Effect of temperature on the structure of adsorption layers formed by adsorption of polymers in the transition region from dilute to semidilute solutions

The measurements of adsorption from solutions of polymers (poly(butyl methacrylate) and polystyrene) and their mixtures at various temperatures in the wide concentration region from dilute to semidilute solution have been made. The adsorption isotherms and fraction of bound segments confirm the existence of the transition concentration region near the critical concentration of the chain overlapping when the change of adsorption mechanisms take place. The effect of temperature on adsorption from the mixtures is different for both the polymers depending on the concentration regime. For PBMA, which adsorbs from the mixtures preferentially, the adsorption isotherms are of the same shape as for adsorption from binary solutions and are characterized by the presence of a small forepart in the transition region and by increasing adsorption with temperature. For less adsorbing PS by transition from dilute to semidilute regime the inversion of the temperature effect on adsorption is observed. These results are confirmed by the estimations of the parameters of preferential adsorption at various temperatures. The data on the fraction of bound segments for dilute regime corresponds to the extended conformation of chains at the surface. The transition to semidilute regime leads to the diminishing of the fraction of bound segments as a result of simultaneous adsorption of macromolecular aggregates. Values of adsorption layer thickness have been calculated for various solution regimes and concentration. The dependence of the adsorption layer thickness on the temperature and on the solution regime at which adsorption occurs was established.     

Radioactivity on the Montenegrin Coast, Yugoslavia

Environmental radioactivity has been investigated on the Montenegrin Coast (Yugoslavia). Radioactivity was measured on 14 beaches and 5 hinterland localities by a method of in situ gamma-spectrometry. At each measuring site two photon countings were performed — in ground and above it. Specific activities of⁴⁰K,²³²Th,²³⁸U,¹³⁷Cs and corresponding exposure rates were then obtained from gamma-spectra and appropriate radiation field models. The results show a washing out effect of the sea-water: radioactivity level on the beach is significantly lower than on its hinterland. In situ spectrometry was also performed inside 16 hotels on the Coast. Radioactivity of building materials is found to be 8 to 20 times lower than the limit permitted by regulations. In 12 of these hotels, indoor radon concentrations were measured with track etch detectors. Winter radon concentrations were in a range (22–90) Bq/m³, i.e., much below the most stringent reference level.     

Electrical interfacial layer at TiO2/poly(4-styrene sulfonate) aqueous interface

The interfacial properties of the system titanium(IV) oxide/poly(4-styrenesulfonate) (PSS) over a broad pH region in the presence of different alkali metal chlorides of different concentrations were investigated by means of electrokinetic, adsorption and surface potential measurements. Adsorption and electrokinetic data were obtained with colloid TiO₂ particles, while surface potential data were obtained using a single crystal rutile electrode with the 001 plane exposed to the liquid medium. The electrokinetic and surface potentials of TiO₂ were measured in the absence and presence of PSS. Since the presence of PSS did not significantly affect surface potentials, it was concluded that negative PSS molecules adsorbed at the surface by forming an outer-sphere surface complex rather than inner-sphere complex. The adsorption decreases significantly with pH, while the electrokinetic potential in the presence of PSS is negative in the whole investigated pH region. Amount of adsorbed PSS molecules is limited by the electrostatic repulsion which suppresses further adsorption, i.e. above critical potential of ?50 millivolts. In the acidic region, where the surface is originally positively charged the amount of adsorbed PSS molecules is high since negative PSS molecules should at first compensate original positive charge and in the second step reverse the charge to reach the critical potential. In the basic region the surface charge is already negative so that small amount of adsorbed PSS molecules creates critical potential that prevents further adsorption.     

Synthesis,spectral characterization,electrochemical properties and antimicrobial screening of sulfur containing acylferrocenes

Several known and eight new sulfur containing acylferrocenes of the general formula FcCO(CH₂)_nSR (where Fc = ferrocenyl, n = 1 or 2 and R = alkyl, 4-bromobenzyl or 2,6-dichlorobenzyl group) were synthesized in order to test their in vitro antimicrobial activity against 11 bacterial and three fungal/yeast strains. It has been shown that only four of the 14 ketones are completely inactive at the tested dose, while the activities of the other ones were noteworthy. All new compounds were well characterized by IR and NMR spectral data, and their electrochemical properties were investigated by cyclic voltammetry. The X-ray crystal structures of two representative ketones are also presented.     

Phosphorus Crown-Ethers with Nitrogen-Containing Heterocycles

Abstract

Phosphorus-containing crown-ethers functionalized by heterocycle fragments have essential advantages over the usual ones. The introduction of structural units of indoles, pyrroles and indolizines to phosphorus atom of the macrocyclic chain is capable to change lipophilic, complexing, biological and other properties of the initial crown-ethers. For synthesis of such compounds we have used dihalidophosphines obtained by direct substitution of the electron-rich aromatic compounds with phosphorus (III) halides. As a result, series of highly efficient macrocyclic compounds of a nowel type have been obtained.     

Dual fluorescence of 2-methoxyanthracene derivatives

The time-resolved emission properties of selected anthracene derivatives, namely anthracene (1a), 2-methylanthracene (1b), 2-chloroanthracene (1c), 2-methoxyanthracene (1d), 2-methoxy-6-methylanthracene (1e), 2-(N,N'-dicyclohexylureidocarbonyl)-6-methoxyanthrace ne (1f), 2-(6-methoxyanthr-2-yl)-4,4-dimethyl-2-oxazoline (1g), 2-(6-methoxyanthr-2-yl)-pyridine (1h), and N-cyclohexylanthracene-2-carboxamide (1i) were investigated. In contrast to anthracene (1a), 1b, and 1c, the 2-methoxy-substituted anthracene derivatives 1d-1h exhibit two emission lifetimes. The determination of the lifetimes at different emission wavelengths and additional time-resolved emission spectroscopy (TRES) reveal that the dual emission originates from two different, interconvertible emissive species, with the s-cis and s-trans conformation relative to the exocyclic C2-O bond. The energy difference between the two emissive species is very small (<0.1 eV) both in the ground and in the excited state. The larger energy difference between the conformers in the excited-state is responsible for the interconversion within the singlet excited-state lifetimes of the s-cis into the s-trans conformations leading to coupled decay kinetics. The proposed mechanism for the dual emission was qualitatively supported by theoretical studies on CASSCF and DFT level. In addition, the emission lifetimes of the fluoride- and pH-sensitive fluorescent probes 1f and 1g change upon addition of fluoride or acid, respectively, so that in these cases the detection of the fluorescence lifetime may be used complementary to the steady-state fluorimetric detection of these analytes.     

Site Isolation Leads to Stable Photocatalytic Reduction of CO2 over a Rhenium‐Based Catalyst

A porous organic polymer incorporating [(α‐diimine)Re(CO)₃Cl] moieties was produced and tested in the photocatalytic reduction of CO₂, with NEt₃ as a sacrificial donor. The catalyst generated both H₂ and CO, although the Re moiety was not required for H₂ generation. After an induction period, the Re‐containing porous organic polymer produced CO at a stable rate, unless soluble [(bpy)Re(CO)₃Cl] (bpy=2,2′‐bipyridine) was added. This provides the strongest evidence to date that [(α‐diimine)Re(CO)₃Cl] catalysts for photocatalytic CO₂ reduction decompose through a bimetallic pathway.     

Effects of Dietary α-Linolenic Acid Treatment and the Efficiency of Its Conversion to Eicosapentaenoic and Docosahexaenoic Acids in Obesity and Related Diseases

The essential fatty acid alpha-linolenic acid (ALA) is present in high amounts in oils such as flaxseed, soy, hemp, rapeseed, chia, and perilla, while stearidonic acid is abundant in echium oil. ALA is metabolized to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) by desaturases and elongases in humans. The conversion of ALA to EPA and DHA is limited, and these long-chain n−3 polyunsaturated fatty acids (PUFAs) are mainly provided from dietary sources (fish and seafood). This review provides an overview of studies that explored the effects of dietary supplementation with ALA in obesity and related diseases. The obesity-associated changes of desaturase and elongase activities are summarized, as they could influence the metabolic conversion of ALA. Generally, supplementation with ALA or ALA-rich oils leads to an increase in EPA levels and has no effect on DHA or omega-3 index. According to the literature data, stearidonic acid could enhance conversion of ALA to long-chain n−3 PUFA in obesity. Recent studies confirm that EPA and DHA intake should be considered as a primary dietary treatment strategy for improving the omega-3 index in obesity and related diseases.     

Spin-wave dispersion in ferromagnetic semiconductor superlattices and thin films in the narrow-band limit

Bulk and surface magnetic excitations of the semi-infinite ferromagnetic semiconductor (FMS) superlattices and thin films described by Heisenberg and s-d model are analyzed using the transfer matrix method, developed in our previous work. Results are discussed in the narrow-band limit. The spin-wave frequencies for the semi-infinite narrow-band semiconductors are analyzed in both low- and high-frequency regions. Energies of localized excitations are compared to the bulk and the results of Green function formalism. Depending on the parameters of the system, the surface spin waves appear as “acoustical” and “optical”, and there are only some quantitative difference in the high-frequency region, comparing our method and the Green function method. In the framework of the same methodology, bulk and surface magnetic excitations of more complicated superlattices and thin films made of the FMS superlattices are analyzed in terms of dependence of the system parameters. It is shown that the s-d interaction governs the behavior of the systems. Dependence on bulk and surface parameters is discussed.     

Rectification by an imprinted phase in a Josephson junction

A Josephson phase shift can be induced in a Josephson junction by a strategically nearby pinned Abrikosov vortex (AV). For an asymmetric distribution of an imprinted phase along the junction (controlled by the position of the AV) such a simple system is capable of rectification of ac current in a broad and tunable frequency range. The resulting rectified voltage is a consequence of the directed motion of a Josephson antivortex which forms a pair with the AV when at local equilibrium. The proposed realization of the ratchet potential by an imprinted phase is more efficient than the asymmetric geometry of the junction itself, is easily realizable experimentally, and provides rectification even in the absence of an applied magnetic field.