Porphyrins as Colorimetric and Photometric Biosensors in Modern Bioanalytical Systems

Advances in porphyrin chemistry have provided novel materials and exciting technologies for bioanalysis such as colorimetric sensor array (CSA), photo-electrochemical (PEC) biosensing, and nanocomposites as peroxidase mimetics for glucose detection. This review highlights selected recent advances in the construction of supramolecular assemblies based on the porphyrin macrocycle that provide recognition of various biologically important entities through the unique porphyrin properties associated with colorimetry, spectrophotometry, and photo-electrochemistry.     

Influence of Poloxamer 407 on Surface Properties of Aqueous Solutions of Polysorbate Surfactants

Owing to their ability to adsorb at interfaces, polysorbates have an important role in pharmaceutical formulations. Because surfactant mixtures can have improved properties, it was hypothesized in this work that introduction of poloxamer 407 to aqueous solutions of polysorbates (polysorbate 60, polysorbate 80 and polysorbate 85) might improve their surface properties. Nonideal behavior of surfactant mixtures at the air/water interface was investigated using Rosen's model and recently introduced method for the determination and quantification of nonideal behavior regarding surface tension reduction and adsorption effectiveness. Although nonideal behavior was noticed in all mixed monolayers, it was shown that the structure of the hydrophobic domain of the polysorbates and the conformation of poloxamer 407 at the interface have strong influence on the nonideality.     

Supramolecular Polymorphism of (G4C2)n Repeats Associated with ALS and FTD

Guanine-rich DNA sequences self-assemble into highly stable fourfold structures known as DNA-quadruplexes (or G-quadruplexes). G-quadruplexes have furthermore the tendency to associate into one-dimensional supramolecular aggregates termed G-wires. We studied the formation of G-wires in solutions of the sequences d(G₄C₂)_n with n = 1, 2, and 4. The d(G₄C₂)_n repeats, which are associated with some fatal neurological disorders, especially amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), represent a challenging research topic due to their extensive structural polymorphism. We used dynamic light scattering (DLS) to measure translational diffusion coefficients and consequently resolve the length of the larger aggregates formed in solution. We found that all three sequences assemble into longer structures than previously reported. The d(G₄C₂) formed extremely long G-wires with lengths beyond 80 nm. The d(G₄C₂)₂ formed a relatively short stacked dimeric quadruplex, while d(G₄C₂)₄ formed multimers corresponding to seven stacked intramolecular quadruplexes. Profound differences between the multimerization properties of the investigated sequences were also confirmed by the AFM imaging of surface films. We propose that π-π stacking of the basic G-quadruplex units plays a vital role in the multimerization mechanism, which might be relevant for transformation from the regular medium-length to disease-related long d(G₄C₂)_n repeats.     

Improved trapped field performance of single grain Y-Ba-Cu-O bulk superconductors containing artificial holes

The intrinsic mechanical properties of single-grain RE-Ba-Cu-O bulk high-temperature superconductors can be improved by employing a thin-wall geometry. This is where the samples are melt-processed with a predefined network of artificial holes to decrease the effective wall thickness. In this study, the tensile strengths of thin-wall YBCO disks were determined using the Brazilian test at room temperature. Compared with conventional single grain YBCO disks, the thin-wall YBCO disks displayed an average tensile strength that is 93% higher when the holes were filled with Stycast epoxy resin. This implies a thin-wall sample should, in theory, be able to sustain a trapped field that is 39% higher without exceeding the mechanical limit of the sample. High-field magnetization experiments were performed by applying magnetization fields of up to 11.5 T, specifically to break the samples in order to verify the effect of increased mechanical strength (and improved cooling) on the ability of bulk (RE)BCO to trap field successfully. The standard YBCO sample failed when it was magnetized with a field of 10 T at 35 K, suffering permanent damage. As a result, the standard sample could only trap a maximum surface field of 7.6 T without failure. On the other hand, the thin-wall YBCO sample survived all magnetization cycles, including a maximum magnetization field of 11.5 T at 35 K, demonstrating a greater intrinsic ability to withstand significantly higher electromagnetic stresses. By subsequently field-cooling the thin-wall sample with 11 T at 30 K, a surface field of 8.8 T was trapped successfully without requiring any external ring reinforcement.     

Repeatability and reproducibility of specular gloss meters in theory and practice

In order to numerically quantify and to ensure consistency of the visual appearance of the end product, many industries perform color and gloss measurements, through the results of which they define maximum tolerances during quality control. For this, they may primarily rely on precision data for repeatability and reproducibility as reported by instrument manufacturers, who develop their instruments according to standardized measurement geometries defined in international standards. This paper reports on an investigation of the inter-instrument agreement between specular gloss meters which conform to universally adopted gloss standards. Six commercially available instruments, manufactured by three different companies, and twenty-five gloss artifacts, with specular gloss values ranging between 2 and 110 gloss units (60° geometry), were selected for use in the study. The repeatability and reproducibility of the instruments were assessed according to the criteria described in ASTM D523-14 and ISO 2813:2014, and to the specifications reported by the instrument manufacturers. Ray tracing simulations were performed by use of the bidirectional reflectance distribution function measurement data of two samples, and based on the standardized optical design of the specular gloss meter, in order to get a better insight on the expected tolerances of the gloss readings from a theoretical point of view. On average, the practical results indicate that both the repeatability and reproducibility values are higher than those specified in the recommendations and by the manufacturers. Ray tracing simulations confirm this finding. While specified repeatability and reproducibility thresholds are based on ideal standards, in practice, there are parameters that can lead to significant higher deviations. Care should therefore be taken when analyzing measurement results obtained from different instruments, and when defining tolerances for evaluation of gloss measurements.     

Kinetic Analysis of Nonisothermal Reduction of Silica-Supported Nickel Catalyst Precursors in a Hydrogen Atmosphere

A series of silica-supported nickel catalyst precursors was synthesized with different SiO₂/Ni molar ratios. Reduction of Ni catalyst precursors with different SiO₂/Ni molar ratios under a hydrogen atmosphere was investigated at different heating rates. Kinetic parameters were determined using Kissinger–Akahira–Sunose isoconversional and invariant kinetic parameter methods. It was found that for all molar ratios, the apparent activation energy (E_a) is practically constant in the conversion range of 0.20 ≤ α ≤ 0.80. In the considered conversion range, following values of E_a were found: 134.5 kJ mol^?1 (SiO₂/Ni = 0.20), 139.6 kJ mol^?1 (SiO₂/Ni = 0.80), and 128.3 kJ mol^?1 (SiO₂/Ni = 1.15). It was established that the reduction of Ni catalyst precursors with different SiO₂/Ni molar ratios is a complex process and can be described by the ?esták–Berggren autocatalytic model. It was found that the reaction is more Langmuir–Hinshelwood type, as hydrogen dissociates rapidly on surface nuclei and the dissociated hydrogen reacts with the Ni–O active system. It was concluded that the reduction process proceeds through bulk nucleation, which is a dominant mechanism, where three-dimensional growth of crystals with polyhedron-like morphology exists. It was found that the Ni/Si ratio decreases after the reduction process. This has been explained by low Ni and higher Si surface concentrations. It has been disclosed that Ni dispersion decreases.     

The effect of extraction techniques on yield,extraction kinetics,and antioxidant activity of aqueous-methanolic extracts from nettle (Urtica dioica L.) leaves

Five extraction techniques, maceration, reflux, Soxhlet, Tillepape, and ultrasonic extraction, were used to obtain the extractive matter from nettle leaves. The antioxidant activity of extracts was assessed by DPPH, FRAP, and H₂O₂ test, while the total phenolic and total flavonoid content was determined according to the Folin–Ciocalteu and aluminium chloride methods, respectively. Model Ponomarev and a non-stationary diffusion model through the plant material were used for modelling extraction process. The extract obtained by Soxhlet extraction, containing higher amounts of extractive matter as well as phenolic and flavonoid compounds, showed better antioxidant activity than those obtained by other extraction techniques.     

Electrocaloric properties of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 ceramics with different grain sizes

We have investigated the electrocaloric (EC) properties of the ceramic 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃. A variety of samples with different median grain sizes, i.e., 1.0, 2.2 and 4.0?μm, and relative densities of about 96% were prepared using atmospheric sintering at 1200^oC for 2, 8 and 16?h. The ceramic material with a median grain size of 2.2?μm exhibited the highest value for the EC temperature change, i.e., 1.27?K at 60?kV?cm^?1, measured with a high-resolution calorimeter. This value is 25 and 19% higher than the value for the ceramics with the finer and the coarser grains, respectively.     

Pilot Studies of Ozonation for Inactivation of Artemia salina Nauplii in Ballast Water

A pilot-plant study was conducted in the Republic of Croatia to determine the applicability of ozonation for inactivation of non-indigenous species and to provide necessary information regarding use of ozone as a ballast water treatment option. Nauplii of the brine shrimp Artemia salina were used as model organisms to investigate the efficacy of ozonation at three different ozone dosages (2.4, 3.7 and 10.9 mg L^?1). Mortality of Artemia nauplii at 98.6%, was achieved after 3 h of exposure in ozone-treated water with the highest ozone dosage. Our results indicated that ozonation is a promising treatment for controlling non-indigenous and potentially invasive species; however, to draw more general conclusions, several species with higher level of resistance to ozone are required and will be studied in the future.     

KINETICS OF THE SIMULTANEOUS SORPTION OF NONIONIC SURFACTANT AND COPPER(II) BY POLY ACRYLIC ACID - FUNCTIONALIZED ION EXCHANGER

ABSTRACT

Kinetics of the simultaneous sorption of nonionic surfactant oxyethylated alcohols (OS-20) and copper(II) by hydrogen containing form of Purolite C 106 polyacrylic acid-functionalized cation exchanger was investigated: kinetic curves measured, effective coefficients of intraparticle diffusion (D), effective kinetic coefficients of the external mass transfer ((β) were calculated. The sorption of copper (II) and OS-20 is controlled by the intraparticle diffusion. The diffusion rate depends on the solution acidity: on increasing the acidity both the rate of copper (II) intraparticle diffusion and the equilibrium sorption decrease while the rate of intraparticle diffusion and the equilibrium sorption of OS-20 increase. The presence of copper (II) results in an increase in OS-20 diffusion rate but leads to a decrease in the equilibrium sorption of OS-20. The action of OS-20 results in the decrease in the equilibrium sorption of copper (II).The simultaneous sorption of oxyethylated alcohols and copper (II) by Purolite C 106 can be applicable for the purification of sewage including copper plating rinsewater A column filled with Purolite C 106 would not limit the productivity if integrated into the system of sewage purification by ion exchange |The simultaneous sorption of OS-20 and copper (II) by Purolite C 106 ion exchanger can be applicable for the purification of sewage including copper plating rinsewater. With respect to the coefficients of intraparticle diffusion for both copper (II) and OS-20 the column filled with Purolite C 106 would not limit the productivity if integrated into the system of sewage purification using ion exchange,