Rajat Saha

A Multifunctional Porous Organic Schottky Barrier Diode

Mesoporous materials: A multifunctional porous organic material (ANPPIT; see picture) has been synthesized and characterized. Multifunctionality of the compound has been determined from nitrogen adsorption, guest-dependent luminescence, and electrical conductivity measurements.

Synthesis, crystal structure, DNA interaction and in vitro anticancer activity of a Cu(II) complex of purpurin: dual poison for human DNA topoisomerase I and II

Although generation of reactive oxygen species (ROS) by anthracycline anticancer drugs is essential for anti-tumor activity, they make these drugs cardiotoxic. Metal–anthracyclines that generate relatively fewer ROS are however, effective antitumor agents. Purpurin (LH3), a hydroxy-9,10-anthraquinone, closely resembles doxorubicin, an established anthracycline drug. This molecule was chosen to study the extent to which simpler analogues are effective. A Cu(II) complex of LH3 [Cu(II)–(LH2)2] was synthesized to mimic the metal–anthracycline complexes. The crystal structure of [Cu(II)–(LH2)2] was determined by Rietveld refinement of PXRD data using an appropriate structural model developed on the basis of spectroscopic data. This is the first report on the crystal structure of any hydroxy-9,10-anthraquinone with a 3d-transition metal ion. The bond lengths and bond angles obtained by structural refinement corroborate those calculated by the DFT method. DNA binding of the complex was slightly better than purpurin. However, more importantly, unlike purpurin, binding constant values did not decrease with increasing pH of the medium. DNA relaxation assays show Cu(II)–(LH2)2 as a novel potent dual inhibitor of human DNA topoisomerase I and topoisomerase II enzymes. Cu(II)–(LH2)2 stabilizes covalent topoisomerase–DNA adducts both in vitro and within cancer cells. The cleavage assay keeps the complex well ahead of LH3 with regard to efficacy. These results paralleled those of cell growth inhibition and showed that the complex was more effective in killing ALL MOLT-4 cells than LH3, suggesting it targets topoisomerase enzymes within cells. The NADH dehydrogenase assay revealed further that the generation of superoxide was less in the case of the complex as compared to LH3.

Two unusual mixed-valent trinuclear CuII2CuI complexes containing copper(I) tribromide dianion as bridging ligand: Identification of an unprecedented doubly hydrogen-bonded water dimer

Two very rare mixed-valent CuII2CuI trinuclear complexes, [Cu2(Br–L1)2CuBr3]·2H2O (1) and [Cu2(L2)2CuBr3]·2CH3OH (2) have been synthesized using CuBr2 and the tridentate reduced Schiff-base ligands HL1 (2-[(2-dimethylamino-ethylamino)-methyl]-phenol) and HL2 (2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol), respectively. The complexes have been characterized by X-ray structural analyses. In both complexes, the deprotonated tridentate reduced Schiff base forms a di-μ-phenoxo bridge between the two CuII centers and the CuBr32− anion acts as an additional bridge between them to result in the trinuclear structures. During complex formation, ligand HL1 has been brominated at the five position of the aromatic ring but HL2 did not undergo any such reaction. In complex 1 an unprecedented doubly hydrogen-bonded water dimer, which is considered as an important transition state for the interchange of hydrogen atoms within the water dimer, has been identified. The dimensions of this water dimer agree quite well to those obtained from theoretical calculations.

Reusable amine-based structural motifs for green house gas (CO2) fixation.

A series of compounds with an amine based structural motif (ASM) have been synthesized for efficient atmospheric CO(2) fixation. The H-bonded ASM-bicarbonate complexes were formed with an in situ generated HCO(3)(-) ion. The complexes have been characterized by IR, (13)C NMR, and X-ray single-crystal structural analysis. ASM-bicarbonate salts have been converted to pure ASMs in quantitative yield under mild conditions for recycling processes.

An efficient size-selective anion binding cleft-shaped receptor: A novel [F2(H2O)3]2− cluster with pseudo-encapsulated F− ion

A cleft-shaped receptor 1 was synthesized and its anion binding properties have been investigated. Receptor 1 can selectively recognize fluoride ion by naked-eye color change and UV-vis spectral changes in aqueous-acetonitrile solvent. The single crystal X-ray analysis of 1 with fluoride ion shows that there are two types of fluoride ions in the unit cell, one of which is pseudoencapsulated within the cleft-shaped cavity and the other type forms a dimer through [F2(H2O)3]2−fluoride-water cluster.

A pharmaceutical cocrystal with potential anticancer activity

The design of pharmaceutical cocrystals has become a prime thrust of crystal engineering and the pharmaceutical industry in recent times – but the use of pharmaceutical cocrystals as regular drugs is yet to be explored. Quinoxaline acts as a basic skeleton of several potential anticancer drugs. We have successfully cocrystallized quinoxaline with another organic molecule 3-thiosemicarbano-butan-2-one-oxime (TSBO, a virus replication inhibitor) and examined the anticancer activity of the cocrystal. The crystal structure of the cocrystal was determined by single crystal X-diffraction study. According to thermogravimetric study the cocrystal exhibits better thermal stability than quinoxaline. UV-Vis spectroscopic study has shown that in solution state the behavior of the cocrystal and the physical mixture of its components (mixture of quinoxaline and TSBO) are significantly different. The solubility of the cocrystal in distilled water has been found to be 31.9 mg mL−1. The cocrystal exhibits a specific cytotoxic effect on lung cancer cells (A549) at 10−7 M concentration while it shows growth inhibitory effect on normal cells. The detailed mechanistic study of the cytotoxicity of the cocrystal suggests that it follows the mitochondrial mediated cell death pathway through activation of Caspase 9 and Bax. It also shows anticancer activity on breast cancer cells (MCF-7).

Synthesis, crystal structure, and antibacterial activity of two new mononuclear nickel(II) complexes of a NNS Schiff base

Two new mononuclear nickel(II) complexes, [Ni(L)(N3)] (1) and [Ni(L)2(NCS)2] (2), where HL = 2-{[phenyl(pyridin-2-yl)methylidene]amino}benzenethiol, a tridentate Schiff base derived from 2-aminothiophenol and 2-benzoylpyridine, have been prepared and characterized. The syntheses of 1 and 2 have been achieved by the reaction of equimolar amounts of nickel perchlorate and HL in the presence of azide and thiocyanate, respectively. The complexes have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction, and other physicochemical studies. Structural studies reveal that 1 and 2 adopt two different geometries, distorted square planar in 1 and octahedral in 2. The two mononuclear complex units are held together by π…π or C–H…π weak intermolecular interactions to develop supramolecular networks in their solid states. The antibacterial activity of 1, 2 and their constituent Schiff base has been tested against some gram(+) and gram(−) bacteria. Graphical Abstract

Co-crystals of 2,3-Dimethylquinoxaline (DMQ) and Dimethylglyoxime (DMG) in 1:1 and 1:2 Ratios and Hirshfeld Surface Analysis

Two co-crystals of 2,3-dimethylquinoxaline (DMQ) and dimethylglyoxime (DMG) have been synthesized and characterized by single crystallographic X-ray, IR and thermal studies. Co-crystal I is colorless while co-crystal II is orange in color. In the co-crystals, both hydrogen-bonding and π··· interactions assemble both DMQ and DMG within the crystal structure. For co-crystal I, 2D supramolecular sheet structure is formed by utilizing both hydrogen bonding and π··· interactions, while for co-crystal II supramolecular 1D chain motifs are formed by O–H···N hydrogen bonding interactions which are held together by C–H···O interactions to form 2D supramolecular network. These 2D supramolecular networks are further stacked by π···π and C–H···π interactions of aromatic rings of DMQ leading to the formation of 3D supramolecular structure. Examination of the intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that most of the close contacts are associated with weak interactions. The fingerprint plots indicate that these weak interactions have significant role in crystal packing. Thermogravimetric analyses of the co-crystals have been carried out.Graphical AbstractTwo concomitant co-crystals of active pharmaceutical ingredients (API) 2,3-dimethylquinaxoline (DMQ) and co-crystallizing agent dimethylglyoxime (DMG) have been synthesized and characterized by X-ray crystal structure, IR analysis along with their detailed Hirshfeld surfaces analyses.

Selective picomolar level fluorometric sensing of the Cr(VI)-oxoanion in a water medium by a novel metal–organic complex

A novel metal–organic complex (MOC) of Cu(II) with n-butylmalonate ligands and protonated 2-aminopyridimium rings has been synthesized and structurally characterized by single-crystal X-ray diffraction. An intriguing supramolecular interaction i.e. hydrogen-bonding pattern (like N–H⋯O and O–H⋯O) assisted lone-pair⋯π/π⋯π assembly is observed in the crystalline form of the MOC. The role of different non-covalent contacts in the formation of the MOC in the solid-state has also been scrutinized through Hirshfeld Surface Analysis. The luminescence properties of the MOC in the water solution were also experimentally investigated. The aqueous solution of the MOC acts as a selective picomolar level fluorescent sensor for Cr(VI)-oxoanion in water medium. Even the presence of several other cations like Li+, Na+, K+, Ca2+, Mg2+, Fe2+, Co2+, Ni2+, Cd2+, Hg2+, Zn2+, another chromium source like Cr3+ and versatile anions including F−, Cl−, Br−, SO42−, N3−, NO3−, BF4−, ClO4−, AsO33−, PO43− do not interfere with the picomolar level Cr(VI)-oxoanion sensing ability of the MOC in water medium. The probable sensing mechanism of the Cr(VI)-oxoanion by the MOC has been investigated experimentally and theoretically.

A new multicomponent salt of imidazole and tetrabromoterepthalic acid: structural, optical, thermal, electrical transport properties and antibacterial activity along with Hirshfeld surface analysis.

Herein, we report the structural, optical, thermal and electrical transport properties of a new multicomponent salt (TBTA(2-))·2(IM(+))·(water) [TBTA-IM] of tetrabromoterepthalic acid (TBTA) with imidazole (IM). The crystal structure of TBTA-IM is determined by both the single crystal and powder X-ray diffraction techniques. The structural analysis has revealed that the supramolecular charge assisted O(-)⋯HN(+) hydrogen bonding and Br⋯π interactions play the most vital role in formation of this multicomponent supramolecular assembly. The Hirshfeld surface analysis has been carried out to investigate supramolecular interactions and associated 2D fingerprint plots reveal the relative contribution of these interactions in the crystal structure quantitatively. According to theoretical analysis the HOMO-LUMO energy gap of the salt is 2.92 eV. The salt has been characterized by IR, UV-vis and photoluminescence spectroscopic studies. It shows direct optical transition with band gaps of 4.1 eV, which indicates that the salt is insulating in nature. The photoluminescence spectrum of the salt is significantly different from that of TBTA. Further, a comparative study on the antibacterial activity of the salt with respect to imidazole, Gatifloxacin and Ciprofloxacin has been performed. Moreover, the current-voltage (I-V) characteristic of ITO/TBTA-IM/Al sandwich structure exhibits good rectifying property and the electron tunneling process governs the electrical transport mechanism of the device.