Name: Supramolecular systems.
Uploaded: 2022-11-10
Duration: 17 min 54 s
Description: Supramolecular systems.. Presented by:. Panchal Manasvi Dinesh.

Supramolecular systems.. Presented by:. Panchal Manasvi Dinesh. 

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St Xavier’s College (Autonomous), Ahmedabad

Content. Introduction. General concepts of supramolecular systems. 

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General concepts of supramolecular systems

Biomedical applications of supramolecular systems

Basic concepts. A supramolecular system is an assembly of molecular subunits that are organized via intermolecular interactions that can be ionic or covalent. These interactions include hydrogen bonds, metallic coordination, hydrophobic interactions, Van der Waals forces and ionic interactions.. 

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A supramolecular system is an assembly of molecular subunits that are organized via intermolecular interactions that can be ionic or covalent. These interactions include hydrogen bonds, metallic coordination, hydrophobic interactions, Van der Waals forces and ionic interactions.

Supramolecular systems can be classified into two types:

1) macrocycle compounds that are formed via cyclic chemical structures and are linked

by covalent bonds (e.g., compounds derived from porphyrin and phthalocyanine); and

2) systems with molecular self-aggregation, such as, micelles and lipid vesicles

Many macrocycles, as well as self-aggregated disperse systems, have the capability to recognize and “capture” substances and, in many cases, to carry them to strategic locations. In general, molecular recognition is not an exclusive property of supramolecular systems.

Introduction. . Molecular recognition was first described for biomacromolecules, such as enzymes, and later for nucleic acids.. 

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Molecular recognition was first described for biomacromolecules, such as enzymes, and later for nucleic acids.

Hermann Emil Fischer [5], was one of the pioneers to identify the systems capable of recognizing molecules in 1902. He described the interactions between an enzyme and its substrate using the “key and lock” model. However, his comprehension of structure was very superficial.

At the beginning of the 20th century, Van der Waals forces (noncovalent molecular interactions) improved the understanding of protein structure and of several biological processes.

The possibility of synthesizing structures capable of recognizing molecules or, at least, of “capturing” them using noncovalent interactions came when Charles J. Pedersen described the synthesis of crown ethers in the 1980s, which improved the understanding of self-organized structures in solutions, such as, micelles and liposomes.

The 1987 Nobel Prize in Chemistry was awarded to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen for their work in developing high selectivity molecules of the “host-guest” type. This can be considered as an acknowledgement of the importance of supramolecular chemistry.

Later, other researchers started to develop molecular machinery with self-organized structures and complex sensors using construction blocks, such as, fullerenes and dendrimer

Molecular recognition. Molecular recognition is a specific interaction between a host molecule and a complementary guest molecule, which results in a host-guest complex.. 

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Molecular recognition is a specific interaction between a host molecule and a complementary guest molecule, which results in a host-guest complex.

. The designation of which substance is a “host” and which one is a “guest” is typically arbitrary.

Molecules are capable of recognizing each other via noncovalent interactions

In the case of template-driven synthesis, self-assembly can be used with reactive species to organize a system for a chemical reaction.

Intermolecular interactions may facilitate the desired chemical interaction by minimizing the effect of side reactions.

. The molecule used as a template can be removed after the reaction.

Molecular recognition. The systems that are formed via molecular printing follow this principle.. 

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The systems that are formed via molecular printing follow this principle.

In these systems, the host is built from small molecules using a species of interest as a template.

Therefore, the molecule (typically a polymer) is synthesized around the template molecule. The model is removed after the construction.

This leaves only the host with a region in its chain (i.e., a cavity) with a molecular geometry that is equal or similar to the geometry of the molecule that was removed. The construction model of the cavity can subtly differ from the guest-molecule, which is a molecule of interest that is to be molecularly recognized later.

Some supramolecular recognition systems are considered “bioinspired” or “biomimetic” because they try to copy some functions of biological systems. This includes the production of biosensors or high-efficiency catalytic systems.

Biomedical applications of supramolecular systems. 

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This Review mainly highlights the current research progress on biomedical applications of host−guest interaction-based supramolecular systems. The specific biomedical applications include

drug delivery, gene delivery, drug/gene codelivery, bioimaging, as well as photodynamic therapy.

Drug delivery: Although lots of anticancer drugs have been developed during the past century, effective cancer treatment is still facing considerable difficulties due to at least the lack of efficient drug delivery strategies.

Therefore, drug delivery systems with new functions are needed for the enhancement of anticancer drug solubility in aqueous environment, targeted drug delivery into tumor sites, and effective internalization into cancer cells.

Supramolecular chemistry strategies have been utilized to achieve these targets in drug delivery.

Direct Host−Guest Systems between Macro- cyclic Molecules and Drugs. 

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Direct Host−Guest Systems between Macro- cyclic Molecules and Drugs

In fact, more than one-half of newly developed chemical drugs have low water solubility, although they show great potentials in cancer therapy.

Thus, it is urgently required to enhance the solubility or dissolution of drugs in aqueous conditions.

In the scope of supramolecular chemistry, a directive method is using the host guest complexation between water-soluble macrocyclic molecules and drugs to enhance the water solubility of drugs.

By forming such host−guest complexes, it is capable of protecting drug molecules from chemical reactions and photochemical/thermal degradation in biological environment.

On account of the host−guest inclusion, the encapsulated drugs can be released sustainably from the cavity of macrocyclic molecules, achieving prolonged therapeutic effect.

Upon external  stimulus, such as thermal change, pH variation, or competitive binding, to disassociate the host−guest complexes, delivered drugs can be released in a controlled manner

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In a review article, Nau et al. discussed the enhancement of bioavailability of drugs by the host−guest complexation with macrocyclic molecules.

Up to now, such host−guest complexation has been successfully demonstrated as a general approach to enhance the water solubility of anticancer drugs, aiming at better chemotherapeutic efficacy

References: 1)  2- supramolecular systems from 'Nanostructures’ by Osvaldo N. Oliveira Jr.,

Supramolecular systems.

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