Steric effect in alkylation reactions by N‐alkyl‐N‐nitrosoureas: a kinetic approach

The alkylation reactions of 4‐(p‐nitrobenzyl)pyridine (NBP), a trap for alkylating agents with nucleophilic characteristics similar to DNA bases, by five N‐alkyl‐N‐nitrosoureas (methyl‐, ethyl‐, propyl‐, butyl‐, and allylnitrosourea) were investigated in 7:3 (v/v) water/dioxane medium in the 5.0–6.5 pH range. Decomposition of alkylnitrosoureas (ANU) gives rise to alkyldiazonium ions that yield NBP‐R adducts directly or through carbocations in certain instances. The NBP alkylation rate constants by these species were determined. The following sequence of alkylating potential was found: methyl‐ > ethyl‐ > allyl‐ > propyl‐ > butyl group. Application of Ingold–Taft correlation analysis to the kinetic results revealed that the NBP alkylation reactions occur mainly through steric control. The values of the molar absorption coefficients of the NBP‐R adducts also reveal the determinant influence of a steric effect in the formation of alkylation adducts. The kinetic results are consistent with the biological activity of ANU. Copyright © 2008 John Wiley & Sons, Ltd.     

Characterization and thermal stability study of efavirenz and solid dispersion with PVPVA 64 by means of thermal analysis and pyrolysis coupled with GC/MS

Journal of Thermal Analysis and Calorimetry - The acquired immunodeficiency syndrome remains a major problem in worldwide public health and its antiretroviral treatment therapy combines at least...     

Development and implementation of thek 0-standardization and other parametric methods of INAA in Cuba. Part II

The main results obtained during the characterization of the Triga Mark III reactor at NNRI, Salazar, Mexico, the development of the nonconventional multimonitor HAV-1, the use of Certified Reference Material (CRM) as multimonitor fork ₀-factors experimental determination, and to study the reactor power and slowing-down thickness dependencies of the reactor flux parameters and its influence ink ₀-INAA are presented. The experience of thek ₀-INAA group at ISCTN, in the application of this analytical technique for different purposes is resumed.     

Analysis of the Influence of the Thickness and the Hole Radius on the Calibration Coefficients in the Hole-Drilling Method for the Determination of Non-uniform Residual Stresses

Experimental Mechanics - The Hole-Drilling method is a semi-destructive technique useful for obtaining residual stress distributions by drilling and measuring relieved strains. The standard for...     

Correction to: Analysis of the Influence of the Thickness and the Hole Radius on the Calibration Coefficients in the Hole-Drilling Method for the Determination of Non-uniform Residual Stresses

Experimental Mechanics - Due to an error introduced during the production process, Fig. 11 appeared incorrectly in the original publication of this article. It appears correctly here.     

High surface water interaction in superhydrophobic nanostructured silicon surfaces: convergence between nanoscopic and macroscopic scale phenomena

In the present work, we investigate wetting phenomena on freshly prepared nanostructured porous silicon (nPS) with tunable properties. Surface roughness and porosity of nPS can be tailored by controlling fabrication current density in the range 40-120 mA/cm(2). The length scale of the characteristic surface structures that compose nPS allows the application of thermodynamic wettability approaches. The high interaction energy between water and surface is determined by measuring water contact angle (WCA) hysteresis, which reveals Wenzel wetting regime. Moreover, the morphological analysis of the surfaces by atomic force microscopy allows predicting WCA from a semiempiric model adapted to this material.     

Alkylating potential of α,β-unsaturated compounds

Alkylation reactions of the nucleoside guanosine (Guo) by the α,β-unsaturated compounds (α,β-UC) acrylonitrile (AN), acrylamide (AM), acrylic acid (AA) and acrolein (AC), which can act as alkylating agents of DNA, were investigated kinetically. The following conclusions were drawn: i) The Guo alkylation mechanism by AC is different from those brought about the other α,β-UC; ii) for the first three, the following sequence of alkylating potential was found: AN > AM > AA; iii) A correlation between the chemical reactivity (alkylation rate constants) of AN, AM, and AA and their capacity to form adducts with biomarkers was found. iv) Guo alkylation reactions for AN and AM occur through Michael addition mechanisms, reversible in the first case, and irreversible in the second. The equilibrium constant for the formation of the Guo-AN adduct is K(eq) (37 °C) = 5 × 10(-4); v) The low energy barrier (≈10 kJ mol(-1)) to reverse the Guo alkylation by AN reflects the easy reversibility of this reaction and its possible correction by repair mechanisms; vi) No reaction was observed for AN, AM, and AA at pH < 8.0. In contrast, Guo alkylation by AC was observed under cellular pH conditions. The reaction rate constants for the formation of the α-OH-Guo adduct (the most genotoxic isomer), is 1.5-fold faster than that of γ-OH-Guo. vii) a correlation between the chemical reactivity of α,β-UC (alkylation rate constants) and mutagenicity was found.     

Characterization of Japanese color sticks by energy dispersive X-ray fluorescence,X-ray diffraction and Fourier transform infrared analysis

This work comprises the use of energy dispersive X-ray fluorescence (EDXRF), X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) techniques for the study of the composition of twentieth century traditional Japanese color sticks. By using the combination of analytical techniques it was possible to obtain information on inorganic and organic pigments, binders and fillers present in the sticks. The colorant materials identified in the sticks were zinc and titanium white, chrome yellow, yellow and red ochre, vermillion, alizarin, indigo, Prussian and synthetic ultramarine blue. The results also showed that calcite and barite were used as inorganic mineral fillers while Arabic gum was the medium used. EDXRF offered great potential for such investigations since it allowed the identification of the elements present in the sample preserving its integrity. However, this information alone was not enough to clearly identify some of the materials in study and therefore it was necessary to use XRD and FTIR techniques.