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Macromolecular Structures (macromolecular + structure)
Selected AbstractsDe-icing: recovery of diffraction intensities in the presence of ice ringsACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010Michael S. Chapman Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality. [source] Application of molecular replacement to protein powder data from image platesACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Jennifer A. Doebbler Macromolecular structures can be solved via molecular replacement from powder diffraction data collected not only on multi-analyzer diffractometers but also on image plates. Diffraction peaks recorded on image plates are generally broader than those collected using an array of crystal analyzer detectors, but the image-plate data often allow the use of powder data to lower d -spacings. Owing to the high incidence of overlaps in powder patterns, which is especially evident for larger structures, a multi-pattern Pawley refinement is necessary in order to distinguish intensity peaks. This work utilized various salt concentrations to produce small lattice distortions, which resulted in shifts of Bragg peak positions, in a suite of five powder patterns. Using reflection structure factors obtained from this combined refinement, the structure of hen egg-white lysozyme was determined by molecular replacement using the 60% identical human lysozyme (PDB code 1lz1) as the search model. This work also expands upon previous work by presenting a full-scale multi-species analysis combined with an investigation of the sensitivity with regard to discrimination between incorrect fold types. To test the limits of this technique, extension to higher molecular-weight structures is ongoing. [source] Surface-Grafted Gel-Brush/Metal Nanoparticle HybridsADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Edmondo M. Benetti Abstract Polymer brushes are classically defined and are to date employed as assemblies of macromolecules tethered at one end to a surface. The concept of preparing surface-grafted gels by crosslinking such brushes is attractive since it gives rise to new opportunities related to the constraints present in this type of structure. Aiming at the development of nanostructured films possessing precisely adjustable chemical, mechanical, and optical properties, the present article describes the preparation of novel grafted layers based on gel-brush/metal nanoparticle hybrids. These films were synthesized by surface-initiated atom transfer radical polymerization of hydroxyethyl methacrylate with a small percentage of a crosslinker. The swelling, morphological, and mechanical properties of the gel-brushes are shown to be highly dependent on the relative amount of crosslinker used. The gel-brushes are subsequently used as matrixes for the controlled synthesis of silver nanoparticles with overall characteristics that are specifically tunable as a function of the macromolecular structure of the brush template. [source] AAA+ superfamily ATPases: common structure,diverse functionGENES TO CELLS, Issue 7 2001Teru Ogura The AAA+ superfamily of ATPases, which contain a homologous ATPase module, are found in all kingdoms of living organisms where they participate in diverse cellular processes including membrane fusion, proteolysis and DNA replication. Recent structural studies have revealed that they usually form ring-shaped oligomers, which are crucial for their ATPase activities and mechanisms of action. These ring-shaped oligomeric complexes are versatile in their mode of action, which collectively seem to involve some form of disruption of molecular or macromolecular structure; unfolding of proteins, disassembly of protein complexes, unwinding of DNA, or alteration of the state of DNA,protein complexes. Thus, the AAA+ proteins represent a novel type of molecular chaperone. Comparative analyses have also revealed significant similarities and differences in structure and molecular mechanism between AAA+ ATPases and other ring-shaped ATPases. [source] Collective Optical Behavior of Cationic Water-Soluble Dendrimers,ADVANCED MATERIALS, Issue 23-24 2004S. Wang Water-soluble dendrimers containing cationic charges and optically active units on the periphery of the macromolecular structure have been designed. Collective optical behavior of the chromophores on the surface was demonstrated by fluorescence quenching and energy-transfer experiments. These water-soluble dendrimers can be used for optically amplified DNA detection (see Figure) in homogeneous media. [source] Synthesis and crystallization behavior of acetal copolymer/silica nanocomposite by in situ cationic ring-opening copolymerization of trioxane and 1,3-dioxolaneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Lanhui Sun Abstract The acetal copolymer/silica nanocomposite was prepared by in situ bulk cationic copolymerization of trioxane and 1,3-dioxolane in the presence of nanosilica. The crystallization behavior of acetal copolymer/silica nanocomposite was studied by AFM, DSC, XRD, and CPOM, and the macromolecular structure of acetal copolymer/silica nanocomposite was characterized by FTIR and 1H-NMR. The 1H-NMR results showed that the macromolecular chain of acetal copolymer had more than two consecutive 1,3-dioxolane units in an oxymethylene main chain, while that of acetal copolymer/silica nanocomposite had only one 1,3-dioxolane unit in an oxymethylene main chain. There existed interaction between the macromolecular chains and nanoparticles (such as hydrogen bonds and coordination). On one hand, nanoparticles acted as nucleation center, which accelerated the crystallization rate but reduced the crystallinity. The spherulite sizes also decreased with addition of nanoparticles attributed to the nucleation effect. On the other hand, the presence of nanoparticles interrupted the spherical symmetry of the crystallite. In conclusion, the high surface energy and small scale of nanoparticles have a prominent impact on the polymerization mechanism and crystallization behavior of nanocomposite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Neuromelanin selectively induces apoptosis in dopaminergic SH-SY5Y cells by deglutathionylation in mitochondria: involvement of the protein and melanin componentJOURNAL OF NEUROCHEMISTRY, Issue 6 2008Makoto Naoi Abstract Parkinson's disease (PD) is characterized by selective depletion of nigral dopamine (DA) neurons containing neuromelanin (NM), suggesting the involvement of NM in the pathogenesis. This study reports induction of apoptosis by NM in SH-SY5Y cells, whereas protease-K-treated NM, synthesized DA- and cysteinyl dopamine melanin showed much less cytotoxicity. Cell death was mediated by mitochondria-mediated apoptotic pathway, namely collapse of mitochondrial membrane potential, release of cytochrome c, and activation of caspase 3, but Bcl-2 over-expression did not suppress apoptosis. NM increased sulfhydryl content in mitochondria, and a major part of it was identified as GSH, whereas dopamine melanin significantly reduced sulfhydryl levels. Western blot analysis for protein-bound GSH demonstrated that only NM reduced S -glutathionylated proteins in mitochondria and dissociated macromolecular structure of complex I. Reactive oxygen and nitrogen species were required for the deglutathionylation by NM, which antioxidants reduced significantly with prevention of apoptosis. These results suggest that NM may be related to cell death of DA neurons in PD and aging through regulation of mitochondrial redox state and S -glutathionylation, for which NM-associated protein is absolutely required. The novel function of NM is discussed in relation to the pathogenesis of PD. [source] Molecular and isotopic indicators of alteration in CR chondritesMETEORITICS & PLANETARY SCIENCE, Issue 9 2006V. K. Pearson However, in contrast to other chondrite groups, the CR organic fraction is poorly characterized. The carbonaceous chondrite literature shows that relatively anhydrous thermal processing results in a condensed, poorly alkylated, O-poor macromolecular material, while for aqueous processing the converse is true. Such characteristics can be used to discern the alteration histories of the carbonaceous chondrites. We have performed bulk elemental and isotopic analysis and flash pyrolysis on four CR chondrites (Renazzo, Al Rais, Elephant Moraine [EET] 87770, and Yamato [Y-] 790112) to determine the nature of their organic component. Renazzo, Al Rais, and Y-790112 release qualitatively similar pyrolysis products, although there are some variations. Al Rais' macromolecular structure contains substantially higher relative abundances of alkylated and oxidized species and relatively lighter ,15N, suggesting that it has endured more extensive aqueous processing than the other CR chondrites. Renazzo appears relatively unprocessed, with a low degree of alkylation, a lack of detectable nitrogen-bearing components, and low methylnaphthalene ratio. EET 87770's low abundance of alkylated species suggests its macromolecular structure may be relatively condensed, with condensation potentially assisted by a period of mild thermal alteration. [source] Inclusion of weak high-resolution X-ray data for improvement of a group II intron structureACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2010Jimin Wang It is common to report the resolution of a macromolecular structure with the highest resolution shell having an averaged I/,(I) , 2. Data beyond the resolution thus defined are weak and often poorly measured. The exclusion of these weak data may improve the apparent statistics and also leads to claims of lower resolutions that give some leniency in the acceptable quality of refined models. However, the inclusion of these data can provide additional strong constraints on atomic models during structure refinement and thus help to correct errors in the original models, as has recently been demonstrated for a protein structure. Here, an improved group II intron structure is reported arising from the inclusion of these data, which helped to define more accurate solvent models for density modification during experimental phasing steps. With the improved resolution and accuracy of the experimental phases, extensive revisions were made to the original models such that the correct tertiary interactions of the group II intron that are essential for understanding the chemistry of this ribozyme could be described. [source] Enhancing MAD FA data for substructure determinationACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2010Hongliang Xu Heavy-atom substructure determination is a critical step in phasing an unknown macromolecular structure. Dual-space (Shake-and-Bake) recycling is a very effective procedure for locating the substructure (heavy) atoms using FA data estimated from multiple-wavelength anomalous diffraction. However, the estimated FA are susceptible to the accumulation of errors in the individual intensity measurements at several wavelengths and from inaccurate estimation of the anomalous atomic scattering corrections f, and f,,. In this paper, a new statistical and computational procedure which merges multiple FA estimates into an averaged data set is used to further improve the quality of the estimated anomalous amplitudes. The results of 18 Se-atom substructure determinations provide convincing evidence in favor of using such a procedure to locate anomalous scatterers. [source] UROX 2.0: an interactive tool for fitting atomic models into electron-microscopy reconstructionsACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2009Xavier Siebert Electron microscopy of a macromolecular structure can lead to three-dimensional reconstructions with resolutions that are typically in the 30,10,Å range and sometimes even beyond 10,Å. Fitting atomic models of the individual components of the macromolecular structure (e.g. those obtained by X-ray crystallography or nuclear magnetic resonance) into an electron-microscopy map allows the interpretation of the latter at near-atomic resolution, providing insight into the interactions between the components. Graphical software is presented that was designed for the interactive fitting and refinement of atomic models into electron-microscopy reconstructions. Several characteristics enable it to be applied over a wide range of cases and resolutions. Firstly, calculations are performed in reciprocal space, which results in fast algorithms. This allows the entire reconstruction (or at least a sizeable portion of it) to be used by taking into account the symmetry of the reconstruction both in the calculations and in the graphical display. Secondly, atomic models can be placed graphically in the map while the correlation between the model-based electron density and the electron-microscopy reconstruction is computed and displayed in real time. The positions and orientations of the models are refined by a least-squares minimization. Thirdly, normal-mode calculations can be used to simulate conformational changes between the atomic model of an individual component and its corresponding density within a macromolecular complex determined by electron microscopy. These features are illustrated using three practical cases with different symmetries and resolutions. The software, together with examples and user instructions, is available free of charge at http://mem.ibs.fr/UROX/. [source] On vital aid: the why, what and how of validationACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2009Gerard J. Kleywegt Limitations to the data and subjectivity in the structure-determination process may cause errors in macromolecular crystal structures. Appropriate validation techniques may be used to reveal problems in structures, ideally before they are analysed, published or deposited. Additionally, such techniques may be used a posteriori to assess the (relative) merits of a model by potential users. Weak validation methods and statistics assess how well a model reproduces the information that was used in its construction (i.e. experimental data and prior knowledge). Strong methods and statistics, on the other hand, test how well a model predicts data or information that were not used in the structure-determination process. These may be data that were excluded from the process on purpose, general knowledge about macromolecular structure, information about the biological role and biochemical activity of the molecule under study or its mutants or complexes and predictions that are based on the model and that can be tested experimentally. [source] Computer programming and biomolecular structure studies: A step beyond internet bioinformaticsBIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION, Issue 1 2006Vladimir A. Liki Abstract This article describes the experience of teaching structural bioinformatics to third year undergraduate students in a subject titled Biomolecular Structure and Bioinformatics. Students were introduced to computer programming and used this knowledge in a practical application as an alternative to the well established Internet bioinformatics approach that relies on access to the Internet and biological databases. This was an ambitious approach considering that the students mostly had a biological background. There were also time constraints of eight lectures in total and two accompanying practical sessions. The main challenge was that students had to be introduced to computer programming from a beginner level and in a short time provided with enough knowledge to independently solve a simple bioinformatics problem. This was accomplished with a problem directly relevant to the rest of the subject, concerned with the structure-function relationships and experimental techniques for the determination of macromolecular structure. [source] Nanostructured Organic,Inorganic Composite Materials by Twin Polymerization of Hybrid MonomersADVANCED MATERIALS, Issue 20 2009Stefan Spange Abstract Forming two structurally different but associated polymer structures in a single step is a possible route for the production of nanostructured materials. By means of twin polymerization of specially constructed monomers consisting of two different covalently bonded building blocks (hybrid monomers), this route is realized. What is important is that two different macromolecular structures are formed from one monomer in a single process. The two polymers formed can be linear, branched, or cross-linked structures. The molecular composition of the hybrid monomer defines the degree of cross-linking of the corresponding macromolecular structures that is theoretically possible. [source] CRUNCH: a phase refinement program for high-resolution macromolecular structuresJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2000David A. Langs A phase refinement program for high-resolution macromolecular structures is described. The mean phase error of an initial structural solution can often be as large as 60° prior to attempting a refinement, but the CRUNCH program procedure may allow one to reduce this phase error to 10 or 20° for all data prior to actually inspecting any map to see how well it may fit a structural model. The procedure is similar to the real/reciprocal space refinement loop incorporated in the half-baked algorithm described by Sheldrick [Sheldrick & Gould (1995). Acta Cryst. B51, 423,431.] Refinement results are presented for nine different structures which diffract to better than 1.2,Å resolution. The program and test data are available via anonymous ftp (nexus.hwi.buffalo.edu). [source] Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structuresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008Michiya Fujiki Abstract Strong chemical forces such as covalent and ionic bonds are responsible for building discrete molecules, nature dwells on noncovalent forces weaker by three orders in magnitude, like the hydrophobic effect, hydrogen bonding, and van der Waals forces. Despite being weak, they possess the potential to drive spontaneous folding or unfolding of proteins and nucleic acids and the recognition between complimentary molecular surfaces. The power of these forces lies in the cooperativity with which they act, thereby generating a cumulative effect of many bonding interactions occurring together. Many ongoing research aims to translate the potential of these forces to the synthetic world to create desired structures with specific chemical functions. Achieving this offers unlimited opportunities for designing and synthesizing the most complex structures with specific applications. This highlight aims to reflect the critical role these noncovalent forces play in controlling macromolecular structures, which hold immense untapped potential for applications defying conventions, and briefly touches on the concept of homochirality in nature based on chiral and weak noncovalent interactions in synthetic nonpolar Si-catenated polymers. It sheds some light on the discovery and characterization of Si/F-C interactions in fluoroalkylated polysilanes in chemosensing of fluoride ions and nitroaromatics with a great sensitivity and selectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4637,4650, 2008 [source] Synthesis and photophysical behavior of a water-soluble coumarin-bearing polymer for proton and Ni2+ ion sensingPOLYMER INTERNATIONAL, Issue 6 2009Bao-Yan Wang Abstract BACKGROUND: In recent years, many fluorescent chemosensors with various macromolecular structures have been prepared for the detection of protons or metal cations in the environment. Most of this research is focused on polymer sensors with fluorescent recognition sites in the main chain. In this case, the fluorescent recognition sites are covalently bonded to the polymer chain, and thus the polymer shows photophysical properties as a chemosensor for protons and metal ions. RESULTS: An acrylic monomer bearing coumarin moieties, 7-hydroxy-4-methyl-8-(4,-acryloylpiperazin-1,-yl)methylcoumarin, was synthesized. This was then copolymerized with N -vinylpyrrolidone to obtain a blue fluorescent material. The fluorescent copolymer has good solubility in aqueous solution. Its main photophysical properties were determined in relation to its use as a sensor for protons and metal cations. It is an efficient ,off-on' switcher for pH between 3.02 and 12.08. Additionally, the polymer sensor is selective to Ni2+ ions, with the increase in the fluorescence intensity depending on Ni2+ ion concentrations in the range 0.33 × 10,5,7.67 × 10,5 mol L,1. CONCLUSION: The results suggest that this copolymer may offer potential as a reusable polymer sensor for protons and Ni2+ ions in aqueous solution. Copyright © 2009 Society of Chemical Industry [source] How to multiply a matrix of normal equations by an arbitrary vector using FFTACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2008Boris V. Strokopytov This paper describes a novel algorithm for multiplying a matrix of normal equations by an arbitrary real vector using the fast Fourier transform technique. The algorithm allows full-matrix least-squares refinement of macromolecular structures without explicit calculation of the normal matrix. The resulting equations have been implemented in a new computer program, FMLSQ. A preliminary version of the program has been tested on several protein structures. The consequences for crystallographic refinement of macromolecules are discussed in detail. [source] Cryoprotection properties of salts of organic acids: a case study for a tetragonal crystal of HEW lysozymeACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Grzegorz Bujacz Currently, the great majority of the data that are used for solving macromolecular structures by X-ray crystallography are collected at cryogenic temperatures. Selection of a suitable cryoprotectant, which ensures crystal stability at low temperatures, is critical for the success of a particular diffraction experiment. The effectiveness of salts of organic acids as potential cryoprotective agents is presented in the following work. Sodium formate, acetate, malonate and citrate were tested, as were sodium potassium tartrate and acetate in the form of potassium and ammonium salts. For each salt investigated, the minimal concentration that was required for successful cryoprotection was determined over the pH range 4.5,9.5. The cryoprotective ability of these organic salts depends upon the number of carboxylic groups; the lowest concentration required for cryoprotection was observed at neutral pH. Case-study experiments conducted using the tetragonal form of hen egg-white lysozyme (HEWL) confirmed that salts of organic acids can successfully act as cryoprotective agents of protein crystals grown from high concentrations of inorganic salts. When crystals are grown from solutions containing a sufficient concentration of organic acid salts no additional cryoprotection is needed as the crystals can safely be frozen directly from the crystallizing buffers. [source] Selenium incorporation using recombinant techniquesACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2010Helen Walden Using selenomethionine to phase macromolecular structures is common practice in structure determination, along with the use of selenocysteine. Selenium is consequently the most commonly used heavy atom for MAD. In addition to the well established recombinant techniques for the incorporation of selenium in prokaryal expression systems, there have been recent advances in selenium labelling in eukaryal expression, which will be discussed. Tips and things to consider for the purification and crystallization of seleno-labelled proteins are also included. [source] The magic triangle goes MAD: experimental phasing with a bromine derivativeACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2010Tobias Beck Experimental phasing is an essential technique for the solution of macromolecular structures. Since many heavy-atom ion soaks suffer from nonspecific binding, a novel class of compounds has been developed that combines heavy atoms with functional groups for binding to proteins. The phasing tool 5-amino-2,4,6-tribromoisophthalic acid (B3C) contains three functional groups (two carboxylate groups and one amino group) that interact with proteins via hydrogen bonds. Three Br atoms suitable for anomalous dispersion phasing are arranged in an equilateral triangle and are thus readily identified in the heavy-atom substructure. B3C was incorporated into proteinase K and a multiwavelength anomalous dispersion (MAD) experiment at the Br,K edge was successfully carried out. Radiation damage to the bromine,carbon bond was investigated. A comparison with the phasing tool I3C that contains three I atoms for single-wavelength anomalous dispersion (SAD) phasing was also carried out. [source] Model-building strategies for low-resolution X-ray crystallographic dataACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2009Anjum M. Karmali The interpretation of low-resolution X-ray crystallographic data proves to be challenging even for the most experienced crystallographer. Ambiguity in the electron-density map makes main-chain tracing and side-chain assignment difficult. However, the number of structures solved at resolutions poorer than 3.5,Å is growing rapidly and the structures are often of high biological interest and importance. Here, the challenges faced in electron-density interpretation, the strategies that have been employed to overcome them and developments to automate the process are reviewed. The methods employed in model generation from electron microscopy, which share many of the same challenges in providing high-confidence models of macromolecular structures and assemblies, are also considered. [source] PURY: a database of geometric restraints of hetero compounds for refinement in complexes with macromolecular structuresACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2008Miha Andreja The number and variety of macromolecular structures in complex with `hetero' ligands is growing. The need for rapid delivery of correct geometric parameters for their refinement, which is often crucial for understanding the biological relevance of the structure, is growing correspondingly. The current standard for describing protein structures is the Engh,Huber parameter set. It is an expert data set resulting from selection and analysis of the crystal structures gathered in the Cambridge Structural Database (CSD). Clearly, such a manual approach cannot be applied to the vast and ever-growing number of chemical compounds. Therefore, a database, named PURY, of geometric parameters of chemical compounds has been developed, together with a server that accesses it. PURY is a compilation of the whole CSD. It contains lists of atom classes and bonds connecting them, as well as angle, chirality, planarity and conformation parameters. The current compilation is based on CSD 5.28 and contains 1978 atom classes and 32,702 bonding, 237,068 angle, 201,860 dihedral and 64,193 improper geometric restraints. Analysis has confirmed that the restraints from the PURY database are suitable for use in macromolecular crystal structure refinement and should be of value to the crystallographic community. The database can be accessed through the web server http://pury.ijs.si/, which creates topology and parameter files from deposited coordinates in suitable forms for the refinement programs MAIN, CNS and REFMAC. In the near future, the server will move to the CSD website http://pury.ccdc.cam.ac.uk/. [source] BALBES: a molecular-replacement pipelineACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2008Fei Long The number of macromolecular structures solved and deposited in the Protein Data Bank (PDB) is higher than 40,000. Using this information in macromolecular crystallography (MX) should in principle increase the efficiency of MX structure solution. This paper describes a molecular-replacement pipeline, BALBES, that makes extensive use of this repository. It uses a reorganized database taken from the PDB with multimeric as well as domain organization. A system manager written in Python controls the workflow of the process. Testing the current version of the pipeline using entries from the PDB has shown that this approach has huge potential and that around 75% of structures can be solved automatically without user intervention. [source] Gd-HPDO3A, a complex to obtain high-phasing-power heavy-atom derivatives for SAD and MAD experiments: results with tetragonal hen egg-white lysozymeACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2002Éric Girard A neutral gadolinium complex, Gd-HPDO3A, is shown to be a good candidate to use to obtain heavy-atom derivatives and solve macromolecular structures using anomalous dispersion. Tetragonal crystals of a gadolinium derivative of hen egg-white lysozyme were obtained by co-crystallization using different concentrations of the complex. Diffraction data from three derivative crystals (100, 50 and 10,mM) were collected to a resolution of 1.7,Å using Cu,K, radiation from a rotating anode. Two strong binding sites of the gadolinium complex to the protein were located from the gadolinium anomalous signal in both the 100 and 50,mM derivatives. A single site is occupied in the 10,mM derivative. Phasing using the anomalous signal at a single wavelength (SAD method) leads to an electron-density map of high quality. The structure of the 100,mM derivative has been refined. Two molecules of the gadolinium complex are close together. Both molecules are located close to tryptophan residues. Four chloride ions were found. The exceptional quality of the SAD electron-density map, only enhanced by solvent flattening, suggests that single-wavelength anomalous scattering with the Gd-HPDO3A complex may be sufficient to solve protein structures of high molecular weight by synchrotron-radiation experiments, if not by laboratory experiments. [source] Validation of macromolecular structures: updating standards for publication of NMR structures in an IUCr journalACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 2 2008Howard Einspahr First page of article [source] Large Di- and Heptafullerene Polyelectrolytes Composed of C60 Building Blocks Having a Highly Symmetrical Hexakisaddition PatternCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2009Patrick Witte Dr. Abstract We report here on the synthesis of three new prototypes (types,I,III) of very large fullerene-based polyelectrolytes which can carry up to 60 charges on their periphery. All fullerene moieties incorporated in these macromolecular structures have an octahedral hexakisaddition pattern. Dumbbell-shaped icosacarboxylate 5 (type,I), which can accumulate up to twenty negative charges, is very soluble in methanol as well as in neutral and basic water. On the other hand, Janus dumbbell 13 (type,II) contains both positively and negatively chargeable fullerene building blocks and is very soluble in acidic and basic media. However, in the region of the isoelectric point at pH,6.0,6.5 it precipitates as a pale orange solid due to pronounced intermolecular Coulomb interactions. Giant heptafullerene 15 (type,III) can store up to 60 positive charges in its periphery and is the largest molecular polyelectrolyte with defined three-dimensional structure. [source] | |||||||||||||||||||