Tuning Excited State Character in Iridium(III) Photosensitizers and Its Influence on TTA-UC.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1H-naphtho[2,3-d]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 µs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1H-naphtho[2,3-d]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

Synthesis of 3,5-Bis(trifluoromethyl)phenyl-Substituted Pyrazole Derivatives as Potent Growth Inhibitors of Drug-Resistant Bacteria.

Enterococci and methicillin-resistant S. aureus (MRSA) are among the menacing bacterial pathogens. Novel antibiotics are urgently needed to tackle these antibiotic-resistant bacterial infections. This article reports the design, synthesis, and antimicrobial studies of 30 novel pyrazole derivatives. Most of the synthesized compounds are potent growth inhibitors of planktonic Gram-positive bacteria with minimum inhibitory concertation (MIC) values as low as 0.25 µg/mL. Further studies led to the discovery of several lead compounds, which are bactericidal and potent against MRSA persisters. Compounds 11, 28, and 29 are potent against S. aureus biofilms with minimum biofilm eradication concentration (MBEC) values as low as 1 µg/mL.

Synthesis of Chimeric Thiazolo-Nootkatone Derivatives as Potent Antimicrobial Agents.

Nootkatone, an approved insecticide, is a well-known natural product from grapefruit. A series of fused-thiazole derivatives of nootkatone have been synthesized, and these new compounds were tested against several strains of bacteria. Some of these compounds are found to be potent antimicrobial agents against Staphylococcus aureus and Enterococcus faecium with minimum inhibitory concentration (MIC) values as low as 1.56 µg/mL. The lead compound is bactericidal and very potent against S. aureus persisters. These compounds are nontoxic to human cancer cell lines at 10 µm concentration.

Benign Synthesis of Fused-thiazoles with Enone-based Natural Products and Drugs for Lead Discovery.

In an effort to synthesize a library of bioactive molecules, we present an efficient synthesis of fused-thiazole derivatives of natural products and approved drugs by using an environmentally usable solvent, acetic acid, and without any external reagent. Cholestenone, ethisterone, progesterone, and nootkatone-derived epoxyketones have been utilized to synthesize 50 novel compounds. The plausible mechanism of the reaction has been determined by theoretical calculation using M06-2X/6-31+G(d,p). These novel molecules have been tested against cancer cell lines and pathogenic bacterial strains. Several ethisterone-based fused-thiazole compounds are found to be potent growth inhibitors of cancer cell lines at submicromolar concentrations.