Kinetics, Equilibrium, and Thermodynamics for Conjugation of Chitosan with Insulin-Mimetic [meso-Tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-) in an Aqueous Solution.

This study investigated the conjugation of chitosan with the insulin-mimetic [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-), VO(tpps), in an aqueous medium as a function of conjugation time, VO(tpps) concentrations, and temperatures. To validate the synthesis of chitosan-VO(tpps) conjugate, UV-visible and Fourier transform infrared spectrophotometric techniques were utilized. Conjugate formation is ascribed to the electrostatic interaction between the NH3+ units of chitosan and the SO3- units of VO(tpps). Chitosan enhances the stability of VO(tpps) in an aqueous medium (pH 2.5). VO(tpps) conjugation with chitosan was best explained by pseudo-second-order kinetic and Langmuir isotherm models based on kinetic and isotherm studies. The Langmuir equation determined that the maximal ability of VO(tpps) conjugated with each gram of chitosan was 39.22 µmol at a solution temperature of 45 °C. Activation energy and thermodynamic studies (Ea: 8.78 kJ/mol, ΔG: -24.52 to -27.55 kJ/mol, ΔS: 204.22 J/(mol K), and ΔH: 37.30 kJ/mol) reveal that conjugation is endothermic and physical in nature. The discharge of VO(tpps) from conjugate was analyzed in freshly prepared 0.1 mol/L phosphate buffer (pH 7.4) at 37 °C. The release of VO(tpps) from the conjugate is a two-phase process best explained by the Higuchi model, according to a kinetic analysis of the release data. Taking into consideration all experimental findings, it is proposed that chitosan can be used to formulate both solid and liquid insulin-mimetic chitosan-VO(tpps) conjugates.

Bioaccumulation and Depletion of the Antibiotic Sulfadiazine 14C in Lambari (Astyanax bimaculatus).

Antibiotics are present in the environment, primarily due to their release through wastewater treatment plants, agricultural practices, and improper disposal of unused medications. In the environment, these drugs can be bioaccumulated by organisms and transferred along the food chain. This is a problem when considering the consumption of fish meat. In the United States, legislation stipulates that the maximum residue limit for sulfadiazine (SDZ) should not exceed 100 µg kg-1. Lambari fishes have potential economic importance in aquaculture, as they are relatively easy to breed and can be raised in small-scale operations. Finally, studying the biology and ecology of lambari could provide valuable information about freshwater ecosystems and their inhabitants. The current work aimed to measure the bioaccumulation and depletion of the antibiotic SDZ 14C in lambari (Astyanax bimaculatus). For this purpose, the tests were divided into two stages; seven days of exposure and seven days of depletion, where one fish was randomly selected and sampled every day. In the exposure phase, the fish were fed the medicated feed three times a day at a concentration of 2.5 mg·g-1. The control fish were fed uncontaminated feed. For the depletion phase, the remaining lambari were transferred to clean tanks and fed uncontaminated feed three times a day. The fish samples were burned in the Oxidizer and the reading of radioactivity was performed in a liquid scintillation spectrometer. It is worth noting that on day 7 and day 14, the water in the aquariums was filtered through filter paper to collect the metabolic excrement. SDZ concentrations increased over the days and accumulation occurred in the fish, with day seven presenting the maximum accumulation value of 91.7 ng·g-1 due to feeding uptake. After the depletion phase on day 13, the value found was 0.83 ng·g-1. The bioconcentration factor calculated was 20 L·kg-1. After the bioaccumulation period, the concentrations of SDZ in the water and excreta were 4.5 µg·L-1 and 363.5 ng·g-1, respectively. In the depletion period, the concentrations in the water and excreta were 0.01 µg·L-1 and 5.96 ng·g-1, respectively. These results imply that there was little SDZ bioaccumulation in the fish, but that it was distributed in larger amounts in the water. This is due to the physicochemical properties of the molecule with the low Log P value. Regarding the maximum residue limit, the value was below the established value. This study contributes to understanding SDZ dynamics in an aquatic species native to Brazil.

Screening for antimicrobial residues in poultry eggs in Bangladesh using Charm II radio-receptor assay technique following validation.

The aim of the study was to screen for the presence of antimicrobial residues in poultry eggs from Bangladesh using the Charm II radio-receptor assay in the absence of expensive confirmatory instrumentation. This was based on cut-off values as set in the validation guidelines according to Commission Decision 2002/657/EC and Commission Implementing Regulation (EU) 2021/808. Fortified eggs spiked with fixed concentrations of doxycycline, erythromycin A, sulphamethazine, and benzylpenicillin were used to determine the cut-off values and detection capabilities (CCß). Other validation parameters included were applicability, ruggedness, and robustness. A total of 201 egg mix samples from native organic chicken, duck, and commercial farm-raised laying hens (both brown and white eggs) were tested and after analysis 13%, 10%, and 4.5% of the egg mix samples showed positive signals for sulphonamides, macrolides/lincosamides, and tetracyclines, respectively. Presence of multiple drug residues were also suspected in 11 out of 201 egg mix samples.