bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional genomics approach to the study of triterpene biosynthesis
Authors: Ebizuka Yutaka , Katsube Yuji , Tsutsumi T. , Kushiro Tetsuo , Shibuya M. 
Published: October 2007

Abstract
The Arabidopsis thaliana genome-sequencing project has identified the presence of 13 oxidosqualene cyclase homologs in this plant. In addition to the already identified clones, namely, CAS1 cycloartenol synthase, LUP1 lupeol synthase, and YUP8H12R.43 multifunctional triterpene synthase, two new cDNAs of the putative oxidosqualene cyclase genes, F1019.4 and T30F21.16, were obtained by polymerase chain reaction (PCR) and functionally expressed in yeast. Liquid chromatography/mass spectrometry (LC/MS) analysis led to the identification of some of their reaction products. Interestingly, except for CAS1 for sterol biosynthesis of primary metabolism, so-far-obtained all triterpene synthases of this plant are multifunctional, producing more than one cyclization product. A feeding experiment of 13C-labeled acetate with LUP1 lupeol synthase transformant demonstrated the stereospecific water addition to lupenyl cation intermediate, yielding 3β,20 dihydroxylupane, which accounts for the multiproduct nature of this synthase.
Mevalonate-independent methylerythritol phosphate pathway for isoprenoid biosynthesis. Elucidation and distribution
Authors: Rohmer M. 
Published: October 2007

Abstract
A long-overlooked metabolic pathway for isoprenoid biosynthesis, the mevalonate-independent methylerythritol phosphate (MEP) pathway, is present in many bacteria and in the chloroplasts of all phototrophic organisms. It represents an alternative to the well known mevalonate pathway, which is present in animals, fungi, plant cytoplasm, archaebacteria, and some eubacteria. This contribution summarizes key steps of its elucidation and the state-of-the-art knowledge of this biosynthetic pathway, which represents a novel target for antibacterial and antiparasitic drugs.
Biotransformation of triptonide by cell suspension cultures of Platycodon grandiflorum
Authors: Ning L. , Guo Hongzhu , Jiang Xiaomei , Bi Kaishun , Guo Dean 
Published: October 2007

Abstract
The biotransformation of triptonide by cell suspension cultures of Platycodon grandiflorum was investigated. After six days of incubation, five products were obtained. On the basis of chemical and spectral evidence, their structures were elucidated as epitriptolide-14-O-β-d-glucoside, 5α-hydroxytriptonide, triptolide, triptodiolide, and 2β-hydroxytriptonide, among which epitriptolide-14-O-β-d-glucoside and 5α-hydroxytriptonide are new compounds.
The deoxyxylulose phosphate pathway of isoprenoid biosynthesis. Discovery and function of the ispDEFGH genes and their cognate enzymes
Authors: Rohdich F. , Hecht Stefan , Bacher Adelbert , Eisenreich Wolfgang 
Published: October 2007

Abstract
Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) serve as the universal precursors for the biosynthesis of terpenes. Besides the well-known mevalonate pathway, a second biosynthetic pathway conducive to IPP and DMAPP via 1-deoxy-d-xylulose-5-phosphate and 2C-methyl-d-erythritol-4-phosphate has been discovered recently in plants and certain eubacteria. 2C-Methyl-d-erythritol-4-phosphate, the first committed intermediate of the deoxyxylulose phosphate pathway, is converted into 2C-methyl-d-erythritol 2,4-cyclodiphosphate by the catalytic action of three enzymes specified by the ispDEF genes. The cyclic diphosphate is reductively opened by the IspG protein affording 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate. This compound can be converted into IPP as well as DMAPP by the catalytic action of IspH protein. The enzymes of this pathway are potential targets for novel antibacterial, antimalarial, and herbicide agents.
Natural and totally synthetic receptors in the innovative design of HPLC chiral stationary phases
Authors: Gasparrini Francesco , D'Acquarica Ilaria , Misiti D. , Pierini M. , Villani C. 
Published: October 2007

Abstract
An overview is presented of the experimental results obtained by our group in the design, realization, and applications of high-performance liquid chromatography (HPLC) enantioselective stationary phases based on surface-linked macrocyclic receptors. Macrocyclic synthetic receptors and macrocyclic glycopeptide receptors have been grafted on silica particles, and the resulting chiral stationary phases are used to monitor differential associations of the enantiomers of selected chiral guests with the immobilized hosts. Practical implications of the chiral phases in enantioselective analysis and in the study of recognition events are highlighted.
Combination of enzymatic procedures with multicomponent condensations
Authors: Ostaszewski R. , Portlock D. E. , Fryszkowska Anna , Jeziorska Katarzyna 
Published: October 2007

Abstract
A new synthetic method based on combination of enzymatic desymmetrization of 3-phenylglutaric anhydrides with multicomponent condensation is outlined. Enzymatic monoesterification of glutaric anhydrides was performed, and the derived monoacids were used as substrates for subsequent Ugi and Passerini multicomponent condensations. Both reactions were combined as two-step, one-pot processes. The choice of solvent and enzyme type has an appreciable effect on the course of reactions.
Synthesis of coumarins by ring-closing metathesis
Authors: Chatterjee A. K. , Toste F. D. , Goldberg S. D. , Grubbs Robert H. 
Published: October 2007

Abstract
Investigations into olefin ring-closing metathesis (RCM) have led to a general method for the synthesis of coumarins. Catalysts with higher activity, such as the second-generation ruthenium catalyst, promote the intramolecular reaction between two-electron deficient olefins. This method allows for convenient access to a variety of coumarins substituted at both the 3- and 4-positions, as well as a tetrasubstituted example.
Bucky ferrocene. Hybrid of ferrocene and fullerene
Authors: Nakamura E. 
Published: October 2007

Abstract
The idea of “bucky ferrocene” intrigues chemists owing to its aesthetic beauty and to its polarized, extended conjugated system, but the idea has remained hypothetical. The synthesis of close analogs of Fe(C60Me5)Cp and Fe(C70Me3)Cp was achieved in two steps from [60] and [70]fullerenes, relying on an oxidative C–H bond activation starting with an iron(I) complex and the corresponding cyclopentadienyl precursors, respectively. The molecules can be regarded as members of a new organometallic conjugated system connected to a graphitic system. Numerous synthetic transformations and self-organization procedures that are known for the parent ferrocenes and fullerenes are expected to be employable toward productive use of the ferrocene/fullerene hybrid molecules in chemistry and materials sciences.
Carbenes. Pincers, chelates, and abnormal binding modes
Authors: Crabtree Robert H. 
Published: October 2007

Abstract
Routes to pincer and chelate carbene complexes of Pd, Rh, and Ir include double geminal CH activation, metallation, and CH activation. Abnormal binding via imidazole C5 can occur, and ion pairing can strongly influence C2 vs. C5 binding. Prior ligand binding via pyridine N before metallation is not essential. Computational methods are used extensively, for example, to compare N vs. C binding in imidazole. The possibility of C binding by histidine in metalloenzymes is discussed.
Challenging metal-based transformations. From single-bond activation to catalysis and metallaquinonoids
Authors: Milstein D. 
Published: October 2007

Abstract
Catalytic reactions resulting from our C–X (X = H, C, O, N, halide) bond activation studies are described. Aryl chlorides can react with aluminum alkyls in preference to bromides. Using PCP-type Pd catalysts, Heck reaction with aryl iodides and bromides can proceed without involvement of Pd(0). Ru-catalyzed oxidative coupling of arenes with alkenes using O2 was accomplished.
Using specifically designed systems, the scope and mechanisms of C–C activation in solution was studied and compared to C–H activation. C–C activation by Rh(I), Ir(I), Ni(II),Pt(II), Ru(II), and Os(II) was observed. Metal insertion into a strong C–C bond can be kinetically and thermodynamically more favorable than the competing C–H activation. Selective, single-step oxidative addition of a strong C–C bond to a metal was observed and kinetically evaluated. Catalytic C–C hydrogenolysis was demonstrated. A combination of C–C activation and C–R formation (R = aryl, silyl) resulted in unusual methylene transfer chemistry. Selective activation of aryl–O and Me–O bonds was observed. New types of interactions between metals and arenes and unusual quinonoid complexes, including quinone methides, xylylenes, methylene arenium, and a metallaquinone, were discovered. C–H and C–C agostic complexes of cationic metals, proposed as intermediates in bond activation, were isolated. Stabilization and controlled release of biologically relevant, extremely unstable, simple quinone methides, was accomplished.
Organometallic chemistry at the nanoscale. Dendrimers for redox processes and catalysis
Authors: Astruc D. 
Published: October 2007

Abstract
An overview of the metal-mediated synthesis and use of nanosized metallodendrimers is given with emphasis on electron-transfer processes (molecular batteries consisting in dendrimers decorated with a large number of equivalent redox-active centers) and catalytic reactions (electron-transfer-chain catalytic synthesis of dendrimers decorated with ruthenium carbonyl clusters, redox catalysis of nitrate and nitrite electroreduction in water by star-shape hexanuclear catalysts).
Strategies in the cyclopentadienyl chemistry of p-block elements
Authors: Jutzi P. 
Published: October 2007

Abstract
Synthetic strategies in the cyclopentadienyl (Cp) chemistry of the groups 13–15 elements, are based on the following phenomena: (1) low barriers for haptotropic and dyotropic shifts, for sigmatropic rearrangements, and for other types of Cp migration; (2) stabilization of elements in their low-oxidation state by π-complexation; (3) tuning of steric andelectronic effects by suitable ring substituents; and (4) easy homolytic and heterolytic cleavage of El-C(Cp) bonds. These strategies are applied to: (a) the formation of a Si2Me4 doubly bridged dicyclopentadienyl cobalt complex, (b) the chemistry of half-sandwich [Me5C5Ga] and sandwich [(Me5C5)2Si] complexes, (c) the formation of P6, (d) the deposition of Al, Ga, Si, Ge, and As from respective Cp-El precursor molecules, and (d) the “dynamic covalent chemistry” in ferrocenylgallium(III) compounds.
Critical evaluation of stability constants for alpha-hydroxycarboxylic acid complexes with protons and metal ions and the accompanying enthalpy changes. Part II. Aliphatic 2-hydroxycarboxylic acids (IUPAC Technical Report)
Authors: Portanova R. , Lajunen L. H. J. , Tolazzi M. , Piispanen J. 
Published: October 2007

Abstract
Stability constants for different aliphatic 2-hydroxycarboxylic acid complexes in aqueous solutions with protons and metal ions published between 1960 and the end of 1994 have been critically evaluated.
Light-powered molecular-scale machines
Authors: Balzani Vincenzo , Credi Alberto , Venturi M. 
Published: October 2007

Abstract
The macroscopic concepts of a machine can be extended to the molecular level. Molecular-level machines are constructed by the molecule-by-molecule bottom-up approach following the guidelines of supramolecular chemistry. Like macroscopic machines, molecular machines are characterized by (i) the kind of energy supplied to make them work, (ii) the kind of movement performed by their components, (iii) the way in which their operation can be controlled and monitored, (iv) the possibility to repeat the operation, (v) the time needed to complete a cycle of operation, and (vi) the function performed. The most convenient way to supply energy to a molecular machine is through photochemical energy inputs. Photochemical techniques offer, indeed, several advantages: (i) photons can make a machine work without formation of waste products, (ii) light can be switched on/off easily and rapidly, (iii) lasers provide the opportunity of working in very small space and very short time domains, (iv) photons can be used to “read” the state of the system and to monitor the operation of the machine. The extension of the concepts of a machine to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology.
New structurally interesting cyclopropane derivatives. A world of wonders and surprises
Authors: de Meijere Armin , Kozhushkov S. I. , Fokin A. A. , Emme I. , Redlich S. , Schreiner P. R. 
Published: October 2007

Abstract
The structurally intriguing [4]- and [5]triangulanes have been prepared in enantiomerically pure form. Their surprisingly high specific rotations are well reproduced by DFT/SCI computations and stem from the fact that these hydrocarbons essentially are σ-helicenes (i.e., rigidly held helical arrangements of σ-bonds). Some light is shed on the properties of radical cations derived from [3]- and [4]rotanes. While the former adopts Cs or C2v symmetry, the latter retains the D4h symmetry of the neutral hydrocarbon, according to highlevel computations. Experimental and computational evidence is also presented that the antiaromatic cyclopentadienyl cation is stabilized as a singlet ground state by five cyclopropyl substituents. Yet, the three cyclopropyl groups in tricyclopropylamine do not favor the formation of its radical cation, because they are not in the proper orientation. When this amine radical cation is generated by cobalt γ-irradiation in a Freon matrix, evidence for a significant conformational change is obtained by EPR spectroscopy. Finally, the conformational dynamics of the newly prepared crowded molecules tetracyclopropyl- and tetraisopropylmethane are discussed.
In control of switching, motion, and organization
Authors: Feringa Ben L. , van Delden R. A. , ter Wiel M. K. J. 
Published: October 2007

Abstract
Nature’s solutions to control organization, switching, and linear and rotary motion are not only extremely elegant, but fascinating if one considers the design and synthesis of artificial molecular systems with such functions in order to add components to the nanotoolbox. The synthesis of chiroptical molecular switches and their application in the control of the organization of liquid crystalline materials is outlined. The first light-driven unidirectional molecular motor is described, and the second-generation motor as well as approaches to control the speed of the rotary motion are discussed.
Catalytic control of electron-transfer processes
Authors: Fukuzumi Shunichi 
Published: October 2007

Abstract
Catalytic control of electron-transfer processes is described for a number of photoinduced and thermal electron-transfer reactions, including back electron transfer in the charge-separated state of artificial photosynthetic compounds. The intermolecular and intramolecular electron-transfer processes are accelerated by complexation of radical anions, produced in the electron transfer, with metal ions that act as Lewis acids. Quantitative measures to determine the Lewis acidity of a variety of metal ions are given in relation with the promoting effects of metal ions in the electron-transfer reactions. The mechanistic viability of metal ion catalysis in electron-transfer reactions is demonstrated by a variety of examples of both thermal and photochemical reactions that involve metal ion-promoted electron-transfer processes as the rate-determining steps, which are made possible to proceed by complexation of radical anions with metal ions.
Salt effects on the conformational behavior of 5-substituted 1,3-dioxanes
Authors: Juaristi Eusebio , Rosquete-Pina G. A. , Vázquez-Hernández M. , Mota A. J. 
Published: October 2007

Abstract
Since their introduction by E. L. Eliel nearly four decades ago, derivatives of 1,3-dioxane have proved useful in conformational analysis. Examples are discussed, where 5-polar substituents permit the evaluation of fundamental phenomena such as attractive and repulsive gauche effects, electrostatic interactions, and stereoelectronic effects. By the same token, 2-substituted 1,3-dioxanes, 1,3-dithianes, and 1,3-oxathianes are useful frameworks for the study of the anomeric effect and the associated structural and spectroscopic manifestations, such as the so-called Perlin effects. In view of the varied and essential involvement of metal ions and inorganic salts in biological processes, 5-substituted 1,3-dioxanes are presently being examined in the presence of Li+, Na+, K+, Ag+, Mg2+, Ca2+, Ba2+, and other cations, with the aim to increase the understanding of biomolecular properties in vivo.
Dynamic barriers and tunneling. New views of hydrogen transfer in enzyme reactions
Authors: Klinman J. P. 
Published: October 2007

Abstract
Hydrogen-transfer processes are expected to show appreciable quantum mechanical behavior. Intensive investigations of enzymes under their physiological conditions show this to be true in practically every example investigated. Initially, tunneling was treated either as a tunneling correction [cf. Bell, The Tunnel Effect in Chemistry, Chapman & Hall, New York, (l980)], or as corner-cutting [Truhlar et al., J. Chem. Phys. 100, 12771 (l996)]. This worked well as long as the observed properties could be explained by “corrections” to transition-state theory. However, over the past several years, enzymatic behaviors have been observed that are so deviant as to lie outside of transition-state theory. This phenomenon is discussed in the context of the enzyme, soybean lipoxygenase. An environmentally coupled hydrogen-tunneling model is presented that derives from the treatments of Kuznetsov and Ullstrup [Can. J. Chem. 77, 689 (l999)], and includes heavy-atom reorganization (temperature-dependent and largely isotope-independent), together with heavy-atom gating (temperature- and isotope-dependent). This treatment can explain a wide range of behaviors and leads to a new view of the origin of kinetic isotope effects in hydrogen-transfer reactions. These properties link enzyme fluctuations to the hydrogen-transfer reaction coordinate, making a quantum view of H-transfer necessarily a dynamic view of catalysis.
Toward replicatable, multifunctional, nanoscaffolded machines. A chemical manifesto
Authors: von Kiedrowski G. , Eckardt L.-H. , Naumann K. , Pankau W. M. , Reimold M. , Rein M. 
Published: October 2007

Abstract
Self-replicating nanorobots were foreseen in technological dreams and visions whose scientific ground found solid criticism from chemical and physical reasoning. If one, however, views such constructs as three-dimensionally defined noncovalent nanoscaffolding of a multitude of modular functions whose array is replicatable in a nonautonomous way, many pieces of technology needed for their implementation became recently available. Gold cluster-labeled molecules were remotely controlled by GHz radio frequency causing local and selective inductive heating, and monoconjugable thermostable gold clusters will become commercially available soon. Charged molecules were electrophoretically steered and manipulated on the surface of microelectrode array chips. Surface-promoted replication and exponential amplification of DNA analogs (SPREAD) may find particular applications for the cloning and copying of informational nanostructures on the surface of such chips. Synthetic trisoligonucleotidyl junctions were reported as covalent building blocks for noncovalent DNA nanostructures, and it was shown that kinetic control during noncovalent synthesis favors small and defined nanostructures instead of polymeric networks. Very recently, it was demonstrated that functionalized DNA nanoscaffolds with stiff tensegrity such as tetrahedra self-assemble from maximally instructed sets of 3- or [3+1]-arm junctions, and that the connectivity information in such nanoscaffolds can be copied. The implications of these developments are discussed with respect to a possible implementation scheme for the issue of the title.
Millimeter-scale self-assembly and its applications
Authors: Boncheva Mila , Bruzewicz D. A. , Whitesides G. M. 
Published: October 2007

Abstract
Self-assembly is a concept familiar to chemists. In the molecular and nanoscale regimes, it is often used as a strategy in fabricating regular 3D structures—that is, crystals. Self-assembly of components with sizes in the µm-to-mm range is less familiar to chemists; this type of self-assembly may, however, become technologically important in the future. In this size range, self-assembly offers methods to form regular 3D structures from components too small or too numerous to be manipulated by other means, and methods to incorporate function into these structures; it also offers simplicity and economy.
This paper focuses on the use of self-assembly to build functional systems of components with sizes in the range from microns to millimeters. It compares the principles of selfassembly at the molecular and millimeter scales, reviews the possible applications of mesoscale, self-assembled systems, and outlines some of the most important issues in the use of self-assembly to build functional systems.
Endocrine disruptors in the environment (IUPAC Technical Report)
Authors: Lintelmann J. , Katayama A. , Kurihara N. , Shore L. , Wenzel A. 
Published: October 2007

Abstract
Many chemical substances of natural or anthropogenic origin are suspected or known to be endocrine disruptors, which can influence the endocrine system of life. This observation has led to increased interest on the part of the public and the media, as well as to a steep rise of research activities in the scientific community. New papers and results are presented so fast that it is impossible to give a complete review of this emerging research field. Therefore, this paper tries to give insight into some topics of the great scope of endocrine disruptors in the environment. To get a general idea of the biochemical and biological background, some parts of the endocrine systems of mammalians and nonmammalians are explained. The sections that follow describe important mechanisms of endocrine disruption such as interactions with hormone receptors. Test strategies for anthropogenic chemicals on various organisms are critically reviewed with respect to their problems and gaps concerning endocrine disruptors. The main emphasis of the paper is on the chemical substances suspected or known to be endocrine disruptors. To get a better comprehension of their behavior in the environment, physicochemical data such as water solubility or Kow, as well as information about their use and/or function are reviewed and compared. The main routes of exposure for most chemicals are shortly described, and data about concentrations in the environment (soil/sediment, water) are detailed.
Molecular thermodynamics for some applications in biotechnology
Authors: Prausnitz J. M. 
Published: October 2007

Abstract
As biotechnology sweeps the world, it is appropriate to remember that the great virtue of thermodynamics is its broad range of applicability. As a result, there is a growing literature describing how chemical thermodynamics can be used to inform processes for old and new biochemical products for industry and medicine.A particular application of molecular thermodynamics concerns separation of aqueous proteins by selective precipitation. For this purpose, we need phase diagrams; for constructing such diagrams, we need to understand not only the qualitative nature of phase equilibria of aqueous proteins, but also the quantitative intermolecular forces between proteins in solution. Some examples are given to show how aqueous protein-protein forces can be calculated or measured to yield a potential of mean force and how that potential is then used along with a statistical-thermodynamic model to establish liquid -liquid and liquid -crystal equilibria. Such equilibria are useful not only for separation processes, but also for understanding diseases like Alzheimer’s, eye cataracts, and sickle-cell anemia that appear to be caused by protein agglomeration.