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We report the synthesis and pH dependent emission spectral behaviour of four emissive iridium(III) complexes (Ir1 - Ir4) with two isomeric pairs of bis-trifluoromethyl appended benzimidazole ligands. The imidazolyl hydrogen(N-H) has been replaced by phenyl groups (N-Ph) in two ligands to understand the impact of hydrogen bonding on the photophysical properties of the complexes and it indeed plays interesting role in the charge-transfer dynamics. The pH dependent electronic spectral change is observed for two of the complexes. The enhancement of emission intensity is observed at different wavelength for pH < 7 and pH > 7 for Ir1 and Ir3. The emission sensing of biogenic amines with pka values ranging from 5.80 - 9.74 is reported along with cellular imaging. The complex Ir1 specifically localizes within lysosome (pH = 4.5 - 5) and thus image this organelle with great precision. The detail electronic spectra and electrochemical behaviour were reported here along with TDDFT results.

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The targeted depletion of potential gut pathogens is often challenging because of their intrinsic ability to thrive in harsh gut environments. Earlier, we showed that Campylobacter jejuni (C. jejuni) exclusively uses the Type-VI Secretion System (T6SS) to target its prey such as Escherichia coli (E. coli), and phenotypic differences between T6SS-negative and T6SS-positive C. jejuni isolates toward bile salt sensitivity. However, it remains unclear how the target-driven T6SS functionality prevails in a polymicrobial gut environment. Here, we investigated the fate of microbial competition in an altered gut environment via bacterial T6SS using a T6SS-negative and -positive C. jejuni or its isogenic mutant of the hemolysin-coregulated protein (hcp). We showed that in the presence of bile salt and prey bacteria (E. coli), T6SS-positive C. jejuni experiences enhanced intracellular stress leading to cell death. Intracellular tracking of fluorophore-conjugated bile salts confirmed that T6SS-mediated bile salt influx into C. jejuni can enhance intracellular oxidative stress, affecting C. jejuni viability. We further investigated whether the T6SS activity in the presence of prey (E. coli) perturbs the in vivo colonization of C. jejuni. Using chickens as primary hosts of C. jejuni and non-pathogenic E. coli as prey, we showed a marked reduction of C. jejuni load in chickens cecum when bile salt solution was administered orally. Analysis of local antibody responses and pro-inflammatory gene expression showed a reduced risk of tissue damage, indicating that T6SS activity in the complex gut environment can be exploited as a possible measure to clear the persistent colonization of C. jejuni in chickens.

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The application of transition metal complexes for antimicrobial photodynamic therapy (PDT) has emerged as an attractive alternative in mitigating a broad range of bacterial pathogens, including multidrug-resistant pathogens. In view of their photostability, long excited-state lifetimes, and tunable emission properties, transition metal complexes also contribute as bioimaging agents. In the present work, we designed mono and trinuclear cyclometalated iridium (III) complexes to explore their imaging application and antibacterial potential. For this, we used Methicillin-resistant S. aureus (MRSA), the most prevalent of community-associated (CA) multidrug-resistant (MDR) bacteria (CA MDR) and Lactococcus lactis (L. lactis) as Gram-positive while Campylobacter jejuni (C. jejuni) and E. coli as Gram-negative bacteria. In addition to differential bioimaging of these bacteria, we assessed the antibacterial effects of both mono and trinuclear Ir(III) complexes under exposure to 427 nm LED light. The data presented herein strongly suggest better efficacy of trinuclear Ir(III) complex over the mononuclear complex in imparting photoinduced cell death of MRSA. Based on the safety profile of these complexes, we propose that trinuclear cyclometalated iridium(III) complex holds great promise for selective recognition and targeting MDR bacteria with minimal off-target effect.

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The organelle-specific localization of mononuclear and trinuclear iridium(III) complexes and their photodynamic behavior within the cells are described herein, emphasizing their structure-activity relationship. Both the IrA2 and IrB2 complexes possess a pair of phenyl-benzothiazole derived from the -CHO moieties of mononuclear organometallic iridium(III) complexes IrA1 and IrB1, which chelates IrCp*Cl (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene) to afford trinuclear complexes IrA3 and IrB3. Insights into the photophysical and electrochemical parameters of the complexes were obtained by a time-dependent density functional theory study. The synthesized complexes IrA2, IrA3, IrB2, and IrB3 were found to be nontoxic to human MCF7 breast carcinoma cells. However, the photoexcitation of complexes using LED light could effectively trigger intracellular reactive oxygen species (ROS) generation, leading to cell death. Furthermore, to check the organelle-specific localization of IrA2 and IrB2, we observed that both complexes could selectively localize in the endoplasmic reticulum. In contrast, trinuclear IrA3 and IrB3 accumulate in the nuclei. The photoexcitation of complexes using LED light could effectively trigger intracellular reactive oxygen species (ROS) generation, leading to cell death.

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In this work, the aggregation-induced photoluminescence emission (AIPE) of three water-soluble heterobimetallic Ir-Pt complexes was reported with insight into their photophysical and electrochemical properties and imaging of bacterial cells. An alkyne appended Schiff's base L, bridges bis-cyclometalated iridium(III) and platinum(II) terpyridine centre. The Schiff's base (N-N fragment) serves as the ancillary ligand to the iridium(III) centre, while the alkynyl end is coordinated to platinum(II). The pH and ionic strength influence the aggregation kinetics of the alkynylplatinum(II) fragment, leading to metal-metal and π-π interactions with the emergence of a triplet metal-metal-to-ligand charge transfer (3MMLCT) emission. The excellent reversibility and photostability of aggregation-induced emission (AIE) of these aqua-friendly complexes were tested for their ability to sense and selectively image E. coli cells at various pH values.

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Emerging mutations in the SARS-CoV-2 genome pose a challenge for vaccine development and antiviral therapy. The antiviral efficacy of Azadirachta indica bark extract (NBE) was assessed against SARS-CoV-2 and m-CoV-RSA59 infection. Effects of in vivo intranasal or oral NBE administration on viral load, inflammatory response, and histopathological changes were assessed in m-CoV-RSA59-infection. NBE administered inhibits SARS-CoV-2 and m-CoV-RSA59 infection and replication in vitro, reducing Envelope and Nucleocapsid gene expression. NBE ameliorates neuroinflammation and hepatitis in vivo by restricting viral replication and spread. Isolated fractions of NBE enriched in Nimbin isomers shows potent inhibition of m-CoV-RSA59 infection in vitro. In silico studies revealed that NBE could target Spike and RdRp of m-CoV and SARS-CoV-2 with high affinity. NBE has a triterpenoids origin that may allow them to competitively target panoply of viral proteins to inhibit mouse and different strains of human coronavirus infections, suggesting its potential as an antiviral against pan-ß-Coronaviruses.

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We report square planar Pt(ii) complexes as luminescent biosensors for DNA detection in solution. The sensing is attributed to the aggregation induced bright red photoluminescence (AIPE) of the complexes in the presence of DNA that can be seen with the naked eye using only a 360 nm light source. Terpyridine appended luminescent geminal bistriazoles (L1-L4, from geminal bisazide A through azide-alkyne 'click' cycloaddition) with versatile chelating sites were explored for metal coordination and reaction with Pt(dmso)2Cl2 yielding tetranuclear and dinuclear complexes of Pt(ii) with different N∩N ligand environments. Thermally stable gem-bisazide and bistriazoles are hardly reported in the literature and this is the first report of terpyridine appended geminal bisazide and bistriazoles.

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The rational synthesis of trinuclear emissive organometallic complexes with two equivalent platinum(II) centres appended to the ancillary substituted 2,2'-bipyridyl ligand of the cyclometalated iridium(III) centre is reported here. The alkynyl-platinum moiety and cyclometalated iridium(III) centres have been separated through a non-conjugated CH2 -O-CH2 linkage. The emission titration with amino acids reveals that the complexes sense free amino acids. The luminescence sensing of BSA is thus attributed to the amino acid sensing ability of the complexes and confirmed by emission anisotropy and Far-UV CD spectral study. The decrease in α-helix in the CD spectra signifies the changes in the secondary structure of protein in presence of the complexes.

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In this study we have analysed the comparative photophysical and electrochemical properties of two isomeric heterotrinuclear PtII -IrIII -PtII complexes 3 and 6 and the four corresponding intermediate isomeric homonuclear cyclometalated iridium(III) complexes 1, 2, 4 and 5. The isomerisation originates from positional differences in the formyl, di-2-picolylamine and Pt-di-2-picolylamine moieties appended to cyclometalated or ancillary ligands. The interaction of 5'-GMP with the trinuclear complexes 3 and 6 shows that platinum centres appended to the cyclometalated ligand in 3 facilitate the binding of two 5'-GMP units per PtII centre in preference to a single 5'-GMP unit per PtII centre as observed in 6. The 1:2 and 1:1 PtII -5'-GMP binding patterns probably arise from the convenient arrangements of the Pt-di-2-picolylamine units in different planes in complex 3, which is absent in complex 6.

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Organometallic complexes have important application in the field of protein staining, with potential for use in proteomic analysis. The rational synthesis of a trinuclear luminescent organometallic complex with two platinum(ii) centres appended to the cyclometalated ligand of the iridium(iii) centre is reported here. Two di-2-picolylamine groups bonded to the cyclometalated phenyl pyridine moiety provide three coordinating sites to each platinum centre. The replacement of chloride in the fourth coordination site of two square planar platinum metal centres with the imidazole nitrogen or sulphur atom of histidine/cysteine is evident from the change in luminescence intensity upon binding these amino acids. The increase in luminescence emission intensity upon binding of histidine to the organometallic complex allowed it to be used as a protein staining agent. Reversibility of staining upon washing with imidazole enhances the possibility of its application in mass spectrometric analysis.

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Cyclometalated rhodium(III) and iridium(III) complexes (1-4) of two Schiff base ligands L1 and L2 with the general formula [M(ppy)2(Ln)]Cl {M = Rh, Ir; ppy = 2-phenylpyridine; n = 1, 2; L = Schiff base ligand} have been synthesized. The new ligands and the complexes have been characterized with spectroscopic techniques. Electrochemistry of the complexes revealed anodic behavior, corresponding to an M(III) to M(IV) oxidation. The X-ray crystal structures of complexes 2 and 4 have also been determined to interpret the coordination behavior of the complexes. Photophysical study shows that all the complexes display fluorescence at room temperature with quantum yield of about 3 × 10-2 to 5 × 10-2. The electronic absorption spectra of all the complexes fit well with the computational studies. Cellular imaging studies were done with the newly synthesized complexes. To the best of our knowledge, this is the first report of organometallic complexes of rhodium(III) and iridium(III) with Schiff base ligands explored for cellular imaging. Emphasis of this work lies on the structural features, photophysical behavior, cellular uptake and imaging of the fluorescent transition metal complexes.

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Cyclometalated iridium complexes have important applications as phosphorescent probes for cellular imaging due to their photophysical properties. Moreover, these properties also make them potential candidates as photosensitizers for photodynamic therapy (PDT) of tumors and skin diseases. Treatment of MCF7 breast carcinoma cells with a heteroleptic phosphorescent cyclometalated iridium(III) complex C2 followed by confocal imaging indicates that the complex selectively localizes and exhibits high fluorescence in the endoplasmic reticulum. In an unprecedented approach, systematic alteration of functional groups or the metal core in C2 to synthesize a series of iridium(III) complexes (C1­C10) and an organometallic rhenium complex C11 with an imidazolyl modified phenanthroline ligand has indicated the functional groups and their interactions that are responsible for this selective localization. Remarkably, the exposure of the cells treated with C2 to irradiation at 405 nm for one hour led to membrane blebbing and cell death, demonstrating a photosensitizing property of the compound.

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Two thiosemicarbazide and semicarbazide functionalized pyrene labeled Schiff base compounds have been synthesized. The pyrene moieties in the compounds result in formation of π-π coupled complexes in aqueous medium in the excited electronic state. Added γ-cyclodextrin allows incorporation of the pyrene head inside its less polar core and promotes hydrogen bonding of the thio and oxo groups of the compounds with its rim hydroxyl groups to "stabilise" the monomers. This is confirmed by FT-IR and absorption spectroscopy. The stabilised monomers lead to formation of stabilised excimers as monitored by steady state and time-resolved fluorescence spectroscopy through varying the experimental conditions. The proposed model for the stabilisation of the Schiff base monomers has been evidenced by comparing with the fluorescence spectroscopic changes of two control compounds. The present work reports a step ahead toward proposing a simple host-guest method to extra stabilise the pyrene based excimers that can be biologically utilised.

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Influence on ionic surfactants by a specially designed terpyridylamine ligand and the ruthenium(II) complex formed with it has been studied in aqueous solution. The ligand coordinates to Ru(2+) into an octahedral geometry in such a way that the final form takes a "nido" or nest-like structure. The substitution on the pyridinyl moiety is kept at the ortho position to acquire the specified geometry. Similar complexes have been reported to have anti-tumor properties and thus the ruthenium complexes can effectively replace platinum complexes that serve the same purpose but with certain drawbacks. The "nido" geometry was chosen to minimize the cytotoxicity that creeps in when para substituents of the pyridinyl moiety are used. The latter variety forms a dendridic scaffold. In presence of both the ligand and the complex, ionic surfactants form elongated aggregates. The surface charge of those aggregates decides the nature of interaction of the ligand and the complex formed therefore. Interaction with anionic surfactant scaffold is found to be stronger than the cationic one.

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[Cp(∗)IrCl(2)](2) is used as an efficient promoter for the synthesis of sugar acetals and ketals with good to excellent yields. The catalyst is found to be general for a wide range of sugars.

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The title complex, [Cu(2)I(2)(C(10)H(11)N(3)O(2)S)(2)(C(18)H(15)P)(2)], is a centrosymmetric sulfur-bridged dimer of Cu(I) with PPh(3) and iodine. The Cu(I) atom shows a distorted tetra-hedral geometry, with bite angles ranging from 98.61 (2) to 120.16 (3)°. The intra-molecular Cu⋯Cu distance is 2.8228 (12) Å. The thio-semicarbazone ligand is coordinated only through the S atom. In the crystal, the complex mol-ecules are linked via inter-molecular N-H⋯O hydrogen bonds, resulting in a hydrogen-bonded chain along the b axis.

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The title compound, C(15)H(12)N(2)O(2)·3H(2)O, has been prepared from the reaction of a Schiff base of benzene-1,2-diamine and iron perchlorate at room temperature. The dihedral angle between the benzimidazole ring and the 4-substituted benzene ring is 0.47 (3)°. Hydrogen bonding involving water mol-ecules, imidazole N, imidazole imine H and ester O atoms stabilizes the crystal structure.

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Reaction of 2-(arylazo)phenols with [Ru(PPh(3))(2)(CO)(2)Cl(2)] affords a family of organometallic complexes of ruthenium(II) of type [Ru(PPh(3))(2)(CO)(CNO-R)], where the 2-(arylazo)phenolate ligand (CNO-R; R = OCH(3), CH(3), H, Cl, and NO(2)) is coordinated to the metal center as tridentate C,N,O-donor. Another group of intermediate complexes of type [Ru(PPh(3))(2)(CO)(NO-R)(H)] has also been isolated, where the 2-(arylazo)phenolate ligand (NO-R) is coordinated to the metal center as bidentate N,O-donor. Structures of the [Ru(PPh(3))(2)(CO)(NO-OCH(3))(H)] and [Ru(PPh(3))(2)(CO)(CNO-OCH(3))] complexes have been determined by X-ray crystallography. All the complexes are diamagnetic and show characteristic (1)H NMR signals and intense MLCT transitions in the visible region. Both the [Ru(PPh(3))(2)(CO)(NO-R)(H)] and [Ru(PPh(3))(2)(CO)(CNO-R)] complexes show two oxidative responses on the positive side of SCE.

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Reaction of chloranilic acid (H2ca) with [Os(bpy)2 Br2] (bpy = 2,2'-bipyridine) affords a dinuclear complex of type [{Os(bpy)2}2 (ca)]2+, isolated as the perchlorate salt. A similar reaction of H2ca with [Os(PPh3)2 (pap)Br2] (pap = 2-(phenylazo)pyridine) affords a dinuclear complex of type [{Os(PPh3)2 (pap)}2 (ca)]2+ (isolated as the perchlorate salt) and a mononuclear complex of type [Os(PPh3)2 (pap)(ca)]. Reaction of H2ca with [Os(PPh3)2(CO)2(HCOO)2] gives a dinuclear complex of type [{Os(PPh3)2(CO)2}2 (r-ca)], where r-ca is the two electron reduced form of the chloranilate ligand. The structures of the [{Os(PPh3)2 (pap)}2 (ca)](ClO4)2, [Os(PPh3)2 (pap)(ca)], and [{Os(PPh3)2(CO)2}2 (r-ca)] complexes have been determined by X-ray crystallography. In the [{Os(bpy)2}2 (ca)]2+ and [{Os(PPh3)2 (pap)}2 (ca)]2+ complexes, the chloranilate dianion is serving as a tetradentate bridging ligand. In the [Os(PPh3)2 (pap)(ca)] complex, the chloranilate dianion is serving as a bidentate chelating ligand. In the [{Os(PPh3)2(CO)2}2 (r-ca)] complex, the reduced form of the chloranilate ligand (r-ca(4-)) is serving as a tetradentate bridging ligand. All the four complexes are diamagnetic and show intense metal-to-ligand charge-transfer transitions in the visible region. The [Os(PPh3)2 (pap)(ca)] complex shows an Os(II)-Os(III) oxidation, followed by an Os(III)-Os(IV) oxidation on the positive side of a standard calomel electrode. The three dinuclear complexes show two successive oxidations on the positive side of SCE. The mixed-valent Os(II)-Os(III) species have been generated in the case of the two chloranilate-bridged complexes by coulometric oxidation of the homovalent Os(II)-Os(II) species. The mixed-valent Os(II)-Os(III) species show intense intervalence charge-transfer transitions in the near-IR region.

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An unprecedented chemical transformation of 2-(2',6'-dimethylphenylazo)-4-methylphenol has been observed upon its reaction with [Ru(PPh(3))(2)(CO)(2)Cl(2)] whereby the methyl group at the 2' position migrates to the 4' or 6' position.