Shaikh A. Ali

Novel cross-linked polymers having pH-responsive amino acid residues for the removal of Cu2+ from aqueous solution at low concentrations.

Two novel cross-linked anionic polyelectrolytes (CAPE) I and II containing pH-responsive amino acid residues have been synthesized via cycloco- and ter-polymerization of a monomer having diallylammonioethanoate motif (90mol%) and a cross-linker 1,1,4,4-tetraallylpiperazinium dichloride (10mol%) in the absence and presence of SO2 (100mol%), respectively. The experimental data for the adsorption of Cu(2+) on the CAPES fitted Lagergren second-order kinetic model thereby indicating the chemical nature of the adsorption process. The fitness order of Freundlich>Langmuir>Temkin for the isotherm models for CAPE I showed the favorability of adsorption on a heterogeneous surface, whereas for CAPE II the fitness order of Langmuir>Freundlich>Temkin certified the favorability toward monolayer adsorption. The adsorption process was spontaneous and endothermic in nature with negative and positive values for ΔG and ΔH, respectively. For the sorbents CAPE I and CAPE II, the efficiency of Cu(2+) removal at an initial metal concentration of 200ppb was found to be 77.5 and 99.4%, respectively. Desorption efficiencies were found to be 88 and 93% for CAPE I and CAPE II, respectively. Treatment of real wastewater samples spiked with Cu(2+) ions showed the excellent ability of the resins to adsorb metal ions.

Synthesis of hydrophobic cross-linked polyzwitterionic acid for simultaneous sorption of Eriochrome black T and chromium ions from binary hazardous waters

Hydrophobic cross-linked polyzwitterionic acid (HCPZA) containing long chain (C18) hydrophobes and residues of a glutamic acid having unquenched nitrogen valency was synthesized. Exploiting the chelating ability of the amino acid residues to scavenge toxic metals and the hydrophobic surface to scoop up the organic contaminants, the resin HCPZA was evaluated for simultaneous removal of chromium and Eriochrome black T (EBT) from wastewaters. The structure and morphology of the polymer before and after sorption were characterized by using FTIR, TGA, EDX and SEM. The effect of various parameters such as contact time, pH and initial concentrations were investigated to arrive at optimum conditions. The adsorption of Eriochrome black T and Cr (III) on HCPZA reached equilibrium in 30 min. The mechanism of adsorption was investigated using kinetic, diffusion and isotherm models. The adsorption kinetic data were described well by the pseudo-second order model and by the Freundlich isotherm model. EDX analysis confirmed the adsorption of Cr (III) and EBT on the polymer. The hydrophobic resin exhibited a remarkable simultaneous adsorption capacity for EBT and Cr (III) and thus demonstrated its potential to be a promising adsorbent for removal of dyes and heavy metal ions from wastewaters.

A comparative study of the infrared and Raman spectra of aniline and o-, m-, p-phenylenediamine isomers

The structural stabilities of o-, m- and p-phenylenediamine (PDA) isomers were investigated by DFT-B3LYP and ab initio MP2 calculations with the 6-311G(**) basis set. From the calculations the three isomers were predicted to exist predominantly in an anti (transoid) structure. In the o-isomer, the syn (cisoid) form is calculated to turn to the anti (transoid) form with the two HNCC torsional angles of about 44 and 10° and the NH2 inversion barrier of 3-4 kcal/mol. The CCNH torsional angles in the m-PDA and p-PDA isomers were calculated to be about 25-26° as compared to 20° in aniline. A comparison of the Raman spectra of the three PDA-s with those of aniline shows the high sensitivity of the ring breathing mode to the nature of substituents in the aniline ring. The vibrational wavenumbers were computed at the DFT-B3LYP for aniline and the o-, m- and p-PDA isomers for the purpose of comparison. Complete vibrational assignments were made on the basis of normal coordinate analyses and potential energy distributions for aniline and the o-, m- and p-PDA molecules.

Synthesis of a unique cross-linked polyzwitterion/anion with an aspartic acid residue and its use for Pb2+ removal from aqueous solution

In this work, a unique cross-linked polyzwitterion/anion with an aspartic acid residue was synthesized via butlers cyclopolymerization protocol involving N,N-diallylaspartic acid hydrochloride, 1,1,4,4-tetraallylpiperazinium dichloride and sulfur dioxide in the presence of azoisobutyronitrile. The structure and morphology of the polymer were characterized by using FTIR, TGA, EDX and SEM. The adsorption performance of the resin was evaluated using lead Pb(II) as a model. The effect of various parameters such as contact time, pH, initial concentration and temperature were investigated to arrive at optimum conditions. An optimum pH of 6.0 and dosage of 1.5 g L−1 were obtained. The mechanism of adsorption was investigated using kinetic, diffusion, isotherm and thermodynamic models. The adsorption kinetic data were described well by the pseudo-second order model with R2 of 0.999. The activation energy (Ea) of the adsorption process was calculated as 39.29 kJ mol−1. The negative ΔGo values indicate a spontaneous adsorption process while the negative ΔHo (−43.87 kJ mol−1) suggests an exothermic reaction. Adsorption data were described well by the Langmuir and Temkin models. EDX analysis confirmed the adsorption of Pb2+ on the polymer. The overall results suggest that the polymer could be employed as an efficient adsorbent for the adsorption of toxic Pb2+ from polluted aqueous solutions.

Tailoring hydrophobic branch in polyzwitterionic resin for simultaneous capturing of Hg(II) and methylene blue with response surface optimization

A new highly efficient cross-linked polymer was synthesized via cyclotetrapolymerization of hydrophilic [(diallylamino)propyl]phosphonic acid hydrochloride (72 mol%), hydrophobic N,N-diallyl-1-[6-(biphenyl-4-yloxy)hexylammonium chloride (18 mol%), cross-linker 1,1,4,4-tetraallylpiperazinium dichloride (10 mol%) with an equivalent amount of alternating SO2 units (100 mol%). The pH-responsive resin chemically tailored with the aminopropylphosphonate chelating ligand and hydrophobic chain of (CH2)6OC6H4-C6H5 is designed to capture toxic metal ions and organic contaminants simultaneously. The developed resin was used for the remediation of Hg(II) ions and methylene blue from aqueous solutions as models. The experimental conditions were optimized utilizing the response surface methodology as an environmentally friendly method. The adsorption efficiency for Hg(II) was ≈100% at 10 ppm initial concentration at pH 5 at 25 °C, while it was 80% for removal of the dye in a single pollutant system. Interestingly, the resin demonstrated its remarkable efficacy in the simultaneous and complete removal of Hg(II) and the dye from their mixture. Increased removal of the dye (≈100%) in the presence of Hg(II) was attributed to the synergistic effect. The equilibrium data were evaluated by employing the Langmuir and Freundlich isotherm models.

A study of internal rotations and vibrational spectra of oxiranemethanol (glycidol)

The conformational stability and the C-O and O-H internal rotations in oxiranemethanol were investigated at the DFT-B3LYP/6-311 G**, MP2/6-311 G** and MP4(SDQ)/6-311 G** levels of theory. Three minima were predicted in the CCOH potential energy scans of the molecule to have relative energies of about 2 kcal/mol or less and all were calculated to have real frequencies upon full optimization of structural parameters at the DFT and the MP2 levels of calculations. The Cg1 (H bond inner) conformation was predicted to be the lowest energy conformation for oxiranemethanol in excellent agreement with an earlier microwave study. The equilibrium mixture was calculated from Gibbs free-energy changes to be about 79% Cg1, 17% G1g and 3% Gg1 at the B3LYP/6-311G** level and about 87% Cg1, 11% G1g and 2% Gg1 at the MP2/6-311 G** level for oxiranemethanol at 298.15 K. No conclusive evidence was obtained for the presence of high-energy form in the liquid phase of oxiranemethanol. The vibrational frequencies of oxiranemethanol in its three stable forms were computed at the B3LYP level and complete vibrational assignments were made for the lowest energy Cg1 form on basis of calculated and experimental data of the molecule.

Biogenic glutamic acid-based resin: Its synthesis and application in the removal of cobalt(II)

Inexpensive biogenic glutamic acid has been utilized to synthesize a cross-linked dianionic polyelectrolyte (CDAP) containing metal chelating ligands. Cycloterpolymerization, using azoisobutyronitrile as an initiator, of N,N-diallylglutamic acid hydrochloride, sulfur dioxide and a cross-linker afforded a pH-responsive cross-linked polyzwitterionic acid (CPZA) which upon basification with NaOH was converted into CDAP. The new resin, characterized by a multitude of spectroscopic techniques as well as Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analyses, was evaluated for the removal of Co(II) as a model case under different conditions. The adsorption capacity of 137mgg-1 does indeed make the resin as one of the most effective sorbents in recent times. The resin leverages its cheap natural source and ease of regeneration in combination with its high and fast uptake capacities to offer a great promise for wastewater treatment. The resin has demonstrated remarkable efficiency in removing toxic metal ions including arsenic from a wastewater sample.

The conformational stability, solvation and the assignments of the experimental infrared, Raman, 1H and 13C NMR spectra of the local anesthetic drug lidocaine

The structure, vibrational and (1)H and (13)C NMR spectra of the local anesthetic drug lidocaine were investigated by the B3LYP/6-311G(∗∗) calculations. The molecule was predicted to have the non-planar cis (NCCN∼0°) structures being about 2-6kcal/mol lower in energy than the corresponding trans (NCCN∼180°) forms. The calculated NCCN (9.6°) and CNCC (-132.2°) torsional angles were in a good qualitative agreement with the reported X-ray angles (3.1 and 13.0°, -102.67 and -77.9°, respectively, for H-bonded dimers). The Gibbs energy of solution of lidocaine in formamide, water, dimethylsulfoxide, acetonitrile, methanol, ethanol and chloroform solutions was estimated at the B3LYP level. The predicted affinity of lidocaine toward the alcohols, acetonitrile and chloroform solutions was in excellent agreement with the reported experimental solubility of the drug in organic solvents. The analysis of the observed vibrational spectra is consistent with the presence of lidocaine in only one conformation at room temperature. The (1)H and (13)C NMR spectra of lidocaine were interpreted by experimental and DFT calculated chemical shifts of the drug. The RMSD between experimental and theoretical (1)H and (13)C chemical shifts for lidocaine is 0.47 and 8.26ppm, respectively.

Studies on a terephthalic acid and dihydroxydiphenyl sulfone liquid crystalline copolymer and its composites with different thermoplastics

A liquid crystalline polymer (LCP) was synthesized by an interfacial polycondensation reaction at room temperature from terephthaloyl chloride and p,p′-dihydroxydiphenyl sulfone. The LCP synthesized was so stable and molecularly rigid that it did not show any phase transition until it degraded at about 320°C. Composites of the LCP with polycarbonate (PC), polystyrene (PS), and sulfonated polystyrene (SPS) were formed by compression molding at a temperature at which the thermoplastic matrix was in the melt state. They were thermally analyzed by differential scanning calorimetry. Tensile specimens were cut from the compression-molded plates, and mechanical tests were performed. The morphology of the material systems was studied by performing scanning electron microscopy analysis on cryogenically fractured specimens. For LCP/PS and LCP/SPS systems, a sharp two-phase morphology was formed, which suggested poor interfacial adhesion. The tensile strength of both systems decreased with LCP addition. The LCP/PC system also revealed a two-phase morphology; however, the interfaces between the LCP domains and the PC matrix were not so well defined, showing better interfacial adhesion than the two previous systems studied. Stronger bonding between the LCP and PC resulted in a significant improvement in the mechanical behavior of PC by LCP addition.

Imidazolines containing single-, twin- and triple-tailed hydrophobes and hydrophilic pendants (CH2CH2NH)nH as inhibitors of mild steel corrosion in CO2–0.5 M NaCl

Inhibition of mild steel corrosion in CO2–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar) by a new series of imidazolines having single-, twin- and triple-tailed phenyl substituents at C(2) and N(1) pendants of CH2CH2NH2 and (CH2CH2NH)2CH2CH2NH2 have been examined. Imidazolines containing twin-tailed (3,5-dioctyloxyphenyl) hydrophobes outperformed their single- and triple-tailed counterparts as well as two commercial imidazolines. The triamine pendant imparted better inhibition at higher temperature and pressure. The XPS study confirmed the presence of an imidazoline film covering the metal surface. The imidazolines prefer to be adsorbed on the metal surface rather than micellization.