Chemija

Title

Lietuvos mokslų akademija — 2025-06-27

Structural analysis of 1-chlorosilacyclopentane by means of vibrational spectroscopy

Jogilė Mačytė — 2025-06-27

The structure of the newly synthesised compound, 1-chlorosilacyclopentane (1-ClSiCP), was investigated using vibrational spectroscopy and theoretical calculations. ATR FT-IR and Raman spectroscopy were used to analyse the liquid sample. Matrix isolation FT-IR spectroscopy was used for the analysis of closely located infrared spectral bands of 1-ClSiCP. Spectroscopic data analysis was performed using theoretical methods such as density functional theory (DTF) and ab initio calculations. FT-IR spectra of 1-ClSiCP isolated in Ne and N2 matrices were collected before and after annealing. During the theoretical structural analysis, the envelope (1E) and twisted (2T3) ring shapes, with the chlorine atom in axial and equatorial positions, were investigated utilising the aug-cc-pVTZ basis set included in the MP2 and DFT calculations. Potential energy surface scans were performed to trace the energy changes and the structure of transition states during the ring conversion. Depending on the method applied, the theoretical results indicate the presence of different conformers, including twisted and envelope ring shapes. The experimental results confirm the existence of only one conformer in the twisted ring configuration. Good agreement between the experimental matrix isolation spectra and in the anharmonic approximation calculated IR absorption spectrum of the 2T3 conformer is observed. The difference between the calculated and experimental frequencies of the normal modes does not exceed 2%.

Integrated geochemical assessment of sediments from Plungė Municipal sewage outfall and sediments from Mažoji Sruoja Stream, Lithuania

Donatas Kaminskas — 2025-06-27

Modern river sediments are complex systems of mechanical, mineral and chemical composition that are sensitive to changes in the physical and chemical conditions of the surrounding environment. Thus, more complex studies on the organic matter, grain-size fractions, chemical and mineralogical composition of the surrounding soil and sediments are necessary for the reliable interpretation of results. The composite samples from the Plungė town sewage outlet and the Mažoji Sruoja River of topsoil and stream sediments were studied. The major goal of the study was to evaluate the contamination of topsoil and stream sediments. The mineralogical, grain-size fraction, organic matter and chemical composition of topsoil and stream sediments were determined. The results obtained have revealed that none of the topsoil samples were contaminated. Some of the elements like Cu, Pb, Zn, Cr, As and Mo in stream sediments have values of the coefficient of concentration exceeding 1 and could be considered as potential contaminants. However, there was no any strong relationship between organic matter, clay, silt particles and chemical composition.

Composition of some macro and micro elements, polyphenol content, antimicrobial and antioxidant activity of Achillea millefolium (L.) grown in Kosovo

Fatmir Faiku — 2025-06-27

This study aimed to determine the composition of several macro and micronutrients (N, P, K, Ca, Mg, Fe, Zn, Cu, Mn, Co, Ni, Cr, Cd and Pb), the composition of polyphenols (total polyphenols, total flavonoids and total phenolic acids), antimicrobial activity and antioxidant activity of the plant Achillea millefolium (L.) grown in Kosovo (the eastern part of Kosovo). The concentrations of the analysed macro and micronutrients are as follows: N 9.95 g/kg, P 6.15 g/kg, K 23.85 g/kg, Ca 21.98 g/kg,
Mg 6.95 g/kg, Fe 59.85 mg/kg, Zn 35.42 mg/kg, Cu 10.75 mg/kg, Mn 31.87 mg/kg, Co 1.15 mg/kg, Ni 3.01 mg/kg, Cr 0.45 mg/kg, Cd 0.035 mg/kg and Pb 0.65 mg/kg. Potassium and calcium were the most abundant macroelements, while iron and zinc were the most abundant micronutrients. The antibacterial efficacy of A. millefolium (L.) was examined using methanol, ethyl acetate, diethyl ether, and water extracts and tested against Staphylococcus aureus (ATTC 25923), Listeria monocytogenes (WSLC 1042) and Escherichia coli (ATCC 25922). Antibacterial activity was determined using the agar disk diffusion method. The inhibition zones from the extracts were compared with that of penicillin G as the standard. Ethyl acetate and diethyl ether extracts showed antibacterial activity against S. aureus and L. monocytogenes, while methanol extracts showed antibacterial activity against S. aureus. The total content of polyphenols (determined using the Folin–Ciocâlteu reagent) was 17.5 ± 0.45 mg GAE/g (GAE-gallic acid equivalent). The total content of flavonoids (determined using the aluminum chloride method) was 8.45 ± 0.65 mg QE/g (QE-quercetin equivalent), and the total phenolic acid content (determined using Arnova reagent) was 13.2 ± 0.17 mg CAE/g (CAE-caffeic acid equivalent). The antioxidant activity determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and phosphomolybdenum methods had values of 9.85 ± 0.15 and 185.7 ± 1.75 mg TE/g, respectively.

FT-IR and Raman spectroscopy for the study of amber and other fossil resins

Gintarė Martinkutė-Baranauskienė — 2025-06-27

This study compares the FT-IR and Raman spectra of amber and other fossil resins from different world regions. The spectra of those resins were analysed based on absorption bands related to the vibrational frequencies of various functional groups present in these compounds. Both spectroscopic methods, FT-IR and Raman, are well-suited for the non-destructive identification of various fossil resins. It was found that FT-IR spectroscopy is particularly suitable for identifying Baltic amber due to its characteristic peak in the 1250–1175 cm–1 wavelength region. Raman spectroscopy can provide helpful information regarding the degree of maturation of resins. The presence of specific Raman bands, such as 1771–1543 and 1510–1400 cm–1, as well as 745 and 696 cm–1, can help determine not only the resin’s maturity but also any structural changes that occurred during burial over the geological time of different lengths.

On the optimisation of the broadband NIR emitter LiScO2:Cr3+

Leoni Frehmeyer — 2025-06-27

Cr3+-activated LiScO2 has emerged as a promising near-infrared (NIR) phosphor with potential applications in medical and optical technologies. In this study, the luminescence properties of LiScO2:Cr3+ were optimised through systematic cation substitutions. The effect of Cr3+-concentration (0.5 to 5 mol.%) was investigated, along with substitutions of Sc3+ by Al3+ and Li+ by Na+. The synthesised phosphors were characterised upon using X-ray diffraction (XRD), reflectance spectroscopy, fluorescence spectroscopy, and decay curve analysis. The results demonstrate that optimal Cr3+ doping concentrations enhance NIR emission, whereas excessive doping leads to concentration quenching. Substitutions of Sc3+ with Al3+ and Li+ with Na+ impact crystal field strength and luminescence properties. These findings contribute to the development of efficient broadband NIR phosphors for future applications.

Synthesis and antimicrobial screening of heterocycles derived from 3-[(4-benzyloxy)phenyl]-1- (3-chlorophenyl)prop-2-ene-1-one

Gheorghe Roman — 2025-06-27

Starting from the title enone (whose single crystal X-ray structure is being reported herein), a small library of structurally diverse heterocycles has been assembled through ring closure reactions with the view to evaluate their antimicrobial activity. A multi-step sequence comprising the reaction of the mentioned chalcone analogue with hydrazine, the N-acylation of the resulting pyrazoline with bromoacetyl bromide and the replacement of the easily leaving halogen atom in the acylated pyrazoline with a 4-methylumbelliferone moiety afforded a pyrazoline–coumarin hybrid. Investigation of the reaction of this chalcone analogue with guanidine allowed the isolation of a 2-aminopyrimidine derivative, while an imidazolone was obtained from guanidine and the epoxide of the chalcone analogue. Cyclocondensation of the chalcone analogue with 2-aminobenzenethiol yielded the expected benzothiazepine derivative. Reaction of the chalcone analogue with malononitrile in the presence of sodium methoxide in methanol led to a mixture of two structurally related pyridines. The heterocycles obtained from the title chalcone analogue were devoid of antimicrobial activity against Staphylococcus aureus, Escherichia coli and Candida albicans at a concentration of 100 mg/mL.