Bis(2,2?-bipyridine)(4,4?-diuntriacontanyl-2,2?-bipyridine)-ruthenium(II) chloride and related hydrophobic complexes

Using inclusion complexes with cyclodextrins to explore the aggregation behavior of a ruthenium metallosurfactant

The aggregation behavior of a chiral metallosurfactant, bis(2,2'-bipyridine)(4,4'-ditridecyl-2,2'-bipyridine)ruthenium(II) dichloride (Ru2(4)C13), synthesized as a racemic mixture was characterized by small-angle neutron scattering, light scattering, NMR, and electronic spectroscopies. The analysis of the SANS data indicates that micelles are prolate ellipsoids over the range of concentrations studied, with a relatively low aggregation number, and the micellization takes place gradually with increasing concentration. The presence of cyclodextrins (β-CD and γ-CD) induces the breakup of the micelles and helps to establish that micellization occurs at a very slow exchange rate compared to the NMR time scale. The open structure of this metallosurfactant enables the formation of very stable complexes of 3:1 stoichiometry, in which one CD threads one of the hydrocarbon tails and two CDs the other, in close contact with the polar head. The complex formed with β-CD, more stable than the one formed with the wider γ-CD, is capable of resolving the Δ and Λ enantiomers at high CD/surfactant molar ratios. The chiral recognition is possible due to the very specific interactions taking place when the β-CD covers-via its secondary rim-part of the diimine moiety connected to the hydrophobic tails. A SANS model comprising a binary mixture of hard spheres (complex + micelles) was successfully used to study quantitatively the effect of the CDs on the aggregation of the surfactant.

Synthesis and characterization of a new trifunctional magnetic-photoluminescent-oxygen-sensing nanomaterial

Magnetic Fe(2)O(3) nanoparticles coated with SiO(2) chemically doped with a Ru(II) complex were prepared using a simple solution based method. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) showed that the Fe(2)O(3) nanoparticles with a mean diameter of ∼115 nm were successfully coated with Ru(II) complex-chemically doped SiO(2) shell with a thickness of ∼30 nm. The obtained nanocomposite material showed a strong magnetic response to a varying magnetic field, exhibited the bright red triplet metal-to-ligand charge transfer ((3)MLCT) emission, and its photoluminescent intensity was sensitive to oxygen concentration. Compared with the Ru(II) complex in silica gels, the Ru(II) complex in the magnetic-optical-oxygen-sensing nanocomposite demonstrated improved thermodynamic stability of emissions. These nanocomposites are also nontoxic and easily conjugated with biomolecules. Their magnetic, photoluminescent and oxygen-sensing properties make them promising candidates for cell separation, biomarkers and optical oxygen sensors, which can measure the O(2) concentration in biological bodies.

Surface and aggregation behavior of aqueous solutions of Ru(II) metallosurfactants. 3. Effect of chain number and orientation on the structure of adsorbed films of [Ru(bipy)2(bipy')]Cl2 complexes

The surface behavior of a range of surfactant [Ru(bipy)(2)(p,p'-dialkyl-2,2'-bipy)]Cl(2) complexes, which we express as Ru(q)(p)C(n) where n is the alkyl chain length, p refers to the substitution position on the bipyridine ligand (=4 or 5), and q (=1 or 2) is the number of substituted alkyl chains, has been examined using neutron reflectometry. The adsorption of the single-chain Ru(1)(4)C(19) and Ru(1)(5)C(19) surfactants is strongly time-dependent, taking in excess of 10 h to form an equilibrium film. It is suggested that the slow adsorption rate is related to the alkyl chain length rather than the low monomer concentration present in the solutions. At concentrations below the critical micelle concentration (cmc) of Ru(1)(4)C(19), the film of Ru(1)(5)C(19) is denser than that of Ru(1)(4)C(19) at comparable concentration, consistent with the mass densities of the bulk solids, whereas at concentrations close to and greater than this cmc the converse pertains. Close to the cmc, the adsorbed films possess an average area per molecule significantly less than the nominal headgroup area of the surfactants (approximately 30 angstroms(2) compared with approximately 100 angstroms(2)). This fact together with consideration of the thickness and density of the adsorbed films leads to the conjecture that surface aggregates may be the adsorbing units. The adsorption of the double-chain surfactant Ru(1)(p)C(19), in contrast to the behavior of the Ru(1)(p)C(19) surfactants, is weak and independent of time. This behavior is attributed to the alkyl chain orientation. The adsorption behavior of a racemic mixture of the Delta and Lambda isomers of Ru(2)(4)C(19) has been compared with that of the Delta isomer. It is found that the film of racemic material is more closely packed than that of the resolved complex.