CaF<Subscript>2</Subscript> thin films obtained by electrochemical processes and the effect of Tb<Superscript>3+</Superscript> doping concentration on their structural and optical properties

In this study, we analyze the effect of Tb³⁺ concentration on the structural and optical properties of CaF₂ terbium-doped thin films deposited on soda-lime glass substrates with an indium tin oxide (ITO)-sputtered coating by means of electrochemical processes. Compositional results showed that thin films have excess of F, which is believed to be the source for defect formation. XRD results showed not only shifting and widening of the CaF₂ peaks as a function of [Tb³⁺] increase in the electrolitic solution but also an additional peak when high [Tb³⁺] are used, promoting thus the formation of secondary phases such as NaTbF₄. According to photoluminescence (PL) results, when using UV excitation (λ?=?325 nm), CaF₂:Tb³⁺ thin films presented green emission (⁵D₄?→?⁷F_J, where J?=?6, 5, 4, 3, 2, 1, 0). Besides, PL studies not only allowed us to establish the quenching for Tb³⁺ concentration in the CaF₂ matrix, but they also showed that there are no changes in intensity or peak position attributed to the presence of cubic NaTbF₄ because its emission coincides with that of CaF₂ terbium-doped thin films.

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Graphical abstract Increase of [Tb³⁺] in the CaF₂ solution and the presence of Na⁺ promotes a competition effect between CaF₂:Tb³⁺ and NaTbF₄ phases under equal deposition conditions

     

New computational approach for the simultaneous photometric determination of catalysts and activators

A new method for the simultaneous kinetic determination of catalysts and activators was developed on the basis of a mathematical model. The parameters and variables are optimized from experimental data obtained by application of a multiple standard-addition method and use of the Gauss-Newton and Simplex method, both of which provide identical results. The proposed method was applied to the simultaneous photometric determination of Mn(II) and Pb(II) on the basis of their catalytic and activating effects, respectively, on the oxidation of Tiron by hydrogen peroxide. Data were both acquired and processed with the aid of software developed by the authors. The linear determination range achieved was 1.00-5.00 ng/ml Mn(II) and 200-800 ng/ml Pb(II). Experimental readings were made at 450 nm with a fibre optics detector. The most serious interference with the method was posed by Cr(III).     

Flow techniques in water analysis

In the present work the main flow techniques for the analysis and monitoring of several parameters of interest in the quality control of different types of waters are reviewed. Firstly, a review involving the advantages and disadvantages of flow techniques, from those currently out-dated, such as segmented flow analysis (SFA), to the most modern techniques, such as flow injection analysis (FIA), sequential injection analysis (SIA) and multi-commutation techniques (MCFA), is carried out. On the other hand, a new technique, the multi-syringe flow analysis (MSFA) is hereby described for the first time as both a fast and robust alternative. Its possibilities, limitations and potential advantages when using this technique either on its own or coupled to SIA, which carries out a previous sample handling, are outlined.     

Structural study of tropane-3-spiro-4'-imidazol-5'-one

Tropane-3-spiro-4'-imidazol-5'-one has been synthesized and its crystal and molecular structures determined by X-ray diffraction, IR, Raman, ¹H-NMR and ¹³C-NMR methods. The tautomeric equilibrium between this structure and the corresponding conjugated form in different solvents is also studied from IR and UV data. The imidazoline ring, the spiranic C(3, 4'), the N(8) and the methyl C(9) atoms are situated in a plane. The piperidine ring adopts a distorted chair conformation in the crystalline form and in solution. The flattening of the C(1), C(2), C(3, 4'), C(4), C(5) part of the chair and the opposite puckering are noticeably large. In order to complete the results, some spectroscopic measurements have also been made for the tropane-3-spiro-4'-imidazol-5'-one hydrochloride.     

Isobaric (vapour + liquid + liquid) equilibrium data for (di-n-propyl ether + n-propyl alcohol + water) and (diisopropyl ether + isopropyl alcohol + water) systems at 100 kPa

Isobaric (vapour + liquid + liquid) equilibria were measured for the (di-n-propyl ether + n-propyl alcohol + water) and (diisopropyl ether + isopropyl alcohol + water) system at 100 kPa.The apparatus used for the determination of (vapour + liquid + liquid) equilibrium data was an all-glass dynamic recirculating still with an ultrasonic homogenizer couple to the boiling flask.The experimental data demonstrated the existence of a heterogeneous ternary azeotrope for both ternary systems. The (vapour + liquid + liquid) equilibria data were found to be thermodynamically consistent for both systems.The experimental data were compared with the estimation using UNIQUAC and NRTL models and the prediction of UNIFAC model.     

Analysis of intact erythropoietin and novel erythropoiesis-stimulating protein by capillary electrophoresis-electrospray-ion trap mass spectrometry

Recombinant human erythropoietin (rHuEPO) and novel erythropoiesis-stimulating protein (NESP) were analyzed by CE-ESI-MS using an IT as analyzer. The IT parameters were optimized by direct infusion of solutions of different intact proteins (myoglobin, transferrin, alpha1-acid glycoprotein and fetuin) with different degrees of glycosylation (from 0 to 35% w/w). Two physically adsorbed capillary coatings from UltraTol Pre-Coats (low normal (LN) and high reverse (HR)) were evaluated for the separation of rHuEPO and NESP glycoforms by CE-ESI-IT-MS. The results obtained with the neutral LN coating suggest that an IT mass spectrometer enables identification of the main glycoforms of a complex glycoprotein such as rHuEPO. Although LN provided acceptable glycoform resolution for rHuEPO, the separation obtained for NESP was less significant due to the higher microheterogeneity of this glycoprotein. Reproducibility studies confirmed the lack of stability and bleeding of the LN coating, which caused problems with MS detection, such as a dramatic loss of sensitivity and the presence of peaks in the mass spectra corresponding to molecular ions in the coating. In contrast, the cationic HR coating gave faster but poorer glycoform separations due to the presence of an anodal EOF. However, the positive charge of the coating provided enhanced hydrolytic stability, making it more suitable than the LN coating for the on-line MS coupling.     

Modeling the migration behavior of rabbit liver apothioneins in capillary electrophoresis

Metallothioneins (MTs) are a group of low-molecular-mass proteins (6-7 kDa) characterized by their great affinity for heavy metal ions. At acidic pH, the bound metal ions are released from the amino acidic structure and MTs lead to apothioneins. In this study, a general equation is used to model the electrophoretic mobility of rabbit liver apothioneins as a function of the pH of the separation electrolyte. The ability of these relationships to explain the migration behavior of these relatively complex polyprotic proteins in the pH range between 2 and 6 has been investigated. Their relevant ionization constant values in the studied pH range were estimated and employed for molecular charge calculations. The classical semiempirical relationships between electrophoretic mobility and charge-to-mass ratio (me vs. q/Malpha) were tested for prediction of their electrophoretic separations. The accuracy of the separations predicted at acidic pH was confirmed by CE-ESI-MS.     

Sulfoxide‐Directed Metal‐Free ortho‐Propargylation of Aromatics and Heteroaromatics

A sulfoxide‐directed, metal‐free ortho‐propargylation of aromatics and heteroaromatics exploits intermolecular delivery of a propargyl nucleophile to sulfur followed by an intramolecular relay to carbon. The operationally simple cross‐coupling procedure is general, regiospecific with regard to the propargyl nucleophile, and shows complete selectivity for products of ortho‐propargylation over allenylation. The use of secondary propargyl silanes allows metal‐free ortho‐coupling to form carbon–carbon bonds between aromatic and heteroaromatic rings and secondary propargylic centres. The ‘safety‐catch’ nature of the sulfoxide directing group is illustrated in a selective, iterative double cross‐coupling process. The products of propargylation are versatile intermediates and they have been readily converted into substituted benzothiophenes.     

Forecasting molecular dynamics energetics of polymers in solution from supervised machine learning

Machine learning techniques including neural networks are popular tools for chemical, physical and materials applications searching for viable alternative methods in the analysis of structure and energetics of systems ranging from crystals to biomolecules. Efforts are less abundant for prediction of kinetics and dynamics. Here we explore the ability of three well established recurrent neural network architectures for reproducing and forecasting the energetics of a liquid solution of ethyl acetate containing a macromolecular polymer–lipid aggregate at ambient conditions. Data models from three recurrent neural networks, ERNN, LSTM and GRU, are trained and tested on half million points time series of the macromolecular aggregate potential energy and its interaction energy with the solvent obtained from molecular dynamics simulations. Our exhaustive analyses convey that the recurrent neural network architectures investigated generate data models that reproduce excellently the time series although their capability of yielding short or long term energetics forecasts with expected statistical distributions of the time points is limited. We propose an in silico protocol by extracting time patterns of the original series and utilizing these patterns to create an ensemble of artificial network models trained on an ensemble of time series seeded by the additional time patters. The energetics forecast improve, predicting a band of forecasted time series with a spread of values consistent with the molecular dynamics energy fluctuations span. Although the distribution of points from the band of energy forecasts is not optimal, the proposed in silico protocol provides useful estimates of the solvated macromolecular aggregate fate. Given the growing application of artificial networks in materials design, the data-based protocol presented here expands the realm of science areas where supervised machine learning serves as a decision making tool aiding the simulation practitioner to assess when long simulations are worth to be continued.

Recurrent neural networks as a machine learning tools are gaining popularity in chemical, physical and materials applications searching for viable methods in the structure and energetics analyses of systems ranging from crystals to soft matter.     

Chip-Based Spectrofluorimetric Determination of Iodine in a Multi-Syringe Flow Platform with and without In-Line Digestion—Application to Salt,Pharmaceuticals, and Algae Samples

In this work, a flow-based spectrofluorimetric method for iodine determination was developed. The system consisted of a miniaturized chip-based flow manifold for solutions handling and with integrated spectrofluorimetric detection. A multi-syringe module was used as a liquid driver. Iodide was quantified from its catalytic effect on the redox reaction between Ce(IV) and As(III), based on the Sandell–Kolthoff reaction. The method was applied for the determination of iodine in salt, pharmaceuticals, supplement pills, and seaweed samples without off-line pre-treatment. An in-line oxidation process, aided by UV radiation, was implemented to analyse some samples (supplement pills and seaweed samples) to eliminate interferences and release iodine from organo-iodine compounds. This feature, combined with the fluorometric reaction, makes this method simpler, faster, and more sensitive than the classic approach of the Sandell–Kolthoff reaction. The method allowed iodine to be determined within a range of 0.20–4.0 µmol L⁻¹, with or without the in-line UV digestion, with a limit of detection of 0.028 µmol L⁻¹ and 0.025 µmol L⁻¹, respectively.