Online Solid-Phase Extraction of Cd(II), Cu(II), and Co(II) Using Covalently Attached Bis(salicylaldimine) to Silica Gel for Determination in Food and Water by Flame Atomic Absorption Spectrometry

In this study, a novel sorbent material bearing a bis(aldimine) group was designed and successfully synthesized by covalently bonding a 2-[N,N′-bis(salicylaldimine)]aminoethyl amine ligand to the silica gel surface that was characterized by carbon, hydrogen, and nitrogen elemental analysis, thermogravimetric analysis, and the Fourier transform infrared spectroscopy technique. The sorbent was used for the online solid-phase extraction (SPE) of Cd(II), Cu(II), and Co(II) ions for their determination at trace concentration levels by flame atomic absorption spectrometry. The effective factors for the online SPE such as the pH and the flow rate of the sample solution, and type, volume, and flow rate of eluent were investigated. The concentration levels of Cd(II), Cu(II), and Co(II) were measured in certified reference materials including Virginia tobacco leaves (CTA-VTL-2) and water-trace elements (NWTM-15.2) to validate this method. The metal levels in environmental water were determined by this method, and the values were checked by spiking and recovery experiments and independent analysis by inductively coupled plasma-mass spectrometry. The adsorption capacities of the sorbent were found to be 41.2, 31.6, and 25.6?mg/g for Cd(II), Cu(II), and Co(II), respectively. This method was also successfully used for the determination of Cd(II), Cu(II), and Co(II) concentrations in rice and molasses.     

Chiral 2-(2-hydroxyaryl)alcohols (HAROLs) with a 1,4-diol scaffold as a new family of ligands and organocatalysts

Efficient and modular syntheses of chiral 2-(2-hydroxyaryl)alcohols (HAROLs), novel 1,4-diols carrying one phenolic and one alcohol hydroxyl group, have been developed which led to generation of a small library of structurally diverse HAROLs in enantiomerically pure form. Of the different HAROLs examined, a HAROL based on the indan backbone exhibited the highest activity and enantioselectivity in the 1,2-addition of certain organometallic compounds to aldehydes in the presence of Ti(OⁱPr)₄ (up to 97% y, 88% ee) and performed as a hydrogen-bond donor organocatalyst in the Morita-Baylis-Hillman reaction, promoted by trialkylphosphines.     

A view about the short histories of the mole and Avogadro’s number

The mole and Avogadro’s number are two important concepts of science that provide a link between the properties of individual atoms or molecules and the properties of bulk matter. It is clear that an early theorist of the idea of these two concepts was Avogadro. However, the research literature shows that there is a controversy about the subjects of when and by whom the mole concept was first introduced into science and when and by whom Avogadro’s number was first calculated. Based on this point, the following five matters are taken into consideration in this paper. First, in order to base the subject matter on a strong ground, the historical development of understanding the particulate nature of matter is presented. Second, in 1811, Amedeo Avogadro built the theoretical foundations of the mole concept and the number 6.022 × 10²³ mol^?1. Third, in 1865, Johann Josef Loschmidt first estimated the number of molecules in a cubic centimetre of a gas under normal conditions as 1.83 × 10¹⁸. Fourth, in 1881, August Horstmann first introduced the concept of gram-molecular weight in the sense of today’s mole concept into chemistry and, in 1900, Wilhelm Ostwald first used the term mole instead of the term ‘gram-molecular weight’. Lastly, in 1889, Károly Than first determined the gram-molecular volume of gases under normal conditions as 22,330 cm³. Accordingly, the first value for Avogadro’s number in science history should be 4.09 × 10²² molecules/gram-molecular weight, which is calculated by multiplying Loschmidt’s 1.83 × 10¹⁸ molecules/cm³ by Than’s 22,330 cm³/gram-molecular weight. Hence, Avogadro is the originator of the ideas of the mole and the number 6.022 × 10²³ mol^?1, Horstmann first introduced the mole concept into science/chemistry, and Loschmidt and Than are the scientists who first calculated Avogadro’s number. However, in the science research literature, it is widely expressed that the mole concept was first introduced into chemistry by Ostwald in 1900 and that Avogadro’s number was first calculated by Jean Baptiste Perrin in 1908. As a result, in this study, it is particularly emphasised that Horstmann first introduced the mole concept into science/chemistry and the first value of Avogadro’s number in the history of science was 4.09 × 10²² molecules/gram-molecular weight and Loschmidt and Than together first calculated this number.     

Common fixed point theorems for sequences of mappings under a new contractive condition of integral type

The purpose of this work is to study common fixed point theorems for six mappings and sequences of mappings satisfying a contractive condition of integral type. Our results improve, extend and generalize corresponding results given by many authors.     

Influence of Macro-pores on DNAPL Migration in Double-Porosity Soil Using Light Transmission Visualization Method

Double porosity is a substantial microstructure characteristic in a wide range of geomaterials. It is a natural phenomenon that can be found in many types of soil, and it can result from biological, chemical or mechanical damage. In this paper, the influence of macro-pores on dense non-aqueous phase liquid (DNAPL) migration in double-porosity medium was investigated using light transmission visualization technique. Three experiments were carried out in two-dimensional flow chambers filled with a double-porosity medium composed of a mixture of local sand and sintered kaolin clay spheres arranged in a periodic manner. In each experiment, a different volumetric fraction of macro-pores and micropores was used. Tetrachloroethylene (PCE) was used to simulate DNAPL, and it was dyed using Oil-Red-O for better visualization. A predetermined amount of PCE was injected into the flow chambers and this amount was re-calculated using image analysis. A very strong correlation was found between the PCE amount injected and the amount calculated from image analysis in each experiment. The experiment was repeated by filling the flow chamber with silica sand to represent single-porosity medium. The results show that the macro-pores have a considerable effect on the PCE migration in double-porosity soil as the PCE movement was the fastest in the third experiment which contained the largest macro-pores volume. The accuracy of the method was validated using statistical analysis. The results show a slight difference between the means of the three experiments, indicating that the method is viable for monitoring NAPL migration in double-porosity medium under different volumetric fractions of macro-pores and micropores.     

Synthesis of Chiral Calix[4]arene Derivative and Evaluation of its Recognition Properties

The article describes the synthesis and extraction properties of a new chiral calix[4]arene Schiff base ligand 5, which has been synthesized from 5,17-diformyl-25,27-bis-(4-nitrobenzyloxy)-26,28-dihidroxycalix[4]arene (4) by treatment with (S)-(-)-1-phenylethylamine. In this synthesis, it was thought to explore the role of chiral, as well as Schiff base sites in the recognition of targeted species ions (such as dichromate anions) as well as neutral/chiral molecules. At low pH, the ligand 5 is more effective for transferring the dichromate anions from an aqueous into a dichloromethane layer; may be due to the protonation of nitrogen atoms.

The extraction properties of ligand 5 towards the some selected α -amino acid methylesters are also reported. However, the ligand 5 did not display any selectivity towards the selected α-amino acid methylesters.