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Seawater splitting remain far-fetched due to interference of corrosive chlorine evolution reaction at anode. The lowering of overpotential with the help of effective electrocatalyst is one way to deal with...

A new supramolecular metal-organic complex 1, [{Ho(H2O)8}4+(TBTA)(bipy)] (where H2TBTA = tetrabromoterephthalic acid and bipy = 4,4'-bipyridyl), has been synthesized hydrothermally at 100 °C by mixing the reactants in stoichiometric ratio. The complex was characterized by single crystal X-ray diffraction (SC-XRD) along with powder X-ray diffraction (PXRD) and other spectroscopic analyses. Structural analysis reveals that 1 crystallized in the tetragonal space group I4cm and is a mononuclear complex. Ho4+ presents octa-coordinated square antiprism geometry having eight coordinated water molecules. Hydrogen bonding interactions between the coordinated water molecules and carboxylate oxygen atoms of TBTA (doubly deprotonated form of H2TBTA) anions form 3D supramolecular metal-organic host (MOSH) having 2D square grid-like supramolecular channels. Guest bipy molecules get stability within the channels through supramolecular π···π interactions between the bipy and TBTA anions. Hirshfeld surface analysis and corresponding 2D fingerprint plots correlate with the experimental findings. C···C short contact, corresponding to π···π interactions, contributes around 10.7% to the total surface.

Herein, we have presented the crystal structure, supramolecular structure and band structure along with dielectric, electrical transport and optoelectronic properties of a [Mg(H2O)6]2+ templated 3D hydrogen bonded supramolecular framework (HSF) {[Co(2,5-Pdc)2,(H2O)2]2−·[Mg(H2O)6]2+·4(H2O)} (where 2,5-pdc = 2,5-pyridinedicarboxylate) synthesized by reflux method. The complex crystallizes in the P space group. The 3D network of the complex has been built up by hydrogen bonding interactions between 2D supramolecular sheets of the complex. The proton conductivity and activation energy of the complex are ∼10−4 S cm−1 at 40 °C and ∼0.3 eV, respectively, under vacuum. It exhibits anomalous dielectric behavior due to the gradual release of guest water molecules above 40 °C. The complex is a semiconductor with a band gap of 1.626 eV and is capable of absorbing electromagnetic radiation in the range of 355–730 nm. The ITO/complex/Al sandwiched device exhibits Schottky barrier diode (SBD)-like behaviour with a rectification ratio of 13 in the dark and 34 under visible light at 1 V. When exposed to visible light (AM 1.5G) the value of its conductivity enhances 1.35 times, compared to that in the dark. It has been shown that the complex is a semiconducting proton conducting photoresponsive HSF.

Herein, we report the crystal structure, supramolecular structure, electronic transport properties and optoelectronic behaviour of a co-crystal made of tetrabromoterephthalic acid (TBTA) and quinoxaline (QUIN) (1 : 1). The sample has been characterized using thermogravimetric analysis and spectral techniques. Moreover, theoretical analyses of noncovalent interactions, optical properties and the band structure of the co-crystal have been performed. The co-crystal has been crystallized in an orthorhombic system with the Pnma space group and the constituent molecules assemble in the solid state by using O–H⋯N hydrogen bonding, π⋯π, Br⋯π and Br⋯O interactions. The ground state geometry optimization over the hydrogen bonded dimer by DFT method indicates that TBTA acts as the donor and QUIN as the acceptor within the self-assembled co-crystal. According to UV-vis spectroscopic study the bandgap of the co-crystal is ∼3.18 eV. In the solid state it exhibits a broad emission band with a maximum at 405 nm while in aqueous medium its photoluminescence emission peaks are obtained at 350 and 403 nm. The values of the average fluorescence lifetime of the sample in aqueous medium are 3.38 ns at 352 nm and 4.94 ns at 403 nm. Under UV-irradiation, the co-crystal emits violet-blue light. The emission spectrum in solution phase shows a relative quantum yield of 0.018. Band structure calculation indicates that the co-crystal is a p-type semiconductor with a bandgap of 2.835 eV. Due to its semiconducting character, the ITO/co-crystal/Al sandwiched structured device acts as a Schottky barrier diode with rectification ratio, ideality factor, barrier height and series resistance of 41, 1.36, 0.70 eV, and 26.97 kΩ, respectively. The current through the device increases substantially under visible light exposure. Upon visible light illumination the values of electrical conductivity, mobility and carrier concentration increase by 35 (±0.5), 54 (±0.5) and 6 (±0.5)%, respectively, with respect to dark conditions. It has been shown that π⋯π and hydrogen bonding interactions can play a crucial role in producing the donor–acceptor (D–A) type co-crystal, semiconducting behaviour can be incorporated in the organic co-crystal utilizing π⋯π and hydrogen bonding interactions and weak intermolecular π⋯π, Br⋯π and Br⋯O interactions can act as the pathway for electrical conduction.

Metal–ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare...

The rational design of organic opto-electronic materials has been one of the prime focuses in recent times, and halogen interactions have become a major tool in crystal engineering to design multi-component organic co-crystals/salts. Tetrabromoterephthalic acid (TBTA), which is able to participate in both hydrogen bonding and halogen bonding, has been used as a co-crystallizing agent to synthesize four different organic co-crystals/salts, TBTA-3-bromopyridine (co-crystal I), TBTA·TBTA2−-2(2-aminopyridine+)·2H2O (co-crystal salt II), TBTA−-4-aminopyridine+·H2O (salt III) and TBTA·TBTA2−-2(nicotinamide+)·2H2O (co-crystal salt IV), by a conventional solvent evaporation method. These compounds were characterized by single-crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD) and spectral and thermal studies. Molecular and supramolecular structural analyses reveal that TBTA interacts with the pyridyl-containing co-formers through hydrogen bonding and exploits several types of halogen bonding (Br⋯O, Br⋯H, Br⋯Br, Br⋯π interactions etc.) and π⋯π interactions to assemble in the solid state. TBTA utilizes Br⋯π interactions to assemble with other co-formers while it utilizes Br⋯O interactions and preferably type I Br⋯Br interactions to assemble with each other in these co-crystals/salts. The supramolecular behaviour of TBTA within these co-crystals/salts analyzed by Hirshfeld surface analysis and associated 2D fingerprint plots also corroborates the crystallographic supramolecular structural patterns. Theoretical analysis has been carried out for geometry optimization and bandgap calculations which were then compared with the optical bandgap values. Charge-separated hydrogen bonding and π⋯ interactions (Br⋯π and π⋯π interactions) have a significant impact on the optical and electrical properties of these samples. Solid-state luminescence studies reveal that all compounds show a blue shift. Electrical conductivity measurements on the ITO/sample/Al sandwich structures of these supramolecular complexes reveal Schottky barrier diode behaviour and photoresponsivity under illumination.

A monomeric complex of ZnII with ornidazole [Zn(Onz)2Cl2] decreases formation of the nitro-radical anion (R–NO2˙−), and this is realized by recording it in an enzyme assay using xanthine oxidase, which is a model nitro-reductase. Although the formation of R–NO2˙− is essential for drug action, as it is also associated with neurotoxic side effects, it is imperative to control its generation in order to avoid excess presence. With a decrease in R–NO2˙−, while the neurotoxic side effects should decrease, it can be expected that a compromise with regard to therapeutic efficacy will be seen since the complex will be less active in the free radical pathway. Since R–NO2˙− is crucial for the functioning of 5-nitroimidazoles, we attempted to find out if its biological activity is affected in any way in our effort to control its formation. For this purpose, Entamoeba histolytica (HM1:IMS Strain) was chosen as a biological target to realize the performance of the complex with respect to ornidazole (R–NO2). The experiments revealed that the complex not only compares well with ornidazole, but in fact, under longer exposure times, it also performs better than it. This efficacy of the complex was seen despite a decrease in R–NO2˙−, as identified by an enzyme assay, and this was probably due to certain attributes of the complex formation that are not known for ornidazole. These attributes outweigh any loss in efficacy in the free radical pathway following complex formation. This is certainly an advantage of complex formation and helps to improve the therapeutic index. This study has attempted to look at some of the possible reasons why the complex performs better than ornidazole. One reason is its ability to bind to DNA better than ornidazole does, and this can be understood by following the interaction of ornidazole and its Zn(II) complex with calf-thymus DNA using cyclic voltammetry. Therefore, this study showed that despite a decrease in R–NO2˙−, the complex does not compromise its efficacy, and this was examined using a biological target. In addition, the complex is likely to have less toxic side effects on the host of the disease-causing microbes.

Herein, we report the molecular and supramolecular structure, photoluminescence, redox behavior and product selective catalytic activity of [Cu2(oxalate)(1,10-phen)2Cl2] (where 1,10-phen = 1,10-phenanthroline) synthesized by using hydrophilic oxalate as bridging ligand and the hydrophobic 1,10-phen as the blocker ligand. Structural analysis reveals that this binuclear Cu(II)-complex crystallizes in achiral monoclinic P21/n space group and it has a 3D supramolecular structure. Each Cu-center displays five coordinated distorted square pyramidal geometry. Two such Cu centers are connected by oxalato-bridge to form the bi-nuclear-metal core and two 1,10-phen molecules block the outer periphery of the core and restrains further polymerization. These binuclear metallic units are connected by supramolecular hydrogen bonding and π⋯π interactions to form a 3D supramolecular architecture. The complex is stable up to 230 °C. A reversible redox couple centered at (E1/2) ∼ −27 mV with ΔEp ∼ 206 mV corresponding to the CuII/I couple was detected in the cyclic voltammogram of the complex in acetonitrile. The complex shows emission maxima at 451 and 480 nm upon excitation at 340 nm due to π-π* transition in the aromatic π-rings of 1,10-phenanthroline. Density functional analysis has been performed to explore the molecular structure and character of the orbitals within the complex. Due to the presence of five coordinated Cu-centers, the lewis acidic catalytic activity of the complex has been studied. It exhibits selective oxidation behavior for alkenes in presence of several oxidants. It shows 100% selectivity with 70% conversion for the oxidation of cis-cyclooctene to corresponding epoxide at 50 °C in presence of H2O2 as oxidant in acetonitrile.

Metal-ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare example where metal-ligand bonds dissociate in an irreversible way, helped by a large number of weak intermolecular interactions that surpass the energy of the metal-ligand bond. Thus, we describe the design and synthesis of trinuclear Mn

A monomeric complex of Zn

Quinalizarin (THAQ), a hydroxy-9,10-anthraquinone analogue of the family of anthracycline anticancer drugs and an inhibitor of protein kinase, was observed for its anticancer activity. Because apart from showing anticancer activity, anthracyclines and their analogues also show cardiotoxic side effects, believed to be addressed through metal complex formation; an effort was made to realize this by preparing a CoII complex of THAQ. The aim of this study was to find out if complex formation leads to a decrease in the generation of intermediates that are responsible for toxic side effects. However, because this also meant that efficacy on cancer cells would be compromised, studies were undertaken on two cancer cell lines, namely, acute lymphoblastic leukemia (ALL) MOLT-4 and HCT116 cells. The complex decreases the flow of electrons from NADH to molecular oxygen (O2) in the presence of NADH dehydrogenase forming less semiquinone than THAQ. It showed increased affinity toward DNA with binding constant values remaining constant over the physiological pH range unlike THAQ (for which decrease in binding constant values with increase in pH was observed). The complex is probably a human DNA topoisomerase I and human DNA topoisomerase II poison acting by stabilizing the covalent topoisomerase-cleaved DNA adduct, a phenomenon not observed for THAQ. Activity of the compounds on cancer cells suggests that THAQ was more effective on ALL MOLT-4 cells, whereas the complex performed better on HCT116 cells. Results suggest that the formation of semiquinone probably dominates the action because of THAQ, whereas the performance of the complex is attributed to increased DNA binding, inhibition of topoisomerase, and so forth. Inspite of a decrease in the generation of superoxide by the complex, it did not hamper efficacy on either cell line, probably compensated by improved DNA binding and inhibition of topoisomerase enzymes which are positive attributes of complex formation. A decrease in superoxide formation suggests that the complex could be less cardiotoxic, thus increasing its therapeutic index.

The manipulation in crystal structure as well as electronic structure of material apart from the morphology play important role in determining electrocatalytic activity. Bismuth molybdate with its special layered structure in orthorhombic phase and hollow sphere morphology performed as potential electrocatalyst for oxygen evolution reaction in alkaline medium. The activity can further be enhanced by promoting iron in the crystal structure. The strain as well as dislocation developed in the crystal structure of Bi2MoO6 upon iron incorporation are well-studied. The presence of optimum amount of iron and thereby creating oxygen vacancies have been found to be beneficial, though higher concentration turns out to be detrimental for the electrocatalytic performance. The optimum iron promoted Bi2MoO6 leads to achieve overpotential value of 286 mV at 10 mA cm−2 current density with Tafel slope of only 44 mV dec-1 for OER. The experimental results are well-supported by the density functional theory simulations, which demonstrate that iron incorporation lowers the energy barrier by promoting the adsorptions of OER intermediates, most distinctly the oxygen adsorption.

Herein, we have reported the synthesis, crystal structure, thermogravimetric property, and photoluminescence activity of a new Cu-based metal organic framework (MOF): {[Cu2(2,5-pdc)2(ald-4)(H2O)2]·3H2O,MeOH}n (where 2,5-pdc = 2,5-pyridine-dicarboxylate, ald-4 = aldrithiol-4) along with catalytic activity of CuO nanoparticles (Cu-NPs) derived from the MOF for green synthesis of organic molecules having biological relevance. The regular arrangement of metal centers and the presence of oxygen and carbon in metal–organic frameworks (MOFs) enable us to utilize them as template/precursor for the synthesis of monodispersed metal-oxide and metal-carbide nanoparticles having a high surface area with well-defined and uniform morphology. The MOF derived oxide nanoparticles generally exhibit improved catalytic activities and product selectivity and significantly reduce the chemical waste production. The structural analysis has revealed that in the complex under investigation the 2,5-pdc bridges the Cu(II) centers to ...

Emodin, a hydroxy-9,10-anthraquinone, resembles anthracycline anticancer drugs at the core and possesses anticancer activities. A CuII complex of emodin [CuII(emod)2]2− was synthesized and its crystal structure was determined by Rietveld refinement of the PXRD data by using an appropriate structural model based on spectroscopy. This is the third report on the crystal structure of a hydroxy-9,10-anthraquinone with a 3d-transition metal ion. Since the formation of reactive oxygen species (ROS) by anthracycline-based anticancer drugs is important for antitumor activity and given the fact that the generation of ROS is responsible for cardiotoxic side effects, it is essential to be able to control their formation. Complex formation decreases ROS generation and could thereby lead to a decrease in cardiotoxic side effects. However, in an attempt to decrease complications, there is also the possibility of compromising the therapeutic efficacy. For this reason, the activities of emodin and its modified form [Cu(II) complex] were studied on the carcinoma cell lines HeLa and Hep G2 to see how they compared with each other in terms of performance. Studies were also performed on WI 38 lung fibroblast normal cells. The studies revealed that, in spite of the decreased ROS formation, followed by the DCFDA assay, the Cu(II) complex showed better activity on carcinoma cell lines. This suggests that the complex has other attributes that enable it to perform better than emodin. Consequently, one such attribute, namely DNA binding, was thoroughly investigated by varying the ionic strength and the temperature of the medium. It was found that the complex was able to bind DNA better than emodin, and, more importantly, since both generate a good amount of anionic species in solution under increased ionic strength of the medium, both bind DNA better; the increase in binding with increase in ionic strength being higher for the complex. The study suggests that with a substantial decrease in ROS generation by the complex, there are likely to be less toxic side effects, which is a key advantage of the complex, leading to an improvement in the therapeutic index. The complex showed almost no activity on WI 38 normal cells.

An alkaline earth metal ion based bi-functional metal-organic framework {[Mg(4,4′-bpdc)(H2O)3](H2O)}n (where 4,4′-bpdc = 4,4′-biphenyl dicarboxylate) has been synthesized by simply stirring the precursors in water. The framework crystallizes in orthorhombic Pbca space group. The metal nodes of the complex are bridged by dicarboxylates in μ3-fashion to form corrugated 2D coordination sheets. The neighbouring 2D sheets are further connected by hydrogen bonding interactions between the coordinated water molecules and the carboxylate oxygen atoms to form a 3D supramolecular structure. The small hydrophilic supramolecular pockets of the 3D supramolecular structure are filled by guest water molecules through hydrogen bonding interactions. The framework exhibits proton conductivity of 1.44 × 10−5 S m−1 at 303 K under vacuum and the proton transport in the framework follows the Grotthuss mechanism where the hydrogen bonded network acts as the proton transport pathway. The evacuated material, after removal of both coordinated and guest water molecules, retains its crystallinity but is not isostructural with the original framework. According to N2 adsorption study the BET surface area and the total pore volume of the evacuated material are 39 m2 g−1 and 0.133 cc g−1, respectively. The evacuated material can adsorb (175 cc g−1 at P/P0 ∼ 0.99) and store (154 cc g−1 at P/P0 = 0.1) a decent amount of water molecules.

In an attempt to overcome limitations of Curcumin from being an important molecule in biology and medicine, a monomeric complex of CuII [Cu(Cur)(OCOCH3)(H2O)] was prepared. Physico-chemical studies in solution using copper acetate and Curcumin indicate formation of a 1:2 CuII:Curcumin species. However, attempts to prepare it always led to the formation of a 1:1 CuII:Curcumin species, if CuII-acetate was used as the starting material. In the absence of a single crystal or an appropriate powder X ray diffraction data that would allow solving of the structure, it was arrived at by spectroscopy guided DFT calculations. Unlike Curcumin, the prepared complex was stable under physiological conditions, an advance achieved through complex formation. Effective binding of the complex to DNA with an ability to enhance cellular uptake owing to the presence of CuII are other benefits of complex formation that might increase its cytotoxic potential. The complex has a reasonably strong affinity for DNA realized from binding constant values obtained with calf thymus DNA at different temperatures in the range 25 °C–35 °C. This enabled an evaluation of thermodynamic parameters (ΔH, ΔS and ΔG), that helped in determining the mode of binding between the complex and DNA as realized from a correlation of thermodynamic signatures to binding types. The study may be considered a case of pseudo-binding of Curcumin to DNA since the complex containing a Curcumin bound the metal ion does not dissociate in solution under physiological conditions, i.e. remains as one unit. Hence binding of the complex to DNA is also the binding of Curcumin to it present as one “single unit”, a major advancement based on a biophysical approach. Besides, aspects like stability of the complex in solution, prevention of degradation of Curcumin in aqueous buffer or biological milieu, binding with mammalian DNA are other aspects that are significant for use of the complex on biological targets.

The formation of reactive oxygen species (ROS) by anthracycline anticancer drugs is essential for their antitumor activity but they also make these drugs cardiotoxic. When complexed with metal ions there is a decrease in ROS formation and therefore in cardiotoxicity. Interestingly, in spite of producing fewer ROS, some of the complexes are effective antitumor agents, often better than the parent anthracycline. Purpurin (LH3), a hydroxy-9,10-anthraquinone, resembles doxorubicin at the core. An MnII complex of LH3 [MnII(LH2)2] was synthesized to see the extent to which the complex resembles metal–anthracyclines with regard to structure and function. The crystal structure was determined by Rietveld refinement of PXRD data using an appropriate structural model developed on the basis of spectroscopic information. This is only the second report on the crystal structure of a hydroxy-9,10-anthraquinone with a 3d-transition metal ion. Bond lengths and bond angles were obtained by structural refinement. The structure is supported by DFT calculations. DNA binding of the complex is slightly better than for purpurin but more importantly unlike purpurin, the binding constant values remained constant even with an increase in the pH of the medium. The NADH dehydrogenase assay and the DCFDA-ROS generation assay showed that generation of superoxide in the former and ROS in general in the latter were significantly less for the complex than for purpurin. Even with decreased ROS formation, the complex is able to maintain the biological activity of purpurin.

Alizarin (DHA), a simple analogue of the anthracycline core was used to form a complex with MnII to see if the complex matches the efficacy of anthracyclines. It was characterized by spectroscopic techniques, mass spectrometry and TGA. In the absence of a single crystal, the structure was obtained by computational techniques. Interaction of the complex with DNA at different ionic strength and pH was compared with anthracyclines to see if it addresses some of the shortcomings of hydroxy-9,10-anthraqunones in general and DHA in particular when compared to anthracyclines. Increased affinity of the complex towards DNA and that its binding constant values do not decrease with increase in pH or decrease in ionic strength of the medium are positive attributes of complex formation. This is significant since cancer patients often experience fluctuation of pH and ionic strength in body fluids during treatment that affect efficacy of drugs. The complex decreases the flow of electrons from NADH to molecular oxygen owing to decreased semiquinone formation; a fact important for controlling cardiotoxicity. Experiments on ROS depletion in HeLa, Hep G2 and WI 38 lung fibroblast cells by the H2DCFDA assay suggests a shift in mechanism for the complex from that of DHA. Loss in efficacy due to decrease in semiquinone formation by the complex is made up by other attributes of complex formation that eventually promote cytotoxicity. Compounds were tried on HeLa, Hep G2 and WI 38 lung fibroblast cells. An effort was made to correlate aspects of semiquinone formation, ROS generation and interaction with DNA with results obtained on two cancer cell lines and a normal cell line.

Herein, we report the structural, optical, thermal and electrical transport properties of a new multicomponent salt (TBTA2−)·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−⋯H N+ 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.