β-Tricarbonyl compounds. I. 2,4-Disubstituted 1,3-cyclopentanediones

Summary Stable enolic isomers of 2-aroyl-4-aracyl-1,3-cyclopentanediones such as3 and4 were prepared by condensation of aryl methyl ketones and diethyl maleate using an excess of sodium ethoxide (Aryl=C₆H₅, 4-C₆H₄CH₃, 4-C₆H₄Br and 4-C₆H₄Cl).

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-Tricarbonyl Verbindungen. I. 2,4-Disubstituierte 1,3-Cyclopentandione

Zusammenfassung Stabile Enol-Isomere von 2-Aroyl-4-aracyl-1,3-cyclopentandionen wie3 und4 wurden durch Kondensation von Arylmethylketonen und Diethylmaleat mit einem Überschuß von Natriumethoxid dargestellt (Aryl=C₆H₅, 4-C₆H₄CH₃, 4-C₆H₄Br und 4-C₆H₄Cl).

     

Fluorescence Characteristics of Schiff Bases Derived from Amino- and Aminoalkylpyridines

The fluorescence characteristics of the Schiff bases 2-(3-pyridylmethyliminornethyl)phenol (1), 2-(2 pyridyliminomethyl)phenol (2), N.N-bis(salicylidene)-2,3-pyridinediamine (3), N,N'-bis(salicylidene)-2,6-pyridinediamine (4) and 2-(2-amino-4-methoxymethyl-6-methyl-3-pyridylmethyliminomethyl)phenol (5) were studied in various solvents at different pH values. Corresponding quantum efficiencies were determined. Compound 1, which showed a tendency towards tautomeric mterconversion to ketoamine in polar protic solvents, was not fluorescent at pH < 8. The fluorescence of other compounds was very sensitive to solvent polarity and the pH of the medium. Compounds 2-4, preferably present as enolimines in all solvents, were not fluorescent in non-polar and moderately polar solvents, whereas weak emission was observed in polar solvents, like methanol, dimethylformamide and dioxane/water 1/1 (0.001 < Q < 0.072). A significant increase in Stokes shifts and in quantum efficiencies was noted as a result of increasing polarity of dioxane/water mixtures, indicating specific interactions with polar water molecules. The emission was promoted at acidic pH values where a pyridinium cation was formed (0.061 < Q < 0.519, in dioxane/water 1/1 at pH 3.4). Compound 5, which was a tautomeric mixture of enoiimine and cyclic diamine in all solvents, was fluorescent in polar as well as in non-polar media. The quantum efficiency varied dependent on the solvent and pH (0.023 <Q< 0.435). The cyclic diamine, i. e. the more rigid structure was supposed to be responsible for the fluorescence in non-polar and aprotic solvents as well as at neutral, and weakly basic pH values.     

Stable isotope composition of the meteoric precipitation in Croatia

The precipitation is the input into the water system. Its stable isotope composition has to be known for the proper use and management of water resources. Croatia is not well represented in the Global Network of Isotopes in Precipitation (GNIP) database, and the geomorphology of the country causes specific local conditions. Therefore, at the Stable Isotope Laboratory (SILab), Rijeka, we monitor the stable isotope composition (δ¹⁸O, δ²H) of precipitation. Since δ¹⁸O and δ²H are well correlated, we concentrate the discussion on the δ¹⁸O distribution. Together with GNIP, our database contains 40 stations in Croatia and in the neighbouring countries. Their different latitudes, longitudes and altitudes give information of great detail, including the influence of the topographic structure on the precipitation in the south-eastern part of Europe, as well as the complex interplay of the different climate conditions in the area. Within a few hundred kilometres, the stable isotope values display a significant change from the maritime character in the south (mean δ¹⁸O around?6 to?8%‰) to the continental behaviour in the north (mean δ¹⁸O around?8 to?11%‰). Depending on the location, the mean δ¹⁸O values vary with altitude at a rate of approximately?0.2%‰/100 m and?0.4%‰/100 m, respectively. Also the deuterium excess has been found to depend on location and altitude. The data are being used to construct a δ¹⁸O map for the entire area.     

Absorption and Fluorescence Characteristics of Some 2-Aryl-and 2-Heteroaryl-benzothiazoles in Different Solvents and at Various pH Values

The parameters characterizing the absorption and fluorescence of seven 2-substituted benzothiazoles in different solvents and at various acid/base concentrations were studied. It was found that both the kind of substituent and the solvent polarity influenced the changes of the spectral properties of the examined molecules. 2-Aryl substituted benzothiazoles exhibit larger Stokes shifts than 2-heteroaryl derivatives. The linear relationship between solvent polarity and pH values against Stokes shift and fluorescence sensitivity, respectively, was observed. The mostly fluorescent compound was 2-(2-benzofuryl)benzothiazole.     

Inhibitory Effect of DMSO on Halohydrin Dehalogenase: Experimental and Computational Insights into the Influence of an Organic Co-solvent on the Structural and Catalytic Properties of a Biocatalyst

Although the application of organic solvents in biocatalysis is well explored, in-depth understanding of the interactions of solvent with proteins, in particular oligomeric ones, is still scant. Understanding these interactions is essential in tailoring enzymes for industrially relevant catalysis in nonaqueous media. In our study, the homotetrameric enzyme halohydrin dehalogenase (HHDH) from Agrobacterium radiobacter AD1 (HheC) was investigated, as a model system, in DMSO/water solvent mixtures. DMSO, the most commonly used co-solvent for biocatalytic transformations, was found to act as a mixed-type inhibitor with a prevalent competitive contribution. Even 5 % (v/v) DMSO inhibits the activity of HheC by half. Molecular dynamics (MD) simulations showed that DMSO keeps close to Ser-Tyr catalytic residues forming alternate H-bonds with them. Stability measurements paired with differential scanning calorimetry, dynamic light scattering methods and MD studies revealed that HheC maintains its structural integrity with as much as 30 % (v/v) DMSO.     

Grapevine as a Rich Source of Polyphenolic Compounds

Grapes are rich in primary and secondary metabolites. Among the secondary metabolites, polyphenolic compounds are the most abundant in grape berries. Besides their important impacts on grape and wine quality, this class of compounds has beneficial effects on human health. Due to their antioxidant activity, polyphenols and phenolic acids can act as anti-inflammatory and anticancerogenic agents, and can modulate the immune system. In grape berries, polyphenols and phenolic acids can be located in the pericarp and seeds, but distribution differs considerably among these tissues. Although some classes of polyphenols and phenolic acids are under strict genetic control, the final content is highly influenced by environmental factors, such as climate, soil, vineyard, and management. This review aims to present the main classes of polyphenolic compounds and phenolic acids in different berry tissues and grape varieties and special emphasis on their beneficial effect on human health.     

Spatial and seasonal variations in the stable C isotope composition of dissolved inorganic carbon and in physico-chemical water parameters in the Plitvice Lakes system

Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002-2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ(13)C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ(13)C(DIC) values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO(3) (I (sat) values 4-10) and with δ(13)C(DIC) values between-11.5 and-8.5 ‰. In spring waters, the δ(13)C(DIC) values were more negative, from-14 to-12 ‰, and I (sat) values of 1-2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ(13)C(DIC) correlated with the increase in the δ(13)C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.     

Spatial and seasonal variations in the stable C isotope composition of dissolved inorganic carbon and in physico-chemical water parameters in the Plitvice Lakes system

Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002–2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ¹³C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ¹³C_DIC values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO₃ (I _sat values 4–10) and with δ¹³C_DIC values between?11.5 and?8.5 ‰. In spring waters, the δ¹³C_DIC values were more negative, from?14 to?12 ‰, and I _sat values of 1–2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ¹³C_DIC correlated with the increase in the δ¹³C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.