Core-softened potentials,multiple liquid–liquid critical points,and density anomaly regions: An exact solution

The pressure versus temperature phase diagram of a system of particles interacting through a multiscale shoulder-like potential is exactly computed in one dimension. The N-shoulder potential exhibits N density anomaly regions in the phase diagram if the length scales can be connected by a convex curve. The result is analyzed in terms of the convexity of the Gibbs free energy.     

Er3+-doped germanate glasses for active waveguides prepared by Ag+/K+ ↔ Na+ ion-exchange

Planar waveguides were prepared by Ag⁺/K⁺ ? Na⁺ ion-exchange on Er⁺³-doped GeO₂–ZnO–Na₂O–Li₂O glasses obtained by a melting–casting method. Optical parameters of the waveguides were measured at 543.5, 632.8, and 1550 nm by m-line technique as a function of the Ag⁺ ion-exchange time. The optimized planar waveguides show an effective diffusion depth (d) of 2.95 μm and well confined propagating TE₀ and TM₀ modes at 1550 nm. Spectroscopic properties as photoluminescence emission and emission decay time were evaluated for the erbium-doped planar waveguide, indicating that Ag⁺ ? Na⁺ ion-exchange enhance the photoluminescence emissions in the green and infrared regions from erbium ions. The glass system studied is promising to be applied as optical amplifiers in the C-telecom band. Green emission sensitized by Ag⁺ was also observed.     

Tandem Transesterification–Esterification Reactions Using a Hydrophilic Sulfonated Silica Catalyst for the Synthesis of Wintergreen Oil from Acetylsalicylic Acid Promoted by Microwave Irradiation

SiO₂–SO₃H, with a surface area of 115 m²/g and pore volume of 0.38 cm³g⁻¹, and 1.32 mmol H⁺/g was used as a 20% w/w catalyst for the preparation of methyl salicylate (wintergreen oil or MS) from acetylsalicylic acid (ASA). A 94% conversion was achieved in a microwave reactor over 40 min at 120 °C in MeOH. The resulting crude product was purified by flash chromatography. The catalyst could be reused three times.     

Phytochemical Profile and Herbicidal (Phytotoxic), Antioxidants Potential of Essential Oils from Calycolpus goetheanus (Myrtaceae) Specimens,and in Silico Study

The essential oil (EO) of Calycolpus goetheanus (Myrtaceae) specimens (A, B, and C) were obtained through hydrodistillation. The analysis of the chemical composition of the EOs was by gas chromatography coupled with mass spectrometry CG-MS, and gas chromatography coupled with a flame ionization detector CG-FID. The phytotoxic activity of those EOs was evaluated against two weed species from common pasture areas in the Amazon region: Mimosa pudica L. and Senna obtusifolia (L.) The antioxidant capacity of the EOs was determined by (DPPH^•) and (ABTS^•+). Using molecular docking, we evaluated the interaction mode of the major EO compounds with the molecular binding protein 4-hydroxyphenylpyruvate dioxygenase (HPPD). The EO of specimen A was characterized by β-eudesmol (22.83%), (E)-caryophyllene (14.61%), and γ-eudesmol (13.87%), while compounds 1,8-cineole (8.64%), (E)-caryophyllene (5.86%), δ-cadinene (5.78%), and palustrol (4.97%) characterize the chemical profile of specimen B’s EOs, and specimen C had α-cadinol (9.03%), δ-cadinene (8.01%), and (E)-caryophyllene (6.74%) as the majority. The phytotoxic potential of the EOs was observed in the receptor species M. pudica with percentages of inhibition of 30%, and 33.33% for specimens B and C, respectively. The EOs’ antioxidant in DPPH^• was 0.79 ± 0.08 and 0.83 ± 0.02 mM for specimens A and B, respectively. In the TEAC, was 0.07 ± 0.02 mM for specimen A and 0.12 ± 0.06 mM for specimen B. In the results of the in silico study, we observed that the van der Waals and hydrophobic interactions of the alkyl and pi-alkyl types were the main interactions responsible for the formation of the receptor–ligand complex.     

Raman scattering investigations of KY3F10

Single crystals of the fluoride compound KY₃F₁₀ (O_h⁵) were studied by Raman scattering from 40 to 950 K. Group theory analysis predicts 3A_1g + 4E_g + 6F_2g Raman-active modes, but the experimental spectra show two F_2g modes missing. Over the whole temperature range the frequency shifts are negligible whereas the line widths show a strong increase with temperature. Both reversible and irreversible line width behaviour are exhibited for different temperature runs, indicating a complex microscopic phenomenon underlying the creation of defects responsible for these line widths and their interaction with the different phonon modes. An approximate activation energy for defect creation of ΔE ≈︁ 0.3 eV can be obtained from the temperature behaviour of the line widths. This activation energy may be connected with the high-temperature ionic conduction mentioned previously for this crystal.     

Application of time domain nuclear magnetic resonance (TD-NMR) for study of the distillation curve of petroleum

Crude oil distillates are a highly useful industrial product, mainly for energy generation. Unfortunately, they are rarely studied, mainly due to the low accessibility to products directly obtained from the distillation process, which is a laborious, expensive, and time-consuming operation. This work presents and discusses the use of time-domain nuclear magnetic resonance (TD-NMR) as a simple, affordable, and straightforward tool for the development of correlations supported on the transverse relaxation time (T₂) and boiling temperature. The results point out a high convergence between TD-NMR experimental data and the ASTM D2892 method for distillates from light, medium, and heavy oils, with up to 52.20% of accumulated mass and boiling point temperature (T_b) up to 400°C. Furthermore, an unprecedented relationship between T₂ values and the accumulated mass of the distillates is first demonstrated. This new insight opens new perspectives for future prediction of accumulated mass for unknown crude oils, placing the TD-NMR relaxometry as an appeal spectroscopy approach with a potential to meaningfully contribute to the daily refining petrochemical industry field operations.     

Simple and rapid determination of clonidine in pharmaceutical samples by voltammetry using a bare glassy carbon electrode

This work presents, for the first time, the voltammetric behavior of clonidine (CLO) drug and its determination, using an unmodified glassy carbon electrode (GCE). CLO exhibited only an irreversible oxidation process on the GCE, with peak potential at +0.85 V in pH 12 (vs Ag/AgCl). CLO oxidation process is pH-dependent and the electrochemical mechanisms on the GCE were proposed in acidic and basic medium. The determination of CLO was optimized in 0.1 mol L⁻¹ phosphate buffer solution at pH 12.0 using differential pulse voltammetry (DPV), which provides a good linear range (0.65 to 106.00 μmol L⁻¹) and low theoretical limit of detection (0.14 μmol L⁻¹) for the quality control of this drug in pharmaceutical samples. In addition, stable responses of CLO at the GCE were obtained in the same day (RSD = 3.4 %; n = 5) and different days (RSD = 2.0 %; n = 3). Moreover, the determination of CLO in a pharmaceutical formulation using the proposed GCE-DPV method presented good accuracy, since the recovery was close to 100 % and the dosing result was in agreement with an official method (HPLC-UV). The proposed method demonstrates a good analytical performance for CLO determination in pharmaceutical samples, providing a faster, simpler and lower-cost alternative for quality control of CLO than other reported methods.     

β-Cyclodextrin PAMAM Dendrimer Surface Doped with Silver and Hexacyanoferrate (III) and its Applications for Dopamine Detection in Synthetic Samples

A synthesis of β-cyclodextrin (β-Cd) functionalized with polyamide dendrimer PAMAM G.0 complexed with silver and potassium hexacyanoferrate (III) forming a mixed-valence complex (β-Cd-PAMAM-Ag/Fe) was proposed. This material was characterized by scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), X-Ray diffraction (XRD), Energy Dispersion Spectroscopy (EDS) and Electron Paramagnetic Resonance (EPR). The hybrid complex was electrochemically investigated using cyclic voltammetry and some parameters (electrolyte, concentration of electrolyte, pH and scan rate) were evaluate in order to obtain optimum analytical responses. The β-Cd-PAMAM-Ag/Fe material was successfully applied in the electrocatalytic oxidation of dopamine (DOP) using Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV).