bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biodesulfurization
Authors: Grossman M. 
Published: November 2010

AbstractRemoval of organic sulfur from crude oil derived fuels is a large‐scale refinery operation that adds significantly to the cost of motor vehicle fuels. This is accomplished by hydrodesulfurization (HDS), a process that converts organic sulfur into hydrogen sulfide using high temperature and hydrogen pressure. To meet the increasingly more stringent regulations on the sulfur content of fuels, more severe and hence more costly HDS operating conditions are required. Biodesulfurization has been viewed as a potentially more cost‐effective alternative to HDS because of the inherently mild conditions at which biological systems operate. Both reductive and oxidative approaches to biodesulfurization have been explored and both have received some level of success. Evaluation of these approaches has shown that selectivity for sulfur, substrate range, and reaction rate are of particular importance for effective desulfurization of fuels. Of the possible candidate systems, the sulfur selective oxidative pathway has emerged as the most promising approach. This pathway involves the selective and sequential oxidation of the sulfur moiety followed by hydrolytic cleavage of the remaining carbon–sulfur bond. Significant progress has been made on understanding the enzymology and genetics of this system. The desulfurization of a wide range of model compounds as well as a variety of fuel oils has been demonstrated. Although the potential exists for application of this technology to fuels desulfurization, perhaps more promising are applications in chemical synthesis.
Catalyst Characterization – Heterogeneous
Authors: Knözinger Helmut , Taglauer Edmund 
Published: November 2010

AbstractPhysical and chemical properties of solid catalysts critically determine their performance. This review summarizes the techniques which permit analysis and determination of these properties. The physical principle and the potential of each technique is briefly discussed and characteristic examples are given. The techniques mentioned include those for determining surface area and porosity, x‐ray diffraction and absorption, electron microscopy, scanning probe microscopy, vibrational spectroscopies (infrared and Raman), nonlinear optical spectroscopy, neutron diffraction and inelastic scattering, nuclear spectroscopy (spectroscopies and nuclear magnetic resonance), electron spectroscopy (Auger and photoelectron spectroscopy), ion scattering spectroscopy, optical absorption and luminescence spectroscopy, electron paramagnetic resonance, and thermoanalytical methods. The review concludes with a brief description of the determination of mechanical strength of solid catalysts.
Hydrogenation – Homogeneous
Authors: Oro Luis A. 
Published: November 2010

AbstractHomogeneous hydrogenation constitutes an important synthetic procedure and is one of the most extensively studied reactions of homogeneous catalysis. A very large number of soluble metal complexes, usually derived from transition metals, are active catalyst under very mild conditions. Detailed mechanistic studies have now firmly established reaction pathways for some hydrogenation catalysts such as the Wilkinson's catalyst, RhCl(P(C6H5)3)3, and rhodium and iridium catalyst precursors of formula [M(diene)2L2]+or [Ir(diene)(py)(PCy3)]+, usually known as Crabtree's catalyst; other well‐known examples are RuHCl(P(C6H5)3)3and OsHCl(CO)(P(i‐C3H7)3)2complexes. Homogeneous hydrogenation reactions have found important applications. One of the most important developments of homogeneous catalysis is the synthesis of optically active compounds by asymmetric hydrogenation of prochiral substrates. On the other hand, transfer hydrogenation, where the addition of hydrogen to an unsaturated substrate is provided by a donor molecule, can be considered as a viable alternative and complement to the classical reduction reactions with molecular hydrogen. The catalysts are usually late transition metal complexes with bidentate nitrogen ligands or tertiary phosphine ligands.
Hydrogenation—Homogeneous
Authors: Oro Luis A. , Carmona Daniel 
Published: November 2010

AbstractThe homogeneous hydrogenation of CC, CO, and CN bonds catalyzed by metallic compounds is reviewed. The transfer hydrogenation of similar types of substrates from hydrogen donors is also considered as a viable alternative to the use of molecular hydrogen. The asymmetric versions of both types of processes are also examined. The metals and ligands that generate the most active and selective systems are illustrated. Special attention has been paid to the currently accepted mechanisms for the different catalytic systems.
Heat Stabilizers
Authors: Mesch Keith A. 
Published: November 2010

AbstractHalogenated polymers, particularly poly(vinyl chloride) (PVC) and poly(vinylidene chloride) (PVDE), require the use of heat stabilizers for effective processing. A variety of chemical classes are effective commercial heat stabilizers since they prevent the catastrophic degradation of these polymers at normal processing temperatures. The most effective class of heat stabilizers are the organotin mercaptides which can provide effective stabilization at dosages of the order of 1% or less of the PVC. Mixed metal products, consisting of combinations of calcium and zinc or barium, calcium and zinc soaps are used extensively in many flexible PVC applications. Heat stabilizers based on lead soaps and salts have been used commercially in PVC since the 1930s. During the past decade, completely new heat stabilizer technologies, based on organic compounds, have been introduced to the market for rigid PVC processing.All heat stabilizers must provide several functions to stabilize PVC. They must neutralize hydrogen chloride, react with “defect sites” on the polymer to replace weakened carbon–chlorine bonds, prevent autoxidation effects, and disrupt conjugated polyenes on polymer. Reactive mechanisms for the major classes of technologies are reviewed. The heat stabilizers must be very cost‐effective in a highly competitive marketplace. Several suppliers and their major products are highlighted. Health and safety concerns for the major classes of heat stabilizers are also presented.
Kinetics of Radical Polymerization
Authors: Russell Gregory T. 
Published: November 2010

AbstractThis contribution expounds the principles of radical polymerization (RP) kinetics. It emphasizes the defining population‐balance equations and shows how everything springs from them. As far as possible, an equation‐ rather than modeling‐based approach is advocated, because this provides much greaterunderstandingof kinetics. Numerous examples in support of this philosophy are presented. The treatment covers both steady‐state and nonsteady‐state polymerization and also presents some of the extra considerations involved in acrylate polymerization, copolymerization, and emulsion polymerization. Methods for measuring the values of rate coefficients are naturally elucidated in the wider context of RP kinetics in general. The strengths and limitations of equations and methods are made clear. It is argued that very little defies explanation when proper attention is given to the necessary fundamentals.
Transitions and Relaxations
Authors: Myasnikova Liubov P. 
Published: November 2010

AbstractThe transitions and relaxation processes in polymers are considered. The recent progress and approaches toward both a phenomenological description and a theoretical understanding of its combined kinetic‐thermodynamic character are outlined. The article discusses some specificity of melting polymers, the nature of glass transition, and the secondary transitions and pays attention to a study of relaxation processes in surface nanolayers.
Weathering of Polymeric Materials
Authors: Searle Norma D. , McGreer Matthew , Zielnik Allen 
Published: November 2010

Abstract
The useful service life of polymeric materials depends on their ability to resist the effects of critical weather factors responsible for the deterioration of either or both the appearance and physical properties necessary in their applications. The effects of weather result from complex interactions of the environmental elements, primarily solar radiation, heat/cold, moisture, oxygen, and pollutants, with the materials. By far, the most destructive environmental factor is the ultraviolet (UV) portion of terrestrial solar radiation absorbed by a material because it is capable of breaking some of the chemical bonds and thus initiating the degradation reactions. Because photodegradation is wavelength specific, close simulation of the spectral power distribution (SPD)of the natural source by the radiation source used for laboratory accelerated weathering is essential for simulating the natural weathering processes. The presence of short wavelengths below the solar UV cut‐on, the absence of long wavelength UV and short wavelength visible radiation, and relative intensities that do not simulate those of solar radiation can produce differences in degradation mechanisms, types of failure, and weatherability rankings of products compared with natural weathering. Sample temperatures and type and amount of moisture have a significant influence on the rate of degradation through their effects on the secondary reactions following bond breakage. Unrealistic levels of all stress factors have to be used with caution to obtain good correlation of degradation processes between accelerated and natural weathering. Because acceleration of weathering by increase in the critical stress factors differs for each material and formulation, the acceleration factor must be determined experimentally for each product. The effects of critical weather factors on polymeric materials and the various types of outdoor and laboratory‐accelerated weathering tests and their test parameters are described. The critical weather factors in natural and artificial weathering are compared and potential methodologies for predicting long‐term performance of polymeric materials are reviewed.
Oligodendrocytes
Authors: Szuchet Sara , Domowicz Miriam S , Hudson Lynn D 
Published: November 2010

Abstract

Oligodendrocytes – a type of central nervous system glial cell – have diverse origins and are morphologically and phenotypically heterogeneous. They present two phenotypes: myelinating and nonmyelinating that derive from a common precursor pool. In the spinal cord, oligodendrocyte precursors and motor neurons arise from the same niche. In the embryonic forebrain, ganglionic eminences harbour sites that generate GABAergic neurons and oligodendrocyte precursors destined to populate the telencephalon. A strict spatio‐temporal expression of transcription factors and signalling molecules ensures the orderly appearance of precursors, their migration and differentiation. The two oligodendrocyte phenotypes are functionally interlocked with neurons. Myelinating oligodendrocytes associate with axons and organise them into segments surrounded by the multilayer membrane, myelin, separated by bare regions – nodes of Ranvier – that express voltage‐gated sodium channels, players in the generation of action potentials. Myelin contributes to axonal architecture. Nonmyelinating oligodendrocytes adhere to neuronal somata, but their code of communication is still unknown. In multiple sclerosis myelin is destroyed, oligodendrocytes die and axons degenerate. This overall knowledge constitutes a scaffold upon which further advancements are built.

Key Concepts:

Oligodendrocytes – one of the neural cell types from the central nervous system that have diverse origins and are morphologically and phenotypically hetererogeneous.

Oligodendrocytes provide support to axons that is independent of their role in the assembly and maintenance of myelin.

Oligodendrocytes are vulnerable cells because the making and sustaining of myelin come at a great metabolic cost.

Myelin is an intricate membrane organelle unique to vertebrate organisms.

Myelin is a multilayer membrane not only essential for fast nerve conduction, but is also a critical determinant of axonal architecture.

The advent of myelin marked an evolutionary leap because it allowed for the development of large organisms, but their existence is irrevocably tied to it.

The interaction between an oligodendrocyte and an axon is one of the most complex cell‐to‐cell communications.

Transcription factors act in a cell context–specific mode and regulate the determination of cellular fate.

Genetic and epigenetic factors exert strict supervision on nervous system development.

Diseases of oligodendrocytes or myelin can be classified as demyelinating or dysmyelinating.
Hepatitis Delta Virus
Authors: Taylor John M 
Published: November 2010

Abstract

Several viruses are important causes of acute and chronic infections of the human liver.

Hepatitis delta virus

(HDV) is a most unusual agent that is found only in association with

Hepatitis B virus

(HBV). HBV is a helper virus for HDV and provides the envelope proteins needed for the assembly of new HDV particles. Otherwise the replication of the HDV RNA (
ribonucleic acid
) genome is independent of HBV. HDV encodes only one protein, the delta antigen, a small basic RNA‐binding protein, which is essential for genome replication. In the animal world, HDV is unique to infections of humans. However, HDV shows some intriguing similarities to plant viroids, which have RNA genomes even smaller than HDV, and encode no known proteins and have no helper viruses.

Key Concepts:

HDV uses HBV as a helper virus to achieve assembly of new virus particles.

HDV has a small single‐stranded circular RNA genome.

During genome replication there arises the antigenome, an exact complement of the genome.

The HDV genome and antigenome are transcribed by redirection of a host RNA polymerase that normally acts on DNA templates.

Antigenomic HDV RNA sequences encode one small basic protein that is essential for genome replication

Site‐specific RNA‐editing on antigenomic RNA leads to the translation of a large delta antigen species, one that supports assembly via HBV envelope proteins.

The HDV RNA genome and its mode of replication show intriguing similarities to the plant viroid RNAs.
Innate Immune Mechanisms: Nonself Recognition
Authors: Quah Ben JC , Parish Christopher R 
Published: November 2010

Abstract

The initial defence of the body against pathogens relies on the innate immune system. The innate immune system recognises unique molecular patterns expressed by pathogens, referred to as pathogen‐associated molecular patterns (PAMPs), through receptors known as pattern recognition molecules (PRMs). PRMs are a diverse range of cell‐bound and soluble proteins that sense extracellular and intracellular pathogens and induce a number of responses to help aid in their destruction including phagocytosis through opsonisation, cytokine production and activation of complement. In addition to pathogen sensing, host cells express proteins, the complement regulatory proteins, that protect them from attack by the alternative pathway of complement activation, whereas foreign organisms lack these protective proteins and are, therefore, susceptible to complement attack.

Key Concepts:

The innate immune system recognises pathogen‐associated molecular patterns (PAMPs) that are unique to pathogens.

Cells of the innate immune system express a large range of pattern recognition molecules (PRM) that bind to PAMPs.

Host cells express complement regulatory proteins that protect them from attack by innate mechanisms.
Origin of Life
Authors: Brack André 
Published: November 2010

Abstract

Primitive life – defined as a chemical system capable of transfering its molecular information via self‐replication and also capable of evolving – probably originated about 4 billion years ago from the processing of organic molecules by liquid water. Organic matter might have been formed in the primitive atmosphere from methane or carbon dioxide but also in submarine hydrothermal vents. A large fraction of prebiotic organic material might have been brought by meteoritic and cometary dust grains decelerated by the atmosphere. Strategies to understand the origin of life include the reconstitution in the laboratory of an artificial life capable of self‐reproduction and evolution, the search for fossil traces of life in Archeaen sediments and the search for another example of natural life beyond the Earth, on Mars, Europa, Titan, Enceladus and exoplanets.

Key Concepts:

Life emerged about 4 billion years ago with organic molecules capable of self‐reproduction and of evolving in liquid water.

A large fraction of the prebiotic organic material came from space.

The reconstruction of life in a test tube lacks a simple synthesis of RNA.

The very early fossil traces of life have been erased.

The oldest accepted fossil traces of life are 3.45 billion years old.

Mars harboured large oceans in the past and was therefore hospitable to life.

Life may be present within the Europa's ocean.

Organic chemistry is universal. Life may therefore arise on appropriate extrasolar planets.
Mitochondria Protein Import: Methods
Authors: Stojanovski Diana , Ryan Michael T 
Published: November 2010

Abstract

Mitochondria are prominent and essential organelles within eukaryotic cells. The majority of proteins residing within mitochondria are nuclear‐encoded and consequently synthesised as precursor proteins on cytosolic ribosomes. These precursors must be imported across one or both of the mitochondrial membranes to reach their final destination where they can acquire their functional state. Currently we have knowledge of at least four different pathways that govern the import and sorting of nuclear‐encoded mitochondrial precursors. The elucidation and characterisation of these pathways has been greatly facilitated by the

in vitro

mitochondrial import assay. The

in vitro

assay is the main biochemical approach for analysing protein import into mitochondria and is performed by incubating a radiolabelled precursor protein with isolated mitochondria.

Key Concepts:

Most mitochondrial proteins are encoded by nuclear DNA and need to be imported into the organelle following translation.

Different pathways exist for the import of proteins into the various mitochondrial subcompartments.

In vitro
translated precursors can be imported into energised isolated mitochondria.

The final residence of the imported precursor can be analysed using various treatments.

In vitro
import reactions can be accompanied with monitoring the assembly of the precursor into complexes.
History of Developmental Biology
Authors: Horder Tim 
Published: November 2010

AbstractDevelopmental biology – or ‘embryology’ – is a subject with a long and distinguished, but uneven, history. It is remarkable for the list of leading scientists and philosophers who have contributed to it from antiquity up to the present era. Because embryos are typically minute and inaccessible direct study and understanding has been slow and relatively recent: before the mid‐nineteenth century theories of reproduction and the origin of living forms were largely speculative. Since then embryology has varied greatly in its importance within mainline biological thinking. At one time it provided key evidence for evolution; later for early theories of genetics. Recently, and even now it can be argued, biologists are divided and unclear about how best to demarcate the subject because it overlaps with many other biological themes as diverse as reproduction, malformation, aging and cancer. Today it tends to be approached through the techniques of molecular biology and molecular genetics, and has acquired renewed interest in the context of fertility enhancement, stem cells and genetic engineering.Key Concepts:Historically, developmental biology has at times been central to biological thinking: for example as key evidence for change and succession in body forms during evolution.The historical theme of whether, in part, ‘ontogeny recapitulates phylogeny’ remains an open question to this day.Investigative embryology created some of the most elegant and decisive experimental designs in the history of biology.Developmental biology remains the repository of some of the greatest remaining challenges within biology: for example how to account for the complexity and dynamic properties of living systems.The concepts of allometry and heterochrony have their origins in the study of embryos.Developmental biology remains a crucial challenge to the currently dominant explanation of biological systems in terms of molecular genetics: it demonstrates the equal importance of frequently overlooked ‘epigenetic’ considerations in accounting for biological form.IVF, the stem cells concept and the potential of regenerative medicine have their theoretical base in the standard concepts derived from developmental biology
DNA
: Mechanical Breakage
Authors: Quail Michael Andrew 
Published: November 2010

Abstract

In order to fragment
deoxyribonucleic acid
(DNA) in a random manner, a variety of methods involving the mechanical breakage of DNA have been employed. These include sonication, needle shear, nebulisation, point‐sink shearing and passage through a French pressure cell. The new sequencing technologies utilise smaller fragments than those traditionally generated by mechanical breakage. As a result a number of higher throughput and more powerful technologies for random shearing of DNA have been developed including focused acoustic shearing (Covaris Inc) and high power sonication devices (e.g. Sonicman and Bioruptor). These are able to efficiently fragment DNA down to 100 bp and options for multiplexed sample processing are available.

This article describes each of these approaches in turn giving the theory behind and the utility of each and giving practical tips where appropriate.

Key Concepts:

Shearing DNA using mechanical breakage produce random fragments.

Shearing DNA by utilising enzymatic action generates bias and produces a set of nonrandom fragments.

Several genomic analysis procedures, especially sequencing, require the shearing of DNA to a set of random DNA fragments.

Heat generated during physical shearing can cause A–T rich regions of DNA to permanently dissociate.

Randomly sheared DNA needs ‘repairing’, typically by incubation with Klenow or T4 polymerase in the presence of dNTPs, in order to make their termini available for ligation.