A Cauchy kernel for slice regular functions

In this article, we show how to construct a regular, non-commutative Cauchy kernel for slice regular quaternionic functions. We prove an (algebraic) representation formula for such functions, which leads to a new Cauchy formula. We find the expression of the derivatives of a regular function in terms of the powers of the Cauchy kernel, and we present several other consequent results.     

Synthesis of polymers containing regularly distributed tetrathia‐[7]‐elicene units along the backbone

A tetrathia‐[7]‐helicene bearing in the 2 and 13 positions cyanovinyl groups was used as comonomer in the Michael‐type polyaddition reaction with N,N′‐bis(β‐mercaptoethyl)piperazine. This led to a new polymer bearing tetrathia‐[7]‐helicene units regularly distributed along the polymer backbone, which may be regarded as the first example of a new family of potentially useful nonlinear optical materials. All products were structurally characterized by ¹H and ¹³C NMR spectroscopy. Differential scanning calorimetry characterizations revealed the presence, in both monomeric and polymeric helicenes, of glass‐transition like temperatures, associated to some conformational variation of the helicene units. The optical properties, the film formation and the morphology of the polymer‐containing tetratia‐[7]‐helicenes were also investigated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Evaluation of the interaction parameter for poly(ε‐caprolactone)/poly(styrene‐co‐acrylonitrile) blends

In this article, the miscibility of poly(ε‐caprolactone) (PCL) with poly(styrene‐co‐acrylonitrile) (SAN) containing 25 wt % of acrylonitrile is studied from both a qualitative and a quantitative point of view. The evidences coming from thermal analysis (differential scanning calorimetry) demonstrate that PCL and SAN are miscible in the whole range of composition. The Flory interaction parameter χ_1,2 was calculated by the Patterson approximation and the melting point depression of the crystalline phase in the blends; in both cases, negative values of χ_1,2 were found, confirming that the system is miscible. The interaction parameter evaluated within the framework of the mean field theory demonstrates that the miscibility of PCL/SAN blends is due to the repulsive interaction between the styrene and acrylonitrile segments in SAN. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

A surface wipe sampling and LC–MS/MS method for the simultaneous detection of six antineoplastic drugs commonly handled by healthcare workers

An effective wipe sampling and LC–MS/MS method was developed to simultaneously analyze six commonly administered antineoplastic drugs in stainless steel surface. The analyzed drugs were methotrexate, paclitaxel, cyclophosphamide, 5-fluorouracil, vincristine, and oxaliplatin, a frequently prepared antineoplastic drug that has not been included among any of the published simultaneous detection methods. The established method was used to evaluate the recoveries of antineoplastic drugs on brand new and worn stainless steel surfaces by wiping the plates with a Whatman filter paper wetted with 0.5 mL of water/methanol (20:80) with 0.1 % formic acid followed by LC–MS/MS before desorbing the filter with a water/methanol (50:50) solution. A significant decrease in the recovery of all evaluated drugs was found when worn plates were used. Additionally, the inter-personnel variability on drug recoveries during wiping procedures was evaluated. Significantly higher recoveries were achieved by the personnel with more training and experience versus personnel without prior experience. Finally, a laboratory stability test was developed to assess the degradation of the antineoplastic drugs during replicated shipping conditions. With the exception of vincristine sulfate which exhibited a significant (p?<?0.05) degradation after 48 h, all evaluated drugs were stable during the first 24–48 h. However, after 144 h, an increase in the degradation of all evaluated drugs was observed, with oxaliplatin and 5-fluorouracil exhibiting the most degradation.     

Contrasting confocal with defocusing microscale spatially offset Raman spectroscopy

The study compares and contrasts conventional confocal Raman microscopy/spectroscopy (CRM) with a recently developed micrometer scale defocusing spatially offset Raman spectroscopy (micro‐SORS), a method providing a new analytical capability for investigating non‐destructively the chemical composition of subsurface, micrometer‐scale‐thick diffusely scattering layers at depths beyond the reach of CRM. Because of close similarities between the two techniques and comparable embodiment of the instrumentations, but radically different interpretations of data, it is crucially important to recognise which type of method is pertinent to a specific measurement. The distinction comes principally from the nature of sample, whether turbid (micro‐SORS measurement) or transparent (CRM measurement) on the spatial scale of the axial (z‐)scan of the measurement. Which type of sample one deals with may not always be easily recognisable with micro‐scale thick layers, and the study therefore also presents a simple method for suggesting whether CRM or micro‐SORS methodology applies. This test relies on an axial (z‐)scan performed through the sample in both the positive and negative directions from the normal, imaged sample surface position using conventional CRM instrument. The absence or presence of symmetry or asymmetry of the intensity profiles of measured Raman signals around the imaged sample surface position as a function of sample axial displacement then suggests which interpretation could apply. The study paves a way for the development of micro‐SORS as a widely applicable analytical tool deployable on conventional Raman microscopes. Copyright © 2015 John Wiley & Sons, Ltd.     

Reversible Mechanical Switching of Magnetic Interactions in a Molecular Shuttle

An acid–base switchable molecular shuttle based on a [2]rotaxane, incorporating stable radical units in both the ring and dumbbell components, is reported. The [2]rotaxane comprises a dibenzo[24]crown-8 ring (DB24C8) interlocked with a dumbbell component that possesses a dialkylammonium (NH₂⁺) and a 4,4′-bipyridinium (BPY²⁺) recognition site. Deprotonation of the rotaxane NH₂⁺ centers effects a quantitative displacement of the DB24C8 macroring to the BPY²⁺ recognition site, a process that can be reversed by acid treatment. Interaction between stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals connected to the ring and dumbbell components could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon displacement of the spin-labelled DB24C8 macroring. The complete base- and acid-induced switching cycle of the EPR pattern was repeated six times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. A system of this kind represents an initial step towards a new generation of nanoscale magnetic switches that may be of interest for a variety of applications.     

Gravitational Field Equations on Fefferman Space–Times

The total space \({\mathfrak M} \approx {\mathbb H}_1 \times S^1\) of the canonical circle bundle over the 3-dimensional Heisenberg group \({\mathbb H}_1\) is a space–time with the Lorentzian metric \(F_{\theta _0}\) (Fefferman’s metric) associated to the canonical Tanaka–Webster flat contact form \(\theta _0\) on \({\mathbb H}_1\). The matter and energy content of \(\mathfrak M\) is described by the energy-momentum tensor \({T}_{\mu \nu }\) (the trace-less Ricci tensor of \(F_{\theta _0}\)) as an effect of the non flat nature of Feferman’s metric \(F_{\theta _0}\). We study the gravitational field equations \(R_{\mu \nu } - (1/2) \, R \, g_{\mu \nu } = {T}_{\mu \nu }\) on \({\mathfrak M}\). We consider the first order perturbation \(g = F_{\theta _0} + \epsilon \, h\), \(\epsilon<< 1\), and linearize the field equations about \(F_{\theta _0}\). We determine a Lorentzian metric g on \({\mathfrak M}\) which solves the linearized field equations corresponding to a diagonal perturbation h.     

Adsorption of chlorhexidine on synthetic hydroxyapatite and in vitro biological activity

The kinetic of chlorhexidine digluconate (CHXDG) uptake from aqueous solution by hydroxyapatite (HA) was investigated by ultraviolet (UV) analysis performed in HA powder (UV-solid) after the CHX adsorption. Adsorption isotherm of chlorhexidine (CHX) uptake was modeled by a combination of Languimir and Langmuir-Freundlich mechanisms. Strong molecule-molecule interactions and positive cooperativity predominated in the surface when CHX concentration was above 8.6 μg(CHX)/mg(HA). UV-solid spectra (shape, intensity and band position) of CHX bound to HA revealed that long-range molecular structures, such as aggregates or micelles, started to be formed at low CHX concentrations (1.52 μg(CHX)/mg(HA)) and predominated at high concentrations. Grazing-incidence X-ray diffraction (GIXRD) analysis from synchrotron radiation discarded the formation of crystalline structures on HA surface or precipitation of CHX crystalline salts, as suggested in previous works. The effect of the HA/CHX association on HA in vitro bioactivity, cytotoxicity and CHX antimicrobial activity was evaluated. It was shown that CHX did not inhibit the precipitation of a poorly crystalline apatite at HA/CHX surface after soaking in simulating body fluid (SBF). Cell viability studies after exposure to extracts of HA and HA/CHX showed that both biomaterials did not present significant in vitro toxicity. Moreover, HA/CHX inhibited Enterococcus faecalis growth for up to 6 days, revealing that binding to HA did not affect antimicrobial activity of CHX and reduced bacterial adhesion. These results suggested that HA/CHX association could result in a potential adjuvant antimicrobial system for clinical use.