Chemical Adaptability: The Integration of Different Kinds of Matter into Giant Molecular Metal Oxides

Unique properties of the two giant wheel‐shaped molybdenum‐oxides of the type {Mo₁₅₄}≡[{Mo₂}{Mo₈}{Mo₁}]₁₄ ( 1 ) and {Mo₁₇₆}≡[{Mo₂}{Mo₈}{Mo₁}]₁₆ ( 2 ) that have the same building blocks either 14 or 16 times, respectively, are considered and show a “chemical adaptability” as a new phenomenon regarding the integration of a large number of appropriate cations and anions, for example, in form of the large “salt‐like” {M(SO₄)}₁₆ rings (M=K⁺, NH₄⁺), while the two resulting {Mo₁₄₆ (K(SO₄))₁₆} ( 3 ) and {Mo₁₄₆ (NH₄(SO₄))₁₆} ( 4 ) type hybrid compounds have the same shape as the parent ring structures. The chemical adaptability, which also allows the integration of anions and cations even at the same positions in the {Mo₄O₆}‐type units of 1 and 2 , is caused by easy changes in constitution by reorganisation and simultaneous release of (some) building blocks (one example: two opposite orientations of the same functional groups, that is, of H₂O{Mo?O} ( I ) and O?{Mo(H₂O)} ( II ) are possible). Whereas Cu²⁺ in [(H₄Cu^II₅)Mo^V₂₈Mo^VI₁₁₄O₄₃₂(H₂O)₅₈]^26? ( 5 a ) is simply coordinated to two parent O^2? ions of {Mo₄O₆} and to two fragments of type II , the SO₄^2? integration in 3 and 4 occurs through the substitution of two oxo ligands of {Mo₄O₆} as well as two H₂O ligands of fragment I . Complexes 3 and now 4 were characterised by different physical methods, for example, solutions of 4 in DMSO with sophisticated NMR spectroscopy (EXSY, DOSY and HSQC). The NH₄⁺ ions integrated in the cluster anion of 4 “communicate” with those in solution in the sense that the related H⁺ ion exchange is in equilibrium. The important message: the reported “chemical adaptability” has its formal counterpart in solutions of “molybdates”, which can form unique dynamic libraries containing constituents/building blocks that may form and break reversibly and can lead to the isolation of a variety of giant clusters with unusual properties.     

A simple empirical model of polyester fibre materials for acoustical applications

A new empirical model has been developed by the authors to predict the flow resistivity, acoustic impedance and sound absorption coefficient of polyester fibre materials. The parameters of the model have been adjusted to best fit the values of airflow resistivity and sound absorption coefficient measured over a set of 38 samples. Calculated results are compared with normal incidence measurements carried out using two different techniques: the transfer-function method in an impedance tube (ISO 10534-2) and the free-field impulse response method (ISO 13472-1). Measurements performed on polyester fibre materials with different density and thickness values, and diameter ranging from 18 to 48 μm, are in good agreement with the predictions of the new model. It is concluded that the new model can predict the basic acoustic properties of common polyester fibre materials with any practical combination of thickness and density².     

Total synthesis of bioactive drimane–epoxyquinol hybrid natural products: macrophorin A, 4′-oxomacrophorin A,and 1′-epi-craterellin A

Total synthesis of novel hybrid natural products, merosesquiterpenoids macrophorin A, 4′-oxomacrophorin A, and 1′-epi-craterellin A has been accomplished following a general strategy based on a sacrificial Diels–Alder–retroDiels–Alder approach to control regio- and stereoselectivity.     

Water Repellency in Hydrophobic Nanocapsules—Molecular View on Dewetting

The hydrophobic effect plays a major role in a variety of important phenomena in chemistry, materials science and biology, for instance in protein folding and protein–ligand interactions. Studies—performed within cavities of the unique metal oxide based porous capsules of the type {(pentagon)₁₂(linker)₃₀}≡{(W)W₅}₁₂{Mo₂(ligand)}₃₀ with different acetate/water ligand ratios—have provided unprecedented results revealing segregation/repellency of the encapsulated “water” from the internal hydrophobic ligand walls of the capsules, while the disordered water molecules, interacting strongly with each other via hydrogen bonding, form in all investigated cases the same type of spherical shell. The present results can be (formally) compared—but only regarding the repellency effect—with the amazing “action” of the (super)hydrophobic Lotus (Nelumbo) leaves, which are self‐cleaning based on water repellency resulting in the formation of water droplets picking up dirt. The present results were obtained by constructing deliberately suitable hydrophobic interiors within the mentioned capsules.     

Stabilization of Paraffin Emulsions Used in the Manufacture of Chipboard Panels by Liquid Crystalline Phases

Paraffin emulsions are commonly used in the manufacture of chipboard panels to provide resistance to water and humidity. The quality and performance of chipboards are improved with the use of paraffin emulsions stabilized by mixed surfactant systems, although little is known about the basic colloidal chemistry of such systems and their implications in the manufacturing and processing of the chipboard panels. In the present work, the stability and the phase behavior of paraffin emulsions stabilized by a mixture of anionic and nonionic surfactants, are described. Stability is studied by applying thermal and ultracentrifugation cycles, and also by rheology (steady state and dynamic determinations). A significant increase of stability is observed at high {anionic surfactant/(anionic surfactant+nonionic surfactant)} ratios. Phase behavior studies have demonstrated the presence of hexagonal liquid crystalline structures at high ionic surfactant/nonionic surfactant ratios and the presence of lamellar structures at low ratios. The stability of emulsions could be related to phase behavior, and, thus, providing a qualitative tool to predict stability.     

AlCl(3) x 6H(2)O/KI/H(2)O/CH(3)CN: a new alternate system for dehydration of oximes and amides in hydrated media

Dehydration of oximes and amides to nitriles was carried out using the AlCl(3) x 6H(2)O/KI/H(2)O/CH(3)CN system. It produced isoquinoline derivatives 8a-c (Bischler Naperialski reaction) when reacted with amides 7a-c in hydrated media. Also, the keto oximes produced anilides (Beckmann rearrangement) with the system under the same reaction conditions.     

KF/Al2O3 mediated 1,3-dipolar cycloaddition of azomethine ylides: a novel and convenient procedure for the synthesis of highly substituted pyrrolidines

The regio- and diastereoselective synthesis of pyrrolidine derivatives through 1,3-dipolar cycloaddition of an azomethine ylide and dipolarophile mediated by KF/Al₂O₃, a versatile solid supported reagent, is reported. KF/Al₂O₃ is sufficiently basic such that it can deprotonate α-imino esters to generate azomethine ylides and it also functions as a solid supported catalyst leading to the cycloadduct rather than the Michael adduct.     

A comparison of methods to compute the "effective duration" of the autocorrelation function and an alternative proposal

The "effective duration" of the autocorrelation function (ACF), τ(e), is an important factor in architectural and musical acoustics. For a general application, an accurate evaluation of τ(e) is relevant. This paper is focused to the methods for the extraction of τ(e) values from the ACF. Various methods have been proposed in literature for the extraction of the τ(e) from a given signal, but these methods are not unambiguously defined or may not work properly in case of particular signals. Therefore, the general use of these methods may sometimes give rise to questionable results. In the present work, the methods existing in literature for extracting τ(e) are analyzed, their advantages and drawbacks are summarized, and finally an alternative method is proposed. The proposed algorithm is compared to those found in previous literature, applying them on the same sound signals (classic literature references and other ones publicly available on the Internet). It is shown that the results obtained with the proposed method are consistent with the results of the previous literature; moreover the proposed method may overcome some of the limitations of the existing methods.     

A comparison of noise models in a hybrid reference spectrum and principal components analysis algorithm for Raman spectroscopy

Raman spectroscopy exploits the Raman scattering effect to analyze chemical compounds with the use of laser light. Raman spectra are most commonly analyzed using the ordinary least squares (LS) method. However, LS is known to be sensitive to variability in the spectra of the analyte and background materials. In a previous paper, we addressed this problem by proposing a novel algorithm that models expected variations in the analyte as well as background signals. The method was called the hybrid LS and principal component analysis (HLP) algorithm and used an unweighted Gaussian distribution to model the noise in the measured spectra. In this paper, we show that the noise in fact follows a Poisson distribution and improve the noise model of our hybrid algorithm accordingly. We also approximate the Poisson noise model by a weighted Gaussian noise model, which enables the use of a more efficient solver algorithm. To reflect the generalization of the noise model, we from hereon call the method the hybrid reference spectrum and principal components analysis (HRP) algorithm. We compare the performance of LS and HRP with the unweighted Gaussian (HRP‐G), Poisson (HRP‐P), and weighted Gaussian (HRP‐WG) noise models. Our experiments use both simulated data and experimental data acquired from a serial dilution of Raman‐enhanced gold‐silica nanoparticles placed on an excised pig colon. When the only signal variability was zero‐mean random noise (as examined using simulated data), HRP‐P consistently outperformed HRP‐G and HRP‐WG, with the latter coming in as a close second. Note that in this scenario, LS and HRP‐G were equivalent. In the presence of random noise as well as variations in the mean component spectra, the three HRP algorithms significantly outperformed LS, but performed similarly among themselves. This indicates that, in the presence of significant variations in the mean component spectra, modeling such variations is more important than optimizing the noise model. It also suggests that for real data, HRP‐WG provides a desirable trade‐off between noise model accuracy and computational speed. Copyright © 2013 John Wiley & Sons, Ltd.     

Higher-order saddle potentials,nonlinear curl forces,trapping and dynamics

Nonlinear Dynamics - The position-dependent non-conservative forces are called curl forces introduced recently by Berry and Shukla (J Phys A 45:305201, 2012). The aim of this paper is to study...