pH-labile sheddable block copolymers by RAFT polymerization: Synthesis and potential use as siRNA conjugates

Well-defined amphiphilic block copolymers composed of hydrophilic and hydrophobic blocks linked through an acid-labile acetal bond were synthesized directly by RAFT polymerization using a new poly(ethylene glycol) (PEG) macroRAFT agent modified with an acid-labile group at its R-terminal. The new macroRAFT agent was used for polymerization of poly(t-butyl methacrylate) (PtBMA) or poly(cholesterol-methacrylate) (PCMA) to synthesize well-defined block copolymers with a PEG block sheddable under acidic conditions. The chain extension polymerization kinetics showed known traits of RAFT polymerization. The molecular weight distributions of the copolymers prepared using the new macroRAFT agent remained below 1.2 during the polymerizations and the molecular weight of the copolymers was linearly proportional to monomer conversions. The acid-catalyzed hydrolysis behavior of the PEG-macroRAFT agent and the PEG-b-PtBMA (Mn = 13,600 by GPC, PDI = 1.10) was studied by GPC, ¹H NMR and UV–vis spectroscopy. The half-life of acid-hydrolysis was 70 min at pH 2.2 and 92 h at pH 4.0. The potential use of the pH-labile shedding behavior of the copolymers was demonstrated by conjugating a thiol-modified siRNA to ω-pyridyldisulfide modified PEG-b-PCMA. The resultant PEG-b-PCMA-b-siRNA triblock modular polymer released PCMA-b-siRNA segment in acidic and siRNA segment in reductive conditions, as confirmed by polyacrylamide gel electrophoresis.     

The relationship between students' mathematical thinking types and representation preferences in definite integral problems

ABSTRACT

Given that curriculum materials serve as cultural artefacts, this study addresses the need for more research on curriculum materials in different contexts. Most studies concerning curriculum materials have been conducted in US and, therefore little is known about the nature of materials in other cultural-educational contexts. The aim of this paper is to identify the underlying cultural norms of potentially constructed classrooms, by analysing recurrent activities in the most commonly used Finnish teacher guides at primary-school level. We identified three norms embedded in them: (1) creating opportunities for learning through a variety of activities and communication; (2) keeping the class gathered around a specific mathematical topic; and (3) concurrent active involvement of teachers and students. The results add to knowledge about both teacher guides and the Finnish educational context. Moreover, it adds to the growing body of methodologies, as our analytical approach is novel in the context of textual analysis.     

Sono-thermal pre-treatment of waste activated sludge before anaerobic digestion

Sonication and thermalization can be applied successfully to disrupt the complex waste activated sludge (WAS) floc structure and to release extra and intra cellular polymeric substances into soluble phase along with solubilization of particulate organic matters, before sludge digestion. In this study, sonication has been combined with thermalization to improve its disintegration efficiency. It was aimed that rise in temperature occurring during the sonication of sludge was used to be as an advantage for the following thermalization in the combined pre-treatment. Thus, the effects of sonication, thermalization and sono-thermalization on physical and chemical properties of sludge were investigated separately under different pre-treatment conditions. The disintegration efficiencies of these methods were in the following descending order: sono-thermalization > sonication > thermalization. The optimum operating conditions for sono-thermalization were determined as the combination of 1-min sonication at 1.0 W/mL and thermalization at 80 °C for 1 h. The influences of sludge pre-treatment on biodegradability of WAS were experienced with biochemical methane potential assay in batch anaerobic reactors. Relative to the control reactor, total methane production in the sono-thermalized reactor increased by 13.6% and it was more than the sum of relative increases achieved in the sonicated and thermalized reactors. Besides, the volatile solids and total chemical oxygen demand reductions in the sono-thermalized reactor were enhanced as well. However, it was determined that sludge pre-treatment techniques applied in this study was not feasible due to their high energy requirements.     

Determination of trace elements in honey by INAA in Turkey

Instrumental neutron activation analysis was applied to the determination of As, Cr, Sb, K, Br, Zn, Fe, Co in Turkish honey. Irradiation time was 6 h underwater at a thermal flux of 10¹³ n cm^–2 s^–1; cooling times of 100 h and 3–4 weeks and counting times of 5000 s and 80.000 sec were used. The detection limit for As is 0.01 ppm for honey matrix under these conditions. A technique was developed for sealing the quartz tube containing the honey with flame.     

Evaluating views of lecturers on the consistency of teaching content with teaching approach: traditional versus reform calculus

This study aims to evaluate the consistency of teaching content with teaching approaches in calculus on the basis of lecturers' views. In this sense, the structures of the examples given in two commonly used calculus textbooks, both in traditional and reform classrooms, are compared. The content analysis findings show that the examples in both textbooks are presented in a rather formal language and generally highlight procedural knowledge. And, even though the examples in the reform book chosen are structured using multiple representations, only a small number of them incorporated the usage of instructional technology. The lecturers' views which were gathered indicated that, although, on the one hand, the example structures of the traditional textbook largely overlapped with the characteristics of the traditional approach, the example structures of the reform textbook, on the other hand, were found to be inconsistent with the characteristics of the reform approach, especially with regard to its environment and knowledge components. At the end of the paper, some suggestions for further studies are provided for book authors and researchers.     

Preparation and characterization of a novel activated carbon component via chemical activation of tea woody stem

Journal of Thermal Analysis and Calorimetry - The novel activated carbon materials were synthesized by the carbonization and chemical activation of agricultural bio-waste from tea woody stems...