Electronic Currents Induced by Optical Fields and Rotatory Power Density in Chiral Molecules

The electric dipole–magnetic dipole polarizability tensor κ′, introduced to interpret the optical activity of chiral molecules, has been expressed in terms of a series of density functions kαβ′, which can be integrated all over the three-dimensional space to evaluate components καβ′ and trace καα′. A computational approach to kαβ′, based on frequency-dependent electronic current densities induced by monochromatic light shining on a probe molecule, has been developed. The dependence of kαβ′ on the origin of the coordinate system has been investigated in connection with the corresponding change of καβ′. It is shown that only the trace kαα′ of the density function defined via dynamic current density evaluated using the continuous translation of the origin of the coordinate system is invariant of the origin. Accordingly, this function is recommended as a tool that is quite useful for determining the molecular domains that determine optical activity to a major extent. A series of computations on the hydrogen peroxide molecule, for a number of different HO–OH dihedral angles, is shown to provide a pictorial documentation of the proposed method.     

Microwave solvent free regioselective 1,3 dipolar cycloaddition in the synthesis of 1,4 substituted [1,2,3]‐triazoles as amide bond isosteres

1,3 Dipolar cycloaddition of Fmoc‐amino azides and acetylenic amides produces under solvent free irradiation a mixture of 1,4 or 1,5 substituted [1,2,3]‐triazoles. The presence of copper (I) iodide, plays a central role on regioselectivity. Four Fmoc‐amino azides characterized by different steric hindrance in side chains, and three different terminal alkynes, provided only the 1,4 substituted regioisomer under thermal microwave heating. Good yields, low consumption of organic solvents and short reaction times are the main aspects of our procedure. Reactions are compared to regioselective copper (I) catalysed solution synthesis performed at room temperature.     

Structure of polyelectrolyte complexes by Brownian dynamics simulation: effects of the bond length asymmetry of the polyelectrolytes

Brownian dynamics simulations were performed to study the structure of polyelectrolyte complexes formed by two flexible, oppositely charged polyelectrolyte chains. The distribution of monomers in the complex as well as the radius of gyration and structure factor of complexes and individual polyelectrolytes are reported. These structural properties were calculated for polyelectrolyte chains with equal number of monomers, keeping constant the bond length of the negative chain and increasing the bond length of the positive chain. This introduces an asymmetry in the length of the chains that modulates the final structure of the complexes. In the symmetric case the distribution of positive and negative monomers in the complex are identical, producing clusters that are locally and globally neutral. Deviations from the symmetric case lead to nonuniform, asymmetric monomer distributions, producing net charge oscillations inside the complex and large changes in the radius of gyration of the complex and individual chains. From the radius of gyration of the polyelectrolyte chains it is shown that the positive chain is much more folded than the negative chain when the chains are asymmetric, which is also confirmed through the scaling behavior of the structure factors.     

Interaction of the acid soap of triethanolamine stearate and stearic acid with water

Stearic acid and triethanolamine (TEA) in a molar ratio of 2:1 were mixed in aqueous solution at 80 degrees C and subsequently cooled to ambient temperature. The structural evolution of the resultant sample during storage was characterized by using light microscopy, Cryo-SEM, differential scanning calorimetery, pH, infrared spectroscopy, elemental analysis, and simultaneous small and wide-angle X-ray diffraction. It was found that a lamellar liquid crystalline phase was formed when stearic acid and TEA solution were mixed at 80 degrees C and multilamellar spheres of a few microns diameter were formed initially after cooling. A hydrolysis reaction (i.e., the reverse reaction of neutralization between stearic acid and TEA) occurred thereafter that caused the breakdown of the lamellar gel phase and the formation of platelet stearic acid crystals. Three polymorphs of stearic acid (defined following previous work as the A, C, and E forms) were formed as the result of hydrolysis reaction, which gave rise to a strong optically pearlescent appearance.     

Analytical quality by design in the development of a cyclodextrin‐modified capillary electrophoresis method for the assay of metformin and its related substances

Quality by Design (QbD) is a new paradigm of quality to be applied to pharmaceutical products and processes, recently encouraged by International Conference on Harmonisation guidelines. In this paper QbD approach was applied to the development of a CE method for the simultaneous assay of metformin hydrochloride (MET) and its main impurities. QbD strategy was focused on electrophoretic process understanding, and the analytical method was thoroughly evaluated by applying risk assessment and chemometric tools. Method scouting allowed CD‐CZE based on the addition of carboxymethyl‐β‐CD to Britton‐Robinson acidic buffer to be chosen as operative mode. Seven critical process parameters (CPPs) were selected, related to capillary, injection, BGE and instrumental settings. The effect of the different levels of the CPPs on critical quality attributes (CQAs), e.g. critical resolution values and analysis time, was evaluated in a screening study. Response surface methodology led to draw contour plots and sweet spot plots. The definition of design space was accomplished by applying Monte‐Carlo simulations, thus identifying by risk of failure maps a multivariate zone where the CQAs fulfilled the requirements with a selected probability. Finally, a control strategy was designed and the method was applied to a real sample of MET tablets.     

The structures, morphologies, and photophysical properties of multiluminescent layered lanthanide-phosphono-carboxylate nanoparticles

A new family of layered metal(III)-phosphono-carboxylate nanostructures (M=Y, Eu, Tb, Er, and Yb) was hydrothermally synthesized and their structures and morphologies were characterized by X-ray powder diffraction and TEM. 4-[Bis(phosphonomethyl)amino]caproic acid and 4- [bis(phosphonomethyl)amino]undecanoic acid, with general formula (H(2)O(3)PCH(2))(2)NR (R=C(5)H(10)COOH(P2CAPR) and C(10)H(22)COOH(P2UND), respectively) were used as building blocks for the preparation of novel layered hybrid materials in which the inorganic layers were composed of MO(7) or MO(8) polyhedra and PO(3)C tetrahedra. The interlayer region was occupied by carboxyalkyl chains. These layered compounds were easily dispersed as stable solutions in alkylamine/water upon ultrasonication. These dispersions were constituted of rectangular elongated nanoparticles (NPs), which showed a distribution of sizes ranging from 20-500 nm. These new materials had interesting photophysical properties because they were multiluminescent compounds. These properties gave rise to several emission bands, which were spread over the broad spectroscopic region, from the near-UV up to the near-IR regions. Each emission band had a specific lifetime, which ranged from the sub-ps to the ms scale.     

Diels-Alder reactions of 3-substituted coumarins in water and under high-pressure condition. An uncatalyzed route to tetrahydro-6H-benzo[c]chromen-6-ones

[reaction: see text] Diels-Alder reactions of 3-substituted coumarins 1a-g with methyl-1,3-butadienes 2a-c carried out in water alone and in CH2Cl2 under 9 kbar pressure are reported. In aqueous medium satisfactory results were obtained by operating at 150 degrees C, whereas under high pressure the cycloadditions were complete at 60-70 degrees C with excellent yields (85-95%). The reactions with isoprene (2b) always resulted in the exclusive formation of para cycloadducts, whereas with (E)-piperylene (2c) only ortho products were detected. The cycloaddition of 3-phenylsulfonylcoumarin (1a) with (E)-piperylene (2c) allowed the endo adduct to be obtained exclusively, whereas 3-carboxycoumarin (1b) reacted with 2c to give a mixture of the corresponding endo/exo adducts in a 58:42 ratio in water and in a 45:55 ratio under high-pressure condition.     

A theoretical study about the structural, electronic and spectroscopic properties of the ground and singlet excited states of curcuminoidic core

Curcumin, a well-known Indian spice, holds a variety of properties in many different fields from medicinal chemistry to dye industry. The peculiar electronic structure makes curcumin a valuable metal chelator. The principal aim of this work is a computational study of the structural and electronic properties of the ground and the first singlet excited states of the curcuminoidic core. Concerning the ground state, tautomeric equilibrium, vibrational and thermochemical analysis and electronic absorption spectra (with ab initio and semi-empirical methodologies) have been studied. A full geometry optimization of the first singlet excited states was obtained, with different computational methodologies. Solvent effects are also implicitly considered. An accurate comparison of the results is presented. Interesting aspects emerge, which suggest successive investigation about the nature of the excited states. The obtained results may be of large applicative interest. If curcuminoids are considered as potential ligands for complexes formation with metallic ions of pharmaceutical, medical–physical and technological interest, exciting the system with photons of appropriate frequencies, a photomodulated release of the metallic ion in the environment might be guessed, because of an important photoinduced geometrical modification.