Several new ligands, azoimidazoles belonging to the class 1-methyl-2-(arylazo)imidazoles (L1 (3)) and 1-benzyl-2-(arylazo)imidazoles (L2 (4)) (R = H (a), Me (b), OMe (c), Cl (d), NO2 (e)) have been synthesized and reacted with RuCl3 in ethanol under refluxing conditions. Two isomers of the composition RuL2Cl2, green (i) and blue (iii), are chromatographically separated. The green isomer is quantitatively transformed to the blue isomer on refluxing in a high boiling solvent. The isomeric structures have been confirmed by X-ray crystallography. Crystal data are as follows. Green complex C38H34Cl2N8Ru (6a):  crystal system monoclinic; space group C2/c; a = 15.680(8) Å; b = 22.766(14) Å; c = 11.473(5) Å; β = 119.27(4)°; V = 3573(3) Å3 Z = 4; R = 3.59%; R w = 4.38%. Blue complex C22H24Cl2N8Ru (7b):  crystal system monoclinic; space group P21/n, a = 9.547(6) Å; b = 22.554(14) Å; c = 11.748(8) Å; β = 99.07(5)°; V = 2498(3) Å3; Z = 4; R = 3.15%; R w = 4.51%. With reference to the pairs of Cl, N(imidazole), and N(azo) bound to Ru, the green isomer (6a) has a trans −cis−cis configuration and the blue isomer (7b) is cis − trans − cis. In both structures the Ru−N(azo) distances are relatively shorter than Ru−N(imidazole), indicating stronger bonding in the former and the presence of a Ru−L π-interaction that is localized in the Ru−azo fragment. The isomer configuration is supported by IR and 1H NMR data. The compounds exhibit t2(Ru) → π*(L) MLCT transitions in the visible region. Redox studies show the Ru(III)/Ru(II) couple in the green complexes (5, 6) at 0.6−0.7 V and in the blue complexes at 0.7−0.8 V versus SCE and two successive azo reductions. The difference in the first metal and ligand redox potentials is linearly correlated with νCT (t2(Ru) → π*(L).

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14-Deoxy-11,12-didehydroandrographolide is a biologically active molecule present in the extract of Andrographis paniculata (Kalmegh), a classic ethnic herbal formula, which has been used for over thousand years as therapeutics to treat numerous infectious diseases like upper respiratory tract infection, urinary tract infection, and many more health issues. The present study is designed to ascertain an inhibitor against biofilm formation from the major metabolites of Andrographis paniculata, because the extract of this herb shows inhibition of bacterial quorum sensing (QS) communication and biofilm development against microorganisms. 14-Deoxy-11,12-didehydroandrographolide at 0.1 mM (sub-MIC dose) with azithromycin (6 μg/mL, sub-MIC) or gentamicin (4 μg/mL, sub-MIC) synergistically inhibits 92% biofilm production by a 48-h treatment against Pseudomonas aeruginosa. Further investigation carried out by atomic force microscopy shows promising reduction in roughness and height of biofilm in the presence of 14-deoxy-11,12-didehydroandrographolide compared with the control group. The content of extracellular polymeric substances, level of pyocyanin production, and synthesis of extracellular protease by P. aeruginosa have also been reduced significantly at around 90% in 14-deoxy-11,12-didehydroandrographolide-treated group. In conclusion, 14deoxy-11,12-didehydroandrographolide could be used as a drug molecule against biofilm development by inhibiting QS pathway in Pseudomonas aeruginosa.