Chemija

Title

Lietuvos mokslų akademija — 2026-03-25

Prof. Habil. Dr. Arūnas Ramanavičius: Life, Career, and Contribution to Chemistry

Ieva Plikusienė — 2026-03-25

A reagentless amperometric glucose biosensor based on 5-amino-1,10-phenanthroline, gold nanoparticles and glucose oxidase

Katažyna Blaževič — 2026-03-25

Glucose monitoring is essential for the management of diabetes and for ensuring an accurate analysis in clinical and food-related applications. In this study, a reagentless amperometric glucose biosensor was developed based on the layer-by-layer adsorption of 5-amino-1,10-phenanthroline (AP), 13 nm diameter gold nanoparticles (AuNPs), and glucose oxidase (GOx) onto a graphite rod electrode, followed by chemical cross-linking of GOx with glutaraldehyde vapour. AP acted as a redox mediator, enabling an efficient electron transfer, while AuNPs facilitated signal amplification. The biosensor exhibited a wide linear range (0.30–10.0 mM), low limits of detection and quantification (LOD 0.05 mM, LOQ 0.17 mM), a high repeatability (RSD 3.19%) and an acceptable reproducibility (RSD 5.51%), along with an excellent selectivity toward glucose and a satisfactory storage stability (86% signal retention over 7 days), and anti-interference performance against uric and ascorbic acids. These features demonstrate the biosensor’s suitability for routine and point-of-care glucose monitoring. Furthermore, the proposed platform is versatile and can be adapted for the detection of other clinically or environmentally relevant analytes, highlighting its potential for broader analytical applications.

Determination of melatonin in sleep supplements by high-performance liquid chromatography

Vilma Olšauskaitė — 2026-03-25

The aim of this study was to quantify the actual melatonin content in commonly available over-the-counter melatonin sleep supplements marketed in Lithuania. For this purpose, a high-performance liquid chromatography (HPLC) method was optimised and validated. The calibration curve was linear (R2 = 0.9996) over a concentration range of 0.5–50.0 mg/L, and the limit of detection was 0.17 mg/L. Recoveries of melatonin from spiked supplement samples ranged from 96.8 to 104.1%, with relative standard deviation values below 3.2%. Melatonin was quantified in 20 commercial sleep supplements representing 10 brands and three dosage forms (capsules, tablets and liquids), with two different lots analysed for each brand. Overall, the measured melatonin content ranged from –7 to +26% relative to the labelled amount, indicating a low variability among melatonin products sold in Lithuania. Only one product contained melatonin amount outside the ±20% margin of the labelled claim. The least variable products were liquid supplements, which generally contained the simplest ingredient compositions.

The effect of gold nanorod dimensions on the electrochemical performance of an enzymatic glucose biosensor

Marina Šapauskienė — 2026-03-25

The nanostructuring of electrode surfaces is commonly employed to enhance the electrochemical performance of enzymatic glucose biosensors. However, the optimisation of nanostructure morphology and dimensions remains an incompletely explored area. In this work, three colloidal solutions of gold nanorods (AuNR), different in size, were synthesised. SEM analysis revealed that nanorods exhibited distinct lengths: 32.8 ± 3.4 nm for AuNRI, 35.0 ± 3.5 nm for AuNRII and 90.0 ± 6.7 nm for AuNRIII. Glucose biosensors based on graphite rod electrodes modified with AuNR and glucose oxidase showed enhanced electrochemical performance. Notably, biosensors fabricated with AuNRI and AuNRIII achieved similar maximal current changes during the enzymatic reaction (∆Imax = 49.31 ± 2.64 and 48.45 ± 2.35 µA, respectively), despite the pronounced difference in the electroactive surface area obtained after AuNR deposition (0.082 ± 0.009 and 0.194 ± 0.005 cm2, respectively). Moreover, the fabricated glucose biosensor based on AuNRI exhibited a linear range of practical relevance (0.1–8 mM), a low limit of detection (4.6 µM), and is suitable for glucose detection in the diluted blood serum. Overall, the results indicate that morphological characteristics, including size, aspect ratio, and spatial organisation, play a crucial role in optimising the design and performance of enzymatic glucose biosensors.

Design of ortho/meta-substituted selective carbonic anhydrase IX inhibitors

Mantas Žvirblis — 2026-03-25

In the search for chemical compounds that strongly and selectively bind and inhibit one out of 12 catalytically active CA isozymes, a series of fluorinated substituted benzenesulfonamides was designed and synthesised. Substituents were intended to be stiff and have a limited conformational flexibility. We determined compound affinities using the fluorescence-based thermal shift assay. Afterward, we subtracted the binding-linked protonation reactions and calculated the intrinsic affinities, which were then used to establish the structure–affinity relationships. Compound 5 (2-(cyclohexylamino)-3,5,6-trifluoro-4-(phenylsulfonyl) benzenesulfonamide) exhibited an improved selectivity profile toward CAIX, a cancer-associated isozyme. The analysis of compound functional group contributions and the comparison with previously designed compounds provided insight toward a deeper understanding of the protein–ligand recognition principles for drug design.

Sustainable corrosion inhibition of carbon steel in 3.5% NaCl using Moringa oleifera leaf extract

Benidir Sofiane — 2026-03-25

Corrosion is an unavoidable process in metals, but it can be effectively managed through various techniques. One such approach involves the use of environmentally friendly corrosion inhibitors, commonly referred to as green corrosion inhibitors. Moringa oleifera (MO) leaves are renowned for their high concentration of antioxidant compounds; however, their applications have primarily been limited to water purification and food ingredients. Addressing this gap, research was conducted to explore the potential of Moringa leaf extract as a green corrosion inhibitor for X70 steel. The study employed varying concentrations of the leaf extract (0.04, 0.08, 0.1 and 0.2 g∙L–1) to identify the optimal performance under 3.5% NaCl conditions. The effectiveness of the MO leaf extract in reducing the corrosion rate was evaluated using Tafel polarisation and electrochemical impedance spectroscopy (EIS) tests. The results demonstrated a significant reduction in the corrosion rate, with the highest inhibition efficiency reaching 83% in the NaCl medium. scanning electron microscopy (SEM) analysis further confirmed the formation of a protective layer on the steel surface, consistent with findings from gravimetric and electrochemical studies. These results highlight the potential of Moringa leaf extract as a sustainable and effective corrosion inhibitor.

Evaluation of the efficiency of talc and bentonite in the dry purification of methyl and ethyl fatty acid esters as biodiesel from babassu

Sinara de F. F. Dos Santos — 2026-03-25

The dry purification of biodiesel using natural adsorbents has emerged as a sustainable alternative to the traditional method of washing with water in biodiesel production. In this context, this study investigates the efficiency of talc and bentonite in the dry purification of biodiesel from babassu, a promising oilseed that is little used for biodiesel production. The biodiesel was produced by alkaline transesterification and purified with different concentrations of talc and bentonite. The adsorbents were characterised by X-ray diffraction, infrared spectroscopy and textural analysis. After purification, the physicochemical parameters of the biodiesel were analysed and compared with water-purified samples. Bentonite showed a higher surface area (76.685 m2/g) and pore volume (0.121 cc/g) compared to talc (8.610 m2/g and 0.029 cc/g). Both adsorbents efficiently reduced the acidity index, with bentonite being more effective, especially at a concentration of 3.0%. Moisture was significantly lower in samples treated with adsorbents, with bentonite standing out in ethyl biodiesel. The dielectric constant decreased with the use of adsorbents, indicating a greater removal of polar contaminants. Dry purification with talc and bentonite is efficient in improving the quality of babassu biodiesel, meeting the specifications of current legislation.

Synthesis and properties of dimethoxytriphenylamine- based enamines

Jūratė Simokaitienė — 2026-03-25

This article describes the synthesis and properties of new methoxy-substituted triphenylamine-based enamines. Thermal, photophysical and electrochemical properties of the compounds are reported. In addition, the ionisation energies estimated by photoelectron emission spectroscopy and hole transporting properties examined by the time-of-flight method are discussed. The compounds form molecular glasses with glass transition temperatures of up to 91°C. They exhibit a high thermal stability with 5% weight-loss temperatures above 420°C. Their characteristic optical band-gaps are of 2.9 eV and the solid-state ionisation energies situate around 5.4 eV. One of the compounds shows a high hole mobility of 8.4 × 10–4 cm2/Vs at the electric field of 4 × 105 V/cm.

Utilisation of spent coffee grounds in biocomposite cup production: Influence of filler source and biopolymer type

Jūratė Jonikaitė-Švėgždienė — 2026-03-25

In this study, two types of spent coffee grounds (SCG, Machine and Turkish) were tested in the production of SCG-biopolymer composite cups. The objective was to develop a simple and sustainable preparation approach for SCG-based biocomposites, ensuring sufficient mechanical and thermal stability for practical applications. Biocomposite cups, containing 55 to 72% of SCG were produced using sodium alginate as the primary polymer binder. To enhance mechanical performance, a secondary binder (additional polymer), either cellulose ether (carboxymethyl cellulose (CMC) or hydroxypropyl cellulose (HPC)) or natural polysaccharides (dextran or pectin), was incorporated. Comprehensive characterisation was performed using fluorescence and FTIR spectroscopy, tensile testing, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Fluorescence spectroscopy/microscopy revealed a higher content of naturally fluorescent organic compounds in Machine SCG compared to Turkish SCG. FTIR spectroscopy confirmed the successful SCG incorporation into the biopolymer matrix. Tensile testing showed that Machine SCG-based biocomposites were slightly more flexible than those prepared with Turkish SCG. Glass transition temperature (T_g) of SCG biocomposites depends on their composition and varied from around 75 to 100°C. The TGA results demonstrated that SCG exhibit a greater thermal stability than both SCG–alginate biocomposites and SCG biocomposites containing additional polymers.

ARVYDAS SURVILA 4 September 1942 – 15 January 2026

Rimantas Ramanauskas — 2026-03-25