Artificial molecule

SET events at elevated temperature. Together with the limited number of free electrons, this may lead us to regard them as artificial atoms. This raises fundamental questions about the design of artificial molecules or artificial solids built up from these nanoscale sub-units [37-39]. Remade and Levine reviewed the ideas associated with the use of chemically fabricated quantum dots as building blocks for a new state of matter [40]. 

Kinbara, K. Aida, T. Toward Intelhgent Molecular Machines Directed Motions of Biological and Artificial Molecules and Assemblies. Chem. Rev. 2005,105, 1377-1400. 

This generalized structure was mimicked by a very simplified artificial molecule 1. The hydrophilic core part 2 was substituted simply by an oligoether carboxylate anion. The carboxylate may act as the polar ionic head group outside the membrane and the ether part of the molecule may be located in the interior part of the membrane to make an ion-conducting pathway. The molecular lengths were adjusted to fit the lipid monolayer in an extended or a helical conformation, with n being 2 or 3 in 1. The hydrophobic exterior was substituted by dioctadecyldimethyl-ammonium cation, which was ion-paired with the carboxylate. 

The studies presented here along with helical bundle approaches provide a vehicle for exploring in detail the structure-function relationships of ion channels through the synthesis of artificial molecules with simple and controllable structural features. The control of electric fields at the ion-selective filter may elucidate the molecular mechanism of K /Na and NaflCa selectivities. Variation of the critical pore size by synthetic elaboration may give direct clues on the magnitude of conductance and discrimination of metal ions. Further studies on voltage depend-... 

When we come to the specific design of artificial molecules capable of signalling the presence of particular analytes to a human observer, it is not sufficient to have only molecular recognition, but also transduction of that recognition event in a process that ultimately leads to an observable signal. A particularly sensitive method of signal production is the emission of visible light either visible to the human... 

Artificial life is an entirely new approach to the fundamental problems of biology, because it allows us to study life in a totally different way, i.e. by building machines that have some of its properties. It must be underlined, however, that silicon-based life is utterly different from carbon-based life because artificial molecules and artificial cells are made of electronic circuits and are therefore two-dimensional creatures. This explains why biologists have not abandoned more traditional approaches, and the search for a proper definition of organic life has never stopped. In this field, an important step forward was made in 1974 by Francisco Varela, Humberto Maturana and Ricardo Uribe, with the paper that introduced in biology the concept of autopoiesis. 

There was a time when the world was inhabited only by natural molecules, but that period did not last forever. At a certain point copied and coded molecules appeared, and the world became also inhabited by artificial molecules, by artifacts made by nature. And that was not just another step toward life. It was the appearance of the very logic of life because, from copymakers and codemakers onward, all living creatures have been artifact-makers. In a very fundamental sense, we can define life itself as artifact-making. 

The field of chemistry is much broader than the field of any language. In Italian we have about 160,000 words, whereas at least 5 million types of molecules can be found in Nature and about 15 million types of artificial molecules have been synthesized by chemists. Leonardo da Vinci did not know chemistry nevertheless, his sentence Where nature finishes producing its species, there man begins with natural things to make with the aid of this nature an infinite number of species [3] is quite appropriate to comment the outstanding development of chemistry. Chemists, indeed, started as explorers of Nature, but very soon they also became inventors and today they continue to play such dual role. As a consequence, chemistry is at the same time a book that we can read and a collection of white sheets that we can write on. A large part of the book has not yet been read (undiscovered natural molecules and processes) and the number of white sheets to be written on (artificial molecules and processes) is endless. 

Besides being important and useful, Chemistry has also a beautiful side that has inspired writers, poets, and sculptors. Chemistry is a wonderful book that continues to expand every day new ideas and new concepts are developed, previously unknown natural molecules are discovered, novel artificial molecules are synthesized, more complex supramolecular species are assembled, and more and more interesting molecular devices and machines are created. 

Kinbara K, Aida T (2005) Toward intelligent molecular machines directed motions of biological and artificial molecules and assemblies. Chem Rev 105 1377-1400... 

In 1967, Pedersen observed that crown ether showed molecular recognition - the first artificial molecule found to do so. Cram developed this concept to cover a wide range of molecular systems and established a new field of chemistry, host-guest chemistry, where the host molecule can accommodate another molecule, called the guest molecule. In 1978, Lehn attempted to organize these novel chemistries, and first proposed the term supramolecular chemistry . This represented the moment that supramolecular chemistry was clearly estabhshed. Together, Pedersen, Cram and Lehn received the Nobel Prize for Chemistry in 1987. 

As described above, ion channels play an important role in biological activity and they can be mimicked using a supramolecular approach. In this area of research, stable pore structures are formed from artificial molecules that are buried in a lipid bilayer membrane. For example, artificial channel structures have been prepared using specifically designed oligopeptides. 

Although in some cases small molecules can be effective at influencing protein-protein or protein-DNA associations, not all interactions can be so targeted, nor do these molecules allow for gain-of-function effects. To surmount these difficulties, researchers are working to create artificial molecules with functional properties akin to those of natural transcription factors. 

Over the last decade, we have shown that DNA can be used to construct a wide range of such nanocrystal molecules. The first such example of using DNA to organize nanocrystal molecules was shown in 1996 by Alivisatos and Schultz [12] (Fig. 9.4). This work appeared simultaneously with the work by Mirkin and Letsinger, who used DNA to assemble arrays of nanoparticles [13]. Indeed, if the nanocrystal is thought of as an artificial atom, then the construction of artificial solids is a complementary activity to the construction of artificial molecules, and this has been investigated extensively as well [14]. 

Use has been made of peptide link formation when making artificial molecules like Nylon. One type of Nylon can be made by the condensation of a dicarboxylic acid and a di-amine (Figure 7.3.10). 

The late 60 s and the early 70 s saw the advent of the first artificial molecules where these concepts were fully utilised, the crown ethers and their sequels the cryptands. Crown ethers or coronands are hetero-cyclic structures where the hetero-atoms are separated with C2-units cryptands are bicyclic analogues... 

In Section VI, along with the scenario introduced in Section V, we reexamine slow motions in liquid water, together with the check of predictability of our hypothesized interpretation. It will be shown that almost all the data examined there are compatible with our scenario, and some simulations using artificial molecules, which are obtained by introducing and changing several parameters in real molecules, are done to test the proposed hypothesis [14],... 

After the completion of the safety evaluation of the above mentioned flavour compounds, the current register will be transferred into the European positive list of flavouring substances, comprising natural, nature-identical and artificial molecules. The status will not be indicated in the foreseen list. As a consequence, the currently existing positive lists for artificial compounds on the level of country-specific legislation will then be obsolete. 

Wang, H., Brandi, D.W., Norlander, P., and Halas, N.J. (2007) Plasmonic nanostrucmres artificial molecules. Accounts of Chemical Research, 40, 53-62. 

---