Headlines 2007
One of the great mysteries of life is its lack of symmetry at the molecular scale. Many biological molecules, like amino acids, exist a priori in two asymmetrical forms, "right” and “left”. Such molecules are referred to as “chiral” . Like the two hands, these forms cannot be superimposed but are mirror images of each other (Fig.). However, in living organisms, proteins are exclusively built up from “left” amino acids. This selection of only one form remains one of the great scientific enigmas, which physicists, chemists and biologists try to solve.
Proteins are extremely long chains of amino acids. Each amino acid is added by formation of a peptide bound (CONH) and release of a water molecule, leaving a residue attached to the chain. Within the cells, the proteins thus formed are folded and their function depends not only on their sequence but also on their conformation. This makes the studies of the fundamental mechanisms of protein folding of strong interest.
By studying both experimentally and theoretically the folding of simple peptides, made of two amino acids, researchers from the "Service des Photons, Atomes et Molécules” of CEA-Saclay have obtained new results documenting the issue of chirality of the living world.
Thomas Blenskia et Bogdan Cichockib
aCEA Saclay, DSM/IRAMIS/LIDYL, Bât 522, F91191 Gif-sur-Yvette Cedex, France
bInstitute of Theoretical Physics, Warsaw University, Hoza 69,
00-681 Warsaw, Poland
Dans un plasma dense et chaud (étoiles, interaction avec un laser nanoseconde, fusion inertielle …), les atomes sont partiellement ionisés et forment un mélange d'ions et d'électrons à la dynamique très complexe. Une bonne modélisation de cet état doit être fondée sur une compréhension du système étudié permettant de reproduire l'ensemble de ses propriétés, pour finalement révéler ses particularités Pour un plasma, le bilan radiatif et les propriétés optiques sont des paramètres macroscopiques particulièrement importants à connaître, mais cela nécessite de disposer d'un modèle quantique prenant bien en compte l'ensemble des états atomiques excités tout en restant thermodynamiquement cohérent. C'est ce type de modèle que les théoriciens tentent de développer activement depuis plus de cinquante ans. La difficulté de construire un modèle quantique et thermodynamique d'un plasma a été récemment surmontée par les travaux [6,7] entrepris au DRECAM/SPAM en collaboration avec B. Cichocki de l’Université de Varsovie.
Clusters consists in a set of several up to million atoms in condensed phase with nanometric finite size. The investigation of their properties as the function of their increasing size is sometimes presented as one way to build a macroscopic condensed world from a gas. This often appears to be too simplistic, because the static and dynamic behavior of clusters has often no equivalence at the macroscopic scale, as they are controlled by their high specific surface and their finite size. These concerns the physical chemistry of the mesoscopic world, as illustrated by the recent experimental study driven by the "Reaction dynamics" group of DRECAM/SPAM-Laboratoire Francis Perrin in collaboration with a theoretician team from Paris VI University.
One of the great mysteries of life is its lack of symmetry at the molecular scale. Many biological molecules, like amino acids, exist a priori in two asymmetrical forms, "right” and “left”. Such molecules are referred to as “chiral” . Like the two hands, these forms cannot be superimposed but are mirror images of each other (Fig.). However, in living organisms, proteins are exclusively built up from “left” amino acids. This selection of only one form remains one of the great scientific enigmas, which physicists, chemists and biologists try to solve.
Proteins are extremely long chains of amino acids. Each amino acid is added by formation of a peptide bound (CONH) and release of a water molecule, leaving a residue attached to the chain. Within the cells, the proteins thus formed are folded and their function depends not only on their sequence but also on their conformation. This makes the studies of the fundamental mechanisms of protein folding of strong interest.
By studying both experimentally and theoretically the folding of simple peptides, made of two amino acids, researchers from the "Service des Photons, Atomes et Molécules” of CEA-Saclay have obtained new results documenting the issue of chirality of the living world.
Service des Photons, Atomes et Molécules DRECAM/SPAM
The very new laser of the "Plateforme Laser Femtoseconde Accordable, PLFA" began to be installed last year within the Service of Photons Atoms and Molecules (SPAM). It belongs to the infrastructure SLIC, member of the European network LASERLAB-EUROPE and is thus accessible to European scientists. It was designed according to several bets: high repetition rate (1 Khz), strong pulse energy (up to 13mJ, at 800nm), broad accordability (500-750nm) and ultra-fast pulses (<35 fs = 35 10-15 s).
The requirement of a wide wavelength range, even difficult to realize, is necessary to allow decisive progress in physico-chemistry of fast reactions. The requirements in pulse duration were chosen to probe efficiently the dynamics of reactions.
Research in that field began within DRECAM at the beginning of the 90's. They led to a revolution in physico-chemistry: the duration of the energy flow within organic or bio-organic molecules often scales within the sub-picosecond time range. This was at variance with the models usually used of redistribution of energy by coupling between electronic excitation and vibration.
The PLFA project is essential to offer a more complete approach: it allows at the same time energy studies, by adjusting the quantity of energy deposited in the system, selectivity by the accordability of the source and time studies at the femtosecond scale.
Clusters consists in a set of several up to million atoms in condensed phase with nanometric finite size. The investigation of their properties as the function of their increasing size is sometimes presented as one way to build a macroscopic condensed world from a gas. This often appears to be too simplistic, because the static and dynamic behavior of clusters has often no equivalence at the macroscopic scale, as they are controlled by their high specific surface and their finite size. These concerns the physical chemistry of the mesoscopic world, as illustrated by the recent experimental study driven by the "Reaction dynamics" group of DRECAM/SPAM-Laboratoire Francis Perrin in collaboration with a theoretician team from Paris VI University.
Service des Photons, Atomes et Molécules DRECAM/SPAM
The very new laser of the "Plateforme Laser Femtoseconde Accordable, PLFA" began to be installed last year within the Service of Photons Atoms and Molecules (SPAM). It belongs to the infrastructure SLIC, member of the European network LASERLAB-EUROPE and is thus accessible to European scientists. It was designed according to several bets: high repetition rate (1 Khz), strong pulse energy (up to 13mJ, at 800nm), broad accordability (500-750nm) and ultra-fast pulses (<35 fs = 35 10-15 s).
The requirement of a wide wavelength range, even difficult to realize, is necessary to allow decisive progress in physico-chemistry of fast reactions. The requirements in pulse duration were chosen to probe efficiently the dynamics of reactions.
Research in that field began within DRECAM at the beginning of the 90's. They led to a revolution in physico-chemistry: the duration of the energy flow within organic or bio-organic molecules often scales within the sub-picosecond time range. This was at variance with the models usually used of redistribution of energy by coupling between electronic excitation and vibration.
The PLFA project is essential to offer a more complete approach: it allows at the same time energy studies, by adjusting the quantity of energy deposited in the system, selectivity by the accordability of the source and time studies at the femtosecond scale.
