Anindita Chakraborty

A Heterometallic (NiII–CuII) Decanuclear Cluster Containing Two Distorted Cubane-like Pentanuclear Cores: Synthesis, Structure, and Magnetic Properties

A new heterometallic Ni(II)-Cu(II) decanuclear cluster, {[Ni(4)Cu(6)(μ-OH(2))(2)(dpkO(2))(8)(OAc)(4)(H(2)O)(4)]·2CH(3)OH·17H(2)O} (1), has been synthesized by self-assembly of the constituent metal ions and the precursor di-2-pyridylketone (dpk) of multinucleating ligand dpkO(2)(2-) and is structurally characterized. The cluster 1 is formed by the union of two symmetry-related distorted cubane-like pentanuclear cores. A magnetic study of 1 reveals strong antiferromagnetic interactions operating through the Ni-O-Ni pathway, which is independent of the assumption D = 0 or D ≠ 0. The pentanuclear cores are ferromagnetically coupled, as supported by density functional theory calculations.

Discrete dinuclear complex to extended 2D compound in a Cu–azido system by controlling coligand stoichiometry: synthesis and magneto-structural correlations

This article describes syntheses, structural characterizations and magnetic studies of two different Cu(II)-azido compounds, a discrete dinuclear complex and an extended 2D network. The compounds, [Cu(μ(1,1)-N3)(N3)(Me2en)]2 (1) and [Cu3(μ(1,1,1)-N3)2(μ(1,1,3)-N3)(μ(1,1)-N3)2(μ(1,3)-N3)(Me2en)]n (2), have been synthesized by controlling the relative concentration of the blocking ligand, N,N-dimethylethylenediamine (Me2en). Compound 1 is a dinuclear compound which is formed by a doubly asymmetric μ(1,1)-N3 bridging ligand, while 2 is a rare Cu-azido system where four different types of binding modes of azide ligands are present in a single compound. Compound 2 contains a hexanuclear core, where the Cu(II) centres are connected to each other by μ(1,1,1), μ(1,1) and μ(1,1,3) bridging azide ligands. The hexanuclear core acts as a secondary building block and further assembles via μ(1,3) and μ(1,1,3) azide groups, forming a 2D network in the crystallographic ac plane. Interestingly, temperature-dependent magnetic study suggests that the dinuclear compound 1 exhibits an antiferromagnetic interaction through the μ(1,1)-N3 bridge, which has also been supported by density functional theory (DFT) calculations. In the case of 2, an overall dominant ferromagnetic interaction is observed while antiferromagnetic interaction operates between the hexanuclear cores.

Naringin inhibits gamma radiation-induced oxidative DNA damage and inflammation, by modulating p53 and NF-κB signaling pathways in murine splenocytes

Abstract The adverse effects of ionizing radiation occur due to the generation of reactive oxygen species (ROS). The aim of this study was to identify the protective effects of naringin (NG), a citrus flavonoid, on ionizing radiation (IR)-induced differential stress response, with an exploration of the mechanisms involved in this process. Isolated murine splenocytes were incubated in the presence and in the absence of different concentrations of NG (50 and 100 μM) for 1 h prior to 6 Gy γ-irradiation, and the molecular mechanisms of action were determined through biochemical, immunoblot, flow cytometric, and immunofluorescence studies. Pretreatment with NG significantly prevented IR-induced intracellular ROS generation, thereby preventing the formation of cellular TBARS and the development of cellular nitrite. NG significantly reduced nuclear DNA damage with respect to the irradiated splenocytes, through the inhibition of DNA-PKcs and p-γH2AX. The reduced cell viability as a result of irradiation was recovered by NG through modulation of the redox-regulated cell signaling system. NG pretreatment resulted in significant inhibition of IR-induced G1/S phase cell cycle arrest through the modulation of p53-dependent p21/WAF1, cyclin E, and CDK2 activation. The results also demonstrated that NG blocked the IR-induced p38 function and reversed IR-mediated differential stress response through inhibition of the NF-κB pathway. Thus, the p38/NF-κB pathway participated in the IR-induced inflammatory development, leading to upregulation of CRP, MCP-1, and iNOS2 gene expression. However, NG pretreatment reversed the inflammatory development through downregulation of NF-κB, and regulated the expression of CRP, MCP-1, and iNOS2. The above results provide a theoretical basis for the preventive use of NG against radiation-induced multiple cellular anomalies.

MOF–aminoclay composites for superior CO2 capture, separation and enhanced catalytic activity in chemical fixation of CO2

We delineate the growth and stabilization of ultra-small (2-3 nm) {Cu3(BTC)2(H2O)2·xH2O} MOF nanoparticles on a 2D layered aminoclay template. The composite shows significant CO2 uptake (5.35 mmol g-1 at 298 K, 1 bar; 46% higher than pristine bulk MOF), superior CO2 separation efficiency from CO2/N2 and CO2/CH4 mixtures and higher catalytic proficiency for chemical fixation of CO2 into cyclic carbonates.

Structural and Magnetic Diversity Based on Different Imidazolate Linkers in Cu(II)-Azido Coordination Compounds

This Article reports the syntheses, structural characterization, and magnetic studies of four different Cu(II)-azido compounds based on imidazole or substituted imidazole ligand. The compounds, [Cu2(μ1,1-N3)2(EtimiH)4(ClO4)2] (1) (EtimiH = 2-ethylimidazole), [Cu2(μ-Meimi(-))(MeimiH)2(μ1,1-N3)2(μ1,3-N3)]n (2) (MeimiH = 2-methylimidazole; μ-Meimi(-) is the bridging mononegative anion of 2-methylimidazole), [Cu2(μ-imi(-))(imiH)2(μ1,1-N3)2(μ1,3-N3)]n (3), and [{Cu2(μ1,1-N3)2(μ1,3-N3)(μ-imi(-))(imiH)3}·H2O]n (4) (imiH = imidazole; μ-imi(-) = bridging mononegative anion of imidazole), have been synthesized by the self-assembly of Cu(II) salts, azide ion, and the corresponding imidazole bridging ligands. By changing the substitution on the second linker (imidazole or substituted imidazole) and varying synthetic conditions, diverse structural and magnetic features have been achieved in compounds 1-4. Compound 1 has a double end-on azido bridged dinuclear core, while the other compounds (2-4) have 2D networks. Compound 2 and 3 contain 1D chains with alternate μ1,1-N3 and μ-Meimi(-) bridging, and such chains are further connected through a μ1,3-N3 bridge to result in the formation of the 2D network. Compound 4 is a novel 2D coordination polymer consisting of a zigzag 1D coordination chain having (μ1,1-N3)2, μ-imi(-), and (μ1,3-N3)2 bridging groups and the chains undergo bridging through a μ1,3-N3 group resulting in the 2D network. Temperature dependent magnetic measurements show diverse magnetic properties of 1-4. Such versatile magnetic behaviors have been correlated to the respective bridging mode of azide and the corresponding imidazole bridging ligands.

Flexible MOF–aminoclay nanocomposites showing tunable stepwise/gated sorption for C2H2, CO2 and separation for CO2/N2 and CO2/CH4

Miniaturization of flexible metal–organic frameworks (F-MOFs) to nanoscale is expected to show interesting structural dynamics and serve numerous applications from separation and drug delivery to sensing. However, nanoscale F-MOFs or their composites have remained largely unexplored to date. Here, we present a new and facile method to stabilize F-MOF nanocrystals on an aminoclay (AC) template and study their tunable, enhanced gas adsorption and separation properties. We demonstrate miniaturization of two different 2D F-MOFs, {[Cu(pyrdc)(bpp)](5H2O)}n (F-MOF1) with a pillared-bilayer structure and {[Cu(dhbc)2(4,4′-bpy)]·H2O} (F-MOF2) with an interdigitated network, on AC that acts as a functional template to grow and stabilize MOF nanocrystals. Different F-MOF1@AC composites were synthesized where the gate/step pressure for specific adsorbate molecules (CO2/C2H2) could be tuned by varying the AC content. Enhanced guest adsorption with stepwise behaviour has also been realized in a certain composite. Breakthrough column experiments with the F-MOF2@AC composite show its capability to separate CO2/N2 and CO2/CH4 gas mixtures under ambient conditions.

Mg-MOF-74@SBA-15 hybrids: Synthesis, characterization, and adsorption properties

Nanocrystals of Mg-MOF-74 have been immobilized into the mesopores of SBA-15 rods to fabricate Mg-MOF-74@SBA-15 hybrid materials. To furnish such composites, a relatively simple synthetic strategy has been adopted by direct dispersion of the metal-organic framework (MOF) precursors in SBA-15 matrix to prepare the hybrid materials in situ. The hybrid materials have been characterized using powder X-ray diffraction and several spectroscopic and microscopic techniques, which suggest growth of the MOF nanocrystals inside the SBA-15 mesopores and the composites exhibit characteristics of both the components. N2 adsorption isotherms at 77 K reveal that the composites contain additional mesopores, compared to only micropores of pristine MOF nanocrystals. In addition to such combination of both micro and mesoporosity, the composites also demonstrate significant CO2 adsorption at room temperature.

A hexanuclear Cu(I) cluster supported by cuprophilic interaction: effects of aromatics on luminescence properties

A hexanuclear Cu(I) cluster {Cu3(L)2}2 (1) based on a novel tripodal linker (L) has been synthesized. 1 shows intense emission (λmax = 560 nm) with lifetime 〈τ〉 = 224 μs and quantum yield = 27.6%. The emission is highly sensitive towards different electron rich and electron deficient aromatics. DFT calculations were performed to understand the origin of emission and sensing properties.

Naringin ameliorates radiation-induced hepatic damage through modulation of Nrf2 and NF-κB pathways

Understanding the mechanism of ionizing radiation (IR)-induced systemic stress and its modulation by phytocomponents has great significance for the development of novel phyto-radioprotectors. The present study was intended to evaluate the radioprotective effect of naringin (NG), a citrus flavonoid on the modulation of IR-induced activation of the redox-regulated signaling system in murine liver. On the basis of survival analysis, mice were treated with 75 mg kg−1 body weight of NG for three consecutive days before irradiation (6 Gy). Pretreatment with NG significantly prevented the IR-induced generation of intracellular reactive oxygen species (ROS), along with the formation of hepatic thiobarbituric acid reactive substances (TBARS) and cellular nitrite. NG also showed significant reduction in IR-induced nuclear DNA damage through the inhibition of DNA-dependent protein kinase (DNA-PK). Further, the IR-induced cell death was arrested in the presence of NG through the inhibition of p53 mediated stress-activated protein kinase/Jun amino-terminal kinase (SAPK/JNK) pathways and modulation of other molecules of apoptosis pathways. Moreover, NG supported the intracellular defense mechanisms, by maintaining the endogenous antioxidants probably through phosphoinositide 3-kinase/protein kinase-B (PI3K/Akt) guided transcriptional activation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In addition, NG inhibited IR-induced inflammation through suppression of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) followed by the alteration of pro inflammatory factors. Taken together, these results suggested that NG reversed the IR-induced redox-imbalance in murine liver, probably by the inhibition of ROS/p38-MAPK/NF-κB, along with the activation of the PI3K/Akt/Nrf2 pathway and the reduction of apoptosis by interfering with the p53/SAPK/JNK/Bax pathway.

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).