In this work, a previously undescribed phenomenon of orientation induced redox isomerism in a Langmuir monolayer is revealed in the case of cerium bis [tetra (15 crown 5) phthalocyaninate] (Ce[(15C5) 4 Pc] 2 ). It was established that intramolecular electron transfer (IET) from the electronic system of phthalocyanine to the 4f orbital of cerium atom occurs upon spreading of a (Ce[(15C5) 4 Pc] 2 ) chloroform solution onto the air−water interface (3D → 2D IET). This process is related to the transformation of Ce 4+ cation in the solution to Ce 3+ in the monolayer. It was also found that reversible Ce 3+ ↔ Ce 4+ IETs occur upon compression (π 1 → π 2 ) and expansion (π 2 → π 1 ) of monolayer (2D π1 ↔ 2D π2 IET, π surface pressure). The mechanism of genuine redox isomerism was confirmed by the results of in situ UV−vis spectral measurements performed on monolayers and Langmuir−Blodgett films, AFM, and XPS studies of Langmuir−Blodgett films transferred at different surface pressures. The understanding of this reversible IET mechanism is especially important due to possible applications of such redox isomeric systems in the development of nanoscale multibit information storage devices.

Despite great innovative and technological promises, nanoparticles (NPs) can ultimately exert an antibacterial activity by affecting the cell envelope integrity. This envelope, by conferring the cell its rigidity and protection, is intimately related to the mechanical behavior of the bacterial surface. Depending on their size, surface chemistry, shape, NPs can induce damages to the cell morphology and structure among others, and are therefore expected to alter the overall mechanical properties of bacteria. Although Atomic Force Microscopy (AFM) stands as a powerful tool to study biological systems, with high resolution and in near physiological environment, it has rarely been applied to investigate at the same time both morphological and mechanical degradations of bacteria upon NPs treatment. Consequently, this study aims at quantifying the impact of the silica NPs (SiO-NPs) on the mechanical properties of E. coli cells after their exposure, and relating it to their toxic activity under a critical diameter. Cell elasticity was calculated by fitting the force curves with the Hertz model, and was correlated with the morphological study. SiO-NPs of 100 nm diameter did not trigger any significant change in the Young modulus of E. coli, in agreement with the bacterial intact morphology and membrane structure. On the opposite, the 4 nm diameter SiO-NPs did induce a significant decrease in E. coli Young modulus, mainly associated with the disorganization of lipopolysaccharides in the outer membrane and the permeation of the underlying peptidoglycan layer. The subsequent toxic behavior of these NPs is finally confirmed by the presence of membrane residues, due to cell lysis, exhibiting typical adhesion features.