A stripe-to-droplet transition driven by conformational transitions in a binary lipid-lipopolymer mixture at the air-water interface

We report the observation of an unusual stripe-droplet transition in precompressed Langmuir monolayers consisting of mixtures of poly(ethylene) glycol (PEG) amphiphiles and phospholipids. This highly reproducible and fully reversible transition occurs at approximately zero surface pressure during expansion (or compression) of the monolayer following initial compression into a two-dimensional solid phase. It is characterized by spontaneous emergence of an extended, disordered stripe-like morphology from an optically homogeneous phase during gradual expansion. These stripe patterns appear as a transient feature and continuously progress, involving gradual coarsening and ultimate transformation into a droplet morphology upon further expansion. Furthermore, varying relative concentrations of the two amphiphiles and utilizing amphiphiles with considerably longer ethylene glycol headgroups reveal that this pattern evolution occurs in narrow concentration regimes, values of which depend on ethylene oxide headgroup size. These morphological transitions are reminiscent of those seen during a passage through a critical point by variations in thermodynamic parameters (e.g., temperature or pressure) as well as those involving spinodal decomposition. While the precise mechanism cannot be ascertained using present experiments alone, our observations can be reconciled in terms of modulations in competing interactions prompted by the pancake-mushroom-brush conformational transitions of the ethylene glycol headgroup. This in turn suggests that the conformational degree of freedom represents an independent order parameter, or a switch, which can induce large-scale structural reorganization in amphiphilic monolayers. Because molecular conformational changes are pervasive in biological membranes, we speculate that such conformational transition-induced pattern evolution might provide a physical mechanism by which membrane processes are amplified.     

Unequal siblings: Adverse characteristics of naphtalene‐based hoveyda‐type second generation initiators in ring opening metathesis polymerization

A family of four different Hoveyda‐type initiators bearing a π‐extended carbene ligand was characterized regarding the activity in ring opening metathesis polymerization. One of the initiators shows high activity at ambient temperature, similar to the second generation Hoveyda–Grubbs catalyst and is even suited for the controlled polymerization of certain norbornene derivatives. The other family members exhibit a pronounced latency at room temperature, and polymerization can be triggered by heat. The scope of these initiators in the thermally triggered polymerizations of norbornene derivatives in general and dicyclopentadiene in particular was disclosed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Copper(I) d10···d10 Interactions and Diselenide(1–) Radical Anions in Mixed Valent Selenides Cu4–δBiSe4I

Melting reactions of copper, CuI, selenium, and Bi₂Se₃ yielded black, shiny needles of Cu₄BiSe₄I = Cu₄BiSe₂(Se₂)I. The compound decomposes peritectically above 635(5) K and crystallizes in the orthorhombic space group Pnma with a = 960.1(1) pm, b = 413.16(3) pm, and c = 2274.7(2) pm (T = 293(2) K). In the crystal structure, strands ${1}\atop{{\infty}}$ [BiSeSe_2/2(Se₂)_2/2]^3– run along [010]. Therein, the bismuth(III) cation is coordinated by five selenium atoms, which form a square pyramid. The copper(I) cations are coordinated tetrahedrally by selenide, diselenide and iodide ions. Edge‐sharing of these tetrahedra results in zigzag chains of copper cations with short distances of 262.7(4) pm. Enhanced dispersion of the 3d bands, the Crystal Orbital Hamilton Populations (COHP), and disynaptic ELI‐D basins indicate weakly attractive d¹⁰···d¹⁰ interactions between the copper cations. The semiconducting properties and the calculated electronic band structure suggest an electron‐precise compound. In copper‐deficient Cu_3.824(8)BiSe₄I, the Cu···Cu distances are 5 pm shorter, and Raman spectroscopy indicates the presence of diselenide(1–) radical anions besides the diselenide(2–) groups. As a result, in Cu_3.824(8)BiSe₄I, selenium coexists in the oxidations states –II, –I, and –0.5.     

Epoxidation of cyclooctene using soluble or MCM-41-supported molybdenum tetracarbonyl-pyridylimine complexes as catalyst precursors

The ligand N-(n-propyl)-2-pyridylmethanimine (pyim) and an immobilised analogue of this ligand (MCM-41-pyim) were prepared by the condensation reaction of 2-pyridinecarboxaldehyde with either propylamine or aminopropyl groups covalently attached to the ordered mesoporous silica MCM-41. Free and immobilised tetracarbonyl complexes of the type cis-[Mo(CO)₄(L)] (L = pyim (1), MCM-41-pyim) were then prepared by microwave-assisted heating of a mixture of Mo(CO)₆ and the organic ligand or ligand-silica in toluene at 110 °C for 30-45 min. The products were characterised by NMR spectroscopy (¹H, ¹³C and ²⁹Si, in solution and in the solid state), elemental analysis, N₂ adsorption, and FT-IR spectroscopy. When used as catalyst precursors for the epoxidation of cis-cyclooctene by tert-butylhydroperoxide at 55 °C (1 mol% catalyst (Mo), no additional co-solvent), 1,2-epoxy-cyclooctane was obtained as the only reaction product in quantitative yield after 5 h for 1 and 36% yield after 24 h for the supported complex. The use of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate as co-solvent led to lower catalytic activities (epoxide selectivity was always 100%) but allowed the catalyst/IL mixtures (homogeneous mixture for IL+1 and a biphasic solid + IL system for IL+MCM-41-pyim/Mo) to be easily recovered and reused in subsequent runs without loss of catalytic performance.     

A convenient approach towards boron cluster modifications with adenosine and 2′-deoxyadenosine

New 2′-deoxyadenosine and adenosoine modifications: 8-[(2-dimethylaminoethyl)amino]-2′-deoxyadenosine and 8-[(2-dimethylaminoethyl)amino]adenosine were prepared and their reactivity towards cyclic oxonium adducts of closo-dodecaborate and cobalt-bis-dicarbollide was studied. The cleavage reactions of clusters oxonium rings by N,N-dimethylanio group of modified nucleosides led to the first [B₁₂H₁₂]²⁻ and new [Co(C₂B₉H₁₁)₂]⁻ conjugates with adenosine and 2′-deoxyadenosine respectively. The proposed methodology provides a convenient route for the synthesis of libraries of boron cluster modified adenosine and 2′-deoxyadenosine derivatives for biological screening.     

Poly(Acrylic Acid-b-Styrene) Amphiphilic Multiblock Copolymers as Building Blocks for the Assembly of Discrete Nanoparticles

In order to expand the utility of current polymeric micellar systems, we have developed amphiphilic multiblock copolymers containing alternating blocks of poly(acrylic acid) and poly(styrene). Heterotelechelic poly(tert-butyl acrylate-b-styrene) diblock copolymers containing an α-alkyne and an ω-azide were synthesized by atom transfer radical polymerization (ATRP), allowing control over the molecular weight while maintaining narrow polydispersity indices. The multiblock copolymers were constructed by copper-catalyzed azide-alkyne cycloaddition of azide-alkyne end functional diblock copolymers which were then characterized by (1)H NMR, FT-IR and SEC. The tert-butyl moieties of the poly(tert-butyl acrylate-b-styrene) multiblock copolymers were easily removed to form the poly(acrylic acid-b-styrene) multiblock copolymer ((PAA-PS)(9)), which contained up to 9 diblock repeats. The amphiphilic multiblock (PAA-PS)(9) (M(n) = 73.3 kg/mol) was self-assembled by dissolution into tetrahydrofuran and extensive dialysis against deionized water for 4 days. The critical micelle concentration (CMC) for (PAA-PS)(9) was determined by fluorescence spectroscopy using pyrene as a fluorescent probe and was found to be very low at 2 × 10(-4) mg/mL. The (PAA-PS)(9) multiblock was also analyzed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The hydrodynamic diameter of the particles was found to be 11 nm. Discrete spherical particles were observed by TEM with an average particle diameter of 14 nm. The poly(acrylic acid) periphery of the spherical particles should allow for future conjugation of biomolecules.     

A polymer inclusion membrane based on the ionic liquid trihexyl(tetradecyl)phosphonium chloride and PVC for solid–liquid extraction of Zn(II) from hydrochloric acid solution

Abstract  

Extraction of Zn(II) from aqueous solution using polymer inclusion membranes based on poly(vinyl chloride) containing the phosphonium-based ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos^? IL 101) is described. Zn(II) could efficiently be extracted from 5 M hydrochloric acid solution with membranes containing 30 wt% Cyphos IL 101, whereas back-extraction was successfully achieved with 1 M sulfuric acid. Prepared membranes were evaluated in terms of stability in air as well as in terms of leaching of the ionic liquid from the membranes in aqueous solution.     

Lipophilicity of Tetraarylporphyrins. Part 1. Tetra-(Hydroxyphenyl)Porphyrins with Long Alkyl Chain in the Molecule

JPC – Journal of Planar Chromatography – Modern TLC - In the phototherapeutic use of photosensitizers, lipophilicity is an important parameter that allows predicting their biological...     

Highly efficient visible-light driven photochromism: developments towards a solid-state molecular switch operating through a triplet-sensitised pathway

We introduce a new highly efficient photochromic organometallic dithienylethene (DTE) complex, the first instance of a DTE core symmetrically modified by two Pt(II) chromophores [Pt(PEt(3))(2)(C≡C)(DTE)(C≡C)Pt(PEt(3))(2)Ph] (1), which undergoes ring-closure when activated by visible light in solvents of different polarity, in thin films and even in the solid state. Complex 1 has been synthesised and fully photophysically characterised by (resonance) Raman and transient absorption spectroscopy complemented by calculations. The ring-closing photoconversion in a single crystal of 1 has been followed by X-ray crystallography. This process occurs with the extremely high yield of 80%--considerably outperforming the other DTE derivatives. Remarkably, the photocyclisation of 1 occurs even under visible light (>400 nm), which is not absorbed by the non-metallated DTE core HC≡C(DTE)C≡CH (2) itself. This unusual behaviour and the high photocyclisation yields in solution are attributed to the presence of a heavy atom in 1 that enables a triplet-sensitised photocyclisation pathway, elucidated by transient absorption spectroscopy and DFT calculations. The results of resonance Raman investigation confirm the involvement of the alkynyl unit in the frontier orbitals of both closed and open forms of 1 in the photocyclisation process. The changes in the Raman spectra upon cyclisation have permitted the identification of Raman marker bands, which include the acetylide stretching vibration. Importantly, these bands occur in the spectral region unobstructed by other vibrations and can be used for non-destructive monitoring of photocyclisation/photoreversion processes and for optical readout in this type of efficiently photochromic thermally stable systems. This study indicates a strategy for generating efficient solid-state photoswitches in which modification of the Pt(II) units has the potential to tune absorption properties and hence operational wavelength across the visible range.     

Crystal structures of Ziegler-Natta catalyst supports

The crystal structures of three MgCl(2)·nEtOH complexes with n=1.5, 2.8, and 3.3 have been fully determined. Such complexes are the fundamental precursors for Ziegler-Natta polymerization catalysts used to produce polyolefins on a multimillion-ton scale worldwide. The ab initio structure solution showed that the structure of MgCl(2)·nEtOH complexes with n=1.5 and 2.8 are based on ribbons of metal-centered octahedra, whereas for n=3.3 this chainlike arrangement breaks into a threadlike structure of isolated octahedra linked by hydrogen bonds. A clear correlation between catalyst performance and the crystal structure of precursors has been found, and reveals the fundamental role of the latter in determining catalyst properties. The direct knowledge of building blocks in the precursor structures will help to develop more accurate models for activated catalysts. These models will not require the arbitrary and oversimplified assumption of locating the catalyst active sites on selected cut surfaces of the α-MgCl(2) crystal lattice.