P.S. Subramanian

Copper(II) diethylenetriamine perchlorato complexes bridged through varying length dicarboxylato spacers: synthesis, characterization and EPR studies

Abstract The synthesis and spectral characterization of dinuclear copper(II) complexes of the composition [(dien)CuLCu(dien)](ClO4)2, where dien = diethylenetriamine and L2 = oxalato, malonato, succinato, phthalato, isophthalato and terephthalato, are reported. IR spectra reveal that the mode of carboxylato coordination is anti-anti for oxalato complexes while it adopts chelate or polymeric syn-anti coordination for the rest of the complexes. The stereochemistry around copper is distorted square pyramidal. Oxalato forms two types of complexes I and II. EPR for I is characterized by a rhombic g tensor with g3 g⊥) suggesting the occupancy of unpaired electron in a dx2−y2 orbital. Frozen solution EPR spectra at 77 K indicate that the solvent molecule coordinates with the metal ion. Magnetic exchange in these complexes is intramolecular and both conjugated and unconjugated spacer dicarboxylato ligands propagate the exchange between the metal ions.

Sensing of Phosphates by Using Luminescent EuIII and TbIII Complexes: Application to the Microalgal Cell Chlorella vulgaris

Phenanthroline-based chiral ligands L(1) and L(2) as well as the corresponding Eu(III) and Tb(III) complexes were synthesized and characterized. The coordination compounds show red and green emission, which was explored for the sensing of a series of anions such as F(-), Cl(-), Br(-), I(-), NO3(-), NO2(-), HPO4(2-), HSO4(-), CH3COO(-), and HCO3(-). Among the anions, HPO4(2-) exhibited a strong response in the emission property of both europium(III) and terbium(III) complexes. The complexes showed interactions with the nucleoside phosphates adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP). Owing to this recognition, these complexes have been applied as staining agents in the microalgal cell Chlorella vulgaris. The stained microalgal cells were monitored through fluorescence microscopy and scanning electron microscopy. Initially, the complexes bind to the outer cell wall and then enter the cell wall through holes in which they probably bind to phospholipids. This leads to a quenching of the luminescence properties.

Coordinatively Unsaturated Lanthanide(III) Helicates: Luminescence Sensors for Adenosine Monophosphate in Aqueous Media

Coordinatively unsaturated double-stranded helicates [(H2 L)2 Eu2 (NO3 )2 (H2 O)4 ](NO3 )4 , [(H2 L)2 Tb2 (H2 O)6 ](NO3 )6 , and [(H2 L)2 Tb2 (H2 O)6 ]Cl6 (H2 L=butanedioicacid-1,4-bis[2-(2-pyridinylmethylene)hydrazide]) are easily obtained by self-assembly from the ligand and the corresponding lanthanide(III) salts. The complexes are characterized by X-ray crystallography showing the helical arrangement of the ligands. Co-ligands at the metal ions can be easily substituted by appropriate anions. A specific luminescence response of AMP in presence of ADP, ATP, and other anions is observed. Specificity is assigned to the perfect size match of AMP to bridge the two metal centers and to replace quenching co-ligands in the coordination sphere.

SYNTHESIS, SPECTRAL CHARACTERIZATION AND MAGNETIC PROPERTIES OF DICARBOXYLATO-BRIDGED DINUCLEAR COPPER(II) COMPLEXES WITH N-PYRIDYLSALICYLIDENAMINATO LIGAND

Abstract The synthesis and characterization of mixed-ligand copper(II) complexes with bridged dicarboxylato groups, of the composition [(PS)Cu] 2 L· n H 2 O, where PS = N-pyridylsalicylidenaminato, L = malonato, phthalato and terephathalato, and n = 8,5,2,respectively, are reported. PS coordinates as a monoanionic bidentate ligand, while carboxylate coordinates as a monodentate ligand. The stereochemistry around copper is distorted octahedral for malonato, square pyramidal for phthalato and square planar for terephthalato complexes. EPR spectra for polycrystalline complexes at room temperature were characterized by axial symmetry ( g ∥ > g ⊥ ) and correspond to non-interacting dimeric units. However, the anomalous magnetic moment data suggest intermolecular interactions as an efficient exchange pathway.

Synthesis and characterization of chiral recyclable dimeric copper(II)–salen complexes and their catalytic application in asymmetric nitroaldol (Henry) reaction

Six new chiral tridentate ditopic ligands with ONO donors possessing different linkers (either achiral or chiral) were synthesized. The characterization of these ligands was accomplished by IR, UV/Vis, NMR, mass spectrometry and optical rotation. These ligands have been treated with a series of metal ions viz., Cu(II), Cu(I), Co(III) and Zn(II), affording varieties of new chiral metal complexes, which have been characterized thoroughly using different analytical and spectroscopic methods. All the complexes were screened for catalytic asymmetric nitroaldol reaction using benzaldehyde as a model substrate. The reaction conditions were optimized and 79% yield with good enantioselectivity (88%) was achieved at RT with the in situ generated catalyst having a piperazine linker and (1R,2S)-2-amino-1,2-diphenylethanol collar in combination with cupric acetate as the metal source. By applying other aromatic and aliphatic aldehydes, similar yields of β-nitroalcohols with improved enantioselectivities (up to 93%) were achieved. The catalytic system worked very well for up to four cycles with retention of activity and enantioselectivity of β-nitroalcohols.

In situ-generated chiral iron complex as efficient catalyst for enantioselective sulfoxidation using aqueous H2O2 as oxidant

A series of amino alcohol-derived, Schiff-base ligands L1–L4 were synthesised and characterized. Iron complexes of these ligands [FeL1(acac)], [FeL2(acac)], [FeL3(acac)] and [FeL4(acac)] were generated in situ to catalyze the asymmetric oxidation of prochiral sulfides using aqueous H2O2 as a terminal oxidant. One of these complexes [FeL1(acac)] was identified as a very efficient catalyst for the enantioselective oxidation of a series of alkyl aryl sulfides with excellent enantioselectivity (75–96% ee), conversion (up to 92%) and chemo selectivity (up to 98%). During the optimization process, a series of electron-donating benzoic acid derivatives were found to favour both conversion and enantioselectivity.

Picking Out Logic Operations in a Naphthalene β-Diketone Derivative by Using Molecular Encapsulation, Controlled Protonation, and DNA Binding.

On–off switching and molecular logic in fluorescent molecules are associated with what chemical inputs can do to the structure and dynamics of these molecules. Herein, we report the structure of a naphthalene derivative, the fashion of its binding to β-cyclodextrin and DNA, and the operation of logic possible using protons, cyclodextrin, and DNA as chemical inputs. The compound crystallizes out in a keto-amine form, with intramolecular N−H⋅⋅⋅O bonding. It shows stepwise formation of 1:1 and 1:2 inclusion complexes with β-cyclodextrin. The aminopentenone substituents are encapsulated by β-cyclodextrin, leaving out the naphthalene rings free. The binding constant of the β-cyclodextrin complex is 512 m−1. The pKa value of the guest molecule is not greatly affected by the complexation. Dual input logic operations, based on various chemical inputs, lead to the possibility of several molecular logic gates, namely NOR, XOR, NAND, and Buffer. Such chemical inputs on the naphthalene derivative are examples of how variable signal outputs based on binding can be derived, which, in turn, are dependent on the size and shape of the molecule.

Copper(II) bis-chelate paddle wheel complex and its bipyridine/phenanthroline adducts

Bola-shaped diester dicarboxylic acid 2-({2-[(2-carboxybenzoyl)-xy]ethoxy}carbonyl)benzoic acid (L1H2) was synthesized by desymmetrizing phthalic anhydride using 1,2-ethane diol. The corresponding dinuclear copper(II)-tetracarboxylate complex [Cu2(L1)2·(DMF)2] (1) has been synthesized. This paddle wheel complex was self-assembled with [15]-membered bis-chelate ring on either sides of the M–M axis. Upon treating with phenanthroline/bipyridine, the symmetrically formed bis-chelate rings in 1 were selectively desymmetrized into monochelate rings. The dinuclear association in 1 rearranged into mononuclear in [Cu(L1)·(bpy)] (2) and [Cu(L1)·(phen)]·(DMF) (3), where bpy = bipyridine and phen = phenanthroline. The paddle wheel arrangement in 1 is very similar to that in dimeric Cu(II) acetate; the symmetric arrangement in 1 rearranged in its corresponding monomeric species on reacting with phen and bpy. The symmetric bis-chelate ring in 1 and the desymmetrized monochelate ring in 2 and 3 are discussed following their crystal structures. The crystal structures for all the complexes and the electronic and fluorescence properties are discussed.

Synthesis, structure, EPR, and DFT calculation on dinuclear paddle wheel Cu(II) complexes with bis-chelate rings

A series of diester-dicarboxylic acids, L1H2, L2H2, L3H2, L4H2, and L5H2 and their dinuclear Cu2 complexes [Cu(L1)CH3CN]2 (1), [Cu(L2)H2O]2 (2), [Cu(L3)CH3CN]2 (3), [Cu(L4)EtOH]2 (4), and [Cu(L5)CH3CN]2 (5), were synthesized. The crystal structures obtained for 1, 2, and 4 and the density functional theory optimized structures for 2, 3, and 5 illustrated the formation of tetracarboxylate “paddle wheel” complexes. The phthalyl and diphenyl head groups and the spacer moieties were appropriately altered and the size of the chelate ring expanded from 15-membered in 1 to 21-membered in 5. The dinuclear units have strong Cu–Cu interaction with EPR spectra exploring spin coupled features.

Green synthesis of biocidal silver-activated charcoal nanocomposite for disinfecting water

We report for the first time the green synthesis of silver nanoparticles using West Indian cherry (Malpighia emarginata) extract known for its high vitamin C content. UV–visible spectroscopy, powder X ray diffraction (PXRD), dynamic light scattering (DLS), scanning electron microscopy (SEM) and energy dispersive X ray spectroscopy (EDX) analysis were used to characterise silver nanoparticles. Silver nanoparticles thus synthesised exhibit antimicrobial activity against gram-negative bacteria such as Pseudomonas aeruginosa, Escherichia coli, and gram-positive bacteria such as Bacillus subtilis and Staphylococcus aureus. The antimicrobial property of nanoparticles thus synthesised was applied in the production of silver-activated charcoal nanocomposite towards fabrication of antimicrobial water filtration columns. The microbial filtration efficiency of the nanocomposite was found to be higher compared to virgin activated charcoal even with reusage.