A kinetic spectrophotometric method for simultaneous determination of phenol and its three derivatives with the aid of artificial neural network

A novel kinetic spectrophotometric method was developed for determination of pyrocatechol, resorcin, hydroquinone and phenol based on their inhibitory effect on the oxidation of Rhodamine B (RhB) in acid medium at pH = 3.0. A linear relationship was observed between the inhibitory effect and the concentrations of the compounds. The absorbance associated with the kinetic reactions was monitored at the maximum wavelength of 557 nm. The effects of different parameters such as pH, concentration of RhB and KBrO₃, and temperature of the reaction were investigated and optimum conditions were established. The linear ranges were 0.22-3.30, 0.108-0.828, 0.36-3.96 and 1.52-19.76 μg mL⁻¹ for pyrocatechol, resorcin, hydroquinone and phenol, respectively, and their corresponding detection limits were 0.15, 0.044, 0.16 and 0.60 μg mL⁻¹. The measured data were processed by several chemometrics methods, such as principal component regression (PCR), partial least squares (PLS) and artificial neural network (ANN), and a set of synthetic mixtures of these compounds was used to verify the established models. It was found that the prediction ability of PLS, PCR and RBF-ANN was similar, however, the RBF-ANN model did perform somewhat better than the other methods. The proposed method was also applied satisfactorily for the simultaneous determination of pyrocatechol, resorcin, hydroquinone and phenol in real water samples.     

Further exploring rm metrics for validation of QSPR models

Quantitative structure-property relationship (QSPR) models are widely used for prediction of properties, activities and/or toxicities of new chemicals. Validation strategies check the reliability of predictions of QSPR models. The classical metrics like Q² and R²_pred (Q²_ext) are commonly used, besides other techniques, for internal validation (mostly leave-one-out) and external validation (test set validation) respectively. Recently, we have proposed a set of novel r_m² metrics which has been extensively used by us and other research groups for validation of QSPR models. In the present attempt, some additional variants of r_m² metrics have been proposed and their applications in judging the quality of predictions of QSPR models have been shown by analyzing results of the QSPR models obtained from three different data sets (n = 119, 90, and 384). In each case, 50 combinations of training and test sets have been generated, and models have been developed based on the training set compounds and subsequently applied for prediction of responses of the test set compounds. Finally, models for a particular data set have been ranked according to the quality of predictions. The role of different validation metrics (including classical metrics and different variants of r_m² metrics) in differentiating the “good” (predictive) models from the “bad” (low predictive) models has been studied. Finally, a set of guidelines has been proposed for checking the predictive quality of QSPR models.     

Cloud point extraction for determination of Diazinon: Optimization of the effective parameters using Taguchi method

Since Diazinon is one of the organophosphorous compounds which are harmful for human organisms, a simple, sensitive and accurate testing method for extraction and determination of this pesticide is mandatory. In this project, Cloud Point Extraction (CPE) method was developed for determination of Diazinon in aqueous samples. CTAB (cetyl trimethyl ammonium bromide) was used as cationic surfactant to extract and preconcentrate of Diazinon at the same time and the extracted Diazinon was determined by UV spectrophotometery. Taguchi L₉ array was employed for design of experiments to investigate influences of surfactant concentration, salt concentration, temperature and incubation time as effective parameters. According to the analysis of variance (ANOVA) results, the most effective parameter of the process is incubation time. The results show that a surfactant concentration of 10^− 5% (w/v), an incubation time of 30 min, a KI concentration of 10^− 6 mol L^− 1 and a temperature of 35 °C are the best operating conditions. Also, the linear calibration graph in the range of 0.02-24 ng ml^− 1 of Diazinon with r = 0.999 was obtained. The limit of detection (LOD) was 0.02 ng ml^− 1 and relative standard deviation (RSD) for 15 ng ml^− 1 of Diazinon was 0.76%.     

Hot deformation behavior of an extruded Mg-Li-Zn-RE alloy

A new Mg-7.8%Li-4.6%Zn-0.96%Ce-0.85%Y-0.30%Zr alloy has been developed. α phase, β phase and RE-containing intermetallics formed in the alloy. It is found that the alloy can easily be extruded at 260 °C with σ_0.2 = 256 MPa, σ_b = 260 MPa and δ = 14%. Hot deformation behavior of the extruded alloy was studied using the processing map technique. Compression tests were conducted in the temperature range of 250-450 °C and strain rate range of 0.001-10 s⁻¹ and the flow stress data obtained from the tests were used to develop the processing map. The different efficiency domains and flow instability region corresponding to various microstructural characteristics have been identified as follows: (1) Domain I occurs in the temperature range of 250-275 °C and strain rate range of 1-10 s⁻¹, with a peak efficiency of about 50% at 250 °C/10 s⁻¹. Incomplete DRX process has occurred in β phase and DRX process hardly occurs in α phase; (2) Domain II occurs in the temperature range of 250-275 ?C and strain rate range of 0.001-0.003 s⁻¹, with a peak efficiency of about 42% at 250 °C/0.001 s ⁻¹. Incomplete DRX process has occurred in β phase and α phase; (3) Domain III occurs in the temperature range of 400-450 °C and strain rate range of 1-10 s⁻¹, with a peak efficiency of about 42% at 450 °C/10 s⁻¹. Complete DRX process has occurred in β phase and α phase. No cracking, cavity and band of flow localization are observed in flow instability region. The optimum parameters for hot working of the alloy are 250 °C/10 s⁻¹ and 250 °C/0.001 s⁻¹, at which fine dynamic recrystallization microstructure will be achieved. RE-containing intermetallics and α phase accelerate the DRX process in β phase. The softer β phase reduces the driving force for DRX process in α phase, so DRX process in α phase is retarded.     

Dynamic tensile behavior of multi phase high yield strength steel

Results of uni-axial tensile testing of multi phase 800 High Yield strength steel (MP800HY) at different strain rates (0.001–750 s⁻¹) are reported here. Flat specimens having gauge length 10 mm, width 4 mm and thickness 2 mm were tested to determine the mechanical properties of MP800HY under tensile loads. The quasi-static tests (0.001 s⁻¹) were performed on electromechanical universal testing machine, whereas, hydro-pneumatic machine and modified Hopkinson bar apparatus were used for testing at intermediate (5 s⁻¹, 25 s⁻¹) and high strain rates (250 s⁻¹, 500 s⁻¹, 750 s⁻¹) respectively. Based on the experimental results, the material parameters of existing Cowper–Symonds and Johnson–Cook models are determined. These models fit the experimental data well in the plastic zone. The fracture surfaces of the broken specimens are studied from their fractographs taken by scanning electron microscope (SEM).     

The electronic properties of metal complexed poly(3-alkylthiophene) films

Dielectric spectroscopy has been used to extract the AC and DC electrical conductivities of P3MT complexed with the paramagnetic ion Fe²⁺, and these were compared to data for uncomplexed P3MT in the frequency range of 1 Hz-10 MHz. The polymers were nominally undoped; however, the presence of residual Fe³⁺ ions from the polymerisation reaction renders the materials p-type semiconductors. Measurements were carried out over the temperature range 123-323 K. An analysis of the frequency-dependent complex conductivity together with the DC conductivity can be used to elucidate whether free charge conduction, charge hopping or quantum tunnelling is the dominant conduction mechanism. The results were compared to the predictions of a variety of theoretical conduction models. It was found that the presence of the Fe²⁺ ions produced greater long-range order at low temperatures by complexing between the sulphur heteroatoms of four 3-methylthiophene monomer units. This provided an additional barrier hopping conduction mechanism at low temperatures (183-243 K), and the hopping occurred over a barrier height within the range 0.45-0.6 eV.     

Simultaneous in situ monitoring of acrylic acid polymerization reaction on N-carboxymethyl chitosan using multidetectors: Formation of a new bioadhesive and gastroprotective hybrid particle

Chitosan and polyacrylic acid (PAA) both have weak, short-lasting bioadhesive properties; therefore, a hybrid particle composed of a chitosan derivative and PAA could be used as a new bioadhesive agent. Using simultaneous in-situ monitoring with a multidetection system, N-carboxymethyl chitosan was ionically bonded to acrylic acid and then polymerized using potassium persulphate as the initiator (N-CMC_A-D_h of 165 nm). The PAA on N-CMC_A was crosslinked using N,N-methylene-bisacrylamide (N-CMC_AC-D_h of 141 nm). During polymerization, the solution developed a milky white appearance, and polymerization kinetics was determined to be 3.2 × 10^−3 ± 4.0 × 10⁻⁶ mmol/min. The reaction for PAA alone was 1.7 times faster than that of the hybrid system. The particles showed an increase in thermal stability and reduction of thermal-mass loss compared with the N-CMC alone. The N-CMC_AC particles showed the highest bioadhesion onto the stomach. The gastroprotection index of N-CMCh_AC particles against ethanol/HCl-induced ulcers in mice was 68.2 ± 6.4%. Similar results were observed for omeprazole (74.2 ± 5.3%). The particles obtained in this work have potential for use in drug delivery to the stomach, perhaps to aid in treating ulceration and inflammation, and can be used as a system for the prevention of ethanol-induced ulcers.     

Energy levels and crystal-field parameters for Pr and Nd ions in rare earth (RE) tellurium oxides RE2Te4O11 revisited - Ascent/descent in symmetry method applied for triclinic site symmetry

Triclinic site symmetry presents considerable challenges in the studies of energy levels and crystal-field parameters (CFPs) for rare earth (RE) ions in crystals. Assignment of the spectral features to the irreducible representations of low symmetry point groups is difficult and may be unreliable. Fittings of large number of CFPs, even if the number of the available experimental energy levels is sufficient, often yield multiple solutions with relatively low and close rms deviations. These challenges call for better methods of fitting and analysis of CFPs. In this paper, we employ the ascent/descent in symmetry (ADS) method and three computational approaches: (i) a crystallographic data analysis program to identify approximated higher symmetry, (ii) the superposition model (SPM) analysis, and (iii) the pseudosymmetry axes method (PAM) for the combined coordination factors obtained using SPM. As a case study, the experimental CF splittings of Pr³⁺ and Nd³⁺ ions at triclinic C₁ sites in tellurium oxides RE₂Te₄O₁₁ are re-analyzed. Two alternative ADS chains C₁ ↔ C₂ ↔ D₂ and C₁ ↔ C_s ↔ C_2v were independently obtained. For each approximation of the actual C₁ symmetry of the REO₈ polyhedron in RE₂Te₄O₁₁, the ligands’ positions are determined and used in SPM to calculate CFP sets, which are used as starting for additional fittings. Comparative analysis of the fitted and calculated CFP sets enables assignment of appropriate axis system to the fitted CFP sets, thus avoiding the ambiguities occurring in previous ADS applications. The very good compatibility and consistency of the newly determined CFP sets indicate high reliability of both approaches. These CFP sets were used to simulate magnetic susceptibility data for polycrystalline samples of Pr₂Te₄O₁₁ and Nd₂Te₄O₁₁. Wider applications of the proposed procedures in optical spectroscopy studies of low symmetry systems may improve reliability of the CFP sets reported in literature.     

Comparison of FANS and ARCS incoherent inelastic neutron scattering measurements of hydrogen trapped at dislocations in deformed Pd

Incoherent inelastic neutron scattering (IINS) measurements of the vibrational density of states (VDOS) of hydrogen trapped at dislocations in deformed PdH_0.0013 have been performed using ARCS at the SNS and FANS at the NCNR. A comparison of data sets at 4 and 295 K indicates good agreement of the measured VDOS for the two instruments. The low hydrogen inventory (∼10^-3 g) provides a test of the response of each instrument over the energy transfer range of 40-100 meV corresponding to the vibrational density of states of the hydrogen modes.     

Synthesis of ordered mesostructured polymer-organosilica composites by the triconstituent co-assembly method

Ordered mesoporous polymer-organosilica composites have been synthesized through a triconstituent co-assembly strategy. These composites have ordered 2-D hexagonal mesostructures (space group p6m) with uniform pore size (6.2-7.3 nm), suitable surface areas (619-794 m² g⁻¹) and pore volumes (0.61-0.88 cm³ g⁻¹). With increasing BTSE (1,2-bis(triethoxysilyl)ethane) content, the surface area and pore volume reduce. The composites have homogeneous interpenetrating frameworks, in which both polymer and organosilica synergistically support the ordered mesostructure. The hybrid materials exhibit good adsorption capacities of benzene (up to 2.0 mmol g⁻¹), suggesting their use as a potential adsorbent for removal of volatile organic compounds.     

Tuning kinetics of controlled-release in disulfide-linked MSN-folate conjugates with different fabrication procedures

A drug delivery system based on disulfide-linked MSN-folate conjugates is fabricated via co-condensation and post-grafting methods. The premature leakage before DDSs reach the specific site is eliminated due to the covalent conjugation, which is desirable for drug delivery, especially for the delivery of those highly toxic anticancer drugs. Interestingly, the controlled release responsive to redox stimuli is tunable by using different fabrication procedure. The system fabricated with co-condensation exhibits first-order release while that with post-grafting exhibits zero-order release. The constant release rate is an especially interesting behavior that avoids peaks in the rate of drug delivery. The cumulative release data were used to fit in Korsmeyer-Peppas model to figure out the release mechanism. The exponent n = 0.22 for MF1 indicates Fick diffusion while n = 0.49 for MF2 indicates non-Fick or anomalous diffusion.     

Optical properties of evaporated poly-Si thin-films on glass

The optical properties of boron- and phosphorus-doped polycrystalline silicon films with light (~ 1 × 10¹⁶ cm⁻³), moderate (~ 5 × 10¹⁷ cm⁻³) and heavy doping (~ 1 × 10¹⁹ cm⁻³) were investigated in this work. The films were prepared by solid-phase crystallization of evaporated amorphous silicon films on borosilicate glass. Tauc-Lorentz models with one or two oscillators were used to model both reflection and transmission data collected by a spectrophotometer over the wavelength range of 400 nm-2000 nm. The results indicate that the crystal quality of the films is improved by phosphorus doping, while boron has a negligible impact on the crystal quality. The poly-Si films exhibit greater absorption than c-Si for visible wavelengths. This enhanced absorption is believed to be associated with defected a-Si material at the grain boundaries and intra-grain defects.     

Measurement of isobaric heat capacity of R125

The specific isobaric heat capacity (c_p) was measured for R125 (pentafluoroethane) in the gas phase by using a flow calorimeter. Twelve measurements for R125 were obtained at temperatures from 313 to 333 K and at pressures from 0.8 to 2.4 MPa. Some of them are close to the saturation curve. The expanded uncertainty (k = 2) of the temperature measurements is estimated to be less than 23 mK, and that of the pressure measurements is less than 14 kPa. The expanded uncertainty for c_p is estimated to range from 12 to 22 J kg⁻¹ K⁻¹. Also, the experimental data were compared with available equations of state. From the results, it became clear that these data will be essential to improve available models so as to represent more reliable thermodynamic properties of R125 and refrigerant mixtures with R125 that are used for refrigeration and air conditioning systems.     

Direct encapsulation of water-soluble drug into silica microcapsules for sustained release applications

Direct encapsulation of water-soluble drug into silica microcapsules was facilely achieved by a sol-gel process of tetraethoxysilane (TEOS) in W/O emulsion with hydrochloric acid (HCl) aqueous solution containing Tween 80 and drug as well as cyclohexane solution containing Span 80. Two water-soluble drugs of gentamicin sulphate (GS) and salbutamol sulphate (SS) were chosen as model drugs. The characterization of drug encapsulated silica microcapsules by scanning electronic microscopy (SEM), FTIR, thermogravimetry (TG) and N₂ adsorption-desorption analyses indicated that drug was successfully entrapped into silica microcapsules. The as-prepared silica microcapsules were uniform spherical particles with hollow structure, good dispersion and a size of 5-10 μm, and had a specific surface area of about 306 m²/g. UV-vis and thermogravimetry (TG) analyses were performed to determine the amount of drug encapsulated in the microcapsules. The BJH pore size distribution (PSD) of silica microcapsules before and after removing drug was examined. In vitro release behavior of drug in simulated body fluid (SBF) revealed that such system exhibited excellent sustained release properties.