Tarun Kanti Mandal

Influence of anionic co-ligands on the structural diversity and catecholase activity of copper(II) complexes with 2-methoxy-6-(8-iminoquinolinylmethyl)phenol

A novel dinuclear copper(II) complex, [Cu2L2(μ1,1-N3)2] (1), and a mononuclear copper(II) complex, [CuL(NCO)] (2), have been synthesized from a planar tridentate ligand 2-methoxy-6-(8-iminoquinolinylmethyl)phenol (HL) together with pseudohalides as coligands, and the solid state structures were determined by X-ray crystallography. Structural characterizations reveal that the geometry of centrosymmetrically related copper(II) centers in 1 is square pyramidal while it is square planar in 2. The impact of the structural diversity was found on their catechol oxidase mimicking activity. Strongly bridging azide ions being substitutionally inert mean complex 1 is inactive towards the catecholase activity, while mononuclear analogue 2 exhibits moderately strong catechol oxidase activity. The ESI-MS positive spectrum of a mixture of complex 2 and 3,5-DTBCH2 shows a peak corresponding to both superoxo and substrate bound species, Na[CuL(O2)(3,5-DTBCH)]+, suggesting that both the dioxygen and substrate simultaneously coordinated to the metal center in the catalytic cycle. Most importantly, complex 2 not only represents the mononuclear class of copper(II) compounds that are rarely visited for the study of catecholase mimicking activity but also the first example of a mononuclear square planar complex exhibiting catechol oxidase activity.

An Interplay of Cooperativity between Cation⋅⋅⋅π, Anion⋅⋅⋅π and CH⋅⋅⋅Anion Interactions

Mixed cation (Li(+), Na(+) and K(+)) and anion (F(-), Cl(-), Br(-)) complexes of the aromatic π-surfaces (top and bottom) are studied by using dispersion-corrected density functional theory. The selectivity of the aromatic surface to interact with a cation or an anion can be tuned and even reversed by the electron-donating/electron-accepting nature of the side groups. The presence of a methyl group in the -OCH3, -SCH3, -OC2H5 in the side groups of the aromatic ring leads to further cooperative stabilization of the otherwise unstable/weakly stable anion⋅⋅⋅π complexes by bending of the side groups towards the anion to facilitate C-H⋅⋅⋅anion interactions. The cooperativity among the interactions is found to be as large as 100 kcal  mol(-1) quantified by dissection of the three individual forces from the total interaction energy. The crystal structures of the fluoride binding tripodal and hexapodal ligands provide experimental evidence for such cooperative interactions.

Degenerate intermolecular and intramolecular proton-transfer reactions: electronic structure of the transition states.

Density functional theory (DFT) calculations are performed on a series of double and single proton-transfer reactions to study the variation in polarizations in complexes during the dynamics of proton transfer from one isoenergetic, hydrogen-bonded ground-state structure to the other. The isotropic average polarizability (alpha(av)) shows an interesting single-humped profile with a maxima coinciding with the transition state of the reaction. Similar profiles are also computed at Nd:YaG frequencies. The origin of the maximal polarizability at the transition state is traced to maximal charge separation and large D (donor)-A (acceptor) distances. Maximal polarizability for the transition state suggests an interesting, novel, and less memory extensive computational tool to locate the transition state for hydrogen-transfer reactions in hydrogen-bonded complexes.

Mn(III) and Cu(II) complexes of 1-((3-(dimethylamino)propylimino)methyl) naphthalen-2-ol): Synthesis, characterization, catecholase and phenoxazinone synthase activity and DFT-TDDFT study

Abstract Two new complexes, [MnL2](ClO4) (1) and [CuL2] (2) (where LH = (E)-1-((3-(dimethylamino)propylimino)methyl)naphthalen-2-ol), have been synthesized and characterized by spectroscopic techniques and their molecular structures are established by single-crystal X-ray diffraction study. Complex 1 adopts an octahedral geometry around the central manganese atom which is in + 3 oxidation state, whereas in complex 2, the Cu+2 ion preferred a square pyramidal environment around it through the ligand donor atoms. Both complexes were tested for catecholase and phenoxazinone synthase activity. Complex 1 catalyzes the oxidation of 3,5-ditertiary-butyl catechol with a kcat value of 6.8424 × 102 h−1 in acetonitrile whereas the same for complex 2 is 3.7485 × 102 h−1 in methanol. Phenoxazinone synthase activity was shown only by complex 2 having kcat = 74.225 h−1. Structures of both the title complexes have been optimized by means of DFT calculations. Experimental electronic spectra of the complexes have been corroborated by TDDFT analysis. Electrochemical investigations by means of cyclic voltammetry have been carried out to study the electron transfer processes in the complexes.