bluuebunny/crossref_metadata_2025_split huggingface dataset:
HES1 Inhibits Cycling of Hematopoietic Progenitor Cells via DNA Binding
Authors: Yu Xiaobing , Alder Jonathan K. , Chun Jong Ho , Friedman Alan D. , Heimfeld Shelly , Cheng Linzhao , Civin Curt I. 
Published: March 2006

Abstract
Notch signaling is implicated in stem cell self-renewal, differentiation, and other developmental processes, and the Drosophila hairy and enhancer of split (HES) 1 basic helix-loop-helix protein is a major downstream effector in the Notch pathway. We found that HES1 was expressed at high levels in the hematopoietic stem cell (HSC)–enriched CD34+/[CD38/Lin]− /low subpopulation but at low levels in more mature progenitor cell populations. When CD34+ cells were cultured for 1 week, the level of HES1 remained high in the CD34+ subset that had remained quiescent during ex vivo culture but was reduced in CD34+ cells that had divided. To investigate the effects of HES1 in human and mouse hematopoietic stem–progenitor cells (HSPCs), we constructed conditional lentiviral vectors (lentivectors) to introduce transgenes encoding either wild-type HES1 or a mutant lacking the DNA-binding domain (ΔBHES1). We found that lentivector-mediated HES1 expression in CD34+ cells inhibited cell cycling in vitro and cell expansion in vivo, associated with upregulation of the cell cycle inhibitor p21cip1/Waf1 (p21). The HES1 DNA–binding domain was required for these actions. HES1 did not induce programmed cell death or alter differentiation in HSPCs, and while short-term repopulating activity was reduced in HES1-transduced mouse and human cells, long-term reconstituting HSC function was preserved. Our data characterize the complex, cell context–dependent actions of HES1 as a major downstream Notch signaling regulator of HSPC function.
CONTROL OF RESPONDING BY SOUNDS OF DIFFERENT QUALITY: AN EVOLUTIONARY ANALYSIS
Authors: Harrison J. M. 
Published: March 2006

Two experiments investigated the acquisition of discriminations between two acoustic stimuli of different quality (noise bursts vs. a 2‐kHz pulsed signal) when features of the everyday environment were incorporated into the experiments. In Experiment 1, rats were trained, using food, to press a lever. Throughout all sessions, 5‐s trials of noise bursts (the random stimulus) were presented, after variable intertrial intervals, through a remote speaker mounted outside the experimental enclosure. The noise bursts occurred randomly with respect to reinforcement of lever pressing and had no programmed relationship to the animal's behavior. When lever pressing was established, the 2‐kHz signal was presented through a speaker adjacent to the response lever according to a different set of variable intertrial intervals. A response in the presence of the 2‐kHz signal terminated the trial and was reinforced. The 2‐kHz signal acquired control of responding within the first few trials, whereas the random stimulus exerted no control of responding. In Experiment 2, rats were trained to press the lever in the presence of the 2‐kHz signal presented through the adjacent speaker on a variable intertrial interval. After 14 sessions, 5‐s trials of noise bursts (random stimulus) were presented through the remote speaker on the second variable intertrial interval. The random stimulus initially elicited exploratory behavior, which then rapidly declined. Subsequently, the random stimulus exerted no or weak control of responding. The introduction of the random stimulus had no effect on responding in the presence of the adjacent stimulus.In Experiments 3 and 4 the random stimulus was presented through the adjacent speaker, and the stimulus correlated with reinforcement was presented through the remote speaker. In both experiments, there was persistent control of responding by the random stimulus and slow development of control by the stimulus correlated with reinforcement. In Experiment 5, both stimuli were presented through the adjacent speaker. There was persistent control of responding by the random stimulus.
OPERANT CONDITIONING OF BEHAVIORAL VARIABILITY USING A PERCENTILE REINFORCEMENT SCHEDULE
Authors: Machado Armando 
Published: March 2006

The present investigation developed and tested a new percentile reinforcement schedule suited to study pattern variability, whose main feature was the relative dissociation it provided between the variability requirement defining criterional responses and overall probability of reinforcement. In a discrete‐trials procedure, pigeons produced patterns of four pecks on two response keys. If the pattern emitted on the current trial differed from the N preceding patterns, reinforcement was delivered with probability u. The schedule continuously adjusted the criterion N such that the probability of a criterional response, estimated from the subject's recent behavior, was always constant. In these circumstances, the criterion corresponded to an invariant percentile in the distribution of recent responses.Using a between‐subjects design, Experiment 1 manipulated the variability requirement—the percentile—while keeping overall reinforcement probability constant. The degree of variability varied directly with the requirement. In addition, an inverse relationship existed between the requirement and within‐group variance. Experiment 2 manipulated probability of reinforcement while maintaining the variability requirement constant. No consistent relationship was found between variability and reinforcement probability. A tentative hypothesis was advanced ascribing the operant conditioning of behavioral variability to a process of probability‐dependent selection.
Actinides: Inorganic & Coordination ChemistryBased in part on the article Actinides: Inorganic & Coordination Chemistry by Grigorii L. Soloveichik which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Keogh D. Webster 
Published: March 2006

Abstract
The Inorganic and Coordination Chemistry of the 5f elements (Actinides) is intermediate between that of the transition metals and the 4f elements (Lanthanides). The first four members of the actinide series, Ac, Th, Pa, and U, are all naturally occurring but have unstable nuclei, making them radioactive. The other elements in the actinide series (transuranium elements or transuranics) are also radioactive and have been made by man through a variety of nuclear transformation processes, for example, neutron irradiation, atom bombardment, and radioactive decay. The actinide series may be broken into two separate groups, the light or early actinides (Ac–Am) and the heavy or late actinides (Cm–Lr). The chemical behaviors of these two groups are distinct. The light actinides are capable of being stabilized in a variety of oxidation states, for example, II to VII, and have been found to exhibit a significant degree of covalency in binding ligands. The heavy actinides are more reminiscent of the lanthanides in that the most persistent oxidation state is the trivalent and the bonding predominately occurs through ionic interactions. This difference has led to a substantial number of studies into the role of the 5f orbitals in structure and bonding of the actinides. One of the ions that has received a great deal of attention is the ubiquitous actinyl ion, AnO22+/+. This ion is the stable form for all aqueous complexes of the pentavalent and hexavalent light actinides. The oxo ligands are always found in a trans geometry and are strongly bound (triple bond) through a combination of σ‐ and π‐bonds with the 5f and 6d orbitals of the actinide metal center. While these strong covalent interactions exist with the axial oxo ligands, the bonding within the equatorial plane is primarily based on ionic interactions.

The ability of the light actinides to access multiple oxidation states leads to rich and, sometimes, complex electrochemistry. For example, under acidic conditions the reduction potentials for PuO
2
2+
, PuO
2
+
, Pu
4+
, and Pu
3+
are all close to 1 V. The physical manifestation of these close reduction potentials is an aqueous solution in which the plutonium can exist in four different oxidation states simultaneously. By careful control of the conditions, oxidation state pure solutions can be obtained for quantitative and qualitative studies. The binding affinities of the actinide ions to ligands follow the general trend An
4+
> An
3+
∼ AnO
2
2+
≫ AnO
2
+
. Since the actinides are strong acids, the ions preferentially bond strong bases, for example, halides, oxygen donors, and so on. Owing to the greater degree of covalency in actinide complexes compared to the lanthanides, complexes with ligands having nitrogen, phosphorus, sulfur, and selenium donors are also found.
Actinides: Organometallic Chemistry
Authors: Burns Carol J. , Clark David L. , Sattelberger Alfred P. 
Published: March 2006

AbstractAn actinide organometallic complex is one containing an actinide‐carbon π‐bond, an actinide‐carbon σ‐bond, or a combination of both. Actinide organometallic complexes are known for the actinide (An) elements from thorium through californium; the vast majority of the reports on organoactinide compounds, however, deal with thorium and uranium. The latter elements have isotopes, for example, thorium‐232 (t1/2 = 1.41 × 1010years) and uranium‐238 (t1/2 = 4.468 × 109years), with extremely long half‐lives. Modern organoactinide chemistry is characterized by the existence not only of actinide analogs to many classes of d transition metal complexes, but increasingly common reports of compounds and types of reactions unique to the actinide series.
Alkali Metals: Inorganic ChemistryBased in part on the article Alkali Metals: Inorganic Chemistry by Francis S. Mair & Ronald Snaith which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Leung Wing‐Por , Wai‐Yan Ip Queenie 
Published: March 2006

AbstractThis article is updated to cover the literature in the area of inorganic chemistry of alkali metals since 1993. The advancement in instrumentation and spectroscopic techniques in the past decade has provided the researchers with more powerful tools for structure determination of compounds. In this respect, alkalides containing mixed‐sandwich complexes of alkali metal cations, complexes with dimers or chains of alkali metal anions, electrides with alkali metal ions intercalating in zeolite, and interstitial hydride enclosed by an unusual (Li+)8cubic cage have been found or studied by NMR. With the successful preparation of Na3N recently, its correct structure has been revealed. The exact composition of ‘NaB6’ has also been determined. The role of alkali metals in trielide clusters of traditional Zintl polyanions has been demonstrated. Trimetallic Li‐Na‐K amides, alkoxide compounds, and highly aggregated cage structures of lithium‐heavier alkali metal alkoxides have been reported.
Alloys
Authors: Giessen Bill C. , Hidalgo Rafael 
Published: March 2006

AbstractThis article treats the current state of fundamental understanding, development, and applications of alloys, with emphasis on alloy chemistry rather than physical metallurgy. First, alloy phases and phase diagrams are treated from a computational viewpoint. Next, technical alloys, including steels, aluminum alloys, superalloys, and titanium alloys, are reviewed; structural intermetallics are treated as a paradigm for theoretical predictive methods. A review of important specialty alloys follows, including hard and soft magnetic alloys, superconductors, shape memory, and magnetostrictive alloys, hydrogen storage alloys, solders, and alloy coatings. A brief survey of current advanced alloy preparation and characterization methods concludes the article.
Aluminum: Inorganic Chemistry
Authors: Apblett Allen W. 
Published: March 2006

AbstractAluminum is the most abundant metal to be found in the earth's crust (8.1%). It is component of gemstones and many common minerals such as granite and clays. Aluminum is a very reactive metal and is not found in an uncombined form in nature. However, the use of its compounds has a very long history. For example, the ancient Greeks and Romans used alum as an astringent and as a mordant in dyeing. The pure metal was isolated first by Wohler in 1827. The modern method for obtaining aluminum metal is the electrolysis of alumina dissolved in cryolite. Aluminum can also be produced from clay, but the process is not economically feasible at present.Pure aluminum, a silvery‐white metal, possesses many desirable characteristics. It is light, nonmagnetic, and nonsparking, and is second amongst all metals in the scale of malleability, and sixth in ductility. It is extensively used for kitchen utensils, outside building materials, airplanes, and in thousands of industrial applications where a strong, light, easily constructed material is needed. Pure aluminum is soft and lacks strength, but when it is alloyed with small amounts of copper, silicon, magnesium, manganese, or other elements these shortcomings can be circumvented. The aluminum compounds of greatest importance are aluminum oxide, aluminum sulfate, aluminum potassium sulfate (alum), and aluminum halides. The oxide, alumina, occurs naturally as ruby (Al2O3), sapphire, corundum, and emery, and is used in glassmaking and refractory ceramic materials. Synthetic ruby and sapphire are used in lasers for producing coherent light. Aluminum nitride, phosphide, and antimonide are important materials for the semiconductor industry. Aluminum halides and oxides are also very important catalyst supports.
Aluminum: Organometallic ChemistryBased in part on the article Aluminum: Organometallic Chemistry by Gregory H. Robinson which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Mason Mark R. 
Published: March 2006

Abstract

The synthesis, reactivity, structures, and applications of the organometallic compounds of aluminum are reviewed. The chapter starts with a discussion of traditional synthetic approaches to aluminum alkyls, aryls, hydrides, and halides and continues with a discussion of their structures and reactivity. The following section focuses on the emerging organometallic chemistry of Al(0), Al(I), and Al(II) and specifically highlights recent developments in aluminum–aluminum bonding, insertions of small molecules and elements into AlAl bonds, and the isolation of large metalloid clusters such as

$\hbox{Al}_{50}\hbox{Cp}^{*}_{12}$

. Organoaluminum heterocycles and cage compounds are the subjects of the next section. This section briefly describes common structural motifs and has separate subsections devoted to cage iminoalanes, alkylaluminoxanes, and alkylaluminophosphinates, ‐phosphates, ‐phosphonates, and ‐arsonates. Structural relationships amongst these groups of compounds and comparisons to secondary building units in aluminophosphate molecular sieves are presented. The importance of alkylaluminoxanes to catalytic activity is also discussed. This chapter includes an independent section on cationic organoaluminum complexes. Although this includes more traditional cationic complexes ligated by crown ether and neutral nitrogen‐donor ligands, the section emphasizes recent developments in generating two‐ and three‐coordinate cationic complexes. Alkide and hydride abstractions by trityl salts of weakly coordinating anions and tris(pentafluorophenyl)borane are described. Common anion decomposition pathways and successful cationic systems for oligomerizing and polymerizing alkenes are discussed. Two additional sections describe the applications of organoaluminum compounds to organic synthesis and applications in industry. Readers are referred to leading works that more adequately describe the extensive use of organoaluminum reagents in organic synthesis. Current and past applications of organoaluminum compounds for the production of long‐chain alkenes and alcohols, as cocatalysts for Ziegler–Natta and metallocene‐catalyzed polymerization of alkenes and dienes, and catalysts for propene dimerization and epoxide polymerization are summarized. Safety issues regarding the handling and disposal of pyrophoric organoaluminum reagents and waste are also discussed. One hundred and twenty‐six reviews and original works are cited.
Ammonia &N‐Donor Ligands
Authors: House Donald A. 
Published: March 2006

AbstractThe coordination chemistry of nonmacrocyclic ligands containing only N, C, and H atoms is surveyed. Such ligands include ammonia and linear polyamines as well as heterocyclic N‐compounds and catenated N‐systems. Among the topics discussed are N‐ligand synthesis, metal–N bond formation, reactions of coordinated N‐donor ligands, and the utilization of metal–N complexes. Structural and theoretical aspects include the consideration of metal–N stability constants, hard‐acid soft‐base concepts, inorganic reaction mechanisms, molecular mechanics, chelate ring stereochemistry, chirality, and supramolecular chemistry.
Antimony: Inorganic ChemistryBased in part on the article Antimony: Inorganic Chemistry by R. Bruce King which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Breunig Hans Joachim 
Published: March 2006

Abstract
An overview of the inorganic chemistry of the element antimony is given in this article, which includes information on the occurrence, production, use, and properties of the element and of compounds with bonds between antimony and main group elements (except carbon) and transition metals.
Antimony: Organometallic ChemistryBased in part on the article Antimony: Organometallic Chemistry by Alan Berry which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Breunig Hans Joachim 
Published: March 2006

AbstractThis article presents a concise overview on the chemistry of organoantimony compounds containing one or more Sb–C bonds. It deals with homoleptic molecules where Sb is bonded exclusively to organic groups R, for example tri‐ or pentorganyls of antimony, and with heteroleptic derivatives where RnSb groups (n = 1, 2, 4) are bonded to other elements. Not only compounds with single bonds between Sb and C but also molecules with double bond character are considered.
Arsenic: Inorganic ChemistryBased in part on the article Arsenic: Inorganic Chemistry by Ralph A. Zingaro which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Muñoz‐Hernández Miguel‐Ángel 
Published: March 2006

Abstract
This article reflects the importance and development of the chemistry of inorganic arsenic compounds. Throughout the text the reader will be taken from the chemistry of simple arsenic species found in minerals to such as those arsenic species that reflect the breath of modern inorganic chemistry. Efforts have been made to show developments in fundamental chemistry, materials science, and aspects of arsenic in the environment. Accordingly, Section 2 covers aspects of the preparation of simple arsenic species like the chalcogenides and halogenides. In Section 3 the important arsenic intermetallic and Zintl phases are discussed emphasizing important technological aspects. The chemistry of inorganic arsenic hydrides and halides is presented in Sections 4 and 5 with many important fundamental issues that are difficult to find in one single textbook. Inorganic simple arsenic compounds that bear pnictogen and/or chalcogen atoms are discussed in Sections 6 and 8. In these two sections the chemistry is presented starting from species that are found in minerals to complexes that have arsenic as the central atom introducing exciting discrete arsenic molecules and aspects of supramolecular chemistry. The chemistry of arsenic–carbon species where the carbon atom is strictly inorganic is shown in Section 7. Finally, Section 9 intends to give a brief introduction of the impact of arsenic in the environment, especially focusing on issues related to living organisms.
Arsenic: Organoarsenic Chemistry
Authors: Krannich Larry K. , Watkins Charles L. 
Published: March 2006

AbstractThis review surveys the chemistry, reactivity, spectroscopic, and structural aspects of several major classes of organometallic arsenic compounds over the time period of 1760 through 2003. These compounds are the core of the field and represent the major areas of research thrusts during this period. We draw heavily from several books, monographs, and review articles to review the primary synthetic routes and reactivity. The primary literature is referenced for all developments that have occurred since the last published review articles. After an extensive review of the fully substituted and AsH bond containing organoarsenic compounds, the focus is on compounds containing AsHalogen, As group 13, As group 14, As group 15, and AsO bonds. Because of the efforts to synthesize As group 13 bonded compounds of the heavier group 13 elements, tables listing the known compounds synthesized after 1985 and their method of preparation are provided.
BiomineralizationBased in part on the article Biomineralization by Richard B. Frankel which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Dauphin Yannicke 
Published: March 2006

Abstract
Three main categories are involved in biominerals: silica, calcium carbonates, and calcium phosphates. The calcium biominerals are usually crystalline, but amorphous types are also known. Within these categories, the shapes and chemical contents of structural units are variable. Moreover, the chemical and physical properties of biominerals are very different from the crystal habits produced inorganically: they depend on the producing plants and animals and the environmental conditions. Biomineral development is permanently controlled by specifically produced organic molecules that remain entrapped within the mineral units. Although biomineralization has been widely studied in the past, the growth mechanisms are still poorly understood, and the most elaborated model is based on the nacreous layer of mollusk shells. Studies on biominerals and biomineralization have various applications, from biology and geology to biomimetics.
Bonding Energetics of Organometallic Compounds
Authors: Dorta Reto , Nolan Steven P. 
Published: March 2006

AbstractThis contribution gives an overview of solution calorimetric studies carried out on organometallic complexes in the last decade. A special focus has been put on a close investigation of metal–ligand exchange reactions involving different ligand and metal systems. Ligand substitution reactions are at the heart of many catalytic transformations, since creation of vacant coordination sites often require liberation of one or more ligands from the coordination sphere of the metal. Detailed analyses of phosphine‐, phosphite‐, and NHC‐ (NHC = N‐heterocyclic carbene) ruthenium, rhodium, and platinum systems show that enthalpies of ligand substitution reactions are associated to electronic and/or steric variation of the ligands. They can be explained in terms of different amounts of these two contributions to the overall enthalpy. Extensive calorimetric studies on ligand substitutions showed that cis disposition of the ligands leads to an overwhelmingly steric contribution to the enthalpy of ligand substitution, whereas trans disposition of the ligands gives enthalpy values that are highly dependent on the electronic nature of the ligand systems studied. Thermodynamic studies of addition reactions of organic molecules to metal fragments are equally crucial in catalysis and gave valuable thermodynamic data for CO, H2, aldehyde, acyl chloride addition reactions to catalytically relevant rhodium systems. Thermodynamic data for different reductive cleavage reactions of organic fragments involving molybdenum systems are also presented.