Studies on the solvatochromic effect and NLO response in new symmetric bimetallic Rhenium compounds

Effect of Chloride, Sulfate, and Ferrate Salts on Electronic Energy Levels of Anthracene Proving it a Potential Candidate as an ON and ON-OFF UV-Vis Sensor

Anthracene molecule possesses remarkable optical activity and till today this molecule is of special interest of scientists. Present study is focused on the study of effects of Chloride, Sulfate, Nitrate and Ferrate salts on absorption and emission spectra of targeted fluorophore in carbontetrachloride, chloroform, dichloromethane and methanol. Prominent solvatochromic effects shows dependence of HOMO-LUMO orbitals on solvent polarity. Anthracene molecules exhibits changes in absorption and emission spectra, and show both ON and ON-OFF behavior on addition of said ions. Based on experimental results it was concluded that fluorophore molecule could be used more effectively as UV-Visible (UV-V) sensors in comparison to the emission sensor.

Effective Treatment against ESBL-Producing Klebsiella pneumoniae through Synergism of the Photodynamic Activity of Re (I) Compounds with Beta-Lactams

BACKGROUND

Extended-spectrum beta-lactamase (ESBL) and carbapenemase (KPC+) producing Klebsiella pneumoniae are multidrug-resistant bacteria (MDR) with the highest risk to human health. The significant reduction of new antibiotics development can be overcome by complementing with alternative therapies, such as antimicrobial photodynamic therapy (aPDI). Through photosensitizer (PS) compounds, aPDI produces local oxidative stress-activated by light (photooxidative stress), nonspecifically killing bacteria.

METHODOLOGY

Bimetallic Re(I)-based compounds, PSRe-µL1 and PSRe-µL2, were tested in aPDI and compared with a Ru(II)-based PS positive control. The ability of PSRe-µL1 and PSRe-µL2 to inhibit K. pneumoniae was evaluated under a photon flux of 17 µW/cm2. In addition, an improved aPDI effect with imipenem on KPC+ bacteria and a synergistic effect with cefotaxime on ESBL producers of a collection of 118 clinical isolates of K. pneumoniae was determined. Furthermore, trypan blue exclusion assays determined the PS cytotoxicity on mammalian cells.

RESULTS

At a minimum dose of 4 µg/mL, both the PSRe-µL1 and PSRe-µL2 significantly inhibited in 3log10 (>99.9%) the bacterial growth and showed a lethality of 60 and 30 min of light exposure, respectively. Furthermore, they were active on clinical isolates of K. pneumoniae at 3-6 log10. Additionally, a remarkably increased effectiveness of aPDI was observed over KPC+ bacteria when mixed with imipenem, and a synergistic effect from 3 to 6log10 over ESBL producers of K. pneumoniae clinic isolates when mixed with cefotaxime was determined for both PSs. Furthermore, the compounds show no dark toxicity and low light-dependent toxicity in vitro to mammalian HEp-2 and HEK293 cells.

CONCLUSION

Compounds PSRe-µL1 and PSRe-µL2 produce an effective and synergistic aPDI effect on KPC+, ESBL, and clinical isolates of K. pneumoniae and have low cytotoxicity in mammalian cells.

An unprecedented pyridine-based dinuclear mixed-valent ReI/VII oxo-bridged complex: a solvatochromic and AIE-active probe for nanomolar detection of picric acid and trinitrotoluene

This paper describes the synthesis of an unprecedented oxo-bridged rheniumI/VII (Re) complex by treating Re2(CO)10 with a pyridyl-linked anthracene-based twisted π-conjugated ligand. The molecular structures of both the ligand and the complex are determined by analyzing IR, NMR, and HR-MS spectra and unequivocally determined using single-crystal X-ray diffraction studies. Unlike previous observations, the complexation occurs uniquely to yield an unprecedented oxo-bridged ReI/VII complex. Such a complex is uncommon, and in most cases, Re(vii) appears as the ReO4- counter ion. The aggregation-induced emission (AIE) feature could have been achieved from this conformationally twisted ligand, but the emission of the ligand was quenched in the aggregated state. The complex exhibited solvatofluorochromic properties with a faint emission. The emission intensity significantly (∼6 times) increased in DMF after the addition of a water fraction of 90%, resulting in a bright orange emission. The AIE is mainly caused by restricted intramolecular rotation (RIR) and is supported by the polarity and viscosity effects. The nanoaggregate formation is captured by SEM, and DLS studies were used to determine the average particle size. After the complexation, the ligand becomes more rigid, and the RIR effect becomes prominent facilitating the AIE effect. The electron-rich aggregate's intense orange emission was used for the selective and sensitive detection of picric acid (PA) and 2,4,6-trinitrotoluene (TNT) at nanomolar levels amongst other nitroaromatics through emission quenching. The detailed mechanistic studies reveal the active role of dynamic quenching and complementary photo-induced electron transfer between the probe and TNT or PA. The easy electron transfer process from the electron-rich to the electron-poor system is confirmed by calculating the lowest unoccupied molecular orbital energy of the associated levels. The application is further extended for on-site PA and TNT detection by permeating the probe on a paper and detected at 10-3 M concentration with the naked eye. The PA/TNT detection efficiency is also confirmed by mixing PA or TNT with soil.