Physico-chemical changes taking place in gamma irradiated bovine globulins studied by thermal analysis

Structural transformations induced in gamma and alpha globulins under influence of gamma irradiation using doses of 2.5 and 24 kGy were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG, DTG). Thermal decomposition of the globulins irradiated in water suspensions occurs at higher temperatures, in comparison to the reference non-irradiated samples. This was related to formation of covalent linkages in the irradiated proteins, apart to chemical changes induced in amino-acids. Essential modification of thermal decomposition was detected already after irradiation with a dose of 2.5 kGy performed for water suspensions. Irradiation of solid native proteins induces decrease in decomposition temperature and gives evidence of proteins degradation.     

DFT studies on tautomeric preferences of 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione in the gas phase and in solution

Density functional theory (DFT) calculations show that in vacuum such α-diketone as 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione is much less stable than its enolimine–enaminone ((1Z,3Z)-3-hydroxy-4-(pyridin-2-yl)-1-(quinolin-2(1H)-ylidene)but-3-en-2-one) and dienaminone tautomers ((1Z,3Z)-1-(pyridin-2-yl)-4-(quinolin-2-yl)buta-1,3-diene-2,3-diol). Other its tautomers (multiple basic and acidic centers in their molecules enable multiple proton transfer to take place) are even more labile. Strength of the intramolecular hydrogen bonds and aromatic character of the (quasi)rings [proved by the Harmonic Oscillator Model of Aromaticity (HOMA) index] in their molecules were found to be responsible for the observed tautomeric preferences. Polar and basic solvent disfavors and favors the enolimine and enaminone tautomers, respectively.     

Synthesis and structural characterization of novel 2-benzimidazolylthioureas: adducts of natural isothiocyanates and 2-amino-1-methylbenzimidazole

Adducts of natural allyl, phenethyl, and benzyl isothiocyanates and 2-amino-1-methylbenzimidazole were synthesized. After optimization of the reaction conditions, the target 2-benzimidazolylthioureas were obtained in reasonable yields. The detailed molecular and crystal structures of these compounds were characterized by spectroscopic and X-ray methods. Spectral analysis demonstrated that N-(1-methylbenzimidazolyl)-N′-allylthiourea, N-(1-methylbenzimidazolyl)-N′-benzylthiourea, and N-(1-methylbenzimidazolyl)-N′-phenethylthiourea exist in solution in an unprecedented three tautomeric forms, whose structures were corroborated unambiguously.     

DFT studies on tautomeric preferences. Part 3: Proton transfer in 2-(8-acylquinolin-2-yl)-1,3-diones

8-Acetyl- and 8-benzoyl-2-(quinolin-2-yl) derivatives of 1,3-diketones were studied from point of view of their tautomeric preferences. Effective electron delocalization and strong hydrogen bonds were found to be responsible for high stability of the enaminone form (the most stable tautomer). Density functional theory (DFT) calculations prove that enolimine and ketimine species are less favored. Contribution of the zwitterionic resonance structures to the enaminone form is most significant in 2-(quinolin-2(1H)-ylidene)-2H-indene-1,3-dione derivatives. Formation of the bifurcated hydrogen bonds was found to take place only in 8-acetyl derivatives. One of these bonds is of the RAHB (Resonance Assisted Hydrogen Bond) type. There is a steric interaction of the pyridine β-hydrogen and carbonyl oxygen atoms in the enaminone tautomers.     

Dispersive liquid–liquid microextraction applied to isolation and concentration of alkylphenols and their short-chained ethoxylates in water samples

Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography with fluorescence detector was applied for the determination of alkylphenols and their short-chained ethoxylates in water samples. Development of DLLME procedure included optimisation of some important parameters such as kind and volume of extracting and dispersing solvents. Under optimised conditions 50 μL of trichloroethylene in 1.5 mL of acetone were rapidly injected into 5 mL of a water sample. After centrifuging the organic phase containing the analytes was taken for evaporation with a gentle nitrogen purge and reconstituted to 50 μL of acetonitrile. The aliquot of this solution was analysed with the use of HPLC. For octylphenol (OP) and octylphenol ethoxylates (OPEOs) linearity was satisfactory in the range 8–1000 μg L⁻¹ and for nonylphenol (NP) and nonylphenol ethoxylates (NPEOs) linearity was in the range from 50 to about 3000 μg L⁻¹. Limit of quantitation was 0.1 μg L⁻¹ for OP and OPEOs and 0.3 μg L⁻¹ for NP and NPEOs. Satisfactory recoveries between 66 and 79% were obtained for environmental samples. The results showed that DLLME is a simple, rapid and sensitive analytical method for the preconcentration of trace amounts of alkylphenols and their ethoxylates in environmental water samples.     

Does Maternal Treatment with Zidovudine Affect Changes in Mandibles of Newborns? Laser Induced Fluorescence Study

The influence of antiretroviral drug zidovudine treatment during pregnancy on mandible development in newborn rats was studied. The fluorescence of mandibles from 7-, 14- and 28-days old individuals was measured by means of fiber-optical fluorescence analyzer with 407 nm laser excitation. Obtained results revealed disturbing effect of maternal zidovudine administration on mandible fluorescence intensity which should decrease with bone development. Small changes in fluorescence of porphyrin forms are maintaining in the first month of newborns life while the changes observed in 440–585 nm range disappear.     

Reverse engineering of Al<Subscript>x</Subscript>Ga<Subscript>1−x</Subscript>As/GaAs structures composition by reflectance spectroscopy

The paper presents the application of non-modulation reflectance method for composition profiling of epitaxial Al_xGa_−xAs/GaAs structures. This non-destructive method is based on spectral measurements and theoretical reflectance spectrum matching. This is a very accurate and sensitive method of determining the Al composition in Al_xGa_1−xAs layers and structures with resolution down to 1 nm. In this work, the authors describe theoretic principles of this method and present experimental results of characterization of different AlGaAs structures to prove the potential of the worked out method.     

On variable discounting in dynamic programming: applications to resource extraction and other economic models

This paper generalizes the classical discounted utility model introduced in Samuelson (Rev. Econ. Stud. 4:155–161, 1937) by replacing a constant discount rate with a function. The existence of recursive utilities and their constructions are based on Matkowski’s extension of the Banach Contraction Principle. The derived utilities go beyond the class of recursive utilities studied in the literature and enable a discussion on subtle issues concerning time preferences in the theory of finance, economics or psychology. Moreover, our main results are applied to the theory of optimal economic growth related with resource extraction models with unbounded utility function of consumption.