This book provides a brief introduction to GC following the objectives for titles in this series. It should appeal to readers with varying levels of education and emphasizes a practical, applied ...approach to the subject. This book provides a quick need-to-know introduction to gas chromatography; still the most widely used instrumental analysis technique, and is intended to assist new users in gaining understanding quickly and as a quick reference for experienced users.
The new edition provides updated chapters that reflect changes in technology and methodology, especially sample preparation, detectors and multidimensional chromatography. The book also covers new detectors recently introduced and sample preparation methods that have become much more easily accessible since the previous edition.
Molecular chirality provides a key challenge in host–guest recognition and other related chemical applications such as asymmetric catalysis. For a molecule to act as an efficient enantioselective ...receptor, it requires multi‐point interactions between host and chiral guest, which may be achieved by an appropriate chiral 3D scaffold. As a consequence of their interlocked structure, catenanes and rotaxanes may present such a 3D scaffold, and can be chiral by inclusion of a classical chiral element and/or as a consequence of the mechanical bond. This Minireview presents illustrative examples of chiral 2catenanes and 2rotaxanes, and discusses where these molecules have been used in chemical applications such as chiral host–guest recognition and asymmetric catalysis.
Mirror image rings and axles: Examples of chiral catenanes and rotaxanes are presented, followed by illustration of the useful application of such molecules in chiral host–guest recognition and asymmetric catalysis.
Talin has emerged as the key cytoplasmic protein that mediates integrin adhesion to the extracellular matrix. In this Review, we draw on experiments performed in mammalian cells in culture and
to ...present evidence that talin is the most important component of integrin adhesion complexes. We describe how the properties of this adaptor protein enable it to orchestrate integrin adhesions. Talin forms the core of integrin adhesion complexes by linking integrins directly to actin, increasing the affinity of integrin for ligands (integrin activation) and recruiting numerous proteins. It regulates the strength of integrin adhesion, senses matrix rigidity, increases focal adhesion size in response to force and serves as a platform for the building of the adhesion structure. Finally, the mechano-sensitive structure of talin provides a paradigm for how proteins transduce mechanical signals to chemical signals.
Many traits of interest are highly heritable and genetically complex, meaning that much of the variation they exhibit arises from differences at numerous loci in the genome. Complex traits and their ...evolution have been studied for more than a century, but only in the last decade have genome-wide association studies (GWASs) in humans begun to reveal their genetic basis. Here, we bring these threads of research together to ask how findings from GWASs can further our understanding of the processes that give rise to heritable variation in complex traits and of the genetic basis of complex trait evolution in response to changing selection pressures (i.e., of polygenic adaptation). Conversely, we ask how evolutionary thinking helps us to interpret findings from GWASs and informs related efforts of practical importance.
Alongside the use of metal cations and π–π stacking, hydrogen bonding is one of the major templating interactions used to prepare rotaxanes and catenanes. In this review, a brief summary of key ...historical milestones will be followed by discussion of developments from over the last decade in both synthetic methodology and application of hydrogen bond templated interlocked molecules. Hydrogen bond templation can allow for rapid access to interlocked molecules in high yields, with select examples having been put to useful purpose, in applications such as organocatalysis and cellular imaging.
This review focuses on progress in the field of hydrogen bond templated rotaxanes and catenanes over the last decade. A summary of key historic examples is followed by discussion of developments in synthetic methodology and useful application of the resulting interlocked molecules.
Since the start of this millennium, remarkable progress in the binding and sensing of anions has been taking place, driven in part by discoveries in the use of hydrogen bonding, as well as the ...previously under‐exploited anion–π interactions and halogen bonding. However, anion supramolecular chemistry has developed substantially beyond anion recognition, and now encompasses a diverse range of disciplines. Dramatic advance has been made in the anion‐templated synthesis of macrocycles and interlocked molecular architectures, while the study of transmembrane anion transporters has flourished from almost nothing into a rapidly maturing field of research. The supramolecular chemistry of anions has also found real practical use in a variety of applications such as catalysis, ion extraction, and the use of anions as stimuli for responsive chemical systems.
Since the start of this millennium, anion supramolecular chemistry has evolved substantially beyond the chemistry of anion receptors. Alongside the research that continues on the binding and sensing of anions, large strides have been made in areas that have previously been underdeveloped, such as the use of anions as templates and for membrane transportation, and importantly in chemical applications including catalysis, ion extraction, and responsive molecular systems.
Optical probes that provide information about local chirality have been developed based on changes to the circular polarisation of emitted light. Highly emissive complexes of lanthanide ions are ...ideally suited for CPL spectroscopy and the design criteria for developing such probes are defined, based on a rigorous stereochemical analysis. The perturbation of a dynamically racemic complex may occur either by a change in complex constitution or by non-covalent association. With complexes of enantiopure ligands, perturbation may involve either dynamic helicity inversion or a reversible change in the lanthanide coordination environment.
A detailed understanding of complex stereochemistry and speciation allows the development of CPL probes.
Prior research shows that positive online reviews are less valued than negative reviews. The authors argue that this is due to differences in causal attributions for positive versus negative ...information such that positive reviews tend to be relatively more attributed to the reviewer (vs. product experience) than negative reviews. The presence of temporal contiguity cues, which indicate that review writing closely follows consumption, reduces the relative extent to which positive reviews are attributed to the reviewer and mitigates the negativity bias. An examination of 65,531 Yelp.com restaurant reviews shows that review value is negatively related to review valence but that this negative relationship is absent for reviews that contain temporal contiguity cues. A series of lab studies replicates these findings and suggests that temporal contiguity cues enhance the value of a positive review and increase the likelihood of choosing a product with a positive review by changing reader beliefs about the cause of the review.
A critical output of metagenomic studies is the estimation of abundances of taxonomical or functional groups. The inherent uncertainty in assignments to these groups makes it important to consider ...both their hierarchical contexts and their prediction confidence. The current tools for visualizing metagenomic data, however, omit or distort quantitative hierarchical relationships and lack the facility for displaying secondary variables.
Here we present Krona, a new visualization tool that allows intuitive exploration of relative abundances and confidences within the complex hierarchies of metagenomic classifications. Krona combines a variant of radial, space-filling displays with parametric coloring and interactive polar-coordinate zooming. The HTML5 and JavaScript implementation enables fully interactive charts that can be explored with any modern Web browser, without the need for installed software or plug-ins. This Web-based architecture also allows each chart to be an independent document, making them easy to share via e-mail or post to a standard Web server. To illustrate Krona's utility, we describe its application to various metagenomic data sets and its compatibility with popular metagenomic analysis tools.
Krona is both a powerful metagenomic visualization tool and a demonstration of the potential of HTML5 for highly accessible bioinformatic visualizations. Its rich and interactive displays facilitate more informed interpretations of metagenomic analyses, while its implementation as a browser-based application makes it extremely portable and easily adopted into existing analysis packages. Both the Krona rendering code and conversion tools are freely available under a BSD open-source license, and available from: http://krona.sourceforge.net.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Significance Why do species’ ranges often end when no obvious change in the environment suggests they should? Our theory explains that there is an inherent limit to adaptation arising in any (finite) ...natural population and identifies the key parameters that determine this limit to a species’ range. Two observable parameters describe the threshold when adaptation fails: ( i ) the loss of fitness due to dispersal to a different environment, and ( ii ) the efficacy of selection relative to stochastic effects in finite populations.
Why do species not adapt to ever-wider ranges of conditions, gradually expanding their ecological niche and geographic range? Gene flow across environments has two conflicting effects: although it increases genetic variation, which is a prerequisite for adaptation, gene flow may swamp adaptation to local conditions. In 1956, Haldane proposed that, when the environment varies across space, “swamping” by gene flow creates a positive feedback between low population size and maladaptation, leading to a sharp range margin. However, current deterministic theory shows that, when variance can evolve, there is no such limit. Using simple analytical tools and simulations, we show that genetic drift can generate a sharp margin to a species’ range, by reducing genetic variance below the level needed for adaptation to spatially variable conditions. Aided by separation of ecological and evolutionary timescales, the identified effective dimensionless parameters reveal a simple threshold that predicts when adaptation at the range margin fails. Two observable parameters determine the threshold: ( i ) the effective environmental gradient, which can be measured by the loss of fitness due to dispersal to a different environment; and ( ii ) the efficacy of selection relative to genetic drift. The theory predicts sharp range margins even in the absence of abrupt changes in the environment. Furthermore, it implies that gradual worsening of conditions across a species’ habitat may lead to a sudden range fragmentation, when adaptation to a wide span of conditions within a single species becomes impossible.
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