Laser-Induced Antibacterial Activity of Novel Symmetric Carbazole-Based Ethynylpyridine Photosensitizers

Abstract

In this study, two kinds of novel carbazole-based ethynylpyridine salts: 3,6-bis[2-(1-methylpyridinium)ethynyl]-9-pentyl-carbazole diiodide (BMEPC) and 3,6-bis[2-(1-methylpyridinium)ethynyl]-9-methyl-carbazole diiodide (BMEMC) have been employed as photosensitizers owing to their excellent antibacterial activity. These molecules possess symmetric A−π–D−π–A-type structures, which would bring in the unique optical properties. The inhibition zone measurement of a gradient concentration from 0 to 100 μM showed BMEPC and BMEMC photoinduced antibacterial activity against Escherichia coli. Diameters of zone of inhibition were up to 15 and 14 mm under laser irradiations. Under the exposure of the laser of 442 nm with a power density of 20 mW/cm2, the minimum inhibitory concentrations (MICs) of BMEPC on E. coli were between 3.5 and 6.9 μM and that of BMEMC were between 9.4 and 18.8 μM, respectively. In the dark experiments as a control, the MIC value is between 6.9 and 13.8 μM for BMEPC, whereas it is between 187.5 and 225.0 μM for BMEMC. By the comparison of the MIC values of BMEPC and BMEMC with laser irradiation and in dark, the laser-induced toxicity on bacteria is more evident, though both of the derivatives have dark toxicity. With the laser irradiation duration of 30 s and 10 min for BMEPC and BMEMC, respectively, the survival rate of E. coli approximates zero. An antibacterial mechanism has been proposed based on the electron paramagnetic resonance characterization, which indicates that a nitride radical is generated under laser irradiation. The carbazole-based ethynylpyridine photosensitizers would provide high potential for further applications in photodynamic therapy.

Prospects for More Efficient Multi-Photon Absorption Photosensitizers Exhibiting Both Reactive Oxygen Species Generation and Luminescence

“…Following on from the above-mentioned study, the same two carbazole-based ethynylpyridine salts, 9 and 10, were further utilized as photosensitizers for antibacterial studies. Their antibacterial activity was tested against Escherichia coli (E. coli) [117]. An antibacterial mechanism was proposed based on electron paramagnetic resonance characterization, which indicated that a nitride radical is generated upon laser irradiation.…”

Alkaloids as Photosensitisers for the Inactivation of Bacteria

“…The different activities are associated with the higher affinity of the longer alkyl chain to the cellular structure which yields a large accumulation of the molecules. In addition, the authors propose nitride radical formation upon light irradiation using EPR measurements and 5,5-dimethyl-1-pyrroline- N -oxide (DMPO) as the spin-trapping agent [ 75 ].…”

Photodynamic and Photothermal Ce6-Modified Gold Nanorod as a Potent Alternative Candidate for Improved Photoinactivation of Bacteria

“…In recent years, bacterial resistance has increased significantly with the excessive use of antibiotics, which has led to a serious crisis of multidrug-resistant bacterial infections, and human health and safety have been threatened once again. , As a result, there is an urgent need to develop new antimicrobial channels to replace traditional antibiotic therapy. Photodynamic therapy (PDT) is a method to inactivate bacteria by producing reactive oxygen species (ROS), such as singlet oxygen ( 1 O 2 ), superoxygen, or hydroxyl radicals with the help of photosensitizers (PSs) under the common conditions of specific light and oxygen. , The obtained 1 O 2 causes irreversible damage to microbial cell membranes and plays a major role in photodynamic damage. , Moreover, due to the broad-spectrum antibacterial properties and nondrug resistance, PDT has been considered as a promising alternative for the replacement of traditional antibiotic therapy. , …”

“…5,6 Moreover, due to the broad-spectrum antibacterial properties and nondrug resistance, PDT has been considered as a promising alternative for the replacement of traditional antibiotic therapy. 4,7 Ce6 has been widely used as a photosensitizer for the low dark toxicity and high ROS yield, which exhibits ideal antibacterial PDT performance. 7 Ce6 has good absorption in the near-infrared wavelength range 600−900 nm, which possesses tissue penetration ability due to the longer wavelengths of light.…”

“…4,7 Ce6 has been widely used as a photosensitizer for the low dark toxicity and high ROS yield, which exhibits ideal antibacterial PDT performance. 7 Ce6 has good absorption in the near-infrared wavelength range 600−900 nm, which possesses tissue penetration ability due to the longer wavelengths of light. 8,9 PSs that can produce ROS has been regarded as the key factor in PDT; however, the poor solubility and easy aggregation of traditional PSs including Ce6 would hinder the release of reactive oxygen species in a physiological environment.…”