Scattering studies of hydrophobic monomers in liposomal bilayers: an expanding shell model of monomer distribution

Hydrophobic monomers partially phase separate from saturated lipids when loaded into lipid bilayers in amounts exceeding a 1:1 monomer/lipid molar ratio. This conclusion is based on the agreement between two independent methods of examining the structure of monomer-loaded bilayers. Complete phase separation of monomers from lipids would result in an increase in bilayer thickness and a slight increase in the diameter of liposomes. A homogeneous distribution of monomers within the bilayer would not change the bilayer thickness and would lead to an increase in the liposome diameter. The increase in bilayer thickness, measured by the combination of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS), was approximately half of what was predicted for complete phase separation. The increase in liposome diameter, measured by dynamic light scattering (DLS), was intermediate between values predicted for a homogeneous distribution and complete phase separation. Combined SANS, SAXS, and DLS data suggest that at a 1.2 monomer/lipid ratio approximately half of the monomers are located in an interstitial layer sandwiched between lipid sheets. These results expand our understanding of using self-assembled bilayers as scaffolds for the directed covalent assembly of organic nanomaterials. In particular, the partial phase separation of monomers from lipids corroborates the successful creation of nanothin polymer materials with uniform imprinted nanopores. Pore-forming templates do not need to span the lipid bilayer to create a pore in the bilayer-templated films.     

High sensitivity of diamond resonant microcantilevers for direct detection in liquids as probed by molecular electrostatic surface interactions

Resonant microcantilevers have demonstrated that they can play an important role in the detection of chemical and biological agents. Molecular interactions with target species on the mechanical microtransducers surface generally induce a change of the beam's bending stiffness, resulting in a shift of the resonance frequency. In most biochemical sensor applications, cantilevers must operate in liquid, even though damping deteriorates the vibrational performances of the transducers. Here we focus on diamond-based microcantilevers since their transducing properties surpass those of other materials. In fact, among a wide range of remarkable features, diamond possesses exceptional mechanical properties enabling the fabrication of cantilever beams with higher resonant frequencies and Q-factors than when made from other conventional materials. Therefore, they appear as one of the top-ranked materials for designing cantilevers operating in liquid media. In this study, we evaluate the resonator sensitivity performances of our diamond microcantilevers using grafted carboxylated alkyl chains as a tool to investigate the subtle changes of surface stiffness as induced by electrostatic interactions. Here, caproic acid was immobilized on the hydrogen-terminated surface of resonant polycrystalline diamond cantilevers using a novel one-step grafting technique that could be also adapted to several other functionalizations. By varying the pH of the solution one could tune the -COO(-)/-COOH ratio of carboxylic acid moieties immobilized on the surface, thus enabling fine variations of the surface stress. We were able to probe the cantilevers resonance frequency evolution and correlate it with the ratio of -COO(-)/-COOH terminations on the functionalized diamond surface and consequently the evolution of the electrostatic potential over the cantilever surface. The approach successfully enabled one to probe variations in cantilevers bending stiffness from several tens to hundreds of millinewtons/meter, thus opening the way for diamond microcantilevers to direct sensing applications in liquids. The evolution of the diamond surface chemistry was also investigated using X-ray photoelectron spectroscopy.     

Atomic Contributions from Spin‐Orbit Coupling to 29Si NMR Chemical Shifts in Metallasilatrane Complexes

New members of a novel class of metallasilatrane complexes [X‐Si‐(μ‐mt)₄‐M‐Y], with M=Ni, Pd, Pt, X=F, Cl, Y=Cl, Br, I, and mt=2‐mercapto‐1‐methylimidazolide, have been synthesized and characterized structurally by X‐ray diffraction and by ²⁹Si solid‐state NMR. Spin‐orbit (SO) effects on the ²⁹Si chemical shifts induced by the metal, by the sulfur atoms in the ligand, and by heavy halide ligands Y=Cl, Br, I were investigated with the help of relativistic density functional calculations. Operators used in the calculations were constructed such that SO coupling can selectively be switched off for certain atoms. The unexpectedly large SO effects on the ²⁹Si shielding in the Ni complex with X=Y=Cl reported recently originate directly from the Ni atom, not from other moderately heavy atoms in the complex. With respect to Pd, SO effects are amplified for Ni owing to its smaller ligand‐field splitting, despite the smaller nuclear charge. In the X=Cl, Y=Cl, Br, I series of complexes the Y ligand strongly modulates the ²⁹Si shift by amplifying or suppressing the metal SO effects. The pronounced delocalization of the partially covalent M←Y bond plays an important role in modulating the ²⁹Si shielding. We also demonstrate an influence from the X ligand on the ²⁹Si SO shielding contributions originating at Y. The NMR spectra for [X‐Si‐(μ‐mt)₄‐M‐Y] must be interpreted mainly based on electronic and relativistic effects, rather than structural differences between the complexes. The results highlight the sometimes unintuitive role of SO coupling in NMR spectra of complexes containing heavy atoms.     

Photomagnetic effect in a cyanide-bridged mixed-valence {Fe(II)2Fe(III)2} molecular square

The self-assembly of [Fe(III)(Tp)(CN)(3)](-) and [Fe(II)(bik)(2)(S)(2)](2+) affords the cyanide-bridged mixed valence {Fe(III)(2)Fe(II)(2)}(2+) molecular square, which exhibits a photomagnetic effect under laser light irradiation at low temperature and also shows thermal spin-state conversion near ambient temperature.     

Femtosecond dynamics of cyclopropenylidene, c-C3H2

The photophysics of the B (1)B(1) state of isolated cyclopropenylidene, c-C(3)H(2), has been studied by femtosecond time-resolved photoionisation and photoelectron spectroscopy. The carbene was produced by flash pyrolysis of 3-chlorocycloprop-1-ene. The bands at 266.9 nm and 264.6 nm have been investigated. The excited state deactivates in a two step process. The first time constant of less than 50 fs corresponds most likely to a nonradiative transition to the A-state, the second one on the order of 200 fs describes the internal conversion to the electronic ground state. The data are compared to those measured for the chlorinated carbene c-C(3)HCl. In the photoelectron spectrum of c-C(3)H(2) resonances were observed which can be assigned to members of a Rydberg d-series.     

Structure and properties of glasses in ZnO-P2O5-TeO2 system

Glasses in the ternary ZnO-P₂O₅-TeO₂ system were prepared and studied in two compositional series (100 − x)[0.5ZnO-0.5P₂O₅]-xTeO₂ (X-series) and 50ZnO-(50 − y)P₂O₅-yTeO₂ (Y-series) within the concentration range of x = 0-60 and y = 0-40 mol% TeO₂. Their structure was studied by Raman and ³¹P MAS NMR spectroscopies. The incorporation of TeO_x units into the structural network is associated with the depolymerisation of phosphate chain structure as revealed by both methods. At a high TeO₂ content isolated PO₄ tetrahedra are formed in the structure of glass series Y, while diphosphate O₃P-O-PO₃ groups are present in the structure of the glass series X. In the structure of glass series Y tellurium atoms form predominantly TeO₃ trigonal pyramids, whereas in the X glass series TeO₄ trigonal bipyramids prevail in the glass structure. The addition of TeO₂ to the parent zinc metaphosphate glass results in a decrease of glass transition temperature in both compositional series associated with the replacement of stronger P―O bonds by weaker Te―O bonds.     

On the spectral accuracy of a fictitious domain method for elliptic operators in multi-dimensions

This work is a continuation of the authors efforts to develop high-order numerical methods for solving elliptic problems with complex boundaries using a fictitious domain approach. In a previous paper, a new method was proposed, based on the use of smooth forcing functions with identical shapes, mutually disjoint supports inside the fictitious domain and whose amplitudes play the role of Lagrange multipliers in relation to a discrete set of boundary constraints. For one-dimensional elliptic problems, this method shows spectral accuracy but its implementation in two dimensions seems to be limited to a fourth-order algebraic convergence rate. In this paper, a spectrally accurate formulation is presented for multi-dimensional applications. Instead of being specified locally, the forcing function is defined as a convolution of a mollifier (smooth bump function) and a Lagrange multiplier function (the amplitude of the bump). The multiplier function is then approximated by Fourier series. Using a Fourier Galerkin approximation, the spectral accuracy is demonstrated on a two-dimensional Laplacian problem and on a Stokes flow around a periodic array of cylinders. In the latter, the numerical solution achieves the same high-order accuracy as a Stokes eigenfunction expansion and is much more accurate than the solution obtained with a classical third order finite element approximation using the same number of degrees of freedom.