Acid-Catalyzed Diels-Alder Reactions of Cycloalkenones

Whereas the Diels-Alder reaction has been in vogue as a facile method of six-membered ring construction for many years, its application to a one-step cis-octalone synthesis was precluded by discouraging, early reports on the conditions required for the interaction of dienes with 2-cyclohexenones and on the yields of the resultant adducts.^1,2 It is quite conceivable that these observations were responsible in part for the minimization of use of an otherwise attractive route toward angularly alkylated six-membered polycycles in the field of steroid total synthesis. The discovery of Lewis acid catalysis of the cycloaddition of α, β-unsaturated carbonyl compounds³ has rekindled interest in the above reactions.⁴ The following discussion illustrates octalone     

How glucosylation triggers physical–chemical properties of curcumin: an experimental and theoretical study

In the present study, we investigate the structures of glucosylated curcumin derivatives with DFT at B3LYP/6‐31G* level. A conformational analysis is performed in order to determine the conformational minimum (GS) and rotational transition state (TS) of curcumin derivatives and then their electronic features are evaluated. HOMO and LUMO frontier orbitals and maps of electron density potential (MEPs) are plotted and compared. In order to correlate their predicted spectroscopic properties with IR, UV–vis and NMR experimental data we extended the theoretical study on electronic properties to different solvents (H₂O, MeOH, ACN, DMSO). The main finding is that the curcuminic core maintains the same geometrical and electronic structures in all compounds miming the metal coordination capability showed by curcumin. Therefore, we may confirm that the presence of glucose does not affect the electronic properties of the derivatives. Copyright © 2010 John Wiley & Sons, Ltd.     

Competitive evaluation of threshold functions in the priced information model

In Charikar et al. (J. Comput. Syst. Sci. 64(4):785–819, 2002) the authors proposed a new model for studying the function evaluation problem based on a variant of the classical decision tree problem for Boolean functions. In this variant each variable of the function to evaluate has an associated cost which has to be paid in order to read the value of the variable. Given a function f and an assignment σ to the variables of f, the performance of an algorithm for evaluating f is measured via the competitive ratio, i.e., the ratio of the total cost spent by the algorithm and the cost of the cheapest set of variables constituting a certificate for the value of the function on the given assignment.     

Conformational analysis of hydrazones. 1H dynamic nuclear magnetic resonance and solvent effects in aryl- and 2-furylaldehyde ethylaminoacetylhydrazones

Aryl- and 2-furylaldehyde ethylaminoacetylhydrazones were examined in different solvents and over a wide temperature range with ¹H NMR in order to study their conformational properties. Nearly equal amounts of the E/Z isomers, relative to the C?N bond, are present, even when the solvents and the substituents on the aldimino carbon produce small changes in the isomeric mixture. The activation parameters of the thermal isomerization process were measured, and the results are in the line with a lateral-shift type mechanism, also supported by theoretical calculations on a model compound. No other internal process was noted from the low-temperature spectral behaviour, and this was interpreted in terms of a highly biased equilibrium concerning the rotation around the C(O)? N bond. Chemical shifts obtained in different solvents also enable the most stable arrangement of the whole molecule of these compounds to be postulated.     

Optimization of impurity profile for p-n-junction in heterostructures

We analyze the dopant diffusion in p-n-junction in heterostructure, by solving the diffusion equation with space-varying diffusion coefficient. For a step-wise spatial distribution we find the optimum annealing time to decrease the p-n-junction thickness and to increase the homogeneity of impurity concentration in p or n regions.     

Polystyryl-supported TBD as an efficient and reusable catalyst under solvent-free conditions

Polystyryl supported-TBD (PSTBD) is an efficient and reusable heterogeneous basic catalyst under solvent-free conditions for a variety of organic transformations such as 1,2-epoxide ring-opening, aldol-type condensation and Michael addition.     

Generation and intramolecular reactivity of acyl radicals from alkynylthiol esters under reducing tin-free conditions

[reaction: see text] The radical chain reaction of benzenethiol with alkynylthiol esters provides a new, valuable protocol for the tin-free generation of acyl radicals that arise from intramolecular substitution at sulfur by the initial sulfanylvinyl radicals.     

Adsorption of citric acid from dilute aqueous solutions by hydroxyapatite

The role of citric acid in the demineralization of dental enamel, which is mainly constituted by hydroxyapatite, is important for periodontal regeneration and in the conditioning of enamel or dentin for bonding restorative resins. The adsorption of citric acid from aqueous solutions onto synthetic hydroxyapatite at 278, 288, 298, and 308 K and pH 4.8 has been studied by means of UV spectroscopy. The adsorption reaction, which takes place by an interaction between phosphate groups and citrate anions at the solid-solution interface, yields an adsorbate-adsorbent complex of high stability. The adsorption isotherms fit the Langmuirian shape. The proposed adsorption model, where citrate species interact in a bidentate manner (one citrate ion links two phosphate sites), is coherent with the experimental data. The activation standard heat and activation standard entropy were calculated. All the thermodynamic and kinetic parameters were in concordance with the adsorption reaction proposed in this work.     

Patient-specific finite element analysis of popliteal stenting

Nitinol self-expanding stents are used for the endovascular management of peripheral artery diseases of the popliteal artery, which is located behind the knee joint. Unfortunately, the complex kinematics of the artery during the leg flexion leads to severe loading conditions, favouring the mechanical failure of the stent, calling for a specific biomechanical analysis. For this reason, in the present study we reconstruct by medical image analysis the patient-specific popliteal kinematics during leg flexion, which is subsequently exploited to compute the mechanical response of a stent model, virtually implanted in the artery by structural finite element analysis (FEA). The medical image analysis indicates a non-uniform configuration change of the artery during the leg flexion, leading to an increase of the vessel curvature above the knee. The computed mechanical response of the stent reflects the non-uniform configuration change of the artery as after the flexion the average stress is higher in the part of the stent located above the knee. Although the proposed analysis is limited to a case-study, it shows the capability of patient-specific FEA simulations to compute the mechanical response of a stent model subjected to the complex and severe loading conditions of the popliteal artery during leg flexion.     

A Combined Theoretical and Experimental Approach to the Study of the Structural and Electronic Properties of Curcumin as a Function of the Solvent

Curcumin, a chemical compound present in the well-known Indian spice turmeric, has uses in many different fields ranging from medicinal chemistry to the dye industry. Its poor water solubility, though, makes Curcumin difficult to handle, making it less appealing for potential uses. The principal aim of this work is to perform a computational study of the structural and electronic properties of Curcumin {IUPAC name: 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione} in several solvents, and a comparison with experimental data. Rotameric equilibria, vibrational and thermochemical analysis, and electronic absorption spectra (with ab initio and semi-empirical methodologies) have been studied, both in vacuum and in three selected solvents. Different computational techniques have been applied and the results compared. Combined approaches resulted in very satisfactory results. Interesting results have emerged, which suggest subsequent investigations about the nature of the excited states and potential derivatives of Curcumin that possibly have non-linear optical applications, as a π-core for innovative materials in laser engineering and photonics.