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Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion03:48

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many different directions before reaching the desired target. At room temperature, a gaseous molecule will experience billions of collisions per second. The mean free path is the average distance a molecule travels between collisions. The mean free path increases with decreasing pressure; in general, the mean free path for a gaseous molecule will be...
Passive Diffusion: Overview and Kinetics01:17

Passive Diffusion: Overview and Kinetics

Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness.
When administered orally, drugs establish a substantial concentration gradient between the gastrointestinal (GI) lumen and the bloodstream, expediting their diffusion into...
Diffusion01:12

Diffusion

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
Diffusion01:21

Diffusion

Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
Facilitated Transport01:19

Facilitated Transport

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and hydrophilic regions, substances need to be able to transverse both regions. The hydrophobic area of membranes repels substances such as charged ions. Therefore, such substances need special membrane proteins to cross a membrane successfully. In  facilitated transport, also known as facilitated diffusion, molecules and ions travel across a membrane via...
Facilitated Transport01:19

Facilitated Transport

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and hydrophilic regions, substances need to be able to transverse both regions. The hydrophobic area of membranes repels substances such as charged ions. Therefore, such substances need special membrane proteins to cross a membrane successfully. In facilitated transport, also known as facilitated diffusion, molecules and ions travel across a membrane via...

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Video Experimental Relacionado

Updated: Jun 8, 2026

All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics
11:33

All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics

Published on: January 19, 2018

Tunabilidad en la difusión de moléculas poliatómicas a través de túneles frente al ritmo.

Zhihai Cheng1, Eric S Chu, Dezheng Sun

  • 1Department of Chemistry, University of California, Riverside, California 92521, USA.

Journal of the American Chemical Society
|September 14, 2010
PubMed
Resumen
Este resumen es generado por máquina.

La temperatura de difusión de los caminantes moleculares se puede ajustar alterando su estructura. Las simulaciones revelan que los caminantes cuadrúpedos muestran movimiento acelerado, lo que afecta la comprensión de la difusión superficial de moléculas orgánicas poliatómicas.

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Área de la Ciencia:

  • Ciencias de la superficie Ciencias de la superficie.
  • Dinámica molecular La dinámica molecular es la dinámica molecular.
  • Química orgánica es la química orgánica.

Sus antecedentes:

  • Los andadores moleculares están diseñados para el movimiento unidireccional a través de sustratos.
  • El ajuste de las propiedades de difusión es crucial para controlar el movimiento molecular en superficies.
  • La comprensión de los mecanismos de difusión informa el diseño de nuevos sistemas moleculares.

Objetivo del estudio:

  • Investigar métodos para ajustar la temperatura de difusión de los caminantes moleculares.
  • Para caracterizar la dinámica de difusión de los caminantes moleculares cuadrúpedos.
  • Evaluar el papel del túnel en la difusión superficial de moléculas orgánicas poliatómicas.

Principales métodos:

  • Se emplearon simulaciones de la teoría funcional de la densidad (DFT) para modelar la dinámica molecular.
  • Las estructuras moleculares fueron modificadas mediante la extensión de columnas vertebrales aromáticas, la adición de enlaces y la sustitución de anillos.
  • Se analizaron los modos de difusión (acelerado, trotamundos, deslizamiento).

Principales resultados:

  • La temperatura de difusión es sintonizable a través de modificaciones estructurales como la extensión de la columna vertebral y la adición de enlaces.
  • Los caminantes moleculares cuadrúpedos exhiben un modo de difusión "acelerado".
  • El modo de difusión identificado proporciona información sobre los efectos del túnel cuántico.

Conclusiones:

  • La ingeniería estructural ofrece una ruta para controlar las temperaturas de difusión de los caminantes moleculares.
  • El movimiento de ritmo de los caminantes cuadrúpedos es una característica clave.
  • La comprensión de los modos de difusión es esencial para elucidar la contribución del túnel a la difusión superficial.