Crystal structure, morphology and crystallization kinetics of melt-crystallized polypropylene and poly(propylene-stat-ethylene) fractions with 2.7 to 11.0 mol% of ethylene were studied by differential scanning calorimeter, wide- and small-angle X-ray scattering, polarized light microscopy, transmission electron microscopy and infrared spectroscopy. With increasing ethylene content the poly(propylene-stat-ethylene) fractions showed unchanged crystallinity, increased unit cell volume and constant crystal thickness in combination with a shortened helix length. This indicated that a fraction of ethylene defects were incorporated into the crystal structure. During the isothermal crystallization both α- and γ-crystals could be formed. The γ-crystal fraction increased with increasing ethylene content and increasing crystallization temperature. For samples with α- and γ-crystal contents, multimodal melting was observed and a noticeable γ- to α-crystal conversion was observed on slow heating. The spherulitic structure of the copolymers was coarser than that for the homopolymer. The crystalline lamellae in copolymers exhibited profound curvature in contrast to the straighter cross-hatched α-crystals typical to the homopolymer. Area dependence of electrical breakdown strength was studied for thin polypropylene homopolymer films. The measurements were performed with an automatic measurement system equipped with a scanning electrode arm. Five different electrodes having areas between 0.045 cm2 and 9.3 cm2 were used and typically 40-80 breakdowns per sample and electrode area were collected. All measurements were performed on dry samples in air at room temperature. The data was analyzed statistically and the Weibull function parameters α and β, the first one related to 63% probability for the sample to break down and the second one to the width of the distribution were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. criteria for the automatic detection of the breakdowns, effect of electrode edge design, partial discharges, DC ramp speed and humidity were critically analyzed. It was concluded that the obtained α-parameter values were stable and repeatable over several years of time. The β-parameter values, however, varied ± 10-30%, more for the large than the small electrodes, and were also sensitive to the changes both in the sample itself and in the measurement conditions. Breakdown strengths of over 50 capacitor grade polypropylene films were analyzed. The obtained α-parameter values were between 450 and 850 V/μm, depending on the film grade and electrode area. In addition to the high breakdown strengths, reflected by the obtained α-values, another, sparse distribution consisting of low breakdown strengths was revealed when the amount of measurement points was high enough. This means that more than one Weibull distribution could be needed to describe the breakdown strength behavior of a polypropylene film. Breakdown values showed decreasing area dependence with decreasing electrode area. Breakdown strengths for larger sample areas were predicted from the small area data by area- and Weibull extrapolation. The area extrapolation led to predicted α-values 50% higher than measured at 4 m2 whereas the Weibull extrapolation showed an accuracy of ±15 % when predicted and measured values were compared. Breakdown strengths were also extrapolated for film areas similar to those in impregnated power capacitors. It turned out that the power capacitors, tested at the factory, performed much better than predicted by the extrapolation. However, a few weak spots with very low breakdown values were also found. For the poly(ethyelene terephtalate) dielectric, which is not swelled by the impregnation liquid, the large area breakdown strength was predictable. This indicates that for polypropylene film processing and impregnation led, in addition to the improved large area breakdown performance, also to sparse weak spots with low breakdown probabilities. Different Weibull distributions were responsible for the breakdown strengths for the processed and impregnated polypropylene than for the dry film samples. / QC 20101027

HIV-1 protease is the most effective target for drugs to treat AIDS, however, the long-term therapeutic efficiency is restricted by the rapid development of drug resistant variants. To better understand the molecular basis of drug resistance, crystallographic and kinetic studies were applied to wild-type HIV-1 protease (PR) and drug-resistant mutants, PRV82A, and PRI84V, in complex with substrate analogues, the current drug saquinavir and the new inhibitor UIC-94017 (TMC-114). UIC-94017 was also studied with mutants PRD30N and PRI50V. The drug-resistant mutations V82A, I84V, D30N and I50V participate in substrate binding. Eighteen crystal structures were refined at resolutions of 0.97-1.60A. The high accuracy of the atomic resolution crystal structures helps understand the reaction mechanism of HIV-1 PR. Different binding modes are observed for different types of inhibitors. The substrate analogs have more extended interactions with PR subsites up to S5-S5', while the clinical inhibitors maximize the contacts within S2-S2'. Hydrophobic interactions are the major force for saquinavir binding since it was designed with enhanced hydrophobic groups based on substrate side-chains. In contrast, the new clinical inhibitor UIC-94017 was designed to mimic the hydrogen bonds between substrates and PR. UIC-94017 forms polar interactions with the PR main-chain atoms of Asp29/30, which have been proposed to be critical for its potency against resistant HIV. The mutants showed different structural and kinetic effects, depending on the inhibitor and location of the mutations. The observed structural changes were consistent with the relative inhibition data. Both PRI84V and PRI50V lost favorable hydrophobic interactions with inhibitor compared with PR. Similarly, in PRD30N the UIC-94017 had a water-mediated interaction with the side-chain of Asn30 rather than the direct interaction observed in PR. However, PRV82A compensated for the mutation by shifts of the backbone of Ala82. Furthermore, the complexes of PRV82A showed smaller shifts relative to PR, but more movement of the peptide analog, compared to complexes with clinical inhibitors. The structures suggest that substrate analogs have more flexibility than the drugs to accommodate the structural changes caused by mutation, which may explain how HIV can develop drug resistance while retaining the ability of PR to hydrolyze natural substrates.

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No description available.

The main focus of this work is the preparation, chemical and structural characterization along with the investigation of physical properties of intermetallic clathrates. Starting from the history of clathrate research, classification of clathrate types, their structural properties and possible application areas are evaluated in chapter 2. The methodologies of sample preparation and materials characterization as well as quantum chemical calculations are discussed in chapter 3. The complete characterization of Ba8Ge433 ( is a Schottky-symbol standing for vacancies),12-14 which is a parent compound for the variety of ternary variants, is the subject of chapter 4. Ba8Ge433 is a high temperature phase,12 which was prepared for the first time as single phase bulk material in this work.15, 16 In this way, the intrinsic transport properties could be investigated without influence of grain boundary and impurity effects. The transport behavior is analyzed at low and high temperatures and referred to the former results. In addition, crystal structure and vacancy ordering in terms of the reaction conditions are discussed. Chemical bonding in Ba8Ge433 is investigated by topological analysis of the electron localizability indicator and the electron density. Chapter 5 deals with the preparation, phase analysis, crystal structure and physical properties of BaGe5, which constitutes a new clathrate type oP60.17, 18 So far, two clathrate types were known in the binary system Ba – Ge, namely the clathrate cP124 Ba6Ge25,19-21 and the clathrate-I Ba8Ge433. Originally, BaGe5 was detected by optical and scanning electron microscopy within the grains of Ba8Ge433.12 Once the preparation of phase-pure Ba8Ge433 was achieved, it became possible to make detailed investigations of its decomposition along with the formation of BaGe5. A detailed theoretical and experimental analysis on the relation between crystal structure and physical properties of BaGe5 is presented. In chapter 6, a thorough structural characterization and the physical properties of clathrates in the system Ba – Ni – Ge is presented based on the subtle relation between the crystal structure containing vacancies and the thermoelectric properties. During the investigations in this system, a large single crystal was grown by Nguyen et al. 22, 23 from the melt with the composition Ba8Ni3.5Ge42.10.4. A systematic reinvestigation of the phase relations in this system was performed and the influence of different Ni content to the crystal structure and physical properties is evaluated. The Si-based ternary clathrate with composition Ba8–δNixySi46–x–y is the subject of chapter 7. The phase relations and the homogeneity range are established. The crystal structure taking into account vacancies in the framework is discussed. Physical properties of bulk pieces are analyzed and the results are related to the sample composition. In addition, first-principles electronic structure calculations are carried out to assess variations in the electronic band structure, phase stability and chemical bonding.24 Chapter 8 reports on the intermetallic compound Ba3Si4,25, 26 which was encountered during the investigations on the Ba – Ni – Si phase diagram. The discussion covers issues related to preparation, crystal structure, phase diagram analysis, electrical and magnetic properties, NMR measurements, quantum mechanical calculations and oxidation to nanoporous silicon with gaseous HCl. Besides my contributions to the NoE CMA, I studied under the Priority Program 1178 of Deutsche Forschungsgemeinschaft “Experimental electron density as the key for understanding chemical interactions” with the project of “Charge distribution changes by external electric fields: investigations of bond selective redistributions of valence electron densities”. Chapter 9 deals with the preparation of chalcopyrites ZnSiP2 and CuAlS2 for experimental charge density analysis. Both phases show semiconducting properties and have non-centrosymmetric structures with high space group symmetry as needed to investigate the structural changes induced by external electric field. In this chapter, I describe the preparation and the crystal structure analyses of ZnSiP2 and CuAlS2 including issues related to the data collection as well as the results of NMR investigation.

The SUMO protein was named Small Ubiquitin-like MOdifier because its 3-D structure was similar to Ubiquitin. In human, three SUMO proteins were discovered, namely, SUMO-1/2/3. The recombinant ¡µ1-8, 94-95 SUMO-2 protein with 10 histidine residues at its N-terminus was expressed using E. coli. BL-21(DE3), purified at 4 oC and crystallized at room temperature. The surface properties of human SUMO-1/2/3 proteins and 3-D structure of ¡µ1-8, 94-95 SUMO-2 protein were analyzed using computer modeling and X-ray diffraction technology respectively. The two-step purification by immobilized metal ion affinity chromatography(IMAC) was developed to yield ¡µ1-8, 94-95 SUMO-2 protein that reached 60 mg/ml for crystallization. On protein expression, 120 mg protein was obtained from 6 L bacterial growth broth. Crystals of ¡µ1-8, 94-95 SUMO-2 were obtained by the hanging-drop vapor diffusion method and many different crystal forms were observed. One of single crystal with triangular plate polyhedron form diffracted to 1.6 Å resolution, the other one with rectangular polyhedron form diffracted to 1.2 Å. Analysis of the diffraction pattern suggests the crystals belong to R3 space group, the former one owned unit cell parameters a= b=75.3 Å, c=29.2 Å, £\=90¢X, £]=90¢X,£^=120¢X, and the later one owned unit cell parameters a= b=74.9 Å, c=33.2 Å and the same angles respectively. The R factor and Rfree of refinement are 0.133 and 0.190 with highly precise phase on 3-D structure of SUMO-2 protein. Comparison of crystal structure between human SUMO-2 and yeast SMT3 showed that the r.m.s. deviation of C£\ coordinate is 1.054 Å. In addition, comparison of SUMO-1 NMR structure and SMT3 crystal structure showed that the r.m.s. deviation of C£\ coordinates is 2.736 Å. Hence, the structures of SUMO-2 and SMT3 are more similar each other than those of SUMO-1and SMT3.

A molecule can crystallise in more than one crystal structure, a common phenomenon in organic compounds known as polymorphism. Different polymorphic forms may have significantly different physical properties, and a reliable prediction would be beneficial to the pharmaceutical industry. However, crystal structure prediction (CSP) based on the knowledge of the chemical structure had long been considered impossible. Previous failures of some CSP attempts led to speculation that the thermodynamic calculations in CSP methodologies failed to predict the kinetically favoured structures. Similarly, regarding the stabilities of co-crystals relative to their pure components, the results from lattice energy calculations and full CSP studies were inconclusive. In this thesis, these problems are addressed using the state-of-the-art CSP methodology implemented in the GRACE software. Firstly, it is shown that the low-energy predicted structures of four organic molecules, which have previously been considered difficult for CSP, correspond to their experimental structures. The possible outcomes of crystallisation can be reliably predicted by sufficiently accurate thermodynamic calculations. Then, the polymorphism of 5- chloroaspirin is investigated theoretically. The order of polymorph stability is predicted correctly and the isostructural relationships between a number of predicted structures and the experimental structures of other aspirin derivatives are established. Regarding the stabilities of co-crystals, 99 out of 102 co-crystals and salts of nicotinamide, isonicotinamide and picolinamide reported in the Cambridge Structural Database (CSD) are found to be more stable than their corresponding co-formers. Finally, full CSP studies of two co-crystal systems are conducted to explain why the co-crystals are not easily obtained experimentally.

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No description available.

Structure I and II gas hydrates were observed in the same sediment cores of a mud volcano in the Kukuy Canyon, Lake Baikal. The sII gas hydrate contained about 13-15% of ethane, whereas the sI gas hydrate contained about 1-5% of ethane and placed beneath the sII gas hydrate. We measured isotopic composition of dissociation gas from both type gas hydrates and dissolved gas in pore water. We found that ethane δD of sI gas hydrate (from -196 to -211 ‰) was larger than that of sII (from -215 to -220 ‰), whereas methane δ13C, methane δD and ethane δD in both hydrate structures were almost the same. δ13C of methane and ethane in gas hydrate seemed several permil smaller than those in pore water. These results support the following idea that the current gas in pore water is not the source of these gas hydrates of both structures. Isotopic data also provide useful information how the “double structure” gas hydrates formed.