A. Rameshkumar

Pyrene Schiff base: photophysics, aggregation induced emission, and antimicrobial properties.

Pyrene containing Schiff base molecule, namely 4-[(pyren-1-ylmethylene)amino]phenol (KB-1), was successfully synthesized and well characterized by using (1)H, (13)C NMR, FT-IR, and EI-MS spectrometry. UV-visible absorption, steady-state fluorescence, time-resolved fluorescence, and transient absorption spectroscopic techniques have been employed to elucidate the photophysical processes of KB-1. It has been demonstrated that the absorption characteristics of KB-1 have been bathochromatically tuned to the visible region by extending the π-conjugation. The extended π-conjugation is evidently confirmed by DFT calculations and reveals that π→π* transition is the major factor responsible for electronic absorption of KB-1. The photophysical property of KB-1 was carefully examined in different organic solvents at different concentrations and the results show that the fluorescence of this molecule is completely quenched due to photoinduced electron transfer. Intriguingly, the fluorescence intensity of KB-1 increases enormously by the gradual addition of water up to 90% with concomitant increase in fluorescence lifetime. This clearly signifies that this molecule has aggregation-induced emission (AIE) property. The mechanism of AIE of this molecule is suppression of photoinduced electron transfer (PET) due to hydrogen bonding interaction of imine donor with water. A direct evidence of PET process has been presented by using nanosecond transient absorption measurements. Further, KB-1 was successfully used for antimicrobial and bioimaging studies. The antimicrobial studies were carried out through disc diffusion method. KB-1 is used against both Gram-positive (Rhodococcus rhodochrous and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial species and also fungal species (Candida albicans). The result shows KB-1 can act as an excellent antimicrobial agent and as a photolabeling agent. S. aureus, P. aeruginosa, and C. albicans were found to be the most susceptible microorganisms at 1 mM concentration among the bacteria used in the present investigation.

Bioimaging, antibacterial and antifungal properties of imidazole-pyridine fluorophores: Synthesis, characterization and solvatochromism

A series of imidazole derivatives connected with pyridine moiety through phenyl groups were synthesized by using Suzuki coupling followed by multicomponent cyclization reaction. Results obtained from spectroscopic ((1)H NMR, (13)C NMR, Mass) and single crystal X-ray diffraction analysis of synthesized compound was in very good agreement with its chemical structure. UV-Vis and fluorescence studies in various solvents with different polarity demonstrated that these compounds were sensitive to the polarity of the microenvironment. In addition, multi linear regression analysis based on Kamlet-Taft and Catalán new four parameter solvent scale results in solvatochromism and was mainly influenced by solvent polarisability and dipolarity of the environment. The electrochemical stability of the compounds was also studied by cyclic voltammetry. An excellent fluorescent nature with high quantum efficiency of the compounds was successfully utilized to probe the bacteria by using fluorescence microscopy. In addition, the antibacterial and antifungal activity of these compounds were also studied in vitro by the disk diffusion assay against one Gram-positive, three Gram-negative bacteria and Candida albicans. MPBI showed relatively good inhibitory action against Gram-negative bacteria and TPBI against Gram-positive bacteria and 3PBI against C. albicans.

Nutritional constituents and medicinal values of Momordica cymbalaria (Athalakkai) – A review

Abstract The plant Momordica cymbalaria ( M. cymbalaria ) belongs to the family Cucurbitaceae, originating in tropical regions of India and South East Asia. M. cymbalaria Hoof. is commonly known as Karchikai (Kannada) or Athalakkai (Tamil) or Kasarakayee (Andra Pradesh) and Kakrol (India). Athalakkai has been used in various Asian traditional medicine systems for a long time. The plant is traditionally used for the treatment of diabetes mellitus, rheumatism, ulcer, skin disease, and diarrhoea. The fruit of this plant have been reported to possess hypoglycaemic, hypolipidemic, cardio protective, hepatoprotective, nephroprotective and antioxidant properties. Owing to anthropogenic activities, such as habitat destruction due to grazing and urbanization, and poor seed viability and germination, M. cymbalaria is under threat of extinction. This review focuses on the cultivation, nutritional and chemical composition, as well as medicinal and therapeutic properties of this plant.