Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry

A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing.     

Cancer protector activity of antioxidant compounds

Considering a DNA to carcinogen electron transfer mechanism for the carcinogenesis process whereas carcinogens react as a electrophilic and DNA as nucleophilic species we propose that the cancer protecting compounds will compete with the DNA for the donation of the electron for the carcinogens. In this work, theoretical calculations of several compounds with well-known protecting activity are performed. The results were treated by a multivariant analysis (principal component analysis) in order to relate the calculated electronic parameters with the protecting activities.     

Dynamic properties of some polymer solutions subjected to a steady shear superimposed on an oscillatory shear flow

Summary Results of measurements of dynamic moduli in parallel superposition of a steady and oscillatory shear flow were compared with different theories.Most of the rheological models which are based on the assumption that the material properties (spectrum of relaxation times) are unaffected by the presence of the steady rates of shear give results incompatible with our experimental results described earlier. From these models the best fit is given by the WJFLMB-model.A much better fit is given by theories based on the assumption that the relaxation spectrum is cut-off at a critical value of the relaxation time depending on the prescribed steady rate of shear. Under certain conditions these theories explain qualitatively the linear relations between the frequency ₀, at whichG (, ) = 0 and the steady rate of shear , as we found experimentally for several polymer solutions.

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Zusammenfassung Die Ergebnisse von Messungen der dynamischen Moduln bei Superposition einer stationären und einer oszillierenden Scherströmungsk omponente werden mit verschiedenen Theorien verglichen.Die meisten rheologischen Modelle sind auf die Annahme gegründet, daß die Stoffeigenschaften (das Relaxationsspektrum) durch das Vorliegen einer stationären Scherströmung nicht verändert werden. Solche Theorien liefern Ergebnisse, die mit unseren früher beschriebenen Ergebnissen unvereinbar sind. Die beste Übereinstimmung liefert noch das WJFLMB-Modell.Eine wesentlich genauere Anpassung ermöglichen diejenigen Theorien, die auf der Annahme gründen, daß das Relaxationsspektrum bei einem kritischen Wert der Relaxationszeit abgeschnitten wird und daß dieser Wert von der überlagerten stationären Scherströmung abhängt. Unter gewissen Bedingungen erklären diese Theorien zumindest qualitativ die lineare Beziehung zwischen der Frequenz ₀, bei welcherG (, ) = 0 wird, und der zugeordneten Schergeschwindigkeit , wie wir sie bei verschiedenen Experimenten gefunden haben.

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With 4 figures     

Identification of Structure–Activity Relationships from Screening a Structurally Compact DNA‐Encoded Chemical Library

Methods for the rapid and inexpensive discovery of hit compounds are essential for pharmaceutical research and DNA‐encoded chemical libraries represent promising tools for this purpose. We here report on the design and synthesis of DAL‐100K, a DNA‐encoded chemical library containing 103 200 structurally compact compounds. Affinity screening experiments and DNA‐sequencing analysis provided ligands with nanomolar affinities to several proteins, including prostate‐specific membrane antigen and tankyrase 1. Correlations of sequence counts with binding affinities and potencies of enzyme inhibition were observed and enabled the identification of structural features critical for activity. These results indicate that libraries of this type represent a useful source of small‐molecule binders for target proteins of pharmaceutical interest and information on structural features important for binding.     

Stabilization of Titanium Dioxide Nanoparticles at the Surface of Carbon Nanomaterials Promoted by Microwave Heating

TiO₂ is frequently combined with carbon materials, such as reduced graphene oxide (RGO), to produce composites with improved properties, for example for photocatalytic applications. It is shown that heating conditions significantly affect the interface and photocatalytic properties of TiO₂@C, and that microwave irradiation can be advantageous for the synthesis of carbon‐based materials. Composites of TiO₂ with RGO or amorphous carbon were prepared from reaction of titanium isopropoxide with benzyl alcohol. During the synthesis of the TiO₂ nanoparticles, the carbon is involved in reactions that lead to the covalent attachment of the oxide, the extent of which depends on the carbon characteristics, heating rate, and mechanism. TiO₂ is more efficiently stabilized at the surface of RGO than amorphous carbon. Rapid heating of the reaction mixture results in a stronger coupling between the nanoparticles and carbon, more uniform coatings, and smaller particles with narrower size distributions. The more efficient attachment of the oxide leads to better photocatalytic performance.     

Growth and fire resistance of colloidal silica-polyelectrolyte thin film assemblies

Thin films of colloidal silica were deposited on cotton fibers via layer-by-layer (LbL) assembly in an effort to reduce the flammability of cotton fabric. Negatively charged silica nanoparticles of two different sizes (8 and 27 nm) were paired with either positively charged silica (12 nm) or cationic polyethylenimine (PEI). PEI/silica films were thicker due to better (more uniform) deposition of silica particles that contributed to more than 90% of the film weight. Each coating was evaluated at 10 and 20 bilayers (BL). All coated fabrics retained their weave structure after being exposed to a vertical flame test, while uncoated cotton was completely destroyed. Micro combustion calorimetry confirmed that coated fabrics exhibited a reduced peak heat release rate, by as much as 20% relative to the uncoated control. The 10 BL PEI-8 nm silica recipe was the most effective because the coating is relatively thick and uniform relative to the other systems. Soaking cotton in basic water (pH 10) prior to deposition resulted in better assembly adhesion and flame-retardant behavior. These results demonstrate that LbL assembly is a useful technique for imparting flame retardant properties through conformal coating of complex substrates like cotton fabric.     

Energy loss measurements and electronic properties of thianthren

Summary The dielectric and electronic properties of thianthren (C₆H₄(S)₂H₄C₆) are determined by means of optical reflectivity, absorption measurements and reflection electron energy loss spectroscopy. The experimental results are interpreted on the basis of a Complete Neglect of Differential Overlap (CNDO) calculation used in three different parametrization schemes. Emphasis is laid on the discussion of the problems which generally affect the analysis of electron energy loss spectra, and a procedure to obtain the complex dielectric function from electron energy loss measurements performed in the reflection mode is suggested. Work partially supported by the MURST through the GNSM.     

Efficient organocatalysis with a calix[4]pyrrole derivative

The 10α,20β-bis(4-nitrophenyl)-calix[4]pyrrole was found to act as an effective organocatalyst for the hetero Diels-Alder reaction of Danishefsky’s diene with aromatic aldehydes. This discovery is the first reported case of a calixpyrrole that exhibits organocatalytic activity.     

Determination of the pair polarizability of argon from the two-body cis spectrum

We present a moment analysis of the experimental two-body collision induced light scattering spectrum of argon which allows the determination of a three-parameter empirical form for the collision induced pair-polarizability anisotropy. The result of the calculation shows that beside the DID and the exponential short-range terms also an intermediate-range term gives an important contribution to the pair polarizability.