A self-consistent field for the H2 molecule

We investigate the simple harmonic oscillator in a 1D box, and the 2D isotropic harmonic oscillator problem in a circular cavity with perfectly reflecting boundary conditions. The energy spectrum has been calculated as a function of the self-adjoint extension parameter. For sufficiently negative values of the self-adjoint extension parameter, there are bound states localized at the wall of the box or the cavity that resonate with the standard bound states of the simple harmonic oscillator or the isotropic oscillator. A free particle in a circular cavity has been studied for the sake of comparison. This work represents an application of the recent generalization of the Heisenberg uncertainty relation related to the theory of self-adjoint extensions in a finite volume.     

NMR evidence for the persistence of a spin superlattice beyond the 1/8 magnetization plateau in SrCu2(BO3)_{2}

We present 11B NMR studies of the 2D frustrated dimer spin system SrCu2(BO3)_{2} in the field range 27-31 T covering the upper phase boundary of the 1/8 magnetization plateau, identified at 28.4 T. Our data provide a clear evidence that above 28.4 T the spin superlattice of the 1/8 plateau is modified but does not melt even though the magnetization increases. Although this is precisely what is expected for a supersolid phase, the microscopic nature of this new phase is much more complex. We discuss the field-temperature phase diagram on the basis of our NMR data.     

Butterfly inclusions in Van Schrieck masterpieces. Techniques and optical properties

Dutch painter Otto Marseus Van Schrieck (1619–1678) is famous for his invention of “sottobosco”. These specific still-life paintings are characterized by the presence of various living organisms (mainly insects and plants) directly on the canvas. We will focus our attention on the painting kept in the museum of Grenoble, France, where a real butterfly is pasted on the canvas. The actual butterfly is a common Nymphalidae, Inachis io, presented in a static position on the dorsal side, without any perspective, compared to the neighboring butterflies. The colors of this butterfly are mainly due to pigments, melanin (black to brown) and ommochromes (yellow, orange, red) often in granules configuration that introduce scattering of light superimposed to the classical selective absorption, except in the ocelli of the hind wings where the blue coloration is due to interferential effects. The nearly perfect refraction index equality between the varnish and the chitin, the main constituent of the butterfly wings, deeply affects its colors. This leads the artist to a final intervention in some parts of the wings, revealed by microscope observation. PACS  42.25.Fx; 42.25.Hz; 78.40.Me; 87.64.Cc; 87.80.Dj     

Incorporation of a minimal nucleotide into DNA

Abasic sites are amongst the most frequent DNA lesions and result from spontaneous hydrolysis of the glycosidic bond or from the removal of damaged nucleobases. These depurination events can also occur on free deoxyribonucleoside triphosphates present in cells and lead to the formation of an abasic site triphosphate of which very little is known. Herein, we report the synthesis and biochemical characterization of the minimal triphosphate dФTP. Unexpectedly, dФTP is tolerated by various DNA polymerases and the incorporation efficiency obeys the A-rule. Single incorporation of dФMP units were also observed opposite abasic sites and the addition of prosthetic molecules mimicking base-pairs do not seem to favor the process.     

Managing evaporation for more robust microscale assays. Part 1. Volume loss in high throughput assays

Evaporation is a well known issue when handling small liquid volumes. Here we present a review of microscale assays prone to evaporation and methods to make them more robust. Applications for these assays span from combinatorial chemistry to cell-biology where the stability of concentrations and osmolarity can be critical. A dimensionless evaporation number Ev is presented and used to characterize volume loss in short term and long term microscale assays. Ev can be used both as a design tool and as an analysis parameter. The advantageous use of evaporation in some applications is also discussed.     

Fire retardancy of polymer clay nanocomposites: Is there an influence of the nanomorphology?

The obvious aspect of nanodispersion and its role when investigating fire retardancy is not often clearly commented upon in the literature. Polymer clay nanocomposites can exhibit different morphologies and these might have consequences for their fire behaviour. Using solid state NMR to quantify the nanodispersion of organoclay in polyamide-6 (PA-6), we have prepared by melt blending PA-6/clay nanocomposite exhibiting different nanomorphologies. NMR results are consistent with transmission electron microscopy (TEM) images but the advantage of NMR is that it is representative of the whole sample and provides a precise quantification. PA-6 nanocomposites exhibit significant reduction of PHRR but the nanomorphology (exfoliation, intercalation and presence of tactoids) does not play any significant role. In other words, we have clearly shown that if nanodispersion is achieved, polymer/clay nanocomposite should exhibit fire retardant properties.     

DFT modeling of reactivity in an ionic liquid: How many ion pairs?

The modeling of reactivity in an ionic liquid is examined with DFT and DFT/MM calculations on the S(N)2 intramolecular rearrangement of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole induced by amines. Experimental research has shown that the reaction occurs in 1-butyl-3-methylimidazolium tetrafluoroborate, and in conventional organic solvents such as acetonitrile with comparable rates. The structure for the reactants, transition states and products for the rate-determining step are optimized, and the energy barrier is computed in three different environments: gas phase, water solvent, and ionic liquid. The results are encouraging in describing the energy barrier in the ionic liquid. A simple model is formulated to explain the effect of the solvent in this particular process, and a procedure to study theoretically the reactivity in an ionic liquid is proposed.     

Flow rate analysis of a surface tension driven passive micropump

A microfluidic passive pumping method relying on surface tension properties is investigated and a physical model is developed. When a small inlet drop is placed on the entrance of a microfluidic channel it creates more pressure than a large output drop at the channel exit, causing fluid flow. The behavior of the input drop occurs in two characteristic phases. An analytical solution is proposed and verified by experimental results. We find that during the first phase the flow rate is stable and that this phase can be prolonged by refilling the inlet drop to produce continuous flow in the microchannel.     

Counterion, temperature, and time modulation of nanometric chiral ribbons from gemini-tartrate amphiphiles

Amphiphile supramolecular assemblies result from the cooperative effects of multiple weak interactions between a large number of subcomponents. As a result, prediction of and control over the morphologies of such assemblies remains difficult to achieve. Here, we described the fine-tuning of the shape, size, and morphology transitions of twisted and helical membranes formed by non-chiral dicationic n-2-n gemini amphiphiles complexed with chiral tartrate anions. We have reported that such systems express the chirality of the tartrate components at a supramolecular level and that the mechanism of the chiral induction by counterions involves specific anion cation recognition and the induction of conformationally labile chirality in the cations. Here, we demonstrate that the morphologies and dimensions of twisted and helical ribbons, as well as tubules, can be controlled and that interconversion between these structures can be induced upon modifying temperature, upon introducing small amounts of additives, or slightly modifying molecular structure. Specifically, electron microscopy, IR spectroscopy, and small-angle X-ray scattering show that (i) varying the hydrophobic chain length or adding gemini having bromide counterions (1%) or the opposite enantiomer (10%) leads to an increase of the diameter of membrane tubules from 33 to 48.5 nm; (ii) further addition (1.5%) of gemini bromide or a slight increase in temperature induces a transition from tubules to twisted ribbons; (iii) the twist pitch of the ribbons can be continuously tuned by varying enantiomeric excess; and (iv) it was also observed that the morphologies of these ribbons much evolve with time. Such unprecedented observations over easy tuning of the chiral supramolecular structures are clearly related to the original feature that the induction of chirality is solely due the counterions, which are much more mobile than the amphiphiles.     

Water-soluble polyesters from long chain alkylesters of citric acid and poly(ethylene glycol)

Long chain aliphatic alcohols have been used as model compounds to develop a preparative method for a water-soluble material, which could be a carrier for triacontanol, a highly hydrophobic plant growth regulator. New polyesters from long chain aliphatic (C = 12, 18 and 22) mono-1-alkyl citrates and poly(ethylene glycol) were synthesized and characterized by NMR spectroscopy. The polyester containing the triacontyl moiety was obtained from mono-1-triacontyl citrate, which was synthesized from the corresponding alcohol extracted from the Agave fourcroydes. The molecular weight of the polyesters depends on experimental conditions during synthesis such as reaction time, atmosphere, catalyst concentration and temperature. The reaction is second order in the early stage of the polyester synthesis. The reaction rate constant is independent of the length of the aliphatic chain, but it decreases with increasing of the poly(ethylene glycol) employed. Turbidity measurements have been used to study the polyester solubility. Solubility characteristics were found to depend on the of poly(ethylene glycol), the aliphatic-chain length and the value of for the polyester. These preparations could potentially be used to release triacontanol.