Redox,ionic strength,and pH sensitive supramolecular polymer assemblies

Formation of micelle‐type assembly from supramolecular complexation of a surfactant and an oppositely charged homopolymer is demonstrated. The lower CAC observed for these assemblies suggest that the electrostatic interaction provides an amphiphilic homopolymer‐like structure. The stimulus‐induced disassembly of these supramolecular structures has been accomplished with variations in redox characteristics, ionic strength, and pH of the medium. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1052–1060, 2009     

Empirical,Semi-Empirical and Experimental Determination of K X-Ray Fluorescence Parameters of Some Elements in the Atomic Range 21 ≤ Z ≤ 30

In this study, the semi-empirical and empirical calculations of K X-ray intensity ratios, K-shell fluorescence yields, and vacancy transfer probabilities have been performed for 3d transition elements. Also, σ_Kα, σ_Kβ production cross-sections, K_β/K_α intensity ratios, ω_K fluorescence yields, and η_KL vacancy transfer probabilities of 3d transition elements have been measured. The samples were excited by 59.5 keV γ-rays from a ²⁴¹Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV.     

Semi-empirical determination of Kα1,2, Kβ1,3, and Kβ2,4 X-ray natural line widths for various elements between 29 ≤ Z ≤ 74 at 123.6 keV

Abstract

In this study, K_α1,2, K_β1,3, and K_β2,4 X-ray natural line widths for various elements were determined semi-empirically at 123.6?keV by using K shell fluorescence yields obtained from energy dispersive X-ray fluorescence measurements. The obtained results contribute to a database for the development of new theoretical models of atomic structure, radiation shielding materials, and designing new technological devices related to the structural analysis of materials. The obtained results were compared with the literature, while new fitting polynomials for the studied parameters were acquired. The results showed that the natural linewidths of K X-ray lines fit fourth-order polynomials except for K_β2,4.     

Subsequence-based feature map for protein function classification

Automated classification of proteins is indispensable for further in vivo investigation of excessive number of unknown sequences generated by large scale molecular biology techniques. This study describes a discriminative system based on feature space mapping, called subsequence profile map (SPMap) for functional classification of protein sequences. SPMap takes into account the information coming from the subsequences of a protein. A group of protein sequences that belong to the same level of classification is decomposed into fixed-length subsequences and they are clustered to obtain a representative feature space mapping. Mapping is defined as the distribution of the subsequences of a protein sequence over these clusters. The resulting feature space representation is used to train discriminative classifiers for functional families. The aim of this approach is to incorporate information coming from important subregions that are conserved over a family of proteins while avoiding the difficult task of explicit motif identification. The performance of the method was assessed through tests on various protein classification tasks. Our results showed that SPMap is capable of high accuracy classification in most of these tasks. Furthermore SPMap is fast and scalable enough to handle large datasets.     

Selective pre-concentration of selenite from aqueous samples using mercapto-silica

Silica gel modified with 3-mercaptopropyl-trimethoxysilane was used for the selective separation and pre-concentration of selenite (Se(IV)) from aqueous solutions containing Se(IV) and selenate (Se(VI)). Over a wide range of acidity, from 2 mol l⁻¹ HCl to pH 9.00, Se(IV) was taken up by the mercaptopropyl-silica with nearly 100% efficiency; Se(VI) however was unretained. Se(IV) content was determined by hydride generation atomic absorption spectrometry (HGAAS), following batch release of the selenium from the pre-concentration medium by acidic periodate. The overall pre-concentration efficiency, including both take-up and elution, in the range of 89-106%. The method was applied to spiked seawater samples containing as low as 800 ng l⁻¹ Se in selenite form. This solid-phase extraction system offers several major advantages over conventional solvent extraction procedures. It firstly exhibits high selectivity for Se(IV) over Se(VI). Using the solid-phase media, pre-concentration of Se(IV) in dilute water samples can be carried out in the field, stabilizing the selenite-selenium in a convenient form for transport and storage. In addition, selenium stored on silica is derived solely from Se(IV) overcoming problems of selenium redox speciation changes and loss during storage.     

Efficient synthesis of ferrocenylenones by Friedel-Crafts acylation with EtAlCl2-Me3Al

Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl₂ or EtAlCl₂-Me₃Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method.     

Bioengineering functional copolymers. III. Synthesis of biocompatible poly[(N‐isopropylacrylamide‐co‐maleic anhydride)‐g‐poly(ethylene oxide)]/poly(ethylene imine) macrocomplexes and their thermostabilization effect on the activity of the enzyme penicillin G acylase

Stimuli‐responsive poly[(N‐isopropylacrylamide‐co‐maleic anhydride)‐g‐poly(ethylene oxide)]/poly(ethylene imine) macrobranched macrocomplexes were synthesized by (1) the radical copolymerization of N‐isopropylacrylamide and maleic anhydride with α,α′‐azobisisobutyronitrile as an initiator in 1,4‐dioxane at 65 °C under a nitrogen atmosphere, (2) the polyesterification (grafting) of prepared poly(N‐isopropylacrylamide‐co‐maleic anhydride) containing less than 20 mol % anhydride units with α‐hydroxy‐ω‐methoxy‐poly(ethylene oxide)s having different number‐average molecular weights (M_n = 4000, 10,000, or 20,000), and (3) the incorporation of macrobranched copolymers with poly(ethylene imine) (M_n = 60,000). The composition and structure of the synthesized copolymer systems were determined by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy, and chemical and elemental analyses. The important properties of the copolymer systems (e.g., the viscosity, thermal and pH sensitivities, and lower critical solution temperature behavior) changed with increases in the molecular weight, composition, and length of the macrobranched hydrophobic domains. These copolymers with reactive anhydride and carboxylic groups were used for the stabilization of penicillin G acylase (PGA). The conjugation of the enzyme with the copolymers significantly increased the thermal stability of PGA (three times at 45 °C and two times at 65 °C). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1580–1593, 2003