The Mystery of Biochemical Chirality

...and homochirality in Living forms

From Google AI:

Assembly Theory incorporates the concept of chirality, particularly in the context of how complexity arises through the assembly of molecules and structures. 

1. Chirality and Assembly Theory's Focus:

• Chirality as a factor in complexity: Assembly theory focuses on measuring the complexity of objects, including molecules, by quantifying the minimum number of steps required to construct them from basic building blocks. Chirality, or "handedness", is a fundamental aspect of many molecules and structures, especially biological ones like proteins and DNA, and plays a vital role in their specific interactions and functions.
• Chirality and self-assembly: Chiral molecules can self-assemble into higher-order structures with specific chiral characteristics. The assembly process can be governed by the chirality of the building blocks themselves or through the induction of chirality in achiral molecules by external factors.
• Assembly theory quantifies selection: Assembly theory provides a framework for understanding how selection, whether in biological evolution or in other complex systems, leads to the emergence of complex objects like those with specific chirality. The theory suggests that the presence of multiple copies of objects with high assembly indices (meaning they require many steps to build) is evidence of selection at play. 

2. How Chirality is Handled in Practice:

• Chiral building blocks: Assembly theory can account for the chirality of building blocks in determining the assembly pathways and ultimately the complexity of the resulting structure. For example, the self-assembly of chiral molecules into helical structures.
• Chiral induction: The theory can also encompass the influence of external factors or other molecules on inducing chirality in self-assembling systems, even if the primary building blocks are achiral. 

3. Example from Research:

• Self-regulating chiral assemblies: Research on stimuli-responsive self-regulating assemblies of chiral and magnetically orientable nanorods demonstrates how chirality is incorporated within assembly theory. In this example, the effective chirality of the system can be modulated by a magnetic field, influencing the self-regulation mechanism that determines the size and shape of the assembled structures. 

In summary, Assembly Theory addresses chirality by incorporating it as a structural property that contributes to the complexity of the assembled objects. The theory's framework, which focuses on assembly pathways and the role of selection, can be used to analyze and understand how chiral structures emerge and evolve. 

Magnetic Fields for limb regeneration?  The bio-electric field that influences structure formation?

More from Google AI:

Chirality can be induced in achiral structures through various mechanisms, including interactions with chiral environments, external stimuli, and self-assembly processes. These methods break the mirror symmetry of the achiral structure, leading to a preferred conformation or handedness that can be detected using chiroptical spectroscopy. 

Methods for Inducing Chirality in Achiral Structures:

• Chiral Interactions:

  Interaction with a chiral environment, like a chiral host molecule or a chiral surface, can constrain the conformational freedom of an achiral guest molecule, leading to a preferred conformation and induced chirality. 
• External Stimuli:

  Applying external stimuli like magnetic fields, pressure-driven flow, or confinement can induce chirality in achiral systems. For example, a pressure-driven flow in a microfluidic cell can create chiral structures in nematic liquid crystals. 
• Self-Assembly:

  Achiral molecules can be organized into chiral supramolecular structures through self-assembly processes, such as those driven by solvophobic effects. 
• Metal-Organic Frameworks (MOFs):

  Achiral precursors can be assembled into chiral MOFs by introducing external stimuli like pyridine or by using a kinetic-controlled assembly process. 
• Chiral Ligand Interactions:

  Achiral and chiral ligands can be used synergistically to assemble inorganics into chiral superstructures by modulating the chiral rotation through coordination chemistry. 

Examples of Chirality Induction:

• DAPI and DNA Interaction:

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  The chiroptical properties of DAPI when bound to DNA can be attributed to conformational changes induced by the interaction with the DNA. 
• Magnetic Field Induction:

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  Using permanent magnets to rotate in space can generate chirality in materials by inducing a chiral structure. 
• Flow-Induced Chirality:

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  Pressure-driven flow in a microfluidic cell can induce chiral structures in nematic liquid crystals. 
• Self-Assembly of Tetraphenylethene (TPE):

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  Achiral TPE molecules can self-assemble into chiral ribbons via solvophobic effects, which can be controlled by adjusting solvent composition and polarity. 
• Chiral MOFs:

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  Pyridine can be used to induce chirality in MOFs assembled from achiral precursors. 

Applications:

• Chiroptical Spectroscopy:

  Inducing chirality allows for the study of chiroptical properties, providing insights into molecular conformation and aggregation. 
• Optical Devices and Metamaterials:

  Chiral structures can be used to create optical devices and metamaterials with applications in imaging, detection, and sensing. 
• Anti-Counterfeiting:

  Chiral structures can be used as invisible signatures that are only visible through polarized lenses. 
• Understanding Biological Chirality:

  Studying the induction of chirality in achiral systems can provide insights into the origin of biological chirality.