Influence of substitution of oxygen by sulfur on maltol properties

Replacing oxygen by sulfur in a maltol molecule generates a family of new very interesting ligands: thiohydroxypyrones. In this work, theoretical calculations have been performed for all possible maltol derivatives created by consecutive substitutions of oxygen atoms by sulfur. The study is focused on molecular properties of thioligands, which are important for the formation of their metal complexes and potentially useful in medicinal and environmental chemistry. Energetic, tautomeric, aromatic, and charge distribution data are reported and the results are compared with maltol properties. It is shown that, similar to maltol, the most stable tautomer for all thio derivatives, is the one with the keto‐enol group. The protonation in cations occurs always on the heteroatom of the (thio)ketone group. The study has been carried out with the aid of some aromaticity indices, such as HOMA, NICS, and ASE. Aromaticity is studied in the heterocyclic pyran ring and in the XCCX part (where X – oxygen or sulfur). All calculations were performed at the B1LYP/6‐311++G(d,p) level of theory. We conclude that the aromaticity order determined previously for maltol (cation > neutral molecule > anion) is also preserved for thiohydroxopyrones. The results of the population analysis indicate that upon protonation, a large portion of additional positive charge delocalizes on the entire molecule, whereas upon deprotonation, negative charge accumulates mainly on the heteroatoms of the XCCX group. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis of Dynamical Responses for the MDF Wooden Material

The nonlinear analysis have been performed on the experimental data of a beam vibration composed of a wooden material MDF (Medium-Density Fiberboard). Firstly, the beam was subjected to the harmonic excitation on the clamp with its first eigenfrequency. After reaching the eigenfrequency, the excitation was switched of and the velocity amplitudes were measured. To identify the frequencies and the damping of vibrations, we applied nonlinear methods including Hilbert transform and wavelets. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Decay of mass for nonlinear equation with fractional Laplacian

The large time behavior of non-negative solutions to the reaction–diffusion equation ${\partial_t u=-(-\Delta)^{\alpha/2}u - u^p}$ , ${(\alpha\in(0,2], \;p > 1)}$ posed on ${\mathbb{R}^N}$ and supplemented with an integrable initial condition is studied. We show that the anomalous diffusion term determines the large time asymptotics for p > 1 + α/N, while nonlinear effects win if p ≤ 1 + α/N.     

Numerical study of ionic current in dielectric liquid layer subjected to ac voltage

Ionic current flowing in a thin layer of dielectric liquid under the action of ac voltage was studied numerically. Strongly blocking electrodes and equal mobilities of anions and cations were assumed. Field dependent dissociation and recombination were taken into account. The spatial distributions of ion concentrations and of electrical potential along coordinate normal to the layer and the ionic current density during a single voltage cycle were calculated as functions of time. At sufficiently low frequency and sufficiently high voltage, the ionic current was non-sinusoidal function of time. Significant contribution of higher harmonics were present. In certain frequency region this contribution gave rise to a bump of the current. The moment at which the bump occurred was not related with the value of ions mobility. These effects resulted from changes of spatial distribution of ions. In most cases the changes occurred simultaneously in the whole layer. In sufficiently thin layer, two gradually diffusing groups of ions wandering across the layer, one formed by cations and the other formed by anions, could be distinguished. Their appearance coincided with the maximum of the bump which was particularly high in such case. In thicker layers, similar groups of ions did not arise, although the current bumps were present.     

Ferrocenyl hetaryl thioketones: A computational study of their conformational stability

In this work, the conformational behavior of ferrocenyl- and hetaryl-functionalized thioketones was studied by means of computational quantum chemical methods. Four hetaryl substituents (furan-2-yl, thiophen-2-yl, selenophen-2-yl, and N-methylpyrrol-2-yl) were taken into account. The conformational space of the four ferrocenyl hetaryl thioketones was explored, and all found conformers were characterized using density functional (B3LYP) and wave function (SCS-MP2) theories. Their stability was explained in terms of intramolecular interactions. Such interactions were described using the methods of natural bond orbitals, “atoms in molecules,” noncovalent interaction index, and localized molecular orbital energy decomposition analysis. The identified conformations essentially differ in the arrangement of hetaryl heteroatom relative to the thiocarbonyl sulfur atom. The furan-2-yl substituent favors an s-trans-like arrangement of its heteroatom, while the remaining hetaryl substituents tend to adopt an s-cis-like arrangement. Such a conformational preference mainly results from the π → π* stabilization between the CS group and the hetaryl ring. Weak intramolecular hydrogen bonding of C H⋯O type was detected in the preferred conformer of ferrocenyl furan-2-yl thioketone. Low-polarity solvents, such as toluene, chloroform, and tetrahydrofuran, have a small effect on the preferred conformers of the four thioketones.     

Soft-phonon dynamics of the thermoelectric β-SnSe at high temperatures

Results of inelastic neutron scattering experiments on SnSe single crystals at high temperatures along with theoretical studies based on the density functional theory are reported. Our experiments reveal significant softening of the transverse acoustic branch along the $[0,\xi ,0]$ direction in the low-temperature α-SnSe of $Pbnm$ symmetry as temperature approaches $T_c=807$ K from below. This process is followed by a condensation of the zone-boundary Y-phonon of the high-temperature β-SnSe with $Cmcm$ symmetry at the onset of phase transition. The employed theoretical approach supports experimental observations and demonstrates that the phase change in SnSe is mediated by an unstable zone-boundary phonon with the $Y_2^{+}$ irreducible representation within the $Cmcm$ symmetry space group of the high-temperature β-SnSe. The present work provides a detailed understanding of the soft-mode dynamics in SnSe and conclusively shows that the $\alpha ?\beta$ structural transformation in this currently topical thermoelectric material is of displacive type.     

GQDs-MSNs nanocomposite nanoparticles for simultaneous intracellular drug delivery and fluorescent imaging

Although number of stimuli-responsive drug delivery systems based on mesoporous silica nanoparticles (MSNs) have been developed, the simultaneous real-time monitoring of carrier in order to guarantee proper drug targeting still remains as a challenge. GQDs-MSNs nanocomposite nanoparticles composed of graphene quantum dots (GQDs) and MSNs are proposed as efficient doxorubicin delivery and fluorescent imaging agent, allowing to monitor intracellular localization of a carrier and drug diffusion route from the carrier.Graphene quantum dots (average diameter 3.65?±?0.81 nm) as a fluorescent agent were chemically immobilized onto mesoporous silica nanoparticles (average diameter 44.08?±?7.18 nm) and loaded with doxorubicin. The structure, morphology, chemical composition, and optical properties as well as drug release behavior of doxorubicin (DOX)-loaded GQDs-MSNs were investigated. Then, the in vitro cytotoxicity, cellular uptake, and intracellular localization studies were carried out. Prepared GQDs-MSNs form stable suspensions exhibiting excitation-dependent photoluminescence (PL) behavior. These nanocomposite nanoparticles can be easily DOX-loaded and show pH- and temperature-dependent release behavior. Cytotoxicity studies proved that GQDs-MSNs nanocomposite nanoparticles are nontoxic; however, when loaded with drug, they enable the therapeutic activity of DOX via its active delivery and release. GQDs-MSNs owing to their fluorescent properties and efficient in vitro cellular internalization via caveolae/lipid raft-dependent endocytosis show a high potential for the optical imaging, including the simultaneous real-time optical tracking of the loaded drug during its delivery and release.

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Multiple solutions of asymmetric potential bistable energy harvesters: numerical simulation and experimental validation

In this paper, we investigate the multiple solutions of nonlinear asymmetric potential bistable energy harvesters (BEHs) under harmonic excitations. Basins of attraction under certain excitations explain the existence of multiple solutions in the asymmetric potential BEHs and indicate that the asymmetric system has a higher probability to oscillate in the deeper potential well under low and moderate excitation levels. Thus, the appearance of asymmetric potentials in BEHs has a negative influence on the output performance. Average output powers under different excitation frequencies and initial conditions illustrate that the asymmetric potential BEHs are more likely to achieve high-energy branch (HEB) with initial conditions in the shallower potential well, and the probability is influenced by the degree of asymmetry of the BEHs. Finally, experiments are carried out, and results under constant and sweep frequency excitations demonstrate that the output performance will be actually improved for the asymmetric potential BEHs if the initial oscillations are from the shallower potential well.     

Extension operators and twisted sums of c0 and C(K) spaces

We investigate the following problem posed by Cabello Sanchéz, Castillo, Kalton, and Yost:Let K be a nonmetrizable compact space. Does there exist a nontrivial twisted sum of $c_0$ and $C(K)$, i.e., does there exist a Banach space X containing a non-complemented copy Y of $c_0$ such that the quotient space $X/Y$ is isomorphic to $C(K)$?Using additional set-theoretic assumptions we give the first examples of compact spaces K providing a negative answer to this question. We show that under Martin's axiom and the negation of the continuum hypothesis, if either K is the Cantor cube $2^{{\omega }_1}$ or K is a separable scattered compact space of height 3 and weight ${\omega }_1$, then every twisted sum of $c_0$ and $C(K)$ is trivial.We also construct nontrivial twisted sums of $c_0$ and $C(K)$ for K belonging to several classes of compacta. Our main tool is an investigation of pairs of compact spaces $K?L$ which do not admit an extension operator $C(K)\to C(L)$.