Needles of two different polymorphs of metanilic acid taken under a microscope at ×20 magnification. Figure (a) shows Form II and (b) shows Form III; Form I was unable to be reproduced by researchers, an instance of a disappearing polymorph.[1]
In materials science, disappearing polymorphs (or perverse polymorphism[citation needed]) describes a phenomenon in which a seemingly stable crystal structure is suddenly unable to be produced, instead transforming into a polymorph, or differing crystal structure with the same chemical composition, during nucleation.[2][3] Sometimes the resulting transformation is extremely hard or impractical to reverse, because the new polymorph may be more stable.[4] It is hypothesized that contact with a single microscopic seed crystal of the new polymorph can be enough to start a chain reaction causing the transformation of a much larger mass of material.[5] Widespread contamination with such microscopic seed crystals may lead to the impression that the original polymorph has "disappeared."
The initial polymorph is in a metastable state (1), which requires overcoming an energy threshold (2) to make it transform into a more stable polymorph with a stronger bond (3). Once (3) exists in a solution during nucleation, the resulting crystal will take the form of the more stable polymorph, making (1) nearly impossible to produce in a typical laboratory environment.
This is of concern to both the pharmaceutical and computer hardware industry, where disappearing polymorphs can ruin the effectiveness of their products, and make it impossible to manufacture the original product if there is any contamination. There have been cases of laboratories growing crystals of a particular structure and when they try to recreate this, the original crystal structure isn't created but a new crystal structure is.[6] The drug paroxetine was subject to a lawsuit that hinged on such a pair of polymorphs, and multiple life-saving drugs, such as ritonavir, have been recalled due to unexpected polymorphism.[7] Although it may seem like a so-called disappearing polymorph has disappeared for good, it is believed that it is always possible in principle to reconstruct the original polymorph, though doing so may be impractically difficult.[8] Disappearing polymorphs are generally metastable forms, that are replaced by a more stable form.[3]
It is hypothesized that "unintentional seeding" may also be responsible for the phenomenon in which it often becomes easier to crystallize synthetic compounds over time.[5]
^Seddon KR, Zaworotko M, eds. (1999). Crystal Engineering: The Design and Application of Functional Solids. Vol. 539. Springer Science & Business Media. ISBN 978-0-7923-5905-0.
^Lowe D (November 26, 2019). "Perverse Polymorphism". In the Pipeline. American Association for the Advancement of Science. Archived from the original on July 5, 2022. Retrieved 2022-07-04.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
^ abDunitz JD, Bernstein J (1995-04-01). "Disappearing Polymorphs". Accounts of Chemical Research. 28 (4): 193–200. doi:10.1021/ar00052a005. ISSN 0001-4842.
In materials science, disappearingpolymorphs (or perverse polymorphism[citation needed]) describes a phenomenon in which a seemingly stable crystal structure...
of the various polymorphs against temperature do not cross before all polymorphs melt. As a result, any transition from one polymorph to another below...
formed by the carboxylic acid groups, both polymorphs form identical dimer structures. The aspirin polymorphs contain identical 2-dimensional sections and...
conversely, 'despite the fact that in evolutionary progress hair is disappearing from the mid-digital region, its presence...may be regarded as the manifestation...
so these are not considered heterozooids. "Female" polymorphs are more common than "male" polymorphs, but specialized zooids that produce sperm are also...
than one of its arguments. This is a generalization of single-dispatch polymorphism where a function or method call is dynamically dispatched based on the...
low-pressure polymorphs of anhydrous silica consists of frameworks of fully corner bonded tetrahedra of SiO4. The higher temperature polymorphs of silica...
to Charles Darwin's On the Origin of Species, with less fit lineages disappearing over time. For Darwin, extinction was a constant side effect of competition...
with some Jewish communities, for example the Kaifeng Jews of China, disappearing entirely. The advent of the Jewish Enlightenment of the 18th century...
in organic solvents. The compound can be crystallized in a variety of polymorphs. Chloral hydrate is also an ingredient used for Hoyer's solution, a mounting...
Corals of order Scleractinia build their endoskeletons from aragonite (a polymorph of calcium carbonate). When used for this purpose, limewater is usually...
Majumder (December 2001), "High-resolution analysis of Y-chromosomal polymorphisms reveals signatures of population movements from central Asia and West...
over the interpretation of patterns of molecular divergence and gene polymorphism, peaking in the 1970s and 1980s. Neutral theory is frequently used as...
their host countries. At the haplogroup level, defined by the binary polymorphisms only, the Y chromosome distribution in Arabs and Jews was similar but...
segments of the funiculus are twice as long and broad in larger workers. Polymorphism occurs in all species and the mandibles bear four teeth. The following...
Jyrki; Tiilikainend, Raisa; Korpelainen, Jan (2007). "Moose Antler Type Polymorphism: Age and Weight Dependent Phenotypes and Phenotype Frequencies in Space...
Keller G, Lecq G, Bourgaux C, Ollivon M (1998). "Phase Transitions and Polymorphism of Cocoa Butter". Journal of the American Oil Chemists' Society. 75 (4)...
although, only in a few cases are genes the primary cause of obesity. Polymorphisms in various genes controlling appetite and metabolism predispose to obesity...
candidate genes have together helped identify specific single nucleotide polymorphisms (SNPs), mostly found in genes with immune regulatory functions. The...
gibbsite, and nordstrandite, which differ in their crystalline structure (polymorphs). Many other intermediate and related structures are also known. Most...
[citation needed] The symptoms of psychosis such as going into a hole, disappearing, feeling as if melting, experiencing colors, and hallucinations are described...
Berg D; et al. (June 15, 2005). "Sun Exposure, Vitamin D Receptor Gene Polymorphisms, and Risk of Advanced Prostate Cancer". Cancer Research. 65 (12): 5470–5479...
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