19 research outputs found
Bound states in a nonlinear Kronig-Penney model
We study the bound states of a Kronig Penney potential for a nonlinear
one-dimensional Schroedinger equation. This potential consists of a large, but
not necessarily infinite, number of equidistant delta-function wells. We show
that the ground state can be highly degenerate. Under certain conditions
furthermore, even the bound state that would normally be the highest can have
almost the same energy as the ground state. This holds for simple periodic
potentials as well.Comment: TeX file, figures available as postscript files upon reques
The influence of lanthanide-(III)-nitrates on adsorbed monolayers of dodecylphosphorylcholine at the air-water interface
Adsorption layers at the air-water interface formed from the soluble zwitterionic surfactant dodecylphosphorylcholine (DPC) serving as a soluble model substance for phospho-lipids were characterized with respect to their equilibrium and dynamic surface properties. To clarify the effect of ionic interactions with electrolyte present in the bulk phase, surface Theological properties upon addition of Ce(NO3)(3) and Yb (NO3)(3) were determined. In order to account for the surface activity of the nitrate ion, comparative measurements using NaNO3 were carried out additionally. Further experimental information on the bulk hydration characteristics of the aqueous solutions was obtained using dielectric relaxation spectroscopy (DRS). A possible mechanism causing the deviating surface dilatational modulus E in terms of ion specificity is suggested. (C) 2019 Published by Elsevier Inc
Helix Formation by Alanine-Based Peptides in Pure Water and Electrolyte Solutions: Insights from Molecular Dynamics Simulations
Specific ion effects on oligopeptide
conformations in solution
are attracting strong research attention, because of their impact
on the protein-folding problem and on several important biological–biotechnological
applications. In this work, we have addressed specific effects of
electrolytes on the tendency of oligopeptides toward formation and
propagation of helical segments. We have used replica-exchange molecular
dynamics (REMD) simulations to study the conformations of two short
hydrophobic peptides [Ace-(AAQAA)<sub>3</sub>-Nme (AQ), and Ace-A<sub>8</sub>-Nme (A8)] in pure water and in aqueous solutions of sodium
chloride (NaCl) and sodium iodide (NaI) with concentrations of 1 and
3 M. The average helicities of the AQ peptide have been analyzed to
yield Lifson–Roig (LR) parameters for helix nucleation and
helix propagation. The salt dependence of these parameters suggests
that electrolytes tend to stabilize the helical conformations of short
peptides by enhancing the <i>helix nucleation</i> parameter.
The helical conformations of longer oligopeptides are destabilized
in the presence of salts, however, because the <i>helix propagation</i> parameters are reduced by electrolytes. On top of this general trend,
we observe a significant specific salt effect in these simulations.
The hydrophobic iodide ion in NaI solutions has a high affinity for
the peptide backbone, which reflects itself in an enhanced helix nucleation
and a reduced helix propagation parameter with respect to pure water
or NaCl solutions. The present work thus explains the computational
evidence that electrolytes tend to stabilize the compact conformations
of short peptides and destabilize them for longer peptides, and it
also sheds additional light on the specific salt effects on compact
peptide conformations
Semi-Interpenetrating Polymer Networks with Predefined Architecture for Metal Ion Fluorescence Monitoring
The development of new synthetic approaches for the preparation of efficient 3D luminescent chemosensors for transition metal ions receives considerable attention nowadays, owing to the key role of the latter as elements in biological systems and their harmful environmental effects when present in aquatic media. In this work, we describe an easy and versatile synthetic methodology that leads to the generation of nonconjugated 3D luminescent semi-interpenetrating amphiphilic networks (semi-IPN) with structure-defined characteristics. More precisely, the synthesis involves the encapsulation of well-defined poly(9-anthrylmethyl methacrylate) (pAnMMA) (hydrophobic, luminescent) linear polymer chains within a covalent poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) hydrophilic polymer network, derived via the 1,2-bis-(2-iodoethoxy)ethane (BIEE)-induced crosslinking process of well-defined pDMAEMA linear chains. Characterization of their fluorescence properties demonstrated that these materials act as strong blue emitters when exposed to UV irradiation. This, combined with the presence of the metal-binding tertiary amino functionalities of the pDMAEMA segments, allowed for their applicability as sorbents and fluorescence chemosensors for transition metal ions (Fe3+, Cu2+) in solution via a chelation-enhanced fluorescence-quenching effect promoted within the semi-IPN network architecture. Ethylenediaminetetraacetic acid (EDTA)-induced metal ion desorption and thus material recyclability has been also demonstrated