Entropy and stability in a stochastic laser model

The asymptotic stability of a microscopic stochastic laser model in the Heisenberg picture is discussed using Liapounov's direct method. By reducing the laser Langevin equations to a classical van der Pol equation for the photon number in the rotating wave approximation, it may be shown that the above-threshold steady state characterized by the cubic non-linearity in the van der Pol equation, is stable. This leads to the definition of a monotonic increasing entropy function far from thermal equilibrium.     

Complexes in polymers: FT-IR spectra and photochemistry of some monomeric organometallic carbonyl complexes in polystyrene,poly(methyl methacrylate), polystyrene—poly(methyl methacrylate) and polystyrene—polyacrylonitrile copolymers

A convenient method for embedding organometallic complexes in polymer films has been developed and the FT-IR spectra of these films have been investigated at room temperature. Infrared data in the n?(CO) stretching region are reported for M(CO)₆ (M = Cr, Mo, W), CpMn(CO)₃ (Cp = η⁵-C₅H₅), η-C₆H₆Cr(CO)₂L [L = CO, P(n-Bu)₃], (η₆-C₆H₅NH₂)Cr(CO)₃, [η⁶-o-C₆H₄(NH₂)MeCr(CO)₃], CpFe(CO)LR [L = CO, PPh₃; R = Me, C(O)Me] embedded in poly(methyl methacrylate) (PMMA), polystyrene (PS), polystyrene-poly(methyl methacrylate) (PS-PMMA), and polystyrene–polyacrylonitrile (PS-AN) plastic films. These matrices appear to approximate the common solvents ethyl acetate, toluene, toluene–ethyl acetate, and toluene–acetonitrile, respectively, with respect to n?(CO) vibrational band behavior. Several of the films have been subjected to UV irradiation and the photoproducts formed have been identified by FT-IR spectroscopy. PS-AN effectively traps photogenerated coordinatively unsaturated species via coordination of its pendant nitrile groups.     

Water-soluble surface-anchored gold and palladium nanoparticles stabilized by exchange of low molecular weight ligands with biamphiphilic triblock copolymers

A study is presented of the stabilization of gold and palladium nanoparticles (NPs) via a place-exchange reaction. Au and Pd NPs of approximately 3.5 nm were prepared by a conventional method using tetraoctylammonium bromide (TOAB) as the stabilizing agent. The resulting nanoparticles, referred to as Au-TOAB or Pd-TOAB, were later used as templates for the replacement of TOAB ligand with poly(ethylene oxide)- b-polystyrene- b-poly(4-vinylpyridine) (PEO- b-PS- b-P4VP) triblock copolymer. This biamphiphilic triblock copolymer was synthesized by atom transfer radical polymerization (ATRP) with control over the molecular weight and polydispersity. The place-exchange reaction was mediated through strong coordination forces between the 4-vinylpyridine copolymer and the metal species located on the surface of the nanoparticles. In addition, the displacement of the outgoing low molecular weight TOAB ligands by high molecular weight polymers is an entropy-assisted process and is believed to contribute to stabilization. The prepared complex, polymer-NP, exhibits greatly improved stability over the metal-NP complex in common organic solvents for the triblock copolymer. Self-assembly in water after ligand exchange resulted in micellar structures of about approximately 20 nm (electron microscopy) with the metal NP found located on the surface of the micelles. The stability of the nanoparticles in water was shown to depend greatly on the grafting density of the copolymer, with high stability (more than 6 months) at high grafting density and low stability, accompanied with irreversible agglomeration, at relatively low grafting densities. The surprising location of the metal NP (for both Au and Pd) on the surface of the micelles in water is explained by the fact that, upon self-assembly in THF/water system, the most hydrophobic chains (i.e., PS) undergo self-assembly first at low water content forming the core, followed by the P4VP (whether or not associated with the metal) forming a shell, and finally the PEO forming the corona. In lower metal content assemblies, the P4VP chains located in the shell undergo swelling in an acidic medium causing a substantial increase in micellar corona size, as confirmed by dynamic light scattering measurements. The present study offers a simple approach for the stabilization of various metal nanoparticles of catalytic interest, using a unique polymeric support that can be dispersed in organic solvents as well as aqueous solutions.     

Construction of C1-symmetric zirconium complexes by the design of new Salan ligands. Coordination chemistry and preliminary polymerisation catalysis studies

The first synthesis of achiral and chiral [ONNO']-type Salan ligands featuring two different phenol arms, and the diastereoselective formation of the corresponding octahedral C1-symmetric zirconium complexes is described; the activity and isospecificity induction of the [ONNO']Zr(bn)2 complexes in 1-hexene polymerisation reflected those of the parent symmetric compounds.     

Breakable Hybrid Organosilica Nanocapsules for Protein Delivery

The direct delivery of specific proteins to live cells promises a tremendous impact for biological and medical applications, from therapeutics to genetic engineering. However, the process mostly involves tedious techniques and often requires extensive alteration of the protein itself. Herein we report a straightforward approach to encapsulate native proteins by using breakable organosilica matrices that disintegrate upon exposure to a chemical stimulus. The biomolecule‐containing capsules were tested for the intracellular delivery of highly cytotoxic proteins into C6 glioma cells. We demonstrate that the shell is broken, the release of the active proteins occurs, and therefore our hybrid architecture is a promising strategy to deliver fragile biomacromolecules into living organisms.     

Thiol-terminated monolayers on oxide-free Si: assembly of semiconductor-alkyl-S-metal junctions

Self-assembled monolayers formed by thermal hydrosilylation of a trifluoroacetyl-protected alkenylthiol on Si-H surfaces, followed by removal of the protecting groups, yield essentially oxide-free monolayers suitable for the formation of Si-C11H22-S-Hg and Si-C11H22-S-Au junctions in which the alkyl chains are chemically bound to the silicon surface (via Si-C bonds) and the metal electrode (via Hg-S or Au-S bonds). Two barriers to charge transport are present in the system: at low bias the current is temperature activated and hence limited by thermionic emission over the Schottky barrier in the silicon, whereas as at high bias transport is limited by tunneling through the organic monolayer. The thiol-terminated monolayer on oxide-free silicon provides a well-characterized system allowing a careful study of the importance of the interfacial bond to the metal electrode for current transport through saturated molecules.     

Pd catalysis on dendronized solid support: generation effects and the influence of the backbone structure

Recent studies revealed that catalysts, prepared on dendronized support, frequently exhibit enhanced activity and selectivity as compared to their non-dendronized analogues. Regretfully, in early studies of the supported dendritic catalysis, no particular attention was paid to the coordinative nature of the dendritic backbone. In this study, we functionalized Wang polystyrene support with three types of dendritic templates: poly(aril benzyl ether), poly(aryl benzyl thioether), and poly(aryl benzyl amine). These dendronized resins were further decorated with phosphine ligands on the periphery and complexed with a Pd(0) catalytic precursor. The catalysis of the Heck and Suzuki reactions of bromobenzene with the first to third generation supported dendritic catalysts was examined and compared to that of the non-dendritic analogues. All of the examined reactions revealed a positive dendritic effect, reflected in up to 5-fold increase in yield, in the most prominent case. The reasons for the observed effect are the proximity of the ligating sites translated into reduced cross-linking and, probably, the increased distance of the catalyst from the polymer matrix. We proved, however, that the latter could not be achieved with a linear spacer. Although the Suzuki reaction was rather insensitive to the backbone structure, the Heck reaction catalysis at 80 degrees C exhibited substantial sensitivity to the nature of the dendritic backbone, with the polyether structure demonstrating the best outcome. This is the first demonstration of the influence of the coordinative ability of the backbone on the activity of a supported dendritic catalyst.