Interaction of isomeric forms of xanthophyll pigment zeaxanthin with dipalmitoylphosphatidylcholine studied in monomolecular layers

Two-component monomolecular layers were formed with DPPC and two stereoisomers of zeaxanthin 9-cis and 13-cis at the argon-water interface. Very distinct over-additivity which represents affection of a lipid arrangement in the membrane has been observed in the case of zeaxanthin 9-cis (maximum at 20 mol%) but not in the case of zeaxanthin 13-cis. The differences in the organization of the isomers of zeaxanthin-DPPC monolayers are interpreted in terms of the different orientation of both xanthophylls at the interface observed at relatively high surface pressures (>25 mN/m) comparable to the surface pressures of biomembranes. The results are consistent with the model according to which zeaxanthin 9-cis adopts a vertical orientation at the polar-nonpolar interface in contrast to zeaxanthin 13-cis, which is oriented horizontally owing to the fact that it interacts by two hydroxyl groups with the same hydrophobic-hydrophilic interface in the monolayer. The findings are discussed in comparison with the behavior of zeaxanthin in the conformation all-trans in the same system. Zeaxanthin all-trans forms efficiently molecular aggregates in the mixed monolayers in contrast to cis isomers. Circular dichroism measurements show the formation of molecular structures by zeaxanthin 13-cis that are interpreted as dimers. FTIR measurements show that these dimers are stabilized by van der Waals interactions unlike aggregated structures formed by all-trans zeaxanthin that are stabilized by hydrogen bonding. Physiological importance of the differences in aggregation and orientation of stereoisomers of zeaxanthin in lipid environment is discussed.     

A dispersive model of radical accumulation in irradiated solids

- A dispersive model of radical accumulation in irradiated solids is discussed by the example of hexagonal ice (Ih) and cubic ice (Ic) obtained by annealing of hyperquenched glassy water at 160 K. The model assumes that radical production upon -irradiation is accompanied by their second-order decay, which proceeds according to dispersive kinetics with the time-dependent specific reaction rate k(t) = Bt ^-1, where B = constant and is the dispersion parameter equal to 0.40 for both the hexagonal and cubic ices. The radicals, OH in Ih, and OH plus HO₂ in Ic are produced at the same rate upon -irradiation. The observed enhancement of radical accumulation in ice Ic in comparison with Ih is due to the marked decrease of radical recombination in ice Ic. This is rationalized by the hindrance of radical transport in the lattice of ice Ic containing substantial amounts of Bjerrum-type L-defects.     

Treatment of effluents from a membrane bioreactor by nanofiltration using tubular membranes

Production of bioproducts is associated with the generation of considerable amounts of effluents from the bioreactors used. Application of the nanofiltration process was proposed for the treatment of these effluents in order to separate both inorganic and organic solutes. Composition of the fermentation broth precludes the utilization of traditional spiral-wound modules (high turbidity) for the solutes separation in the NF process. The tubular module with AFC30 membranes applied in this work enables such a possibility. Transport and separation characteristics of the NF membrane were determined for the reference solutions containing components present in the effluents generated during the fermentation of glycerol with the use of bacteria.     

Photochemical stability of poly(vinyl alcohol) in the presence of collagen

The photochemical stability of poly(vinyl alcohol) (PVA) in the presence of 1%, 3% and 5% of collagen has been studied by Fourier Transform Infrared (FTIR) Spectroscopy, UV-vis spectroscopy, and Differential Scanning Calorimetry (DSC). PVA samples containing 1%, 3% and 5% of collagen were irradiated with UV light wavelength λ = 254 nm in air.The results have shown that PVA in the presence of 1%, 3% and 5% of collagen is less stable under UV radiation than pure PVA. A small amount of collagen in PVA enhances photooxidation in the PVA. The amount of crystallinity in PVA containing 1%, 3% and 5% of collagen decreases faster with UV irradiation time than that for pure PVA films.     

Coumarin 153 emission thermochromism studied in non-specifically and specifically interacting solvents

We report a study of the thermochromic shifts observed for coumarin 153 (C153) emission spectra in several selected chloroalkanes and several solvents potentially specifically interacting with the probe. It has been found that the shifts observed in five 1-chloroalkanes can be successfully predicted using the McRae molecular interaction model [E.G. McRae, J. Phys. Chem. 61 (1957) 562]. However, the shifts observed in two other chloroalkanes have been found not to correspond to the value, which can be derived using the same C153 molecular parameters (dipole moments, molecular radius and gas phase emission spectrum position) as in the analysis of shifts in 1-chloroalkanes. This observation suggests that 1-chloroalkanes may interact specifically, contrary to what was assumed in our previous papers. The temperature dependence of changes in the energy of these specific interactions, after C153 excitation, also in the solvents known to interact in this way, is discussed in view of the thermochromic results reported in this paper and literature data. We show that even for C153, one of the most often studied probe, one cannot definitively state in what kind of specific interactions it takes or does not take part.     

Influence of Fluorine Substitution on Nonbonding Interactions in Selected Para-Halogeno Anilines

A series of 4-halogeno aniline derivatives was studied employing combined theoretical and experimental methods (i. e. crystal structure analysis and vibrational spectroscopies). This simplified model system was selected to shed light on the impact of fluorine substitution on the formation of noncovalent interactions such as halogen bonds (XBs) and hydrogen bonds (HBs), which are key interactions in fluorinated/halogenated drug-protein complex formation. Comparative analysis of three previously reported and five newly determined crystal structures indicated that, in most cases, 2-fluoro and 2,6-difluoro substitution of 4-X anilines increases the ability of adjacent amine to form strong N−H⋅⋅⋅N HBs. Additionally, fluorine substituents in the difluorinated derivatives are competitive and attractive HB and XB acceptors and increase the probability of halogen-halogen contacts. A peculiar observation was made for 4-iodoaniline and 2,6-difluoro-4-iodoaniline, which form distinct interaction patterns compared to the corresponding 4-Cl and 4-Br analogs. The observed intramolecular N−H⋅⋅⋅F interactions lead to additional NH bands in the FT-IR spectra.     

Correlation between glass transition effect and structural changes in multicomponent iron phosphate-silicate glasses

Iron phosphate-silicate glasses from P₂O₅–SiO₂–K₂O–MgO–CaO–Fe₂O₃ system were subjected to the thermal and spectroscopic studies in order to gain information about their structure and thermal behavior in the range of glass transition effect. Research includes results obtained via DSC, MIR and DRIFT spectroscopy. Designated values of glass transition temperature and specific heat change slightly increases with Fe₂O₃ incorporation. Spectra collected during thermal treatment of glasses containing 2 and 30 mol% Fe₂O₃ exhibited various changes. Fe₂O₃ addition affected the glass structure by its reinforcement and led to its preservation during thermal treatment. The connection between density, molar volume, oxygen packing density and the chemical composition’s alteration were also established because of the direct dependence of physical properties and the structure. Obtained results supported thermal and spectroscopic studies. Conducted research is considered as a contribution to the knowledge about the family of iron phosphate glasses, which are known from their interesting properties and widely used applications.

     

Sorption of Cu(II) and Ni(II) ions in the presence of the methylglycinediacetic acid by microporous ion exchangers and sorbents from aqueous solutions

In the presented paper the use of a novel environmentally friendly aminopolycarboxylate chelating agent trisodium salt of methylglycinediacetic acid (MGDA) to inactivate various metal ions by complex formation in microporous anion exchangers and sorbents was tested. MGDA is a new generation of chelator, undergoing biodegradation.     

The role of the βAsp residue in copper(II) binding by modified peptides

The synthesis and binding abilities of peptides containing β-amino acids towards Cu(II) ions are presented. The peptides studied were: Ala-βAsp-Ser-Gly and Arg-Lys-βAsp-Val-Tyr. Potentiometric titrations were carried out to establish the stoichiometry of the resulting metal-ligand complexes. The copper(II) coordination mode of the complexes was investigated by performing detailed spectroscopic analyses (UV–Vis, CD) in strict correlation with potentiometric measurements. The results obtained on the β-peptides studied allowed the characterization of the influence of this structural modification on the coordination abilities of the peptides. Moreover, the role of the α-Asp position in the peptide chain was also described.