Rheological behavior in the didodecyldimethylammonium bromide/water system

The phase behavior in the dilute region of the didodecyldimethylammonium bromide (DDAB)/water system is studied with a battery of techniques. The critical vesicle concentration (cvc), measured by tensiometry, conductimetry, ion-selective-electrode potentiometry and dye solubilization, is similar to the value reported in the literature. Moreover, the combination of surfactant-ion-selective- electrode and bromide-ion-selective-electrode potentiometry indicates that the vesicles are substantially ionized (α ≈ 0.5) in the proximity of the cvc. The transition from small unilamellar vesicles to larger multilamellar liposomes was detected at 0.2 wt% by viscometry, conductimetry and dye solubilization measurements. The rheology of the DDAB/water system was studied as a function of surfactant concentration and temperature. Non- Newtonian behavior, viscoelasticity, yield stresses and time-dependent flow behavior were observed. Maxima and minima in the dynamic moduli and in conductivity are related to structural changes and phase transitions. Moreover, in time-dependent shear flow, the microstructure is modified and the rheological response shifts from thixotropic to antithixotropic or vice versa, depending on the DDAB concentration and the level and duration of the final applied stress. The conductivity behavior in the Lam₁ phase region can be qualitatively explained by the capillary superconductivity theory. This conductivity behavior occurs when the thickness of the aqueous lamella is of the same order of magnitude as the Debye length. Received: 4 January 1999/Accepted in revised form: 1 September 1999     

Cava Wine Authentication Employing a Voltammetric Electronic Tongue

The application of an Electronic Tongue for the classification of cava samples based on their different ageing times is reported. As such, voltammetric responses were obtained from an array of six bulk‐modified graphite‐epoxy electrodes, which exhibited marked mix‐responses towards the different samples. Obtained responses were then preprocessed employing FFT and the resulting coefficients were input to a LDA model which allowed the classification of the samples according to its vintage time. Besides, a quantitative model employing ANNs was built for the prediction of the total amount of sugar present in the samples, a parameter also used to classify cava samples.     

Simultaneous determination of enrofloxacin and its primary metabolite, ciprofloxacin, in chicken tissues

Summary An HPLC method with fluorescence detection is presented for the analysis of enrofloxcin (ENR) and ciprofloxacin (CIP) in chicken tissue using sarafloxacin (SAR) as internal standard. Tissue sample preparations were carried out by adding a phosphate buffer (pH 7.4, 0.1 M), followed by extraction with trichloromethane. Fluoroquinolones were separated on a reversed-phase column with a mobile phase of aqueous phosphate buffer-acetonitrile (80:20). The concentrations of CIP, ENR and SAR eluted off the column, with retention times of 2.28, 3.30 and 4.40, respectively, were monitored by fluorescence detection atλ _ex 338 andλ _em 425 nm. The detection limit was 32 ng g⁻¹ for CIP and 10 ng g⁻¹ for ENR. The standard curves were linearly related to concentration in the range of 1 to 2000 ng g⁻¹. Recovery was determinated as 91.3% and 78.3% for ENR and CIP, respectively. The measurement of the tissue levels of ENR and CIP in the chicken after oral administration confirmed the utility of the proposed analytical methodology.     

Counterion specificity of the micelle surface and its implications on micellar catalysis

Dodecyltrimethylammonium bromide — Dodecyltrimethyl-ammonium hydroxide — water mixtures were studied with ion-selective electrodes, and the aggregation behavior, degree of ionization of the micelles and the distribution constants of bromide and hydroxide ions between water and micelles were found, showing that some suppositions about the interpretation of micellar catalysis are incorrect, and these interpretations must be revised. The results support the mass action model for the theoretical treatment of micellar catalysis.     

On the Brauer–Glauberman correspondence

The purpose of the present paper is two-fold: on the one hand, to show the existence of a correspondence unifying Brauer's and Glauberman's ones (see Theorem 4.6), and, on the other hand, to give an alternative proof of Watanabe's equivalence in [Atumi Watanabe, The Glauberman character correspondence and perfect isometries for blocks of finite groups, J. Algebra 216 (1999) 548–565]. By the way, we give a short proof of the coincidence of the Clifford extensions associated with a pair of Glauberman correspondent irreducible representations (see Corollary 4.16), a question that, surprisingly enough, has only been partially solved recently (see [Morton Harris, Markus Linckelmann, On the Glauberman and Watanabe correspondences for blocks of finite p-solvable groups, Trans. Amer. Math. Soc. 354 (2002) 3435–3453] and [Shigeo Koshitani, Gerhard Michler, Glauberman correspondence of p-blocks of finite groups, J. Algebra 243 (2001) 504–517]).     

Effects of electrolyte concentration and counterion valence on the microstructural flow regimes in dilute cetyltrimethylammonium tosylate micellar solutions

The shear thickening behavior and the transition to shear thinning are examined in dilute cetyltrimethylammonium tosylate (CTAT) micellar solutions as a function of surfactant concentration and ionic strength using electrolytes with different counterion valence. Newtonian behavior at low shear rates, followed by shear thickening and shear thinning at higher shear rates, are observed at low and intermediate surfactant and electrolyte concentrations. Shear thickening diminishes with increasing surfactant concentration and ionic strength. At higher surfactant or electrolyte concentration, only a Newtonian region followed by shear thinning is detected. A generalized flow diagram indicates two controlling regimes: one in which electrostatic screening dominates and induces micellar growth, and another, at higher electrolyte and surfactant concentrations, where chemical equilibrium among electrolyte and surfactant counterions controls the rheological behavior by modifying micellar breaking and reforming. Analysis of the shear thickening behavior reveals that not only a critical shear rate is required for shear thickening, but also a critical deformation, which appears to be unique for all systems examined, within experimental error. Moreover, a superposition of the critical shear rate for shear thickening with surfactant and electrolyte concentration is reported.     

MR imaging of the her2/neu and 9.2.27 tumor antigens using immunospecific contrast agents

Molecular imaging of tumor antigens using immunospecific magnetic resonance (MR) contrast agents is a rapidly evolving field, which can potentially aid in early disease detection, monitoring of treatment efficacy, and drug development. In this study, we designed, synthetized, and tested in vitro two novel monocrystalline iron oxide nanoparticles (MION) conjugated to antibodies against the her2/neu tyrosine kinase receptor and the 9.2.27 proteoglycane sulfate. MION was synthetized by coprecipitation of iron II and iron III salts in 12-kD dextran solution; antibody coupling was performed by reductive amination. The relaxivity of the conjugates was 24.1-29.1 mM(-1) s(-1), with 1.8 to 2.1 antibody molecules per nanoparticle. A panel of cultured melanoma and mammary cell lines was used for testing. The cells were incubated with the particles at 16-32 microg Fe/ml in culture medium for 3 h at 37 degrees C, and investigated with immune fluorescence, transmission electron microscopy (TEM), MRI of cell suspensions in gelatine, and spectrophotometric iron determination. All receptor-positive cell lines, but not the controls, showed receptor-specific immune fluorescence, and strong changes in T(2) signal intensity at 1.5 T. The changes in 1/T(2) were between 1.5 and 4.6 s(-1) and correlated with the amount of cell-bound iron (R = 0.92). The relaxivity of cell-bound MION increased to 55.9 +/- 10.4 mM(-1) s(-1). TEM showed anti-9.2.27 conjugates binding to the plasma membrane, while the anti-her2/neu conjugates underwent receptor-mediated endocytosis. In conclusion, we obtained receptor-specific T(2) MR contrast with novel covalently bound, multivalent MION conjugates with anti-9.2.27 and anti-her2/neu to image tumor surface antigens. This concept can potentially be expanded to a large number of targets and to in vivo applications.     

Networks of innovation or networks of opportunity? The making of the Spanish antibiotics industry

The pharmaceutical industry is a typically research-intensive, first world-industry. This article seeks to explain why it has been so difficult for late industrialised nations to reproduce the networks of innovation on which the design and manufacturing of new drugs has historically based, and why alternative concepts are needed in order to understand the dynamics of science-based industries in emerging countries. The article analyses the development of the Spanish antibiotics industry, build after the World War II under the strong influence of the new international order and Spain's political framework, academic traditions and business groups. Focusing on the long-term relationships established between two Spanish companies (Antibióticos SA and Compa?ía Espa?ola de Penicilina y Antibióticos, CEPA), their American technological partners (Schenley and Merck), and their social and scientific environment, the article identifies networks of opportunity as the key institutional arrangement of this new industry in Spain. Opportunity (as opposed to innovation) networks are thus proposed to conceptualise the development of technologically complex industries in the European periphery.