Exclusive alpha-coupling in the aldol reaction of unsaturated trimethylsilyl esters: an efficient and practical direct synthesis of unsaturated beta-hydroxy acids

The lithium enolates of trimethylsilyl but-3-enoate and 3-methylbut-3-enoate reacted with aldehydes and saturated or aromatic ketones at -70 degrees C to give exclusively the alpha-condensation products in excellent yields. The unsaturated beta-hydroxy acids thus obtained were directly identified, and the usual conversion into their methyl esters with diazomethane was not necessary. Unsaturated ketones underwent Michael reaction through alpha-addition leading to the unsaturated 5-oxo acids.     

Dianions d'aldoximes: preparation et applications en synthese

Aldoximes are converted to their dilithium derivatives by lithium diisopropylamide at 0°C in THF solution. These dianions react with electrophiles to give α-substituted aldoximes.     

Fluorescence and Label Free Impedimetric DNA Detection on SnO2 Nanopillars

SnO₂ is a n‐type semiconductive oxide with attractive characteristics mainly based on easy elaboration and functionalization routes in addition to chemical robustness. We have fabricated SnO₂ nanopillars based DNA sensor to perform the label free (without any redox compound) impedimetric DNA detection. The non faradaic electrochemical impedance spectroscopic (EIS) behavior and more particularly the evolution of the polarization resistance the SnO₂ nanopillars has been thoroughly investigated upon the different steps of their functionalization process up to DNA hybridization. Similarly to our previous study on planar 2D SnO₂ surfaces, the DNA hybridization induces a systematic increase of the polarization resistance, the magnitude of which decreases with the target DNA concentration. This DNA concentration dependence matches the one obtained from epifluorescence intensity measurements. A common value of DNA detection limit, i.e. 2 nM, is found from both measurement techniques. Interestingly the 3D view intensity obtained by confocal scanning laser fluorescence microscopy confirms that the DNA molecules are mainly grafted along the SnO₂ nanopillars. Finally both impedance and fluorescence measurements obtained in the case of 1‐ and 2‐base mismatch hybridizations demonstrate the selectivity of the SnO₂ nanopillars based DNA sensor. These preliminary results open the way to further investigations on the influence of both the shape ratio and electrical properties of the SnO₂ nanopillars on the impedance variations related to DNA hybridization, notably in view of improving the sensor performances.     

Quasi-stability and upper semicontinuity for coupled parabolic equations with memory

This current study deals with the long-time dynamics of a nonlinear system of coupled parabolic equations with memory. The system describes the thermodiffusion phenomenon where the fluxes of mass diffusion and heat depend on the past history of the chemical potential and the temperature gradients, respectively, according to Gurtin-Pipkin's law. Inspired by the works of Chueshov and Lasiecka on the property of quasi-stability of dynamic systems, we prove this property for the problem considered in this study. This property allows us to analyze certain properties of global and exponential attractors in a more efficient and practical way. This approach is applied for the first time for coupled parabolic equations. We analyze the continuity of global attractors with respect to a pair of parameters in a residual dense set and their upper semicontinuity in a complete metric space. Finally, we analyze the upper semicontinuity of global attractors with respect to small perturbations of the damping terms.     

Stability aspects in a nonsimple thermoelastic diffusion problem

In this article, we investigate the asymptotic behaviour of a one-dimensional problem of linear theory of nonsimple thermoelastic diffusion. We show that the corresponding semigroup is exponentially stable but not analytic. We conclude by showing the impossibility of localization in time of the solutions.     

Computation of the electronic structure and direct-gap absorption spectra in Ge-rich Si<Subscript>1−x</Subscript> Ge<Subscript>x</Subscript>/Ge/Si<Subscript>1−x</Subscript>Ge<Subscript>x</Subscript> type-I quantum wells

This paper presents the results of conduction band discontinuities calculation for strained/relaxed Si_1?x Ge _x /Si_1?y Ge _y heterointerfaces in Γ _15C , Γ _2′C and L upper bands minima, as well as the room-temperature strained (vs. relaxed) band gaps deduced from the classical model-solid theory. Based upon the obtained data, we propose a type-I W-like Si_1?y Ge _y /Si_1?x Ge _x /Ge/Si_1?x Ge _x /Si_1?y Ge _y quantum wells heterostructure optimized in terms of compositions and thicknesses. Electronic states and wave functions are found by solving Schrödinger equation without and under applied bias voltage. An accurate investigation of the optical properties of this heterostructure is done by calculating the energies of the interband transitions and their oscillator strengths. Moreover, a detailed computation of the bias-voltage evolution of the absorption spectra is presented. These calculations prove the existence of type-I band alignment at Γ _2′C point in compressively strained Ge quantum wells grown on relaxed Ge-rich Si_1?y Ge _y buffers. The strong absorption coefficient (> 8 × 10³ cm^-1) and the large Stark effect (0.1 eV @ 2 V) of the Γ _2′C transitions thresholds open up perspectives for application of these heterostructures for near-infrared optical modulators.     

Stability constants determination of successive metal complexes by hyphenated CE‐ICPMS

The study of radionuclides speciation requires accurate evaluation of stability constants, which can be achieved by CE‐ICPMS. We have previously described a method for 1:1 metal complexes stability constants determination. In this paper, we present its extension to the case of successive complexations and its application to uranyl‐oxalate and lanthanum‐oxalate systems. Several significant steps are discussed: analytical conditions choice, mathematical treatment by non‐linear regression, ligand concentration and ionic strength corrections. The following values were obtained: at infinite dilution, log(β₁°(UO₂Oxa))=6.93±0.05, log(β₂°(UO₂(Oxa)₂^2?))=11.92±0.43 and log(β₃°(UO₂(Oxa)₃^4?))=15.11±0.12; log(β₁°(LaOxa⁺))=5.90±0.07, log(β₂°(La(Oxa)₂^?))=9.18±0.19 and log(β₃°(La(Oxa)₃^3?))=9.81±0.33. These values are in good agreement with the literature data, even though we suggest the existence of a new lanthanum‐oxalate complex: La(Oxa)₃^3?. This study confirms the suitability of CE‐ICPMS for complexation studies.     

Temperature dependence of an elastic modulus in generalized linear micropolar thermoelasticity

The model of the equations of generalized linear micropolar thermoelasticity with two relaxation times in an isotropic medium with temperature-dependent mechanical properties is established. The modulus of elasticity is taken as a linear function of reference temperature. Laplace and exponential Fourier transform techniques are used to obtain the solution by a direct approach. The integral transforms have been inverted by using a numerical technique to obtain the temperature, displacement, force and couple stress in the physical domain. The results of these quantities are given and illustrated graphically. A comparison is made with results obtained in case of temperature-independent modulus of elasticity. The problem of generalized thermoelasticity has been reduced as a special case of our problem.     

Tangent circle graphs and ‘orders’

Consider a horizontal line in the plane and let γ(A) be a collection of n circles, possibly of different sizes all tangent to the line on the same side. We define the tangent circle graph associated to γ(A) as the intersection graph of the circles. We also define an irreflexive and asymmetric binary relation P on A; the pair (a,b) representing two circles of γ(A) is in P iff the circle associated to a lies to the right of the circle associated to b and does not intersect it. This defines a new nontransitive preference structure that generalizes the semi-order structure. We study its properties and relationships with other well-known order structures, provide a numerical representation and establish a sufficient condition implying that P is transitive. The tangent circle preference structure offers a geometric interpretation of a model of preference relations defined by means of a numerical representation with multiplicative threshold; this representation has appeared in several recently published papers.     

Application of molecular topology to the prediction of mosquito repellents of a group of terpenoid compounds

A topological-mathematical model based on multilinear regression analysis has been built to search new terpenoid actives as mosquito repellents. The structural depiction was performed using topological indices, and a four-variable model for the prediction of corrected repellent ratio (r ² = 0.9672, Q ² = 0.9435) was selected. The model was checked by cross-validation, internal validation, and randomization test. The results confirm its capability to predict the property analyzed. After carrying out a virtual screening upon such a model, new structures with potential repellent activity against mosquitoes are proposed.