Self-assembly of stimuli-responsive water-soluble [60]fullerene end-capped ampholytic block copolymer

A well-defined, water-soluble, pH and temperature stimuli-responsive [60]fullerene (C(60)) containing ampholytic block copolymer of poly((methacrylic acid)-block-(2-(dimethylamino)ethyl methacrylate))-block-C(60) (P(MAA-b-DMAEMA)-b-C(60)) was synthesized by the atom transfer radical polymerization (ATRP) technique. The self-assembly behavior of the C(60) containing polyampholyte in aqueous solution was characterized by potentiometric and conductometric titration, dynamic light scattering (DLS), and transmission electron microscopy. This amphiphilic mono-C(60) end-capped block copolymer shows enhanced solubility in aqueous medium at room and elevated temperatures and at low and high pH but phase separates at intermediate pH between 5.4 and 8.8. The self-assembly of the copolymer is different from that of P(MAA-b-DMAEMA). Examination of the association behavior using DLS revealed the coexistence of unimers and aggregates at low pH at all temperatures studied, with the association being driven by the balance of hydrophobic and electrostatic interactions. Unimers and aggregates of different microstructures are also observed at high pH and at temperatures below the lower critical solution temperature (LCST) of PDMAEMA. At high pH and at temperatures above the LCST of PDMAEMA, the formation of micelles and aggregates coexisting in solution is driven by the combination of hydrophobic, electrostatic, and charge-transfer interactions.     

Nickel(II) and copper(II) complexes of ONS ligands formed from 2-hydroxyacetophenone and S-alkyldithiocarbazates and the X-ray crystal structure of the [Ni(Ap-SMe)py] complex (Ap-SMe = anion of the 2-hydroxyacetophenone Schiff base of S-methyl-dithiocarbazate)

Summary New nickel(II) and copper(II) complexes of general formulae [M(Ap-SR)] and [Ap-SR)B] (Ap-SR = dianionic forms of the Schiff bases of 2-hydroxyacetophenone and S-alkyl esters of dithiocarbazic acid; M = Ni^II or Cu^II; R = Me or CH₂Ph; B = py, phen or dipy have been synthesized and characterized by a variety of physicochemical techniques. Magnetic and spectroscopic data support an oxygen-bridged binuclear structure for the [M(Ap-SR)] complexes. The [M(Ap-SR)py] complexes are four-coordinate and square planar, whereas the [M(Ap-SR)B] complexes (B = phen or dipy) are five-coordinate and probably trigonal bipyramidal. The [Cu(Ap-SR)B] complexes (B = py, phen or dipy) obey the Curie-Weiss law over the 298-93 K range.The structure of the [Ni(Ap-SMe)py] complex has been determined by X-ray crystallography. It has an approximately square-planar structure in which the doubly-deprotonated Schiff base is coordinated to the Ni^II ion via the azomethine N atom, the phenolic O atom and the thiolato S atom. The fourth coordination position around the Ni^II ion is occupied by the N of the pyridine ligand.     

Floc strength characterization technique. An insight into silica aggregation

This paper tests an approach to the estimation of relative particle bond strength based on the nondimensional floc and aggregation factors. The strength of flocs formed by aggregating nanosized silica particles with the addition of potassium chloride (KCl) or cationic surfactants, alkyltrimethylammonium bromide (mixture of CTAB, DTAB, and MTAB) was analyzed. The bonding force of the flocs formed in surfactant compared to that formed in the KCl system was estimated using the new dimensional analysis approach. This force ratio was then compared to that obtained by atomic force microscopy.     

Educational aspects of sonochemistry: The role of sonochemistry at high school level

The applications of sonochemistry have attracted a great deal of attention. However, conventional chemistry textbooks used in universities and high schools cover traditional chemistry plus thermo,- photo- and electrochemistry. The effect of sound on chemical systems has completely been ignored. Although the mechanisms of many sonochemical reactions remain unresolved, the rapid expansion of knowledge in sonochemistry has already justified its inclusion in present chemistry curricula. Moreover, the interesting and unusual phenomena encountered under sonication conditions can be used for motivation purposes. Furthermore, exploring and equipping students with a new tool for investigating chemistry is also important based on educational principles. This paper examines some chemical systems (in a high school chemistry syllabus) which are affected by sound energy. It is hoped that these sonochemical applications will facilitate the learning of chemistry in terms of cognitive, psychomotor and affective domains.