Design, Synthesis, and Anticancer Studies of a p-Cymene-Ru(II)-Curcumin Organometallic Conjugate Based on a Fluorescent 4-Amino-1,8-naphthalimide Tröger's Base Scaffold.

A unique V-shaped "chiral" supramolecular scaffold, N-(4-pyridyl)-4-amino-1,8-naphthalimide Tröger's base (TBNap), was synthesized in good yield from a precursor N-(4-pyridyl)-4-amino-1,8-naphthalimide (Nap). TBNap was characterized using different spectroscopic methods and the molecular structure was elucidated by diffraction analysis. A new p-cymene-Ru(II)-curcumin conjugate (TB-Ru-Cur) was designed by reacting TBNap dipyridyl donor and ruthenium-curcuminato acceptor [RuCur = (p-cymene)Ru-(curcuminato)Cl] in the presence of silver triflate. TB-Ru-Cur was isolated in quantitative yield and characterized using Fourier transform infrared (FT-IR), NMR (1H, 13C, and 19F), and electrospray ionization mass spectrometry (ESI-MS), and the molecular structure has been predicted using a computational study. Both TBNap and TB-Ru-Cur exhibited intramolecular charge transfer (ICT)-based fluorescence emission. Furthermore, the anticancer properties of TBNap, Ru-Cur, and TB-Ru-Cur were assessed in different cancer cell lines. Gratifyingly, the conjugate TB-Ru-Cur displayed fast-cellular internalization and good cytotoxicity against HeLa, HCT-116, and HepG2 cancer cells and the estimated IC50 value was much lower than that of the precursors (TBNap and Ru-Cur) and the well-known chemotherapeutic drug cisplatin.

Noncovalent interaction of carbon nanostructures.

The potential application of carbon nanomaterials in biology and medicine increases the necessity to understand the nature of their interactions with living organisms and the environment. The primary forces of interaction at the nano-bio interface are mostly noncovalent in nature. Quantifying such interactions and identifying various factors that influence such interactions is a question of outstanding fundamental interest in academia and industry. In this Account, we have summarized our recent studies in understanding the noncovalent interactions of carbon nanostructures (CNSs), which were obtained by employing first-principles calculations on various model systems representing carbon nanotubes (CNTs) and graphene. Bestowed with an extended sp(2) carbon network, which is a common feature in all of these nanostructures, they exhibit π-π interactions with aromatic molecules (benzene, naphthalene, nucleobases, amino acids), cation-π type of interactions with metal ions, anion-π interactions with anions, and other XH···π type of interactions with various small molecules (H2O, NH3, CH4, H2, etc.). CNTs are wrapped-up forms of two-dimensional graphene, and hence, it is interesting to compare the binding abilities of these two allotropes that differ in their curvature. The chirality and curvature of CNSs appear to play a major role in determining the structural, energetic, and functional properties. Flat graphene shows stronger noncovalent interactions than the curved nanotubes toward various substrates. Understanding the interactions of CNSs with organic molecules and biomolecules has gained a great deal of research interest because of their potential applications in various fields. Aromatic hydrocarbons show a strong propensity to interact with CNSs via the π-π mode of interaction rather than CH···π interaction. As DNA sequencing appears to be one of the most important potential applications of carbon nanomaterials, the study of CNS-nucleobase interactions has become quite important. The nucleobases are physisorbed on the surface of CNSs in the order G > T ≈ A > C > U, exhibiting π-π-stacking type of interaction. These interactions become stronger as the curvature of the CNSs decreases. It is also indispensable to study the interaction of nanomaterials with proteins and especially with amino acids at a molecular level to understand the drug delivery mechanism of CNSs. We have shown that the CNSs interact with small molecules by means of physisorption and thus show potential for sensor applications. The prime requisite for the exploitation of these CNSs in nanoelectronics is the tunable energy gap. We have revealed that metal ion doping modulates the HOMO-LUMO energy gap of the nanotubes significantly and thus provides a handle to tune the electronic and conductivity properties of CNTs. Moreover, metal ions tend to selectively bind with nanotubes of different chirality such as armchair and zigzag nanotubes. The reduction of planar hydrocarbon materials by lithium atoms has also been studied very systematically. We also illustrate the way in which noncovalent interactions can be used to optimize and fine-tune the properties of CNSs.

Graphane versus graphene: a computational investigation of the interaction of nucleobases, aminoacids, heterocycles, small molecules (CO2, H2O, NH3, CH4, H2), metal ions and onium ions.

Graphane has emerged as a two-dimensional hydrocarbon with interesting physical properties and potential applications. Understanding the interaction of graphane with various molecules and ions is crucial to appreciate its potential applications. We investigated the interaction of nucleobases, aminoacids, saturated and unsaturated heterocycles, small molecules, metal ions and onium ions with graphane by using density functional theory calculations. The preferred orientations of these molecules and ions on the graphane surface have been analysed. The binding energies of graphane with these molecules have been compared with the corresponding binding energies of graphene. Our results reveal that graphane forms stable complexes with all the molecules and ions yet showing lesser binding affinity when compared to graphene. As an exemption, the preferential strong binding of H2O with graphane than graphene reveals the fact that graphane is more hydrophilic than graphene. Charge transfer between graphane and the molecules and ions have been found to be an important factor in determining the binding strength of the complexes. The effect of the interaction of these molecules and ions on the HOMO-LUMO energy gap of graphane has also been investigated.

Porous organic polymers-based fluorescent chemosensors for Fe(III) ions-a functional mimic of siderophores.

Extended organic polymers such as amorphous Covalent Organic Polymers (COPs) and crystalline Covalent Organic Frameworks (COFs) are emerging functional polymeric materials that have recently been shown promises as luminescent materials for chemosensing applications. A wide variety of luminescence COPs and COFs have been synthesized and successfully used as fluorescence-sensing materials for hazardous environmental pollutants and toxic contaminants. This review exemplifies various COPs and COFs-based fluorescence sensors for selective sensing of Fe(III) ions. The fluorescence sensors are sorted according to their structural features and each section provides a detailed discussion on the synthesis and fluorescence sensing ability of different COPs and COFs towards Fe(III) ions. Also, this review highlights the limitations of the existing organic polymer-based chemosensors and future perspectives on translating COPs and COFs-based fluorescence sensors for the practical detection of Fe(III) ions.

Impact of the chirality and curvature of carbon nanostructures on their interaction with aromatics and amino acids.

Understanding noncovalent interactions on the surfaces of carbon nanostructures (CNSs) is of fundamental importance and also has implications in nano- and biotechnology. The interactions of aromatic compounds such as benzene, naphthalene, and aromatic amino acids with CNSs of varying diameter, chirality, and curvature were systematically explored by using density functional theory. Planar graphene exhibits stronger binding affinity than curved carbon nanotubes (CNTs), whereas zigzag CNTs appear to show stronger binding affinity than armchair CNTs. For hydrocarbons, there exist two competing modes, namely, π-π stacking interactions and CH···π interactions, which bring the aromatic motifs into parallel and perpendicular dispositions with respect to the CNSs, respectively. Our results reveal that π-π stacking interactions override CH···π interactions in such cases. However, in the case of aromatic amino acids, π-π interactions can exist simultaneously along with a range of other interactions, including CH···π. The polarizability and HOMO energy of the CNSs were found to be the key factors that determine the binding energies. The HOMO-LUMO energy gaps of the CNSs were found to be undisturbed by the noncovalent functionalization of the aromatic molecules.

Contrasting preferences of N and P substituted heteroaromatics towards metal binding: probing the regioselectivity of Li+ and Mg2+ binding to (CH)(6-m-n)N(m)P(n).

High level ab initio and hybrid DFT methods have been employed to investigate the interactions of metal ions (Li(+) and Mg(2+)) with N and P substituted six membered heteroaromatics (CH)(6-m-n)N(m)P(n). The binding energy (BE) of metal ions with the N and P substituted heteroaromatics has been computed at the CCSD(T)/cc-pVTZ//MP2/cc-pVTZ level with counterpoise correction. In the present study we systematically examined the preferential modes of binding of metal ions to the heteroaromatics. N-Substituted heteroaromatics show a strong preference for cation-σ mode of binding whereas the P-substituted heteroaromatics prefer cation-π mode of binding with the metal ions. Energy decomposition analysis (EDA) using the DFT-SAPT scheme has been carried out to analyse the contribution of various energy components to the BE. The results illustrate that for the cation-π complexes, the contribution of the induction term is more whereas in the case of cation-σ there is a competition between induction and electrostatic terms in the interaction energy.

Hierarchical supramolecular co-assembly formation employing multi-component light-harvesting charge transfer interactions giving rise to long-wavelength emitting luminescent microspheres.

Charge transfer (CT) interaction induced formation of a hierarchical supramolecular assembly has attracted attention due to its wide diversity of structural and functional characteristics. In the present work, we report the generation of green luminescent microspheres from the charge transfer interaction induced co-assembly of a bis-naphthyl dipicolinic amide (DPA) derivative with tetracyanobenzene (TCNB) for the first time. The properties of these self-assemblies were studied both in solution and the solid-state using spectroscopic and a variety of microscopy techniques. The X-ray crystal structure analysis showed a mixed stack arrangement of DPA and TCNB. The molecular orbital and energy level calculations confirm the charge transfer complex formation between DPA and TCNB. Furthermore, energy transfer was observed from the green luminescent CT complex to a red-emitting dye, pyronin Y, in the microsphere matrix, leading to the formation of a light-harvesting tri-component self-assembly.

Aggregation induced emission (AIE) active 4-amino-1,8-naphthalimide-Tröger's base for the selective sensing of chemical explosives in competitive aqueous media.

The 4-amino-1,8-naphthalimide-Tröger's base fluorophore, TBNap-TPy, adorned with phenyl-terpyridine moiety was synthesised and assessed for its aggregation-induced emission (AIE) behaviour. TBNap-TPy was further employed as a fluorescent sensor for the discriminative sensing of π-electron-deficient nitroaromatic; the TBNap-TPy displaying the largest fluorescence quenching with high selectivity for picric acid, a harmful environmental pollutant widely used in the dye industries.

Quasiparticle GW Calculations on Lead-Free Hybrid Germanium Iodide Perovskite CH3NH3GeI3 for Photovoltaic Applications.

Lead-free organic-inorganic halide perovskites have gained much attention as nontoxic alternatives to CH3NH3PbI3 in next-generation solar cells. In this study, we have examined the geometric and electronic properties of methylammonium germanium iodide CH3NH3GeI3 using density functional theory. Identifying a suitable functional to accurately model the germanium halide perovskites is crucial to allow the theoretical investigation for tuning the optoelectronic properties. The performance of various functionals (PBE, PBE+D3, PBEsol, PBEsol+D3, HSE06, and HSE06+D3) has been evaluated for modelling the structure and properties. The calculation of electronic properties was further refined by using the quasiparticle GW method on the optimized geometries, and that has an excellent agreement with the experiment. We report from our GW calculations that the characteristic of the density of states for CH3NH3GeI3 resembles the density of states for CH3NH3PbI3 and the effective masses of the charge carriers of CH3NH3GeI3 are comparable to the effective masses of CH3NH3PbI3 as well as silicon used in commercially available solar cells.

"Turn-on" fluorescence sensing of volatile organic compounds using a 4-amino-1,8-naphthalimide Tröger's base functionalised triazine organic polymer.

The 4-amino-1,8-naphthalimide Tröger's base functionalized triazine covalent organic polymer TB-TZ-COP was synthesised and employed as a "turn-on" fluorescent and a colorimetric sensor for the discriminative sensing of volatile organic compounds; the TB-TZ-COP displaying the largest fluorescent enhancement and high sensitivity for 1,4-dioxane, a harmful environmental pollutant classified as a Group 2B carcinogen.

Synthesis, structural characterisation and antiproliferative activity of a new fluorescent 4-amino-1,8-naphthalimide Tröger's base-Ru(ii)-curcumin organometallic conjugate.

The synthesis, photophysics and biological investigation of fluorescent 4-amino-1,8-naphthalimide Tröger's bases (TB-1-TB-3) and a new Tröger's base p-cymene-Ru(ii)-curcumin organometallic conjugate (TB-Ru-Cur) are described; these compounds showed fast cellular uptake and displayed good luminescence and cytotoxicity against cervical cancer cells.

A supramolecular Tröger's base derived coordination zinc polymer for fluorescent sensing of phenolic-nitroaromatic explosives in water.

A V-Shaped 4-amino-1,8-napthalimide derived tetracarboxylic acid linker (L; bis-[N-(1,3-benzenedicarboxylic acid)]-9,18-methano-1,8-naphthalimide-[b,f][1,5]diazocine) comprising the Tröger's base (TB) structural motif was rationally designed and synthesised to access a nitrogen-rich fluorescent supramolecular coordination polymer. By adopting the straight forward precipitation method, a new luminescent nanoscale Zn(ii) coordination polymer (TB-Zn-CP) was synthesized in quantitative yield using Zn(OAc)2·2H2O and tetraacid linker L (1 : 0.5) in DMF at room temperature. The phase-purity of as-synthesised TB-Zn-CP was confirmed by X-ray powder diffraction analysis, infra-red spectroscopy, and elemental analysis. Thermogravimetric analysis suggests that TB-Zn-CP is thermally stable up to 330 °C and the morphological features of TB-Zn-CP was analysed by SEM and AFM techniques. The N2 adsorption isotherm of thermally activated TB-Zn-CP at 77 K revealed a type-II reversible adsorption isotherm and the calculated Brunauer-Emmett-Teller (BET) surface area was found to be 72 m2 g-1. Furthermore, TB-Zn-CP displayed an excellent CO2 uptake capacity of 76 mg g-1 at 273 K and good adsorption selectivity for CO2 over N2 and H2. The aqueous suspension of as-synthesized TB-Zn-CP showed strong green fluorescence (λmax = 520 nm) characteristics due to the internal-charge transfer (ICT) transition and was used as a fluorescent sensor for the discriminative sensing of nitroaromatic explosives. The aqueous suspension of TB-Zn-CP showed the largest quenching responses with high selectivity for phenolic-nitroaromatics (4-NP, 2,4-DNP and PA) even in the concurrent presence of other potentially competing nitroaromatic analytes. The fluorescence titration studies also provide evidence that TB-Zn-CP detects picric acid as low as the parts per billion (26.3 ppb) range. Furthermore, the observed fluorescence quenching responses of TB-Zn-CP towards picric acid were highly reversible. The highly selective fluorescence quenching responses including the reversible detection efficiency make the nanoscale coordination polymer TB-Zn-CP a potential material for the discriminative fluorescent sensing of nitroaromatic explosives.

Saturated vs. unsaturated hydrocarbon interactions with carbon nanostructures.

The interactions of various acyclic and cyclic hydrocarbons in both saturated and unsaturated forms with the carbon nanostructures (CNSs) have been explored by using density functional theory (DFT) calculations. Model systems representing armchair and zigzag carbon nanotubes (CNTs) and graphene have been considered to investigate the effect of chirality and curvature of the CNSs toward these interactions. Results of this study reveal contrasting binding nature of the acyclic and cyclic hydrocarbons toward CNSs. While the saturated molecules show stronger binding affinity in acyclic hydrocarbons; the unsaturated molecules exhibit higher binding affinity in cyclic hydrocarbons. In addition, acyclic hydrocarbons exhibit stronger binding affinity toward the CNSs when compared to their corresponding cyclic counterparts. The computed results excellently corroborate the experimental observations. The interaction of hydrocarbons with graphene is more favorable when compared with CNTs. Bader's theory of atoms in molecules has been invoked to characterize the noncovalent interactions of saturated and unsaturated hydrocarbons. Our results are expected to provide useful insights toward the development of rational strategies for designing complexes with desired noncovalent interaction involving CNSs.