Chemija

Title

Lietuvos mokslų akademija — 2025-03-04

Functionalisation of silver nanoparticles with 4-mercaptophenylacetic acid for iron ions detection using surface-enhanced Raman spectroscopy

Tatjana Charkova — 2025-03-04

The detailed synthesis of silver nanoparticles (30 ± 5 nm) functionalised with 4-mercaptophenylacetic acid and their interaction with iron ions are presented. The study shows the morphological changes of the nanostructures due to the interaction with iron ions, leading to aggregation. The formation of bulky complexes is proved by UV–Vis, HR-TEM and SEM data. The complexes increase the SERS sensitivity of 4-mercaptophenylacetic acid, expanding wider analytical applications.

Electrocatalytic oxidation of L-lactate by Saccharomyces cerevisiae flavocytochrome b2 on redox mediator-modified glassy carbon electrodes

Mindaugas Lesanavičius — 2025-03-04

In order to expand the variety of redox mediator-modified electrodes potentially used for the determination of L-lactate, in this work we investigated the reactions of Saccharomyces cerevisiae flavocytochrome b2 (fcb2) with quinones and its electrocatalytic reactions on glassy carbon electrodes, modified either by their electrochemical pretreatment, or by the products of the electrochemical reduction of dinitrobenzenes. The obtained electrochemically reversible surface redox groups were characterised by a midpoint potential of 0.06–0.10 V (vs Ag/AgCl, pH 7.0) and an electron transfer rate constant of 0.62–0.72 s–1. In the presence of surface-entrapped fcb2, the electrocatalytic oxidation of L-lactate started at
ca. 0.10 V, and was characterised by a current density of 4.5–18 µA/cm2 at 0.20 V. The linear part of the response was observed up to 0.3–0.4 mM L-lactate. However, the prepared electrodes were less stable than those using fcb2 of other origin, most likely due to the modification of specific cysteine groups in the enzyme active center.

On the application of Koutecky–Levich analysis to electrochemical processes involving metal complexes. 1. Theoretical background

Arvydas Survila — 2025-03-04

The applicability of the Koutecky–Levich (KL) approach for the processes occurring in the systems of labile metal complexes is considered. According to the analysis of simulated RDE voltammograms, the use of classical KL relationships is possible if the predominant complexes are involved in the charge transfer process. In the opposite case, corrections to the initial voltametric data, taking into account the surface distribution of complexes and ligands, are required. The rationale and methodology for correction functions are presented. Inaccuracies in the estimation of kinetic and diffusion characteristics arising from ignoring the peculiarities of mass transfer of chemically interacting particles are analysed.

On the application of Koutecky–Levich analysis to electrochemical processes involving metal complexes. 2. Experimental examples

Arvydas Survila — 2025-03-04

Cathodic RDE voltammograms obtained for the reduction of Ag(I) complexes with glycine, sulfite and cyanide were analysed using a modified Koutecky–Levich approach. To extend this method to processes involving ligands, the composition of the electrically active complex was taken into account. For this purpose, the initial experimental data were modified using special correction functions. Experimental data were analysed with the involvement of information on the complexation characteristics and the mechanism of charge transfer. The scope of the basic model and factors requiring further evaluation were discussed.

Aqueous two-phase systems based on hexafluoroisopropanol and hydrophilic organic solvents: phase diagrams and extraction studies

Vytautas Kavaliauskas — 2025-03-04

This study explores a novel type of the aqueous two-phase system (ATPS) consisting of hexafluoroisopropanol (HFIP) and hydrophilic organic solvent as a phase separation inducing agent. Six solvents (acetone, acetonitrile, dimethyl sulfoxide, ethanol, methanol and tetrahydrofuran) were tested as HFIP-based ATPS inducing agents. Only aprotic solvents induced the formation of ATPS. The results suggest that the hydrogen bonding interaction between HFIP and aprotic solvent is the main driving force of phase separation. The phase separation ability of solvents increased with their log P values: less hydrophilic solvents induced phase separation at lower concentrations. HFIP/acetonitrile ATPS was evaluated as an extractant for organic compounds from various classes in aqueous solutions. Obtained extraction efficiencies can be ordered according to the following sequence: amines > esters ≈ aromatic hydrocarbons > hydroxy esters ≈ phenols > carboxylic acids. Interestingly, the proposed system shows an exceptionally good extractability of relatively hydrophilic neutral and positively charged basic compounds. The water immiscible phase possesses a high volatility, a higher than water density and a low viscosity. These properties make ATPS very promising as an extractant for conventional liquid–liquid extraction and particularly well-suited for liquid–liquid microextraction techniques.

Evaluation of compatibility of FluidCrystal® formulations with fibre-type hemp (Cannabis sativa L.) extracts

Aušra Linkevičiūtė-Dumčė — 2025-03-04

The main objective of the present study was to investigate mixtures of soy phosphatidylcholine (SPC) and glycerol dioleate (GDO) as encapsulation matrices for Cannabis sativa L. phytocannabinoids. The effects of cannabinoids loading into non-aqueous formulations and non-lamellar liquid crystalline phases were studied using synchrotron small-angle X-ray diffraction and dynamic light scattering methods. The incorporation of phytocannabinoids is discussed with respect to the lipid aggregation behaviour, self-assembled nanostructures, and long-term chemical stability. The obtained results showed that SPC/GDO-based formulations can incorporate relatively high amounts of cannabinoids and could serve as liquid crystalline delivery vehicles in the form of bulk phases.