluronic acid (HA) is a biopolymer with important applications in the pharmaceutical, medical, and cosmetic fields. This work explores the potentialities of a cylindrical polyurethane foam dowel with central aeration as a novel packed bed bioreactor for the production of HA. The goals were to provide a large surface area for oxygen transfer through the patches of liquid film that form in the pores of the foam in which cell proliferation and HA production occur and to easily recover the HA produced. The resulting yields of HA/cell were higher than 1, and the produced HA was completely recovered by pressing the foam. The external conditions that inhibit catabolism, the deviation of energetic metabolism toward the production of HA, were modulated by aeration and the initial glucose concentration. The production of HA was reproducible in 12 successive fermentation cycles. These findings contribute to the development of efficient strategies for the controlled production and recovery of HA.     

(9E)‐9‐Benzylidene‐3‐methyl‐2‐methylsulfanyl‐5‐phenyl‐5,6,7,8,9,10‐hexahydropyrimido[4,5‐b]quinolin‐4(3H)‐one: polarized molecules within hydrogen‐bonded bilayers

The molecules of the title compound, C₂₆H₂₅N₃OS, which was prepared by means of an acid‐catalysed cyclocondensation reaction between a 6‐aminopyrimidinone and 2,6‐dibenzylidenecyclohexanone, exhibit a polarized electronic structure, namely (9E)‐9‐benzylidene‐3‐methyl‐2‐methylsulfanyl‐5‐phenyl‐3,5,6,7,8,9‐hexahydropyrimido[4,5‐b]quinolin‐10‐ium‐4‐olate, involving charge separation in the vinylogous amide portion. Four hydrogen bonds, two each of the C—H...O and C—H...π(arene) types, link the molecules into bilayers comprising inversion‐related pairs of sheets, each containing a single type of R₄³(36) ring.     

Spectroscopic studies of bridge contributions to electronic coupling in a donor-bridge-acceptor biradical system

Variable-temperature electronic absorption and resonance Raman spectroscopies are used to probe the excited state electronic structure of Tp(Cum,Me)Zn(SQ-Ph-NN) (1), a donor-bridge-acceptor (D-B-A) biradical complex and a ground state analogue of the charge-separated excited state formed in photoinduced electron transfer reactions. Strong electronic coupling mediated by the p-phenylene bridge stabilizes the triplet ground state of this molecule. Detailed spectroscopic and bonding calculations elucidate key bridge distortions that are involved in the SQ(π)(SOMO) → NN-Ph (π*)(LUMO) D → A charge transfer (CT) transition. We show that the primary excited state distortion that accompanies this CT is along a vibrational coordinate best described as a symmetric Ph(8a) + SQ(in-plane) linear combination and underscores the dominant role of the phenylene bridge fragment acting as an electron acceptor in the D-B-A charge transfer state. Our results show the importance of the phenylene bridge in promoting (1) electron transfer in D-Ph-A systems and (2) electron transport in biased electrode devices that employ a 1,4-phenylene linkage. We have also developed a relationship between the spin density on the acceptor, as measured via the isotropic NN nitrogen hyperfine interaction, and the strength of the D → A interaction given by the magnitude of the electronic coupling matrix element, H(ab).