Abstract The purpose of this quasi‐experimental study was to document the benefits of teaching chemistry through history. The experimental group consisted of seniors enrolled in a teacher preparation program in which they learned how to teach chemistry through the history of science. Their understanding of the nature of science was compared with that of a control group, which consisted of juniors in the same department. The results of the analysis of covariance revealed that the experimental group outperformed the control group on an instrument documenting respondents' understanding of the nature of science. Additional frequency analysis and interview data indicated that the experimental group students had a better understanding of the nature of creativity, the theory‐based nature of scientific observations, and the functions of theories. In the pretreatment interviews, students in the experimental group based their explanations concerning the nature of science primarily on their intuition. In the posttreatment interview, however, they were able to explain their beliefs by using scientists' arguments or hypotheses as examples. This result indicates that the experimental group's understanding about the nature of science was enhanced by learning to teach through the history of science. © 2002 Wiley Periodicals, Inc. J Res Sci Teach 39: 773–792, 2002
Keys to the study of chemistry the components of the matter stoichiometry - mole-mass relationships in chemical systems the major classes of chemical reactions gases and the kinetic-molecular theory thermochemistry - energy flow and chemical change quantum theory and atomic structure electron configuration and chemical periodicity models of chemical bonding molecular shape and theories aof covalent bonding intermolecualr forces - liquids, solids, and changes of state the properties of mixtures - solutions and colloids periodic patterns in the main-group elements - bonding, structure, and reactivity organic compound and the atomic properties of carbon kinetics - rates and mechanisms of chemical reactions equilibrium - the extent of chemical reactions acid-base equilibria in aqueous systems ionic equilibria in aqueous systems thermodynamics - entropy, free energy, and the direction of chemical reactions electrochemistry - chemical change and electrical work nuclear reactions and their applications the transition elements and their coordination compounds the elements in nature and industry. Appendices: math review reference tables answers to selected problems glossary credits index.
Much scholarship in chemical education draws upon the model of there being three ‘levels’ at which the teaching and learning of chemistry operates, a notion which is often represented graphically in terms of a triangle with the apices labelled as macroscopic, submicroscopic and symbolic. This model was proposed by Johnstone who argued that chemistry education needs to take into account ideas deriving from psychological research on cognition about how information is processed in learning. Johnstone's model, or the ‘chemistry triplet’, has been widely taken-up in chemistry education, but has also been developed and reconceptualised in diverse ways such that there is no canonical form generally adopted in the community. Three decades on from the introduction of Johnstone's model of the three levels, the present perspective article revisits both the analysis of chemical knowledge itself, and key ideas from the learning sciences that can offer insights into how to best teach the macroscopic, submicroscopic and symbolic aspects of chemical knowledge.
ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTMultireference Nature of Chemistry: The Coupled-Cluster ViewDmitry I. Lyakh*, Monika Musiał, Victor F. Lotrich, and Rodney J. BartlettView Author Information Quantum Theory Project, University of Florida, Gainesville, Florida 32611, United States*Phone: 352-392-6714. E-mail: [email protected]Cite this: Chem. Rev. 2012, 112, 1, 182–243Publication Date (Web):December 28, 2011Publication History Received27 April 2011Published online28 December 2011Published inissue 11 January 2012https://pubs.acs.org/doi/10.1021/cr2001417https://doi.org/10.1021/cr2001417review-articleACS PublicationsCopyright © 2011 American Chemical SocietyRequest reuse permissionsArticle Views8377Altmetric-Citations425LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Cluster chemistry,Determinants,Hamiltonians,Mathematical methods,Wave function Get e-Alerts
Abstract This study assessed the representations of nature of science (NOS) in high school chemistry textbooks and the extent to which these representations have changed during the past four decades. Analyses focused on the empirical, tentative, inferential, creative, theory‐driven, and social NOS, in addition to the myth of “The Scientific Method,” the nature of scientific theories and laws, and the social and cultural embeddedness of science. A total of 14 textbooks, including five “series” spanning one to four decades, were analyzed. The textbooks commanded significant market shares in the United States and were widely used in some of the most populace states. Relevant textbook sections were scored on each of the target NOS aspects on a scale ranging from −3 to +3, which reflected the accuracy, completeness, and manner (explicit versus implicit) in which these aspects were addressed. The textbooks fared poorly in their representations of NOS. Additionally, with a few exceptions, textbook scores either did not change or decreased over the past four decades. These trends are incommensurate with the discourse in national and international science education reform documents, which has witnessed an increasing emphasis on the centrality of NOS to scientific literacy and pre‐college science education during the same time period. Assessment and evaluation strategies, and policies need to be targeted if substantial and desired changes in the ways NOS is addressed in science textbooks are to be effected. © 2008 Wiley Periodicals, Inc. J Res Sci Teach 45: 835–855, 2008
PREFACE. ACKNOWLEDGMENT. Chapter 1 THE SCOPE OF THE FIELD OF HETEROCYCLIC CHEMISTRY. References. Appendix. Chapter 2 COMMON RING SYSTEMS AND THE NAMING OF HETEROCYCLIC COMPOUNDS. 2.1. General. 2.2. Naming Simple Monocyclic Compounds. 2.3. Handling the Extra Hydrogen. 2.4. Substituted Monocyclic Compounds. 2.5. Rings With More Than One Heteroatom. 2.6. Bicyclic Compounds. 2.7. Multicyclic Systems. 2.8. The Replacement Nomenclature System. 2.9. Saturated Bridged Ring Systems. References. Review Exercises. Chapter 3 NATURE AS A SOURCE OF HETEROCYCLIC COMPOUNDS. 3.1. General. 3.2. Naturally Occurring Nitrogen Heterocyclic Compounds. 3.3. Oxygen Compounds. 3.4. Sulfur and Phosphorus Heterocyclic Compounds in Nature. References. Chapter 4 PRINCIPLES OF SYNTHESIS OF AROMATIC HETEROCYCLES BY INTRAMOLECULAR CYCLIZATION. 4.1. General. 4.2. Some of the Classic Synthetic Methods. 4.3. Cyclizations Involving Metallic Complexes as Catalysts. 4.4. Cyclizations with Radical Intermediates. 4.5. Cyclizations by Intramolecular Wittig Reactions. 4.6. Synthesis of Heterocycles by the Alkene Metathesis Reaction. References. Review Exercises. Chapter 5 SYNTHESIS OF HETEROCYCLIC SYSTEMS BY CYCLOADDITION REACTIONS. 5.1. The Diels Alder Reaction. 5.2. Dipolar Cycloadditions. 5.3. [2 + 2] Cycloadditions. References. Review Exercises. Chapter 6 AROMATICITY AND OTHER SPECIAL PROPERTIES OF HETEROCYCLES: PI-DEFICIENT RING SYSTEMS. 6.1. General. 6.2. Review of the Aromaticity of Benzene. 6.3. Pi-Deficient Aromatic Heterocycles. References. Review Exercises. Chapter 7 AROMATICITY AND OTHER SPECIAL PROPERTIES OF HETEROCYCLES: PI-EXCESSIVE RING SYSTEMS AND MESOIONIC RING SYSTEMS. 7.1. Pi-Excessive Aromatic Heterocycles. 7.2. Mesoionic Heterocycles. References. Review Exercises. Chapter 8 THE IMPORTANCE OF HETEROCYCLES IN MEDICINE. 8.1. General. 8.2. Historical. 8.3. Pyridines. 8.4. Indoles. 8.5. Quinolines. 8.6. Azepines. 8.7. Pyrimidines. 8.8. Concluding Remarks. References. Chapter 9 SYNTHETIC METHODS FOR SOME PROMINENT HETEROCYCLIC FAMILIES: EXAMPLES OF PHARMACEUTICALS SYNTHESIS. 9.1. Scope of the Chapter. 9.2. Pyrroles. 9.3. Furans. 9.4. Thiophenes. 9.5. 1,3-Thiazoles. 9.6. 1,3-Oxazoles. 9.7. Imidazoles. 9.8. Pyrazoles. 9.9. 1,2,4-Triazoles. 9.10. Tetrazoles. 9.11. 1,3,4-Thiadiazoles and other 5-Membered Systems. 9.12. Indole. 9.13. Pyridines. 9.14. Quinolines and Isoquinolines. 9.15. Benzodiazepines. 9.16. Pyrimidines. 9.17. Fused Pyrimidines: Purines and Pteridines. 9.18. 1,3,5-Triazines. 9.19. Multicyclic Compounds. References. Review Exercises. Chapter 10 GEOMETRIC AND STEREOCHEMICAL ASPECTS OF NONAROMATIC HETEROCYCLES. 10.1. General. 10.2. Special Properties of Three-Membered Rings. 10.3. Closing Heterocyclic Rings: Baldwin s Rules. 10.4. Conformations of Heterocyclic Rings. 10.5. Chirality Effects on Biological Properties of Heterocycles. References. Review Exercises. Chapter 11 SYNTHETIC HETEROCYCLIC COMPOUNDS IN AGRICULTURAL AND OTHER APPLICATIONS. 11.1. Heterocyclic Agrochemicals. 11.2. Applications of Heterocyclic Compounds in Commercial Fields. References. Appendix UNIFIED AROMATICITY INDICES (IA) OF BIRD. INDEX.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry.K. S. PitzerCite this: J. Am. Chem. Soc. 1960, 82, 15, 4121Publication Date (Print):August 1, 1960Publication History Published online1 May 2002Published inissue 1 August 1960https://pubs.acs.org/doi/10.1021/ja01500a088https://doi.org/10.1021/ja01500a088research-articleACS PublicationsRequest reuse permissionsArticle Views1010Altmetric-Citations47LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
The nature of organic carbon in the < 2, 2–20, 20–53, 53–200, and 200–2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS). Analyses were repeated after high energy ultraviolet photo-oxidation was performed on the three finest fractions. All four soils, studied contained appreciable amounts of physically protected carbon while three of the soils contained even higher amounts of charcoal. It was not possible to measure the charcoal content of soils directly, however, after photo-oxidation, charcoal remained and was identified by its wood-like morphology revealed by scanning electron microscopy (SEM) together with a highly aromatic chemistry determined by solid state 13C n.m.r. Charcoal appears to be the major contributor to the 130 ppm band seen in the n.m.r. spectra of many Australian soils. By using the aromatic region in the n.m.r. spectra, an approximate assessment of the charcoal distribution through the size fractions demonstrated that more than 88% of the charcoal present in two of the soils occurred in the < 53 µm fractions. These soils contained up to 0.8 g C as charcoal per 100 g of soil and up to 30% of the soil carbon as charcoal. Humic acid extractions performed on soil fractions before and after photo-oxidation suggest that charcoal or charcoal-derived material may also contribute significantly to the aromatic signals found in the n.m.r. spectra of humic acids. Finely divided charcoal appears to be a major constituent of many Australian soils and probably contributes significantly to the inert or passive organic carbon pool recognised in carbon turnover models.
Supramolecular chemistry has developed over the last forty years as chemistry beyond the molecule. Starting with the investigation of the basis of molecular recognition, it has explored the implementation of molecular information in the programming of chemical systems towards self-organisation processes, that may occur either on the basis of design or with selection of their components. Supramolecular entities are by nature constitutionally dynamic by virtue of the lability of non-covalent interactions. Importing such features into molecular chemistry, through the introduction of reversible bonds into molecules, leads to the emergence of a constitutional dynamic chemistry, covering both the molecular and supramolecular levels. It considers chemical objects and systems capable of responding to external solicitations by modification of their constitution through component exchange or reorganisation. It thus opens the way towards an adaptive and evolutive chemistry, a further step towards the chemistry of complex matter.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe General Nature of the Proportionality of Polar Effects of Substituent Groups in Organic ChemistryRobert W. Taft Jr.Cite this: J. Am. Chem. Soc. 1953, 75, 17, 4231–4238Publication Date (Print):September 1, 1953Publication History Published online1 May 2002Published inissue 1 September 1953https://pubs.acs.org/doi/10.1021/ja01113a027https://doi.org/10.1021/ja01113a027research-articleACS PublicationsRequest reuse permissionsArticle Views856Altmetric-Citations296LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Examination of nature's favorite molecules reveals a striking preference for making carbon-heteroatom bonds over carbon-carbon bonds-surely no surprise given that carbon dioxide is nature's starting material and that most reactions are performed in water. Nucleic acids, proteins, and polysaccharides are condensation polymers of small subunits stitched together by carbon-heteroatom bonds. Even the 35 or so building blocks from which these crucial molecules are made each contain, at most, six contiguous C-C bonds, except for the three aromatic amino acids. Taking our cue from nature's approach, we address here the development of a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries through heteroatom links (C-X-C), an approach we call "click chemistry". Click chemistry is at once defined, enabled, and constrained by a handful of nearly perfect "spring-loaded" reactions. The stringent criteria for a process to earn click chemistry status are described along with examples of the molecular frameworks that are easily made using this spartan, but powerful, synthetic strategy.
Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.
A number of heterogeneous reactions of atmospheric importance occur in thin water films on surfaces in the earth's boundary layer. It is therefore important to understand the interaction of water with various materials, both those used to study heterogeneous chemistry in laboratory systems, as well as those found in the atmosphere. We report here studies at 22 °C to characterize the interaction of water with such materials as a function of relative humidity from 0–100%. The surfaces studied include borosilicate glass, both untreated and after cleaning by three different methods (water, hydrogen peroxide and an argon plasma discharge), quartz, FEP Teflon film, a self assembled monolayer of n-octyltrichlorosilane (C8 SAM) on glass, halocarbon wax coatings prepared by two different methods, and several different types of Teflon coatings on solid substrates. Four types of measurements covering the range from the macroscopic level to the molecular scale were made: (1) contact angle measurements of water droplets on these surfaces to obtain macroscopic scale data on the water-surface interaction, (2) atomic force microscopy measurements to provide micron to sub-micron level data on the surface topography, (3) transmission FTIR of the surfaces in the presence of increasing water vapor concentrations to probe the interaction with the surface at a molecular level, and (4) X-ray photoelectron spectroscopy measurements of the elemental surface composition of the glass and quartz samples. Both borosilicate glass and the halocarbon wax coatings adsorbed significantly more water than the FEP Teflon film, which can be explained by a combination of the chemical nature of the surfaces and their physical topography. The C8 SAM, which is both hydrophobic and has a low surface roughness, takes up little water. The implications for the formation of thin water films on various surfaces in contact with the atmosphere, including building materials, soil, and vegetation, are discussed.
The 20th century can properly be called the age of organic chemistry. Coastal environments receive a variety of land‐derived organic inputs, both natural and synthetic. Among them, detergents are probably the largest class of technical products of domestic use. Detergent science has undergone revolutionary changes since its early beginnings in the 1930s. The dramatic increase in the production of detergents has completely altered our immediate human environment and has provided a wealth of new materials. Depending on the compositions of detergent molecules, they have transformed our natural environment both intentionally and unintentionally. Thus, during the last 2 decades, most of the published literature regarding detergent analysis has concentrated on the determination of low levels of surfactants and their metabolites in environmental materials. In order to study the nature, chemistry, and behavior of detergents in the aquatic environment, our goals in this paper concern two main parts. The first is to present a complete review of the chemical compositions of detergent molecules, including surfactants, builders, and additives, showing the different types available. The second goal is to provide a complete and comprehensive review of the analytical technqiues used for the determination of surfactants. These techniques involve volumetric, colorimetric, Chromatographic, electrophoretic, spectroscopic, and electrochemical methods.
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Alkaloids are an important class of natural products that are widely distributed in nature and produced by a large variety of organisms. They have a wide spectrum of biological activity and for many years were used in folk medicine. These days, alkaloids also have numerous applications in medicine as therapeutic agents. The importance of these natural products in inspiring drug discovery programs is proven and, therefore, their continued synthesis is of significant interest. The condensation discovered by Pictet and Spengler is the most important method for the synthesis of alkaloid scaffolds. The power of this synthesis method has been convincingly proven in the construction of stereochemicaly and structurally complex alkaloids.
Polymeric nanoparticles are promising delivery platforms for various biomedical applications. One of the main challenges toward the development of therapeutic nanoparticles is the premature disassembly and release of the encapsulated drug. Among the different strategies to enhance the kinetic stability of polymeric nanoparticles, shell- and core-crosslinking have been shown to provide robust character, while creating a suitable environment for encapsulation of a wide range of therapeutics, including hydrophilic, hydrophobic, metallic, and small and large biomolecules, with gating of their release as well. The versatility of shell- and core-crosslinked nanoparticles is driven from the ease by which the structures of the shell- and core-forming polymers and crosslinkers can be modified. In addition, postmodification with cell-recognition moieties, grafting of antibiofouling polymers, or chemical degradation of the core to yield nanocages allow the use of these robust nanostructures as "smart" nanocarriers. The building principles of these multifunctional nanoparticles borrow analogy from the synthesis, supramolecular assembly, stabilization, and dynamic activity of the naturally driven biological nanoparticles such as proteins, lipoproteins, and viruses. In this review, the chemistry involved during the buildup from small molecules to polymers to covalently stabilized nanoscopic objects is detailed, with contrast of the strategies of the supramolecular assembly of polymer building blocks followed by intramicellar stabilization into shell-, core-, or core-shell-crosslinked knedel-like nanoparticles versus polymerization of polymers into nanoscopic molecular brushes followed by further intramolecular covalent stabilization events. The rational design of shell-crosslinked knedel-like nanoparticles is then elaborated for therapeutic packaging and delivery, with emphasis on the polymer chemistry aspects to accomplish the synthesis of such nanoparticulate systems.
This article aims to review nature-inspired chemical sensors for enabling fast, relatively inexpensive, and minimally (or non-) invasive diagnostics and follow-up of the health conditions. It can be achieved via monitoring of biomarkers and volatile biomarkers, that are excreted from one or combination of body fluids (breath, sweat, saliva, urine, seminal fluid, nipple aspirate fluid, tears, stool, blood, interstitial fluid, and cerebrospinal fluid). The first part of the review gives an updated compilation of the biomarkers linked with specific sickness and/or sampling origin. The other part of the review provides a didactic examination of the concepts and approaches related to the emerging chemistries, sensing materials, and transduction techniques used for biomarker-based medical evaluations. The strengths and pitfalls of each approach are discussed and criticized. Future perspective with relation to the information and communication era is presented and discussed.
The title to a seminar presentation by I. C. Gunsalus in 1973 was Oxygen: An essential toxin, referring to the complex \nrole that atmospheric dioxygen has in biology. The relatively simple function as terminal oxidant for aerobic life was dramatically \naugmented by Osamu Hayaishi with his identification of an enzyme that catalyzes the conversion of catechol to muconic acid by \noxidative cleavage.1 He named this biological catalyst pyrocatechase, which proved to be the landmark discovery of an enzyme \nthat incorporated atmospheric dioxygen into the carbon chain of the substrate, thereby initiating cleavage of the benzene ring. \nThis review of the oxygenase cytochrome P450 is dedicated to Dr. Hayaishi and his pioneering discovery in what is now the 50th anniversary of his work!\n\nWe now realize that Nature has found many ways to utilize atmospheric dioxygen to functionalize molecules through the use of a diverse \nset of cofactors. Flavin, non−heme iron, copper, and metalloporphyrin complexes have all been conscripted to metabolize atmospheric \ndioxygen in an oxygenase catalytic cycle, resulting in the incorporation of one or both oxygen atoms into a substrate. This review focuses \non one of the heme−containing classes, termed cytochrome P450s and abbreviated CYP. Although but one member in the large group of \noxygenases, the cytochrome P450s play a variety of critical roles in biology.\n\nMany members of the cytochrome P450 superfamily of hemoproteins are currently known, and the numbers continue to grow as more genomes \nare sequenced. There are almost 4000 identified P450 genes at the date of this writing, and they are collected and annotated in a variety \nof web sites, such as that maintained by Nelson (http://drnelson. utmem.edu/CytochromeP450.html). The cytochrome P450s have been found in \nall branches of the tree of life that catalogs the diversity of life forms. In the broadest terms, there are two main functional roles for \nthese oxygenases. One is the metabolism of xenobiotics (compounds exogenous to the organism) as a protective role of degradation or provision \nof polar handles for solubilization in preparation for excretion. A second broad functional role is in the biosynthesis of critical signaling \nmolecules used for control of development and homeostasis. In mammalian tissues the P450s play these roles through the metabolism of drugs \nand xenobiotics and the synthesis of steroid hormones and fat−soluble vitamin metabolism and the conversion of polyunsaturated fatty \nacids to biologically active molecules, respectively. Similar roles are fulfilled in plants (hormone biosynthesis and herbicide degradation) \nand insects (control of development via hormone biosynthesis or provision of insecticide resistance). For instance, plants have an unusually \nlarge number of P450 genes. A reason is their sessile nature: for example, plants defend themselves through breakdown of herbicides by \ncatalyzing the synthesis of a large number of secondary metabolites or by synthesizing defense molecules such as DIMBOA.2,3 In addition, \nthe biosynthesis of critical metabolic regulators is also often carried out by the cytochrome P450s.\n\nThe important metabolic role together with the unique chemistry and physical properties of the cytochrome P450s provide a strong attraction \nfor scientists in many disciplines. Relevance to human health was the initial focus of pharmacologists and toxicologists. The role of metal \ncenters and their associated unique spectral properties in the cytochrome P450s is a magnet for bioinorganic chemists and biophysicists. The \ndifficult conversion of unactivated hydrocarbons attracted the bioorganic chemist. With the genome revolution and insights into the complex \nprocess of transcriptional and translational regulation, biochemists and molecular biologists found exciting problems in the study of CYPs.\n\nA continuing challenge is to understand how the diverse set of substrate specificities and metabolic transformations are determined by the \nprecise nature of the heme−iron oxygen and protein structure. The structure and electronic configuration of the active oxygen \nintermediates which serve as efficient catalysts remains an area of active research. Complicating this richness in metabolic potential \nis the importance of genetic differences, including single nucleotide polymorphisms, which can alter the physiological responses of the \ncytochrome P450s. Thus, over the past five−plus decades one has seen the evolution from a whole−organ and animal pharmacology \napproach to a quest for the molecular details necessary for precise understanding of structure and function of the P450 systems in \nmaintaining cellular homeostasis. The P450s are now recognized to occupy a great variety of phylogenetically distributed isoform \nactivities, and these variations in metabolic profile and substrate specificity are ultimately dictated by the bioinorganic chemistry \nof heme iron and oxygen as controlled by the protein environment.\n\nWith the elucidation of precise structures for many P450 hemoproteins as well as the application of varied biochemical and biophysical \nmethodologies, this diverse class of oxygenases is beginning to yield its secrets. Much remains to be learned, however, as many of the \nfundamental chemical entities and catalytic details, though perhaps described in textbooks, are in fact still poorly understood. The \nfocus of this review is to place the current knowledge base of cytochrome P450 structure−function in context with the general \naspects of metalloenzyme function. In 2006 Dr. Hayaishi, the founder of this broad field of oxygen metabolism, will celebrate an \nimportant birthday. Hopefully, in reading this review, he will be struck with the outstanding progress that has been realized with \nthis one particular oxygenase and at the same time perhaps provide some important suggestions as to pathways for solving the remaining problems.4\n\nCytochrome P450 has benefited from the attention of inorganic, organic, and physical chemists since its discovery due to its unique \nspectral properties as well as its ability to efficiently catalyze a variety of difficult biotransformations. With the discovery of \nP450 involvement in steroid biosynthesis in the 1970s, joined with its central function in drug metabolism, with its role in a variety \nof other pharmaceutical applications, P450 became one of the most intensively investigated biochemical systems. Multiple monographs, \nprinted conference proceedings, and thematic books have been published as well as special Methods in Enzymology volumes, only a few \nof which can be referenced here.5−12\n\nThe cytochrome P450s became most known for their efficiency in hydroxylation of unactivated alkanes as only a select few oxygenases \npossess the requisite active oxygen state. With equal efficacy, P450s can carry out a wide variety of biotransformations. The list \nin ref 13 includes more than 20 different chemical reactions. Some more unusual reactions catalyzed by P450 were recently reviewed by Guengerich.14\n\nThe mechanism of P450 is a complex cascade of individual steps involving the interaction of protein redox partners and consumption of \nreducing equivalents, most commonly in the form of NAD(P)H. It is somewhat humbling that the earliest versions of the enzymatic cycle \npublished over 30 years ago had much of the important steps characterized by physical and chemical methods.15 Continual refinement has \nled to more detailed versions and the direct observation and structural characterization of new adducts of iron and oxygen. The current \nversion contains eight intermediates, including highly transient caged radical pairs, and has been reviewed from various perspectives.11,12,16−19\n\nWhile the basic concepts central to P450 catalysis were appreciated by early 1970, notable progress in the detailed understanding of these \nmechanisms has been made in the past decade. This has been possible due to the accumulation of exciting data generated through application \nof a wide set of new methodologies, including systematic directed mutagenesis, high−resolution X−ray crystal structure \ndetermination, multiparametric spectroscopic characterization of intermediates, isolation of critical steps using cryogenic or fast \nkinetic techniques, and many excellent quantum chemical and molecular dynamics computational studies. The current view of the oxygen \nactivation mechanisms, catalyzed by metal centers in heme enzymes (as well as in non−heme enzymes, which lie outside the scope \nof this review), ensures one with a much better opportunity to see the common mechanistic picture than was possible earlier.20 \nSuccessful mechanistic studies of other heme enzymes which use different forms of so−called 'active oxygen \nintermediates', such as peroxidases,21,22 heme oxygenases (HO),23−25 catalases,26 nitric oxide synthases \n(NOS),27,28 peroxygenases,29,30 provide a vision of a highly diverse cofactor. Mechanistic insight from each of these various \nsystems has provided important complementary insight into cytochrome P450 mechanism. A fundamental question remaining is how the \nprotein controls efficient performance of such different functions using similar highly reactive heme−oxygen complexes. The \ncomparison of similar reactive intermediates in different enzymes helps to distinguish between the essential features of each of the \nenzymes and so provides additional clues to the revelation of the active role of the protein in heme−enzyme catalysis. The \nrecent progress in isolation and cryogenic stabilization of some of these intermediates makes possible direct spectroscopic and \nstructural studies of this type.\n\nAn exhaustive review of all achievements in oxygen activation chemistry is clearly difficult, even if the field is limited to \nthe processes directly relevant to P450 catalysis. Discussion of the P450 cat
Anion recognition plays a critical role in a range of biological processes, and a variety of receptors and carriers can be found throughout the natural world. Chemists working in the area of supramolecular chemistry have created a range of anion receptors, drawing inspiration from nature as well as their own inventive processes. This book traces the origins of anion recognition chemistry as a unique sub-field in supramolecular chemistry while illustrating the basic approaches currently being used to effect receptor design. The combination of biological overview and summary of current synthetic approaches provides a coverage that is both comprehensive and comprehensible. First, the authors detail the key design motifs that have been used to generate synthetic receptors and which are likely to provide the basis for further developments. They also highlight briefly some of the features that are present in naturally occurring anion recognition and transport systems and summarise the applications of anion recognition chemistry. Providing as it does a detailed review for practitioners in the field and a concise introduction to the topic for newcomers, Anion Receptor Chemistry reflects the current state of the art. Fully referenced and illustrated in colour, it is a welcome addition to the literature.