What is behind the plastic strain rate?

The plastic strain rate plays a central role in macroscopic models on elasto-viscoplasticity. In order to discuss the concept behind this quantity, we propose, first, a kinetic toy model to describe the dynamics of sliding layers representative of plastic deformation of single crystalline metals. The dynamic variable is given by the distribution function of relative strains between adjacent layers, and the plastic strain rate emerges as the average hopping rate between energy wells. We demonstrate the behavior of this model under different deformations and how it captures the elastic-to-plastic transition. Second, the kinetic toy model is reduced to a closed evolution equation for the average of the relative strain, allowing us to make a direct link to macroscopic theories. It is shown that the constitutive relation for the plastic strain rate does not only depend on the stress, but also on the macroscopic applied deformation rate, contrary to common practice.     

Recognition of the carbon thin films sub-structures: thermo-optical measurements

Carbon thin films oxidation was investigated on-line by high-sensitivity optical transmission (OT) method. The films have been prepared by common vacuum arc discharge and subsequently air oxidized at linear heating rates until temperatures of their complete gasification. The shape of the optical curves acquired was interpreted in light of deduced partial optical changes, each of them being ascribed by simple sigmoidal dependence. The dependencies converted to their derivative form ordered respective to the temperature scale conveniently represent an inter-relationship among the sequentially evolved films’ optical events, considered as being closely related to the individual carbon-replenishing steps. The dependencies correspond well to the ones obtained on thicker films by means of the thermogravimetry (TG) measurements.     

γ‐Butyrolactone Copolymerization with the Well‐Documented Polymer Drug Carrier Poly(ethylene oxide)‐block‐poly(ε‐caprolactone) to Fine‐Tune Its Biorelevant Properties

Polymeric drug carriers exhibit excellent properties that advance drug delivery systems. In particular, carriers based on poly(ethylene oxide)‐block‐poly(ε‐caprolactone) are very useful in pharmacokinetics. In addition to their proven biocompatibility, there are several requirements for the efficacy of the polymeric drug carriers after internalization, e.g., nanoparticle behavior, cellular uptake, the rate of degradation, and cellular localization. The introduction of γ‐butyrolactone units into the hydrophobic block enables the tuning of the abovementioned properties over a wide range. In this study, a relatively high content of γ‐butyrolactone units with a reasonable yield of ≈60% is achieved by anionic ring‐opening copolymerization using 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene as a very efficient catalyst in the nonpolar environment of toluene with an incorporated γ‐butyrolactone content of ≈30%. The content of γ‐butyrolactone units can be easily modulated according to the feed ratio of the monomers. This method enables control over the rate of degradation so that when the content of γ‐butyrolactone increases, the rate of degradation increases. These findings broaden the application possibilities of polyester‐polyether‐based nanoparticles for biomedical applications, such as drug delivery systems.     

Sequential injection analysis (SIA)-chemiluminescence determination of indomethacin using tris[(2,2'-bipyridyl)]ruthenium(III) as reagent and its application to semisolid pharmaceutical dosage forms

Automated sequential injection (SIA) method for chemiluminescence (CL) determination of nonsteroidal anti-inflammatory drug indomethacin (I) was devised. The CL radiation was emitted in the reaction of I (dissolved in aqueous 50% v/v ethanol) with intermediate reagent tris(2,2′-bipyridyl)ruthenium(III) (Ru(bipy)₃³⁺) in the presence of acetate. The Ru(bipy)₃³⁺ was generated on-line in the SIA system by the oxidation of 0.5 mM tris(2,2′-bipyridyl)ruthenium(II) (Ru(bipy)₃²⁺) with Ce(IV) ammonium sulphate in diluted sulphuric acid. The optimum sequence, concentrations, and aspirated volumes of reactant zones were: 15 mM Ce(IV) in 50 mM sulphuric acid 41 μL, 0.5 mM Ru(bipy)₃²⁺ 30 μL, 0.4 M Na acetate 16 μL and I sample 15 μL; the flow rates were 60 μL s⁻¹ for the aspiration into the holding coil and 100 μL s⁻¹ for detection. Calibration curve relating the intensity of CL (peak height of the transient CL signal) to concentration of I was curvilinear (second order polynomial) for 0.1–50 μM I (r = 0.9997; n = 9) with rectilinear section in the range 0.1–10 μM I (r = 0.9995; n = 5). The limit of detection (3σ) was 0.05 μM I. Repeatability of peak heights (R.S.D., n = 10) ranged between 2.4% (0.5 μM I) and 2.0% (7 μM I). Sample throughput was 180 h⁻¹. The method was applied to determination of 1 to 5% of I in semisolid dosage forms (gels and ointments). The results compared well with those of UV spectrophotometric method.     

Van der Waals complexes of Cu, Ag, and Au with hydrogen sulfide. The bonding character

The electronic and structural features of the Cu...SH2, Ag...SH2, and Au...SH2 complexes are investigated by using the spin-adapted restricted open-shell HF coupled cluster CCSD(T) method combined with the second-order spin-free Douglas-Kroll-Hess (DKH) relativistic approach. M...SH2 complexes are nonplanar with bonding energies -5.99, -1.99, and -9.08 mHartree, respectively. Comparison with analogous M...OH2 and M...NH3 complexes allows us to establish general features of the bonding between coinage metal atoms and ligand molecules with the participation of their lone electron pairs. Consistent interpretation of the interaction effects can be obtained by using the molecular orbital picture of the M...L region. The bonding character is explained by stressing the importance of the charge transfer from the lone pair of the ligand to the metal atom. Relativistic changes of the metal element electron affinity and polarizability facilitate the understanding of major trends in the pattern of interactions between the coinage metal atoms and different lone pair donating ligands.     

Electrochemical detection of DNA triplet repeat expansion

Hereditary neurodegenerative diseases are connected with the expansion of trinucleotide repetitive sequences in genomic DNA. Molecular diagnosis of these diseases is based on the determination of the triplet repeat length. Currently used methods involve PCR amplification followed by electrophoretic determination of the amplicon size. We propose a novel electrochemical technique based on hybridization of target DNA (tDNA) immobilized at magnetic beads with a reporter probe (RP) complementary to the triplet repeats (12 units per RP). The biotin-labeled RP is detected via an enzyme-linked electrochemical assay involving binding of streptavidin-alkaline phosphatase conjugate and transformation of electroinactive 1-naphthyl phosphate to electroactive 1-naphthol. Pyrimidine residues within sequences flanking the homopurine (GAA)n repeat in tDNA are premodified with osmium tetroxide, 2,2'-bipyridine (Os,bipy), introducing electroactive labels in tDNA. The length of the triplet expansion is calculated from the ratio of the intensities of electrochemical signals of hybridized RP/tDNA-Os,bipy. The normalized signal increases linearly with the repeat length between 0 and about 200 triplet units, allowing for discrimination between normal, premutated, and mutated alleles. Application of this method for the detection of the asymptomatic heterozygous carrier of expanded alleles is demonstrated.     

Optical Properties and Sensitivity of Xerogel Detection Layers for Fiber-Optic Hydrocarbon Sensors

Xerogel layers were prepared on fiber-optic substrates and glass slides by the dip-coating method from sols composed of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES) and phenyltriethoxysilane (PTES), ethanol or isopropan, HCl and water, and by drying the gels at 80°C.Layers with a thickness ranging from 200 to 1500 nm were prepared. Optical properties of the layers applied on the fibers and their sensitivity to toluene and hexane were determined from angular and temporal changes of the output power of the fibers excited by an inclined collimated light beam. These changes were measured at a wavelength of 670 nm and in a range of 1600–1800 nm.The results obtained at 670 nm show that the layers refractive index can be increased from 1.39 to 1.5 by using the PTES sols instead of the MTES or TEOS ones. High optical losses of the layers of the order of 10³ dB/cm can be explained by their porosity. The best detection limits of 0.01 vol.% of toluene and 0.2 vol.% of hexane were obtained for layers containing methyl groups. The presence of toluene in the layers was deduced from spectral bands of toluene in a range of 1600–1800 nm.     

Thermal curing and water re‐exposure of silane–PVA/PVAc complex film on glass fiber surface

Because glass fiber reinforced composites are in industrial demand, chemistry and topography of the glass fiber sizing are of interest. Silane–PVA/PVAc (polyvinyl alcohol/polyvinyl acetate) complex film on the glass fiber surface is studied during thermal curing and water re‐exposure by using atomic force microscopy. The complex film consists of silane with the honeycomb structure film and PVA/PVAc with the hexagonal close pack structure of ellipsoidal shaped microspheres (270 × 620 nm). The thermal curing at 100 °C is leading to the evaporation of water contained in the microspheres. Because of water evaporation, the average roughness value of 1‐min thermal curing decreases from initial 7.3 to only 2.7 nm. Such a collapse of microsphere is followed by an intermixing between silane film and PVA/PVAc microspheres leading to a change of silane honeycomb structure along with silane tips. The average value of the silane honeycomb structure wall width decreases from 144 nm to 54 nm, for curing times of 15 and 30 min, respectively. A re‐exposure to an aqueous environment after 100 °C curing leads to almost completely restored microspheres regarding shape and size. The average complex film thickness increases from 180 nm for thermal curing for 30 min to 225 nm for water re‐exposed film. Interestingly, the pits in the microsphere structure are observed presumably because of the tips from intermixing. The thermal curing at 200 °C enhances the intermixing, and after 15 min, an intramixing is suggested to occur between PVAc core and PVA shell of the microsphere. The water re‐exposure after 15 min of 200 °C curing leads to a re‐containing of water but without restored microsphere structure; Because of the intramixing, leaving the silane–PVA/PVAc film is not complex anymore. Copyright © 2014 John Wiley & Sons, Ltd.     

Voltammetric microanalysis of DNA adducts with osmium tetroxide,2,2'-bipyridine using a pyrolytic graphite electrode

DNA and synthetic polynucleotides modified with a complex of osmium tetroxide with 2,2'-bipyridine (Os,bipy) produce specific voltammetric signals at pyrolytic graphite electrodes. Based on a sufficient potential separation between the peaks of Os,bipy-modified DNA (DNA-Os,bipy) and of free Os,bipy, and using an adsorptive transfer stripping voltammetric procedure involving extraction of free Os,bipy from the electrode by chloroform, DNA-Os,bipy can be determined in an excess of the free reagent. Under certain conditions, 140 pg of DNA-Os,bipy can be detected after a 5 min accumulation period. This analysis displays a more favorable sensitivity and a better selectivity for DNA structure than oxidation of DNA guanine moieties, and offers detection of osmium DNA markers at carbon electrodes.