Spontaneous and induced dynamic correlations in glass formers. II. Model calculations and comparison to numerical simulations

We study in detail the predictions of various theoretical approaches, in particular, mode-coupling theory (MCT) and kinetically constrained models (KCMs), concerning the time, temperature, and wave vector dependence of multipoint correlation functions that quantify the strength of both induced and spontaneous dynamical fluctuations. We also discuss the precise predictions of MCT concerning the statistical ensemble and microscopic dynamics dependence of these multipoint correlation functions. These predictions are compared to simulations of model fragile and strong glass-forming liquids. Overall, MCT fares quite well in the fragile case, in particular, explaining the observed crucial role of the statistical ensemble and microscopic dynamics, while MCT predictions do not seem to hold in the strong case. KCMs provide a simplified framework for understanding how these multipoint correlation functions may encode dynamic correlations in glassy materials. However, our analysis highlights important unresolved questions concerning the application of KCMs to supercooled liquids.     

Spontaneous and induced dynamic fluctuations in glass formers. I. General results and dependence on ensemble and dynamics

We study theoretically and numerically a family of multipoint dynamic susceptibilities that quantify the strength and characteristic length scales of dynamic heterogeneities in glass-forming materials. We use general theoretical arguments (fluctuation-dissipation relations and symmetries of relevant dynamical field theories) to relate the sensitivity of averaged two-time correlators to temperature and density to spontaneous fluctuations of the local dynamics. Our theoretical results are then compared to molecular dynamics simulations of the Newtonian, Brownian, and Monte Carlo dynamics of two representative glass-forming liquids, a fragile binary Lennard-Jones mixture, and a model for the strong glass-former silica. We justify in detail the claim made by Berthier et al. [Science 310, 1797 (2005)] that the temperature dependence of correlation functions allows one to extract useful information on dynamic length scales in glassy systems. We also discuss some subtle issues associated with the choice of microscopic dynamics and of statistical ensemble through conserved quantities, which are found to play an important role in determining dynamic correlations.     

Synthesis, structure and properties of {M4O4} cubanes containing nickel(II) and cobalt(II)

A survey of the crystal structures containing simple {M4O4} cubane units is reported. It shows that the average M-M distance in these complexes is relatively constant for a given metal ion M. The structures are all distorted from the idealised cube to a T(d) structure, and most show a further distortion which, however, usually maintains some elements of symmetry. A system for classifying the different types of ligand in these complexes is proposed. Two new cubanes of cobalt(II) and nickel(II) with the ligand (R,R)-bis-1,2-(1-methylbenzimidazol-2-yl)ethane-1,2-diol, (R,R)- or its enantiomer have been isolated and the crystal structure of the cobalt(II) complex confirms the cubane structure. Electronic, CD and (1)H NMR spectra and magnetic susceptibility data are reported. The magnetic data for these and other compounds in the literature are discussed in terms of the structural parameters.     

Improved Transversal Relaxivity for Highly Crystalline Nanoparticles of Pure γ‐Fe2O3 Phase

Pure and highly crystalline γ‐Fe₂O₃ nanocrystals (NCs) are obtained when hydrolysis and oxidation of a Fe^II organometallic precursor are performed in successive steps. Their synthesis in pure alkylamine leads to NCs of about 6 nm. In aqueous solutions of poly(vinyl)pyrrolidone, such pristine NCs form aggregates of about 150 nm that exhibit a high transversal relaxivity (r₂=466 mM ^?1 s^?1) about four times higher than that of a commercial Feridex magnetic resonance imaging (MRI) contrast agent. Consequently, they provide a significant decrease in the NMR signal at very short echo time (8 ms), which is of paramount importance in clinical practice because of the reduced duration of MRI measurements.     

Efficient mutation detection in MEN1 gene using a combination of single-strand conformation polymorphism (MDGA) and heteroduplex analysis

For facilitated genotypic analysis of multiple endocrine neoplasia type 1 (MEN1), a familial syndrome associated with tumors of the parathyroid and neuroendocrine tissues, we developed two screening methods, heteroduplex mutation assay (HMA) and mutation detection gel analysis (MDGA), both based on electrophoretic discrimination of polymerase chain reaction (PCR) products, to detect the mutations. Forty-three genomic DNA samples were used for the evaluation of these techniques. The whole coding region of MEN1 was PCR-amplified with fluorescent primers and then denatured/renatured before electrophoresis on an automated sequencer. 100% of the mutations were detected, subsequently confirmed and identified by sequencing. "Negative" samples were used to evaluate the specificity and reproducibility of the two techniques. The combination of the two methods allows high throughput cost-effective mutation screening which is less laborious than systematic sequencing of the whole coding region of MEN1. Together, these methods provide an efficient screen for MEN1 mutations.     

Synthesis of amorpha-4,11-diene from dihydroartemisinic acid

Amorphadiene is a natural product involved in the biosynthesis of the antimalarial drug artemisinin. A convenient four-step synthesis of amorphadiene, starting from commercially available dihydroartemisinic acid, is reported. The targeted molecule is isolated with an overall yield of 85% on a multi-gram scale in four steps with only one chromatography.     

Synthesis and characterization of new thiazolidinones containing coumarin moieties and their antibacterial and antioxidant activities

New coumarin derivatives, namely (2-(4-methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2-phenylthiazolidin-3-yl)acetamide, N-(2-(3-methoxyphenyl)-4-oxothiazolidin-3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide, 2-(4-methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2-(2,3,4trimethoxyphenyl)thiazolidin-3-yl)acetamide and N-(2-(4-bromophenyl)-4-oxothiazolidin-3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide) were synthesized starting from 4-methyl-7-hydroxycoumarin. The structures of the obtained compounds were confirmed by analytical IR and NMR spectra to elucidate the different positions of protons and carbons and as well as theoretical studies (DFT/B3LYP). The new compounds were screened for antibacterial activity. Most of them are more active against E. coli S. aureus and B. subtilis than standard references.     

Towards near-infrared photosensitisation: a photosensitising hydrophilic non-peripherally octasulfanyl-substituted Zn phthalocyanine

A Zn(II) phthalocyanine substituted with eight hydroxylated sulfanyl moieties in non-peripheral positions was designed to exhibit properties desired for photodynamic therapy: hydrophilicity, isomeric purity and near-infrared absorption in addition to high singlet oxygen generation. Photophysical and photochemical studies proved to be promising.     

Theoretical and photophysical study of photoisomerism of cyanine dyes: bisphenylaminopentamethine cyanine (BPPC)

The trans-cis photoisomerism of BPPC was investigated as part of a comprehensive, both theoretical and experimental, study on the photophysical and photochemical properties of cyanines having pentamethine cyanine as a common chromophore. In this work the determination of the trans → cis photoisomerization and thermal back isomerizatkm kinetics in alcohols was combined with CS INDO CI calculations of S₀ and S₁ potential energy curves for the paths leading to mono-cis isomers, where the dielectric solvent effects were taken into account by the simple virtual charge model. In agreement with the indications of a previous steady-state spectroscopy study, it was concluded that irradiation of BPPC into the visible absorption region gives rise to formation of the C(3)–C(4) cis planar isomer, already observed with the parent chromophore (BMPC), and an additional isomer, N(1)-C(2) cis, peculiar to BPPC. The role of the solute-solvent interactions is discussed with reference to the purely intramolecular model previously proposed for the cyanine photoisomerization.     

Acetaldehyde on Pt(111) and Pt/Sn(111): a DFT study of the adsorption structures and of the vibrational spectra

The relative stability of the eta1mu1 (atop) and eta2mu2 (di-sigma) geometries of acetaldehyde are compared on Pt(111) and on two PtSn alloys ((2 x 2) and (square root(3) x square root(3))R30 degrees) by means of density functional theory (DFT) calculations. At low coverage on Pt (1/9 ML), the two forms are equivalent in energy, with eta1mu1 being slightly more stable. At high coverage (1/4 and 1/3 ML), eta2mu2 is less competitive and acetaldehyde is adsorbed through the aldehydic hydrogen. The evolution of the adsorption energy with the coverage and the apparition of the structure adsorbed through the aldehydic hydrogen are explained by the existence of attractive dipole-dipole interactions. On PtSn, only the eta1mu1 geometry is stable with an adsorption energy equal to that on Pt, in agreement with temperature-programmed desorption (TPD) experiments. The calculated vibrational spectra allow us to conclude that the experimental spectrum corresponds to a mixture of eta1mu1 (majority) and eta2mu2 (minority) structures on Pt and to only eta1mu1 on PtSn. The various interactions and the relative stability of the species on Pt and PtSn are explained by the density of states (DOS) curves.