Single-photon ionization dynamics of two conformers of glycine is studied by classical trajectory simulations using the semiempirical PM3 potential surface in ``on the fly'' calculations. Initial conditions for the trajectories are weighted according to the Wigner distribution function computed for the initial vibrational ground state. Vertical ionization in the spirit of the classical Franck-Condon principle is assumed. The dynamics of the two conformers are compared during the first 10 ps. The comparison shows very different dynamical behavior for the two conformers. In particular, the chemical fragmentation pathways differ in part. Also, one of the conformers gives much higher rates of conformational transitions, while the other conformer gives larger chemical fragmentation yields. The example shows significantly different chemical dynamics for two conformers close in energy and separated by a low barrier. (c) 2005 American Institute of Physics.
A study hypothesized that the pattern of event-related potentials (ERP) responses in the binary condition would be similar to the pattern obtained with no physical cues and would differ from the responses to the ternary structure. The differences were mainly observed in a late, attention-dependant component of the ERPs, corresponding to rather high-level processing.
In vitro compartmentalization (IVC) uses water-in-oil emulsions to create artificial cell-like compartments in which genes can be individually transcribed and translated. Here, we present a new application of IVC for the selection of DNA-nuclease inhibitors. We developed a nano-droplets delivery system that allows the transport of various solutes, including metal ions, into the emulsion droplets. This transport mechanism was used to regulate the activity of colicin nucleases that were co-compartmentalized with the genes, so that the nucleases were activated by nickel or cobalt ions only after the potential inhibitor genes have been translated. Thus, genes encoding nuclease inhibitors survived the digestion and were subsequently amplified and isolated. Selection is therefore directly for inhibition, and not for binding of the nuclease. The stringency of selection can be easily modulated to give high enrichments (100-500-fold) and recoveries. We demonstrated its utility by selecting libraries of the gene encoding the cognate inhibitor of colicin E9 (immunity protein 9, or Im9) for inhibition of another colicin (ColE7). The in vitro evolved inhibitors show significant inhibition of ColE7 both in vitro and in vivo. These Im9 variants carry mutations into residues that det. the selectivity of the natural counterpart (Im7) while completely retaining the residues that are conserved throughout the family of immunity protein inhibitors. The in vitro evolution process confirms earlier hypotheses regarding the "dual recognition" binding mechanism and the way in which new colicin-immunity pairs diverged from existing ones. [on SciFinder(R)]
Peripheral proteins can trigger the formation of domains in mixed. uid- like lipid membranes. We analyze the mechanism underlying this process for proteins that bind electrostatically onto a. at two- component membrane, composed of charged and neutral lipid species. Of particular interest are membranes in whichthe hydrocarbon lipid tails tend to segregate owing to nonideal chain mixing,but the ( protein- free) lipid membrane is nevertheless stable due to the electrostatic repulsion between the charged lipid headgroups. The adsorption of charged, say basic, proteins onto a membrane containing anionic lipids induces local lipid demixing, whereby charged lipids migrate toward ( or away from) the adsorption site, so as to minimize the electrostatic binding free energy. Apart from reducing lipid headgroup repulsion, this process creates a gradient in lipid composition around the adsorption zone, and hence a line energy whose magnitude depends on the protein's size and charge and the extent of lipid chain nonideality. Above a certain critical lipid nonideality, the line energy islarge enough to induce domain formation, i. e., protein aggregation and, concomitantly, macroscopic lipid phase separation. We quantitatively analyze the thermodynamic stability of the dressed membrane based on nonlinear Poisson- Boltzmann theory, accounting for both the microscopic characteristics of the proteins and lipid composition modulations at and around the adsorption zone. Spinodal surfaces and critical points of the dressed membranes are calculated for several different model proteins of spherical and disklike shapes. Among the models studied we. nd the most substantial protein- induced membrane destabilization for disk- like proteins whose charges are concentrated in the membrane- facing surface. If additional charges reside on the side faces of the proteins, direct protein- protein repulsion diminishes considerably the propensity fordomain formation. Generally, a highly charged. at face of a macroion appears most ef. cient in inducing large compositional gradients, hence a large and unfavorable line energy and consequently lateral macroion aggregation and, concomitantly, macroscopic lipid phase separation.
An iterative approach for calculating the frequency domain linear response of molecular systems within time-dependent density-functional theory is presented. The method completely avoids computing the exchange-correlation kernel which is typically the most expensive step for large systems. In particular, virtual orbitals are not needed. This approach may be useful for treating the response of large systems. We give an outline of the theory and a demonstration on a jellium model of an elliptic gold cluster. A detailed theory is appended discussing the computation of conductance and ac impedance of molecular junctions under bias.
Conduction spectroscopy measures the current I through a nanosystem as a function of the voltage V between two electrodes. The differential conductance, dl/dV, has peaks that can be assigned to resonance conditions with different electronic levels of the system. Between these increments, the current has roughly constant plateaus. We discuss how measurements of the current vs. voltage can be used to perform Boolean operations and hence construct finite state logic machines and combinational circuits. The inputs to the device are the source-drain voltage, including its sign, and a gate voltage applied in a manner analogous to optical Stark spectroscopy. As simple examples, we describe a two-state set-reset machine (a machine whose output depends on the input and also on its present state) and a full adder circuit (a circuit that requires three inputs and provides two outputs).
The present invention provides an electrochem. method for depositing a thin film comprising metal oxides or silicon oxides on a conductive surface placed on a non-conductive substrate by electrodeposition of sol-gel precursors on the conductive surface selectively. The sol-gel precursors may further comprise various dopants thereby patterning the conductive layer. [on SciFinder(R)]
This book is a historical study of the survey and mapping system of Palestine under the British Mandate. It traces the background and the reasoning behind the establishment of the survey programme, examines the foundations upon which the system was based, and strives to understand the motivation of those who implemented it. This study shows that the roots of the modern survey system of Palestine are to be sought in the Balfour Declaration and its implications regarding land in Palestine. The land issue was at the core of the mapping of Mandatory Palestine, and it remains as a core issue at the heart of the Israeli-Palestinian dispute.
The Modern Welsh epistolary texteme is here introduced and briefly examined, on the basis of the correspondence of Kate Roberts and Saunders Lewis. Following some preliminary general comments on the texteme, six syntactical topics are discussed – the nynegocentric deixis and tensing; presentation; focalization, topicalization and related issues; the epistolary narrative; allocutive and reactive elements; parenthesis – with a view to demonstrating the special grammatical systems of this texteme which, despite its affinities with the dialogue, is idiosyncratic in perspective and juncture.
Matter under extreme conditions can be generated by a collision of a hypersonic cluster with a surface. The ultra-high-pressure interlude lasts only briefly from the impact until the cluster shatters. We discuss the theoretical characterization of the pressure using the virial theorem and develop a constrained molecular-dynamics procedure to compute it. The simulations show that for rare-gas clusters the pressures reach the megabar range. The contribution to the pressure from momentum transfer is comparable in magnitude and is of the same sign as that (''the internal pressure'') due to repulsive interatomic forces. The scaling of the pressure with the reduced mechanical variables is derived and validated with reference to the simulations.
A review. The implications of organically-modified SiO2-based materials in electrochem. science is reviewed along with some selected recent trends in the field of functionalized and sol-gel SiO2 electrochem. These recent trends include the electro-assisted generation of organosilica films on solid electrode surfaces, the prepn. and applications of sol-gel derived composite (C, Au, nanotubes) electrodes, the electrochem. characterization of mass transfer reactions in porous functionalized silicas, solid-state electrochem. and gas sensors involving sol-gel materials, imprinted functionalized SiO2, and the electrochem. characterization and applications of ordered mesoporous organosilicas. [on SciFinder(R)]
Fluid membranes containing charged lipids enhance binding of oppositely charged proteins by mobilizing these lipids into the interaction zone, overcoming the concomitant entropic losses due to lipid segregation and lower conformational freedom upon macromolecule adsorption. We study this energetic-entropic interplay using Monte Carlo simulations and theory. Our model system consists of a flexible cationic polyelectrolyte, interacting, via Debye-Huckel and short-ranged repulsive potentials, with membranes containing neutral lipids, 1% tetravalent, and 10% ( or 1%) monovalent anionic lipids. Adsorption onto a fluid membrane is invariably stronger than to an equally charged frozen or uniform membrane. Although monovalent lipids may suffice for binding rigid macromolecules, polyvalent counter-lipids ( e. g., phosphatidylinositol 4,5 bisphosphate), whose entropy loss upon localization is negligible, are crucial for binding flexible macromolecules, which lose conformational entropy upon adsorption. Extending Rosenbluth's Monte Carlo scheme we directly simulate polymer adsorption on fluid membranes. Yet, we argue that similar information could be derived from a biased superposition of quenched membrane simulations. Using a simple cell model we account for surface concentration effects, and show that the average adsorption probabilities on annealed and quenched membranes coincide at vanishing surface concentrations. We discuss the relevance of our model to the electrostatic-switch mechanism of, e. g., the myristoylated alanine-rich C kinase substrate protein.
