Properties of organo‐clay/natural rubber nanocomposites: Effects of organophilic modifiers

The effect of various modifiers on the structure and properties of clay/natural rubber nanocomposites are investigated with the aim to evaluate the effect of size and structure of the modifier. Nanocomposites are prepared by melt intercalation method. Mechanical properties of the cured rubber containing nanoclay are compared with the reference compound without the filler. No improvement of mechanical properties is observed for small organic cations; however, stress and strain at break of clay/rubber nanocomposites increase with rising number of octyl chains in the interlayer spaces of organo‐clays. Concerning organo‐cations with the same number of carbon atoms, more effective are the modifiers with several shorter carbon chains compared to those with one long chain. The composites exhibit hybrid structure of nanocomposite and microcomposite as revealed by X‐ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The details of the structure are supported by DMTA and hysteresis measurements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigation of the Interaction Between Cu2-x S +So Coatings and Pd(II) Ions by Cyclic Voltammetry and X-ray Photoelectron Spectroscopy

The interaction between Pd²⁺ ions and Cu_2-xS coating formed by three cycles and containing ~30 at.% of elementary S has been investigated by the methods of cyclic voltammetry and photoelectron spectroscopy (one cycle of coating formation includes treatment of the surface with Cu(I)+Cu(II) ammoniate solution, hydrolysis of the adsorbed copper compounds and sulphidation of copper oxygen compounds in Na₂S_n solution). After exposure of such a coating to Pd²⁺ ions (1.7 mM PdCl_2’ pH-2), an exchange as well as a redox interaction between the coating components and Pd²⁺ ions has been shown to occur. Due to this the amount of copper in the coating decreases from 2 to 4 times and that of sulphur from 1.5 to 5 times. The coating modified in such a way has been found to contain up to 75 at.% of palladium, ~90% of it being in a metallic state.

It has been determined that at the beginning S^o is bound into a soluble compound:

2Pd²⁺ + S^o + 3H₂O → 2Pd^o + H₂SO₃ + 4H⁺.

The Cu₂S present in the coating is considered to interact with Pd²⁺, with the formation of Pd⁰ and CuPdS_2’, while CuS reacts most likely according to the reaction:

CuS + 3Pd²⁺ + 3H₂O → 3Pd^o; + H₂SO₃ + Cu²⁺ + 4H⁺.

The Cu_2-xS +S^o coating formed on a dielectric and modified with Pd²⁺, contrary to the initial Cu_2-xS +S^o coating, can be plated with copper from any electrolyte for copper deposition.     

Dietary n-3 HUFA Affects Mitochondrial Fatty Acid β-Oxidation Capacity and Susceptibility to Oxidative Stress in Atlantic Salmon

Atlantic salmon (Salmo salar) (90 g) were fed four different diets for 21 weeks (final weight 344 g). The levels of n-3 highly unsaturated fatty acids (HUFA) ranged from 11% of the total fatty acids (FA) in the low n-3 diet to 21% in the intermediate n-3 diet, to 55 and 58% in the high n-3 diets. The high n-3 diets were enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA). Increasing dietary levels of n-3 HUFA led to increasing percentages (from 31 to 52%) of these FA in liver lipids. The group fed the highest level of DHA had higher expressions of peroxisome proliferator-activated receptor (PPAR) β and the FA β-oxidation genes acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase (CPT)-II, compared to the low n-3 groups. The high n-3 groups had reduced activity of mitochondrial cytochrome c oxidase and β-oxidation capacity, together with increased activities of superoxide dismutase (SOD) and caspase-3 activities. In the group fed the highest level of n-3 HUFA, decreased percentages of major phospholipids (PL) in the mitochondrial and microsomal membranes of the liver were also apparent. The percentage of mitochondrial cardiolipin (Ptd₂Gro) was 3.1 in the highest n-3 group compared to 6.6 in the intermediate group. These data clearly show an increased incidence of oxidative stress in the liver of fish fed the high n-3 diets.     

Temperature dependence of the intensity of fluorescence of poly(n-vinylcarbazole) films

Summary The fluorescence spectra of thin films of poly(N-vinylcarbazole), PVCA, were measured at temperatures between 103 K and 535 K by constant excitation light intensity. Below 300 K, the corrected spectra were divided into bands belonging to different emitting species of PVCA. Temperature changes of the intensity of fluorescence of the two main excitation energy traps in PVCA are discussed using the simplified kinetic model of Johnson. Local anomalies on the curves of intensity of excimer fluorescence versus temperature measured at constant wavelength reflex the - and - relaxation regions in PVCA.     

Influence of ionic strength and HPMC viscosity grade on drug release and swelling behavior of HPMC matrix tablets

Matrix tablets containing paracetamol and hydroxypropyl methylcellulose (HPMC 2906) of different viscosity grades (50, 400, 1500, and 4000 mPa·s) were evaluated for drug release and change in matrix tablet mass [ΔM (%)] after exposure to 0.09, 0.15, 0.31, and 0.52M ionic strengths of dissolution media. At 0.09 and 0.15M ionic strength, drug‐release profiles reflected the extended release characteristic; in addition the increase in ΔM was slow and continuous within first few hours. At 0.31M the higher viscosity grade matrices showed extensive initial swelling and the loss of extended release whereas at 0.52M a similar tablet performance is observed for the matrices of all viscosity grades. Notably, when extensive increase in ΔM occurs in the very beginning of exposure to medium the loss of extended release from the matrix is expected. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43604.     

Lasioglossins: Three Novel Antimicrobial Peptides from the Venom of the Eusocial Bee Lasioglossum laticeps (Hymenoptera: Halictidae)

Three novel structurally related pentadecapeptides, named lasioglossins, were isolated from the venom of the eusocial bee Lasioglossum laticeps. Their primary sequences were established as H‐Val‐Asn‐Trp‐Lys‐Lys‐Val‐Leu‐Gly‐Lys‐Ile‐Ile‐Lys‐Val‐Ala‐Lys‐NH₂ (LL‐I), H‐Val‐Asn‐Trp‐Lys‐Lys‐Ile‐Leu‐Gly‐Lys‐Ile‐Ile‐Lys‐Val‐Ala‐Lys‐NH₂ (LL‐II) and H‐Val‐Asn‐Trp‐Lys‐Lys‐Ile‐Leu‐Gly‐Lys‐Ile‐Ile‐Lys‐Val‐Val‐Lys‐NH₂ (LL‐III). These lasioglossins exhibited potent antimicrobial activity against both Gram‐positive and Gram‐negative bacteria, low haemolytic and mast cell degranulation activity, and a potency to kill various cancer cells in vitro. The lasioglossin CD spectra were measured in the presence of trifluoroethanol and sodium dodecyl sulfate solution and indicated a high degree of α‐helical conformation. NMR spectroscopy, which was carried out in trifluoroethanol/water confirmed a curved α‐helical conformation with a concave hydrophobic and convex hydrophilic side. To understand the role of this bend on biological activity, we studied lasioglossin analogues in which the Gly in the centre of the molecule was replaced by other amino acid residues (Ala, Lys, Pro). The importance of the N‐terminal part of the molecule to the antimicrobial activity was revealed through truncation of five residues from both the N and C termini of the LL‐III peptide. C‐terminal deamidation of LL‐III resulted in a drop in antimicrobial activity, but esterification of the C terminus had no effect. Molecular modelling of LL‐III and the observed NOE contacts indicated the possible formation of a bifurcated H‐bond between hydrogen from the Lys15 CONH peptide bond and one H of the C‐terminal CONH₂ to the Ile11 oxygen atom. Such interactions cannot form with C‐terminal esterification.     

Comparison of non-traditional technologies for material cutting from the point of view of surface roughness

The contribution deals with comparing non-traditional cutting technologies from the point of view of generated surface roughness. The comparison is carried out for technologies of abrasive waterjet cutting, oxygen cutting, laser and plasma cutting. As an experimental material, EN S355J0 structural steel and titanium CP-Ti Grade 2 was used. Surface topography measurement was done using a Mitutoyo Surftest SJ-401 instrument, and an optical profilometer MicroProf FRT was used for comparison and verification of acquired surface data. The aim of the contribution is to clarify, on the basis of experimental measurements, the behaviour of a topographic function after various ways of cutting; the knowledge of the function is necessary for solving both theoretical and practical technological tasks. The topographic function, which is a basis for the prediction of quality and control of the cutting processes, was derived in an original way. The use of individual technologies depends on technical and economical possibilities and on environmental influences. The results of measurement of cut surface roughness are in good accordance with the results of theoretical analysis.     

The synthesis of bi- and trichromophoric dyes bearing an s-triazinyl ring spacer

An alternative procedure has been described for the syntheses of several bi- and trichromophoric compounds consisting of 1-aminopyrene and 3-aminobenzanthrone chromophoric subsystems connected by an s-triazinyl ring spacer. The synthetic method used, which utilises an autoclave under autogenous pressure, is suitable for the nucleophilic substitution of both chlorine atoms within the triazinyl ring by weakly basic aromatic amines. The structures of the synthesized compounds were confirmed using elemental analysis, ¹H NMR, and mass spectra. UV/vis absorption and fluorescence spectra and fluorescence quantum yields were measured. The dependence of fluorescence intensity and fluorescence quantum yields on solvent polarity was investigated.     

Representativity of the singular stress state in the failure of adhesively bonded joints between metals and composites

Several critical points, where both geometry and material properties change abruptly, arise in an adhesively bonded lap joint between a metallic and a composite material. These critical points, called multimaterial corners or cross-points, at which the linear theory of elasticity predicts unbounded (singular) stresses, are potential points for failure initiation. In this work, a complete stress characterization at these multimaterial corners has been carried out to analyze, after a preliminary experimental test program, the suitability of the application of the parameters defining the singular stress state in the characterization of the failure of these joints. The comparative analysis of the numerical and experimental results obtained show that the singular stress state controlled by a series of the generalized stress intensity factors is controlling the failure path at these corners.