Dark field microscopy for diffraction analysis of amorphous carbon solids

Diffraction methods for determining structure in non-crystalline materials often rely solely on the determination of pair correlation functions, extracted from measurements of the diffracted intensity. A dark field image of a non-crystalline solid taken with a conventional transmission electron microscope contains phase information lost in the measurement of the diffracted intensity which can be accessed by evaluating a variance function. This variance function is defined in terms of spherical averages of the diffracted intensity and the mean square of the diffracted intensity. The latter contains higher order correlation information derived from correlations between two pairs of atoms. We examine the sensitivity of the variance function, to subtle atomic structural differences between carbon network structures. The structures have similar pair correlations, but different levels of diamond like bonding. The variance function is shown to give improved discrimination between the networks.     

Study of Cadmium Extraction with Aliquat 336 from Highly Saline Solutions

A large number of model solutions with high ionic strength were synthesised to mimic industrial conditions and were used as a first approach to study Cd extraction in the presence of chloride at high salinity, as experienced in real industrial solutions. The extractant used throughout in this work was Aliquat 336, a quaternary ammonium salt well known to the hydrometallurgical industry. The effects of some selected anions in addition to chloride (i.e., perchlorate, nitrate, and sulfate) were studied. The distribution of cadmium was measured using ¹⁰⁹Cd as a tracer. Liquid-scintillation spectroscopy quantified the concentration of ¹⁰⁹Cd in both phases. Raman and NMR spectroscopy were employed to gain further insight into the extraction chemistry. A careful analysis of all Cd extraction data showed that within specific windows of the reactant concentrations the chemical reactions could be represented by simplified equations, as discussed thoroughly in the text. Equilibrium constants for the extraction of \({\text{CdCl}}_{3}^{ - }\) from chloride and chloride/sulfate media were determined to be log₁₀K_ext?=?4.9?±?0.8 and log₁₀K_ext?=?5.7?±?0.5, respectively. For the nitrate environment, an exchange reaction involving a LiNO₃ ion pair is proposed and agrees with the experimental data, but was not proven. ¹⁴N-NMR and Raman spectroscopy confirmed that the relative affinity of Aliquat 336 for the relevant anions followed the order: perchlorate?>?nitrate?>?chloride?>?sulfate. Finally, ¹⁴N-NMR enabled the equilibrium constant of the exchange reaction between nitrate and chloride for Aliquat 336 to be determined.     

Studies directed to understanding the structure of chitosan-metal complexes: investigations of mono- and disaccharide models with platinum(II) group metals

X-ray and NMR experiments were performed with simple chitosan models based on glucosamine monosaccharides and disaccharides to understand the binding properties and structures of the complexes formed between this polysaccharide and platinum(II) metals. Subjection of the glucosamine derivatives with [PdCl2(PhCN)2] provided trans-diamine complexes which upon further treatment with excess (NH4)PF6 generated complexes possessing two 5-membered chelate rings involving the C2-amine and the C3-hydroxyl group of the two individual glucosamine units.     

Counting Dyck Paths by Area and Rank

The set of Dyck paths of length 2n inherits a lattice structure from a bijection with the set of noncrossing partitions with the usual partial order. In this paper, we study the joint distribution of two statistics for Dyck paths: area (the area under the path) and rank (the rank in the lattice). While area for Dyck paths has been studied, pairing it with this rank function seems new, and we get an interesting (q, t)-refinement of the Catalan numbers. We present two decompositions of the corresponding generating function: One refines an identity of Carlitz and Riordan; the other refines the notion of γ-nonnegativity, and is based on a decomposition of the lattice of noncrossing partitions due to Simion and Ullman. Further, Biane’s correspondence and a result of Stump allow us to conclude that the joint distribution of area and rank for Dyck paths equals the joint distribution of length and reflection length for the permutations lying below the n-cycle (12· · ·n) in the absolute order on the symmetric group.     

Clocking the melting transition of charge and lattice order in 1T-TaS2 with ultrafast extreme-ultraviolet angle-resolved photoemission spectroscopy

We use time- and angle-resolved photoemission spectroscopy with sub-30-fs extreme-ultraviolet pulses to map the time- and momentum-dependent electronic structure of photoexcited 1T-TaS(2). This compound is a two-dimensional Mott insulator with charge-density wave ordering. Charge order, evidenced by splitting between occupied subbands at the Brillouin zone boundary, melts well before the lattice responds. This challenges the view of a charge-density wave caused by electron-phonon coupling and Fermi-surface nesting alone, and suggests that electronic correlations play a key role in driving charge order.     

New synthetic route to substituted dihydroazulene photoswitches

A new procedure for functionalization of the dihydroazulene photoswitch on its seven-membered ring was developed, which has allowed isolation of the first dihydroazulene with a phenyl substituent at position 5 from a mixture of regioisomers. Light-induced ring-opening to the corresponding vinylheptafulvene and the thermal back-reaction was studied in detail.     

Synthesis of 1,4-naphthoquinone methides via acid-catalyzed cascade cyclizations of benzannulated enediynyl alcohols

Treatment of benzannulated enediynyl alcohols with trifluoroacetic acid at room temperature promoted a cascade sequence of cyclization reactions, leading to 1,4-naphthoquinone methides. The transformation involved an unusual two-carbon ring expansion from the cyclic alcohols and the construction of the p-quinone methide ring from an acyclic system along the reaction pathway.     

Photon Counting Histogram Analysis for Two‐Dimensional Systems

Photon counting statistics in 3D photon counting histogram analysis for one‐photon excitation is a function of the number of molecules of particular brightness in the excitation‐detection volume of a confocal microscope. In mathematical form that volume is approximated by a three‐dimensional Gaussian function which is embedded in the PCH theoretical equations. PCH theory assumes that a molecule can be found anywhere inside the excitation‐detection volume with equal probability. However, one can easily imagine systems in which this assumption is violated because molecules are constrained by the geometry of the sample. For example, molecules on a surface or in a membrane would be constrained to two dimensions. To enable the analysis of such systems by PCH, the theoretical framework requires modification. Herein, we present an extension of the PCH analysis to systems where molecules exist in thin structures that are effectively two‐dimensional. The method, aptly called two‐dimensional photon counting histogram (2D PCH), recovers the number of fluorescent particles per unit area and their molecular brightness. Both theoretical background and experimental results are presented. The theory was tested using computer‐simulated and experimental 2D PCHs obtained from confocal experiments. We demonstrate that this modification of the theoretical framework provides a tool to extract data that reveal states of aggregation, surface photophysics, and reactivity.