From Amorphous Silicones to Si-Containing Highly Ordered Polymers: Some Romanian Contributions in the Field

Polydimethylsiloxane (PDMS), in spite of its well-defined helical structure, is an amorphous fluid even at extremely high molecular weights. The cause of this behavior is the high flexibility of the siloxane backbone and the lack of intermolecular interactions attributed to the presence of methyl groups. These make PDMS incompatible with almost any organic or inorganic component leading to phase separation in siloxane-siloxane copolymers containing blocks with polar organic groups and in siloxane-organic copolymers, where dimethylsiloxane segments co-exist with organic ones. Self-assembly at the micro- or nanometric scale is common in certain mixed structures, including micelles, vesicles, et cetera, manifesting reversibly in response to an external stimulus. Polymers with a very high degree of ordering in the form of high-quality crystals were obtained when siloxane/silane segments co-exist with coordinated metal blocks in the polymer chain. While in the case of coordination of secondary building units (SBUs) with siloxane ligands 1D chains are formed; when coordination is achieved in the presence of a mixture of ligands, siloxane and organic, 2D structures are formed in most cases. The Romanian research group’s results regarding these aspects are reviewed: from the synthesis of classic, amorphous silicone products, to their adaptation for use in emerging fields and to new self-assembled or highly ordered structures with properties that create perspectives for the use of silicones in hitherto unexpected areas.

Synthesis, structures, and fluorescence properties of one novel Cobalt metal–organic framework based on a tetraphenylethene-core ligand

A new three-dimensional luminescent cobalt (II) metal–organic framework, [Co(Titpe)(bcpf)·(DMF)]·(H2O)2·(DMF) (compound 1, JUST-8) (Titpe = 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethane, bcpf = 4,4′-sulfonyldibenzoic acid; DMF = N, N-dimethylformamide), has been solvothermally synthesized by using CoCl2·6H2O and a mixture of ligands: Titpe ligand and bcpf ligand. Single crystal X-ray analysis reveals that 1 crystallizes in the triclinic system and [Formula: see text] space group with a = 13.2097(14) Å, b = 13.9519(14) Å, c = 14.4413(15) Å, α = 89.949(7)°, β = 70.303(7)°, γ = 80.322(7)°, V = 2465.7(5) Å3, Z = 2, Mr =1032.97, Dc = 1.391 g/cm3, μ = 0.455 mm−1, F(000) = 1070, R = 0.0585, and wR = 0.1540 for 8674 observed reflections ( I > 2σ( I)). Its overall structure is a double-fold interpenetrated framework, and it shows a porosity of 12.97% based on a calculation by PLATON and a 4- c type topological network with the point symbol of {6^5.8}. The Co atom bridges the Titpe ligands to form the one-dimensional chains into a two-dimensional layered structure and then connects the auxiliary ligands to get a three-dimensional structure. Compound 1 showed a blue fluorescence emission with the peak maximum at 431 nm (λex = 314 nm).

The Role of PEG Conformation in Mixed Layers: From Protein Corona Substrate to Steric Stabilization Avoiding Protein Adsorption.

<p>Although nanoparticles have been traditionally modified with a single ligand layer, mixture of ligands might help to combine different functionalities and to further engineer the NP surface. A detailed study of the competition between an alkanethiol (11-mercaptoundecanoic acid) and SH-PEG for the surface of AuNPs and the resultant behaviors of this model nanoconjugate is presented here. As a result, the physicochemical properties of these conjugates can be progressively tuned by controlling the composition and especially the conformation of the mixed monolayer. This has implications in the physiological stability. The controlled changes on the SH-PEG conformation rather than its concentration induces a change in the stabilization mechanism from electrostatic repulsion to steric hindrance, which changes the biological fate of NPs. Importantly, the adsorption of proteins on the conjugates can be tailored by tuning the composition and conformation of the mixed layer.</p>

Narcissistic self-sorting vs. statistic ligand shuffling within a series of phenothiazine-based coordination cages

The self-assembly of heterogeneous or homogeneous cages from a mixture of ligands is a function of the ligand length and reaction kinetics.