Aggregation-induced emission enhancement (AIEE) of tetrarhenium(I) metallacycles and their application as luminescent sensors for nitroaromatics and antibiotics.

The self-assembly of tetrarhenium metallacycles [{Re(CO)3}2(µ-dhaq)(µ-N-N)]2 (3a, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene; 3b, N-N = 1,3-bis(1-octylbenzimidazol-2-yl)benzene), (H2-dhaq = 1,4-dihydroxy-9,10-anthraquinone) and [{Re(CO)3}2(µ-thaq)(µ-N-N)]2 (4, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene), (H2-thaq = 1,2,4-trihydroxy-9,10-anthraquinone) under solvothermal conditions is described. The metallacycles 3a,b and 4 underwent aggregation-induced emission enhancement (AIEE) in THF upon the incremental addition of water. TEM images revealed that metallacycle 3a in a 60% aqueous THF solution formed rectangular aggregates with a wide size distribution, while a 90% aqueous THF solution resulted in the formation of a mixture of nanorods and amorphous aggregates due to rapid and abrupt aggregation. UV-vis and emission spectral profiles supported the formation of nanoaggregates of metallacycles 3a,b and 4 upon the gradual addition of water to a THF solution containing metallacycles. Further studies indicated that these nanoaggregates were excellent probes for the sensitive and selective detection of nitro group containing picric acid (PA) derivatives as well as antibiotics.

Advances of Inorganic Materials in the Detection and Therapeutic Uses against Coronaviruses.

Coronaviruses (CoVs) are enveloped viruses with particle-like characteristics and a diameter of 60-140 nm, positively charged, and single-stranded RNA genomes, which caused a major outbreak of human fatal pneumonia in the beginning of the 21st century. COVID-19 is currently considered a continuous potential pandemic threat across the globe. Therefore, considerable efforts have been made to develop innovative methods and technologies for suppressing the spread of viruses as well as inactivating the viruses but COVID-19 vaccines are still in the development phase. This perspective focuses on the sensing, detection and therapeutic applications of CoVs using inorganic- based nanomaterials, metal complexes, and metal-conjugates. Synthetic inorganic- based nanoparticles interact strongly with proteins of viruses due to their morphological similarities, and therefore, numerous antivirals have been tested for efficacy against different viruses in vitro through colorimetric and electrochemical assays. Metal complexes- based agents such as bismuth complexes form an attractive class of drugs with a number of therapeutic applications, including the inhibition and duplex-unwinding activity of SARS-CoV helicase by quantitative real-time PCR (Q-RT-PCR), phosphate release assay and radioassay studies. Metal-conjugates show major effects on inhibiting the 3Clike protease of SARS-CoV and the replication of RNA-dependent RNA polymerase (RdRp). We anticipate that these approaches will provide rapid and accurate antiviral strategies in the development of these innovative sensors for the detection, inhibition and antiviral activities of coronaviruses.

Selective anions mediated fluorescence "turn-on", aggregation induced emission (AIE) and lysozyme targeting properties of pyrene-naphthalene sulphonyl conjugate.

We have designed and synthesized a novel pyrene-naphthalene sulphonyl conjugate, 1-((1Z)-(4-((Z)-4-(pyrene-1-yl)methyleneamino)phenylsulfonyl)phenylimino)methyl)naphthalene-2-ol (PSN) through a facile two-step reactions. It was characterized by various spectral techniques. Fluorescence spectral studies showed that compound PSN featured fluorescence enhancement upon increasing the water content in THF. This can be attributed to the phenomena of aggregated induced emission (AIE), which is confirmed by SEM and AFM studies, due to the restriction of CHN isomerization of PSN. The anion sensing of PSN was examined with various anions. Among these anions, H2PO4- and F- ions were selectively sensing with a low detection limit of 3.52 × 10-7 M and 7.23 × 10-7 M, respectively, and an obvious color change from yellow to orange was observed by the naked eye. The mechanism of sensing involved the formation of hydrogen bonding interaction between O-H group of PSN and H2PO4-/ F- ions. The binding of PSN with LYZ was also examined by docking studies, which shows that H-bonding and hydrophobic interactions play crucial roles for the interaction of LYZ toward PSN.

Host-guest interaction studies of polycyclic aromatic hydrocarbons (PAHs) in alkoxy bridged binuclear rhenium (I) complexes.

The interaction of two neutral alkoxy bridged binuclear rhenium(I) complexes, 1 and 2 [{Re(CO)3(1,4-NVP)}2(µ2-OR)2] (1, R = C4H9; 2, R = C10H21; 1,4-NVP = 4-(1-naphthylvinyl)pyridine] with polycyclic aromatic hydrocarbons (PAH) is investigated. UV-vis absorption, emission, 1H NMR spectral titrations, TCSPC lifetime studies and DFT theoretical calculations were carried out to examine the binding responses of complexes 1 and 2 with various PAHs such as pyrene, naphthalene, anthracene and phenanthrene. The UV-Vis absorption spectra showed an increase in absorbance of the metal-to ligand charge-transfer (MLCT) and ligand centered (LC) bands upon addition of various PAH molecules to 1 and 2, whereas the emission behavior was found to show emission quenching, which might occur through energy transfer pathway. The binding constants (K) of complexes 1 and 2 for various PAHs are found to be in the order of 104 M-1 with a 1:1 binding mode, as determined from UV-vis absorption and emission spectral titration studies. 1H NMR spectral studies show that the chemical shifts of pyrene guest and the 1,4-NVP moiety of 2 are shifted up-field, whilst the alkoxy protons do not show any appreciable change in their chemical shifts. It is believed that the open cavities present in the Re(I) complexes may lead to the recognition of PAHs via CH···π interaction.

Aggregation-induced emission enhancement of anthracene-derived Schiff base compounds and their application as a sensor for bovine serum albumin and optical cell imaging.

Three anthracene-based Schiff base complexes, R1-R3 (R1 = (E)-N´-((anthracen-10-yl)methylene)benzohydrazide; R2 = (E)-1-((anthracen-10-yl)methylene)-4-phenylsemicarbazide; and R3 = (E)-1-((anthracen-10-yl)methylene)-4-phenylthiosemicarbazide) were synthesized from 9-anthracenecarboxaldehyde, benzohydrazide, 4-phenylsemicarbazide and 4-phenylthiosemi-carbazide respectively, and characterized by various spectral techniques. The absorption spectral characteristics of R1-R3 were bathochromically tuned to the visible region by extending the π conjugation. These target compounds were weakly fluorescent in tetrahydrofuran (THF) solution because of rapid isomerization of the C=N double bond in the excited state. However, the aqueous dispersion of R1-R3 in the THF/water mixture by the gradual addition of water up to 90% resulted in an increase in the fluorescence intensity mainly due to aggregation-induced emission enhancement (AIEE) properties. The formation of nanoaggregates of R1-R3 were confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The compounds R1-R3 are ideal probes for the fluorescence sensing of bovine serum albumin (BSA) and breast cancer cells by optical cell imaging.

Development of luminescent sensors based on transition metal complexes for the detection of nitroexplosives.

The detection of chemical explosives is a major area of research interest and is essential for the military as well as homeland security to counter the catastrophic effects of global terrorism. In recent years, tremendous effort has been devoted to the development of luminescent materials for the detection of explosives in the vapor, solution, and solid states with a high degree of selectivity and sensitivity and a rapid response time. Apart from the wide range of organic fluorescent chemosensors, transition metal complexes play a prominent role in the sensing of nitroaromatic explosives owing to their rich photophysical characteristics. This review briefly summarizes the salient features of the design and preparation of transition metal (Zn(ii), Ir(iii), Pd(ii), Pt(ii), Re(i) and Ru(ii)) complexes/metallacycles/metallosupramolecules with emphasis on their photophysical properties, sensing behavior, mechanism of action, and the driving forces for detecting explosives and future prospects and challenges. Most of the probes that have been reported to date act as "turn-off" luminescent sensors because their emission (intensity, lifetime, and quantum yield) is eventually quenched upon sensing with nitroaromatic compounds (NACs) through photo-induced electron or energy transfer. These unique properties of transition metal complexes in response to explosives open up new vistas for the development of real world applications such as on-site detection, in-field security, forensic research, etc.

Aggregation induced emission enhancement (AIEE) characteristics of quinoline based compound - A versatile fluorescent probe for pH, Fe(III) ion, BSA binding and optical cell imaging.

Novel benzimidazoquinoline derivative (AVT) was synthesized through a substitution reaction and characterized by various spectral techniques. Analyzing the optical properties of AVT under absorption and emission spectral studies in different environments exclusively with respect to solvents and pH, intriguing characteristics viz. aggregation induced emission enhancement (AIEE) in the THF solvent and 'On-Off' pH sensing were found at neutral pH. Sensing nature of AVT with diverse metal ions and bovine serum albumin (BSA) was also studied. Among the metal ions, Fe3+ ion alone tunes the fluorescence intensity of AVT probe in aqueous medium from "turn-on" to "turn-off" through ligand (probe) to metal charge transfer (LMCT) mechanism. The probe AVT in aqueous medium interacts strongly with BSA due to Fluorescence Resonance Energy Transfer (FRET) and the conformational change in BSA was further analyzed using synchronous fluorescence techniques. Docking study of AVT with BSA reveals that the active site of binding is tryptophan residue which is also supported by the experimental results. Interestingly, fluorescent AVT probe in cells was examined through cellular imaging studies using BT-549 and MDA-MB-231 cells. Thus, the single molecule probe based detection of multiple species and stimuli were described.

Sensing and inhibition of amyloid-ß based on the simple luminescent aptamer-ruthenium complex system.

Aggregation of amyloid-ß (Aß) peptide has been known to be pathologically associated with Alzheimer and dementia diseases. Amyloid-ß fibrils serve as an important target for the drugs development and diagnosis of neurodegenerative diseases. Herein, we report a new [Ru(dmbpy)(dcbpy)dppz)] complex (dmbpy; 4,4'-dimethyl-2,2'-bipyridine, dcbpy; 4,4'-dicorboxy-2,2'-bipyridine, dppz; dipyridophenazine) intercalated aptamer based recognition of amyloid-ß. Interestingly, aforementioned Ru(II) complex shows weak luminescence intensity in the aqueous medium but it shows strong luminescence intensity in the presence of RNA aptamer. Upon addition of amyloid-ß monomers, the luminescence intensity of Ru(II) complex is reduced due to the strong interaction of aptamer with amyloid-ß monomer/small oligomers. Furthermore, present study implies that our system has ability to inhibit the formation of amyloid-ß fibrils, which is confirmed from the AFM morphological structures in the absence and presence of aptamer. This work may contribute the rapid diagnosis and inhibition of amyloid-ß aggregation in the clinical applications.

Alkoxy bridged binuclear rhenium (I) complexes as a potential sensor for ß-amyloid aggregation.

Alkoxy bridged binuclear rhenium(I) complexes are used as a probe for the selective and sensitive detection of aggregation of ß-amyloid fibrils that are consorted with Alzheimer's disease (AD). The strong binding of the complexes is affirmed by the fluorescence enhancement and calculated binding constant value in the order of 10(5)M(-1) is obtained from the Scatchard plots. The binding of ß-amyloid can be attributed to π-π stacking interaction of naphthalene moiety present in rhenium(I) complexes, and it is supported by docking studies. The selectivity is quite high towards other proteins and the formation of fibrils can be observed in the range of 30-40 nm through the AFM and TEM techniques.

Electron transfer reactions of ruthenium(II)-bipyridine complexes carrying tyrosine moiety with quinones.

Three ruthenium(II)-bipyridine complexes carrying a tyrosine moiety were synthesized and photophysical and electron transfer studies with quinones were carried out using absorption and emission spectral techniques. The binding efficiency of quinones with ruthenium(II)-bipyridine complexes was also studied using these techniques. The binding efficiency was moderate and similar for all complexes with all quinones. The quenching modes were also similar and efficient for all complexes with all quinones. The quenching processes were diffusion controlled. The rate of electron transfer was calculated using semiclassical theory.

Aggregation-induced emission enhancement in alkoxy-bridged binuclear rhenium(I) complexes: application as sensor for explosives and interaction with microheterogeneous media.

The aggregation-induced emission enhancement (AIEE) characteristics of the two alkoxy-bridged binuclear Re(I) complexes [{Re(CO)3(1,4-NVP)}2(µ2-OR)2] (1, R = C4H9; 2, C10H21) bearing a long alkyl chain with 4-(1-naphthylvinyl)pyridine (1,4-NVP) ligand are illustrated. These complexes in CH2Cl2 (good solvent) are weakly luminescent, but their intensity increased enormously by almost 500 times by the addition of poor solvent (CH3CN) due to aggregation. By tracking this process via UV-vis absorption and emission spectral and TEM techniques, the enhanced emission is attributed to the formation of nanoaggregates. The nanoaggregate of complex 2 is used as a sensor for nitroaromatic compounds. Furthermore, the study of the photophysical properties of these binuclear Re(I) complexes in cationic, cetyltrimethylammonium bromide (CTAB), anionic, sodium dodecyl sulfate (SDS), and nonionic, p-tert-octylphenoxypolyoxyethanol (TritonX-100, TX-100), micelles as well as in CTAB-hexane-water and AOT-isooctane-water reverse micelles using steady-state and time-resolved spectroscopy and TEM analysis reveals that the nanoaggregates became small and compact size.