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Article Highlights • The highest content of fatty acid was converted to ester with primary alcohols • Secondary and tertiary alcohols and alcohols with branched chains react more slowly • The presence of the double bond in unsaturated fatty acids reduces the conversion of acid to ester • The increase of the molar ratio of acid/alcohol increases the speed and yield • The increase of the number of carbon atoms in the alcohol decreases activation energy

ABSTRACT. The use of aquatic plants to analyze the heavy metal pollution of a lake environment has a number of advantages over the standard chemical methods of the analysis of metal presence in water and sediment. The macrophyta Lemna minor L., sampled from Lake Skadar in Montenegro has been used as a bio-indicator. Floating macrophyte L. minor accumulates metals from water through its submerged roots and floated leaves. The contents of Cd, Cu, Co, Cr, Mn, Ni, Pb, Zn, Sr and V were determined in sediments, water and the plant. The results obtained indicated a very high capacity of L. minor for the accumulation of Mn. In addition, higher Zn concentration was found in root tissue comparing to the sediment. The concentration of the other metals under investigation decreases in the following order: sediment > L. minor (root) > L. minor (leaf) > water. Higher concentrations of all metals in the tissue of L. minor were observed at the end of the growing season. A higher metal content was recorded in the root compared to the leaf. In descending order, the concentrations in plant tissues were found for the following metals: Mn > Zn > Sr > Cu > Ni > Pb > Co > V > Cr > Cd, while the series of bioaccumulation is, in descending order: Mn > Zn > Ni > Co > Pb > Cu > Cr > V > Sr > Cd.

Lacustrine systems are very complex water systems in terms of the transport of and interaction with heavy metals. Primarily due to its high variability and current chemical parameters, the tissue of macrophytes is a more plausible bio-indicator of the load level of metals within lake ecosystems than are water or sediment analyses. The macrophyte, Ceratophyllum demersum, sampled from the Skadar Lake in Montenegro was used as a bio-indicator. Sediments, water and plants were examined for their contents of ten metals in four different periods of 2011. The concentrations of the metals followed the trend: sediment > leaf C. demersum > stem C. demersum > water. There were differences in the sequences of the metal content in the plant compared to the sequences of their bioaccumulation ability. These differences suggest a different capacity of macrophytes for different metals. The accumulation of Mn was several times higher than the accumulation of the other analyzed metals. The highest ratio of leaf/stem concentrations was recorded for Mn (2.19) and the lowest was for Pb (1.04). The highest contents of Cd, Co, Cr, Pb, V and Sr were found in the tissues of C. demersum at the beginning of the growing season, whereas Ni, Zn, Cu and Mn were found at the end of the vegetative phase.

Macrophytes react to changes in the quality of the environment in which they live (water/sediment), and they are good bioindicators of surface water conditions. In the present study, the content of the metals cobalt (Co) and nickel (Ni) was determined in the sediment, the water, and different organs of macrophytes from six localities around Lake Skadar, across four different seasons of year. The aquatic macrophytes that have been used as bioindicator species in this study are Phragmites australis (an emerged species), Ceratophyllum demersum (a submerged species), and Lemna minor (a floating species). The aim of this study was to determine the distribution of metals in macrophyte tissues and also to discover the degree of bioaccumulation of the investigated metals, depending both on the location and on the season. The content of Co and Ni in the examined parts of the macrophytes was in the range of 0.04-8.78 and 0.30-28.5 ppm, respectively. The greatest content of the investigated metal in the organs of P. australis and C. demersum was recorded at the beginning of and during the growing season. Greater concentrations of metals in the tissue of L. minor were observed at the end of the growing season.

Indium promoted allylation of carbonyl compounds with 4-(bromomethyl)-1,3-dioxol-2-one diastereoselectively affords anti-α,β-dihydroxyketones, protected as enol carbonates. These initial products can be deprotected to free dihydroxyketones or transformed under mild conditions into the corresponding cyclic carbonates, which constitutes a useful approach to hydroxyacetone aldols.

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Humulones and iso-humulones are potent natural antioxidants found in beer. In this study, density functional theory (DFT) method was applied for elucidating the structure-antioxidant activity relationship and molecular mechanism of antioxidant activity of eight bioactive humulones previously identified in different beer samples: isoxanthohumol, ( R )- and ( S )-adhumulone, cis - and trans -iso-adhumulone, cis - and trans -iso-n-humulone, and desdimetyhyl-octahydro-iso-cohumulone. The calculated bond dissociation enthalpies (BDEs) suggest that desdimethyl-octahydro-iso-cohumulone was the most potent compound with BDEs 5.1 and 23.9 kJ/mol lower compared to the values for resveratrol in gas phase and water, respectively. The enolic –OH is the most reactive site for hydrogen atom transfer (HAT). The presence of β-keto group with respect to enolic –OH diminishes the HAT potency via the formation of a strong intramolecular hydrogen bond. Another common antioxidant mechanism, single electron transfer followed by proton transfer (SET-PT), is only feasible for isoxanthohumol. The results of this study indicate a strong correlation between the increased antioxidant activity of beer products and the higher content of reduced iso-α-acids.