The summer leaves of Thymbra spicata var. spicata
and Satureja thymbra, two Labiatae
aromatic
shrubs growing wild in the East Mediterranean region of Turkey, and, in
addition, the leaves of
Salvia fruticosa, Mentha pulegium, Laurus
nobilis, and Inula viscosa were collected in
4-week
intervals to follow plant development and essential oil composition.
The essential oils extracted
from leaves (and flowering tops) were estimated during the growing
season by means of GC−FID,
and 19 terpenic constituents were identified. The changes in the
essential oil content (quantity
and composition) varied for all six plant species, according to
corresponding environmental and
growth factors and the major adaptive strategy toward summer drought
that each plant species
has evolved. The concentration of the fungitoxic components in the
essential oils of Thymbra spicata
and Satureja thymbra, the phenolic constituents carvacrol
and thymol, were low in the early
phenological stage and increased gradually with plant development.
The maximum was reached
in June/July, shortly after flowering. Taking this into account,
the harvest of these two species in
order to obtain their essential oils offers acceptable economic
possibilities for their use as a natural
fungicide. The main compounds of the essential oils found in
Salvia fruticosa, Laurus nobilis, and
Mentha pulegium were the oxygen-containing monoterpenes
1,8-cineole and pulegone, respectively,
and a periodic increase and decrease in their concentrations was
observed. The essential oil of
Inula viscosa contained only small amounts of some of the
investigated components. The best time
of harvest to gain the essential oils with the highest active
ingredients is July for Thymbra spicata,
Satureja thymbra, Salvia fruticosa, and
Mentha pulegium (Labiatae) and September for
Laurus
nobilis (Lauraceae).
Keywords: Essential oils; seasonal variations; thymol;
carvacrol;
Thymbra spicata; Satureja
thymbra
The degradation of 12 sulfonylurea herbicides in buffers at different pH levels and in anaerobic sediments was investigated in laboratory studies. Reaction products, which are not commercially available, were synthesized in order to follow degradation kinetics. Different hydrolysis processes were shown to occur under acidic, neutral, and alkaline conditions. At 40°C, pseudo‐first‐order reaction rate constants between pH 4 and 10 covered two orders of magnitude. Activation energies of the acid‐catalyzed hydrolysis were about 100 kJ/mol. Reaction rate‐pH profiles were different for all compounds. In native sediments at neutral pH, microbial degradation was prevalent. At lower pH, chemical hydrolysis became more important. Pseudo‐first‐order dissipation rate constants between 12.50 × 10−2 d−1 and 0.19 × 10−2 d−1 were determined. Quantum‐chemical molecular descriptors were calculated with MOPAC, and steric, electronic, and geometrical descriptors with Molecular Modeling Pro. Quantitative structure‐reactivity relationships were found between bond orders, atomic charges, lowest unoccupied molecular orbitals, and pKa values on one hand and rate constants on the other. Disappearance rates in native sediments could be assessed with a multiple correlation considering calculated octanol water partition coefficients, parachors, and the atomic charges at the main reactive site of the molecules.
Abstract-The degradation of 12 sulfonylurea herbicides in buffers at different pH levels and in anaerobic sediments was investigated in laboratory studies. Reaction products, which are not commercially available, were synthesized in order to follow degradation kinetics. Different hydrolysis processes were shown to occur under acidic, neutral, and alkaline conditions. At 40ЊC, pseudo-first-order reaction rate constants between pH 4 and 10 covered two orders of magnitude. Activation energies of the acid-catalyzed hydrolysis were about 100 kJ/mol. Reaction rate-pH profiles were different for all compounds. In native sediments at neutral pH, microbial degradation was prevalent. At lower pH, chemical hydrolysis became more important. Pseudo-first-order dissipation rate constants between 12.50 ϫ 10 Ϫ2 d Ϫ1 and 0.19 ϫ 10 Ϫ2 d Ϫ1 were determined. Quantum-chemical molecular descriptors were calculated with MOPAC, and steric, electronic, and geometrical descriptors with Molecular Modeling Pro. Quantitative structure-reactivity relationships were found between bond orders, atomic charges, lowest unoccupied molecular orbitals, and pK a values on one hand and rate constants on the other. Disappearance rates in native sediments could be assessed with a multiple correlation considering calculated octanol water partition coefficients, parachors, and the atomic charges at the main reactive site of the molecules.
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