Carvacrol is a major component of many essential oils of the genusThymus, Satureja,andOriganum, determining their antimicrobial, antioxidant, and other properties. The aim of the present study was to investigate some physicochemical and biological properties of pure carvacrol. The surface tension and density were measured at six different temperatures (30, 40, 50, 60, 70, and 80°C). The surface tension values were between 53.11 and 60.38 mN/m, while density varied from 0.978 to 0.99 kg/m³. The antibacterial activity against seven pathogenic and conditionally pathogenic bacteria was investigated. The diameter of the inhibition zones was determined in the range of 3.9–4.9 mm. The antioxidant activity was determined by the oxygen radical absorbance capacity (1687.0 µmol TE/mL) method.

The density functional theory (at the B3LYP level using 6-311++G(2d,2p) basis set) was used for the investigation of the geometry and electronic properties of the carvone. The electronic properties and chemical activity of the titled compound were investigated by means of several theoretical approaches, molecular electrostatic potential surface, natural bond orbital, and frontier molecular orbital analyses. It was established that the oxygen atom in the structure characterized the electrophilic reactivity; the positive regions are localized on the hydrogen atoms, which can be considered as possible sites for nucleophilic attack. A detailed analysis of the intermolecular interactions via Hirshfeld surface analysis and fingerprint plots revealed that the carvone structure is stabilized mainly by the formation of O. . .H/H. . .O hydrogen bonds. However, close contacts were established between C. . .H/H. . .C and H. . .H contacts.

Garden thyme (Thymus vulgaris L.) is an annual herbaceous plant of the family Lamiaceae. It can be found both in the wild and as a cultivated plant in Bulgaria. This study is aimed at assessing the garden thyme essential oil composition and antioxidant activities, which were collected from three different areas in Bulgaria. The essential oils were obtained by hydrodistillation and analyzed by gas chromatography–mass spectrometry (GC-MS). The main compounds in the garden thyme essential oils (over 2%) were as follows: thymol (42.88–53.55%), p-cymene (14.25–25.51%), γ-terpinene (6.58–15.51%), borneol (2.75–3.57%), carvacrol (2.00–3.02%), β-linalool (2.07–2.31%), cis-sabinene hydrate (4.05%), eucalyptol (1.08–3.65%), α-terpinene (1.01–3.24%), carvacrol methyl ether (1.18–3.02%), and thymol methyl ether (2.26–3.16%). The oils were mainly composed of oxygenated phenyl propanoids, and all the essential oils belonged to the chemotype thymol. Antioxidant activities were measured by DPPH (2,2-diphenyl-1-picrylhydrazyl radical) and ABTS [2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] assays. All the samples exhibited antioxidant activity relative to the DPPH radical (from 143.20 mM TE/mL to 165.91 mM TE/mL) and by the ABTS method (from 121.67 mM TE/mL to 127.62 mM TE/mL). These garden thyme essential oils could be used as natural antioxidants for food and as nutraceuticals.

Agricultural and processing activities generate enormous amounts of tobacco waste, and the stalks left after harvesting of the leaves constitute a significant share. The stalks of common tobacco (N. tabacum L.) were considered a promising source for processing and recycling, but very little is known about the properties of the stalks from other Nicotiana species. The aim of present study was to examine the performance of stalk powders from three Nicotiana species grown side-by-side in Bulgaria for the ability to remove Cr (VI) ions from aqueous solutions. The characterization of applied biosorbents was conducted by FTIR analysis. Batch experiments were carried out and the effects of different adsorption process parameters were determined. Maximum removal efficiencies of 99.13±0.55%, 98.33±0.58% and 95.00±0.50% for N. tabacum, N. rustica L. and N. alata Link&Otto, respectively, were obtained at pH 3.0, adsorbent dosage 5 g/L, initial Cr (VI) concentration 10 mg/L, temperature 25.0 ± 0.5oC, agitation speed 200 rpm and contact time 60 min. The Langmuir and Freundlich models fitted well the equilibrium isotherms experimental data. Based on the values determined for the maximum adsorption capacity, the powder from N. alata stalks was found to have higher affinity (9.87 mg/g) for Cr (VI) ions than those obtained from N. tabacum (8.38 mg/g) and N. rustica (6.96 mg/g) stalks.

The present study aimed to investigate the physicochemical and energy characteristics of Pinus nigra Arn. (Pinaceae family) coniferous biomass used after the production of essential oil. The biomass, comprised of needles and needles with twigs, was milled and subjected to sieve analysis, thus producing three groups of particle fractions (between 384 and 413 μm). The infrared spectrum was recorded as 4000–400 сm–1. The results from the study revealed significant differences in the phytochemical composition. Particle fractions were characterized in terms of moisture content (7.10-7.95%), ash (1.96-2.89%), cellulose (21.30-29.20%), total chlorophyll (225.54-896.04 μg/g), total carotenoids (23.52-145.43 μg/g), and polysaccharides (0.14-2.06%). The basic energy indices used in the assessment of biomass potential as conditional fuel were calculated as follows: calorific value (16748.79-16877.86 kJ/kg), the density of wood biomass (390.99-421.17 kg/m3), and heat equivalent (0.224-0.243 J/m3).

Lavender (Lavandula angustifolia Mill.) fam. Lamiaceae is a cultivated plant in Europe, Asia and the Americas. The aim of present work is study on chemical composition, physicochemical and thermodynamic properties of lavender essential oil from Bulgaria. The main essential oil constituents are linalyl acetate (26.19%), β-linalool (21.39%), β-caryophyllene (6.80%), (Z)-β-ocimene (6.78%), terpinen-4-ol (5.01%), lavandulol acetate (4.39%), (E)-β-ocimene (3.02%), (E)-β-farnesene (2.73%), 1-octen-3-yl-acetate (2.65%), and α-terpineol (2.36%). Physicochemical (refractive index and relative density), thermodynamic (Gibbs energy, enthalpy, entropy, and activation energy) and thermal properties (heat capacity, thermal conductivity, thermal diffusivity, dynamic, and kinematic viscosity) of lavender essential oil and its main components are investigated.