Sourav Kr. Saha

Exploratory studies towards various anion recognition chemistry by two different sized cleft shaped organic ligands

Indole and urea based two organic receptors have been synthesized by an easy synthetic process. These two receptors have strong sensitivity and selectivity for several bio-relevant anions. Receptor 1 and 2 were synthesized from indole-2-carboxylic acid and p-anisidine respectively, which are low cost starting materials. Receptor 1 can selectively sense anions like F(-), OAc(-) and H2PO4(-), while receptor 2 can only sense F(-) and H2PO4(-). Both receptors are silent toward anions like Cl(-), Br(-), I(-) and NO3(-). It is the difference in their shape and size which are responsible for different anion sensing. The nature of these host-guest type interactions was analyzed by convenient spectrophotometric techniques like UV-Vis, fluorescence, (1)H NMR, FT-IR studies and also confirmed by electrochemical techniques like cyclic voltammetry studies of the two ligand receptors with convenient anions. Between receptor 1 and 2, receptor 2 was crystallographically characterized also.

Theoretical evaluation of some benzotriazole and phospono derivatives as aluminum corrosion inhibitors: DFT and molecular dynamics simulation approaches

The adsorption and corrosion inhibition properties of some benzotriazole and phospono derivatives namely, 1-(2-pyrrolecarbonyl)-benzotriazole (PBTA), 1-(2-thienylcarbonyl)-benzotriazole (TBTA), 2-phosphonoacetic acid (PAA) and 4-phosphonobutyric acid (PBA) on the corrosion of aluminum were investigated by quantum chemical calculations and by molecular dynamics simulations. Global reactivity descriptors such as EHOMO, ELUMO, HOMO–LUMO energy gap (ΔE), chemical hardness (η), softness (σ), electronegativity (χ), proton affinity (PA), electrophilicity (ω) and nucleophilicity (e) have been calculated and discussed. The analysis of the adsorption behavior of these mentioned inhibitors on the Al (111) surface was investigated using molecular dynamics simulations. The binding energies on the Al (111) surface of the studied compounds followed the order: PBTA > TBTA > PBA > PAA. The results obtained in this study are compatible with experimental data and it is proposed that the above mentioned molecules can be successfully used to prevent the corrosion of aluminum metal.

Evaluating corrosion inhibition property of some Schiff bases for mild steel in 1 M HCl: competitive effect of the heteroatom and stereochemical conformation of the molecule

To evaluate the effect produced by the heteroatom present in organic Schiff bases along with overall stereochemical conformation of such bases towards corrosion inhibition performance, three Schiff bases, namely 2-pyridyl-N-(2′-methylamino phenyl) methyleneimine (PMAM), 2-pyridyl-N-(2′-methylthiophenyl) methyleneimine (PMTM) and 2-pyridyl-N-(2′-methoxyphenyl) methyleneimine (PMPM), are assessed for mild steel in 1 M HCl. Chemical similarity exists among these three molecules, varying only in the nature of the heteroatom present away from the imine group. Results from weight loss, potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques demonstrate that the Schiff bases form a resistive layer on the metal surface, and thereby block the cathodic as well as the anodic reaction sites effectively. Experimentally obtained corrosion inhibition efficiency follows the sequence: PMAM > PMTM > PMPM, and this is also confirmed following surface electron microscopy (SEM) images. The Langmuir isotherm is found to provide a sufficiently good description of adsorption behavior of the compounds on the metal surface. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations are done to correlate the efficiency of these compounds with their intrinsic molecular parameters, as well as energy optimized molecular orientation.

Introduction of newly synthesized Schiff base molecules as efficient corrosion inhibitors for mild steel in 1 M HCl medium: an experimental, density functional theory and molecular dynamics simulation study

The purposeful incorporation of aliphatic, branched chain and substituted aromatic moieties in the molecular skeleton of organic Schiff bases, in line with corrosion inhibition performance, has been conducted. Three Schiff bases, namely, 2-((2-hydroxyethylimino)methyl)-6-methoxyphenol (L1), 2-((1-hydroxybutan-2-ylimino)methyl)-6-methoxyphenol (L2) and 2-(2-hydroxy-3-methoxybenzylideneamino)phenol (L3) were synthesized and subsequently assessed for the inhibition of mild steel corrosion in 1 M HCl medium. The corrosion inhibition proficiencies of the synthesized inhibitors on the mild steel surface have been investigated by gravimetric measurements, electrochemical analysis (potentiodynamic polarization, electrochemical impedance spectroscopy), surface morphological studies (FESEM and AFM), contact angle measurement and, most importantly, theoretical studies. The results obtained from the gravimetric as well as electrochemical measurements revealed that the studied Schiff bases are mixed-type inhibitors that show maximum inhibition efficiency up to ∼97% at the concentration of 5 mM. In theoretical studies, atomic-level calculations give deeper insights into the corrosion inhibition mechanism and the relative performance of present inhibitors. However, it has been found that normal density functional theory (DFT) calculations are not sufficient to deal with the interactions between inhibitors and metal surfaces in complex systems. As such, in order to investigate inhibitor–metal interactions, herein, the density functional tight binding (DFTB) approach has been introduced as formulated by Hohenberg, Kohn and Sham (KS-DFT). Furthermore, for more insightful studies, e.g., growth characteristics, as well as the selection of a more stable surface of the α-Fe crystal morphology studies, have also been performed using the “morphology” module. The morphology of the α-Fe crystal in equilibrium was analyzed using the Wulff construction plot. In DFTB calculations, the trans3d Slater–Koster library set has been implemented for possible pairs of interactions between inhibitor–metal complex systems (C, N, O, H and Fe). Some salient features like equilibrium adsorption configuration and charge density difference obtained from DFTB calculations have been described in detail. Furthermore, for comparison with the real world of corrosion inhibition, molecular dynamics (MD) simulation was employed in the presence of all concerned species (inhibitor molecule, Fe surface, H2O, H3O+ and Cl−), which revealed the actual adsorption configurations of the inhibitor molecule on the desired metallic surfaces.