Video Experimental Relacionado
Updated: May 14, 2026
16:24
Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
Published on: August 2, 2012
Control estereoquímico de las transiciones polimórficas en reactores a nanoescala
Qi Jiang1, Chunhua Hu, Michael D Ward
1Molecular Design Institute, Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003-6688, USA.
Journal of the American Chemical Society
|February 2, 2013
Resumen
Los nanocristales de beta-glicina metastables formados en nanoporos se transforman en alfa-glicina a una alta humedad. Los auxiliares de aminoácidos pueden suprimir esta transición de fase al bloquear el acceso del agua a las caras críticas del cristal.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- La cristalografía es una técnica de cristalografía.
- Nanotecnología La nanotecnología es la nanotecnología.
Sus antecedentes:
- La glicina, un aminoácido, existe en múltiples formas polimórficas, incluida la beta-glicina metastable y la alfa-glicina estable.
- El nanoconfinamiento puede alterar las vías de cristalización y la estabilidad polimórfica.
- Los nanoporos de óxido de aluminio anódico (AAO) proporcionan un entorno controlado para el estudio de la formación de nanocristales.
Objetivo del estudio:
- Para investigar la cristalización de la glicina en los nanoporos de AAO.
- Para determinar el comportamiento de transición de fase de los nanocristales de beta-glicina bajo diferentes humedades.
- Para explorar el papel de los auxiliares de aminoácidos en el control de las transiciones polimórficas de glicina.
Principales métodos:
- Cristalización de la glicina dentro de los nanoporos de AAO de diferentes diámetros.
- Microdifracción bidimensional de rayos X para el análisis estructural.
- Experimentos controlados de humedad para inducir transiciones de fase.
- Uso de auxiliares de aminoácidos racémicos y enantiopuros durante la cristalización.
Principales resultados:
- Beta-glicina metastable formada en nanoporos AAO < 200 nm, con el eje [010] alineado con la dirección de los poros.
- Los nanocristales de beta-glicina se transforman en alfa-glicina a un 90% de humedad relativa, con una reorientación del eje [010].
- Los auxiliares de aminoácidos racemicos suprimieron la transición beta a alfa al unirse selectivamente a {010} caras.
- Los auxiliares de enantiopuro no impidieron la transición, lo que indica la unión estereoselectiva y la importancia del acceso al agua.
Conclusiones:
- La orientación del eje [010] de la beta-glicina en los nanoporos de AAO es similar a la de los monolitos de polímeros.
- La alta humedad induce una transición de fase de la beta-glicina a la alfa-glicina con una reorientación molecular significativa.
- Los auxiliares de aminoácidos pueden actuar como modificadores de la cristalización, impidiendo las transiciones de fase al obstaculizar estéricamente las moléculas de agua.
- La unión estereoselectiva de aminoácidos a caras cristalinas específicas es crucial para controlar el polimorfismo de la glicina en entornos nanoconfinados.
Más Videos Relacionados
Videos de Conceptos Relacionados
02:23SN2 Reaction: Stereochemistry
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:17Ziegler–Natta Chain-Growth Polymerization: Overview
Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta catalyst, high molecular...
01:18Bioreactor Controls-II
In aerobic fermentations, oxygen is vital for microbial growth and metabolite production. Since air comprises only about 20% oxygen and the gas is poorly soluble in water—just 9 ppm at 20°C—supplying sufficient oxygen becomes a critical challenge, especially in high-demand processes like yeast growth or citric acid production. Even a fully saturated broth may offer only a few seconds of oxygen availability.To address this, sterile or scrubbed air is introduced into the fermentor via a sparger...
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
01:28Bioreactor Controls-I
Maintaining optimal conditions within fermenters is essential for maximizing microbial productivity and ensuring process efficiency. This lesson focuses on key parameters—temperature, foam, pH, carbon dioxide, oxygen, and pressure—and their precise measurement and control strategies in fermentation systems.Temperature ControlTemperature regulation is critical due to the exothermic nature of many fermentation processes. In small laboratory fermenters, temperature is commonly monitored using...