Influence of β-substituents in aldol reactions of boron enolates of β-alkoxy methylketones

Moderate to good levels of substrate-based 1,5-syn-stereocontrol could be achieved in the boron-mediated aldol reactions of β-tert-butyl methylketones with achiral aldehydes, independent of the nature of the β-alkoxy protecting group (P = PMB or TBS). The analysis of the relative energies of the transition structures by theoretical calculations using the density functional B3LYP shows relative energies favoring the corresponding OUT-1,5-SYN transition structures, explaining the observed 1,5-syn stereoinduction.     

A Density Functional Theory Study of Poly (vinyl chloride) (PVC) Free Radical Polymerization

Summary: Quantum chemistry was applied to the free radical polymerization of Vinyl Chloride with the aim of elucidating the reaction kinetics and especially the formation of structural defects and low molecular weight polymer. The radical reactions were studied using the Density Functional Theory. All calculations were performed with B3LYP functionals and in particular the 6-31G(d,p) basis set was selected to evaluate the exchange and correlation energies. The computational method was first validated by predicting the rate constant of the propagation step and comparing the calculated values to experimental ones. Then intramolecular chain transfer, β-scission and branching reactions were also investigated, due to their direct connection with the production of defects in the growing chains. A comparison of the evaluated kinetic constants of such secondary reactions with other computational evaluations and experimental data was finally made.     

One- and two-photon absorption and emission properties of a Zn(II) chemosensor

This paper presents the synthesis and two photon-induced absorption (TPA) properties of a functionalized distyrylbenzene (DSB) 1 containing a tetra-azacyclododecane (cyclen) receptor for Zn(II). The influence of Zn(II) on one- and two-photon absorption characteristics of 1 has been investigated in dimethyl sulfoxide. The experiments show that the TPA action spectrum of uncomplexed 1, at 750 nm employing nanosecond-long excitation pulses, is 5 times more intense than that of the complexed form. This moderate contrast between the bound and unbound species confirms, however, the potential of this design scheme for the development of molecular structures with enhanced sensitivity and contrast to be used as Zn(II) sensors through TPA-induced fluorescence microscopy.     

ADMM for the SDP relaxation of the QAP

Semidefinite programming, SDP, relaxations have proven to be extremely strong for many hard discrete optimization problems. This is in particular true for the quadratic assignment problem, QAP, arguably one of the hardest NP-hard discrete optimization problems. There are several difficulties that arise in efficiently solving the SDP relaxation, e.g., increased dimension; inefficiency of the current primal–dual interior point solvers in terms of both time and accuracy; and difficulty and high expense in adding cutting plane constraints. We propose using the alternating direction method of multipliers ADMM in combination with facial reduction, FR, to solve the SDP relaxation. This first order approach allows for: inexpensive iterations, a method of cheaply obtaining low rank solutions; and a trivial way of exploiting the FR for adding cutting plane inequalities. In fact, we solve the doubly nonnegative, DNN, relaxation that includes both the SDP and all the nonnegativity constraints. When compared to current approaches and current best available bounds we obtain robustness, efficiency and improved bounds.     

Essential oils of Daucus carota subsp. carota of Tunisia obtained by supercritical carbon dioxide extraction

The essential oils and supercritical CO2 extracts of wild Daucus carota L. subsp. carota from two different sites in Tunisia were investigated. The main components of the essential oil of the flowering and mature umbels with seeds from Sejnane were eudesm-7(11)-en-4-ol (8.2 - 8.5%), carotol (3.5 - 5.2%), sabinene (12.0 -14.5%), a-selinene (7.4 - 8.6) and 11-alpha-(H)-himachal-4-en-1-beta-ol (12.7 - 17.4%), whereas the oils from Tunis were predominantly composed of elemicin (31.5 - 35.3%) and carotol (48.0 - 55.7%). The antimicrobial activity of the essential oils were assayed by using the broth dilution method on Escherichia coli ATCC 35218 and Staphylococcus aureus ATCC 43300, and clinical strains of Candida albicans and C. tropicalis 1011 RM. The MIC values obtained were all > 2.5% (v/v).     

New water-soluble platinum(II) phenanthroline complexes tested as cisplatin analogues: First-time comparison of cytotoxic activity between analogous four- and five-coordinate species

Four- and five-coordinate platinum(II) complexes, cis-[PtCl2(A2)] (1) and [PtCl2(A2)(eta2-ethylene)] (2) {A2 = 4,7-diphenyl-1,10-phenanthroline disulfonic acid disodium salt, BPS (mixture of isomers) (a); 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline disulfonic acid disodium salt, BCS (mixture of isomers) (b)} have been synthesized and characterized by 1H, 13C, and 195Pt NMR spectroscopy. The stability and high water solubility of complexes 1a, 1b and 2b, due to the presence of the polar SO3- groups on the ligands skeleton, allowed to test their in vitro cytotoxicity on HeLa tumour cells in a wide range of drug concentration. At low and medium incubation doses (<200 microM) 1a, 1b and 2b all showed similar in vitro cytotoxicity, negligible or much lower with respect to cisplatin. At doses higher than 200 microM their activity increased and 1b, the most active among the new complexes, exhibited a cytotoxicity comparable, although still lower, with respect to cisplatin. GFAAS Platinum analytical data showed that the tested compounds 1a, 1b and 2b, although carrying sulfonate charged groups, may undergo cellular uptake, which, in the case of 1b and 2b, is even higher with respect to cisplatin. Furthermore, in the case of 1b and 2b it has been possible to compare, for the first time, the cytotoxic activity for square-planar four-coordinate and trigonal-bipyramidal five-coordinate platinum(II) complexes having the same carrier ligand. The tendency of the five-coordinate species 2b to give at longer incubation time similar cytotoxicity with respect to the square-planar compound 1b suggests a possible use of the trigonal-bipyramidal five-coordinate complexes as prodrugs.     

Ferroelectricity of pyridinium perchlorate, a molecular level point of view

The behavior of ferroelectric and thermodynamic parameters of pyridinium perchlorate (PyClO(4)) was simulated based on experimental NMR data and properties of the individual constituting ions. Dynamic (2)H NMR spectroscopy was used to investigate the order-disorder character of ferroelectricity in PyClO(4). Quadrupole echo and inversion recovery experiments were performed in the range from 140 to 300 K. The spectra can be simulated by a rotational jump motion of the pyridinium cations about their pseudo-C(6) axis. This confirms that the ferroelectricity of this compound below a first-order phase transition at 248 K is primarily due to the ordering of cations along a ferroelectric axis. In an intermediate phase between 248 and 233 K, the cation-anion sublattice displacement mechanism also gives a small positive contribution to ferroelectricity. In the family of the ferroelectric pyridinium salts, the paraelectric-ferroelectric phase transition temperature increases with the size and polarizability of the constituting anions, suggesting that the main interaction for ferroelectric ordering occurs via an indirect superexchange mechanism, whereas in compounds with small anions of low polarizability the direct dipole-dipole interaction dominates and leads to antiferroelectric order.     

Local characterization of massless radiation from point sources

We show that the energy-momentum tensor for the massless fields generated by a multipolar source, confined to a world-line, can be split into a radiation and a bound part, both of them having zero divergence off the source world-line. This allows us to compute in a simple way the energy of radiation emitted by the source. Scalar, vector, and tensor fields are studied. An exact expression for the radiated energy of a spinning electron is exhibited. By analizing a system of two electrons we show that radiation from extended sources cannot be described locally in the manner mentioned above.     

Nonlinear vibration of a nonlocal functionally graded beam on fractional visco-Pasternak foundation

Nonlinear Dynamics - A (3+1)-dimensional coupled nonautonomous NLS model with partially nonlocal coupled nonlinearities under the linear and harmonic potentials becomes the center of attention. Two...     

Conformational and electronic properties of a microperoxidase in aqueous solution: a computational study.

A theoretical study of the conformational properties of a small heme peptide in aqueous solution is carried out by classical, long-timescale molecular dynamics simulations. The electronic properties of this species, that is, the relative energies of its excited electronic states and the redox potential, are reproduced and related to the conformational behavior using the perturbed matrix method and basic statistical mechanics. Our results show an interesting coupling between the conformational transitions and the electronic properties. These investigations, beyond the biophysically relevant results addressing the long-standing question of the actual role of the enzyme structure on the enzyme activity, are also of some methodological interest since they offer a further computational perspective for including the electronic degrees of freedom into the modeling of rather complex molecular systems.