Application of artificial neural networks for gradient elution retention modelling in ion chromatography

Gradient elution in ion chromatography (IC) offers several advantages: total analysis time can be significantly reduced, overall resolution of a mixture can be increased, peak shape can be improved (less tailing) and effective sensitivity can be increased (because there is little variation in peak shape). More importantly, it provides the maximum resolution per time unit. The aim of this work was the development of a suitable artificial neural network (ANN) gradient elution retention model that can be used in a variety of applications for method development and retention modelling of inorganic anions in IC. Multilayer perceptron ANNs were used to model the retention behaviour of fluoride, chloride, nitrite, sulphate, bromide, nitrate and phosphate in relation to the starting time of gradient elution and the slope of the linear gradient elution curve. The advantage of the developed model is the application of an optimized two-phase training algorithm that enables the researcher to make use of the advantages of first- and second-order training algorithms in one training procedure. This results in better predictive ability, with less time required for the calculations. The number of hidden layer neurons and experimental data points used for the training set were optimized in terms of obtaining a precise and accurate retention model with respect to minimization of unnecessary experimentation and time needed for the calculation procedures. This study shows that developed, ANNs are the method of first choice for retention modelling of inorganic anions in IC.     

Atomistic Simulation Study of Cu0.327Ni0.673 Alloys: from Solid Solution to Phase Segregation

We present a combined Monte‐Carlo/molecular dynamics study of a Cu_0.327Ni_0.673 alloy system. On the basis of nearest‐neighbor coordination number analyses atomic clustering and phase segregation is explored. Along this line, free energy profiles are calculated and separated into entropic and energetic contributions. The competition of both terms was found in accordance to the experimental phase diagrams (phase separation of the solid solution below about 600 Kelvin). Two independent simulation runs were performed. At 1000 Kelvin the observed configurations correspond to solid solutions exhibiting a weak tendency to cluster atoms of identical species. At room temperature the energetic favoring of atomic separation is clearly dominant and leads to the formation of Ni‐rich and Cu‐rich domains. The latter are separated by interfacial regions whose width ranges from 0.5 to 1 nanometers.     

Extraction of aroma compounds in a HFMC: Dynamic modelling and simulation

In the present work the dynamic behaviour of hollow-fiber membrane contactors (HFMCs) used for the recovery of aroma compounds from an aqueous feed phase with the help of a conventional solvent has been studied. Many aroma compounds play a significant role in the production of flavorants, which are used in the food industry to flavor, improve and increase the appeal of their products. Various aroma compounds with different physico-chemical characteristics have been chosen for this study. A real dynamic model of membrane-based solvent extraction (MBSE) process was developed. In the studied system, the aqueous feed and solvent phases are re-circulated to their respective storage tanks after contacting in a hollow fibres membrane contactor. The developed dynamic model was verified with experimental data from the literature and good level of agreement was found. It has been used as a tool to simulate and conclude about the influence of various module configurations, membrane characteristics and hydrodynamic conditions on the extraction of various aroma compounds. It was noted that transient models of membrane-based separation need attention to improve the simulation studies and experimental validity to encourage it at larger scales.     

Application of retention modelling to the simulation of separation of organic anions in suppressed ion chromatography

The ion-exchange separation of organic anions of varying molecular mass has been demonstrated using ion chromatography with isocratic, gradient and multi-step eluent profiles on commercially available columns with UV detection. A retention model derived previously for inorganic ions and based solely on electrostatic interactions between the analytes and the stationary phase was applied. This model was found to accurately describe the observed elution of all the anions under isocratic, gradient and multi-step eluent conditions. Hydrophobic interactions, although likely to be present to varying degrees, did not limit the applicability of the ion-exchange retention model. Various instrumental configurations were investigated to overcome problems associated with the use of organic modifiers in the eluent which caused compatibility issues with the electrolytically derived, and subsequently suppressed, eluent. The preferred configuration allowed the organic modifier stream to bypass the eluent generator, followed by subsequent mixing before entering the injection valve and column. Accurate elution prediction was achieved even when using 5-step eluent profiles with errors in retention time generally being less than 1% relative standard deviation (RSD) and all being less than 5% RSD. Peak widths for linear gradient separations were also modelled and showed good agreement with experimentally determined values.     

Time-Gel

Can creation of matter be modelled? This communication proposes the idea of Time-Gel to address this question. Using existing framework of temporal dynamics of gelation, crystallization, criticality, time-crystal, and the idea of space-time symmetry breaking, with appropriate approximations, it is proposed Time-Gel concept can be used to this end.     

La-Mn-Ni-O催化剂组成、结构、还原性能及氧化活性

用硝酸盐分解法合成了LaMn_(1-x)Ni_xO_3(0≤2≤1.0), 研究了组成、晶体结构及其与还原性能、CO和CH_3OH催化氧化活性的关系。XRD证实在0.0≤x≤1.0范围内, 本体系都生成单一钙钛矿结构: 0.0≤x≤0.4, 0.8相似文献   

LaS1.9, CeS1.9, PrS1.9, NdS1.9 und GdS1.9: Fünf neue Lanthanoidpolysulfide – Synthese und Kristallstrukturen und ihre Strukturbeziehung zum ZrSSi‐Typ

LaS_1.9, CeS_1.9, PrS_1.9, NdS_1.9, and GdS_1.9: Five new Lanthanide Polysulfides – Syntheses, Crystal Structures and their Structural Relationship to the ZrSSi Type Crystals of the five new lanthanide polysulfides LaS_1.9, CeS_1.9, PrS_1.9, NdS_1.9, and GdS_1.9 have been prepared by different synthetic routes. According to X‐ray structure analyses, the compounds adopt the tetragonal CeSe_1.9 type structure (space group: P4₂/n, no. 86) with the lattice parameters a = 9.111(1) Å, c = 16.336(2) Å (LaS_1.9), a = 9.015(3) Å, c = 16.168(4) Å (CeS_1.9), a = 8.947(3) Å, c = 16.054(4) Å (PrS_1.9), a = 8.901(3) Å, c = 16.022(4) Å (NdS_1.9), and a = 8.714(1) Å, c = 15.791(1) Å (GdS_1.9), respectively. The crystal structure consists of puckered [LnS] double slabs and planar sulfur layers alternating along [001]. Each planar sulfur layer contains disulfide dumbbells, isolated anions and ordered vacancies.     

Crystallographic Studies of Cesium Tetrafluorobromates(III)

This article describes CsBr₂F₇ (1) which has been obtained in the form of colorless single crystals. Shown by the X-ray diffraction on single crystals its Br₂F₇⁻ anion is neither planar nor is its Br−μ-F−Br unit linear, as previously deduced from Raman spectra. Also a regular tetrafluorobromate CsBrF₄ (2) has been obtained in the form of a colorless powder. Compound 2 can also be obtained from compound 1 by evacuation. The crystal structure of CsBrF₄ (2) has been elucidated by the Rietveld refinement on its X-ray powder pattern.     

Acid-base chemistry of red wine: analytical multi-technique characterisation and equilibrium-based chemical modelling

In this paper an attempt is made to model the alkalimetric titration trend (pH<7) of a series of red wines on the basis of an equilibrium-based calculation involving as input the chemical equilibria of the acid-base active substances, whose analytical concentration was determined in each wine under consideration. The chemical model (14 acid-base active substances and 22 protonation equilibria were considered) has been built in reliable conditions with respect to the chemical environment of the fluids under study, in order to describe the acid-base properties at a thermodynamic level using specific professional software. In this connection, protonation constant values of the substances involved were necessary, paying attention to: solvent composition, background salt, ionic strength and temperature. A series of synthetic solutions (based on mixed ethanol/water solvents at known ionic strength) was then pH-metrically titrated (25 °C) in order to refine suitable protonation constant values.Analytical measurements of carboxylic acids, amino acids, inorganic anions and metals were executed to know the concentration of a series of acid-base active reactants (pH<7) and the ionic strength state of each wine. Finally, a comparison between the experimental trend of the alkalimetric titration of each wine and the calculated one via the chemical model tested by means of a computer-assisted simulation has been performed. As an overall check of our job, the charge balance principle was adopted. During the alkalimetric titrations of each wine conductometric detection was performed as well, with the aim of confirming the values of ionic strength calculated using both analytical and equilibrium concentrations. The agreement we found when comparing the calculated values of ionic strength with varying pH with the trend of the conductometric signal can be considered as a significant validation of the chemical model proposed. The jump from the analytical to the equilibrium composition may allow the prediction of the effect on red wines consequent to chemical actions (addition of substances) or natural phenomena.     

Crystallographic and conformational analysis of two novel trans-azo benzene compounds

The molecular and crystal structure of (E)-2-Acetyl-4-(2-bromophenyldiazenyl)phenol (1) and (E)-2-Methyl-4-(o-tolyldiazenyl)phenol (2) were characterized and determined by single crystal X-ray diffraction method besides spectroscopic means. The periodic organization of 1 is stabilized by C–H···O type weak H-bond and Br···O type weak halogen bonding and thus, a two dimensional puckered network is established almost parallel to () the plane. Molecules of 2 are linked into C(7) chains generated by translation along the [1 0 1] direction with the aid of O–H···N type H-bonds, and these chains are strengthened by C–H···π interactions involving o-tolylphenol ring. Quantum chemical studies at B3LYP/6-311 ++G(d,p) level reveal that potential barrier of the compounds around Ar–N torsions is of double minimum character unless it is defected by the presence of o-substituent groups in the vicinity of the azo bridge. The results from crystallographic and quantum chemical studies suggest that azo benzene compounds may adapt non-planar geometry apart from the most stable planar conformation, which is located on the secondary minima of double potential barrier regarding rotational motion around Ar–N bonds.     

Coordination Chemistry of the Magic Inorganic Building Block {Fe<Superscript>II</Superscript>[Mo<Subscript>6</Subscript>P<Subscript>4</Subscript>O<Subscript>31</Subscript>]<Subscript>2</Subscript>}: Hydrothermal Synthesis and Crystal Structure of a New Reduced Ferrous Molybdophosphate

A new reduced ferrous molybdophosphate composite solid of the formula, [(C₁₀H₁₄N₂)H]₄[Fe^II ₁₀Mo^V ₂₄(H₂PO₄)₄(HPO₄)₁₂(PO₄)₄(H₂O)₁₆(OH)₁₆O₄₄]·12H₂O, has been synthesized from a reaction mixture of MoO₃, FeSO₄·7H₂O, C₂H₂O₄·2H₂O, nicotine, H₃PO₄, and H₂O under hydrothermal conditions. The crystal data: monoclinic, space group C2/m, a = 24.4349(124), b = 12.9935(66), c = 14.7281(74) Å, β = 104.87(1) Å, V = 4520(4) Å³, Z = 2, R ₁  = 0.0874, wR ₂  = 0.2179. The structure is built from the building blocks of the formula, {Fe^II[Mo₆P₄O₃₁]₂}, consisting of a network of MO₆ (M = Fe, Mo) octahedral and PO₄ tetrahedral linked through their vertices. The connectivity of the building blocks with two pairs of face-sharing dinuclear Fe(II) clusters of the formula of [Fe^II ₂(H₂O)₄O₅] on which a phosphate group is hanging gives rise to one-dimensional chains with eight-membered apertures. The remarkable hydrogen bonded interactions between the chains form a unique and interesting framework with three-dimensional intersecting tunnels where the protonated nicotine molecules as structuring templates and crystallization water molecules are situated.     

Computer modelling: Future directions

Summary Recent developments in computing and in the theory of simulation have extended greatly the successes of the modelling of ionic crystals pioneered by Mott and Littleton. This has changed the way in which computer experiments are brought to bear on an increasing range of solid-state phenomena. Yet applied science creates new demands, both in the form of new types of system and in terms of the complexity and subtlety of what is studied. The author's brief survey looks at some of the successes and gaps from interfaces and catalysts to neurotransmitters and from superconductors to slags.     

全同立构聚丙烯晶体结构的对称性研究

本文利用对称理论,研究了全同立构聚丙烯的α(型)晶及β(型)晶的可能的晶体结构.1.推导了与C2/c空间群有关的有色空间群,研究了聚丙烯分子链在它们中的排布,得出其中5种是聚丙烯α(型)晶晶体结构可能存在的空间群;2.从晶畴理论出发,得出具有Cc空间群与P2_(1/c)空间群的两种晶畴共存于一个体系中,3.聚丙烯β(型)晶的晶体结构的可能排列方式是聚丙烯分子链按R型晶胞的半无规排列。     

Two pillared-layer architectures constructed from copper molybdate sheets and linear organonitrogen ligands

In this article, we report the syntheses and structures of two new inorganic–organic hybrid copper molybdates with organonitrogen ligands, [Cu₂(bpe)(Mo₂O₈)]?·?3H₂O (1) (bpe?=?1,2-bis(4-pyridyl)ethene) and [{Cu(4,4′-bpy)}₂(Mo₂O₈)] (2) (bpy?=?4,4′-bipyridine). Elemental analyses, IR spectra, EPR spectra, XPS spectra, TG analyses and single crystal X-ray diffraction were used to characterize these compounds. The structure of 1 exhibits a pillared-layer framework built up from unusual bimetallic two-dimensional sheets pillared by linear bpe ligands. Compound 2 features a pillared-layer structure constructed from copper molybdate 4,8-net sheets connected by 4,4′-bpy ligands.     

Internet resources in GPCR modelling1

G-Protein coupled receptors (GPCRs), one of the most important families of drug targets, belong to the super family of integral membrane proteins characterized by seven transmembrane helices. Because they are difficult to crystallize, the three dimensional structure of these receptors have not yet been determined by X-ray crystallography, except one. In the absence of a 3-D structure, in-silico approaches for solving the structure of this class of proteins are widely used and provide valuable information for structure based drug design. There are several web servers and computer programs available that automate the modelling process of GPCRs. Some of these include Modeller, Swiss-Model server, Homer, etc. Using these tools reliable homology models of human histamine H1 receptor (HRH1) and thrombin receptor (PAR-1) have been generated which explain the binding mode of the standard antagonists of these receptors and may be useful in designing their novel antagonists.     

Computer-aided molecular modelling: Research study or research tool?

Summary Developments in computational methods and equipment have produced a new type of research chemist, who prefers to calculate properties as well as measure them, either to gain a better understanding of microscopic molecular behaviour per se, or to guide a broader scientific study using a so-called rational approach. While there is good reason to believe that significant results can be obtained this way, it is clear that only some of the tools of the trade are sufficiently robust to present to those who are not experts in the field.This paper discusses the underlying basis for molecular modelling techniques, describing their history, state of maturity and prospects for future development. The intention is to outline the scope that these play in an industrial research environment, and to examine how they can successfully be incorporated as routine research tools.Computer-based molecular modelling is not a unique discipline. Some comparisons are drawn between it and other computer-based techniques that have reached a greater degree of maturity, in order to highlight the points made.