Hydrogen-bonded liquid crystals derived from supramolecular complexes of pyridylated poly(propyleneimine) dendrimers and a cholesterol-based carboxylic acid

Diaminobutane poly(propyleneimine) dendrimers of second to fifth generations were functionalized by the introduction of pyridyl moieties at their primary amino groups through their interaction with 3-pyridyl isothiocyanate. These pyridylated diaminobutane poly (propyleneimine) dendrimers were subsequently mixed with 3-cholesteryloxycarbonylpropanoic acid to form the corresponding hydrogen-bonded supramolecular complexes. The materials obtained exhibit smectic A phases over a relatively broad temperature range from about 60°C to 140°C. Within the smectic layer the cholesteryl moieties are almost orthogonal above and below to the dendrimeric portion of the molecule. On cooling, the materials form liquid crystalline glasses which retain the structural characteristics of the smectic A phase.     

Growth format, electronic architecture, magnetic, and optical properties of aromatic cyclo-Cu3Au3 homotops

Bimetallic Cu(3)Au(3) clusters have been investigated using electronic structure calculation techniques (DFT) to understand their electronic, magnetic, and optical properties as well as the geometrical structures. The most stable homotop is the planar cyclo-[Cu(3)(micro-Au)(3)] form consisting of a triangular positively charged Cu(3) structural core with negatively charged Au atoms occupying exposed positions. This structure is characterized by the maximum number of heterobonds and peripheral positions of Au atoms. Possible growth formats of the cyclo-[Cu(3)(micro-Au)(3)] homotops have been explored following both the edge-capping and the stepwise metal atom substitution mechanism. The bonding pattern along with the density of states (DOS) plots of the cyclo-[Cu(3)(micro-Au)(3)] homotop are thoroughly analyzed and compared with those of the pure cyclo-[Cu(3)(micro-Cu)(3)] and cyclo-[Au(3)(micro-Au)(3)] clusters. Particular attention was paid on the stability of these bimetallic clusters in relation with the ring-shaped electron density distribution (aromaticity). It was found that all 3-membered metal rings exhibit significant aromatic character, which was verified by a number of established criteria of aromaticity, such as structural, energetic, magnetic (NICS profiles), and out-of-plane ring deformability criteria. The NICS (1) values correlate well with the out-of-plane ring deformation energy. Finally, a comprehensive analysis of the optical spectra of the CuAu, Cu(2), and Au(2) diatomics and the cyclo-[Cu(3)(micro-Au)(3)], cyclo-[Cu(3)(micro-Cu)(3)], and cyclo-[Au(3)(micro-Au)(3)] clusters placed the electronic assignments of the optical transitions on a firm footing.     

Modeling of contaminant transport resulting from dissolution of nonaqueous phase liquid pools in saturated porous media

A mathematical model for transient contaminant transport resulting from the dissolution of a single component nonaqueous phase liquid (NAPL) pool in two-dimensional, saturated, homogeneous porous media was developed. An analytical solution was derived for a semi-infinite medium under local equilibrium conditions accounting for solvent decay. The solution was obtained by taking Laplace transforms to the equations with respect to time and Fourier transforms with respect to the longitudinal spatial coordinate. The analytical solution is given in terms of a single integral which is easily determined by numerical integration techniques. The model is applicable to both denser and lighter than water NAPL pools. The model successfully simulated responses of a 1,1,2-trichloroethane (TCA) pool at the bottom of a two-dimensional porous medium under controlled laboratory conditions.Notation a,a ₁ defined in (45a) and (45b), respectively - b defined in (45c) - b vector of true model parameters (n×1) - vector of estimated model parameters (n×1) - c liquid phase solute concentration (solute mass/liquid volume), M/L³ - c _s aqueous saturation concentration (solubility), M/L³ - C dimensionless liquid phase solute concentration, equal toc/c _s - molecular diffusion coefficient, L²/t - ^e effective molecular diffusion coefficient, equal to / ^*, L²/t - D _x longitudinal hydrodynamic dispersion coefficient, L²/t - D _z hydrodynamic dispersion coefficient in the vertical direction, L²/t - e random vector with zero mean (m×1) - erf[x] error function, equal to (2/ ^1/2) - f vector of fitting errors or residuals (m×1) - Fourier operator - _-1 Fourier inverse operator - g vector of model simulated data (m×1) - k mass transfer coefficient, L/t - average mass transfer coefficient, L/t - K _d partition or distribution coefficient (liquid volume/solids mass), L³/M - pool length, L - _o distance between the pool and the origin of the specified Cartesian coordinate system, L - Laplace operator - _-1 Laplace inverse operator - m number of observations - M Laplace/Fourier function defined in (38) - n number of model parameters - N Laplace/Fourier function defined in (39) - p defined in (46) - Pe _x Péclet number, equal toU _x /D _x - Pe _z Péclet number, equal toU _x /D _z - q defined in (47) - R retardation factor - s Laplace transform variable - S objective function - Sh local Sherwood number, equal tok/ _e - Sh _o overall Sherwood number, equal to l/ _e - t time,t - T dimensionless time, equal toU _x t/ - u dummy integration variable - u vector of independent variables - U _x average interstitial velocity, L/t - x spatial coordinate in the longitudinal direction, L - X dimensionless longitudinal length, equal to (x–)/ - y vector of observed data (m×1) - z spatial coordinate in the vertical direction, L - Z dimensionless vertical length, equal toz/ - Fourier transform variable - defined in (37) - defined in (50) - porosity (liquid volume/aquifer volume), L³/L³ - defined in (52a) and (52b), respectively - decay coefficient, t^–1 - dimensionless decay coefficient, equal to /U _x - bulk density of the solid matrix (solids mass/aquifer volume), M/L³ - dummy integration variable - ^* tortuosity     

A novel NMR method for the determination and monitoring of evolution of hydrogen peroxide in aqueous solutions

A novel NMR method that allowed the rapid and direct quantitative analysis of hydrogen peroxide in protic solvents was developed. The method was based on the highly deshielded ¹H NMR signal of the H₂O₂ protons (δ?～?11.15 ppm at 298 K) in H₂O and the combined use of cryoprotective (antifreeze) mixtures of H₂O?DMSO-d₆, low temperatures (～260 K), and pH effects in order to achieve minimum proton exchange rate and, thus, sharp ¹H line widths. Extremely broad resonances with line widths above 550 Hz at room temperature in H₂O were observed in a wide range of pH values, which were reduced below 2 Hz with the use of the above method which resulted in a detection limit of 20.0 μmol L^?1 (in tube) even when using very short total experimental time of 10 min. The method was applied in aqueous extract of Greek oregano and in aqueous instant coffee. Line widths below 10 Hz for oregano samples and 17 Hz for instant coffee samples were obtained which resulted (i) in the unequivocal assignment of H₂O₂ with spiking experiments precluding any confusion with interferences from intrinsic phenolics in the extracts and (ii) in the quantitative investigation of the evolution of H₂O₂ in real time with parameters easily accessible experimentally.

Traces of self-organisation and long-range memory in variations of environmental radon in soil: comparative results from monitoring in Lesvos Island and Ileia (Greece)

This paper addresses issues of self-affinity, long-memory and self-organisation in variations of radon in soil recorded in Lesvos Island, Greece. Several techniques were employed, namely (a) power-law wavelet spectral fractal analysis, (b) estimation of Hurst exponents through (b1) rescaled-range, (b2) roughness-length, (b3) variogram and (a), (c) detrended fluctuation analysis, (d) investigation of fractal dimensions and (e) analysis of five block entropies: (e1) Shannon entropy, (e2) Shannon entropy per letter, (e3) conditional entropy, (e4) Tsallis entropy, and (e5) normalised Tsallis entropy. Long-lasting antipersistency was identified during a period of anomalous radon variations following fractional Brownian modelling. Remaining variations did not exhibit analogous behaviour and followed fractional Gaussian modelling. Antipersistent power-law-beta-exponent-values between 1.5 and 2.0 were detected during anomalies. Persistent values were also found. Hurst exponents were mainly within 0 < H < 0.5. Some persistent exponents (0.5 < H < 1) were also observed. Fractal dimensions were within 1.5 < D < 2. Radon anomalies presented lower fractal dimensions. Shannon entropy ranged between 0.77 ≤ H(n) ≤ 2.38, Shannon entropy per letter, between 0.19 ≤ h ⁽ⁿ⁾ ≤ 0.59, conditional entropy, between 0.01 ≤ h _(n) ≤ 0.58, Tsallis entropy, between 0.55 ≤ S _q  ≤ 1.01 and normalised Tsallis entropy between, 0.98 ≤  $\hat{S}$  ≤ 5.42 (block-size n = 4). Entropies were lower during anomalies, indicating strong self-organisation. Persistency–antipersistency switching was observed, consistent with long-memory dynamics. Potential geological sources were discussed. The asperity-model was proposed. Findings were compared to results obtained under analogous methodologies in Ileia, Greece.     

Liquid chromatography coupled to on-line post column derivatization for the determination of organic compounds: A review on instrumentation and chemistries

Analytical derivatization either in pre or post column modes is one of the most widely used sample pretreatment techniques coupled to liquid chromatography. In the present review article we selected to discuss the post column derivatization mode for the analysis of organic compounds. The first part of the review focuses to the instrumentation of post-column setups including not only fundamental components such as pumps and reactors but also less common parts such as static mixers and back-pressure regulators; the second part of the article discusses the most popular “chemistries” that are involved in post column applications, including reagent-less approaches and new sensing platforms such as the popular gold nanoparticles. Some representative recent applications are also presented as tables.     

Hydrosilylation, hydrocyanation, and hydroamination of ethene catalyzed by bis(hydrido-bridged)diplatinum complexes: Added insight and predictions from theory

Details on the reaction mechanism of the catalytic cycle of hydrosilylation, hydrocyanation and hydroamination of ethene catalyzed by bis(hydrido-bridged)diplatinum complexes were obtained with the aid of DFT by calculating the relevant intermediates and transition state structures. The catalytically “active” species identified are the 16e coordinatively unsaturated mononuclear [Pt(X)(H)(PH₃)(η²-C₂H₄)] (X = SiH₃, CN, NH₂) species formed upon addition of the ethene molecule on the monomeric [Pt(X)(H)(PH₃)] precursors. All crucial reaction steps encapsulated in the entire catalyzed courses have been scrutinized. The following three steps are found to be critical for these catalytic reactions: (i) the migration of the hydride to the acceptor C atom of the coordinated ethene substrate, (ii) the reductive elimination of the final product and (iii) the oxidative addition process that regenerates the catalyst with activation barriers of 13.1, 16.5 and 13.3 kcal/mol for hydrosilylation, 7.1, 31.0 and 2.8 kcal/mol for hydrocyanation and 11.7, 39.7 and 39.0 kcal/mol for hydroamination reactions. In all cases the rate-determining step is that of the reductive elimination of the final product having always the highest activation barrier. The overall catalytic processes are exergonic with the calculated exergonicities being −13.5 (−8.0), −16.1 (−10.4) and −38.8 (−46.7) kcal/mol for the hydrosilylation, hydrocyanation and hydroamination of ethene, respectively, at the B3LYP (CCSD(T)) levels of theory. According to energetic span of the cycle called δE, which determines the frequency of the catalytic cycle, we found that the catalytic efficiency of the hydrido-bridged diplatinum complexes follows the trend: hydrocyanation ≈ hydrosilylation > hydroamination.     

Acoustically Enhanced Ganglia Dissolution and Mobilization in a Monolayer of Glass Beads

A pore network consisting of a monolayer of glass beads was constructed for experimental investigation of the effects of acoustic waves on the dissolution and mobilization of perchloroethylene (PCE) ganglia. Dissolution experiments were conducted with acoustic wave frequencies ranging from 75 to 225 Hz at a constant pressure amplitude of 3.68 kPa applied to the inlet of the monolayer. Ganglia mobilization experiments were conducted with a constant acoustic wave frequency of 125 Hz and acoustic pressure amplitudes ranging from 0 to 39.07 kPa. Effluent dissolved PCE concentrations were observed to increase in the presence of acoustic waves with the greatest increase (over 300%) occurring at the lowest frequency employed (75 Hz). Acoustic waves were also observed to mobilize otherwise immobile PCE ganglia, break them apart, and further enhance dissolution.     

Equation-Free multiscale computational analysis of individual-based epidemic dynamics on networks

The surveillance, analysis and ultimately the efficient long-term prediction and control of epidemic dynamics appear to be some of the major challenges nowadays. Detailed individual-based mathematical models on complex networks play an important role towards this aim. In this work, it is shown how one can exploit the Equation-Free approach and optimization methods such as Simulated Annealing to bridge detailed individual-based epidemic models with coarse-grained, system-level analysis within a pair-wise representation perspective. The proposed computational methodology provides a systematic approach for analyzing the parametric behavior of complex/multiscale epidemic simulators much more efficiently than simply simulating forward in time. It is shown how steady state and (if required) time-dependent computations, stability computations, as well as continuation and numerical bifurcation analysis can be performed in a straightforward manner. The approach is illustrated through a simple individual-based SIRS epidemic model deploying on a random regular connected graph. Using the individual-based simulator as a black box coarse-grained timestepper and with the aid of Simulated Annealing I compute the coarse-grained equilibrium bifurcation diagram and analyze the stability of the stationary states sidestepping the necessity of obtaining explicit closures at the macroscopic level.