Cabinet of Chemistry Curiosities - Part 2

In the previous issue of the chemistry section, several compounds from the chemical freak show were presented (judging by the name of the series, you definitely won’t learn about them in school). These are quite respectable "persons" who, despite their unusual appearance, were awarded the Nobel Prize, and their properties in a number of areas can hardly be overestimated. In this article, it's time to get acquainted with the next original characters from the realm of chemistry, no less interesting than crown ethers and their derivatives.

chemical trees

Podands, compounds with long chains attached to the central part of the molecule, have given rise to a new class of substances (more on "chemical octopuses" in last month's article). Chemists decided to increase the number of "tentacles". To do this, to each of the arms ending in a group of atoms capable of reacting, another molecule was added, ending in the corresponding groups (two or more; the point is to increase the number of sites that could be combined with other particles). More molecules reacted with it, then more, and so on. The increase in the size of the entire system is illustrated by the diagram:

Chemists have linked the new compounds to the growing branches of trees, hence the name dendrimeria (from the Greek dendron = tree, meros = part). Initially, it competed with the terms "arborole" (this is Latin, where arbor also means tree) or "cascading particles". Although the author looks more like the tangled tentacles of jellyfish or inactive anemones, the discoverers, of course, have the right to names. The association of dendrimers with fractal structures is also an important observation.

1. Model of one of the original dendrimers

branch growth stage

Dendrimers cannot grow indefinitely (1). The number of branches grows exponentially, and after a few to ten stages of attachment of new molecules on the surface of a spherical mass, free space ends (the whole reaches nanometer dimensions; a nanometer is a billionth of a meter). On the other hand, the possibilities of manipulating the properties of the dendrimer are almost limitless. Fragments present on the surface can be hydrophilic ("water-loving", i.e. having an affinity for water and polar solvents) or hydrophobic ("avoiding water", but prone to come into contact with non-polar liquids, for example, most organic solvents) . solvents). Similarly, the interior of a molecule can be polar or non-polar in nature. Under the surface of the dendrimer, between the individual branches, there are free spaces into which selected substances can be introduced (at the stage of synthesis or later, they can also be attached to surface groups). Therefore, among chemical trees, everyone will find something suitable for their needs. And you, the reader, before you read this article to the end, think about what you can use molecules that, by their structure, will be “comfortable” in any environment, and what other substances can contain?

Of course, as containers for transporting selected compounds and protecting their contents. (2). These are the main applications of dendrimers. Although most of them are still at the research stage, some of them are already being applied in practice. Dendrimers are excellent for transporting drugs in the body's aquatic environment. Some drugs need to be specially modified to dissolve in body fluids - the use of conveyors will avoid these transformations (they can adversely affect the effectiveness of the drug). In addition, the active substance is slowly released from within the capsule, which means that doses can be reduced and taken less frequently. The attachment of various molecules to the surface of the dendrimer leads to the fact that they are recognized only by cells of individual organs. This, in turn, allows the drug to be transported directly to its destination, without exposing the entire body to unnecessary side effects, for example, in anti-cancer therapy.

2. Model of a dendrimer containing another molecule

(top)

Cosmetics are created on the basis of both water and fats. However, often the active substance is fat-soluble, and the cosmetic product is in the form of an aqueous solution (and vice versa: the water-soluble substance must be mixed with the fat base). The addition of emulsifiers (allowing the formation of a stable water-fat solution) does not always work favorably. Therefore, cosmetics laboratories are trying to use the potential of dendrimers as conveyors that can be easily adapted to needs. The crop protection chemicals industry faces similar problems. Again, it is often necessary to mix the non-polar pesticide with water. Dendrimers facilitate the connection and, in addition, gradually releasing the pathogen from the inside, reduce the amount of toxic substances. Another application is the processing of metallic silver nanoparticles, which are known to destroy microbes. Research is also underway on the use of dendrimers to transport antigens in vaccines and DNA fragments in genetic studies. There are more possibilities, you just need to use your imagination.

Buckets

Glucose is the most abundant organic compound in the living world. It is estimated that it is produced annually in the amount of 100 billion tons! Organisms use the main product of photosynthesis in different ways. Glucose is a source of energy in cells, serves as a reserve material (vegetable starch and animal glycogen) and building material (cellulose). At the turn of the nineteenth and twentieth centuries, products of the partial breakdown of starch by the action of bacterial enzymes (abbreviated KD) were identified. As the name suggests, these are cyclic or ring compounds:

They consist of six (variant a-CD), seven (b-CD) or eight (g-CD) glucose molecules, although larger rings are also known. (3). But why are the metabolic products of some bacteria so interesting that they are given a place in the "Young Technical School"?

3. Models of cyclodextrins. From left to right: a - KD, b - KD, g - KD.

First of all, cyclodextrins are water-soluble compounds, which should not come as a surprise - they are relatively small and consist of highly soluble glucose (starch forms too large particles to form a solution, but can be suspended). Secondly, numerous OH groups and glucose oxygen atoms are able to bind other molecules. Thirdly, cyclodextrins are obtained by a simple biotechnological process from cheap and available starch (currently in the amount of thousands of tons per year). Fourth, they remain completely non-toxic substances. And, finally, the most original is their form (which you, the Reader, should suggest when using these compounds): A bottomless bucket, i.e. cyclodextrins are suitable for carrying other substances (a molecule that has passed through a larger hole will not fall out). container at the bottom, and, moreover, it is bound by interatomic forces). Due to their harmlessness to health, they can be used as an ingredient in medicines and foods.

However, the first use of cyclodextrins, discovered shortly after the description, was catalytic activity. It turned out by chance that some reactions with their participation proceed in a completely different way than in the absence of these compounds in the environment. The reason is that the substrate molecule ("guest") gets inside the bucket ("host") (4, 5). Therefore, a part of the molecule is inaccessible to the reagents, and the transformation can occur only in those places that protrude. The mechanism of action is similar to the action of many enzymes, which also "mask" parts of the molecules.

4. Model of a cyclodextrin molecule containing another molecule.

5. Another look at the same complex

What molecules can be stored inside cyclodextrins? Pretty much anything that will fit inside - guest and host size matching is crucial (as with corona ethers and their derivatives; see last month's article) (6). This property of cyclodextrins

6. Cyclodextrin strung on another chain

molecules, i.e. rotaxane (more details: in the issue

January)

makes them useful for selectively capturing compounds from the environment. Thus, substances are purified and separated from the mixture after the reaction (for example, in the manufacture of drugs).

Other use? It would be possible to cite excerpts from the previous article in the cycle (models of enzymes and transporters, not only ionic ones - cyclodextrins transport various substances) and an excerpt describing dendrimers (transporting active substances in medicines, cosmetics and plant protection products). The benefits of cyclodextrin packaging are also similar - everything dissolves in water (unlike most drugs, cosmetics and pesticides), the active ingredient is released gradually and lasts longer (which allows for smaller doses), and the used container is biodegradable (microorganisms decompose quickly). natural product, it is also metabolized in the human body). The contents of the package are also protected from the environment (reduced access to the stored molecule). Plant protection products placed in cyclodextrins have a form that is convenient for use. It is a white powder, similar to potato flour, which is dissolved in water before use. Therefore, there is no need to use dangerous and flammable organic solvents.

When browsing through the list of uses for cyclodextrin, we can find several other "flavors" and "smells" in it. While the former is a commonly used metaphor, the latter may surprise you. However, chemical buckets serve to remove bad odors and to store and release desired aromas. Air fresheners, odor absorbers, perfumes and scented papers are just a few examples of the use of cyclodextrin complexes. An interesting fact is that flavoring compounds packaged in cyclodextrins are added to washing powders. During ironing and wearing, the fragrance is gradually broken down and released.

Time to try. "A bitter medicine cures best," but it tastes terrible. However, if it is administered in the form of a complex with cyclodextrin, there will be no unpleasant sensations (the substance is isolated from the taste buds). The bitterness of grapefruit juice is also removed with the help of cyclodextrins. Extracts of garlic and other spices are much more stable in the form of complexes than in the free form. Similarly packaged flavors enhance the taste of coffee and tea. In addition, the observation of their anticholesterol activity speaks in favor of cyclodextrins. Particles of "bad" cholesterol bind inside the chemical bucket and are excreted from the body in this form. So cyclodextrins, products of natural origin, are also health itself.