Amrita Saha

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.

Secure connectivity model in Wireless Sensor Networks (WSN) using first order Reed-Muller codes

In this paper, we suggest the idea of separately treating the connectivity and communication model of a Wireless Sensor Network (WSN). We then propose a novel connectivity model for a WSN using first order Reed-Muller Codes. While the model has a hierarchical structure, we have shown that it works equally well for a Distributed WSN. Though one can use any communication model, we prefer to use the communication model suggested by Ruj and Roy [1] for all computations and results in our work. Two suitable secure (symmetric) cryptosystems can then be applied for the two different models, connectivity and communication respectively. By doing so we have shown how resiliency and scalability are appreciably improved as compared to Ruj and Roy [1].

Syntheses, crystal structures, DNA binding, DNA cleavage, molecular docking and DFT study of Cu(II) complexes involving N2O4 donor azo Schiff base ligands

Here, we have reported three novel copper(II) complexes (1–3) involving azo Schiff base ligands. All the complexes have been well characterized using different spectroscopic tools and single crystal X-ray diffraction analysis. Structural and electronic parameters of the complexes have been justified by DFT and TDDFT computation. All the complexes showed minor groove binding to the AT-rich sequence of DNA. The binding properties of the complexes have been extensively studied, and are further supported by a molecular docking analysis. These complexes also showed H2O2-mediated DNA cleavage properties involving a hydroxyl radical. MTT assay of the complexes was performed and they were found to be cytotoxic. The intrinsic binding constants (Kb) were calculated to be 7.11 × 105 M−1, 8.36 × 105 M−1 and 10.81 × 105 M−1 for complexes 1–3, respectively. The complexes show interesting supramolecular architectures in the solid state mainly supported by π–π stacking interactions.

A robust fluorescent chemosensor for aluminium ion detection based on a Schiff base ligand with an azo arm and application in a molecular logic gate

In this present work we have reported the synthesis and structural characterisations of a N2O2 donor Schiff base chemosensor with an azo arm (H2L). Various spectroscopic tools like single crystal X-ray, NMR, UV-vis, FTIR, ESI-mass spectrometry etc. have been deployed to develop the present work. In recent years a number of azo derived chemosensors have been reported by different research groups. This is first time we are reporting the design and properties of an azo derived chemosensor (H2L) for the detection of aluminium ions in semi aqueous medium. It has been found that it selectively senses Al3+ ions in semi aqueous solution. Here, the sensing process is mainly based on a chelation enhanced fluorescence process (CHEF). It has very high selectivity over other metal ions and anions. A detailed literature survey has been carried out and compared with this work. It has an appreciably low detection limit i.e. 6.93 nM. 1H NMR titration was carried out to support the plausible complexation process. 1 : 1 stoichiometry binding between the chemosensor and Al3+ ions has been confirmed from Jobs plot. An inhibition molecular logic gate has been constructed using chemosensor (H2L), where Al3+ and EDTA act as inputs and fluorescence emission is the output. The structural and electronic parameters of the chemosensor (H2L) and complex [AL(L)]NO3 have been studied in detail using theoretical tools like DFT and TDDFT.

Mono- and di-nuclear nickel(II) complexes derived from NNO donor ligands: syntheses, crystal structures and magnetic studies of dinuclear analogues

The present report deals with the synthesis and structural characterisation of a mononuclear (1), a di(phenoxido)-bridged dinuclear (2) and a phenoxido/azide bridged dinuclear (3) nickel(II) complexes derived from NNO donor Schiff base ligands. Structural studies reveal that, in all complexes, the nickel(II) ions are hexa-coordinated in a distorted octahedral environment in which tridentate NNO ligand binds the metal centre in the meridional configuration. The variable-temperature (2–300 K) magnetic susceptibility measurements of dinuclear analogues (2 and 3) show that the interaction between the metal centres is moderately ferromagnetic (J = 15.6 cm−1 for 2 and J = 15.3 cm−1 for 3). Broken symmetry density functional calculations of exchange interaction have been performed on complexes 2 and 3 and provide a good numerical estimate of J values (J = 10.31 cm−1 for 2 and J = 17.63 cm−1 for 3) to support the experimental results. Most importantly, compound 2 is only the second example where ferromagnetic coupling is operative in the class of di(phenoxido)-bridged dinickel(II) complexes. The bridging Ni–O–Ni angle being close to the crossover region would provide significant information to get better insight into the magneto-structural correlation in these systems. On the other hand, compound 3 is an important addition to a family of very few hetero-bridged (phenoxido/azide) discrete compounds of nickel(II).

Exploration of unconventional π–hole and C–H⋯H–C types of supramolecular interactions in a trinuclear Cd(II) and a heteronuclear Cd(II)–Ni(II) complex and experimental evidence for preferential site selection of the ligand by 3d and 4d metal ions

In this present work we report the synthesis and structural characterisation of a trinuclear cadmium(II) (1) and a di(phenoxido)-bridged dinuclear cadmium(II)–nickel(II) (2) complex derived from a bicompartmental (N2O4) Schiff base ligand, H2L. It has been observed that, in bicompartmental ligands the relatively small inner core is suitable for 3d metal ions and outer core can be occupied by different metal centers like 3d, 1s, 2s, 4d and 4f. We have experimentally established the above fact. In homotrinuclear complex 1 both inner (N2O2) and outer (O4) core has been occupied by cadmium(II) ions. Complex 1 upon reaction with NiCl2·6H2O produces heterodinuclear complex 2. Structural studies reveal that, in complex 1 terminal Cd units acquire trigonal prismatic geometry whereas the central Cd unit is eight coordinated. In case of complex 2 both nickel(II) and cadmium(II) ions are hexa-coordinated in a distorted octahedral environment. Both the complexes are studied using different spectroscopic techniques. Complexes 1 and 2 exhibit important and relatively unexplored group of supramolecular interactions like π–hole, C–H⋯π and C–H⋯H–C along with other hydrogen bonding interactions. Theoretical DFT calculations are devoted to analyze these non covalent interactions. Several computational tools like MEP surface analysis and NCI analysis are utilized to explain and illustrate such interactions.

A new end-on (μ1,1) azido bridged [Zn2(L)2(Na)N3]n 1D chain derived from a trinuclear zinc complex: syntheses, crystal structures, photoluminescence properties and DFT study

Abstract A bicompartmental N2O4 donor symmetric Schiff base ligand has been deployed to synthesize a trinuclear zinc complex [Zn3(L)2Cl2], which upon treatment with sodium azide produces a new μ1,1-azido-bridged 1-D polymer [Zn2(L)2(Na)N3]n. Both complexes have been characterized using IR, NMR, UV–vis, and X-ray diffraction techniques. In order to have better understanding of electronic transitions of the complexes, a time-dependent DFT study has been performed. Lifetime measurements have also been performed to learn about the stability of excited states of both complexes. The average fluorescence decay lifetime has been found to be 1.42 and 0.59 ns for 1 and 2, respectively. In Hirshfeld surface mapping, X⋯H/H⋯X (X = O, Cl) contacts are found to be only 2.7% of the total surface, which indicates that no significant X⋯H/H⋯X contacts are present in either of the complexes. Unconventional interactions such as C–H⋯π and π⋯π stacking interactions are found in supramolecular architectures of both complexes.

Anion-dependent structural diversity of cadmium(II) complexes: synthesis, crystal structures, luminescence properties, and unusual C-H/σ supramolecular interactions involving σ-aromatic M2X2 cores

Abstract Four complexes based on N,N′-bis(2-pyridylmethylene)-1,3-propanediamine (L) and different Cd(II) salts have been synthesized and characterized by single-crystal X-ray diffraction analysis. The complexes are [Cd2(L)2(μ-Cl)2](ClO4)2 (1), [Cd2(L)2(μ-Br)2](ClO4)2 (2), [Cd(L)I](ClO4) (3), and [Cd(L)(NCS)2] (4). L exhibits the same coordination mode in 1–4. The radius of each anion plays a role in affecting the structures and luminescent intensities of the final products. CdCl2, CdBr2, and CdI2 react with L to produce chloride or bromido-bridged binuclear complexes and mononuclear iodido complex, respectively, whereas an unusual mononuclear trigonal prismatic (TP) 4 is obtained when thiocyanate was used as a coligand. Photoluminescence properties of all the complexes show that the trend of fluorescence intensity is 1 > 4 > 2 > 3. All four complexes exhibit different supramolecular interactions such as C–H/σ, π–π, and C–H/π and hydrogen bonding interactions. The experimental findings are complemented by density functional theory (DFT) calculations.

Nuclearity versus oxidation state in the catalytic efficiency of MnII/III azo Schiff base complexes: computational study on supramolecular interactions and phenoxazinone synthase-like activity

A novel mononuclear Mn(III) complex, [MnIII(L1)Cl(H2O)]·H2O (1), and a tetranuclear Zn(II)–Mn(II) complex, [{ZnII2(L2)2Cl2}MnII2(μ1,1-N3)2(H2O)2]·2H2O (2), have been synthesized involving azo Schiff base ligands, viz. H2L1 = (E)-6,6′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxy-4-((E)-p-tolyldiazenyl)phenol) and H2L2 = (E)-6,6′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxy-4-((E)-p-tolyldiazenyl)phenol), respectively. The solid-state structures were determined by single crystal X-ray crystallography. In complex 1, the Mn(III) centre adopts slightly distorted octahedral geometry, while in complex 2 the Mn(II) centre residing in the outer core of the ligand adopts a distorted pentagonal bipyramidal geometry. In complex 1, the chloride ion simply acts as a terminal coligand, while in complex 2, azide ions bind the metal centres in an end-on bridging fashion to produce a tetranuclear complex. The phenoxazinone synthase-like activity of both complexes has been examined and a detailed investigation of the structure–property correlation has been performed. Whereas the mononuclear complex 1 exhibits significant phenoxazinone activity, complex 2 is almost inactive, although in both complexes labile sites are available at manganese centres for substrate binding. The present work therefore highlights the importance of higher oxidation states of manganese over nuclearity for the development of better in vitro catalysts. In addition, extensive efforts have been made to visualize and quantify all supramolecular interactions present in 1 and 2.

[RuIII(EDTA)(H2O)]− mediated oxidation of cellular thiols by HSO5−

The [RuIII(EDTA)(H2O)]− (EDTA4− = ethylenediaminetetraacetate) complex is shown to mediate the oxidation of thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, and penicillamine), with peroxomonosulfate ion (HSO5−). The kinetics of the catalytic oxidation process were studied using stopped-flow and rapid scan spectrophotometry as a function of [RuIII(EDTA)(H2O)−], [HSO5−], and [RSH] at a constant pH (6.2). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with the [RuIII(EDTA)] catalyst complex to form [RuIII(EDTA)(SR)]2− intermediate species. In a subsequent step the HSO5− ion reacts directly with the coordinated S-atom of [RuIII(EDTA)(SR)]2− yielding the disulfido species, RSSR, as a major oxidation product (as identified using HPLC and ESI-MS analyses) under the employed conditions. Based on the experimental data, a working mechanism is proposed for the [RuIII(EDTA)] catalyzed oxidation of thiols.