Fluorescent naphthalimide boronates as theranostics: structural investigations, confocal fluorescence and multiphoton fluorescence lifetime imaging microscopy in living cells

New design and synthetic strategies were developed to generate functional phenyl boronic acid (BA)-based fluorescent probes incorporating the 1,8-naphthalimide (NI) tag. This fluorescent core was anchored onto the BA unit through small organic linkers consisting of nitrogen groups which can arrest, and internally stabilise the phenyl-boronate units. The newly synthesised fluorophores were characterised spectroscopically by NMR spectroscopy and mass spectrometry and evaluated for their ability to bind to a naturally occurring polysaccharide, β-d-glucan in DMSO and simultaneously as act as in vitro cell imaging reagents. The uptake of these new NI-boronic acid derivatives was studied living cancer cells (HeLa, PC-3) in the presence, and absence, of β-d-glucan. Time-correlated single-photon counting (TCSPC) of DMSO solutions and two-photon fluorescence-lifetime imaging microscopy (FLIM) techniques allowed an insight into the probes' interaction with their environment. Their cellular uptake and distributions were imaged using laser scanning confocal fluorescence microscopy under single- and two-photon excitation regimes (λmax 910 nm). FLIM facilitated the estimation of the impact of the probe's cellular surroundings using the fluorophore lifetime. The extent to which this was mediated by the β-d-glucan was visualised by 2-photon FLIM in living cells. The fluorescence lifetime observed under a range of temperatures varied appreciably, indicating that changes in the environment can be sensed by these probes. In all cases, the cellular membrane penetration of these new probes was remarkable even under variable temperature conditions and localisation was widely concentrated in the cellular cytoplasm, without specific organelle trapping: we conclude that these new probes show promise for cellular imaging in living cancer cells.

Self-Assembly Driven Formation of Functional Ultralong "Artificial Fibers" to Mitigate the Neuronal Damage Associated with Alzheimer's Disease

Fibrillation of amyloid beta (Aβ) is the key event in the amyloid neurotoxicity process that induces a chain of toxic events including oxidative stress, caspase activation, poly(ADP-ribose) polymerase cleavage, and mitochondrial dysfunction resulting in neuronal loss and memory decline manifesting as clinical dementia in humans. Herein, we report the development of a novel, biologically active supramolecular probe, INHQ, and achieve functional nanoarchitectures via a self-assembly process such that ultralong fibers are achieved spontaneously. With specifically decorated functional groups on INHQ such as imidazole, hydroxyquinoline, hydrophobic chain, and hydroxyquinoline molecules, these ultralong fibers coassembled efficiently with toxic Aβ oligomers and mitigated the amyloid-induced neurotoxicity by blocking the aforementioned biochemical events leading to neuronal damage in mice. These functional ultralong "Artificial Fibers" morphologically resemble the amyloid fibers and provide a higher surface area of interaction that improves its clearance ability against the Aβ aggregates. The efficacy of this novel INHQ molecule was ascertained by its high ability to interact with Aβ. Moreover, this injectable, ultralong INHQ functional "artificial fiber" translocates through the blood-brain barrier and successfully attenuates the amyloid-triggered neuronal damage and pyknosis in the cerebral cortex of wild-type mouse. Utilizing various spectroscopic techniques, morphology analysis, and in vitro, in silico, and in vivo studies, these ultralong INHQ fibers are proven to hold great promise for treating neurological disorders at all stages with a potential to replace the existing medications, reduce complications in the brain, and eradicate the amyloid-triggered neurotoxicity implicated in numerous disorders in human through a rare synergistic mechanism.

Polarity-Driven Isomerization of a Hydroxynaphthalimide-Containing Spiropyran at Room Temperature

Design of spiropyrans showing spontaneous isomerization driven by the polarity of solvents is an important consideration for the synthesis of optical sensory materials. Although some spiropyrans undergo polarity-driven isomerization, they must be heated owing to the high activation energy required for isomerization. In this study, we describe that a spiropyran containing a hydroxynaphthalimide unit (1) exhibits a polarity-driven isomerization at room temperature. It exists as a colorless spirocyclic (SP) form in less polar solvents but is isomerized to a colored merocyanine (MC) form in polar solvents. The equilibrium amount of the MC form increases with an increase in the polarity of solvents. The MC form involves two resonance structures-the quinoidal and zwitterionic forms. In polar media, the zwitterionic form dominates mainly owing to solvation by polar molecules. Solvation stabilizes the negative charge of the zwitterionic form and decreases its ground state energy, thereby enhancing SP → MC isomerization. The SP ⇌ MC isomerization terminates within barely 30 s even at room temperature because the naphthol moiety with high π-electron density lowers the activation energy for the rate-determining rotational step.

Interaction of ruthenium(Ⅱ) polypyridyl complexes [Ru(phen)2(L)]2+ (L = PIP, p-HPIP and m-HPIP) with RNA poly(A)•poly(U): each complex unexpectedly exhibiting a destabilizing effect on RNA

To further explore the binding properties of Ru(Ⅱ) polypyridine complexes with RNA, three Ru(Ⅱ) complexes [Ru(phen)₂(PIP)]²⁺ (Ru1), [Ru(phen)₂(p-HPIP)]²⁺ (Ru2), and [Ru(phen)₂(m- HPIP)]²⁺ (Ru3) have been synthesized and characterized in this work. The binding properties of three Ru(Ⅱ) complexes with RNA duplex poly(A)•poly(U) have been investigated by spectral and viscosity experiments. These studies all support that these three Ru(Ⅱ) complexes bind to poly RNA duplex poly(A)•poly(U) by intercalation, and Ru1 without substituents has a stronger binding affinity for poly(A)•poly(U). Interestingly, the thermal melting experiments show that these three Ru(Ⅱ) complexes all destabilize RNA duplex poly(A)•poly(U), and the destabilizing effect can be explained by the conformational changes of duplex structure induced by intercalating agents. To the best of our knowledge, this work report for the first time a small molecule capable of destabilizing an RNA duplex, which reflects that the substitution effect of intercalated ligands has an important influence on the affinity of Ru(Ⅱ) complexes to RNA duplex, and that not all Ru(Ⅱ) complexes show thermal stability effects on an RNA duplex.

Nickel-Catalyzed C-N Cross-Coupling of 4-Chloro-1,8-naphthalimides and Bulky, Primary Alkylamines at Room Temperature

4-Amino-1,8-naphthalimides, potentially useful fluorescent probes in biological applications, are prepared via Ni(cod)₂/IPr-catalyzed cross-couplings between 4-chloro-1,8-naphthalimide electrophiles and α,α,α-trisubstituted, primary alkylamines at room temperature. This method represents the first synthesis of 4-amino-1,8-naphthalimides using Ni-catalyzed C-N cross-coupling and provides the first examples of 4-amino-1,8-naphthalimides incorporating such bulky primary alkylamines, thereby highlighting the utility of Ni-catalyzed processes in synthesizing naphthalimide scaffolds that were inaccessible using established methods (S_NAr; Pd or Cu catalysis).

N, Kumara K, Lokanath NK, Butcher RJ, Kumbar V, Bhat K. Copper(i) complexes with quinolone appended 1,8-naphthalimide conjugates: structural characterization, DNA and protein binding and cytotoxicity studies

Cytotoxicity, cellular uptake of copper(i) complexes containing 1,8-naphthalimide conjugates have been investigated.

DNA-Intercalative Platinum Anticancer Complexes Photoactivated by Visible Light

Photoactivatable agents offer the prospect of highly selective cancer therapy with low side effects and novel mechanisms of action that can combat current drug resistance. 1,8-Naphthalimides with their extended π system can behave as light-harvesting groups, fluorescent probes and DNA intercalators. We conjugated N-(carboxymethyl)-1,8-naphthalimide (gly-R-Nap) with an R substituent on the naphthyl group to photoactive diazido PtIV complexes to form t,t,t-[Pt(py)2 (N3 )2 (OH)(gly-R-Nap)], R=H (1), 3-NO2 (2) or 4-NMe2 (3). They show enhanced photo-oxidation, cellular accumulation and promising photo-cytotoxicity in human A2780 ovarian, A549 lung and PC3 prostate cancer cells with visible light activation, and low dark cytotoxicity. Complexes 1 and 2 exhibit pre-intercalation into DNA, resulting in enhanced photo-induced DNA crosslinking. Complex 3 has a red-shifted absorption band at 450 nm, allowing photoactivation and photo-cytotoxicity with green light.

Structure illumination microscopy imaging of lipid vesicles in live bacteria with naphthalimide-appended organometallic complexes

There is a lack of molecular probes for imaging bacteria, in comparison to the array of such tools available for the imaging of mammalian cells. Here, organometallic molecular probes have been developed and assessed for bacterial imaging, designed to have the potential to support multiple imaging modalities. The chemical structure of the probes is designed around a metal-naphthalimide structure. The 4-amino-1,8-naphthalimide moiety, covalently appended through a pyridine ancillary ligand, acts as a luminescent probe for super-resolution microscopy. On the other hand, the metal centre, rhenium(i) or platinum(ii) in the current study, enables techniques such as nanoSIMS. While the rhenium(i) complex was not sufficiently stable to be used as a probe, the platinum(ii) analogue showed good chemical and biological stability. Structured illumination microscopy (SIM) imaging on live Bacillus cereus confirmed the suitability of the probe for super-resolution microscopy. NanoSIMS analysis was used to monitor the uptake of the platinum(ii) complex within the bacteria and demonstrate the potential of this chemical architecture to enable multimodal imaging. The successful combination of these two moieties introduces a platform that could lead to a versatile range of multi-functional probes for bacteria.

Syntheses and evaluation of acridone-naphthalimide derivatives for regulating oncogene PDGFR-β expression

Upregulation of platelet-derived growth factor receptor β (PDGFR-β) has been found to be associated with development of various types of cancers, which has become an attractive target for anti-tumor treatment. Previously, we have synthesized and studied an acridone derivative B19, which can selectively bind to and stabilize oncogene c-myc promoter i-motif, resulting in down-regulation of c-myc transcription and translation, however its effect on tumor cells apoptosis requires improvement. In the present study, we synthesized a variety of B19 derivatives containing a known anti-cancer fluorescent chromophore naphthalimide for the purpose of enhancing anti-cancer activity. After screening, we found that acridone-naphthalimide derivative WZZ02 could selectively stabilize PDGFR-β promoter G-quadruplex and destabilize its corresponding i-motif structure, without significant interaction to other oncogenes promoter G-quadruplex and i-motif. WZZ02 down-regulated PDGFR-β gene transcription and translation in a dose-dependent manner, possibly due to above interactions. WZZ02 could significantly inhibit cancer cell proliferation, and induce cell apoptosis and cycle arrest. WZZ02 exhibited tumor growth inhibition activity in MCF-7 xenograft tumor model, which could be due to its binding interactions with PDGFR-β promoter G-quadruplex and i-motif. Our results suggested that WZZ02 as a dual G-quadruplex/i-motif binder could be effective on both oncogene replication and transcription, which could become a promising lead compound for further development with improved potency and selectivity. The wide properties for the derivatives of 1,8-naphthalimide could facilitate further in-depth mechanistic studies of WZZ02 through various fluorescent physical and chemical methods, which could help to further understand the function of PDGFR-β gene promoter G-quadruplex and i-motif.

Synthesis, structural characterization, protein binding, DNA cleavage and anticancer activity of fluorophore labelled copper(ii) complexes based on 1,8-naphthalimide conjugates

The synthesized copper complexes have good anticancer activity and induce an apoptotic mode of cell death.

Fluorescent 4-amino-1,8-naphthalimide Tröger's bases (TBNaps) possessing (orthogonal) 'α-amino acids', esters and di-peptides and their solvent dependent photophysical properties

The synthesis of fifteen luminescent bis-naphthalimide based Tröger's bases (TBNaps) derived from 4-amino-1,8-naphthalimide (4-Amino-Nap) precursors is described; these scaffolds possess α-amino acids, esters or di-peptides conjugated at the imide site and show minor fluorescence in aqueous solution while being highly emissive in organic solvents. The investigation shows that these TBNaps possessing ICT excited state properties are capable of generating either positive or negative solvatochromic effects in response to changes in polarity and/or the hydrogen bonding capabilities of the medium.

Naphthalimide-containing coordination polymer with mechanoresponsive luminescence and excellent metal ion sensing properties

Mechanoresponsive luminescent materials coupled with other functionalities are of particular interest due to their multiple external stimuli responsive properties. In this paper, a new sensitive mechanoresponsive luminescent coordination polymer, [Cd(INI)(DMF)2·DMF] (1) (H2INI = N-(5-isophthalic acid)-1,8-naphthalimide), has been successfully designed and synthesized. Complex 1 exhibits interesting mechanoresponsive and grinding-enhanced luminescence properties, and its luminescence colour changed from weak blue-green to bright blue upon grinding owing to the external pressure-induced destruction of ππ stacked arrangements in local defective areas. Moreover, the luminescence properties and uncoordinated carbonyl groups of well-ground g-1 endow it with excellent sensing ability for Cr3+ ions. This work will provide a new perspective to rationally design multifunctional coordination polymers that can serve as practical multi-responsive sensors to pressure and chemicals.

Mitochondrial DNA targeting and impairment by a dinuclear Ir–Pt complex that overcomes cisplatin resistance

A dinuclear complex [(ppy)Ir(tpy)PtCl]²⁺ (Ir–Pt) can exhibit strong antitumor activity towards cisplatin-resistant cancer cells and induce cell necrosis via mtDNA damage and mitochondrial dysfunction.

Enhancing Cytotoxicity of a Monofunctional Platinum Complex via a Dual-DNA-Damage Approach

Mitochondrial DNA (mtDNA) is an attractive cellular target for anticancer agents in addition to nuclear DNA (nDNA). The cationic platinum(II) complex cis-[Pt(NP)(NH₃)₂Cl]NO₃ (PtNP, NP = N-(2-ethylpyridine)-1,8-naphthalimide) bearing the DNA-intercalating moiety NP was designed. The structure of PtNP was fully characterized by single-crystal X-ray crystallography, NMR, and HRMS. PtNP is superior to cisplatin in both in vitro and in vivo anticancer activities with low systemic toxicity. The interaction of PtNP with CT-DNA demonstrated that PtNP could effectively bind to DNA through both covalent and noncovalent double binding modes. In addition to causing significant damage to nDNA and remarkable inhibition to DNA damage repair, PtNP also distributed in mitochondria, inducing mtDNA damage and affecting the downstream transcriptional level of mitochondrion-encoded genes. In addition, PtNP disturbed the physiological processes of mitochondria by reducing the mitochondrial membrane potential and promoting the generation of reactive oxygen species. Mechanistic studies demonstrate that PtNP induced apoptosis via mitochondrial pathways by upregulating Bax and Puma and downregulating Bcl-2 proteins, leading to the release of cytochrome c and activation of caspase-3 and caspase-9. As a dual-DNA-damage agent, PtNP is able to improve the anticancer activity by damaging both nuclear and mitochondrial DNA, thus providing a new anticancer mechanism of action for the naphthalimide monofunctional platinum(II) complexes.

Platinum(ii) complexes showing high cytotoxicity toward A2780 ovarian carcinoma cells

2,6-Bis(thiazol-2-yl)pyridines functionalized with 9-anthryl (L¹), 9-phenanthryl (L²), and 1-pyrenyl (L³) groups were used for the preparation of [Pt(Lⁿ)Cl]CF₃SO₃ (1-3). The constitution of the Pt(ii) complexes was determined by ¹H and ¹³C NMR spectroscopy, HR-MS spectrometry, elemental analysis and X-ray analysis (for (1)). The electrochemical and photophysical properties of [Pt(Lⁿ)Cl]CF₃SO₃ were compared with the behaviour of the Pt(ii) complexes with aryl-substituted 2,2':6',2''-terpyridine ligands. What is noteworthy is that the coordination ability of dtpy toward the Pt(ii) centre was investigated for the first time. All complexes were tested in vitro by MTS assay on four tumor cell lines, A2780 (ovarian carcinoma), HTC116 (colon rectal carcinoma), MCF7 (breast adenocarcinoma), and PC3 (prostate carcinoma) and on normal primary fibroblasts. Compounds (1-3) showed a dose dependent antiproliferative effect in the A2780 cell line with (3) > (2) > (1) and this loss of A2780 cell viability was due to a combination of an apoptotic cell death mechanism via mitochondria and autophagic cell death. Exposure to IC₅₀ concentration of (2) induced an increase in the number of apoptotic nuclei and a depolarization of the mitochondrial membrane which is consistent with the induction of apoptosis while exposure to IC₅₀ concentration of (3) showed an increase in the apoptotic nuclei with a slight hyperpolarization of the mitochondrial membrane that might indicate an initial step of apoptosis induction. The complexes (2) and (3) induce an increase in the production of intracellular ROS which is associated with the trigger of the apoptotic pathways. The ROS production was augmented by the presence of oxidants and correlated with an increase of oxygen radicals. The IC₅₀ of (2) and (3) (4.4 μM and 2.9 μM, respectively) was similar to the IC₅₀ of cisplatin (3.4 μM) in the A2780 cell line, which together with their low cytotoxicity in normal fibroblasts, demonstrates their potential for further studies.

Third-strand stabilizing effects of the RNA poly(U)·poly(A)*poly(U) triplex by a ruthenium(II) polypyridine complex and its hexaarginine peptide conjugate

In this work, a Ru(II) complex [Ru(bpy)₂(pip-CO₂H)]²⁺ (Ru1) and its hexaarginine peptide conjugate [Ru(bpy)₂(pic-Arg₆)]⁸⁺ (Ru2) have been synthesized and characterized. The binding of Ru1 and Ru2 with poly(U)•poly(A)*poly(U) triplex has been studied. Results suggest that Ru1 binds in the surface of the minor groove while Ru2 binds to the minor groove of the triplex. Consequently, the triplex stabilization is barely affected by Ru1, while with Ru2 the triplex stabilizing effect is so strong that that dissociation of the triplex shows an overlapping of both melting processes with the melting temperature increased to a maximum of 56.1 °C at the C_Ru2/C_UAU ratio of 0.05, where ΔT_m1 and ΔT_m2 are 19.6 and 10.1 °C, respectively. Furthermore, the effect of Ru2 stabilizing the third strand at such a low binding ratio of 0.05 is more marked than what obsereved for flavone luteolin and [Ru(bpy)₂(mdpz)]²⁺, which are so far the strongest triplex stabilizers in the reported organic small molecules and metal complexes, respectively. Considering the structure natures of Ru2, conceivably except for electrostatic interaction, the forces stabilizing the triplex should also involve hydrophobic interaction and hydrogen bingding. To our knowledge, this work represents a first example of improving the triplex stabilization by a metallopeptide.

Ribosomal RNA-Selective Light-Up Fluorescent Probe for Rapidly Imaging the Nucleolus in Live Cells

RNA-based fluorescent probes are currently limited by their low selectivity toward RNA versus DNA, and low specificity to different RNA structures. Poor membrane permeability is another defect of existing fluorogenic RNA probes for intracellular imaging. In this work, a naphthalimide derivative, probe 1, was developed for the rapid and selective detection of intracellular rRNA (rRNA). Probe 1 exhibited a 32-fold fluorescent enhancement in response to rRNA binding and showed desirable selectivity for rRNA versus DNA and other nucleic acids in phosphate buffer at pH 7.2. Importantly, probe 1 displayed excellent permeability of the nucleolus, could be taken up in 1 min by four different cell lines, and may be the fastest nucleolus dye. The excellent selectivity of probe 1 toward rRNA is attributed to the specific interaction between the complicated 3D structures of rRNA, which was confirmed by quantum calculations using molecular docking simulations. An appropriate lipophilic balance in 1 with the hydrophilic amine group and hydrophobic naphthalimide, as well as its high water solubility, guarantees the high permeability of 1 in cell membranes and nucleolus pores, compared to other analogues (e.g., probes 2-8 in this work). Furthermore, enlarged confocal laser micro images of nucleoli and RNase digestion tests revealed that 1 remained highly selective toward rRNA, even for intracellular imaging. As a live cell probe, 1 also exhibited better photostability than the commercial RNA dye, SYTO RNA select.

A safe and efficacious Pt(ii) anticancer prodrug: design, synthesis, in vitro efficacy, the role of carrier ligands and in vivo tumour growth inhibition

Diaminocyclohexane-Pt(ii)-phenalenyl complexes (1 and 2) showed an appropriate balance between efficacy and toxicity. Compound 2 showed nearly two-fold higher tumour growth inhibition than oxaliplatin in a murine NSCLC tumour model, when a combined drug development approach was used. The fluorescent properties of phenalenone were utilized to understand the mechanistic details of the drug.

A study of 99mTc/Re-tricarbonyl complexes of 4-amino-1,8-naphthalimides

4-Amino-1,8-naphthalimide ligands were coordinated to fac-Re/^99mTc(CO)₃ giving complexes of varying charge for applications in fluorescence microscopy and as components of SPECT imaging agents.

Glycosylated naphthalimides and naphthalimide Tröger's bases as fluorescent aggregation probes for Con A

We report the synthesis of glycosylated naphthalimide compounds and their application as fluorescent probes for Concanavalin A (Con A) lectin.

Crystallographic studies of 2-picolyl substituted naphthalene diimide and bis-phthalimide ligands and their supramolecular coordination chemistry

The coordination chemistry of two 2-picolyl substituted bis-imide ligands is explored, revealing fascinating metallosupramolecular assemblies but an apparent barrier to chelation compared to monoimide congeners.

l,8-Naphthalimide based DNA intercalators and anticancer agents. A systematic review from 2007 to 2017

In this review, we describe a detailed investigation about the structural variations and relative activity of 1,8-naphthalimide based intercalators and anticancer agents. The 1,8-naphthalimides binds to the DNA via intercalation, and exert their antitumor activities through Topoisomerase I/II inhibition, photoinduced DNA damage or related mechanism. Here, our discussion focused on works published over the last ten years (2007-2017) related to therapeutic applications, in the order of cancer treatment followed by other properties of 1,8-naphthalimides. In preparing for this review, we considered that several seminal reviews have appeared over the last fifteen years and focused on closely related subjects, however, none of them is exhaustive.

Anionic cyclometalated Pt(ii) and Pt(iv) complexes respectively bearing one or two 1,2-benzenedithiolate ligands

Novel anionic cyclometalated Pt(ii) square-planar complexes NBu4[(C^N)PtII(S^S)], containing 2-phenylpyridine H(PhPy), 2-(2,4-difluorophenyl)-pyridine H(F2PhPy) and benzo[h]quinoline H(Bzq), respectively, as a cyclometalated ligand and the dianionic 1,2-benzenedithiolate (Thio)2- fragment as an (S^S) ligand, were synthesised. By the simple addition of an equivalent of (Thio)2- to the NBu4[(C^N)PtII(Thio)] complexes, octahedral anionic NBu4[(C^N)PtIV(Thio)2] analogues were obtained, representing, to the best of our knowledge, the first examples of Pt(iv) anionic cyclometalated complexes. The molecular structures of the obtained complexes in the case of the NBu4[(Bzq)PtII(Thio)] and the NBu4[(Bzq)PtIV(Thio)2] complexes were confirmed by single crystal X-ray diffraction analysis. Furthermore, the electrochemical and photophysical properties of the two series of Pt(ii) and Pt(iv) newly synthesised complexes were studied and DFT and TD-DFT calculations were performed in order to comprehensively investigate the displayed behaviour. All Pt(ii) and Pt(iv) complexes show intense luminescence in the solid state, with remarkable enhancement of the emission quantum yields, proving to be excellent examples of aggregation-induced emission systems.

Fluorescent organometallic rhodium(I) and ruthenium(II) metallodrugs with 4-ethylthio-1,8-naphthalimide ligands: Antiproliferative effects, cellular uptake and DNA-interaction

Fluorescent 4-ethylthio-1,8-naphthalimides containing rhodium(I) N-heterocyclic carbene (NHC) and ruthenium (II) NHC fragments were synthesised and evaluated for their antiproliferative effects, cellular uptake and DNA-binding activity. Both types of organometallics triggered ligand dependent efficient cytotoxic effects against tumor cells with the rhodium(I) NHC derivatives causing stronger effects than the ruthenium (II) NHC analogues. Antiproliferative effects could also be observed against several pathogenic Gram-positive bacterial strains, whereas the growth of Gram-negative bacteria was not substantially affected. Cellular uptake was confirmed by atomic absorption spectroscopy as well as by fluorescence microscopy indicating a general ligand dependent accumulation in the cells. An in-depth study on the interaction with DNA confirmed insertion of the naphthalimide moiety between the planar bases of B-DNA via an intercalation mechanism, as well as its stacking on top of the quartets of G-quadruplex structures. Furthermore, additional coordinative binding of the organometallic complexes to the model DNA base 9-ethylguanine could be detected. The studied compounds thus represent promising bioorganometallics featuring strong pharmacological effects in combination with excellent cellular imaging properties.

Unveiling the Potential of Unfused Bichromophoric Naphthalimide To Induce Cytotoxicity by Binding to Tubulin: Breaks Monotony of Naphthalimides as Conventional Intercalators

In the development of small-molecule drug candidates, naphthalimide-based compounds hold a very important position as potent anticancer agents with considerable safety in drug discoveries. Being synthetically and readily accessible, naphthalimide compounds with planar architecture have been developed mostly as DNA-targeting intercalators. However, in this article, it is demonstrated, for the first time, that an unfused naphthalimide-benzothiazole bichromophoric compound 2-(6-chlorobenzo[ d] thiazol-2-yl)-1 H-benzo[ de] isoquinoline-1,3(2 H)-dione (CBIQD), seems to expand the bioactivity of naphthalimide as anti-mitotic agent also. Preliminary studies demonstrate that CBIQD interferes with human lung cancer (A549) cell proliferation and growth and causes cellular morphological changes. However, the underlying mechanism of its antitumor action and primary cellular target in A549 cells remained skeptical. Confocal microscopy in A549 cells revealed disruption of interphase microtubule (MT) network and formation of aberrant multipolar spindle. Consistent with microscopy results, UV-vis, steady-state fluorescence, and time-resolved fluorescence (TRF) studies demonstrate that CBIQD efficiently binds to tubulin ( K_b = 2.03 × 10⁵ M^-1 ± 1.88%), inhibits its polymerization, and depolymerizes preformed microtubules (MTs). Low doses of CBIQD have also shown specificity toward tubulin protein in the presence of a nonspecific protein like bovine serum albumin as well as other cytoskeleton component, actin. The in vitro determination of binding site coupled with in silico studies suggests that CBIQD may prefer to occupy the colchicine binding site. Further, CBIQD perturbed tubulin conformation to some extent and protected ∼1.4 cysteine residues toward chemical modification by 5,5'-dithiobis-2-nitrobenzoic acid. We also suggest the possible mechanism underlying CBIQD-induced cancer cell cytotoxicity: CBIQD, when bound to tubulin, may prevent it to maintain a straight conformation; consequently, the α- and β-heterodimers might be no longer available for MT growth. Thus, the consolidated spectroscopic research described herein explores the potential of CBIQD as a new paradigm in the design and development of novel unfused or nonring-fused naphthalimide-based antimitotic cancer therapeutics in medicinal chemistry research.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

Pendant chain engineering to fine-tune the nanomorphologies and solid state luminescence of naphthalimide AIEEgens: application to phenolic nitro-explosive detection in water

Strategically, a series of five angular "V" shaped naphthalimide AIEEgens with varying pendant chains (butyl, hexyl, octyl, cyclohexyl and methylcyclohexyl) have been synthesized to fine-tune their nanomorphological and photophysical properties. With similar aromatic cores and electronic states, unexpected tuning of the condensed state emission colors and nanomorphologies (reproducible on any kind of surface) of naphthalimides has been achieved for the first time simply by varying their side chains. Conclusive analysis by various spectroscopic techniques (SC-XRD, powder-XRD, DLS, FESEM) and DFT computational studies confirmed the full control of the pendant chain (in terms of bulkiness around the naphthalimide core, which restricts the ease of intermolecular π-π interactions) over the nanoaggregate morphology and solid state emissive properties of the AIEEgens; this can be rationalized to all aggregation-prone systems. These comprehensive studies establish a conceptually unique yet simple and effective method to precisely tune the nanomorphologies and the emission colors of aggregation-prone small organic molecules by judicious choice of the non-conjugated pendant chain. Thus, considering the prime role of the active layer nanomorphology in all organic optoelectronic devices, this methodology may emerge as a promising tool to improve device performance. Among all the congeners, the hexyl chain-containing congener (HNQ) forms well-defined nanoribbons with smaller diameters (as confirmed from DLS: 166 nm and FESEM: 150 nm) and provides a larger surface area. Consequently, the HNQ-nanoribbons were employed as a fluorescent sensor for the discriminative detection of trinitrophenol (TNP) in pure aqueous media. FE-SEM images revealed that, upon gradual addition of TNP (10 nM to 100 μM), these nanoribbons undergo an aggregation/disaggregation process, forming non-fluorescent co-aggregates with TNP, and provide highly enhanced sensitivity compared to existing state-of-the-art on aggregation-prone systems. Fluorescence titration studies confirmed that HNQ can detect the presence of TNP as low as 16.8 ppb and can serve as a cost-effective portable device incorporated with UV-light for on-site visual detection of TNP, even in the presence of potentially competing nitroaromatic compounds.

Metal NHC Complexes with Naphthalimide Ligands as DNA-Interacting Antiproliferative Agents

Naphthalimide-based N-heterocyclic carbene (NHC) complexes of the type [(1,5-cyclooctadiene)(NHC)RhCl)] (4 a-c), [(p-cymene)(NHC)RuCl₂ )] (5 a-c), and [(NHC)CuBr] (6 a-c) were synthesized and investigated as antiproliferative agents that target DNA. The cytotoxic effects were largely driven by the naphthalimide structure, which is a DNA-intercalating moiety. Regarding the metal center, the highest activities were observed with the rhodium complexes, and cytotoxic activity was significantly lower for the ruthenium derivatives. The stable coordination of the NHC ligands of selected complexes 4 b and 5 b in solution was confirmed, and their DNA binding properties were studied by UV/Vis spectroscopy, mass spectrometry, and circular dichroism. Stable intercalative binding into the DNA for all selected naphthalimide-based complexes is indicated by high DNA binding constants. Particularly efficient binding was observed in the case of the rhodium complex 4 b. More detailed biological studies on 4 b showed promising activities against multidrug-resistant Nalm-6 cells and confirmed an important role for mitochondrial pathways in 4 b-induced apoptosis.

Synthesis, G-quadruplex binding properties and cytotoxicity of naphthalimide–thiourea conjugates

The hydrogen bonding between a thiourea moiety and a G-quadruplex plays a crucial role in the sequence-specific DNA binding of naphthalimide–thiourea conjugates.

Anionic cyclometallated Pt(ii) square-planar complexes: new sets of highly luminescent compounds

Novel anionic Pt(ii) complexes were synthesized, displaying an outstanding enhancement of the emission efficiency in the solid state.

Coordination chemistry of N-picolyl-1,8-naphthalimides: colourful low molecular weight metallo-gelators and unique chelation behaviours

A family of N-picolyl-1,8-napthalimide ligands display fascinating coordination chemistry and produce a series of robust and chemically responsive supramolecular metallo-gels.

One-pot facile synthesis of 4-amino-1,8-naphthalimide derived Tröger's bases via a nucleophilic displacement approach

We report here a novel one-pot synthetic strategy for the synthesis of a family of N-alkyl-1,8-naphthalimide derived Tröger's bases (in overall yield of 65–96%) via a nucleophilic substitution reaction.

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

A Tröger’s base functionalized luminescent nanoscale Zn(II) coordination polymer (TB-Zn-CP) is synthesized and used as selective fluorescence sensor for phenolic nitroaromatics 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 (λ_max = 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.

PdII and PtII complexes with a thio-aza macrocycle ligand containing an intercalating fragment: Structural and antitumor activity studies

Two new Pt^II and Pd^II complexes of formula [LMCl₂] (M=Pt, Pd) were synthesized and characterized both in solution and solid state. They were obtained using the thio-aza macrocycle 9,18-dimethyl-12,17dithia-9,18,27,28-tetraaaza-29-oxatetracyclo[24.2.1.0^2,7.0^20,25]enneicosa-2,4,6,20,22,24,26,28¹-octaene (L) containing the 2,5-diphenyl [1, 3, 4]oxadiazole as intercalating fragment. M^II is coordinated in cis-position by the two S atoms of L. The two crystal structures of [LPtCl₂] and [LPdCl₂] complexes showed that the M^II ion is located outside the macrocyclic cavity. The square planar coordination sphere is fulfilled by two chloride anions in a cisplatin-like arrangement with the chloride leaving groups exposed to the environment. The biological activity of both [LPtCl₂] and [LPdCl₂], monitored towards a leukemic cellular model (U937), is coherent with their ability to interfere, at different levels, with the DNA structure.

Ruthenium(II) polypyridyl complexes with 1,8-naphthalimide group as DNA binder, photonuclease, and dual inhibitors of topoisomerases I and IIα

Two ruthenium(II) polypyridyl complexes containing 1,8-naphthalimide group as DNA binders, photonucleases, and inhibitors of topoisomerases I and IIα are evaluated. The binding properties of [Ru(phen)₂(pnip)]²⁺ {1; phen=1,10-phenanthroline; pnip=12-[N-(p-phenyl)-1,8-napthalimide]- imidazo[4',5'-f] [1,10]phenanthroline} and [Ru(bpy)₂(pnip)]²⁺ (2; bpy=2,2'-bipyridine) with calf thymus DNA increases with increasing the bulkiness and hydrophobic character of ancillary ligands, although the two complexes possess high affinities for DNA via intercalation. Moreover, photoirradiation (λ=365nm) of the two complexes are found to induce strand cleavage of closed circular pBR322 plasmid DNA via singlet oxygen mechanism, while complex 1 displays more effective photocleavage activity than complex 2 under the same conditions. Topoisomerase inhibition and DNA strand passage assay reflect that complexes 1 and 2 are efficient dual poisons of topoisomerases I and IIα.