Simulations of the active transport of a neutral solute based on a kinase-channel-phosphatase topology

Simulations of coupled interactions involving two opposite enzymatic reactions, solute diffusions, and electrostatic interactions between membrane charges and charged solutes were conducted under a fixed kinase-channel-phosphatase (KCP) topology oriented from the outside to the inside of a porous membrane structure. Depending on the kinase and phosphatase locations, we recently demonstrated that an active transport of a phosphorylated substrate may occur via the opposite topology, that is, a PCK topology. The present analysis demonstrates that, under a KCP membrane topology, which also behaves as a specific ATP-dependent transporter, the active transport of a neutral substrate may occur. This analogous active transport appears to be dependent on the phosphatase location and on the membrane surface potentials. A broad analysis of the role played by the main parameters taken into account in the model was conducted in order to define precisely the physico-chemical conditions and the membrane topology needed for the highest active transports within the shortest time.     

Structure-activity relationship of Ca2+ channel blockers: A study using conformational analysis and chemometric methods

Summary A structure-activity relationship study has been done on 8 compounds with the activity known as Ca²⁺ channel blockers. Conformational analysis was carried out using a molecular mechanics method. The 3D-QSAR approach was used and the most polar functional groups present in all the molecules were considered. Eight interatomic distances are necessary to define the relative spatial disposition of these relevant molecular fragments. The structure-activity relationship between interatomic distances and biological activity was performed using statistic and chemometric methods. In particular, with Principal Component Analysis, it was possible to reduce the number of interatomic distances: only six of the eight distances are sufficient to describe the system in a useful way. A classification method was iteratively used to select the most probable conformations linked to the biological activity and to build a model able to classify conformations according to their biological behaviour. Cluster analysis on the active selected conformations subsequently allowed the identification of two different geometrical patterns for the active compounds. Finally the validity of the model was verified by correctly predicting the activity of other molecules not used in the construction of the model but possessing known activity.     

Benchmark studies of the BCRLM reactive scattering code: Implications for accurate quantum calculations

Summary The Bending Corrected Rotating Linear Model (BCRLM), developed by Hayes and Walker, is a simple approximation to the true multidimensional scattering problem for reactions of the type: A + BC AB + C. While the BCRLM method is simpler than methods designed to obtain accurate three-dimensional quantum scattering results, this turns out to be a major advantage in terms of our benchmarking studies. The computer code used to obtain BCRLM scattering results is written for the most part in standard FORTRAN and has been ported to several scalar, vector, and parallel architecture computers including the IBM 3090-600J, the Cray XMP and YMP, the Ardent Titan, IBM RISC System/6000, Convex C-1 and the MIPS 2000. Benchmark results will be reported for each of these machines with an emphasis on comparing the scalar, vector, and parallel performance for the standard code with minimum modifications. Detailed analysis of the mapping of the BCRLM approach onto both shared and distributed memory parallel architecture machines indicates the importance of introducing several key changes in the basic strategy and algorithms used to calculate scattering results. This analysis of the BCRLM approach provides some insights into optimal strategies for mapping three-dimensional quantum scattering methods, such as the Parker-Pack method, onto shared or distributed memory parallel computers.     

An approach to channel type molecular structures. 1. Synthesis ofBouquet-shaped molecules based on an [18]-O6 polyether macrocycle

An approach to a transmembrane cation channel is described. It is based on the grafting of oxygen bearing side-chains on a macrocyclic polyether unit that constitutes the organizing core. The resulting species has a structure of overall bouquet shape. The synthesis of such a molecule . _M ⁰ ,14a is described, together with that of its analogue bearing polymethylene side-chains _M ^C ,14b. The physicochemical properties of these molecules indicate that they possess the features expected on the basis of their structure.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Homologies cyclique et de Hochschild de certains espaces homogènes quantiques

Nous quantifions certaines inclusions d'algèbres de Lie semi-simpleshg. Nous calculons les homologies associées aux quantifications, surC((h)), d'une part des algèbres de fonctions formelles surG/H, pourHG une inclusion de groupes de Lie semi-simples associée, et d'autre part des fonctions algébriques sur SL(2,C)/T.We quantize certain inclusions of semisimple Lie algebrashg. We compute the cyclic and Hochschild homologies for theC((h))-quantizations of

Field and photo-field electron emission from self-assembled Ge–Si nanostructures with quantum dots

Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was 10 nm and cluster density was 10¹⁰ cm⁻². A stable field electron emission was obtained from these structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current–voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 μm.     

van der Waals corrections to density functional theory calculations: Methane,ethane, ethylene,benzene, formaldehyde,ammonia, water,PBE, and CPMD

Parameters are developed for a practical application of the empirical van der Waals (vdW) correction infrastructure available in the CPMD density functional theory (DFT) code. The binding energy, geometry, and potential energy surface (PES) are examined for methane, ethane, ethylene, formaldehyde, ammonia, three benzene dimer geometries, and three benzene–water geometries. The vdW corrected results compare favorably with MP2 and CCSD(T) calculations near the complete basis set limits, and with experimental results where they are available.     

Silica/Proteoliposomal Nanocomposite as a Potential Platform for Ion Channel Studies

The nanostructuration of solid matrices with lipid nanoparticles containing membrane proteins is a promising tool for the development of high-throughput screening devices. Here, sol-gel silica-derived nanocomposites loaded with liposome-reconstituted KcsA, a prokaryotic potassium channel, have been synthesized. The conformational and functional stability of these lipid nanoparticles before and after sol-gel immobilization have been characterized by using dynamic light scattering, and steady-state and time-resolved fluorescence spectroscopy methods. The lipid-reconstituted KcsA channel entrapped in the sol-gel matrix retained the conformational and stability changes induced by the presence of blocking or permeant cations in the buffer (associated with the conformation of the selectivity filter) or by a drop in the pH (associated with the opening of the activation gate of the protein). Hence, these results indicate that this novel device has the potential to be used as a screening platform to test new modulating drugs of potassium channels.     

Modification of Polymeric Carbon Nitride with Au–CeO2 Hybrids to Improve Photocatalytic Activity for Hydrogen Evolution

The construction of a multi-component heterostructure for promoting the exciton splitting and charge separation of conjugated polymer semiconductors has attracted increasing attention in view of improving their photocatalytic activity. Here, we integrated Au nanoparticles (NPs) decorated CeO₂ (Au–CeO₂) with polymeric carbon nitride (PCN) via a modified thermal polymerization method. The combination of the interfacial interaction between PCN and CeO₂ via N-O or C-O bonds, with the interior electronic transmission channel built by the decoration of Au NPs at the interface between CeO₂ and PCN, endows CeAu–CN with excellent efficiency in the transfer and separation of photo-induced carriers, leading to the enhancement of photochemical activity. The amount-optimized CeAu–CN nanocomposites are capable of producing ca. 80 μmol· H₂ per hour under visible light irradiation, which is higher than that of pristine CN, Ce–CN and physical mixed CeAu and PCN systems. In addition, the photocatalytic activity of CeAu–CN remains unchanged for four runs in 4 h. The present work not only provides a sample and feasible strategy to synthesize highly efficient organic polymer composites containing metal-assisted heterojunction photocatalysts, but also opens up a new avenue for the rational design and synthesis of potentially efficient PCN-based materials for efficient hydrogen evolution.     

水溶性量子点纳米微球的制备、表征及其在生物检测中的应用

通过超声乳化(O/W)法, 在CdSe/CdS荧光量子点外包覆一层双亲性高分子外壳, 制得水溶性量子点纳米微球. 用荧光发射光谱(PL)和透射电子显微镜(TEM)等手段对产品进行了表征. 结果表明, 此种方法简单易行, 制得的量子点纳米微球(70 nm)具有良好的水溶性、稳定性以及较强的荧光发射强度. 用这种改性后的量子点标记的免疫球蛋白分子能够识别专一抗原, 因此这种纳米粒子将有望进一步应用于生物检测.