Quite a few organic acids, like citric acid, malic acid and lactic acid, are commercially produced by various techniques. Amongst them, citric acid is the most commonly used one in the food and pharmaceutical industry because of its high solubility, strong chelating power and low toxicity, and therefore it is highly desired to produce it in a purified form. The use of fermentation broth process for production of citric acid is a more viable option, rather than using chemical methods; on the other hand, its extraction by organic solvent is often expensive. In the first article, “Reactive Extraction of Citric Acid from Aqueous Solution Using Tri-N-Octylamine in MIBK”, the authors Kailas L Wasewar, Amit Keshav, Vijay K Agarwal and S S Sonawane have used a tertiary long chain amine in methylisobutylketone (MIBK) to recover citric acid by reactive extraction. This paper reports citric acid-TOA (1:1) complex formation and TOA-MIBK system with distribution coefficient KD (average) = 90 and the extraction equilibrium constant, KE = 234 m3/kmol.

The second paper, “Simple and Efficient Oxathioacetalization of Aldehydes Using Anhydrous Cobalt (II) Bromide Under Solvent-Free Condition”, by Vishvanath D Patil and G A Meshram, describes a novel and facile oxathioacetalization of carbonyl compounds in the presence of a small amount of anhydrous cobalt (II) bromide as a catalyst in solvent-free condition. The significance of this procedure lies in the multi-step organic synthesis, where protection of carbonyl group is required under both acidic and basic conditions. Hence, a simple and convenient approach is always sought. Acetals, oxathioacetals and dithioacetals are frequently used for the protection of aldehydes or ketones. In this paper, a comparative study of oxathioacetalization of benzaldehyde with mercaptoethanol in the presence of cobalt (II) bromide in different solvents and solvent-free conditions has been reported, and it has been found that solvent-free condition gives the maximum yield, and hence preferred.

In recent years, tremendous focus has been received by the applications of schiff bases and their metal complexes in pharmacological and non-pharmacological fields. New salen-derived Schiff bases were synthesized and their ligation properties profoundly studied in the third paper, “A Study on Synthesis, Characterization, and Electrochemical and Antibacterial Properties of Cobalt (II) Complexes of Salen-Derived Ligands”, by Nallamuthu Ananthi, Umesh Balakrishnan, M Babu, Sivan Velmathi, Davoodbasha Mubarak Ali and Nooruddin Thajudin. The investigation in this paper shows the characterization of Schiff bases by FTIR and 1H NMR spectroscopy and their complex formation with cobalt (II). The coordination of the ligand to the metal ions is reported through the imine nitrogen atom and the oxygen atom of the Schiff base. Moreover, these Schiff base cobalt complexes also showed antibacterial activity.

Investigating structural similarity and molecular similarity has an important role in analyzing large compound databases; the Tanimoto coefficient is the most commonly used measure of similarity or chemical distance between two compounds. In the fourth paper, “An Analysis of Structural Similarity of Capsaicin, Zingerone, Vanillin and Eugenol Using Tanimoto Coefficient and Euclidean Distance”, by Ajay Kumar, structural similarity of six pairs—capsaicin and zingerone, capsaicin and vanillin, capsaicin and eugenol, zingerone and vanillin, zingerone and eugenol, and vanillin and eugenol—is investigated using Tanimoto coefficient and Euclidean distance measurements. Amongst these pairs, vanillin and eugenol has the highest similarity and the pairs of capsaicin and vanillin, capsaicin and zingerone have least similarity.

Inorganic ion exchange materials have always remained the focus of scientists due to their growing applications in the area of analytical chemistry, electrochemistry, environmental chemistry, biochemistry and radiochemistry. Besides, they often demonstrate specificity towards certain metal ions. It is for these reasons that there has been a revolutionary growth in the field of synthetic ion exchange materials. Acidic salts of multivalent metals, prepared in combination with anions of phosphate, tungstate, arsenate and tellurate, are studied most intensively. The fifth paper, “The Selectivity of Zirconium (IV) Iodomolybdate for Some Metal-Ammine Complexes”, by Nafisur Rahman, Lutfullah, Syed Taufeeq Ahmad and Syed Najmul Hejaz Azmi, describes the adsorption of Cu (II), Ni (II), Zn (II) and Cd (II)-ammine complexes on zirconium (IV) iodomolybdate, a cation exchanger. The difference in the sorption capacity of various ions has been attributed to the metal-ammine complexes.

Hydrogels are water-absorbing crosslinked network of hydrophilic polymers. The presence of hydrophilic groups in their backbone makes hydrogels absorb huge quantities of water and swell. Various parameters determine the extent of swelling, such as nature of the crosslinker, ionic strength of the solution, temperature, pH, and the presence and the extent of hydrophilic groups. These functional groups in the hydrogel networks can also be utilized for the toxic metal ion removal. Hydrogels are modified from time to time by incorporating new functionalities or prepared as composites with clays and with other materials to increase the metal ion absorption capacities. The characteristic high water absorbing capacity and electrical conductivity of polymers containing AMPS monomer make them ideally suited for medical hydrogels. The sixth paper, “Preparation and Water Binding Study of AMPS-Based Hydrogel with Hydrophilic and Hydrophobic Chains”, by Arandao Narzary and Nirada Devi, describes a novel pH-sensitive hydrogel—composed of AMPS, vinyl pyrolidone (VP), acrylamide (AM) and acrylonitrile (AN)—and its water uptake potential. The hydrogel is pH-sensitive and attains an equilibrium swelling value at slightly acidic pH ~ 5.0.

-- Sushama Viladkar
Consulting Editor