三螺旋蛋白质的孤立子解研究

在作者得到的三螺旋蛋白质分子各向生耦合的薛定谔方程组的基础上，给了出了该方程组的孤立子解，并对其解进行了分析和讨论。     

Structural and ITC Characterization of Peptide-Protein Binding: Thermodynamic Consequences of Cyclization Constraints,a Case Study on Vascular Endothelial Growth Factor Ligands

Macrocyclization constraints are widely used in the design of protein ligands to stabilize their bioactive conformation and increase their affinities. However, the resulting changes in binding entropy can be puzzling and uncorrelated to affinity gains. Here, the thermodynamic (Isothermal Titration Calorimetry) and structural (X-ray, NMR and CD) analysis of a complete series of lactam-bridged peptide ligands of the vascular endothelial growth factor, and their unconstrained analogs are reported. It is shown that differences in thermodynamics arise mainly from the folding energy of the peptide upon binding. The systematic reduction in conformational entropy penalty due to helix pre-organization can be counterbalanced by an unfavorable vibrational entropy change if the constraints are too rigid. The gain in configurational entropy partially escapes the enthalpy/entropy compensation and leads to an improvement in affinity. The precision of the analytical ITC method makes this study a possible benchmark for constrained peptides optimization.     

Graph‐theoretical identification of dissociation pathways on free energy landscapes of biomolecular interaction

Biomolecular association and dissociation reactions take place on complicated interaction free energy landscapes that are still very hard to characterize computationally. For large enough distances, though, it often suffices to consider the six relative translational and rotational degrees of freedom of the two particles treated as rigid bodies. Here, we computed the six‐dimensional free energy surface of a dimer of water‐soluble alpha‐helices by scanning these six degrees of freedom in about one million grid points. In each point, the relative free energy difference was computed as the sum of the polar and nonpolar solvation free energies of the helix dimer and of the intermolecular coulombic interaction energy. The Dijkstra graph algorithm was then applied to search for the lowest cost dissociation pathways based on a weighted, directed graph, where the vertices represent the grid points, the edges connect the grid points and their neighbors, and the weights are the reaction costs between adjacent pairs of grid points. As an example, the configuration of the bound state was chosen as the source node, and the eight corners of the translational cube were chosen as the destination nodes. With the strong electrostatic interaction of the two helices giving rise to a clearly funnel‐shaped energy landscape, the eight lowest‐energy cost pathways coming from different orientations converge into a well‐defined pathway for association. We believe that the methodology presented here will prove useful for identifying low‐energy association and dissociation pathways in future studies of complicated free energy landscapes for biomolecular interaction. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Pesticides in water and the performance of the liquid-phase microextraction based techniques. A review

The control of pesticides in surface, drinking and groundwater is nowadays a real necessity. In the European Community, their concentration must comply with the established parametric and environmental quality standards (EQSs). Regarding the new legislation, this article updates the information concerning the monitoring of pesticides and the technical specifications for their measurement in water samples where ultra-sensitive analytical methods are required. For some compounds, like pesticides, there is still a need to improve the performance of the existing methods. High sensitive techniques like gas chromatography tandem mass spectrometry (GC–MS/MS) and liquid chromatography coupled with mass spectrometry (LC–MS) have been developed. However, for most of the substances present at trace and ultra-trace levels the extraction and preconcentration steps are so far essential for their detection. Advances at a micro scale have been made and different types of microextractions are being developed. Liquid-phase microextraction (LPME) is an example. The study of this technique has increased in the last years and some innovations have been recently reported for pesticides water analysis. This article reviews the new developed LPME-based techniques and compares its performance with the analytical specifications established for pesticides water monitoring. The results show that LPME-based techniques can be a promising tool to improve the nowadays performance of methods used in pesticides water control.     

Star-shaped fluorescent polypeptides

Two series of novel, four-arm, star-shaped polypeptides were prepared via the ring-opening polymerization of γ-benzyl-L -glutamate N-carboxyanhydride and ϵ-benzyloxycarbonyl-L -lysine N-carboxyanhydride with a tetra-amino-substituted perylene fluorophore as the initiator. The removal of the α-amino acid side-chain-protecting groups resulted in unprecedented water-soluble, perylene-functionalized, star-shaped polypeptides that showed strong fluorescence in aqueous solution. One of the features that distinguished these water-soluble star polypeptides from most other star polymers was that the conformation of the arms could be reversibly changed from a random coil into an α helix by variations in the pH of the aqueous solution. These star polypeptides might be of interest for the development of novel fluorescent probes or as traceable, stimuli-sensitive molecular containers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1572–1583, 2001     

Chirality sensing of chiral pyrrolidines and piperazines with a liquid crystalline dynamic helical poly(phenylacetylene) bearing ethyl phosphonate pendant groups

Stereoregular cis‐transoidal poly(phenylacetylene) bearing a phosphonic acid monoethyl ester as the pendant group (poly‐ 1 ‐H) was found to form a preferred‐handed helix upon complexation with various optically active pyrrolidines and piperazines in dilute dimethyl sulfoxide and water, and the complexes exhibited characteristic induced circular dichroisms (ICDs) in the UV‐vis region of the polymer backbone. The Cotton effect signs in water reflect the absolute configuration of the pyrrolidines. The sodium salt of poly‐ 1 ‐H (poly‐ 1 ‐Na) and poly‐ 1 ‐H in the presence of optically active amines formed lyotropic nematic and cholesteric liquid crystalline phases in concentrated water solutions, respectively, indicating the rigid‐rod characteristic of the polymer main chain regardless of the lack of a single‐handed helix, as evidenced by the long persistence length of about 18 nm before and after the preferred‐handed helicity induction in the polymer. X‐ray diffraction of the oriented films of the nematic and cholesteric liquid crystalline polymers exhibited almost the same diffraction pattern, suggesting that both polymers have the same helical structure; dynamically racemic and one‐handed helices, respectively. On the basis of the X‐ray analysis, a possible helical structure of poly‐ 1 is proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1383–1390, 2010     

Efficient synthesis of extended guanine analogues designed for recognition of an A·T inverted base pair in triple helix based-strategy

We report herein an efficient synthesis of new nucleosides N1, N2, and N3 as extended guanine analogues, derived from aminobenzimidazole and thymine or 5-substituted uracil. These nucleosides were devised for the recognition of an A·T inverted base pair by three hydrogen bonds, in triple helix-based technology.     

Synthese und Einkristallröntgenstrukturanalyse von Bromdi(isopropenyl)bismutan

Synthesis and Single Crystal X‐Ray Structure Analysis of Bromodi(isopropenyl)bismuthane Tri(isopropenyl)bismuthane ( 1 ) reacts with bromine to form bromodi(isopropenyl)bismuthane ( 2 ) and dibromo(isopropenyl)bismuthane ( 3 ). The single crystal X‐ray structure determination of 2 (monoclinic, P 2₁/c; a = 1058.6(3), b = 1127.0(3), c = 1561.3(4) pm, and β = 109.26(2)°; Z = 8 molecules; d_c = 2.803 g/cm³; R = 0.059) shows two crystallographically independent molecules which are connected by Bi–Br…Bi bridges (Bi–Br 282.3(2) and 284.7(2); Br…Bi 302.9(2) and 303.6(2) pm) forming helical chains directed along the b‐axis of the unit cell. Every turn of the helix (360°) consists of four molecules and corresponds to the length of the b‐axis (1127.0(3) pm).