The process of front-to-side collision of motor vehicles in terms of energy balance

Nonlinear Dynamics - The reconstruction of a road accident can be treated as the resolution of an “inverse problem” in mechanics using analytical or numerical models. In the road...     

An efficient synthesis of the phytoestrogen 8-prenylnaringenin from isoxanthohumol with magnesium iodide etherate

Xanthohumol was isolated from supercritical carbon dioxide-spent hop and transformed into isoxanthohumol. The demethylation of isoxanthohumol with the best yield 93% occurred when MgI₂ etherate in anhydrous THF was applied. Salts such as MgBr₂, MgCl₂, CaI₂, Mg(OAc)₂, Mg(OMe)₂ were also investigated. A convenient method for the xanthohumol isolation from supercritical carbon dioxide-spent hop is also described.     

Enantioselective 1,3‐dipolar cycloaddition reactions using chiral lanthanide catalysts

Regio‐ and stereoselective 1,3‐dipolar cycloaddition of nitrile oxides to internal 2‐pentenols, α,β‐unsaturated esters and amides catalyzed by R‐(+) BINOL‐lanthanide complexes affords corresponding 3‐aryl‐2‐isoxazolines with enantioselectivities up to 89% ee.     

Vibrational Properties of LaNb0.8M0.2O4-δ (M=As,Sb, V,and Ta)

LaNb_0.8M_0.2O_4-δ (where M=As, Sb, V, and Ta) oxides with pentavalent elements of different ionic sizes were synthesized by a solid-state reaction method. The vibrational properties of these oxides have been investigated. These studies revealed that the substituent element influences both Debye temperature value as well as the Raman active vibrational modes. Additionally, the low-temperature vibrational properties of LaNb_0.8Sb_0.2O_4-δ have been determined to show the phase transition occurrence at 260 K which is lower than previously reported.     

Enolate Stabilization by Anion–π Interactions: Deuterium Exchange in Malonate Dilactones on π‐Acidic Surfaces

Of central importance in chemistry and biology, enolate chemistry is an attractive topic to elaborate on possible contributions of anion–π interactions to catalysis. To demonstrate the existence of such contributions, experimental evidence for the stabilization of not only anions but also anionic intermediates and transition states on π‐acidic aromatic surfaces is decisive. To tackle this challenge for enolate chemistry with maximal precision and minimal uncertainty, malonate dilactones are covalently positioned on the π‐acidic surface of naphthalenediimides (NDIs). Their presence is directly visible in the upfield shifts of the α‐protons in the ¹H NMR spectra. The reactivity of these protons on π‐acidic surfaces is measured by hydrogen–deuterium (H–D) exchange for 11 different examples, excluding controls. The velocity of H–D exchange increases with π acidity (NDI core substituents: SO₂R>SOR>H>OR>OR/NR₂>SR>NR₂). The H–D exchange kinetics vary with the structure of the enolate (malonates>methylmalonates, dilactones>dithiolactones). Moreover, they depend on the distance to the π surface (bridge length: 11–13 atoms). Most importantly, H–D exchange depends strongly on the chirality of the π surface (chiral sulfoxides as core substituents; the crystal structure of the enantiopure (R,R,P)‐macrocycle is reported). For maximal π acidity, transition‐state stabilizations up to ?18.8 kJ mol^?1 are obtained for H–D exchange. The Brønsted acidity of the enols increases strongly with π acidity of the aromatic surface, the lowest measured pK_a=10.9 calculates to a ΔpK_a=?5.5. Corresponding to the deprotonation of arginine residues in neutral water, considered as “impossible” in biology, the found enolate–π interactions are very important. The strong dependence of enolate stabilization on the unprecedented seven‐component π‐acidity gradient over almost 1 eV demonstrates quantitatively that such important anion–π activities can be expected only from strong enough π acids.     

Blue-shifting intramolecular C-H...O interactions

Two model systems, 3-methylacroleine and 3-(difluoromethyl)acroleine, are investigated computationally with respect to the character of the C-H...O interaction in their chelate-type (ZZ) conformers. By selecting the appropriate reference conformers, the C-H...O interaction is shown to result in the increase of the C-H stretching frequency (i.e., in the blue shift of the C-H stretching band). This is accompanied by the shortening of the C-H bond distance as compared to its values in reference molecules. Parallel to calculations of the C-H bond distance and stretching frequency, the energy contribution of the C-H...O interaction to the total energy (i.e., the energy associated with the C-H...O contact) is evaluated by using the methods proposed recently for the estimation of the energies of intramolecular hydrogen bonds. It is found that the C-H...O contact in the chelate-type forms of 3-methylacroleine and 3-(difluoromethyl)acroleine corresponds to the negative energy contribution and is repulsive. It is concluded that, despite the stability of the ZZ conformers of the two molecules and their deceptive structural shape, no hydrogen bond in the usual sense is formed between the C-H bond and the lone pair donor. The results are interpreted in terms of the steric compression, which leads to the dominance of the valence repulsion contribution in the C-H...O contact. This mechanism suggests that blue-shifting intramolecular interactions should not be that uncommon, although their recognition requires a careful consideration of the reference system.     

Computer analysis of microporous structure by employing the LBET class models with various variants of the adsorption energy distribution in comparison to the classical equations

The paper presents a properties study of the new LBET class models for heterogeneous multilayer adsorption and its applicability to analysis of microporous carbonaceous adsorbents in comparison to the selected classical equations. This paper shows that the LBET formulas give a good insight into the pore size distribution and dominant pore shape. Moreover, they provide more reliable evaluation of material surface area than the popular classical equations. This research constitutes a significant development and completion of the author's earlier works and provides a basis for the evaluation of reliability of parameters calculated for real systems.     

Projection-Algebraic Scheme of Discrete Approximations for Linear and Nonlinear Differential Operator Equations in Banach Spaces

The solution set, realizability and convergence of the projection-algebraic method of discrete approximations for linear and nonlinear differential operator equations are studied. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of 3-aryl substituted benzo[1,2,5]triazepin-4-ones via intramolecular imine formation

3-Aryl substituted benzo[1,2,5]triazepin-4-ones and their pyrido counterparts have been synthesized in five steps from commercially available starting materials. The key step involves base-induced cleavage of trifluoroacetyl-protected hydrazine intermediates and in situ intramolecular imine formation.     

AFM diagnostics of graphene-based quantum Hall devices

In this paper we present the results of morphological, mechanical and electrical investigation of the properties of prepared graphene flakes and graphene-based quantum Hall devices. AFM imaging allowed us to identify the local imperfections and unintentional modifications of the graphene sheets which had caused severe deterioration of the device electrical performance. Utilizing the NanoSwing imaging method, based on the time-resolved tapping mode, we could observe non-homogeneities of the structural and mechanical properties. We also diagnosed the device under working conditions by Kelvin probe microscopy and detected its local electric field distribution.