Selective Permeability of Chiral Molecules Through ZIF Membrane

Cracking Chirality: How a New ZIF Membrane Could Revolutionize Chemical Separations

Lena Voss in Tech & Innovation August 2025 • 4 min read.

"Scientists have developed a homochiral zeolitic imidazolate framework (ZIF) membrane that significantly improves chiral separation, opening doors for more efficient drug manufacturing and food chemistry."

Chirality, the property of molecules existing as non-superimposable mirror images, plays a pivotal role in various fields, from medicine and life sciences to food chemistry and drug manufacturing. Each enantiomer of a chiral molecule can exhibit vastly different biological activities, making the ability to separate them crucial. Traditional methods such as spontaneous crystallization and enzymatic kinetic resolution are often complex and energy-intensive.

In recent years, metal-organic frameworks (MOFs) have emerged as promising materials for molecular separation due to their tunable pore sizes, high surface areas, and good adsorption properties. However, creating MOF membranes with the ability to efficiently separate chiral molecules has remained a significant challenge, requiring precise control over the introduction of chiral functionalities.

Now, researchers have announced a breakthrough in the creation of a homochiral zeolitic imidazolate framework-8 (ZIF-8) membrane, modified with the natural amino acid L-histidine (L-His). This innovative membrane demonstrates exceptional selectivity in separating the enantiomers of 1-phenylethanol, achieving a high enantiomeric excess value of up to 76%.

The Innovation: L-His-ZIF-8 Membrane

Selective Permeability of Chiral Molecules Through ZIF Membrane

The research team successfully synthesized a homochiral L-His-ZIF-8 membrane using a contra diffusion method, where L-histidine was incorporated into the ZIF-8 framework. This membrane exhibited a remarkable preference for the R-enantiomer of 1-phenylethanol over the S-enantiomer. Selectivity arises from specific interactions between the S-enantiomer and the chiral MOF framework, paving the way for highly efficient chiral separation.

To confirm the successful incorporation of L-His, the researchers conducted a series of rigorous tests. Scanning electron microscopy (SEM) revealed a continuous, well-intergrown film of L-His-ZIF-8 on a porous aluminum oxide support. X-ray diffraction (XRD) patterns confirmed that the L-His-ZIF-8 maintained a similar crystal structure to ZIF-8, with slight shifts indicating the presence of L-His within the framework.

Further analysis using various methods provided strong evidence of L-His incorporation:

Energy-dispersive X-ray spectroscopy (EDX) showed the presence of oxygen atoms associated with the carboxy group of L-His.
Fourier-transform infrared (FTIR) spectroscopy detected adsorption peaks corresponding to the carboxy and amine groups of L-His.
X-ray photoelectron spectroscopy (XPS) identified the binding energy of the carboxylic group in L-His-ZIF-8.
Solid-state nuclear magnetic resonance (NMR) revealed additional peaks attributed to L-His.

The membrane's performance was evaluated through gas chromatography (GC) analysis, which directly demonstrated the ability of L-His-ZIF-8 to perform chiral separation. The R-(+)-1-phenylethanol enantiomer permeated the membrane faster than the S-(-)-1-phenylethanol. Single-component permeation experiments showed a significantly higher flux for the R-enantiomer, indicating a strong preference for its passage through the membrane. This innovative membrane showed an R-(+)-1-phenylethanol flux of 1.42 × 10-6 molm-2s¯¹ and S-(-)-1-phenylethanol flux of 0.193 x 10-6 mol m-2L-¹ in the first 2 h.

Future Implications and Sustainability

This breakthrough in creating a highly selective homochiral MOF membrane opens up new avenues for chiral separation. The L-His-ZIF-8 membrane demonstrates exceptional selectivity and stability, making it a promising candidate for practical applications in the pharmaceutical, chemical, and food industries. It represents a significant step toward more efficient, sustainable, and cost-effective chiral separation processes, potentially revolutionizing the way we produce essential compounds and drugs. The successful incorporation of a natural amino acid into the MOF framework highlights the potential for designing even more sophisticated and biocompatible membranes for a wide range of separation challenges.

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This article is based on research published under:

DOI-LINK: 10.1002/anie.201810925, Alternate LINK

Title: Incorporation Of Homochirality Into A Zeolitic Imidazolate Framework Membrane For Efficient Chiral Separation

Subject: General Chemistry

Journal: Angewandte Chemie International Edition

Publisher: Wiley

Authors: Jun Yong Chan, Huacheng Zhang, Yada Nolvachai, Yaoxin Hu, Haijin Zhu, Maria Forsyth, Qinfen Gu, David E. Hoke, Xiwang Zhang, Philip J. Marriot, Huanting Wang

Published: 2018-11-27

Everything You Need To Know

Why is chiral separation important in fields like medicine and drug manufacturing?

Chirality refers to the property of molecules that exist as non-superimposable mirror images, much like our left and right hands. This is crucial because each enantiomer (mirror image) of a chiral molecule can have different biological effects. For example, one enantiomer of a drug might be effective, while the other could be toxic or inactive. Therefore, separating these chiral molecules is essential in drug manufacturing, life sciences, and food chemistry to ensure product safety and efficacy.

How does the L-His-ZIF-8 membrane actually separate chiral molecules like the enantiomers of 1-phenylethanol?

The L-His-ZIF-8 membrane achieves chiral separation by incorporating the amino acid L-histidine into the zeolitic imidazolate framework-8 (ZIF-8). This creates a homochiral environment within the membrane's pores. The R-enantiomer of 1-phenylethanol permeates the membrane faster than the S-enantiomer. This occurs because the S-enantiomer interacts more strongly with the chiral L-His-ZIF-8 framework, causing it to move through the membrane more slowly, leading to separation.

How does the L-His-ZIF-8 membrane compare to traditional methods of chiral separation?

Traditional methods for chiral separation, like spontaneous crystallization and enzymatic kinetic resolution, can be complex and energy-intensive. The L-His-ZIF-8 membrane offers a more efficient and potentially sustainable alternative. Metal-organic frameworks (MOFs), like ZIF-8, have tunable pore sizes and high surface areas, making them ideal for molecular separation. The modification with L-histidine enhances the membrane's ability to distinguish between enantiomers, leading to better separation performance compared to conventional methods. While not mentioned, other methods such as chromatography also exist, but can be costly.

What are the potential future implications of the L-His-ZIF-8 membrane for industries like pharmaceuticals and food chemistry?

The creation of the L-His-ZIF-8 membrane has several implications for the pharmaceutical, chemical, and food industries. The improved efficiency and selectivity in chiral separation can lead to more cost-effective drug manufacturing processes and higher purity of chiral compounds used in various applications. Furthermore, the use of L-histidine, a natural amino acid, in the membrane design suggests the potential for developing more biocompatible and sustainable separation technologies. Not covered in the text but an interesting future is that this could reduce waste and energy consumption compared to traditional methods.

What methods were used to confirm the presence of L-histidine within the ZIF-8 framework?

Researchers confirmed the presence of L-histidine (L-His) within the ZIF-8 framework using multiple techniques. Scanning electron microscopy (SEM) showed a continuous film of L-His-ZIF-8 on a support. X-ray diffraction (XRD) confirmed the crystal structure was similar to ZIF-8, with slight shifts indicating L-His incorporation. Energy-dispersive X-ray spectroscopy (EDX) detected oxygen atoms from L-His. Fourier-transform infrared (FTIR) spectroscopy identified adsorption peaks of L-His functional groups, X-ray photoelectron spectroscopy (XPS) detected the binding energy of the carboxylic group in L-His-ZIF-8, and Solid-state nuclear magnetic resonance (NMR) revealed additional peaks attributed to L-His.