A simple approach to sensor discovery and fabrication on self-assembled monolayers on glass

Self-assembled monolayers (SAMs) on glass were used as a platform to sequentially deposit fluorophores and small molecules for ion sensing. The preorganization provided by the surface avoids the need for complex receptor design, allowing for a combinatorial approach to sensing systems based on small molecules. The resulting libraries are easily measured and show varied responses to a series of both cations and anions. This technology is transferable from the macro- to the microscale both via microcontact printing (microCP), where the fluorophore is printed onto a glass surface, and via direct attachment of the fluorophore to microchannel walls. The ease of miniaturization of this technology may make the generation of a wide variety of simple yet efficient microarrays possible.     

The measurement temperature: an important factor relating physicochemical and adhesive properties of yeast cells to biomaterials

Flow chambers applied to the study of the initial adhesion process of Candida parapsilosis are rarely found in the literature. The ability of these microorganisms to proliferate and form biofilms in environments at temperatures around 22 or 37 degrees C is reflected in the contamination of laboratory instruments and material or in human implant infections, respectively. The initial interaction between yeasts and substrata is mediated by physicochemical forces, which in turn originate from the physicochemical surface properties of both interacting phases. In this context, this work aims to relate the initial rates of adhesion rates to glass and silicone of Candida parapsilosis, strains 294 and 289, grown at 22 and 37 degrees C with the theoretical predictions of the adhesion process, expressed by the interaction free energies and calculated through the physicochemical parameters, which are also measured at 22 and 37 degrees C. The results indicate that physicochemical parameters of yeasts are changed not only by the culture temperature but also by the measurement temperature; only when the measurement temperature is equal to the growth temperature a coherent relation between in vitro adhesion data and interaction free energies can be established. In this sense, the adhesion to glass is mediated by long-range forces or, what amounts to the same thing, by Lifshitz-van der Waals interaction free energy. On the other hand, the adhesion to silicone rubber seems to be moderated by acid-base interaction free energy, which involves the presence of short-range forces. Based on these results, it can be assumed that the substratum surface properties are directly related to the kind of force acting on the initial microbial adhesion process, while cell surface properties dictate the changes in the strength of the force between different samples.     

In situ UV-vis absorbance measurements for Langmuir films of poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13) azopolymer

In situ UV-vis absorbance measurements are used to investigate aggregation in Langmuir films from the azopolymer poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13), a methacrylate derivative of DR13. The level of aggregation in a Langmuir film is intermediate between that of HPDR13 in chloroform solution and in a deposited LB film, as expected. Absorption is negligible at large areas per monomer, and starts to increase at a critical area that is the same as the one obtained in surface potential isotherms, being close to twice the area per monomer for a condensed film. This indicates that the onset for light absorption coincides with a critical packing density where monolayer structuring occurs and there is a sharp change in the effective dielectric constant of the film/water interface. Consistent with a featureless pressure-area isotherm for HPDR13, denoting no significant molecular rearrangement upon film compression, the UV-vis spectra did not vary with the surface pressure. The intensity of absorbed light increased, though, as the film was compressed owing to a higher density of chromophores. At higher subphase temperatures, larger flexibility of HPDR13 chains led to a more compact arrangement, causing the area per monomer to decrease and the absorbed light to increase-with approximately opposite trends.     

Ionic surfactant adsorption onto activated carbons

The adsorption of sodium dodecyl sulfate onto a set of activated carbons from aqueous solutions has been studied in the low concentration range. The adsorption isotherms are reasonably well fitted by a double Langmuir equation but the calorimetry of adsorption enthalpies shows a rather wide distribution of energies. This distribution is related to direct adsorbate-adsorbent interactions in pores of different size, without noticeable contributions from the chemical nature of the surface. The adsorbate-adsorbent interaction free energy through water is evaluated using the model proposed by van Oss and co-workers for the interfacial free energy. The obtained results indicate that the calculated free energy is in good agreement with that found from application of the double Langmuir equation to the adsorption isotherms.     

Voltammetric and drift spectroscopy investigation in dithiophosphinate-chalcopyrite system

The mechanism of dithiophosphinate (DTPI) adsorption on chalcopyrite was investigated by diffuse reflectance Fourier transformation (DRIFT) spectroscopy and by cyclic voltammetry (CV) at various pHs. CV experiments showed that the redox reactions occurred at a certain degree of irreversibility on the chalcopyrite surface in the absence of a collector due to preferential dissolution of iron ions in slightly acid solution and irreversible surface coverage by iron oxyhydroxides in neutral and alkaline solutions. In the presence of DTPI, CV experiments failed to identify the type of the adsorbed DTPI species and electrochemical processes occurring on chalcopyrite due to formation of an electrochemically passive surface layer preventing electron transfer. However, DRIFT spectroscopy tests showed this passive layer to be mainly CuDTPI + (DTPI)2. Both CV and DRIFT spectroscopy established that the activity of collector species decreased with increasing pH due to formation of stable hydrophilic metal oxyhydroxides on the chalcopyrite surface.     

A chiral molecular conductor: synthesis, structure, and physical properties of [ET]3[Sb2(L-tart)2].CH3CN (ET = bis(ethylendithio)tetrathiafulvalene; L-tart = (2R,3R)-(+)-tartrate)

The salt [ET](3)[Sb(2)(L-tart)(2)].CH(3)CN (1) has been obtained by electrocrystallization of the organic donor bis(ethylendithio)tetrathiafulvalene (ET or BEDT-TTF) in the presence of the chiral anionic complex [Sb(2)(L-tart)(2)](2-) (L-tart = (2R,3R)-(+)-tartrate). This salt crystallizes in the chiral space group P2(1)2(1)2(1) (a = 11.145(2) angstroms, b = 12.848(2) angstroms, c = 40.159(14) angstroms, V = 5750.4(14) angstroms(3), Z = 4) and is formed by alternating layers of the anions and of the organic radicals in a noncentrosymmetric alpha-type packing. This compound shows a room temperature electrical conductivity of approximately 1 S.cm(-1) and semiconducting behavior with an activation energy of approximately 85 meV. Analysis of the magnetic susceptibility and band structure, however, suggests that this compound should be a narrow band gap semiconductor.     

Efficient synthesis of enantiomerically pure alpha-alkyl cyclopropanecarbonitrile derivatives from pyrazolines

[reaction: see text] Thermolysis of enantiopure sulfonyl pyrazolines 4 and 5, easily obtained from (Z)-3-p-tolylsulfinylacrylonitriles (1), afforded sulfonyl cyclopropanes (6, 7) in a completely stereoselective manner in almost quantitative yields. Both cyclopropanes and alkylidenecyclopropanes, containing one or two chiral carbon atoms, one of them being quaternary, were obtained by hydrogenolysis of the C-S bonding and under the conditions reported by Julia, respectively. The highly stereoselective extrusion of nitrogen suggests a concerted mechanism.     

Magnetite, a model system for mixed-valence oxides, does not show charge ordering

We have investigated the charge ordering (CO) in magnetite below the Verwey transition. A new set of half-integer and mixed-integer superlattice reflections of the low-temperature phase have been studied by x-ray resonant scattering. None of these reflections show features characteristic of CO. We demonstrate the absence of CO along the c axis with the periodicity of either the cubic lattice q=(001) or the doubled cubic lattice q=(001/2). This result suggests that the Verwey transition is caused by strong electron-phonon interaction instead of an electronic ordering on the octahedral Fe atoms.     

Ultrasonic inspection of batters for on-line process monitoring

A new method for on-line batter monitoring using ultrasound techniques is presented. Air or gas incorporation is done during the beating process which produces bubbles in the mixture. The density and the compressibility of the batter vary as a function of mixing time and are quality index of batter. Traditionally, a batter sample of a fixed volume is removed and weighted in order to determine its density. This is a time consuming process. Batters are air filled mixtures of high viscosity which do not support significant transmission of ultrasound. For this reason conventional ultrasonic density sensors for liquids are not suitable for this application. Therefore, a special transducer has been developed. The sensor was constructed using a piezoelectric ceramic at the fundamental frequency of 1 MHz. Instead of measuring density, in this work, changes in compressibility in batters are monitored by measuring the acoustic impedance of the batter. Main advantage of this novel approach is that changes in acoustic impedance are easier to detect than changes in density especially when air incorporation is in small quantities. Experimental results on different liquids and batters with different gas contents are presented and discussed.