Ultrafast dynamics of myoglobin without the distal histidine: stimulated vibrational echo experiments and molecular dynamics simulations

Ultrafast protein dynamics of the CO adduct of a myoglobin mutant with the polar distal histidine replaced by a nonpolar valine (H64V) have been investigated by spectrally resolved infrared stimulated vibrational echo experiments and molecular dynamics (MD) simulations. In aqueous solution at room temperature, the vibrational dephasing rate of CO in the mutant is reduced by approximately 50% relative to the native protein. This finding confirms that the dephasing of the CO vibration in the native protein is sensitive to the interaction between the ligand and the distal histidine. The stimulated vibrational echo observable is calculated from MD simulations of H64V within a model in which vibrational dephasing is driven by electrostatic forces. In agreement with experiment, calculated vibrational echoes show slower dephasing for the mutant than for the native protein. However, vibrational echoes calculated for H64V do not show the quantitative agreement with measurements demonstrated previously for the native protein.     

On the generalized mean curvature

We study some properties of graphs whose mean curvature (in distributional sense) is a vector Radon measure. In particular, we prove that the distributional mean curvature of the graph of a Lipschitz continuous function u is a measure if and only if the distributional divergence of T u is a measure. This equivalence fails to be true if Lipschitz continuity is relaxed, as it is shown in a couple of examples. Finally, we prove a theorem of approximation in W ^(1,1) and in the sense of mean curvature of C ² graphs by polyhedral graphs. A number of examples illustrating different situations which can occur complete the work.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Synthesis and chromatographic enantioresolution of anti-HIV quinolone derivatives

The successful enantioseparation of five 6-desfluoroquinolones with three polysaccharide-based stationary phases (namely, the cellulose-based Chiralpak IB and the two amylose-based Chiralpak AD-H and Lux Amylose-2) is herein described. The investigated species differ for the nature of substituents and/or the position of the stereogenic centre on the quinolone scaffold.The effect on the enantioseparation performance exerted by the different morphology of the cellulose-based and amylose-based polymers, was systematically evaluated for all compounds. In this frame, the impact of alternative alcoholic (ethanol, 2-ethoxyethanol, methanol, 2-propanol) and acidic (acetic, methanesulfonic and trifluoroacetic acid) modifiers as well as of a “non-standard” solvent (chloroform), was investigated in normal phase conditions along with the stereo-electronic peculiarities of the selected polymers. While 7-[4-(1,3-benzothiazol-2-yl)-2-methyl-1-piperazinyl]-1-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylic acid (1) was enantioresolved with conventional normal-phase conditions by means of the largely employed amylose-based Chiralpak AD-H column, the recruitment of a bulky alcohol (2-ethoxyethanol) succeeded in the enantioresolution of 6-amino-1-methyl-7-[2-methyl-4-(2-pyridinyl)-1-piperazinyl]-4-oxo-1,4-dihydro-3-quinolinecarboxylic acid (2) and 6-amino-1-[1-(hydroxymethyl)propyl]-4-oxo-7-(4-pyridin-2-ylpiperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic acid (3) with the same column. The use of the amylose-based Lux Amylose-2 column, carrying both an electro-withdrawing (chlorine) and an electro-donating (methyl) group on the carbamate residue, allowed to get 6-amino-1-methyl-4-oxo-7-[3-(2-pyridinyl)-1-pyrrolidinyl]-1,4-dihydro-3-quinolinecarboxylic acid hydrochloride (4) enanantioresolved, and 6-amino-1-methyl-4-oxo-7-(3-pyridin-2-ylpiperidin-1-yl)-1,4-dihydroquinoline-3-carboxylic acid (5) enantioseparated.     

On sets with variational mean curvature in L^{n}(\mathbf{R}^{n})

In this paper we give an example of a singular set with finite perimeter in the plane which is a subgraph with variational curvature in $L^2(\mathbf R ^2)$ . This is a extension to the class of graphs of a well celebrated example suggested by De Giorgi, where the boundary of the set was the union of two spiral curves.