Mohamed I.M. Wazeer

Synthesis and solution properties of a new pH-responsive polymer containing amino acid residues

Abstract The amine salt, N,N-diallyl-N-carboethoxymethylammonium chloride was cyclopolymerized in water using ammonium persulfate as an initiator to afford a cationic polyelectrolyte which on acidic hydrolysis of the pendant ester groups gave the corresponding cationic acid salt (CAS). The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB). The solution properties of the APE having two basic functionalities were investigated in detail by potentiometric and viscometric techniques. Basicity constants of the amine as well as the carboxylate groups in APE are ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation; as the degree of protonation (α) of the whole macromolecule increases, the protonation of the amine nitrogens and carboxylate groups becomes increasingly more difficult and easier, respectively. While the APE, PB and CAS were found to be soluble in salt-free water, the corresponding PB and CAS of the SO2 copolymers of the amine salt 1 were found to be insoluble in water.

Synthesis and solution properties of a new ionic polymer and its behavior in aqueous two-phase polymer systems

Abstract The amine salt, N , N -diallyl- N -carboethoxymethylammonium chloride was copolymerized in dimethyl sulfoxide using ammonium persulfate or azo-bis-isobutyronitrile (AIBN) to afford the cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) having the equivalent of chloride salt of N , N -diallylammonio ethanoic acid as monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB) [having the monomeric unit equivalent of sodium N , N -diallylaminoethanoate and N , N -diallylammonioethanoate] by treatment with two and one equivalent of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. Basicity constant of the amine functionality in APE is found to be ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation; the protonation of the APE becomes more and more difficult as the degree of protonation ( α ) of the whole macromolecule increases. The composition and phase diagram of the aqueous two-phase systems of APE and poly(ethyelene glycol) (PEG) has been studied for the first time for this class of ionic polymers. The CAS and PB were found to be virtually insoluble in water.

Zinc halide complexes of imidazolidine-2-thione and its derivatives: X-ray structures, solid state, solution NMR and antimicrobial activity studies

The preparation and characterization of zinc complexes of formula ZnL2X2 (X = Cl and Br), with L = 1,3-diazinane-2-thione (Diaz), 1,3-diazipane-2-thione (Diap), imidazolidine-2-thione (Imt) and its methyl and n-propyl substituted derivatives, are described. The complexes dichlorobis(1-methylimidazolidine-2-thione-S)-zinc(II) (1) and dichlorobis(1-propylimidazolidine-2-thione-S)-zinc(II) (2) have been characterized by single-crystal X-ray methods. Both complexes adopt distorted tetrahedral geometry. Only intramolecular hydrogen bonding interactions are observed in 1 and 2. Solution and solid state 13C NMR show a significant shift of the C=S carbon resonance of the ligands, while other resonances are relatively unaffected, indicating that most likely the solid state structure is maintained in solution. Antimicrobial activity studies of the free ligands and their complexes show that ligands exhibit substantial antibacterial activities compared to the complexes.

Silver(I) complexes of imidazolidine-2-thione and triphenylphosphines: Solid-state, solution NMR and antimicrobial activity studies

Mixed ligand complexes of Ag(I) with triphenylphosphine (PPh3), triphenylphosphine sulfide (SPPh3), triph- enylphosphine selenide (SePPh3) and Imidazolidine-2-thione (Imt) have been prepared. The solution as well as solid state NMR studies have been carried out to characterize these complexes. Both solid and solution NMR show the coordination via thione group on one side and (S/Se) or PPh3 on the other side. A higher antimicrobial activity is shown by (ImtAgPPh3)Cl complex against gram negative Pseudomonas aeruginosa (P. aeruginosa )a ndEscherichia coli (E. coli) compared to the other two complexes i.e. (ImtAgSPPh3)Cl and (ImtAgSePPh3)Cl.

CYCLIC NITRONE-ETHENE CYCLOADDITION REACTIONS

Abstract Addition reactions of ethene onto several cyclic nitrones afforded [n,3,0]heterobicyclicalkanes devoid of any substituents in the ring skeleton. These fused ring systems with a bridgehead nitrogen, capable of undergoing nitrogen inversion, allowed us to determine the stereochemistry of the ring fusion and the thermodynamic stability of the cis, trans isomers. Some of the cycloadducts on peracid induced ring opening gave a new series of nitrones capable undergoing further cycloaddition reactions.

Solid state NMR study of 1,3‐imidazolidine‐2‐thione, 1,3‐imidazolidine‐2‐selenone and some of their N‐substituted derivatives

Solid-state NMR spectra were recorded for 1,3-imidazolidine-2-thione, 1,3-imidazolidine-2-selenone and some of their N-substituted derivatives. Spinning side-bands of thione and selenone carbons were analysed to yield chemical shift anisotropies for these carbons. The NMR spectrum of imidazolidine-2-thione (Imt) showed some evidence for the presence of thiol tautomer. Molecular computations were carried out for Imt and its N-methyl derivative to yield relative energies of various tautomers.

Synthesis of aurocyanide and auricyanide complexes of phosphines, phosphine sulfides and phosphine selenides, and their characterization by IR, far-IR, UV solution, and solid-state NMR spectroscopic methods

A series of aurocyanide and auricyanide complexes of phosphines, phosphine sulfides, and phosphine selenides were synthesized. These new complexes have the general formula [L n Au(CN) m ], where L could be Cy3P, (2-CN-Et)3P, Me3PS, Et3PS, Ph3PS, Me3PSe, or Ph3PSe. Auricyanide was reacted with L at 1 : 2 ratio. Products were characterized using elemental analysis, melting point, UV, IR, far-IR solution, and solid-state NMR spectroscopy. Phosphine ligands cause gold(III) reduction to gold(I); less redox tendency was found for phosphine sulfides and phosphine selenides. Tri-coordinate complexes [L2AuCN] were produced from phosphine ligands with gold-tetracyanide. IR and UV spectroscopic methods were used to identify gold oxidation state in the synthesized complexes.

A 13C NMR study of the interactions of Ag13CN and Ag(CN)2– with thiomalic acid, L-methionine and DL-selenomethionine

Complexation of Ag + as AgNO3, solid AgCN and Ag(CN) − by labeled and unlabeled L-methionine, DL- selenomethionine and d,l-thiomalate were studied by nuclear magnetic resonance methods. The 13 C NMR indicates that only Ag + react with the both L-methionine, DL-selenomethionine at neutral and higher pH via CO − and S or Se atom forming a chelate. The Ag(CN) − and AgCN do not bind to either of these two ligands at any pH. The Ag 13 CN, which is an insoluble polymer, can react with thiomalate to form chelate complexes at neutral pH. Various structures for the chelate formations are proposed.

Nitrogen inversion and N–O bond rotation in some hydroxylamine and isoxazolidine derivatives

A series of trisubstituted hydroxylamine derivatives, both cyclic and acyclic, has been prepared. The energy barriers in these hydroxylamines are found to be dominated either by nitrogen inversion or N–O bond rotation depending on the nature of the substituents attached to the nitrogen. In several series of compounds, having XC6H4CH2 substituents attached to nitrogen, Hammett free energy correlations are obtained with positive ρ values, indicating increased electron density at the transition state for the inversion process. Isoxazolidines with C(5) ethoxy substituents demonstrate a strong anomeric effect.

Nuclear spin relaxation in some phenyl phosphorus compounds

Abstract 13 C and 31 P spin-lattice relaxation times ( T 1) and nuclear Overhauser effects were measured in triphenylphosphine, triphenylphosphine oxide, triphenylphosphine sulphide, and triphenylphosphine selenide, over a temperature, range −40°C to +55°C. Isotropic reorientation correlation times were calculated from the dipolar relaxation times for phosphorus and that for the para carbon. The spin-rotation mechanism is the dominant relaxation mechanism for phosphorus in triphenylphosphine, whereas the chemical shift anisotropy is the dominant mechanism in triphenylphosphine oxide at low temperatures. In triphenylphosphine sulphide and triphenylphosphine selenide, the dipolar and the chemical shift anisotropy mechanisms are important in phosphorus relaxation. The motional anisotropy of internal rotation of phenyl rings and overall tumbling is determined from the ratio of T 1 s of ortho or meta carbon to para carbon, and is found to increase with the decrease in temperature and with the increase in mol. wt. The angular momentum correlation times were calculated from phosphorus spin-rotation relaxation rates. From viscosity data, reduced correlation times were calculated and compared with that calculated using Stokes-Einstein-Debye, Gierer-Wirtz, and Hu-Zwanzig models.