Crystallography

High-level composite, ab initio and density functional theory (DFT) procedures have been employed to study O–H bond dissociation energies (BDEs), as well as radical stabilization energies (RSEs) in the oxygen-centred radicals that are formed in the dissociation of the O–H bonds. Benchmark values are provided by Wn results up to W3.2 and W4.x. We are able to recommend revised BDE values for FO–H (415.6 ± 3 kJ mol–1), MeC(O)O–H (459.8 ± 6 kJ mol–1) and CF3CH2O–H (461.9 ± 6 kJ mol–1) on the basis of high-level calculations. We find that Gn-type procedures are generally reliable and cost-effective, and that some contemporary functionals and double-hybrid DFT procedures also provide adequate O–H BDEs/RSEs. We note that the variations in the O–H BDEs are associated with variations in the stabilities of not only the radicals but also the closed-shell precursor molecules. Most substituents destabilize both species, with σ-electron-withdrawing groups having larger destabilizing effects, whil...

The objective of this present study is to determine the optimum concentration for glutathione in the cryopreservation of seurukan fish (Osteochilus vittatus) spermatozoa. A completely randomized design (CRD) was used with 6 treatments and 3 replications. The Seurukan fish sperm was diluted in extender with a ratio of 1:20 (sperm: extender), then glutathione was added at a concentration of 0, 10, 20, 30, 40 and 50 mg L À1. Next, the sperm thawed at 39e40 C for 3 min and mixed with 100 eggs which were randomly selected. The success of the fertilized egg was observed 6 h after fertilization, while the hatching rate was examined 60 h after fertilization. The ANOVA test showed that the addition of glutathione significant affected the sperms motility, fertility and hatching rate of seurukan fish Osteo-chilus vittatus eggs (P < 0.05). By segregation the fresh sperm, a higher sperm motility rate was recorded with an addition of 30 mgL À1 of glutathione (63.00 ± 5.89), however, this value was not significantly different from using concentration of 10 and 20 mg L À1. A higher fertilization rate was produced using glutathione concentration of 50 mg L À1 (51.33 ± 17.01); however, it was also not significantly different from the concentration of 20, 30 and 40 mgL À1. In addition, a higher hatching rate was also recorded using glutathione concentration of 50 mg L À1 (40.33 ± 12.89), this value was not significantly different from using 40 mgL À1 glutathione. Hence, a conclusion was drawn that the optimum concentration of glutathione is 40 mg L À1 of diluent.

The exoskeleton of the lobster Homarus americanus is a multiphase biological composite material which consists of an organic matrix (crystalline α-chitin fibers and various types of non-crystalline proteins) and minerals (mainly calcite). In this study we discuss experimental data about the mesoscopic structure and the crystallographic texture (orientation distribution) of the α-chitin–protein fiber network in this material. The synchrotron measurements reveal very strong crystallographic textures of the α-chitin. According to these data, a large fraction of the α-chitin lattice cells is arranged with their longest axis parallel to the normal of the surface of the exoskeleton. Additionally, a smaller fraction of the α-chitin cells is oriented with their longest axis perpendicular to the cuticle surface. These structural investigations reveal the pronounced role of crystallographic orientation distributions in mineralized biological composite materials which may be of relevance for an improved understanding of biological and bio-inspired nano-composites.

Crystals of E. coli cytochrome b1, alias bacterioferritin, were grown fr om a low ionic strength solution. The resulting monoclniic P21 structure was solved by molecular replacement and refined using noncrystallographi c symmetries applied to the fundamental unit, consisting of two protein subunits and a single haem. From the Patterson self-rotation results it was shown that the asymmetric unit of the monoclinic crystal consists of 12 such dimers and corresponds to a complete, nearly spherical, molecule of bacterioferritin (M4 = 450 kDa) of 432 point-group symmetry. It is thus the most symmetrical cytochrome. As previously determined for the tetragonal form, the haem is located in a special position on a local twofold axis of the dimer. A bimetal centre is also observed within the four-helix bundle of each monomer; a metal-binding site is located on the fourfold axis.

Using an open-access distribution model, the Crystallography Open Database (COD, http://www.crystallography.net) collects all known &#x27;small molecule / small to medium sized unit cell&#x27; crystal structures and makes them available freely on the Internet. As of today, the COD has aggregated ~150,000 structures, offering basic search capabilities and the possibility to download the whole database, or parts thereof using a variety of standard open communication protocols. A newly developed website provides capabilities for all registered users to deposit published and so far unpublished structures as personal communications or pre-publication depositions. Such a setup enables extension of the COD database by many users simultaneously. This increases the possibilities for growth of the COD database, and is the first step towards establishing a world wide Internet-based collaborative platform dedicated to the collection and curation of structural knowledge.

We describe an x-ray absorption method for in situ density measurement of non-crystalline materials in the diamond anvil cell using a monochromatic synchrotron x-ray microbeam. Sample thickness, which is indispensable in the absorption method, can be determined precisely by extrapolating the thickness profile of the gasket obtained by x-ray absorption and diffraction measurements. Diamond deformation across the sample chamber becomes

The advances in studies of trace metal speciation and bioavailability since Mark Florence’s 1982 review of the topic, published in Talanta, have been comprehensively reviewed. While the relative merits of kinetic and equilibrium approaches are still being determined, advances in the applications of stripping voltammetry, including the application of microelectrodes and an appreciation of detection windows in both CSV and ASV, have been matched by the introduction of new dynamic techniques including diffusive gradients in thin films (DGTs), permeation liquid membranes (PLMs), and improved applications of chelating resins. There have also been improvements in equilibrium techniques such as ion-selective electrodes and Donnan dialysis. The ability of geochemical speciation models to predict metal complexation by natural organic matter has greatly improved, yet the models still require validation against field measurements. More reliable and relevant bioassays have been developed using ...

Over 30 colorful photographs of snowflakes, taken through a microscope, are included in this show -- work that has been used in a variety of schools for about 15 years. This PowerPoint show also explains how the black and white microphotographs of snow crystals by W.A. "Snowflake" Bentley in 1885 were converted to colored images. Using a technique similar to staining, Rick Doble colored the original Bentley images (in the public domain) to bring out the structure of the crystals. Doble explains his process in this presentation along with a lavish display of his colored snowflakes. These colored photographs have been widely used in elementary schools and also at the college level. They have also been featured in libraries and in the national media. Documentation about these mentions are included at the end of this presentation. Permission is given to educators and non-profit organizations to use these images, as long as the artist is credited.

The structure of the stable polymorph of tamoxifen citrate (form B) has been analyzed by single crystal X-ray diffraction [monoclinic, a = 15.998 (4), b = 21.964 (3), c = 8.624 (5) Å, β = 96.28 (3)°, space group P21/c]. The results include conformational details of the molecular structure as well as a description of the observed packing arrangement in the solid which is dominated by hydrogen-bonding interactions between the ionic entities. The proton transfer to the nitrogen atom of tamoxifen is from the central carboxyl group of the citric acid. There is a satisfactory correlation between the solid infrared spectrum of the carboxylic functions and the asymmetric environment observed around them in the crystal lattice. Additional results obtained from thermal and spectral analyses suggest that the second polymorph of tamoxifen citrate (form A) represents a metastable form of this compound. The two polymorphs are characterized by their powder diffraction spectra.

The asymmetric unit of the title compound, 2C6H12N4- C8H12O4, contains one half-molecule of e,e-trans-cyclohexane- 1,4-dicarboxylic acid (the complete molecule being generated by inversion symmetry) and one molecule of hexamethylenetetramine (HMTA), which are connected by O—H. . .N hydrogen bonds. This forms isolated trimers that pack in a herringbone fashion.

 The kinetics of the dehydroxylation of chrysotile was followed in situ at high temperature using real-time conventional and synchrotron powder diffraction (XRPD). This is the first time kinetics parameters have been calculated for the dehydroxylation of chrysotile. The value of the order of the reaction mechanism calculated using the Avrami model indicates that the rate-limiting step of the reaction is a one-dimensional diffusion with an instantaneous nucleation or a deceleratory rate of nucleation of the reaction product. Hence, the rate-limiting step is the one-dimensional diffusion of the water molecules formed in the interlayer region by direct condensation of two hydrogen atoms and an oxygen atom. The calculated apparent activation energy of the reaction in the temperature range 620–750 °C is 184 kJ mol−1. The diffusion path is along the axis of the fibrils forming the fibers. The amorphous or short-range ordered dehydroxylate of chrysotile is extremely unstable because forsterite readily nucleates in the Mg-rich regions. Moreover, it is less stable than the dehydroxylate of kaolinite, the so-called metakaolinite, which forms mullite at about 950 °C. This difference is interpreted in terms of the different nature of the two ions Mg2+ and Al3+ and their function as glass modifier and glass-forming ion, respectively.

Chemical crystallography is considered one of the essential characterization techniques of inorganic chemistry since it is a critical tool in the structural determination of molecules small and large. Several attempts have been made to introduce crystallography topics at the undergraduate level, but the one present obstacle is the availability of instrumentation for undergraduates to run experiments in. State of the art X-ray diffraction instruments typically reach the ~$500,000 range and are rarely available to primarily undergraduate institutions. While accessibility to high-tech instrumentation is indeed an obstacle, there are educational sources that are quite accessible for undergraduate students, merely requiring a working computer to make use of them. Thus, the aim of this article is to touch upon the attempts to introduce the topic of crystallography to undergraduates of the inorganic chemistry laboratory at Georgia College and State University (GCSU). Two guided inquiry research type assignments are herein discussed that expose students to crystallography and enhance literature review/analysis skills that allows them to become better undergraduate researchers.

The author discusses the benefits for forensic science from greater engagement with basic and other applied areas of chemistry and gives examples of how his organization, the Australian Federal Police, have partnered with academia and others to promote the use of chemistry in areas of trace evidence, illicit drugs, fingerprint detection, and explosives.

Os campos magnéticos estão em todos os lugares. A partir de ímãs naturais até a própria Terra, existe um campo magnético, que influencia diversos materiais. O material cristalino, que possui um arranjo de átomos periódico, tem um padrão tridimensional repetitivo. Como é capaz de criar corrente elétrica, o campo magnético neste tipo de material é significativo por conter propriedades como a polarização espontânea, em meio a sua tridimensionalidade singular, incluindo o mais simples arranjo cristalino, originado a partir de soluções supersaturadas de cloreto de sódio. Com o preparo destas soluções, submeteu-se os cristais em ímãs de neodímio. Por meio de microscopia e espectrofotometria, pôde-se observar mais detalhadamente as diferenças existentes entre os cristais sob influência de campo e os que não sofreram influência, sendo principalmente no quesito espacial: cristais muito próximos uns dos outros, regulares e organizados, sob influência das linhas de campo magnético. O próprio arranjo cristalino tridimensional sofreu intervenção da submissão do ímã, o que indica uma possível mudança nas características físico-químicas destes materiais. Com um estudo experimental preliminar, pôde-se observar como cristais de cloreto de sódio, presentes em cálculos renais, por exemplo, sofrem expressiva ingerência de campo magnético em suas estruturas.

"New Zealand-based Pacific Lithium Limited (PLL) was established in 1994 to develop a world-competitive business based on the extraction of lithium from seawater, using a new adsorption technology developed by chemical engineer John Bloom (Sun, Mellalieu & Willis, 1999). Through the fundraising efforts of entrepreneur Robin Johannink, the company subsequently raised NZ $10 million from shareholders, including a 12% stake in the company from Vertex Asia (a technology subsidiary of the Singapore government) and a further 8.6% from a key customer: Japanese trading company Nisho Iwai. By late 1995, the company had started building a processing plant at Whakerewa, near the Thames Estuary, but later suspended construction of the facility as its seawater lithium adsorption technology had not achieved optimum economic levels of lithium recovery. Since the company’s foundation, several new companies had entered the world lithium supply market (Sun & Mellalieu, 1999).

Note:
This is the THIRD installment in a series of cases. For a Case Resource library providing Part A, Part B and other resources, see:
Mellalieu, P. (n.d.). Pacific Lithium Ltd - Case resource library. Retrieved January 24, 2014, from https://www.academia.edu/1513410/Pacific_Lithium_Ltd_-_Case_resource_library

Citation:
Mellalieu, P. J., & Sun, J. G. (2000). Pacific Lithium (C): Flight of the Phoenix. In Proceedings of the Annual Educators Conference of the New Zealand Strategic Management Society (Vol. 1). Canterbury University, Christchurch: New Zealand Strategic Management Society. Retrieved from https://www.academia.edu/1510450

During the last two decades, optical stellar interferometry has become an important tool in astronomical investigations requiring spatial resolution well beyond that of traditional telescopes. This book, first published in 2006, was the first to be written on the subject. The authors provide an extended introduction discussing basic physical and atmospheric optics, which establishes the framework necessary to present the ideas and practice of interferometry as applied to the astronomical scene. They follow with an overview of historical, operational and planned interferometric observatories, and a selection of important astrophysical discoveries made with them. Finally, they present some as-yet untested ideas for instruments both on the ground and in space which may allow us to image details of planetary systems beyond our own.