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Atoms, Molecules and Their Structure

Date: (2/10/2009)

Facultad de Ciencias Químicas

Every five minutes, there is a new compound which is determined through the diffraction X-ray technique in a pharmaceutical, academic and industrial level, but what does it mean and which is its use?

Doctor Sylvain Jean Bernes Flouriot, FCQ research and professor.

By Gabriela Hernandez Villanueva

Research’s advance represents for most of the scientists the main objective, but the progress also depends of several constants. In Chemical Sciences, these constants represent the basis.

Beyond chemical compunds’ discoveries and developments made before, there are different researches’ practices in X-rays diffraction techniques, which are an essential part on their colleagues’ work.

Universidad Autonoma de Nuevo Leon (UANL) School of Chemistry (FCQ, Spanish abbreviation) some researchers are Doctor Sylvain Jean Bernes Flouriot, who uses this technique for characterizing the molecules that synthesize in othe laboratories.

The X-ray diffraction makes sense if there is a tidy disposition of atoms, and if Bragg’s Law, which relates X-ray wavelength and the interatomic distance to diffracted beam’s incidence angle.

“X-ray diffraction on mono crystals is a tool used to support specific research’s projects. Sometimes the support is absolutely essential, and sometimes is a little part in another person’s project.”

“The researches managed by my colleagues in FCQ are focused on new compounds in order to advance on chemistry, and when they synthesize a new compound, they need to characterize it. It could be easy synthesize it; however, it is so difficult to know what they have prepared, to know its structure, formula and composition,” explained Dr. Sylvain Jean Bernes.

One of the techniques used to establish the structure of a molecular compound (the technique has to be enough pure in crystalline state) is X-ray diffraction.

“The matter in crystalline state can diffract X-ray. I use that energy source (X-ray) which is known by all of us, because it is presented in the hospitals, but not the same physical phenomenon.”

“What I do is produce a diffraction phenomenon on the same compound prepared by my colleagues, also to measure diffraction pattern through a theory, determine the positions of the atoms and molecules. At the end, I get the crystallized molecule’s structure.”

“To have molecule’s structure means to know how the atoms get linked, to know which molecule’s structure is, which that link’s length is and more information. The most important thing is to generate a very rich content; if we know molecule’s structure, we get a characterization that is –practically- total.”

Even though, not everything is characterized such as energy atoms’ levels which are in the molecule (because this process needs techniques totally different), to obtain atoms’ positions in the molecules is like having a microscope, but with a giant enlargement in order to see the atoms inside the matter,” explained FCQ researchers and professor.

In the next article, we will talk about the pharmaceutical and industrial importance of defining molecules’ structure.

** Sylvain Jean Bernes Flouriot got a Doctorate Degree in Inorganic chemistry by the University Pierre and Marie Curie, Paris. He is National Council on Science and Technology (CONACYT, Spanish abbreviation) National System of Researches member, and actually, he is UANL School of Chemistry professor and he is also working in the School of Chemistry Division of Postdegree Studies.

Note

Bragg’s Law allow us to study the directions in which X-ray diffraction produces constructive interferences (on a crystal’s surface), all of this happens when X-ray reaches an atom and they interact with its external electrons, and the electrons reemit the incident electromagnetic radiation in different directions with the same frequency. This phenomenon is known as Rayleigh dispersion or elastic dispersion. The reemitted X-ray –from closing atoms- interferes among themselves constructively or destructively. This is the diffraction phenomenon.

We invite you to read the second part of this article: “Mirror Molecules.”