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Liesegang rings based on a chemical reaction, not a conventional precipitation reaction, have been developed by appropriate design of the nucleation dynamics in a system involving complex formation in a matrix. The periodic and concentric rings consisted of well-dispersed Ag nanoparticles with diameters of a few nanometers. The approach modeled here could be applied to form novel micropatterns out of inorganic salts, metal nanoparticles, organic nanocrystals, or polymeric fibers, and it could also offer a scaffold for novel models of a wide variety of reaction-diffusion phenomena in nature.

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The reaction of RcC⋮CH [Rc = (η5-C5H5)Ru(η5-C5H4)] with RuClL2(η5-C5R5) [R = H or Me; L2 = 2PPh3 or Ph2PCH2CH2PPh2 (dppe)] in the presence of NH4PF6 and subsequent treatment with base gave Ru(II) ruthenocenylacetylide complexes RcC⋮CRuL2(η5-C5R5) in good yields. In a similar manner, the pentamethylruthenocene analogues, Rc‘C⋮CRuL2(η5-C5R5) [Rc‘ = (η5-C5Me5)Ru(η5-C5H4)], were also prepared. Cyclic voltammograms of the complexes showed two reversible one-electron-oxidation processes, consisting of the processes [Ru(II)Ru‘(II)] to [Ru(III)Ru‘(II)] and then to [Ru(III)Ru‘(III)]. Chemical oxidation of the complexes induced novel structural rearrangement. The two-electron oxidation of complex RcC⋮CRu(PPh3)2(η5-C5H5) afforded a kind of allenylidene complex, a cyclopentadienylidenethylidene complex, [(η5-C5H5)Ru{μ-η6:η1-C5H4CC}Ru(PPh3)2(η5-C5H5)]2+, in 90% yield. The one-electron oxidation of Rc‘C⋮CRu(PPh3)2(η5-C5H5) gave the vinylidene complex (Rc‘CHC)Ru(PPh3)2(η5-C5H5) in 62% yield, while the two-electron oxidation led to the fulvene−vinylidene complex [(η6-C5Me4CH2)Ru{μ-η5:η1-C5H4CHC}Ru(PPh3)2(η5-C5R5)]2+ by an intramolecular hydrogen transfer in 59% yield.

The Hofmeister series has long been of both scientific and technological importance because it allows systematic predictions of the interaction between ions and molecules to be made. In this work, three different polyoxometalate (POM) anions and three different lipid monolayers were used to investigate the interplay between electrostatic and hydrophobic interactions. We used three Keggin-type POMs with different charges ([PW 12 O 40 ] 3− , [SiW 12 O 40 ] 4− , and [H 2 W 12 O 40 ] 6− ) to eliminate any effects of morphology and to focus on the effects of the charge and hydrophobicity of the POM anions. The POMs adsorb onto cationic lipid monolayers via electrostatic interactions, while hydrophobic interaction is the dominant factor for adsorption onto anionic lipid monolayers when charge neutralization is provided by cationic counterions. In contrast, the dominant interactions experienced by zwitterionic lipid monolayers can switch between electrostatic interactions for POMs with higher charge density and hydrophobic interactions for POMs with lower charge density. Furthermore, the dominant interaction could also switch as a function of lipid density. In the gas phase, lipid monolayers mostly interact with POMs through electrostatic interactions, and the strength of the influence of the POM varies in the order [PW 12 O 40 ] 3− < [SiW 12 O 40 ] 4− < [H 2 W 12 O 40 ] 6− . In contrast, the order switches to [PW 12 O 40 ] 3− > [SiW 12 O 40 ] 4− > [H 2 W 12 O 40 ] 6−when the POM interacts with a compressed lipid monolayer (surface pressure = 40 mN/m), which reflects the Hofmeister series and the chaotropic nature of the POMs. Thus, hydrophobic interactions govern the penetration of the lipid monolayer for condensed cell membranes irrespective of the charge of the lipid. The observed switch implies the importance of the interplay between the electrostatic and hydrophobic interactions. Our findings provide new insight into the switchable binding modes of POMs for cell membranes with different lipid composition, density, and hydrophobicity, enabling the design of tailor-made POM-based materials for a new generation of antimicrobial agents.

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