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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...

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.

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.

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.

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.