Multivariate curve resolution of pH gradient flow injection mixture analysis with correction of the Schlieren effect

Multivariate curve resolution using alternating least squares (MCR-ALS) was used to quantify ascorbic (AA) and acetylsalicylic (ASA) acids in four pharmaceutical samples using a flow injection analysis (FIA) system with pH gradient and a diode array (DAD) spectrometer as a detector. Four different pharmaceutical drugs were analyzed, giving a data array of dimensions 51 x 291 x 61, corresponding respectively to number of samples, FIA times and spectral wavelengths. MCR-ALS was applied to these large data sets using different constraints to have optimal resolution and optimal quantitative estimations of the two analytes (AA and ASA). Since both analytes give an acid-basic pair of species contributing to the UV recorded signal, at least four components sholuld be proposed to model AA and ASA in synthetic mixture samples. Moreover, one additional component was needed to resolve accurately the Schlieren effect and another additional component was also needed to model the presence of possible interferences (like caffeine) in the commercial drugs tablets, giving therefore a total number of 6 independent components needed. The best quantification relative errors were around 2% compared to the reference values obtained by HPLC and by the oxidation-reduction titrimetric method, for ASA and AA respectively. In this work, the application of MCR-ALS allowed for the first time the full resolution of the FIA diffusion profile due to the Schlieren effect as an independent signal contribution, suggesting that the proposed MCR-ALS method allows for its accurate correction in FIA-DAD systems.     

Multiplicity of Radial Ground States for the Scalar Curvature Equation Without Reciprocal Symmetry

Journal of Dynamics and Differential Equations - We study existence and multiplicity of positive ground states for the scalar curvature equation $$\begin{aligned} \varDelta u+ K(|x|)\,...     

Mathematical models for the non‐isothermal Johnson–Segalman viscoelasticity in porous media: stability and wave propagation

We present a nonlinear model for Johnson–Segalman type polymeric fluids in porous media, accounting for thermal effects of Oldroyd‐B type. We provide a thermodynamic development of the Darcy's theory, which is consistent with the interlacement between thermal and viscoelastic relaxation effects and diffusion phenomena. The appropriate invariant convected time derivative for the flux vector and the stress tensor is discussed. This is performed by investigating the local balance laws and entropy inequality in the spatial configuration, within the single‐fluid approach. For constant parameters, our thermomechanical setting is of Jeffreys type with two delay time parameters, and hence, in the linear/linearized version, it is strictly related to phase‐lag theories within first‐order Taylor approximations. A detailed spectral analysis is carried out for the linearized version of the model, with a scrutiny to some significant limit situations, enhancing the stabilizing effects of the dissipative and elastic mechanisms, also for retardation responses. For polymeric liquids, rheological aspects, wave propagation properties and analogies with other theories with lagging are pointed out. Copyright © 2014 John Wiley & Sons, Ltd.     

Theoretical study of spectroscopic properties of insulated molecular wires formed by substituted oligothiophenes and cross‐linked α‐cyclodextrin

The inclusion compound formed between cross‐linked α‐cyclodextrin dimer and substituted oligothiophene, was investigated using density functional theory (DFT). Energy gap, spectroscopy (IR, UV–vis, ¹³C NMR, and ¹H NMR) and first hyperpolarizability data were analyzed for the free species and inclusion compound, pp‐PT@(αCD–αCD). The semiconducting property of the included pp‐PT was not substantially affected on inclusion, with the energy gap increasing by only 10% after interaction with αCD–αCD. On the other hand, the nonlinear optical (NLO) response was significantly decreased, with the first hyperpolarizability, β, predicted to be just more than 60% lower for the [2]rotaxane than for free pp‐PT, but still having considerable magnitude. This was explained by the two‐state model based on the charge‐transfer contribution to the electronic transitions. The sensitivity of electronic spectra might also be useful for the inclusion complex characterization. The IR spectrum was slightly sensitive to the host–guest interaction and the calculated ¹³C NMR and ¹H NMR chemical shifts for the pp‐PT guest showed appreciable variations of 5–10 and 1–1.5 ppm, respectively, and so can be used for the characterization of inclusion compounds. We concluded that the formation of inclusion complexes with CDs, seems indeed very promising and the use of encapsulating conducting material should be experimentally pursued. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Complex palytoxin‐like profile of Ostreopsis ovata. Identification of four new ovatoxins by high‐resolution liquid chromatography/mass spectrometry

Over the past decades, Italian coastlines have been plagued by recurring presence of the benthic dinoflagellate Ostreopsis ovata. Such an alga has caused severe sanitary emergencies and economic losses due to its production of palytoxin‐like compounds. Previous studies have confirmed the presence of ovatoxin‐a (OVTX‐a) as the major toxin of the algal toxin profile together with small amounts of putative palytoxin (PLTX). In our ongoing research on O. ovata toxins we report herein on in‐depth investigation of an O. ovata culture carried out by high‐resolution (HR) liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (MS²). Particularly, the presence of putative PLTX and OVTX‐a was confirmed and the occurrence in the extract of four new palytoxin‐like compounds, OVTX‐b, ‐c, ‐d, and ‐e, was highlighted. Elemental formulae have been assigned to the new ovatoxins and information has been gained about their structural features. A quantitative study of the O. ovata culture extract indicated that the whole of the new ovatoxins represents about 46% of the total toxin content and, thus, their presence has to be taken into account when LC/MS‐based monitoring programs of either plankton or contaminated seafood are carried out. Copyright © 2010 John Wiley & Sons, Ltd.     

2-Acetylpyridine- and 2-benzoylpyridine-derived thiosemicarbazones and their antimony(III) complexes exhibit high anti-trypanosomal activity

Complexes [Sb(2Ac4oClPh)Cl₂] (1), [Sb(2Ac4oFPh)Cl₂] (2), [Sb(2Ac4oNO₂Ph)Cl₂] (3), [Sb(2Bz4oClPh)Cl₂] (4), [Sb(2Bz4oFPh)Cl₂] (5) and [Sb(2Bz4oNO₂Ph)Cl₂] (6) were obtained with 2-acetylpyridine-N(4)-ortho-chlorophenyl thiosemicarbazone (H2Ac4oClPh) and its N(4)-ortho-fluor (H2Ac4oFPh) and N(4)-ortho-nitro (H2Ac4oNO₂Ph) analogues, and with the corresponding 2-benzoylpyridine-derived thiosemicarbazones (H2Bz4oClPh, H2Bz4oFPh, H2Bz4oNO₂Ph). The studied compounds are excellent inhibitors of Trypanosoma cruzi growth. H2Bz4oClPh and complexes (4) and (1) were the most trypanosomicidal.Upon coordination of H2Ac4oClPh to antimony(III) in 1, the therapeutic index (TI) goes from 10.58 to 14.35. However, the best values of TI were found for H2Bz4oClPh (TI = 1240) and H2Ac4oNO₂Ph (TI = 773). Structure-activity relationship (SAR) studies did not allow the establishment of correlations between the anti-trypanosomal activity and physico-chemical parameters, but correlations were found between the cytotoxicities and physico-chemical properties.     

Uncatalyzed, diastereoselective vinylogous Mukaiyama aldol reactions on aqueous media: pyrrole vs furan 2-silyloxy dienes

The first uncatalyzed, diastereoselective vinylogous Mukaiyama aldol reaction is reported, between pyrrole/furan-based dienoxy silanes and aromatic aldehydes on salty water/methanol medium, at almost human body temperature, under ultrasonic irradiation. With pyrrole dienes the reaction is anti-selective, while that of furan dienes is syn-selective. The dual role of water as both reaction medium and promoter is highlighted.     

Ultra‐fast adenosine 5′‐triphosphate,adenosine 5′‐diphosphate and adenosine 5′‐monophosphate detection by pressure‐assisted capillary electrophoresis UV detection

Herein, we report a new CE method to measure adenine nucleotides adenosine 5′‐triphosphate, adenosine 5′‐diphosphate, and adenosine 5′‐monophosphate in red blood cells. For this purpose, 20 mmol/L sodium acetate buffer at pH 3.80 was used as running electrolyte, and the separation was performed by the simultaneous application of a CE voltage of 25 kV and an overimposed pressure of 0.2 psi from inlet to outlet. A rapid separation of these analytes in less than 1.5 min was obtained with a good reproducibility for intra‐ and inter‐assay (CV<4 and 8%, respectively) and an excellent analytical recovery (from 98.3 to 99%). The applicability of our method was proved by measuring adenine nucleotides in red blood cells.