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nanotechnology

Molecular architects

Research which intervenes in the structure of the lowermost blocks of a material produces compounds such as a sensor for the conserving of wines

In the 21st century the world of science will become smaller, according to those who dedicate themselves to the emergent area of molecular nanotechnology. The specialists in this branch of nanosciences propose that they can dominate the manipulation of molecules and of the smallest particle of material capable of retaining the chemical characteristics of an element – the atom. This is the proposal of Henrique Toma, of the Chemical Institute at the University of São Paulo (IQ-USP). In the project Development of Supermolecules and Molecular Arrangements, financed by FAPESP, Dr. Toma is dedicating himself to the creation in the laboratory of stable systems on the scale of a nanometer, what are being called supermolecules.

A nonometer is equal to 10-9 meters, a billionth part of a meter or a millionth part of a millimeter – in short, the space which can hold at the maximum ten atoms. In the manipulation of the majority of the supermolecules to which the project refers, the objective is to reproduce in them some chemical reaction present in Nature or in the human body such as photosynthesis – in which the plant uses light to convert water, carbon dioxide and minerals into oxygen and compounds rich in energy – or the products of the action of enzymes.

In theory, the full control of molecular nanotechnology, a dream still a long way off, would permit man to be able to re-arrange negligible blocks of material into whatever he would desire and in this way, remake existing molecules or create new ones. “There is hardly any field of human activity in which molecular nanotechnology would not be useful to mankind, from the production of food to the treatment of diseases.” said Toma.

A Balanced wine
One of the compounds which he most uses are the porphyries, a type of pigment abundant in Nature and which take part in various biological processes. In man, for example, porphyries rich in iron are present in hemoglobin and are responsible for the transportation and the storage of oxygen in living tissues. It they who the red color to blood and to muscles. Also the green plants distinguish themselves by the presence of a substance derived from porphyries – chlorophyll, essential in photosynthesis.

By way of the combination of two types of porphyries, Dr. Toma and his colleague at the Department of Fundamental Chemistry of IQ-USP, Dr. Koiti Araki, produced some interesting compounds. One of them was a supermolecule which organized itself spontaneously, forming a photochemical film (which reacts to light) or as a catalyst (capable of accelerating a chemical reaction). Another compound forms a molecular film which functions as a sensor for sulfite – a discovery which is worth toasting.

Explanation: if explored commercially this sensor could be useful for wine producers. The wineries use sulfite for conserving – an antioxidant, a substance capable of removing the air from the drink. However, to avoid any danger to health, the quantity of sulfite should be constantly monitored. In the prototype developed in collaboration with Lucio Angnes, of IQ-USP, the film of porphyries created to serve as a sensor is coated on a small tube linked to an electrode. When the wine enters in contact with the sensor by flowing from the tube, the electrode indicates an electric current, by way of which, indirectly, the quantity of sulfite in the drink can be known – the greater the sulfite, the higher the electric current.

Dr. Toma cites two advantages of the sulfite sensor developed at USP in relation to the usual equipment: low cost and immediate measurement. “in 30 seconds the result comes out.” said Dr. Toma. As well as this, the measurement is made in only a few milliliters of the drink, which avoids wastage.

Simple equipment
Not always does one need to revert to equipment of the latest generation to produce supermolecules. To produce some of their supermolecules of porphyries – consumable material found in any laboratory – Drs. Toma and Koiti only used, as well as the reagents, sheets of glass and three recipients with solutions and followed a method equally trivial in the construction of the compounds, that of immersion.

In a general manner, the procedure followed in the immersion method can be summarized in the following manner. Dr. Toma separated three recipients and filled the first with a solution of porphyries with a positive electric charge (in fact, a molecule of porphyries linked to four molecules of ruthenium – a rare metal used to harden alloys of platinum and palladium). Next, he poured into the second recipient a solution of a porphyries with a negative charge ( a porphyries linked to four sulfonate groups) and the third recipient was filled with water. The following step was to take a sheet of glass and to submerge it into the recipients in the order of one, two and then three.

The result: over the glass a film formed with two layers, the first with the positive porphyries and the second with the negative porphyries (the water served only to remove the excess of the two compounds). The immersion can be repeated various times amplifying the thickness of the resulting film – which is an example of a chemical supermolecule. As can be seen in the structural representation of a new mounting of a supermolecule, the two original porphyries don’t mix. The atoms of the negative solution fit themselves over the atoms of the positive solution, forming a new architectural molecule – a compound with properties totally different from the substances of its origin. “The creation of this compound is the fruit of a process of molecular engineering. The supermolecule doesn’t happen by accident, it was planned.” affirmed Dr. Koiti Araki.

This single procedure hides a complicated reasoning for molecular architecture. Before the experiment one needs to know how the atoms and molecules will rearrange themselves structurally at the end of the reaction and if the arrangement will be permanent or temporary. This is something much more subtle and complex than simply imagining that the result of a reaction will be the sum of the atoms involved in the experiment. The structure of the supermolecule, the form in which its atoms interlace and create a physical-chemical web which gives it origin, is as or is more important than its simple chemical formula.

Diamond and graphite
To compare diamond and graphite is a good example. Both are minerals formed exclusively from atoms of carbon, only their structures are totally different. Graphite has a layered structure of rings of six carbon atoms, arranged in horizontal layers distant from each other. In diamond, each atom is linked to four other equidistant atoms, in a closed, dense and resistant 3-dimensional structure in the form of a tetrahedral or octahedral.

It is in fact this distinct internal structure which makes diamond a transparent material and with a hardness without equal in Nature, whilst graphite is dark, soft and can be broken. If one day the nanotechnicians have full control of the molecules, they could reorganize the atoms of graphite and transform them into diamond. More than a century ago, man made use of the benefit of the nano world: the tire industry, for example, uses nanoparticles of carbon to re-inforce the rubber of its product. “The nano world is here. It is people who have not paid any attention to it.” said Dr. Elson Longo, a researcher of the Department of Chemistry at the Federal University of São Carlos (UFSCar).

The basis of the modern notions of molecular nanotechnology, however, are more recent. At the end of 1959, at the annual meeting of the American Society of Physic, Richard P. Feynman gave a provocative speech which would enter into history as the initial kick. “Why can’t we write the whole of the 24 volumes of the Encyclopaedia Britannica on the head of a pin?” was one of his most inciting phrases.

Since then, we have been looking, more than using possible beneficial properties of nanoparticles, to act at the nano level: to manipulate atoms. To construct, to re-construct, to perfect and to invest molecules. At the moment, the new science holds many promises and modest practical results. To accelerate the rhythm the Foresight Institute of Palo Alto, California, reverted to an old and efficient way of stimulating inventiveness: a large prize in money.

A prize for small things
To take home the large Feynman Prize – and US$ 250,000 – the researcher or group of researchers who will be the first to design and construct two appliances: a robotic arm which can be enclosed inside a cube of at the maximum 100 nanometers of dimension and which will be capable of manipulating atoms and molecules in larger structures, and a type of computer which can fit into a cube of up to 50 nanometers and can carry out the same functions as a calculator of 8 bits. The challenge was launched in 1996 and continues valid. It is admitted that the Foresight Institute will raise the prize toUS$ 1 million if it receives sufficient donations.

As yet far from producing an ingenious revolution as asked for, Dr. Toma can display a recognition: in 1996 he won the chemistry prize of the Third World Academy of Science, situated in Italy, for his studies on the development of supermolecules based on polymetallic complexes. To advance more, Dr. Toma pretends to put in his laboratory a basic item of the nanoworld: an atomic force and tunneling microscope. These two techniques of microscopy permit visualizing and interfering with each atom of a molecule, though yet in a precarious manner. According to Dr. Toma, if the adepts of molecular nanotechnology were astronomers, the atomic force and tunneling microscope would be his more powerful telescope.

Admirable new nanoworld

Many things will change if the scientists and technicians of nanoscience manage to produce their gadgets. There is no lack of theoretical examples. Nanocompounds taken in by a human being would look after the maintaining of a healthy organism, unblocking arteries and combating infectious agents. Nanorobots would produce fuel at low cost, without offending the environment or consuming its resources. Nanotubes of carbon would take the place of transistors and substitute silicon in the manufacture of powerful nanochips. The supreme invention would be a factory of molecular structures – a fitter of molecules capable of making any compound, even copies of itself.

A delirium according to the skeptics. Even worse, say the apocalyptics: if we were to completely dominate the atoms, man could provoke the destruction of himself and even of the planet. In truth, the clear domination of the universe of the molecule is still a long way off. Zyvex, one of the new companies working in this field in California, calculates that in five or ten years there will be some invention on the market, but they don’t know what. After all, they argue, in 2005 or 2010 people will have different necessities than those of today.

Brazil invites interested parties

To judge by the investments that the developed countries are beginning to make in the area, the science of the small has already turned into a filed of billionaire research. In October last, the Congress of the United States approved an annual budget of almost US$ 500 million which the Government will requisition top launch its National Program of Nanotechnology. In 2001, Japan itself pretends to spend US$ 400 million on nanoscience, 41% more than in 2000. The Europeans maintain isolated and group initiatives, also pushed forward by large investments. And Brazil?

Until now, there have been isolated initiatives in São Paulo and other States, with work which could be covered within a wide national incentive. The country still does not have a national program of nanoscience, but that appears to be for only a short time. On the 22nd of November last, the National Council of Scientific and Technological Development (CNPq) called a meeting in Brasilia of those interested in participating in a possible national program of nanotechnology. 32 researchers appeared and at the end of the meeting they formed a commission which is collecting suggestions for the program which will be launched during the second semester of 2001.

The wide world of nanoscience was divided into three thematic groups, as in the North American program: 1) nanoappliances, nanosensors, nanoelectronics (semiconductors, magnetic materials, nanotubes, optoelectronics, photonics); 2) nanostructured materials; 3) nanobiotechnology/nanochemistry. “We are attempting to detect the needy areas of national science. We know that nanotechnology is an emerging sector and very important. Through this meeting, we could feel the interest of the scientific community. Now we want to map in detail who is doing what in this field, so that afterwards we can formulate a possible national program.” said Celso Pinto de Melo, Director of horizontal and instrumental policies of CNPq. The electronic address of the commission is: nano@cnpq.br is receiving e-mails of those interested.

The project
The development of Supermolecules and Molecular Appliances (nº 96/01434-7); Modality Thematic project; Coordinator Henrique Toma – Institute of Chemistry of USP; Investment R$ 104,000.00 and US$ 186,000.00

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