Guanidinium ion as a symmetrical template in the formation of cubic hydrogen-bonded borate networks with the boracite topology

Reaction between boric acid and guanidinium salts in methanolic solution at room temperature in the presence of various bases and anions gives well-formed solvated crystals of composition {[B(OCH3)4]3[C(NH2)3]4}+X-. The products in which X- = Cl- and PF6- are characterized by single-crystal X-ray diffraction. The tetramethoxyborate and guanidinium components form a highly symmetrical (cubic) hydrogen-bonded 3D network having the "boracite topology" [i.e., the (63)(6284) topology]. Highly disordered solvent molecules and anions occupy methyl-surfaced cavities and channels that represent more than 30% of the space.     

Co(NH3)6]3[Cu4(OH)(CO3)8].2H2O--a new carbonato-copper(II) anion stabilized by extensive hydrogen bonding

Addition of Co(NH3)6(3+) to aqueous solutions of Cu(II) in excess carbonate promotes the assembly of a new highly charged carbonato-copper(II) anion, [Cu4(OH)(CO3)8](9-), which contains an unusual mu4 hydroxo-bridged square Cu4 arrangement, stabilised in the crystal by no less than forty hydrogen bonds (< 3 Angstrom) to hexammine cations.     

Accuracy and efficiency of two numerical methods of solving the potential flow problem for highly nonlinear and dispersive water waves

The accuracy and efficiency of two methods of resolving the exact potential flow problem for nonlinear waves are compared using three different one horizontal dimension (1DH) test cases. The two model approaches use high‐order finite difference schemes in the horizontal dimension and differ in the resolution of the vertical dimension. The first model uses high‐order finite difference schemes also in the vertical, while the second model applies a spectral approach. The convergence, accuracy, and efficiency of the two models are demonstrated as a function of the temporal, horizontal, and vertical resolutions for the following: (1) the propagation of regular nonlinear waves in a periodic domain; (2) the motion of nonlinear standing waves in a domain with fully reflective boundaries; and (3) the propagation and shoaling of a train of waves on a slope. The spectral model approach converges more rapidly as a function of the vertical resolution. In addition, with equivalent vertical resolution, the spectral model approach shows enhanced accuracy and efficiency in the parameter range used for practical model applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Kinetics of n-butoxy and 2-pentoxy isomerization and detection of primary products by infrared cavity ringdown spectroscopy

The primary products of n-butoxy and 2-pentoxy isomerization in the presence and absence of O(2) have been detected using pulsed laser photolysis-cavity ringdown spectroscopy (PLP-CRDS). Alkoxy radicals n-butoxy and 2-pentoxy were generated by photolysis of alkyl nitrite precursors (n-butyl nitrite or 2-pentyl nitrite, respectively), and the isomerization products with and without O(2) were detected by infrared cavity ringdown spectroscopy 20 μs after the photolysis. We report the mid-IR OH stretch (ν(1)) absorption spectra for δ-HO-1-C(4)H(8)?, δ-HO-1-C(4)H(8)OO?, δ-HO-1-C(5)H(10)?, and δ-HO-1-C(5)H(10)OO?. The observed ν(1) bands are similar in position and shape to the related alcohols (n-butanol and 2-pentanol), although the HOROO? absorption is slightly stronger than the HOR? absorption. We determined the rate of isomerization relative to reaction with O(2) for the n-butoxy and 2-pentoxy radicals by measuring the relative ν(1) absorbance of HOROO? as a function of [O(2)]. At 295 K and 670 Torr of N(2) or N(2)/O(2), we found rate constant ratios of k(isom)/k(O(2)) = 1.7 (±0.1) × 10(19) cm(-3) for n-butoxy and k(isom)/k(O(2)) = 3.4(±0.4) × 10(19) cm(-3) for 2-pentoxy (2σ uncertainty). Using currently known rate constants k(O(2)), we estimate isomerization rates of k(isom) = 2.4 (±1.2) × 10(5) s(-1) and k(isom) ≈ 3 × 10(5) s(-1) for n-butoxy and 2-pentoxy radicals, respectively, where the uncertainties are primarily due to uncertainties in k(O(2)). Because isomerization is predicted to be in the high pressure limit at 670 Torr, these relative rates are expected to be the same at atmospheric pressure. Our results include corrections for prompt isomerization of hot nascent alkoxy radicals as well as reaction with background NO and unimolecular alkoxy decomposition. We estimate prompt isomerization yields under our conditions of 4 ± 2% and 5 ± 2% for n-butoxy and 2-pentoxy formed from photolysis of the alkyl nitrites at 351 nm. Our measured relative rate values are in good agreement with and more precise than previous end-product analysis studies conducted on the n-butoxy and 2-pentoxy systems. We show that reactions typically neglected in the analysis of alkoxy relative kinetics (decomposition, recombination with NO, and prompt isomerization) may need to be included to obtain accurate values of k(isom)/k(O(2)).     

Colloid dispersion in a uniform-aperture fracture

This research investigates the dispersion of colloids through fracture systems by exploring experimentally and numerically the transport and dispersion of 1.0-, 0.11-, and 0.043-mum diameter fluorescent carboxylate-modified microspheres and chloride at various flow rates through variable-length, synthetic Plexiglas fractures (flow cells). A dimensionless number describing each experiment is varied by changing the colloid size, flow rate, and fracture length. Surface characteristics of the microspheres and Plexiglas favor repulsive interactions, thereby minimizing the chance of colloid filtration and remobilization. Full recovery of the colloids is typically observed, thereby supporting the assumption of negligible colloid filtration. In comparison to chloride transport, there is increased tailing for colloid plumes traveling through the flow cell. This increased tailing is attributed to Taylor dispersion phenomena (dispersion due to an advection gradient). In the synthetic fractures investigated here, colloid dispersion due to the velocity gradient is evident, but fully developed Taylor conditions are not realized. A particle-tracking algorithm is run inversely to estimate the effective dispersion rate for the colloid plume in each experiment as a function of the experimental parameters (flow rate, fracture length, and colloid size). Results suggest that the log of the effective dispersion rate of the colloid plume increases linearly with the log of the dimensionless number comprising experimental parameters.     

Novel Tetraspiroorthocarbonates as Successful Anti-shrinking Agents for the Photopolymerization of Epoxy Monomers

A pair of novel tetrafunctional spiroorthocarbonates (TETRASOC) was prepared in three stages. First, glycerol was reacted with tetraethyl orthocarbonate to form a pair of isomeric hemi spiroorthocarbonates (HEMI SOC-OLs) by monocyclization of glycerol. Formation of these two isomers depends on terminal or adjacent hydroxyl groups of glycerol reacting with the tetraethylorthocarbonate to form five and six-membered ring HEMI SOC-OLs. Second, the HEMI SOC-OLs were made to undergo another cyclization reaction by reacting with 1,3-propanediol, to form a pair of spiroorthocarbonates with one hydroxyl group (SOC-OL). In the third stage, the SOC-OL was used as nucleophylic reactant to displace the bromine atom of pentaerythritol bromide to form the final product TETRASOC. A volume change study was carried out to determine the efficiency of TETRASOC as an anti-shrinking additive finding that even at a low concentration of 7 mol%, it caused a 2.18% expansion of the polymeric volume of a bis epoxycyclohexane monomer (3,4-EP). Dynamic Mechanical Analysis (DMA) determined that the flexibilization induced by the TETRASOC in the polyether derived from 3,4-EP did not adversely impact the mechanical properties of the polymer.     

Liquid extraction surface analysis mass spectrometry (LESA-MS) as a novel profiling tool for drug distribution and metabolism analysis: the terfenadine example

Liquid extraction surface analysis mass spectrometry (LESA-MS) is a novel surface profiling technique that combines micro-liquid extraction from a solid surface with nano-electrospray mass spectrometry. One potential application is the examination of the distribution of drugs and their metabolites by analyzing ex vivo tissue sections, an area where quantitative whole body autoradiography (QWBA) is traditionally employed. However, QWBA relies on the use of radiolabeled drugs and is limited to total radioactivity measured whereas LESA-MS can provide drug- and metabolite-specific distribution information. Here, we evaluate LESA-MS, examining the distribution and biotransformation of unlabeled terfenadine in mice and compare our findings to QWBA, whole tissue LC/MS/MS and MALDI-MSI. The spatial resolution of LESA-MS can be optimized to ca. 1 mm on tissues such as brain, liver and kidney, also enabling drug profiling within a single organ. LESA-MS can readily identify the biotransformation of terfenadine to its major, active metabolite fexofenadine. Relative quantification can confirm the rapid absorption of terfendine after oral dosage, its extensive first pass metabolism and the distribution of both compounds into systemic tissues such as muscle, spleen and kidney. The elimination appears to be consistent with biliary excretion and only trace levels of fexofenadine could be confirmed in brain. We found LESA-MS to be more informative in terms of drug distribution than a comparable MALDI-MS imaging study, likely due to its favorable overall sensitivity due to the larger surface area sampled. LESA-MS appears to be a useful new profiling tool for examining the distribution of drugs and their metabolites in tissue sections.     

Empirical Balanced Truncation of Nonlinear Systems

Novel constructions of empirical controllability and observability gramians for nonlinear systems are proposed for subsequent use in a balanced truncation style of model reduction. The new gramians are based on a generalisation of the fundamental solution for a Linear Time-Varying system. Relationships between the given gramians for nonlinear systems and the standard gramians for both Linear Time-Invariant and Linear Time-Varying systems are established as well as relationships to prior constructions proposed for empirical gramians. Application of the new gramians is illustrated through a sample test-system.     

Electrochemical electron transfer and its relation to charge transport in single molecule junctions

Ability to control charge transport at nanometer scale lies in the heart of design of fast reliable electronic devices. Molecular electronics thrive to use functional molecules for such transport. If the molecule contains redox center(s), a diode-like or transistor-like behavior can be easily explored by controlling not only the voltage difference between two metallic contacts of the molecular junction but also the potential of one of the contacting electrodes with respect to some reference. Thus, one needs to understand the relationship between electrochemical electron transfer and charge transport in metal–molecule–metal junctions. This review presents latest theoretical approaches toward understanding of such relationship and discusses pivotal experimental works to validate them. Tunneling and hopping pathways may operate in parallel (two-channel model), but experimental conditions dictate the channel preference.     

Thermodynamic modeling of mineralogical phases formed by continuous casting powders

A great amount of mineralogical phases were predicted and represented in stability phase diagrams, which were obtained by the use of the thermodynamic software FACTSage considering both the chemical composition and the melting temperature of the mould flux. Melting-solidification tests on commercial mould flux glasses for thin slab casting of steel revealed the existence of cuspidine (Ca₄Si₂O₇F₂) as the main mineralogical phase formed during the flux solidification by X-ray powder diffraction (XRD). This phase directly influences the heat transfer phenomena from the strand to the mould and it is obtained with higher fluorite content (22% CaF₂). Cuspidine is desirable only in fluxes to produce medium carbon (included peritectic grade) steels, because it reduces the heat flux from the strand to the mould, thus controlling the shrinkage rate during the flux solidification. The experimental results are in agreement with those obtained by the thermodynamic software. The stability phase diagrams could be used as an important tool in the flux design for continuous casting process.