bluuebunny/crossref_metadata_2025_split huggingface dataset:
From an Insecticide to Plato's Universe—The Pagodane Route to Dodecahedranes: New Pathways and New Perspectives
Authors: Prinzbach Horst , Weber Klaus 
Published: December 2003

AbstractThe original concept for the synthesis of pentagonal dodecahedranes by the conversion of structurally similar, high‐energy [1.1.1.1]pagodanes relied on catalytic dehydrocyclizations. As a consequence, preparative limitations were preprogrammed. With multiple functionalization of these pagodanes, alternative cyclization methods became viable. These efficient processes allowed access to a multitude of pentagonal and nonpentagonal, carba‐ and heterocyclic dodecahedral skeletons with widely variable substitution patterns. Such a roundabout route provided the (CH)20 basic framework with high efficiency, and long‐lacking thermochemical data could be ascertained calorimetrically. In spite of the unusually pronounced pyramidalization of their olefinic centers, singly and doubly unsaturated dodecahedranes with isolated CC bonds proved to be kinetically quite stable, but underwent dimerization on thermal activation. Dodecahedranes with a higher degree of unsaturation (trienes–decaenes, C20 fullerene?) have been found so far only in the gas phase. Higher fullerenes, including C60, have been identified by mass spectrometry after exposure of halogenated dodecahedranes and pagodanes to a 248‐nm excimer laser. Transannular electron delocalization has been verified for the “slender” pagodane/isopagodane and even for the “spherical” dodecahedrane cages.
100 Years “Schlüssel‐Schloss‐Prinzip”: What Made Emil Fischer Use this Analogy?
Authors: Lichtenthaler Frieder W. 
Published: December 2003

AbstractEmil Fischer's famous lock‐and‐key analogy (Schlüssel‐Schloss‐Prinzip) for the specifity of enzyme action has provided successive generations of scientists with a mental picture of molecular recognition processes, and thus has shaped to a marked degree the development not only of organic chemistry, but, through its extension to basic live processes, that of biology and medicine as well. The hundredth anniversary of the first use of this most fertile metaphor provides a welcome opportunity not only for highlighting its paramount importance, but for gaining an understanding and appreciation of the creative processes involved, of the constructive reasoning and the thought patterns underlying the fundamental insight. Accordingly, this account attempts to trace how Fischer was led to the lock‐and‐key analogy, based on the state of knowledge and the views prevailing at the time. It reveals that Fischer, who had a pronounced tendency against any sort of theoretical speculation, refrained from taking this metaphor any further, that is to the obvious extensions of what turns the key, and what kind of doors are then opened. Except for a small refinement–the differentiation of main key and special keys to account for the fact that some yeasts can ferment a larger number of hexoses than others—he rather expounded on the scope of the lock‐and‐key picture: “I am far from placing this hypothesis side by side to the established theories of our science, and readily admit, that it can only be thoroughly tested, when we are able to isolate the enzymes in a pure state and thus investigate their configuration.” Others, most notably P. Ehrlich und F. Lillie, by introduction of the concept of stereocomplementarity into medicine and biology, induced the lock‐and‐key analogy to become something of a dogma for explaining principal life processes.
Fine Feathers Make Fine Birds: The Heck Reaction in Modern Garb
Authors: de Meijere Armin , Meyer Frank E. 
Published: December 2003

AbstractThe palladium‐catalyzed coupling of haloarenes and haloalkenes with alkenes, which was discovered by Richard F. Heck in the late sixties, has been a topic of fluctuating interest; however, in the last six years activity in this area has flourished. Careful choice of substrates and skillful tailoring of reaction conditions lead to impressive sequences consisting of even different reaction types that occur not only in a consecutive mode, but also in a single operation. The wellestablished Heck reaction, together with other mechanistically related palladiumcatalyzed transformations with arene, alkene, and alkyne derivatives, opens the door to a tremendous variety of elegant and highly convergent routes to structurally complex molecules. The reaction is not disturbed by heteroatoms such as oxygen and nitrogen (nor by sulfur and phosphorus with some limitations). The spectrum of recent achievements starts with a range of chemoselective and regioselective monocouplings of highly functionalized substrates with unsymmetrical and multisubstituted reaction partners. Other advances include cascade reactions in which three, four, five, and even eight new CC bonds are formed to yield oligofunctional and oligocyclic products with impressive molecular complexity. Even the enantioselective construction of complex natural products with quaternary stereocenters has been achieved with Heck reactions in key steps, as exemplified by the synthesis of crinan, picrotoxinin, and morphine. Today, the Heck reaction is indispensible in the arsenal of synthetic methods available to organic chemists. Certainly it is only a matter of time before the Heck reaction is applied in industrial syntheses.
Enzymes in Organic Synthesis: Application to the Problems of Carbohydrate Recognition (Part 1)
Authors: Wong Chi‐Huey , Halcomb Randall L. , Ichikawa Yoshitaka , Kajimoto Tetsuya 
Published: December 2003

AbstractCarbohydrates on cell surfaces are information molecules. Although only seven or eight monosaccharides are commonly used as building blocks in mammalian systems, the multifunctionality of these monomers can lead to the assembly of an immense variety of complex structures. Millions of different tetrasaccharide structures, for example, can be constructed from this small number of building blocks, if branching, the stereochemistry of glycosidic linkages, and the modification of hydroxyl and amino groups are taken into consideration. Oligosaccharides therefore represent an effective class of biomolecules that code for a vast amount of information required in various biological recognition processes, such as intercellular communication, signal transduction, cell adhesion, infection, cell differentiation, development and metastasis. The pace of development of pharmaceuticals based on carbohydrates has, however, been slower than that based on other classes of biomolecules. Part of the reason is the lack of technologies for the study of complex carbohydrates. There is no method to amplify oligosaccharides for sequence analysis. There is no machine available for automated synthesis of oligosaccharides. In addition, the possibly poor bioavailability and difficulties in the large‐scale synthesis of carbohydrates have undoubtedly contributed to this slow pace. The enzymatic and chemoenzymatic methods, especially those based on aldolases and glycosyltransferases, described here appear to be useful for the synthesis of mono‐ and oligosaccaharides and related molecules. Further advances in glycobiology will probably lead to the development of new technologies for the study of carbohydrate recognition and for the synthesis of bioactive carbohydrates and mimetics to control the recognition processes.
Enzymes in Organic Synthesis: Application to the Problems of Carbohydrate Recognition (Part 2)
Authors: Wong Chi‐Huey , Halcomb Randall L. , Ichikawa Yoshitaka , Kajimoto Tetsuya 
Published: December 2003

AbstractRecognition of carbohydrates by proteins and nucleic acids is highly specific, but the dissociation constants are relatively high (generally in the mM to high μM range) because of the lack of hydrophobic groups in the carbohydrates. The high specificity of this weak binding often comes from many hydrogen bonds and the coordination of metal ions as bridge between sugars and receptors. Though weak hydrophobic interactions between sugars and proteins have also been identified, the unique shape of a complex carbohydrate under the influence of anomeric and exo anomeric effects (the glycosidic torsion angles are therefore often not flexible but are typically somewhat restricted) and the topographic orientation of the hydroxyl and charged groups contribute most significantly to the recognition process. Studies on the structure–function relationship of a complex carbohydrate therefore require deliberate manipulation of its shape and functional groups, and synthesis of oligosaccharide analogs from modified monosaccharides is often useful to address the problem. The availability of various monosaccharides and their analogs for the synthesis of complex carbohydrates together with the information resulting from structural studies (such a NMR or X‐ray studies on sugar–protein complexes) will certainly provide a basic understanding of complex carbohydrate recognition. An ultimate goal is to develop simple and easy‐to‐make non‐carbohydrate molecules that resemble the active structure involved in carbohydrate–receptor interaction or the transition‐state of an enzyme‐catalyzed transformation (for example, glycosidase or glycosyltransferase reactions) and have the approprite bioavailability to be used to control the carbohydrate function in a specific manner. In part one of this review we described various enzymatic approaches to the synthesis of monosaccharides, analogs, and related structures. We describe in this part enzymatic and chemoenzymatic approaches to the synthesis of oligosaccarides and analogs, including those involved in E‐selectin recognition, and strategies to inhibit glycosidases and glycosyltransferases.
Biosynthesis of Vitamin B1 (Thiamin): An Instance of Biochemical Diversity
Authors: Spenser Ian D. , White Robert L. 
Published: December 2003

AbstractThe elucidation of the biosynthetic pathway to thiamin (Vitamin B1) and its pyrophosphate ester, the important coenzyme “cocarboxylase”, has challenged researchers for many years and continues to do so. The problem of the origin of thiamin can be separated into three parts: the independent pathways to the pyrimidine moiety 4‐amino‐5‐hy‐droxymethyl‐2‐methylpyrimidine and to the thiazole moiety 5‐(2‐hydroxyethyl)‐4‐methylthiazole, and the route from these subunits to the vitamin. The steps in the latter process were fully established some twenty years ago, and it was shown that the route in aerobic bacteria and yeast differs to some extent from that in enteric bacteria. The pathways to the subunits, on the other hand, are still not clarified. Significant differences exist in the routes whereby each of the two subunits, the pyrimidine moiety and the thiazole moiety, originate in bacteria and yeast. One difficulty that delayed progress was that the incorporation patterns of labeled precursors, which were observed by different research groups in different microorganisms, could not be reconciled on the basis of a single pathway to each of the two subunits. It is now accepted that in each case different pathways exist in enteric bacteria and yeast, and that the biosynthesis of Vitamin B1 represents an instance of biochemical diversity. A second factor that added to the difficulties is the minute amount of thiamin synthesized in microbiological cultures (about 15 μg per L culture). This limited the investigations until very recently either to the use of radioactive tracers or to the use of stable isotopes in conjunction with mass spectrometric analysis. It is widely recognized that both methods are associated with pitfalls in the interpretation of results. High‐field 13C NMR, the most powerful modern method available for the determination of incorporation patterns, has only very recently been successfully employed in investigations of thiamin biosynthesis. As a result of the conceptual and experimental problems, even the primary precursors of each of the two relatively simple heterocyclic subunits of thiamin are still not completely established. A search for committed intermediates, the study of the enzymes, and identification of the genes that are involved are the matter of current research.
The Covalent Chemistry of Higher Fullerenes: C70 and Beyond
Authors: Thilgen Carlo , Herrmann Andreas , Diederich François 
Published: December 2003

AbstractAlthough higher fullerenes are not yet available in larger amounts, their accessibility, like that of C60, has gradually improved since the early days of fullerence chemistry. Today, many of the soluble larger carben can be purchased either in pure form or as isomeric mixtures. In particular, pure C70 is available in preparative amounts from fullerene soot without the need for tedious separation by high‐performance liquid chromatography; this has had a major impact on the progress of the chemistry of this higher fullerene. Over the last years C70 has been functionalized in many ways, and pure derivatives of even the larger, more complex carbon spheres C76, C84, and recently also C78, have been isolated and characterized. From the collected body of data, first general principles of reactivity and selectivity begin to emerge for these fullerenes, which are all less symmetric than C60. Important information is provided by multiple additions to higher fullerenes, in which certain isomers are formed with a remarkable selectivity that exceedes that observed for C60. A particularly attractive aspect is the chirality of certain allotropes and many derivatives. Although the chirality of fullerene derivatives is not restricted to the larger carbon cages, it was sofar mostly explored through their chemistry and can be related to different structural characteristics. A recently proposed system allows simple specification by a single descriptor of the configuration of chiral fullerenes and fullerene derivatives with a chiral functionalization pattern, including highly branched carbon frameworks with a multitude of possible stereogenic centers.
Understanding Reactivity Patterns of Radical Cations
Authors: Schmittel Michael , Burghart Armin 
Published: December 2003

AbstractOver the last 15 years electron transfer activation has emerged as a valuable concept for accomplishing novel reactions and has found widespread application in the selective transformation of increasingly complex molecules. This review presents in a conceptualized manner the vast number of radical cation reactions obtained after chemical, electrochemical, and photoinduced one‐electron oxidation. To familiarize the reader with the concepts of electron transfer a simple and straightforward classification of radical cation reactions has been devised to allow the presentation of a manifold of reactions in a readily understandable manner. Whenever possible, thermochemical and kinetic data are provided.
Altered course of the right testicular artery
Authors: Özdemir M. Bülent , Çelik H. Hamdi , Aldur M. Mustafa 
Published: December 2003

AbstractAn unusual course of the right testicular artery was observed during routine dissection of the posterior abdominal wall of a 60‐year‐old male cadaver. It arose from the abdominal aorta, inferior and posterior to the origin of the right renal artery, and passed posterior to the inferior vena cava and right renal vein; it then arched anterior to the inferior pole of the right kidney and descended anterior to the psoas major muscle, crossing anterior to the genitofemoral nerve, ureter and the proximal part of the external iliac artery. Finally, it passed to the deep inguinal ring and through the inguinal canal to enter the spermatic cord with the other constituents. The left testicular artery arose from the abdominal aorta about 1 cm higher than the right testicular artery and followed a normal course. The embryologic basis and clinical importance of this case are discussed. Clin. Anat. 17:67–69, 2004. © 2003 Wiley‐Liss, Inc.
Micro‐venous valves in the superficial veins of the human lower limb
Authors: Phillips M.N. , Jones G.T. , van Rij A.M. , Zhang M. 
Published: December 2003

AbstractIt is commonly believed that venous valves are not present in veins smaller than 2 mm in diameter. Venous valves, however, have been identified recently in small veins in several regions of the body. This study was undertaken to determine the size distribution of venous valves in the human lower limb micro‐venous circulation. Vascular casts were made from six adult lower limbs and the sampled areas were viewed by scanning electron microscopy. In total, 2,376 valves were identified from 410 cm3 of subcutaneous tissue. The vast majority (94%) of the valves were in veins less than 300 μm in luminal diameter, with 65% of the valves present in venous channels less than 100 μm in luminal diameter. The smallest valves identified were present in venous channels 18 μm in diameter. All valves were bicuspid and often associated with a tributary. Endothelial cells on the vein wall not associated with a valve were fusiform and arranged parallel to the long axis of the vessel, however, the endothelial cells on the luminal and valve sinus surfaces of the cusp were more polyhedral in shape and showed no obvious pattern of alignment. This study provides direct evidence to show that small superficial veins of the human lower limb do contain abundant venous valves and, for the first time, shows that the majority of these valves are present within venous channels less than 100 μm in luminal diameter. Clin. Anat. 17:55–60, 2004. © 2003 Wiley‐Liss, Inc.
Main trunk of the left coronary artery: Anatomic study of the parameters of clinical interest
Authors: Reig J. , Petit M. 
Published: December 2003

AbstractThe objective of this study was to analyze in one single series all the characteristics of the main trunk of the left coronary artery (MT) that may be of use in the diagnosis and treatment of its pathologies. One‐hundred human hearts from autopsies were used. The average age of the sample studied was 63.15 years ± 18.76 (range = 17–94 years). The heart was removed after resection of the costosternum and placed in 10% formaldehyde. With gradual separation and retraction of the myocardial fasciculi the MT was exposed. The length of the MT, the luminal diameter of the MT at its midpoint, and the luminal diameter of the left coronary orifice were measured with a caliper. The angle of division between the anterior interventricular and circumflex branches was also measured, and the number of terminal branches originating from the MT was recorded. In four cases, there was no MT and the anterior interventricular and circumflex branches originated directly from the left aortic sinus. The average length of the MT was 10.8 ± 5.52 mm (range = 2–23 mm); the average diameter at its midpoint was 4.86 ± 0.80 mm; and there was no significant difference noted between the midpoint diameter of the MT and the diameter of the left coronary orifice. The most frequent type of division of the MT was bifurcation (62%); in 38% of cases the MT divided into three or more branches. An average value of 86.7 ± 28.8° was obtained for the angle of division of the terminal branches of the MT (range = 40–165°). There was a positive correlation between the length of the MT and the angle of division of its terminal branches, with the longest MTs having the largest angle of division. Clin. Anat. 17:6–13, 2004. © 2003 Wiley‐Liss, Inc.
Neonatal behaviors associated with ultrasonic vocalizations in mice (mus musculus): A slow‐motion analysis
Authors: Branchi Igor , Santucci Daniela , Puopolo Maria , Alleva Enrico 
Published: December 2003

AbstractInfant rodents emit ultrasonic vocalizations (USVs) when isolated from the mother and littermates. While USVs reportedly promote maternal behavior, their communicatory role is still controversial. We performed a detailed behavioral characterization in 7‐day‐old CD‐1 Swiss mice to describe (a) behavioral patterns accompanying or immediately preceding or following the USV and (b) how selected USV features are modulated according to the behavioral pattern being performed. The present results represent an ethogram of mouse pup behavior in close temporal proximity to USV, providing further information to evaluate the functional role of USVs in the framework of the mother–offspring relationship. A significant increase of head rising behavior immediately prior to the USV and a behavioral activation displayed by pups in conjunction with it suggest that pups behave in a way that may favor interaction with their mothers. © 2003 Wiley Periodicals, Inc. Dev Psychobiol 44: 37–44, 2004.
Comparative psychology, a new perspective for the 21st century: Up the spiral staircase
Authors: Greenberg Gary , Partridge Ty , Weiss Emily , Pisula Wojciech 
Published: December 2003

AbstractThis article responds to the continuing obituaries for Comparative Psychology. We understand the field to be ageneralpsychology, a way of understanding the origins of all behavior of all species. We outline a methodological and conceptual foundation for comparative psychology to enter the new millennium—with an anagenetic and dynamic systems perspective. We see an important role to be played by comparative psychologists in managing resources, increasing our activity in social and political issues, and transcending our traditional role as the study of animal behavior to one that makes significant contributions to psychology and humanity by studying relationships between animals and changing environments, and by providing a historical perspective on human evolution. © 2003 Wiley Periodicals, Inc. Dev Psychobiol 44: 1–15, 2004.
Diet quality differentially affects breeding effort of Mastomys coucha and M. natalensis: Implications for rodent pests
Authors: Jackson Timothy P. , Van Aarde Rudi J. 
Published: December 2003

AbstractIn this study we compare the reproductive ability of Mastomys natalensis, an agricultural rodent pest and that of the closely related species M. coucha, which has not been ascribed as a pest. We suggest that the ability of M. natalensis to plague, as well as dominate, resource‐limited habitats, may in part be related to its differential breeding response to variation in diet quality. Thus, we examined the reproductive response of M. coucha and M. natalensis mothers to variation in dietary protein intake. Our results demonstrated that typical levels of reproduction extended over a narrower range of dietary protein content for M. coucha than M. natalensis females. Only M. natalensis females bred on 6% protein diets, while on 20% protein diets the reproductive output of M. coucha was lower than on diets containing 10– and 15% protein. M. natalensis responded to low protein diets by reducing litter size and litter mass but not individual pup mass. Thus, providing diet quality improves before parturition, conception under sub‐optimal conditions may not compromise individual pup growth. Furthermore, the ability of M. natalensis to breed under conditions of low diet quality may advance their breeding season compared to species that cannot breed until diet quality improves, allowing M. natalensis to produce additional litters through the season, while more daughters could reproduce during the season of their birth, both factors that are known to contribute to the plaguing tendency of M. natalensis. J. Exp. Zool. 301A:97–108, 2004. © 2004 Wiley‐Liss, Inc.
The labour market effects of globalization in Kenya
Authors: Manda Damiano Kulundu , Sen Kunal 
Published: December 2003

AbstractSince the 1980s, Kenya has been gradually integrating with the global economy. Using both industry‐level and firm‐level data, the paper examines the effects of globalization on employment and earnings in the Kenyan manufacturing sector. The industry‐level analysis suggests that the overall effect of international trade on manufacturing employment has been negative in the 1990s. The firm‐level analysis indicates that less skilled workers experienced losses in earnings, and that the inequality in earnings between skilled and unskilled workers increased during this period. This suggests that globalization has been associated with adverse labour market outcomes in Kenya. Copyright © 2004 John Wiley & Sons, Ltd.