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X-ray Crystallography

X-ray Crystallography

The size of the unit cell and the arrangement of atoms in a crystal may be determined from measurements of the diffraction of X-rays by the crystal, termed X-ray crystallography.
Diffraction
Diffraction is the change in the direction of travel experienced by an electromagnetic wave when it encounters a physical barrier whose dimensions are comparable to those of the wavelength of the light. X-rays are electromagnetic radiation with wavelengths about as long as the distance between neighboring...

Crystal Field Theory - Octahedral Complexes

Crystal Field Theory - Octahedral Complexes

Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...

Determination of Crystal Structures

Determination of Crystal Structures

In the late 1800s, the revelation that light extended beyond visible wavelengths led to the discovery of X-rays by Wilhelm Roentgen. Recognized as high-energy electromagnetic radiation with short wavelengths, X-rays prompted exploration into their interaction with crystals. Max von Laue proposed in 1912 that the periodic arrangement of atoms, ions, or molecules in crystals would cause them to diffract X-rays, a hypothesis confirmed through experiments with copper sulfate and zinc sulfide...

Imperfections in Crystal Structure: Point, Line and Plane Defects

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A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...

Imperfections in Crystal Structure: Stoichiometric Point Defects

Imperfections in Crystal Structure: Stoichiometric Point Defects

Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...

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$Microcrystallography of Protein Crystals and In Cellulo Diffraction$

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Selección y descubrimiento de polimorfos cristalinos con heteronúcleos de polímeros.

Christopher P Price¹, Adam L Grzesiak, Adam J Matzger

¹Department of Chemistry and the Macromolecular Science and Engineering Program, The University of Michigan, Ann Arbor, Michigan 48109-1055, USA.

Journal of the American Chemical Society

|April 14, 2005

Resumen

Este estudio introduce un nuevo método que utiliza heteronúcleos de polímeros para controlar polimorfas cristalinas, lo que permite el descubrimiento de alto rendimiento y la producción selectiva de diversas formas farmacéuticas.

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Área de la Ciencia:

Química del estado sólido.
Ciencia de los materiales ciencia de los materiales.
Ciencia de la ciencia de la cristalización.

Sus antecedentes:

El control de los polimorfos cristalinos es crucial para industrias como las farmacéuticas y los pigmentos.
Los métodos existentes carecen de fiabilidad para producir todas las polimorfas estables de un compuesto.

Objetivo del estudio:

Desarrollar una metodología confiable para el control del polimorfismo cristalino.
Para permitir el descubrimiento de alto rendimiento y la producción selectiva de polimorfos utilizando sustratos de polímeros.

Principales métodos:

Utilizó diversas bibliotecas de heteronúcleos de polímeros, incluidos polímeros comerciales y combinatorios.
Empleó cribado de cristalización de alto rendimiento con microscopía óptica y espectroscopia Raman.
Producción selectiva demostrada de polimorfos mediante la variación del sustrato del polímero bajo solvente y temperatura constantes.

Principales resultados:

El polimorfismo controlado con éxito para acetaminofén, sulfametoxazol, carbamazepina y ROY.
Se identificó la producción selectiva de dos polimorfos de acetaminofén y los seis polimorfos de ROY.
Descubrió nuevas formas de carbamazepina y sulfametoxazol, lo que permitió la caracterización estructural de nuevos sistemas tetramórficos.

Conclusiones:

El enfoque de los heteronúcleos poliméricos ofrece una plataforma versátil para explorar y controlar el espacio polimórfico.
Este método facilita el descubrimiento eficiente y la cristalización selectiva de las formas sólidas deseadas.
Los hallazgos avanzan en la producción industrial de materiales cristalinos, en particular los productos farmacéuticos.