Orthorhombic crystal form

Occurrence. The principal strontium mineral is celestite, naturally occurring strontium sulfate. Celestite and celestine [7759-02-6] both describe this mineral. However, celestite is the form most widely used in Knglish-speaking countries. Celestite has a theoretical strontium oxide content of 56.4 wt %, a hardness of 3—3.5 on Mohs scale, and a specific gravity of 3.96. It is usually white or bluish white and has an orthorhombic crystal form. 

It is usually believed that the growth of dendritic crystals is controlled by a bulk diffusion-controlled process which is defined as a process controlled by a transportation of solute species by diffusion from the bulk of aqueous solution to the growing crystals (e.g., Strickland-Constable, 1968 Liu et al., 1976). The appearances of feather- and star-like dendritic shapes indicate that the concentrations of pertinent species (e.g., Ba +, SO ) in the solution are highest at the corners of crystals. The rectangular (orthorhombic) crystal forms are generated where the concentrations of solute species are approximately the same for all surfaces but it cannot be homogeneous when the consumption rate of solute is faster than the supply rate by diffusion (Nielsen, 1958). 

Figure 5.7 Structures of the alternative conformations of the iron-binding sites in the orthorhombic crystal form of the recombinant N-lobe of human transferrin. Reproduced with permission from MacGillivray et ah, 1998. Copyright (1998), American Chemical Society. 

In the thermodynamic sense, a phase is defined as part of a chemical system in which all the material has the same composition and state. Appropriately, the word comes from the Greek phasis, meaning appearance . Ice, water and steam are the three simple phases of H20. Indeed, for almost all matter, the three simple phases are solid, liquid and gas, although we must note that there may be many different solid phases possible since H20(S) can adopt several different crystallographic forms. As a related example, the two stable phases of solid sulphur are its monoclinic and orthorhombic crystal forms. 

Figure 4 shows a C backbone trace of the asymmetric unit of the orthorhombic crystal form of bovine heart cytochrome c oxidase (Tsukihara et al., 1996). The structure revealed that cytochrome c oxidase is a... 

PROP White or colorless platelets or orthorhombic crystals formed from quartz temperamres >870° (NTIS PB246-697). Stable from 870-914° at atmospheric pressure, but persists as a metastable phase below 8° forming low tridymite below 1° and middle tridymite from 117-1°. IDLH 25 mg/m ... 

Polyethylene conforms to the situation of Figure la, l.e. under normal conditions it does not display a mesophase, only the familiar orthorhombic crystal form (o). Nevertheless, there exists a virtual mesophase which can be "uncovered" the ways in which this can be achieved is the subject of what follows. 

The electron density maps published so far have been based on the orthorhombic crystal form. The anions Pt(CN)4 - and Au (CNlz and the mercury complex ethyl mercurythiosalicylate were used to prepare heavy atom derivatives (106,107). The overall dimensions of the molecule... 

Monoclinic or orthorhombic crystals, forming as plates or leaflets from acetic acid mp 266°C (510°F) sublimes insoluble in water, slightly soluble iu alcohol and ether, soluble in most other organic solvents. 

Principal Values and Axes of Chemical Shift of trans-trans Methylene Chains in the Orthorhombic Crystal Form... 

Molecular packing in the various crystalline forms can produce additional chemical shifts. In -paraffins, differences of 1 ppm are observed between the triclinic and orthorhombic crystal forms [27]. 

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