Fluorogenic Detection of Sulfite in Water by Using Copper(II) Azacyclam Complexes

Copper(II) azacyclam complexes (azacyclam = 1,3,5,8,12-pentaazacyclotetradecane) containing naphthyl or dansyl subunits can be prepared by template synthesis involving proper sulfonamide derivatives as locking fragments. The macrocyclic complexes are very poorly emissive due to the fluorescence-quenching behavior displayed by Cu²⁺ ions. However, the fluorescence can be recovered as a result of the decomposition of the complexes, which induces the release of free light-emitting subunits to the solution. This reaction takes place very slowly in neutral water but its rate is increased by the presence of sulfite. Therefore, [Cu(azacyclam)]²⁺ derivatives have been investigated as simple chemical probes for the fluorogenic detection of sulfite both on laboratory and real samples. Preliminary tests performed on samples of white wine provided sulfite concentration values that are in agreement with those obtained by a standard analytical method.     

On the physical meaning of the power factor in acoustics

Following recent advancements in the study of time-averaged properties of energy propagation in linear acoustic fields, the well established concept of power factor known from the electric AC circuits analysis, is here extended to acoustics. This allows our outline of a complete acousto-electro-mechanic analogy, where the fundamental physical concept of energy trajectory is assimilated to a continuous line network of electric circuits, and the complex intensity vector field is defined by means of three special spatial directions: the tangent, the principal normal and the binormal direction at each point of any energy path. The notions of sound energy conductance and susceptance are then introduced and their relationship with complex intensity is highlighted. Finally, the frequency distributions of the defined quantities are measured in different acoustical contexts, thus illustrating their practical utility for advanced intensimetric metrology.     

Excitation of ultrasonic Lamb waves using a phased array system with two array probes: Phantom and in vitro bone studies

Long bones are good waveguides to support the propagation of ultrasonic guided waves. The low-order guided waves have been consistently observed in quantitative ultrasound bone studies. Selective excitation of these low-order guided modes requires oblique incidence of the ultrasound beam using a transducer-wedge system. It is generally assumed that an angle of incidence, θ_i, generates a specific phase velocity of interest, c_o, via Snell’s law, θ_i = sin⁻¹(v_w/c_o) where v_w is the velocity of the coupling medium. In this study, we investigated the excitation of guided waves within a 6.3-mm thick brass plate and a 6.5-mm thick bovine bone plate using an ultrasound phased array system with two 0.75-mm-pitch array probes. Arranging five elements as a group, the first group of a 16-element probe was used as a transmitter and a 64-element probe was a receiver array. The beam was steered for six angles (0°, 20°, 30°, 40°, 50°, and 60°) with a 1.6-MHz source signal. An adjoint Radon transform algorithm mapped the time-offset matrix into the frequency-phase velocity dispersion panels. The imaged Lamb plate modes were identified by the theoretical dispersion curves. The results show that the 0° excitation generated many modes with no modal discrimination and the oblique beam excited a spectrum of phase velocities spread asymmetrically about c_o. The width of the excitation region decreased as the steering angle increased, rendering modal selectivity at large angles. The phenomena were well predicted by the excitation function of the source influence theory. The low-order modes were better imaged at steering angle ?30° for both plates. The study has also demonstrated the feasibility of using the two-probe phased array system for future in vivo study.     

Calibration of pressure-velocity probes using a progressive plane wave reference field and comparison with nominal calibration filters

A procedure for calibrating pressure-velocity (p-v) sound intensity probes using a progressive plane wave as reference field is presented here. The procedure has been checked for a microelectromechanical system technology-based Microflown(?) match-size probe by comparing the calibration results with the nominal correction curves available from the manufacturer. The reference field was generated along a wave guide by means of a dual cone loudspeaker supplying acoustic energy in the range 20 Hz-20 kHz through an impedance adaptor. Different from the current in-field procedures, the one proposed here allows the calibration of probes under test to be executed at once up to 10 kHz without any change in the experimental setup. After a detailed review of the general principles of calibration, the procedure has been finalized with three main stages: (a) determination of the full coherence calibration bandwidth of the probe, (b) comparison calibration of the probe built-in pressure microphone over the full coherence frequency range, and (c) relative calibration of the velocity sensor over the calibrated pressure one. Calibration results for the probe under test have been best fitted against the calibration filters modeled by the manufacturer and the direct comparison of the obtained data with the factory ones has been reported.     

Supramolecular Functions Related to the Redox Activity of Transition Metals

Abstract

The combination of the properties of different subunits in a multicomponent system may give rise to a function which is defined supramolecular. The presence of transition metals in one or more subunits may induce inter-component processes related to their redox and electron transfer (eT) properties, which trigger the supramolecular function (SF). The following examples are considered: (1) a receptor for transition metals is covalently linked to a fluorescent fragment; following recognition, a metal-to-fluorophore eT process quenches the fluorescence. SF: fluorosensing. (2) an azacyclam macrocycle, hosting the Ni^II/Ni^III redox couple, is covalently linked to a photoactive fragment: the Ni^III state quenches the neighboring fluorophore through an eT mechanism, the Ni^II state does not. SF: redox switching of a fluorescent signal. (3) a Cu^II ion is coordinated by two 2,2′-bipyridine molecules, each bearing a cyclam subunit containing a nickel centre; when nickel is in the divalent state, an inorganic anion X^? (N₃ ^?,NCO^?,NCS^?) is bound to Cu^II; on oxidation, X^? moves to the Ni^III centre. SF: electrochemically triggered translocation of X^? from copper to nickel and vice versa.     

Ethylene‐based copolymers with tunable content of polymerizable hindered phenols as nonreleasing macromolecular additives

Four comonomers bearing a highly efficient phenolic antioxidant unit and different methylene spacers between the aromatic ring and the double bond have been prepared and tested in copolymerization with ethylene using metallocene‐based catalysts. The possibility of obtaining a “masterbatch” suitable for melt blending with commercial polyolefins has been evaluated by modifying: (i) the structure of the functionalized comonomer, (ii) the kind of catalyst, and (iii) the polymerization conditions. Characterization of monomers and copolymers was accomplished by using ¹H and ¹³C NMR, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Using the comonomer with the longest methylene spacer between the aromatic ring and the double bond, and rac‐(EBTHI)ZrCl₂ as catalyst, adjustable amounts of the antioxidant moiety can be incorporated into the polyethylene chains. TGA analysis carried out on some of the copolymers containing the antioxidant group showed no oxygen uptake before decomposition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6393–6406, 2008     

Detection of sigma phase in 22% Cr duplex stainless steel by electrochemical methods

Duplex stainless steels (DSS) may undergo various structural transformations as a function of temperature, leading to formation of secondary phases when exposed to temperatures in the range 600–1000°C for prolonged periods of time. Among these phases, apart from carbides and nitrides, sigma is the most prominent intermetallic compound, since it is known to adversely affect mechanical properties and corrosion resistance of DSS as a consequence of Cr and Mo depletion in the boundary zones of ferrite grains. As a result of sigma precipitation, DSS become susceptible to localized corrosion via a mechanism resembling sensitization in austenitic stainless steels. Electrochemical methods, known to successfully detect sensitization in austenitic SS, have been used to identify reliable test conditions with appropriate sensitivity also for DSS. A modified electrochemical potentiokinetic reactivation method was developed to investigate 22% Cr DSS sensitivity under different thermal cycles. Modifications were designed by closely analysing DSS anodic behaviour changes with respect to the operating testing conditions. All findings were confirmed by SEM, optical microscopy and XRD.