Suberin: a biopolyester of plants' skin

Suberin is a biopolymer that acts as a barrier between plants and the environment. It is known to be a complex polyester based on glycerol and long-chain alpha,omega-diacids and omega-hydroxyacids. How these monomeric units are assembled at a macromolecular level remains mostly unknown. The knowledge gathered in the last 10 years has opened new insights into suberin structure. Suberin oligomeric blocks have been obtained after the partial depolymerization of the biopolymer, and in-situ studies by solid-state (13)C NMR spectroscopy have shown different molecular domains and how they are spatially related. Based on these latter developments, a model is proposed for the suberin macromolecular structure. The uniqueness of the suberin polyester opens perspectives for its use as a source of bio-based materials.     

Synthesis and cellular studies of PEG-functionalized meso-tetraphenylporphyrins

The total syntheses of four PEG-functionalized porphyrins, containing one to four low molecular weight PEG chains linked via amide bonds to the para-phenyl positions of meso-tetraphenylporphyrin, are reported. The hydrophobic character of the PEG-porphyrins decreases with the number of PEG chains linked to the porphyrin ring, while their tendency for aggregation in buffered aqueous solution increases. The porphyrins containing one or two PEG chains accumulated within human HEp2 cells to a much higher extent than those having three or four PEGs at the macrocycle periphery. All PEG-porphyrins were found to be non-toxic in the dark, and only those containing one or two PEG chains were phototoxic (IC(50)=2 microM at 1J/cm(2) light dose). The preferential sites of subcellular localization of the porphyrins containing one or two PEG chains were found to be the mitochondria and endoplasmic reticulum (ER), while those containing three or four PEG chains localize preferentially in the lysosomes.     

Two distinct manganese(II) complexes with hexadentate 1,3-propanediaminetetraacetate ligand: The ability of metal(II) complexes with 1,3-pdta ligand to form solid solutions

The ability of Mn(II) ion to form two distinctly different complexes with 1,3-propanediaminetetraacetate (1,3-pdta) ligand has been demonstrated by performing X-ray analyses of their crystalline Mg(II) salts. The two types of Mn(II) complexes have been obtained by different synthetic routes and their crystals constitute, respectively, the solid solution of the composition [Mg(H₂O)₆][Mg_0.5Mn_0.5(1,3-pdta)] · 2H₂O (1) and the ordered crystals of the composition [Mg(H₂O)₆][Mn(1,3-pdta)(H₂O)] · 2H₂O (2). In both, six- 1 and seven-coordinated 2 Mn(II) complexes the 1,3-pdta ligand acts as a hexadentate. As 2 makes the second example of the seven-coordinated 1,3-pdta complex with divalent transition metal ion, the other being the [Mg(H₂O)₆][Cd(1,3-pdta)(H₂O)] · 2H₂O (3) complex, the paper reports the results of X-ray investigations of both of these complexes at 130 K.     

DNA gel particles: particle preparation and release characteristics

Aqueous mixtures of oppositely charged polyelectrolytes undergo associative phase separation, resulting in coacervation, gelation, or precipitation. This phenomenon has been exploited here to form DNA gel particles by interfacial diffusion. We report the formation of DNA gel particles by mixing solutions of DNA (either single-stranded (ssDNA) or double-stranded (dsDNA)) with solutions of cationic surfactant CTAB and solutions of the protein lysozyme. Swelling, surface morphology, and DNA release determinations indicate different interaction of ssDNA and dsDNA with both the surfactant and the protein. By using CTAB and lysozyme as the base material, the formation of a DNA reservoir hydrogel, without adding any kind of cross-linker or organic solvent, was demostrated.     

Modeling of vacuum desorption of multicomponent moisture in freeze drying

A mathematical model of multicomponent vacuum desorption, which occurs in the vacuum freeze drying process has been developed. Drying with conductive heating and constant contact surface temperature was considered. Pressure drop in the layer of the material to be dried was taken into account in the model formulation and process simulation. Equilibrium moisture content for pure water, toluene, and m-xylene and their two- and three-component mixtures on zeolite DAY 20F were described by means of the multitemperature extended Langmuir isotherm equation. Model equations were solved by the numerical method of lines. Moisture content and temperature distributions within the drying material were predicted from the model as a function of drying time.     

On the concept of an equivalent column in the stability problem of compressed helical springs

Summary A more exact equivalent column for buckling of helical springs is introduced. It accounts for the pitch angle and possible buckling in two planes. Non-linear compression rigidity, local bending and shear rigidities as well as lower bounds for the mean values of these rigidities are established. The problem of anisotropy of buckling of helical springs is investigated in detail.

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Zum konzept äquivalenter stäbe für das knickproblem von Schraubenfedern

Übersicht Vorgeschlagen wird ein verbessertes Konzept äquivalenter Stäbe für die Knickung von Schraubenfedern. Der Steigungswinkel der Schraubenlinie sowie Knickung in zwei Ebenen werden berücksichtigt. Nichtlineare Drucksteifigkeit, lokale Biege- und Schubsteifigkeiten sowie untere Schranken für Mittelwerte dieser Steifigkeiten werden ermittelt. Das Problem der Anisotropie der Knickung von Schraubenfedern wird eingehend untersucht.

     

Synthesis and thermal behaviour of new benzo-1,2-thiazine long-chain aryl-piperazine derivatives

A series of potential biologically active 2-[3-(4-phenyl-1-piperazinyl)propyl]-3-(4-substituted-benzoyl)-4-hydroxy-2H-1,2-benzothiazine 1,1-dioxides was synthesized in a straightforward manner by condensation of respective 3-substituted-4-hydroxy-1,2-benzothiazine 1,1-dioxides with 1-(1-chloropropyl)-4-phenylpiperazine. The structures of all of the newly formed compounds were identified by elemental analysis, FTIR and ¹H NMR. The synthesized compounds were subjected to preliminary evaluation using differential scanning calorimetry (DSC) to determine the existence of multiple crystal forms. The DSC scans for all compounds show more than one endothermic effect, which might suggest dynamic proton transfer between two or three possible tautomeric forms: O-keto/O-enol, O-enol/O-keto and O-keto/O-keto/CH₂ in crystals 2-[3-(4-phenyl-1-piperazinyl)propyl]-3-(4-substituted-benzoyl)-4-hydroxy-2H-1,2-benzothiazine 1,1-dioxides.     

The influence of the method of addition of Al2O3 to 3YSZ material on its thermal and electrical properties

The properties of tetragonal yttria-stabilized zirconia composites with the small addition of alumina (Al₂O₃?Y₂O₃?ZrO₂ composite) obtained on two ways of synthesis were studied in terms of usability for anode materials in solid oxide fuel cell. Both methods were based on citric synthesis: in the first one, Al₂O₃ was coprecipitated with the tetragonal ZrO₂ in the form of citrate by citric acid, while in the second Al₂O₃ was impregnated in the form of aluminium nitrate precursor on tetragonal ZrO₂ matrix. The obtained materials were analysed by X-ray diffraction, dilatometry and impedance spectroscopy. The results of measurements show that regardless of synthesis method, the addition of Al₂O₃ influences the conductivity of samples by increasing their grain boundaries conductivity as an effect of removing of SiO₂ and decreasing of conductivity activation energy. The impregnation of Al₂O₃ on tetragonal ZrO₂ and sintering of this material above shrinking temperature cause, however, radical decrease of porosity of materials, which disqualifies these samples as anode materials. In the case of samples obtained by coprecipitation the significant decrease of porosity is not observed.     

Tautomeric and Microscopic Protonation Equilibria of Anthranilic Acid and Its Derivatives

The acid–base chemistry of three zwitterionic compounds, namely anthranilic (2-aminobenzoic acid), N-methylanthranilic and N-phenylanthranilic acid has been characterized in terms of the macroconstants K _a1, K _a2, the isoelectric point pH _I, the tautomerization constant K _z and microconstants k ₁₁, k ₁₂, k ₂₁, k ₂₂. The potentiometric titration method was used to determine the macrodissociation constants. Due to the very poor water solubility of N-phenylanthranilic acid the dissociation constants pK _a1 and pK _a2 were determined in MDM–water mixtures [MDM is a co-solvent mixture, consisting of equal volumes of methanol (MeOH), dioxane and acetonitrile (MeCN)]. The Yasuda–Shedlovsky extrapolation procedure has been used to obtain the values of pK _a1 and pK _a2 in aqueous solutions. The pK _a1 and pK _a2 values obtained by this method are 2.86 ± 0.01 and 4.69 ± 0.03, respectively. The tautomerization constant K _z describing the equilibrium between unionized form ? zwitterionic form was evaluated by the K _z method based on UV–VIS spectrometry. The method uses spectral differences between the zwitterionic form (found at isoelectric pH in aqueous solution) and the unionized form (formed in an organic solvent of low dielectric constant). The highest value of the K _z constant has been observed in the case of N-methylantranilic acid (log₁₀ K _z = 1.31 ± 0.04). The values of log₁₀ K _z for anthranilic and N-phenylanthranilic acids are similar and have values of 0.93 ± 0.03 and 0.90 ± 0.05, respectively. The results indicate that the tested compounds, in aqueous solution around the isoelectric point pH_I, occur mainly in the zwitterionic form. Moreover, the influence of the type of substituent and pH of the aqueous phase on the equilibrium were analyzed with regard to the formation and the coexistence of different forms of the acids in the examined systems.     

Cosmogenic 22Na, 7Be and terrestrial 137Cs, 40K radionuclides in ground level air samples collected weekly in Kraków (Poland) over years 2003–2006

A low background gamma spectrometer with an Etruscan, 2500 years old lead shield and a muon veto detector were applied to study ²²Na and ⁷Be activity concentration in ground level air aerosol samples collected weekly over the years 2003–2006 in Kraków. Each sample was formed with ca 100 000 m³ of passed air, collected with two parallel ASS-500 high volume air samplers. The results for ⁴⁰K and ¹³⁷Cs are also presented for reference and comparison. Presented frequency distributions for activity concentration and correlation between the obtained results are discussed. The activity concentration results confirmed seasonal variation of activity to be different for all the investigated radionuclides. Moreover, the seasonal variation in nucleus activity ratio was also noticed for ²²Na and ⁷Be. Cosmogenic radionuclides being mainly of stratospheric origin, are subsequently attached to fine aerosols, via which they are transported to the ground level air. The mean aerosol transport time within the troposphere was estimated as equal to 7.5 days on average, reaching even 50 days in warm seasons. Limitations of the applied model were identified.