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Molecular Complexity (molecular + complexity)
Selected AbstractsTitelbild: Achieving Molecular Complexity by Organocatalytic One-Pot Strategies,A Fast Entry for Synthesis of Sphingoids, Amino Sugars, and Polyhydroxylated ,-Amino Acids (Angew. Chem.ANGEWANDTE CHEMIE, Issue 37 200937/2009) Wie ein Uhrwerk: Durch eine organokatalytische Reaktionskaskade mit chiraler Abgangsgruppe lassen sich komplexe Molekülstrukturen effizient aufbauen. K.,A. Jørgensen und Mitarbeiter beschreiben in ihrer Zuschrift auf S.,6976,ff. einen solchen Prozess mit natürlichem Vorbild, der zu 4,5-disubstituierten Isoxazolin- N -oxiden führte. Die Produkte sind vielseitige Bausteine für die De-novo-Synthese von Naturstoffen wie Ribophytosphingosin, Aminozuckern und hoch funktionalisierten ,-Aminosäure-Derivaten. [source] Achieving Molecular Complexity by Organocatalytic One-Pot Strategies,A Fast Entry for Synthesis of Sphingoids, Amino Sugars, and Polyhydroxylated ,-Amino Acids,ANGEWANDTE CHEMIE, Issue 37 2009Hao Jiang Einfach komplex: Eine neuartige organokatalytische Strategie mit chiralen Abgangsgruppen führt ausgehend von einfachen Startmaterialien schnell und effizient zu komplexen Molekülen. In einer organokatalytischen dreistufigen Eintopfreaktion wurden in hoher Ausbeute und Enantioselektivität 4,5-disubstituierte Isoxazolin- N -oxide erhalten, die Anwendung als vielseitige Bausteine für Naturstoffe fanden (siehe Schema). [source] ChemInform Abstract: Building Molecular Complexity via Tandem Ru-Catalyzed Isomerization/C,H Activation.CHEMINFORM, Issue 36 2009Agnieszka Bartoszewicz Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] The Domino Chemistry Approach to Molecular Complexity: High-Yielding Bis-hetero Intramolecular Diels,Alder Reactions with Ketone Components.CHEMINFORM, Issue 11 2007Angeline Chanu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Mild Protocols for Generating Molecular Complexity: A Comparative Study of Hetero-Domino Reactions Based on the Oxidant and the Substitution Pattern.CHEMINFORM, Issue 24 2005Jose I. Candela Lena Abstract For Abstract see ChemInform Abstract in Full Text. [source] Proteolytically Degradable Photo-Polymerized Hydrogels Made From PEG,Fibrinogen Adducts,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Daniel Dikovsky Abstract We develop a biomaterial based on protein,polymer conjugates where poly(ethylene glycol) (PEG) polymer chains are covalently linked to multiple thiols on denatured fibrinogen. We hypothesize that conjugation of large diacrylate-functionalized linear PEG chains to fibrinogen could govern the molecular architecture of the polymer network via a unique protein,polymer interaction. The hypothesis is explored using carefully designed shear rheometry and swelling experiments of the hydrogels and their precursor PEG/fibrinogen conjugate solutions. The physical properties of non-cross-linked and UV cross-linked PEGylated fibrinogen having PEG molecular weights ranging from 10 to 20,kDa are specifically investigated. Attaching multiple hydrophilic, functionalized PEG chains to the denatured fibrinogen solubilizes the denatured protein and enables a rapid free-radical polymerization cross-linking reaction in the hydrogel precursor solution. As expected, the conjugated protein-polymer macromolecular complexes act to mediate the interactions between radicals and unsaturated bonds during the free-radical polymerization reaction, when compared to control PEG hydrogels. Accordingly, the cross-linking kinetics and stiffness of the cross-linked hydrogel are highly influenced by the protein,polymer conjugate architecture and molecular entanglements arising from hydrophobic/hydrophilic interactions and steric hindrances. The proteolytic degradation products of the protein,polymer conjugates proves to be were different from those of the non-conjugated denatured protein degradation products, indicating that steric hindrances may alter the proteolytic susceptibility of the PEG,protein adduct. A more complete understanding of the molecular complexities associated with this type of protein-polymer conjugation can help to identify the full potential of a biomaterial that combines the advantages of synthetic polymers and bioactive proteins. [source] Proteolytic processing of the receptor-type protein tyrosine phosphatase PTPBR7FEBS JOURNAL, Issue 1 2007Gönül Dilaver The single-copy mouse gene Ptprr gives rise to different protein tyrosine phosphatase (PTP) isoforms in neuronal cells through the use of distinct promoters, alternative splicing, and multiple translation initiation sites. Here, we examined the array of post-translational modifications imposed on the PTPRR protein isoforms PTPBR7, PTP-SL, PTPPBS,42 and PTPPBS,37, which have distinct N-terminal segments and localize to different parts of the cell. All isoforms were found to be short-lived, constitutively phosphorylated proteins. In addition, the transmembrane isoform, PTPBR7, was subject to N-terminal proteolytic processing, in between amino acid position 136 and 137, resulting in an additional, 65-kDa transmembrane PTPRR isoform. Unlike for some other receptor-type PTPs, the proteolytically produced N-terminal ectodomain does not remain associated with this PTPRR-65. Shedding of PTPBR7-derived polypeptides at the cell surface further adds to the molecular complexity of PTPRR biology. [source] On the Scope of a Prins -Type Cyclization of Oxonium IonsHELVETICA CHIMICA ACTA, Issue 11 2004Georg Fráter The Prins cyclization of an aldehyde 1 with a homoallylic alcohol 2, affording tetrahydro-2H -pyrans 4via the oxonium ion 3 as central intermediate, was conceptually transferred to (alk-3-enyloxy)acrylates 6, which form a related oxonium ion 7 upon treatment with acids (Scheme,1). The scope and utility of this modification of the Prins -type cyclization of oxonium ions is discussed exemplarily by means of the syntheses of ten tetrahydro-2H -pyran and tetrahydrofuran derivatives, featuring diverse substitution patterns as well as different degrees of molecular complexity. These target structures include (±)-ethyl (2RS)-2-[(2RS,4SR,6RS)- and (2SR,4RS,6SR)-2-tetahydro-4-hydroxy-6-methylpyran-2-yl]propanoate (23), (±)-ethyl [(2RS, 3RS)-tetrahydro-3-isopropenylfuran-2-yl]acetate (32), (±)-ethyl (2Z)-3-(tetrahydro-2,2-dimethylfuran-3-yl)acrylate (37), (±)-(3aRS,6RS, 7aRS)-octahydro-7a-methylbenzofuran-6-yl formate (42), (±)-ethyl (2RS,3RS,4aRS,8SR,8aRS)-hexahydro-2,5,5,8-tetramethyl-7-oxo-2H,5H -pyrano[4,3- b]pyran-3-carboxylate (48), and (±)-ethyl (2RS,3RS,6SR)-tetrahydro-6-(2-methoxy-2-oxoethyl)-3-methyl-2H -pyran-2-carboxylate (53) (see Schemes,3 and 5,8). Besides the stereochemistry and mechanistic details of this versatile oxonium-ion cyclization, the synthesis of suitable starting materials is also described. [source] Polyphenylene-Based Materials: Control of the Electronic Function by Molecular and Supramolecular ComplexityADVANCED MATERIALS, Issue 10-11 2009Bruno Schmaltz Abstract Organic electronics is one of the hottest and most exciting research topics today. However, its performance still lags behind that of inorganic-based electronics. This Progress Report demonstrates that by controlling the complexity of organic molecules at the molecular and at the supramolecular level as well as by choosing suitable processing techniques, the desired function for applications in electronics can be achieved. Our main focus is on polyphenylene-based nanomaterials, versatile organic molecules that allow access to novel intricate materials. We emphasize the molecular complexity as well as the supramolecular organization and the interfacing of novel organic materials as key guidelines. [source] Trapping of Active Methylene Intermediates with Alkenes, Indoles or Thiols: Towards Highly Selective Multicomponent ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Yanlong Gu Abstract In this paper, a basic method to access new multicomponent reactions (MCRs) is reported. The mechanism of these MCRs is based on the trapping of methylene intermediates, formed in situ by reaction of formaldehyde with electron-rich carbons, with alkene, thiol or indole derivatives. According to our strategy, a wide range of valuable skeletons has been obtained in a one-pot reaction, thus allowing a minimization of waste, cost and labor. The presented methodology exhibits a broad substrate scope and electron-rich carbons in the ,-position of a hydroxy or carbonyl group were found to be particularly efficient. More generally, this work offers new tools for creating molecular complexity and diversity from one of the simplest organic building blocks, formaldehyde. [source] Synthesis of water-soluble near-infrared cyanine dyes functionalized with [(succinimido)oxy]carbonyl groupJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2003Lucjan Strekowski Two hetamethine cyanine dyes suitable for labeling of biomolecules at a primary amino group with a near-infrared chromophore/fluorophore (,max/(,em = 800/830 nm and 837/864 nm) have been synthesized from readily available starting materials. Despite the high molecular complexity of intermediate and final products, all these compounds have been obtained in an analytically pure form by using crystallization only. [source] Activation of large lons in FT-ICR mass spectrometryMASS SPECTROMETRY REVIEWS, Issue 2 2005Julia Laskin Abstract The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has enabled the extension of mass spectrometric methods to large molecules and molecular complexes. This both greatly extends the applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of these applications. This review emphasizes the most promising methods for activation and dissociation of complex ions and presents this discussion in the context of general knowledge of reaction kinetics and dynamics largely established for small ions. We then introduce the characteristic differences associated with the higher number of internal degrees of freedom and high density of states associated with molecular complexity. This is reflected primarily in the kinetics of unimolecular dissociation of complex ions, particularly their slow decay and the higher energy content required to induce decomposition,the kinetic shift (KS). The longer trapping time of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) significantly reduces the KS, which presents several advantages over other methods for the investigation of dissociation of complex molecules. After discussing general principles of reaction dynamics related to collisional activation of ions, we describe conventional ways to achieve single- and multiple-collision activation in FT-ICR MS. Sustained off-resonance irradiation (SORI),the simplest and most robust means of introducing the multiple collision activation process,is discussed in greatest detail. Details of implementation of this technique, required control of experimental parameters, limitations, and examples of very successful application of SORI-CID are described. The advantages of high mass resolving power and the ability to carry out several stages of mass selection and activation intrinsic to FT-ICR MS are demonstrated in several examples. Photodissociation of ions from small molecules can be effected using IR or UV/vis lasers and generally requires tuning lasers to specific wavelengths and/or utilizing high flux, multiphoton excitation to match energy levels in the ion. Photodissociation of complex ions is much easier to accomplish from the basic physics perspective. The quasi-continuum of vibrational states at room temperature makes it very easy to pump relatively large amounts of energy into complex ions and infrared multiphoton dissociation (IRMPD) is a powerful technique for characterizing large ions, particularly biologically relevant molecules. Since both SORI-CID and IRMPD are slow activation methods they have many common characteristics. They are also distinctly different because SORI-CID is intrinsically selective (only ions that have a cyclotron frequency close to the frequency of the excitation field are excited), whereas IRMPD is not (all ions that reside on the optical path of the laser are excited). There are advantages and disadvantages to each technique and in many applications they complement each other. In contrast with these slow activation methods, the less widely appreciated activation method of surface induced dissociation (SID) appears to offer unique advantages because excitation in SID occurs on a sub-picosecond time scale, instantaneously relative to the observation time of any mass spectrometer. Internal energy deposition is quite efficient and readily adjusted by altering the kinetic energy of the impacting ion. The shattering transition,instantaneous decomposition of the ion on the surface,observed at high collision energies enables access to dissociation channels that are not accessible using SORI-CID or IRMPD. Finally, we discuss some approaches for tailoring the surface to achieve particular aims in SID. © 2004 Wiley Periodicals, Inc., Mass Spec Rev 24:135,167, 2005 [source] Highly Efficient Access to Bi- and Tricyclic Ketals through Gold-Catalyzed Tandem Reactions of 4-Acyl-1,6-diynesCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2009Jia Meng Dr. Abstract Single step: Fused bicyclic and bridged tricyclic ketals were synthesized in a single step from the reactions of easily available 4-acyl-1,6-diynes with H2O and alkanols (see scheme). The highly efficient AuCl3 -catalyzed multicomponent domino reactions, involving five CO bond formations, can proceed in a highly regio- and diastereoselective manner at room temperature under air and lead to structures of high molecular complexity from simple starting materials in an atom economic way. [source] Proceedings of the Australian Physiological and Pharmacological Society Symposium: New Frontiers in Muscle Research Hybrid skeletal muscle fibres: a rare or common phenomenon?CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 8 2001Gabriela MM Stephenson SUMMARY 1. The main aim of the present review is to raise awareness of the molecular complexity of single skeletal muscle fibres from ,normal' and ,transforming' muscles, in recognition of the many types of hybrids that have been observed in vertebrate skeletal muscle. The data used to illustrate various points made in the review were taken from studies on mammalian (mostly rat) and amphibian muscles. 2. The review provides a brief overview of the pattern and extent of molecular heterogeneity in hybrid muscle fibres and of the methodological problems encountered when attempting to identify and characterize such fibres. Particular attention is given to four types of skeletal muscle hybrids: (i) myosin heavy chain (MHC) hybrids; (ii) mismatched MHC,myosin light chains (MLC) hybrids; (iii) mismatched MHC,regulatory protein hybrids; and (iv) hybrids containing mismatched MHC,sarcoplasmic reticulum protein isoforms. 3. Some of the current ideas regarding the functional significance, origin and cognitive value of hybrid fibres are examined critically. [source] | |||||||||||||||||||||||||