Acta et Commentationes Exact and Natural Sciences

Remediation of pollutions with oily products using polymer-based fibers as sorbents

Corneliu Cojocaru — 2026-07-23

Fibrous polymeric materials gained particular interest, owing to their significant contact surface area and tunable porous morphology. A fibrous--porous sorbent based on electrospun poly(vinylidene fluoride-co-hexafluoropropylene) was fabricated and investigated for oil sorption applications. The copolymer was electrospun under optimized operating conditions, aiming to obtain a porous, hydrophobic nonwoven composed of submicronic fibers. The material was characterized by FT-IR, EDAX, SEM, and mechanical testing. Its sorption performance was assessed for the uptake of the motor oil (0.843 g/mL, 67 cP), yielding a sorption capacity of 9.3 g/g, and oil recovery from the spent sorbent was demonstrated by centrifugation. Additionally, a comparative analysis was performed between the electrospun nonwovens (submicronic fibers) and conventional textile nonwovens (microfibers). Thus, it was pointed out that the influence of fiber diameter and inter-fiber spacing affects the sorption capacity and oil recovery efficiency by centrifugation.

Pentanuclear pivalate cluster with a Co(III)₂Ce(IV)₃ core

Ecaterina Beleaev — 2026-07-23

The reaction of cobalt(II) pivalate and cerium(III) chloride with triethanolamine in acetonitrile led to the formation of a new pentanuclear cluster with the formula [Co₂Ce₃O₂(piv)₇(Htea)₂(tea)]·2.5CH₃CN·H₂O (1) (where H₃tea = triethanolamine, Hpiv = pivalic acid). A single crystal X-ray diffraction analysis revealed that 1 consists of a heterometallic pentanuclear assembly with a mixed-valent Co₂Ce₃ metal core composed of two Co(III) and three Ce(IV) ions. The metal atoms in 1 are connected by mu₃-O and mu₄-O oxo-bridges surrounded by seven pivalate groups. In addition, two partially deprotonated Htea²⁻ and one fully deprotonated tea³⁻ ligands unite the metal atoms. The outer coordination sphere includes one water and two and a half acetonitrile molecules. The influence of the various types of intermolecular interactions between clusters and solvent molecules on the crystal packing in this system was evaluated using Hirshfeld surface analysis and 2D fingerprint plots.

Template synthesis, crystal and electronic structure of trinuclear Co(II) complex based on new 15-dentate macrocyclic Schiff base ligand

Olga Danilescu — 2026-07-23

The new 15-dentate macrocyclic Schiff base ligand, derived from 2,6-diacetylpyridine and malonic acid dihydrazide, was synthesized using a template condensation approach. The deprotonation-protonation behaviour of this polydentate macrocyclic Schiff base in Co(II) coordination compounds was investigated and exploited as a strategy for the assembly of a novel trinuclear macrocyclic complex. The chemical composition and crystal structure of the resulting complex [Co₃(H₆L)(H₂O)₆](ClO₄)₆ · 8H₂O were elucidated by single-crystal X-ray diffraction, infrared spectroscopy, and elemental analysis. The TB2J python package and SIESTA code were used to analyse the magnetic exchange interactions in trinuclear macrocyclic Co(II) complex in the crystal.

A heterometallic hexanuclear Fe₄Sm₂ cluster supported by pivalate and phenyldiethanolamine ligands

Daniel Podgornîi — 2026-07-23

A new hexanuclear heterometallic [Fe₄Sm₂(OH)₂ (piv)₄(phdea)₄(N₃)₂(H₂O)₂] Cl₂ ·3MeCN (1) cluster has been synthesized using a mu-oxo [Fe₃O(piv)₆(H₂O)₃](piv)·Hpiv (Hpiv = pivalic acid) precursor, SmCl₃ ·6H₂O, NaN₃, and N-phenyldiethanolamine (H₂phdea). Single-crystal X-ray diffraction analysis reveals that 1 possesses a nonplanar butterfly-type core with an open-dicubane topology. Continuous Shape Measure (CShM) and Bond Valence Sum (BVS) analyses confirm the distorted octahedral geometry for six-coordinate Fe(III) centers and square-antiprismatic geometries for eight-coordinate Sm(III) ions, consistent with trivalent oxidation states.

Coordination compounds of copper(II) based on the coordinating agent 1,5-bis(2-hydroxy-1-naphthaldehyde)carbohydrazone

Natalia Talmaci — 2026-07-23

Upon the interaction of copper(II) nitrate with 1,5-bis(2-hydroxy-1-naphthalde-hyde)carbohydrazone (H₄L¹), by modifying the solvent system, two coordination compounds were synthesized: the tetranuclear complex [Cu₂(HL¹)(MeOH)₂(NO₃)]₂ (1) and the polymeric structure [Cu₂(HL¹)(HCOO)]ₙ·H₂O (2). The chemical composition and structural features of complexes 1 and 2 were determined by single-crystal X-ray diffraction and IR spectroscopy.

Antioxidant activity of ionic liquids formed by carnitine and food acids: a correlation between the data of their FRAP assay and their pKₐ values

Mikhail Gorbaciov — 2026-07-23

The usage of the restricted open-shell Hartree-Fock (ROHF) method to the calculation of electronic structures of the complex Fe(III) with 2,4,6-tripyridyl-s-triazine (TPTZ): [Fe(III)(TPTZ)₂]³⁺ and its adduct with the ionic pair [Carnitine-H]^+ [gentisic acid anion]^- (formed by a protonated carnitine zwitterion and an anion of gentisic acid) allows one to reveal that the anion entering this pair retains its ability to quench free radicals. Antioxidant activity of the studied ionic liquids in their reaction with the complex [Fe(III)(TPTZ)₂]³⁺ is determined by the food acids anions included in their ionic pairs. It is also shown that the values of the antioxidant activity of the studied ionic liquids defined by the FRAP assay correlate with the pKₐ values of their precursor food acids.

Optimization of holocellulose extraction from spent coffee grounds using factorial design

Lucas Repecka Alves — 2026-07-23

Spent coffee grounds (SCG) represent a substantial environmental challenge due to the massive generation of solid waste and its high organic load. However, SCG is a promising source of lignocellulosic biomass for the production of high-value biopolymers. This study aimed to optimize the extraction of holocellulose from SCG via oxidative bleaching using sodium hypochlorite (NaOCl), employing a 2³ factorial design with a central point. The effects of NaOCl concentration (1.0--2.5%), reaction time (15--45 min), and temperature (25--55 °C) on the extraction yield were evaluated. Statistical analysis revealed that temperature was the most significant variable, accounting for approximately 52% of the yield variation, followed by NaOCl concentration (~37%). High temperatures and concentrations led to excessive oxidative degradation and hydrolysis of the polysaccharide chains, drastically reducing yields to below 20%. Conversely, mild conditions resulted in insufficient delignification. The experimental results indicated that the central point conditions (1.75% NaOCl at 40 °C for 30 min) offered the optimal balance, providing a yield of approximately 38% with adequate brightness and reduced degradation. These findings demonstrate the feasibility of using statistical design to obtain holocellulose from SCG for future applications in biocomposites and packaging.

Study of the antiradical activity of wine polyphenols using UV--VIS and DFT methods

Crina Vicol — 2026-07-23

This study investigates the antiradical activity of the wine polyphenols catechin (Cat) and quercetin (Que) in ethanol and wine-model solution, combining experimental DPPH• scavenging assays with Density Functional Theory (DFT) calculations. Quercetin exhibited similar activity in both media, one mol of polyphenol scavenging approximately 3.4 moles of DPPH•, whereas catechin showed enhanced performance in wine-model solution, neutralizing up to 4 moles of DPPH• compared to 2.8 moles in ethanol. Theoretical and experimental correlations indicate that catechin predominantly follows a SET-PT mechanism in wine-model solution, while quercetin likely undergoes alternative pathways, including possible dimerization.

Low-carbon hydrogen production under Brazilian law 14.948/2024

Matheus da Silva Costa — 2026-07-23

Hydrogen is an element with great energy potential and is emerging as a clean fuel compared to other alternative energy sources. However, its production methods can have high greenhouse gas emissions, making it necessary to apply low-emission production methodologies, resulting in what is known as low-carbon hydrogen. This paper presents methods currently used on a large scale to produce this fuel, as presented in The Future of Hydrogen report by the International Energy Agency (2019), and compares the emissions data from these methods with the limits imposed by Brazilian law 14.948/2024, which sets a limit of 7 kilograms of carbon dioxide emitted per kilogram of hydrogen produced. Alternative hydrogen production methodologies are also presented, whether they are improvements to already consolidated processes or new methods under development, through the systematic review.

Evaluation of the structural and compositional properties of carbon adsorbents derived from local waste by the SEM-EDX technique

Eugenia Moraru — 2026-07-23

Activated carbon is one of the most widely used adsorbents due to its high specific surface area and well-developed porosity. Its performance in various applications, such as environmental, industrial, and biomedical fields, is directly related to its morphological structure and the elemental composition of its surface. In this context, scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDX), represents an essential technique for the characterization of activated carbons. The article provides a detailed interpretation of the information obtained by SEM--EDX in the study of activated carbon, analyzing SEM images and EDX spectra in correlation with carbonization, activation, and chemical modification processes.

SO(2,R)-invariant polynomials of a differential system which are involved in solving the stability problem of unperturbed motion in the case of a center and a focus

Natalia Neagu — 2026-07-23

We consider a two-dimensional polynomial differential system s(1,m₁,...,mₗ) (l<∞), for which the origin is a singular point of the second group (center or focus). Using the Lie operator of the linear representation of the rotation group SO(2,R) in the space of phase variables and coefficients of the system s(1,m₁,...,mₗ) (l<∞), an upper bound is determined for the number of functionally independent SO(2,R)-invariant polynomials involved in solving the stability problem of the unperturbed motion described by this system.

The ordinary Hilbert series for Sibirsky graded algebras of the differential system s(5,7)

Lidia Mușinschi — 2026-07-23

In this paper are examined the construction of ordinary Hilbert series for Sibirsky graded algebras of comitants and invariants in autonomous polynomial differential systems. These series are highly significant for addressing specific problems within the qualitative theory of differential systems. However, constructing them for more complex systems typically presents insurmountable computational difficulties, particularly for generalized Hilbert series, from which ordinary Hilbert series are derived. To overcome these massive calculation barriers, this study shows how adapting Molien's formula can effectively solve the problem. Using this approach, the ordinary Hilbert series for the Sibirsky graded algebras of comitants and invariants was obtained for the differential system s(5,7).

The effect of the application of cyanobacterial biofertilizers from the genus Nostoc on the quantitative parameters of the species Monarda fistulosa L.

Sergiu Dobrojan — 2026-07-23

The present study evaluates the effects of cyanobacterial biofertilizers from the genus Nostoc (N. gelatinosum, N. punctiforme, N. linckia) on the growth, biomass accumulation, and essential oil content of Monarda fistulosa L. cultivated under open-field conditions. Experiments were conducted in 2024 in Dobrogea, Sîngera, Moldova, using three application rates (20, 30, and 40 kg/ha) with untreated plants as control. Results indicated that cyanobacterial biofertilizers significantly increased plant height and green biomass, with the highest effects observed at 40 kg/ha. Essential oil content showed a slight, non-significant increase (0.02--0.05 %) compared to control, likely influenced by drought conditions. The study confirms that Nostoc-based biofertilizers enhance plant productivity and represent an ecologically sustainable alternative to chemical fertilizers, improving soil quality and promoting growth of medicinal plants.

Rare species proposed for inclusion in the Red Book of the Republic of Moldova (4th edition)

Pavel Pînzaru — 2026-07-23

The article presents the results of the study on vascular plants, conducted during 2024-2025, with the aim of assessing the current status of rare plant populations for inclusion in the 4th edition of the Red Book of the Republic of Moldova. A total of 23 rare species were identified and classified as follows: 16 species -- Critically Endangered (CR), 3 -- Endangered (EN), and 4 -- Vulnerable (VU). The name in Latin and Romanian, synonyms if any, growing localities, habitat, biological and ecological features, territorial protection, and some recommendations for protection measures are indicated for each species.

Contributions to the knowledge of some insects (Coleoptera, Hymenoptera and Diptera) from the urban ecosystems of the municipality of Chișinău

Svetlana Bacal — 2026-07-23

The study of insects from the orders Coleoptera, Diptera and Hymenoptera is essential for understanding the biodiversity and functioning of urban ecosystems in Chisinau. These insects fulfil important ecological roles, such as pollination, biological pest control and recycling of organic matter. At the same time, phytophagous or xylophagous species have also been reported that can become problematic for urban trees. The research was based on material collected by various methods from parks, botanical gardens and other urban green spaces and stored in the entomological museums from the Chișinău city. As a result of the study, 42 species of coleoptera, 19 of syrphids and 10 of ants were identified. The results highlight the importance of the conservation and sustainable management of urban green spaces for maintaining entomofauna and ecological balance.

The eutrophication process of lakes within the Emerald site "Vila Nisporeni”

Elena Moșanu — 2026-07-23

Water pollution is an imperative of the current times, which disrupts the drinking water supply as well as the natural processes in aquatic basins. Eutrophication, representing one of these processes, which has a direct impact on the biodiversity and functioning of aquatic ecosystems, especially lakes. Thus, the present study analyzes the eutrophication process of lakes from the Emerald site "Vila Nisporeni", located in the center of the Republic of Moldova, by evaluating nutrient concentrations (total mineral nitrogen) and trophic state indicators (chlorophyll "alpha" and transparency) relevant for assessing the ecological state of the lakes. The results indicate a moderate to advanced level of eutrophication, mainly driven by excessive nutrient inputs originating from surface runoff, agricultural activities, and land use in adjacent areas. The waters in the lakes of the Emerald "Vila Nisporeni" site correspond to the eutrophic and hypereutrophic trophic state, and some lakes are subject to the clogging process.

Ex situ conservation of the species Carpinus orientalis (Mill.) in national botanical gardens

Ghenadie Titica — 2026-07-23

This study presents recent data resulting from the research of the endangered hornbeam species, oriental hornbeam (Carpinus orientalis Mill.). The protection status of the oriental hornbeam a rare endangered species is regulated at the national level by the Law on the State Protected Natural Areas Fund and by its inclusion in the Red Book of the Republic of Moldova, indicating a high risk of disappearance from the gene pool of the spontaneous flora. Currently, the monitoring and conservation of the Oriental hornbeam are carried out in two institutions in Chișinău: the "Alexandru Ciubotaru" National Botanical Garden (Institute) of USM and the Botanical Garden of the National Museum of Ethnography and Natural History. Furthermore, ex situ conservation in planned forest micro-exhibitions represents an efficient strategy for reducing the threat of future extinction of this valuable species for the national spontaneous flora.