SUMMARY / RELATED TOPICS

Polymorphism (materials science)

In materials science, polymorphism is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can be found in any crystalline material including polymers and metals, is related to allotropy, which refers to chemical elements; the complete morphology of a material is described by polymorphism and other variables such as crystal habit, amorphous fraction or crystallographic defects. Polymorphism is relevant to the fields of pharmaceuticals, pigments, dyestuffs and explosives; when polymorphism exists as a result of a difference in crystal packing, it is called packing polymorphism. Polymorphism can result from the existence of different conformers of the same molecule in conformational polymorphism. In pseudopolymorphism the different crystal types are the result of solvation; this is more referred to as solvomorphism as different solvates have different chemical formulae. An example of an organic polymorph is glycine, able to form monoclinic and hexagonal crystals.

Silica is known to form many polymorphs. A classical example is the pair of minerals and aragonite, both forms of calcium carbonate. An analogous phenomenon for amorphous materials is polyamorphism, when a substance can take on several different amorphous modifications. In terms of thermodynamics, there are two types of polymorphic behaviour. For a monotropic system, a plot of the free energy of the various polymorphs against temperature do not cross before all polymorphs melt—in other words, any transition from one polymorph to another below melting point will be irreversible. For an enantiotropic system, a plot of the free energy against temperature shows a crossing point threshold before the various melting points, it may be possible to revert interchangeably between the two polymorphs by heating or cooling, or through physical contact with a lower energy polymorph. The first observation of polymorphism in organic materials is attributed to Friedrich Wöhler and Justus von Liebig when in 1832 they examined a boiling solution of benzamide: upon cooling, the benzamide crystallised as silky needles, but when standing these were replaced by rhombic crystals.

Present-day analysis identifies three polymorphs for benzamide: the least stable one, formed by flash cooling is the orthorhombic form II. This type is followed by the monoclinic form III; the most stable form is monoclinic form I. The hydrogen bonding mechanisms are the same for all three phases. Polymorphs have different stabilities and may spontaneously convert from a metastable form to the stable form at a particular temperature. Most polymorphs of organic molecules only differ by a few kJ/mol in lattice energy. 50% of known polymorph pairs differ by less than 2 kJ/mol and stability differences of more than 10 kJ/mol are rare. They exhibit different melting points, solubilities, X-ray crystal and diffraction patterns. Various conditions in the crystallisation process is the main reason responsible for the development of different polymorphic forms; these conditions include: Solvent effects Certain impurities inhibiting growth pattern and favour the growth of a metastable polymorphs The level of supersaturation from which material is crystallised Temperature at which crystallisation is carried out Geometry of covalent bonds Change in stirring conditionsDespite the potential implications, polymorphism is not always well understood.

In 2006 a new crystal form of maleic acid was discovered 124 years after the first crystal form was studied. Maleic acid is a chemical manufactured on a large scale in the chemical industry and is a salt forming component in medicine; the new crystal type is produced when a co-crystal of caffeine and maleic acid is dissolved in chloroform and when the solvent is allowed to evaporate slowly. Whereas form I has monoclinic space group P21/c, the new form has space group Pc. Both polymorphs consist of sheets of molecules connected through hydrogen bonding of the carboxylic acid groups. 1,3,5-Trinitrobenzene is more than 125 years old and was used as an explosive before the arrival of the safer 2,4,6-trinitrotoluene. Only one crystal form of 1,3,5-trinitrobenzene was known in the space group Pbca. In 2004, a second polymorph was obtained in the space group Pca21 when the compound was crystallised in the presence of an additive, trisindane; this experiment shows. Walter McCrone has stated that "every compound has different polymorphic forms, that, in general, the number of forms known for a given compound is proportional to the time and money spent in research on that compound."

Ostwald's rule or Ostwald's step rule, conceived by Wilhelm Ostwald, states that in general it is not the most stable with the least amount of free energy but the least stable polymorph closest in energy to the original state that crystallizes first. See for examples the aforementioned benzamide, dolomite or phosphorus, which on sublimation first forms the less stable white and the more stable red allotrope; this is notably the case for the

Cattleya cernua

Cattleya cernua known as the Nodding Sophronitis, is a species of orchid occurring from Brazil to northeastern Argentina. It was the type species of the genus Sophronitis. Twenty plants of C. cernua have received a total of 22 AOS awards. The described flowers range from 1.9 cm to 3.2 cm horizontal spread and from 2.0 cm to 3.0 cm vertical spread. In nature, Cattleya cernua is pollinated by hummingbirds drawn to the blooms' warm colors; the orchid's cryptic pollinia provide an interesting adaptation to hummingbird pollination. C. cernua is pollinated. While most orchid pollinia are yellow, hummingbird pollinated orchids' pollinia are darker colored. A bright yellow pollen would produce a sharp visual contrast against the color of the beak, the bird would be stimulated to clean his beak; such a behavior which would be a reproductive disaster for the orchid. Therefore, to avoid detection, half of all hummingbird-pollinated orchids evolved dark pollinia−blue, gray or brown−which most approaches the colors which predominate in the birds' beaks and blend in more successfully.

Blooms with 2-4 bright red-orange blooms, 1" to 1 1/4" in size Monofoliate pseudobulbs with appx 1" leaves flowers in Spring in nature, but can bloom year-round in cultivation warm growing orchid, temps range from 50-110F in natural environment can be found growing epiphytically or lithophytically chromosome count: 2n= 40 In cultivation, this species grows best when mounted, in warm and bright conditions. Cattleya cernua var. aurea: bright yellow flowers Cattleya cernua var mineira: has an average of 10 to 14 brilliant red, smaller flowers and silver-grey leaves with violet midribs and margins. Cattleya cernua ssp. cernua: has single rows of pseudobulbs, spoon-shaped leaves, 2 to 5 flowers per inflorescence of pale orange colour with a yellow lip base and two lilac column wings. It grows along the coast and sometimes is called var. littoreana. Cattleya cernua var. lowii: a rare variety with lemon yellow flowers. Cattleya cernua ssp. mineira var. endsfeldzii: an "albino" form that has pale yellow flowers

Robert A. Holekamp

Robert August Holekamp was a businessman and apiarist from the St. Louis suburb of Webster Groves, Missouri. Holekamp was significant in the development of Webster Groves, had state and national influence in the field of beekeeping. Holekamp was born the son of a Lutheran minister in Hanover Province, Germany. At the age of 14, he went to Hildesheim to attend college. In 1868 he served for two years, leaving as a non-commissioned officer. In 1870, he settled in St. Louis. Upon arriving in St. Louis, Holekamp worked for various employers before becoming the manager at a door and sash dealer. In 1879, Holekamp and James Gray organized the firm Gray & Holekamp, a wholesale manufacturer and distributor of sashes and doors, grew the company into the largest dealer in St. Louis. In early 1885, Holekamp bought Gray's ownership interest and in December of that year he sold the company to Charles H. Huttig for $40,000. Gray & Holekamp is known today as Huttig Building Products, is one of the largest distributor of building products in the United States, is traded publicly on the NASDAQ Exchange.

As a result of the coal pollution in St. Louis and following his doctor's advice, in 1896 Holekamp moved to a farm located three miles outside of Annapolis in Iron County, Missouri, he purchased and operated a saw mill in that area. In 1901, Holekamp returned to St. Louis where he purchased a surgical instrument company which he named Holekamp, Grady & Moore, he sold the company after operating it for 7 years. In 1908, Holekamp co-founded the Holekamp Lumber Company in Webster Groves with his four sons. Holekamp served as the firm's president. In addition to the wholesale and retail sale of lumber and hardware, the firm was active in real estate development. Holekamp and his sons established many of the subdivisions and built many of the homes in Webster Groves, in neighboring Kirkwood, in the surrounding southwestern suburbs of St. Louis. By the time of Holekamp's death, Holekamp Lumber operated six lumberyards, the company would remain in business until the mid-1980s. While living in rural Annapolis, Holekamp developed an interest in apiology and began beekeeping.

He continued the hobby upon his return to St. Louis, Holekamp became among the first to engage in urban apiculture in the United States. Concerned about the spread of foulbrood disease among bees in Missouri, Holekamp proposed a bill and lobbied both houses of the Missouri State Legislature to pass a law to address the epidemic; when the measure was unexpectedly vetoed by Governor Joseph W. Folk in 1908, Holekamp appealed to the Governor and convinced him to change his mind. Holekamp's bill created the state office of bee inspector, making Missouri among the first states to regulate the commercial beekeeping industry. Holekamp advised the new bureau, continued to testify for the state on matters of apiculture. Holekamp was a judge at the Missouri State Fair for several years, was the superintendent of the bee exhibit at the 1920 Oklahoma State Fair, was the apiary superintendent for the University of Missouri, served as a member of the Executive Board of the Honey Producers' League, served for several years on the board of directors for the National Beekeepers’ Association of the United States and Canada.

Holekamp died in 1922 after a brief heart trouble. The banks in Maplewood and Webster Groves were closed on the day of his funeral in observance of his passing