bluuebunny/crossref_metadata_2025_split huggingface dataset:
Capillary Electrochromatography
Authors: Zhang Kai , Gao Ruyu 
Published: November 2015

Abstract

Capillary electrochromatography (
CEC
) is a hybrid microseparation technique that combines the high selectivity of high‐performance liquid chromatography (
HPLC
) and the high efficiency of capillary electrophoresis (
CE
).
CEC
holds unique advantages such as high separation power, high selectivity, high sensitivity, short analysis time, low consumption of samples and chemicals, and good compatibility with mass spectrometry (
MS
). Accordingly, it has attracted extensive attentions over the past decades. Recent progresses in
CEC
, especially the development of
CEC
stationary phases, such as fused silica‐packed columns, open tubular coating columns, monolithic columns, and molecular imprinted polymer columns, as well as the application of CEC in chiral separation and peptide/protein analysis, are summarized in this chapter.
High‐Performance Thin‐Layer Chromatography
Authors: Cebolla Vicente L. , Membrado Luis , Jarne Carmen , Garriga Rosa 
Published: November 2015

AbstractThe instrumental modularity of its basic steps, that is, sample application, chromatographic development, and detection, confersHPTLCa high degree of flexibility. Automated and computer‐controlled instruments with different levels of sophistication for each of these steps have been developed, for example, spray‐on sample applicators and chambers including the possibility of gradient separation. Detection techniques such as scanning densitometers, electronic documentation systems, bioactivity detection methodologies, and online coupling with mass spectrometry have come to be easily and firmly established in laboratories. Particularly, the introduction of an elution‐basedTLC–MSinterface has not only allowed original and efficient hyphenated systems to be designed but also opened the possibility of expanding the connection with other detectors. Thanks to this instrumental development,HPTLChas become a reliable, accurate, and sensitive analytical technique.
Preparative Chromatography: Batch and Continuous
Authors: Aniceto José P.S. , Silva Carlos M. 
Published: November 2015

AbstractChromatography, although initially prevalent in the analytical field, is increasingly extended as a preparative process for the commercial scale production of several chemicals whose separation from feed streams is difficult to achieve by conventional methods. In this chapter, the most relevant and recent preparative chromatography approaches are presented and discussed, divided in terms of batch and continuous processes. The fundamental conservation equations, kinetic laws, and equilibrium relations governing chromatographic systems are presented in detail as they are common to all processes modeling. Several models and approaches are presented in an order of higher approximation to reality that necessarily results in an increasing degree of mathematical sophistication. This complexity trend is linked to the sequential introduction of the various phenomena that take place inside the adsorption bed. In particular, the influence of finite mass transfer resistances and axial dispersion upon the dynamic behavior of the chromatographic system is highlighted. With regard to batch chromatography, the most frequent techniques, such as preparativeHPLCand supercritical fluid chromatography are covered, along with key chromatography concepts. Closed loop recycling chromatography and steady‐state recycling chromatography are recycling techniques that may be situated between batch and continuous strategies, being able to enhance the performance of batch systems while avoiding the higher complexity inherent to continuous approaches. Regarding continuous chromatography, the development of the simulated moving bed (SMB) technology has allowed improved productivity, product's purities, and lower operating costs compared to batch processing. Since its inception, several different strategies and modifications to the conventionalSMBhave been proposed. The well‐established and the most innovativeSMBoperation modes, such as intermittent‐SMB, supercriticalSMB, and variable external streams systems, are presented and discussed, along with the necessary equipment designs that allow their implementation. Other continuous chromatographic processes include the high‐speed countercurrent chromatography and the centrifugal partition chromatography, both involving two immiscible liquid phases, and annular chromatography that permits continuous operation while using a stationary phase. Some brief remarks are made on equipment and system designs.
Dispersive Solid‐Phase Extraction
Authors: Socas‐Rodríguez Bárbara , Herrera‐Herrera Antonio V. , Asensio‐Ramos María , Hernández‐Borges Javier 
Published: November 2015

AbstractDispersive solid‐phase extraction (dSPE) is a sorbent‐based technique widely applied in sample preparation for both sample clean up or analite preconcentration. It shows considerable benefits over conventionalSPE, especially in terms of the simplicity of the procedure. This chapter aims at providing a general overview ofdSPE, its different extraction approaches (dSPE, µ‐dSPEand magnetic‐dSPE), and the principal factors which influence the extraction process (including the sorbents most frequently used) as well as its most common applications.
Analytical Supercritical Fluid Extraction
Authors: Martínez Julian , de Aguiar Ana Carolina 
Published: November 2015

AbstractThe principles of analytical supercritical fluid extraction (SFE) are discussed. Specific sections include supercritical fluids, SFE, and supercritical fluid fractionation, instrumentation for SFE for a basic extraction system, comparison between SFE and conventional techniques, and applications of analytical SFE. The chapter concludes with a discussion on the present scenario and prospects for SFE as an analytical technique.
Extraction Methods Facilitated by the use of Magnetic Nanoparticles
Authors: Rocío‐Bautista Priscilla , Pino Verónica 
Published: November 2015

Abstract

Magnetic nanoparticles (MNPs) are a group of nanoparticles (NPs) that present superparamagnetic properties. MNPs are composed of a magnetic solid phase that is responsible for the magnetic properties. The characterization of MNPs is usually accomplished using techniques such as X‐ray diffraction (XRD), transmission electron microscopy (TEM), or scanning electron microscopy (SEM). Several review articles have been recently devoted to MNPs in analytical chemistry and particularly to sample preparation. This chapter presents extraction methods facilitated by the use of MNPs, with particular emphasis on MNP types and extraction applications. The relatively simple tuneability of MNPs, by easily anchoring task‐specific sorbents of quite different nature (silica based, carbon and derivatives based, polymeric based, and so on), opens a number of possible combinations and enormously extends its future applications
Sample Derivatization in Separation Science
Authors: Cardinael Pascal , Casabianca Hervé , Peulon‐Agasse Valerie , Berthod Alain 
Published: November 2015

Abstract

Chromatographic methods have made so much progress that they are today the method of choice in analytical laboratories. Not all molecules can be separated by the desired method. Derivatization reactions are simple chemical modification of the sample that will render it compatible with the selected separation method. Gas chromatography (
GC
) can separate volatile and thermostable compounds. The possible derivatization reactions that will enhance both volatility and thermal resistance of the solutes are summarized and the protocols are outlined.
Liquid chromatography
(
LC
) can separate solutes soluble in the mobile phase. The main problem is to detect them. Derivatization reactions in
LC
will modify the solutes adding a chomophore for easy
UV
detection or a fluorophore for sensitive fluorescent detection. Different protocols including pre‐ or postcolumn reactions are described. Capillary electrophoresis (
CE
) separates solutes by difference in electrophoretic mobility. Derivatization reactions in
CE
are similar to derivatization in
LC
when detection is the problem. On‐column and postcolumn derivatizations are common in
CE
. Derivatization to change the solute electrophoretic mobility can also be performed.
Validation of Analytical Methods Based on Chromatographic Techniques: An Overview
Authors: Peris‐Vicente Juan , Esteve‐Romero Josep , Carda‐Broch Samuel 
Published: November 2015

AbstractMethod validation is an important requirement in the analysis by liquid (HPLC) or gas (GC) chromatography. However, some analytical chemists seem unaware about its importance. They show serious doubt about the main aspects of validation: need, when it must be performed, its relationship with the development of the method and the correct procedure. Although a large number of indications and advices about validation can be found in the literature, they refer to specific methods, and are often underutilized. Several analysts consider that the validation must be mandatorily performed by a collaborative trial between several laboratories, and they are not willing to carry it out. A wide range of guidelines describing the parameters and indicating directives about the achievement of validation have also been issued. The understanding of the analysts about the process of method validation is inhibited because the terminology and methodology of the validation parameters depend on the scope and the guideline. The validation is applied with a specific objective, through a defined protocol, for the determination of a specific analyte inside an explicit working range. The validation should usually verify that the method effectively provides reliable results when applied to the predefined scope and using the established operating conditions. The scope of the analysis, a description of the analytical requirements needed to achieve the objectives of the analysis, must be clearly defined before starting the validation to select the adequate guideline and correctly conduct the validation process.This chapter describes the concept of method validation, referred to the analysis of organic compounds in liquid and gas chromatography. The need to establish the performances and the limits of a method and to evaluate its suitability for a specific purpose is revised. The increasing interest from researchers and regulatory agencies on validation during the past few years has been discussed by surveying the articles published and guidelines issued on this topic. Several approaches to correctly accomplish the validation have been detailed. Furthermore, the validation parameters, which should be evaluated, will be methodically described, and a thorough comparison between the main validation guides is provided.
Chiral Liquid Chromatography: Recent Applications with Special Emphasis on the Enantioseparation of Amino Compounds
Authors: Ilisz István 
Published: November 2015

AbstractThe biological and chemical properties determined by the molecular asymmetry play an especially important role in nature. If a racemic compound comes in contact with a chirally selective living system, the effects of the enantiomers may be different, resulting in different biological consequences, division, metabolism, excretion, and so on. Accordingly, a demand has arisen in pharmaceutical and other therapeutic fundamental research for the analytical qualification and quantification of chiral products. High‐performance liquid chromatography (HPLC) on chiral stationary phases is an effective analytical tool for the resolution of chiral compounds on both analytical and preparative scales. This chapter summarizes the directHPLCseparations applying different types of chiral stationary phases; however, indirect methods are also briefly discussed.
Tooth wear and feeding ecology in mountain gorillas from Volcanoes National Park, Rwanda
Authors: Galbany Jordi , Imanizabayo Olive , Romero Alejandro , Vecellio Veronica , Glowacka Halszka , Cranfield Michael R. , Bromage Timothy G. , Mudakikwa Antoine , Stoinski Tara S. , McFarlin Shannon C. 
Published: November 2015

ABSTRACTObjectivesEcological factors have a dramatic effect on tooth wear in primates, although it remains unclear how individual age contributes to functional crown morphology. The aim of this study is to determine how age and individual diet are related to tooth wear in wild mountain gorillas (Gorilla beringei beringei) from Volcanoes National Park, Rwanda.Material and MethodsWe calculated the percent of dentine exposure (PDE) for all permanent molars (M1–M3) of known‐age mountain gorillas (N = 23), to test whether PDE varied with age using regression analysis. For each molar position, we also performed stepwise multiple linear regression to test the effects of age and percentage of time spent feeding on different food categories on PDE, for individuals subject to long‐term observational studies by the Dian Fossey Gorilla Fund International's Karisoke Research Center.ResultsPDE increased significantly with age for both sexes in all molars. Moreover, a significant effect of gritty plant root consumption on PDE was found among individuals. Our results support prior reports indicating reduced tooth wear in mountain gorillas compared to western gorillas, and compared to other known‐aged samples of primate taxa from forest and savanna habitats.DiscussionOur findings corroborate that mountain gorillas present very low molar wear, and support the hypothesis that age and the consumption of particular food types, namely roots, are significant determinants of tooth wear variation in mountain gorillas. Future research should characterize the mineral composition of the soil in the Virunga habitat, to test the hypothesis that the physical and abrasive properties of gritty foods such as roots influence intra‐ and interspecific patterns of tooth wear. Am J Phys Anthropol 159:457–465, 2016. © 2015 Wiley Periodicals, Inc.
QM/MM‐Simulationen ergeben synergetische Substrat‐ und Sauerstoffaktivierung in Salicylat‐Dioxygenase
Authors: Roy Subhendu , Kästner Johannes 
Published: November 2015

AbstractSalicylat‐1,2‐Dioxygenase (SDO) ist das erste bekannte Enzym, das die oxidative Spaltung eines einfach hydroxylierten Aromaten, Salicylat, statt der wohlbekannten elektronenreichen Substrate katalysiert. Wir haben den Mechanismus der Sauerstoffaktivierung in SDO mit QM/MM‐Simulationen untersucht. Unsere Ergebnisse zeigen, dass das Nicht‐Häm‐FeII‐Zentrum in SDO Salicylat und O2 gemeinsam durch eine starke kovalente Wechselwirkung aktiviert, um die reduktive Spaltung von O2 zu ermöglichen. Die reaktive Sauerstoffspezies ist ein kovalenter Salicylat‐FeII‐O2‐Komplex, wobei die Elektronenstruktur zwischen den beiden Grenzfällen FeII‐O2 und FeII‐O2.− mit partiellem Elektronentransfer vom aktivierten Salicylat zu O2 über das Fe‐Zentrum liegt. Folglich verwendet SDO eine synergetische Strategie der Substrat‐ und Sauerstoffaktivierung, um die katalytische Reaktion auszuführen, die einmalig in der Familie der Eisendioxygenasen ist. Darüber hinaus erfolgt die O2‐Aktivierung in SDO ohne die Hilfe einer Protonenquelle. Unsere Studie zeigt eine bisher unbekannte Möglichkeit für den Mechanismus der O2‐Aktivierung.
Capture of CO2 by a Cationic Nickel(I) Complex in the Gas Phase and Characterization of the Bound, Activated CO2 Molecule by Cryogenic Ion Vibrational Predissociation Spectroscopy
Authors: Menges Fabian S. , Craig Stephanie M. , Tötsch Niklas , Bloomfield Aaron , Ghosh Subrata , Krüger Hans‐Jörg , Johnson Mark A. 
Published: November 2015

AbstractWe describe a systematic method for the preparation and spectroscopic characterization of a CO2 molecule coordinated to an activated bisphenoidal nickel(I) compound containing a tetraazamacrocyclic ligand in the gas phase. The resulting complex was then structurally characterized by using mass‐selected vibrational predissociation spectroscopy. The results indicate that a highly distorted CO2 molecule is bound to the metal center in an η2‐C,O coordination mode, thus establishing an efficient and rational method for the preparation of metal‐activated CO2 for further studies using ion chemistry techniques.
Plasmonic/Nonlinear Optical Material Core/Shell Nanorods as Nanoscale Plasmon Modulators and Optical Voltage Sensors
Authors: Yin Anxiang , He Qiyuan , Lin Zhaoyang , Luo Liang , Liu Yuan , Yang Sen , Wu Hao , Ding Mengning , Huang Yu , Duan Xiangfeng 
Published: November 2015

AbstractHerein, we report the design and synthesis of plasmonic/non‐linear optical (NLO) material core/shell nanostructures that can allow dynamic manipulation of light signals using an external electrical field and enable a new generation of nanoscale optical voltage sensors. We show that gold nanorods (Au NRs) can be synthesized with tunable plasmonic properties and function as the nucleation seeds for continued growth of a shell of NLO materials (such as polyaniline, PANI) with variable thickness. The formation of a PANI nanoshell allows dynamic modulation of the dielectric environment of the plasmonic Au NRs, and therefore the plasmonic resonance characteristics, by an external electrical field. The finite element simulation confirms that such modulation is originated from the field‐induced modulation of the dielectric constant of the NLO shell. This approach is general, and the coating of the Au NRs with other NLO materials (such as barium titanate, BTO) is found to produce a similar effect. These findings can not only open a new pathway to active modulation of plasmonic resonance at the sub‐wavelength scale but also enable the creation of a new generation of nanoscale optical voltage sensors (NOVS).
Transferhydrosilylierung
Authors: Oestreich Martin 
Published: November 2015

AbstractEs steht außer Frage, dass Transferhydrierung ein gängiges Verfahren in der Industrie und der akademischen Welt ist. Trotz ihrer Vielfältigkeit war die konzeptionell verwandte Transferhydrosilylierung bis zur jüngsten Entwicklung einer radikalischen und einer ionischen Variante im Grunde unbekannt gewesen. Die neuen Methoden basieren beide auf dem Motiv eines siliciumsubstituierten Cyclohexa‐1,4‐diens und hängen von der Aromatisierung der entsprechenden radikalischen bzw. kationischen Cyclohexadienylzwischenstufen begleitet von homo‐ oder heterolytischer Spaltung der Si‐C‐Bindung ab. Die radikalische und ionische Transferhydrosilylierung werden in diesem Kurzaufsatz miteinander in Bezug gesetzt, und frühe Hinweise auf die Möglichkeit einer Transferhydrosilylierung werden auch berücksichtigt. Der derzeitige Stand der Forschung befindet sich zweifellos noch in den Anfängen, aber die jüngsten Fortschritte lassen das vielversprechende Potenzial von Transferhydrosilylierungen bereits erkennen.
Synergistic Substrate and Oxygen Activation in Salicylate Dioxygenase Revealed by QM/MM Simulations
Authors: Roy Subhendu , Kästner Johannes 
Published: November 2015

AbstractSalicylate 1,2‐dioxygenase (SDO) is the first enzyme to be discovered to catalyze the oxidative cleavage of a monohydroxylated aromatic compound, namely salicylate, instead of the well‐known electron‐rich substrates. We have investigated the mechanism of dioxygen activation in SDO by QM/MM calculations. Our study reveals that the non‐heme FeII center in SDO activates salicylate and O2 synergistically through a strong covalent interaction to facilitate the reductive cleavage of O2. A covalent salicylate–FeII–O2 complex is the reactive oxygen species in this case, and its electronic structure is best described as being between the two limiting cases, FeII−O2 and FeII−O2.−, with partial electron transfer from the activated salicylate to O2 via the Fe center. Thus SDO employs a synergistic strategy of substrate and oxygen activation to carry out the catalytic reaction, which is unprecedented in the family of iron dioxygenases. Moreover, O2 activation in SDO happens without the assistance of a proton source. Our study essentially shows a new mechanistic possibility for O2 activation.
Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten
Authors: Fukuda Tetsuya , Hashimoto Hisako , Sakaki Shigeyoshi , Tobita Hiromi 
Published: November 2015

AbstractTreatment of pyridine‐stabilized silylene complexes [(η5‐C5Me4R)(CO)2(H)WSiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe3)3) with an N‐heterocyclic carbene MeIiPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) caused deprotonation to afford anionic silylene complexes [(η5‐C5Me4R)(CO)2WSiH(Tsi)][HMeIiPr] (R=Me (1‐Me); R=Et (1‐Et)). Subsequent oxidation of 1‐Me and 1‐Et with pyridine‐N‐oxide (1 equiv) gave anionic η2‐silaaldehydetungsten complexes [(η5‐C5Me4R)(CO)2W{η2‐OSiH(Tsi)}][HMeIiPr] (R=Me (2‐Me); R=Et (2‐Et)). The formation of an unprecedented W‐Si‐O three‐membered ring was confirmed by X‐ray crystal structure analysis.
Transfer Hydrosilylation
Authors: Oestreich Martin 
Published: November 2015

AbstractTransfer hydrogenation is without question a common technology in industry and academia. Unlike its countless varieties, conceptually related transfer hydrosilylations had essentially been unreported until the recent development of a radical and an ionic variant. The new methods are both based on a silicon‐substituted cyclohexa‐1,4‐diene and hinge on the aromatization of the corresponding cyclohexadienyl radical and cation intermediates, respectively, concomitant with homo‐ or heterolytic fission of the SiC bond. Both the radical and ionic transfer hydrosilylation are brought into context with one other in this Minireview, and early insight into the possibility of transfer hydrosilylation is included. Although the current state‐of‐the‐art is certainly still limited, the recent advances have already revealed the promising potential of transfer hydrosilylation.
Production of New Cladosporin Analogues by Reconstitution of the Polyketide Synthases Responsible for the Biosynthesis of this Antimalarial Agent
Authors: Cochrane Rachel V. K. , Sanichar Randy , Lambkin Gareth R. , Reiz Béla , Xu Wei , Tang Yi , Vederas John C. 
Published: November 2015

AbstractThe antimalarial agent cladosporin is a nanomolar inhibitor of the Plasmodium falciparum lysyl‐tRNA synthetase, and exhibits activity against both blood‐ and liver‐stage infection. Cladosporin can be isolated from the fungus Cladosporium cladosporioides, where it is biosynthesized by a highly reducing (HR) and a non‐reducing (NR) iterative type I polyketide synthase (PKS) pair. Genome sequencing of the host organism and subsequent heterologous expression of these enzymes in Saccharomyces cerevisiae produced cladosporin, confirming the identity of the putative gene cluster. Incorporation of a pentaketide intermediate analogue indicated a 5+3 assembly by the HR PKS Cla2 and the NR PKS Cla3 during cladosporin biosynthesis. Advanced‐intermediate analogues were synthesized and incorporated by Cla3 to furnish new cladosporin analogues. A putative lysyl‐tRNA synthetase resistance gene was identified in the cladosporin gene cluster. Analysis of the active site emphasizes key structural features thought to be important in resistance to cladosporin.
Building Giant Carbocycles by Reversible C−C Bond Formation
Authors: Beaudoin Daniel , Levasseur‐Grenon Olivier , Maris Thierry , Wuest James D. 
Published: November 2015

AbstractWe describe a simple way to build giant macrocyclic hydrocarbons by the reversible formation of carbon–carbon bonds. Specifically, extended spirobifluorene‐substituted derivatives of Wittig's hydrocarbon were synthesized and found to undergo oligomerization, giving the largest hydrocarbon that has been crystallized and characterized by X‐ray diffraction to date.