AIE-active cyclometalated iridium(III) complexes for the detection of lipopolysaccharides and wash-free imaging of bacteria.

Infectious diseases caused by bacteria pose a major threat to human health and are currently one of the leading causes of mortality worldwide. Therefore, the development of probes for rapid detection of bacteria and their pathogenic components is highly essential. Aggregation-induced emission (AIE)-active compounds have shown great promise for the diagnosis of bacterial infections. In this study, we have synthesized three cationic AIE-active cyclometalated iridium(III) polypyridyl complexes viz., [Ir(C^N)2(N^N)]Cl2 (Ir1-Ir3), where C^N is a cyclometalating ligand such as pq = 2-phenylquinoline (in Ir1), pbt = 2-phenylbenzothiazole (in Ir2), and dfppy = 2-(2,4-difluorophenyl)pyridine (in Ir3), and N^N is a 2,2'-bipyridine derivative, for detection of lipopolysaccharide (LPS) in aqueous solution and wash-free imaging of bacteria. These complexes exhibit rapid sensing of LPS also known as endotoxin released by the bacteria, with a detection limit in the nanomolar range being determined by fluorescence spectroscopy within 5 min. Detection of both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria by the complexes is visible to the naked eye and was also observed by fluorescence microscopy imaging. The above features of the complexes make them a promising scaffold for the detection of bacterial contamination in aqueous samples.

Graphene quantum dot-porphyrin/phthalocyanine multifunctional hybrid systems: from interfacial dialogue to application.

Engineered well-ordered hybrid nanomaterials are symbolically at a pivotal point, just ahead of the long-anticipated transformation of the human race. Incorporating newer carbon nanomaterials like graphene quantum dots (GQDs) with tetrapyrrolic porphyrins (Pp) and phthalocyanines (Pc) is crucial for achieving exquisite molecular nanoarchitectures that are superior to their individual components. The outcomes of this, particularly in the case of graphene quantum dot-porphyrin/phthalocyanine (GQD-Pp/Pc) hybrids, remain comprehensively unexplored to date. Interestingly, GQD-Pp/Pc hybrids provide a modern strategy to regulate matter by utilising intramolecular and organisational properties to create well-defined nanocomposites via a synergistic enhancement effect. The high molar absorption coefficient and enhanced energy transfer, hole and electron transfer abilities capabilities allow Pp and Pc to exhibit a wide spectrum of photophysical and photochemical features. However, their low biostability, non-specific tumor-targeting properties, hydrophobicity, and low cellular internalisation efficiency limit their extensive biomedical utility. Conjugating Pp/Pc to nanocarriers such as GQDs improves their targeted delivery, immunological tolerance, and longevity. Due to the zero-order release kinetics of GQDs, they can assist in maintaining a steady rate of photosensitiser (PS) delivery at the desired site. To completely rationalise the functionalization of GQD-Pp/Pc species at interfaces, we investigate the current prominence and future potential of porphyrin-related graphene nanosystems, especially GQDs, for the development of various applications. This encouraging report demonstrates how GQD-Pp/Pc species can be used to examine new phenomena at the multidisciplinary level. Notably, a customised hybrid system optimises amendable and diverse functional properties, yielding a ray of hope in the fields of photodynamic therapy (PDT), photocatalysis, solar cells, sensing, and beyond via various photo-physicochemical approaches such as electron transfer, catalytic transformation, light-harvesting, and axial/peripheral ligation of adducts. Gratifyingly, the covalent and non-covalent coupling of functional molecular units at interfaces enable new properties to be generated in hybrid systems.

Mitochondria-Targeted Photoactivatable Real-Time Monitoring of a Controlled Drug Delivery Platform.

The current anticancer therapies are limited by their lack of controlled spatiotemporal release at the target site of action. We report a novel drug delivery platform that provides on-demand, real-time, organelle-specific drug release and monitoring upon photoactivation. The system is comprised of a model anticancer drug doxorubicin, an alkyltriphenylphosphonium moiety to target mitochondria in cancer cells, and a hydroxycinnamate photoactivatable linker that is covalently attached to the drug and mitochondria-targeting moieties such that it can be phototriggered by either UV (one-photon) or NIR (two-photon) light to form a fluorescent coumarin product and facilitate the release of drug payload. The extent of drug release is quantified by the fluorescence intensity of the coumarin formed. Further, the photoactivatable prodrug accumulates in the mitochondria and shows light-triggered temporally controlled cell death. In the future, our platform can be tuned for any biological application of interest, offering immense value in biomedicine.

Iridium-Triggered Allylcarbamate Uncaging in Living Cells.

Designing a metal catalyst that addresses the major issues of solubility, stability, toxicity, cell uptake, and reactivity within complex biological milieu for bioorthogonal controlled transformation reactions is a highly formidable challenge. Herein, we report an organoiridium complex that is nontoxic and capable of the uncaging of allyloxycarbonyl-protected amines under biologically relevant conditions and within living cells. The potential applications of this uncaging chemistry have been demonstrated by the generation of diagnostic and therapeutic agents upon the activation of profluorophore and prodrug in a controlled fashion within HeLa cells, providing a valuable tool for numerous potential biological and therapeutic applications.

Correction: Aggregation-induced emission active metal complexes: a promising strategy to tackle bacterial infections.

Correction for 'Aggregation-induced emission active metal complexes: a promising strategy to tackle bacterial infections' by Puja Prasad et al., Chem. Commun., 2021, 57, 174-186, DOI: 10.1039/D0CC06037B.

Aggregation-induced emission active metal complexes: a promising strategy to tackle bacterial infections.

Bacterial infection is a major global threat to human health and currently one of the leading causes of death worldwide. The development of probes for rapid diagnosis of bacteria with desired sensitivity and selectivity along with antibacterial activity against multidrug-resistant (MDR) bacteria has remained a great challenge. Whilst the traditional methods such as cell culture and colony counting, polymerase chain reaction and immunoassays are used for bacterial infection detection, these are time consuming, laborious and require a skilled operator. On the other hand, the rapid emergence of MDR bacteria is also posing another serious public health threat. Hence, it is an utmost urgency to develop novel therapeutics and rapid diagnostic agents for tackling MDR bacteria. Over the last few years, significant progress has been made towards the development of metal-based aggregation-induced emission luminogens (AIEgens) for bacterial management. These AIEgen materials offer potential applications for simultaneous detection and image-guided elimination of bacteria for the treatment of bacterial infections. In this Feature Article, we have highlighted the recent progress in the development of metal-based AIEgens for detection, discrimination and decimation of bacteria. In addition, the potential challenges in developing antibacterial agents and several future perspectives of metal-based AIEgens in this field have also been discussed.

Simultaneous Ultrasensitive Detection and Elimination of Drug-Resistant Bacteria by Cyclometalated Iridium(III) Complexes.

Antimicrobial resistance has become a major threat to public health due to the rampant and empirical use of antibiotics. Rapid diagnosis of bacteria with the desired sensitivity and selectivity still, however, remains an open challenge. We report a special class of water-soluble metal-based aggregation-induced emission luminogens (AIEgens), namely, cyclometalated iridium(III) polypyridine complexes of the type [Ir(PQ)2(N^N)]Cl (1-3), where PQ = 2-phenylquinoline and N^N = 2,2'-bipyridine derivatives, that demonstrate dual capability for detection and elimination of drug-resistant bacteria in aqueous solutions. These AIEgens exhibit selective and rapid sensing of endotoxins, such as lipopolysaccharides (LPS) and lipoteichoic acid (LTA) released by the bacteria, with a detection limit in the lower nanomolar range. Targeting these naturally amplified biomarkers (approximately 1 million copies per cell) by iridium(III) complexes induces strong AIE in the presence of different Gram-negative and Gram-positive bacteria including carbapenem-resistant A. baumannii (CRAB) and methicillin-resistant S. aureus (MRSA) at concentrations as low as 1.2 CFU/mL within 5 min in spiked water samples. Detection of bacteria by the complexes is also visible to the naked eye at higher (108 CFU/mL) cell concentrations. More notably, complexes 1 and 2 show potent antibacterial activity against drug-resistant bacteria with low minimum inhibitory concentrations (MICs) ≤ 5 µg/mL (1-4 µM) via ROS generation and cell membrane disintegrity. To the best of our knowledge, this work is the "first-in-class" example of a metal-based theranostic system that integrates selective, sensitive, rapid, naked-eye, wash-free, and real-time detection of bacteria using broad-spectrum antibiotics into a single platform. This dual capability of AIEgens makes them ideal scaffolds for monitoring bacterial contamination in aqueous samples and pharmaceutical applications.

A Single Step in vitro Bioassay Mimicking TLR4-LPS Pathway and the Role of MD2 and CD14 Coreceptors.

Acute systemic Gram-negative bacterial infections are accompanied by release of lipopolysaccharide (LPS) endotoxins into the bloodstream and an innate immune host response via the well-known toll like receptor 4 (TLR4) pathway. In this, LPS associates non-covalently with TLR4 to form an activated heterodimer (LPS/MD2/TLR4)2 complex in vivo, assisted by a coreceptor CD14. This complexation process has been illustrated ex vivo using indirect methods such as cytokine, interleukin, TNF-α measurements and by direct demonstration of sequential binding events on a surface using advanced optics. We are the first ones to carry out homogeneous self-assembly of LPS-rTLR4-MD2 conjugates in vitro in a single step, and further demonstrate the role of CD14 as a catalyst during this process. The assay comprises of LPS, MD2, CD14, and recombinant TLR4-conjugated magnetic particles co-incubated in a buffer at room temperature. The complexes are removed by magnetic separation and the extent of binding is estimated by quantifying the unbound biomolecules in the supernatant using standard biophysical techniques. Our results show that rTLR4-MD2-LPS complexes form in an hour and follow a 1:1:1 stoichiometry, in agreement with the in vivo/ex vivo studies. The assay is also highly specific; addition of known LPS-binding ligands decreased the LPS-rTLR4 complexation, allowing its use as a rapid tool for molecular inhibitor screening.

ε-Polylysine Nanoconjugates: Value-Added Antimicrobials for Drug-Resistant Bacteria.

Antimicrobial resistance poses a serious threat to human health and is evidently not restricted to any one part of the globe. Over the last few decades, no new antibiotics have been discovered, and many antibiotics currently available are failing against several critical pathogenic strains due to emerging drug resistance. We have designed a strategy to combat deadly drug-resistant bacteria by using nanocargos that consist of gold nanoparticles (AuNPs) conjugated to ε-polylysine (PLL) and octadecanethiol (C18) either alone or in combination. These nanocargos when tested against reference strains of carbapenem-resistant Acinetobacter baumannii (CRAB) and methicillin-resistant Staphylococcus aureus (MRSA) showed 15-20-fold higher antibacterial activity compared to free PLL. The minimum inhibitory concentration (MIC) of the nanoconjugates was found to lie between 8 and 15 µg/mL for both these bacteria, and they were also found to be nonhemolytic and nontoxic to mammalian cells. The mechanistic evaluation of antibacterial action showed alternate pathways of uptake for free PLL and the nanoconjugates. Further, the nanocargos were successfully used and found to be superior to free PLL in preventing biofilm formation in MRSA and CRAB. The PLL nanoconjugates may find applications in prevention of bacterial biofilm formation on surfaces such as surgical instruments and indwelling devices like stents, catheters, cannulas, orthopedic implants, and pacemakers.

Nanobioconjugates: Weapons against Antibacterial Resistance.

The increase in drug resistance in pathogenic bacteria is emerging as a global threat as we swiftly edge toward the postantibiotic era. Nanobioconjugates have gained tremendous attention to treat multidrug-resistant (MDR) bacteria and biofilms due to their tunable physicochemical properties, drug targeting ability, enhanced uptake, and alternate mechanisms of drug action. In this review, we highlight the recent advances made in the use of nanobioconjugates to combat antibacterial resistance and provide crucial insights for designing nanomaterials that can serve as antibacterial agents for nanotherapeutics, nanocargos for targeted antibiotic delivery, or both. Also discussed are different strategies for treating robust biofilms formed by bacteria.

Evaluation of intraductal delivery of poly(ethylene glycol)-doxorubicin conjugate nanocarriers for the treatment of ductal carcinoma in situ (DCIS)-like lesions in rats.

Ductal carcinoma in situ is the most commonly diagnosed early stage breast cancer. The efficacy of intraductally delivered poly(ethylene glycol)-doxorubicin (PEG-DOX) nanocarriers, composed of one or more DOX conjugated to various PEG polymers, was investigated in an orthotopic ductal carcinoma in situ-like rat model. In vitro cytotoxicity was evaluated against 13762 Mat B III cells using MTT assay. The orthotopic model was developed by inoculating cancer cells into mammary ducts of female Fischer 344 retired breeder rats. The ductal retention and in vivo antitumour efficacy of two of the six nanocarriers (5 kDa PEG-DOX and 40 kDa PEG-(DOX)4) were investigated based on in vitro results. Mammary retention of DOX and PEG-DOX nanocarriers was quantified using in vivo imaging. Histopathologic effects of DOX and PEG-DOX nanocarriers on mammary ductal structure were also investigated. Cytotoxicities of small linear PEG-DOX nanocarriers (5 and 10 kDa) were not different from DOX whereas larger PEG-DOX nanocarriers showed reduced potency. The order of mammary retention was 40 kDa PEG-(DOX)4 > 5 kDa PEG-DOX >> DOX, in normal and tumour-bearing rats. Intraductally administered PEG-DOX nanocarriers and DOX were effective in reducing tumour incidence and increasing survival rate, with no significant differences found among the three treatment groups. However, nanocarriers administered intravenously at the same doses were not effective, and intraductally administered free DOX caused severe local toxicity. Intraductal administration of PEG-DOX nanocarriers is effective and less toxic than that of free DOX, as well as IV DOX/PEG-DOX. Furthermore, PEG-DOX nanocarriers demonstrate the added benefit of prolonging DOX ductal retention, which would necessitate less frequent dosing.

Regenerative Core-Shell Nanoparticles for Simultaneous Removal and Detection of Endotoxins.

Detection and removal of lipopolysaccharides (LPS) from food and pharmaceutical preparations is important for their safe intake and administration to avoid septic shock. We have developed an abiotic system for reversible capture, removal, and detection of LPS in aqueous solutions. Our system comprises long C18 acyl chains tethered to Fe3O4/Au/Fe3O4 nanoflowers (NFs) that act as solid supports during the separation process. The reversible LPS binding is mediated by facile hydrophobic interactions between the C18 chains and the bioactive lipid A component present on the LPS molecule. Various parameters such as pH, solvent, sonication time, NF concentration, alkane chain length, and density are optimized to achieve a maximum LPS capture efficiency. The NFs can be reused at least three times by simply breaking the NF-LPS complexes in the presence of food-grade surfactants, making the entire process safe, efficient, and scalable. The regenerated particles also serve as colorimetric labels in dot blot bioassays for simple and rapid estimation of the LPS removed.

Remarkable enhancement in photocytotoxicity and hydrolytic stability of curcumin on binding to an oxovanadium(IV) moiety.

Oxovanadium(IV) complexes of polypyridyl and curcumin-based ligands, viz. [VO(cur)(L)Cl] (1, 2) and [VO(scur)(L)Cl] (3, 4), where L is 1,10-phenanthroline (phen in 1 and 3), dipyrido[3,2-a:2',3'-c]phenazine (dppz in 2 and 4), Hcur is curcumin and Hscur is diglucosylcurcumin, were synthesized and characterized and their cellular uptake, photocytotoxicity, intracellular localization, DNA binding, and DNA photo-cleavage activity studied. Complex [VO(cur)(phen)Cl] (1) has V(IV)N2O3Cl distorted octahedral geometry as evidenced from its crystal structure. The sugar appended complexes show significantly higher uptake into the cancer cells compared to their normal analogues. The complexes are remarkably photocytotoxic in visible light (400-700 nm) giving an IC50 value of <5 µM in HeLa, HaCaT and MCF-7 cells with no significant dark toxicity. The green emission of the complexes was used for cellular imaging. Predominant cytosolic localization of the complexes 1-4 to a lesser extent into the nucleus was evidenced from confocal imaging. The complexes as strong binders of calf thymus DNA displayed photocleavage of supercoiled pUC19 DNA in red light by generating ˙OH radicals as the ROS. The cell death is via an apoptotic pathway involving the ROS. Binding to the VO(2+) moiety has resulted in stability against any hydrolytic degradation of curcumin along with an enhancement of its photocytotoxicity.

Mitochondria-targeting oxidovanadium(IV) complex as a near-IR light photocytotoxic agent.

Oxidovanadium(IV) complexes [VO(L(1))(phen)]·Cl (1) and [VO(L(2))(L(3))]·Cl (2), in which HL(1) is 2-{[(benzimidazol-2-yl)methylimino]-methyl}phenol (sal-ambmz), HL(2) is 2-[({1-[(anthracen-9-yl)methyl]-benzimidazol-2-yl}methylimino)-methyl]phenol (sal-an-ambmz), phen is 1,10-phenanthroline and L(3) is dipyrido[3,2-a:2',3'-c]phenazine (dppz) conjugated to a Gly-Gly-OMe dipeptide moiety, were prepared, characterized, and their DNA binding, photoinduced DNA-cleavage, and photocytotoxic properties were studied. Fluorescence microscopy studies were performed by using complex 2 in HeLa and HaCaT cells. Complex 1, structurally characterized by X-ray crystallography, has a vanadyl group in VO2N4 core with the VO(2+) moiety bonded to N,N-donor phen and a N,N,O-donor Schiff base. Complex 2, having an anthracenyl fluorophore, showed fluorescence emission bands at 397, 419, and 443 nm. The complexes are redox-active exhibiting the V(IV)/V(III) redox couple near -0.85 V versus SCE in DMF 0.1 M tetrabutylammonium perchlorate (TBAP). Complex 2, having a dipeptide moiety, showed specific binding towards poly(dAdT)2 sequence. The dppz-Gly-Gly-OMe complex showed significant DNA photocleavage activity in red light of 705 nm through a hydroxyl radical ((.) OH) pathway. Complex 2 showed photocytotoxicity in HaCaT and HeLa cells in visible light (400-700 nm) and red light (620-700 nm), however, the complex was less toxic in the dark. Fluorescence microscopy revealed the localization of complex 2 primarily in mitochondria. Apoptosis was found to occur inside mitochondria (intrinsic pathway) caused by ROS generation.

Planar triazinium cations from vanadyl-mediated ring cyclizations: the thiazole species for efficient nuclear staining and photocytotoxicity.

Planar triazinium cationic species from vanadyl-assisted cyclization of 1-(2-thiazolylazo)-2-naphthol (H-TAN, 1), 1-(2-pyridylazo)-2-naphthol (H-PAN, 2), 2-(2'-thiazolylazo)-p-cresol (H-TAC, 3) and 6-(2'-thiazolylazo)-resorcinol (H-TAR, 5) were prepared and characterized. A dioxovanadium(V) species [VO(2)(TAR)] (4) was also isolated. Compounds 1, 2 and 4 were structurally characterized. Both 1 and 2 have planar structures. Complex 4 has V(V)O(3)N(2) coordination geometry. The cyclised triazinium compound forms a radical species within -0.06 to -0.29 V vs. SCE in DMF-0.1 M tetrabutylammonium perchlorate with a second response due to formation of an anionic species. A confocal microscopic study showed higher nuclear uptake for 1 having a fused thiazole moiety than 2 with a fused pyridine ring. The compounds showed a partial intercalative mode of binding to calf thymus DNA. Compound 1 showed plasmid DNA photo-cleavage activity under argon and photocytotoxicity in HeLa and MCF-7 cells with IC(50) values of 15.1 and 3.4 µM respectively in visible light of 400-700 nm, while being essentially non-toxic in the dark with IC(50) values of 90.4 and 21.9 µM. A TDDFT study was done to rationalize the experimental data.

Remarkable photocytotoxicity of curcumin in HeLa cells in visible light and arresting its degradation on oxovanadium(IV) complex formation.

Curcumin (Hcur) as a cellular imaging and PDT agent shows remarkable photocytotoxicity in HeLa cells in visible light of 400-700 nm giving IC(50) = 8.2 ± 0.2 µM and its degradation is arrested on formation of photocytotoxic dipyridophenazine (dppz) complex [VO(cur)(dppz)Cl] (IC(50) = 3.3 ± 0.4 µM), while both are less toxic in the dark.

Planar triazinium cations from VO(2+)-assisted ring cyclizations: a remarkably efficient thiazole species for nuclear staining, PDT and anaerobic photocleavage of DNA.

Planar triazinium cationic species, from VO(2+)-assisted cyclization of 1-(2-thiazolylazo)-2-naphthol, shows efficient DNA intercalative binding, visible light-induced anaerobic plasmid DNA photocleavage activity and photocytotoxicity in HeLa and MCF-7 cancer cells by an apoptotic pathway with selective localization of the compound in the nucleus as evidenced from the nuclear staining and confocal imaging.