Formation of poly-L-lysine monolayers on silica : modeling and experimental studies

Modification of solid substrates by poly-l-lysine (PLL) layers has been widely employed in order to improve their biocompatibility, for promoting protein and cell immobilization for fabrication of biosensor arrays and antibacterial coatings. However, despite many studies conducted in the literature, there is a deficiency in a quantitative description of PLL adsorption processes. It is postulated that this becomes feasible by applying direct experimental techniques combined with thorough theoretical modeling. In this work, the kinetics of PLL adsorption on silica for various ionic strengths was determined in situ under controlled flow conditions using the optical reflectometry and the streaming potential methods. Both the initial adsorption rates and longer time kinetic runs were acquired and quantitatively interpreted in terms of the convective diffusion and the random sequential adsorption theoretical modeling based on the coarse-grained Monte Carlo approach. This unique combination of experimental and theoretical approaches enabled us to gain new insight into the mechanism of macroion adsorption controlled by the electrostatic interactions, which affect both the molecule conformations and the blocking effects. Besides significance for basic science, the results obtained in this work can be exploited for developing reliable procedures for preparing stable PLL monolayers of well-controlled coverage and electrokinetic properties

A mixed-integer linear program for real-time train platforming management

Unexpected events may perturb operations and generate conflicts that must be addressed promptly to limit delay propagation and other negative impacts on the network. The real-time railway traffic management problem deals with disruptions in railway networks, including tracks, junctions and stations. When they happen in station areas, new decisions involving train platforming, rerouting, ordering and timing must be made in real time. This paper explores a mesoscopic approach to deal with disruptions at rail stations. A mathematical programming-based model is proposed to determine re-routing and re-scheduling decisions for railway traffic in a station area. The key steps of the approach, which simulate what happens in real-time traffic management, are: i) an initial off-line preprocessing stage of the set of feasible routes originally planned, ii) a second preprocessing stage which analyses the disruption and sets the necessary parameters for the last step iii), which consists of an integer programming model that seeks solutions which minimise deviations from planned train schedules and assigns new and appropriate platforms (if necessary). Computational experiments show that realistic instances can be solved near to optimality using CPLEX in very short times. This allows to consider this methodology for solving real time traffic management problems.Peer ReviewedPostprint (published version

Automated Nuclear Analysis of Leishmania major Telomeric Clusters Reveals Changes in Their Organization during the Parasite's Life Cycle

Parasite virulence genes are usually associated with telomeres. The clustering of the telomeres, together with their particular spatial distribution in the nucleus of human parasites such as Plasmodium falciparum and Trypanosoma brucei, has been suggested to play a role in facilitating ectopic recombination and in the emergence of new antigenic variants. Leishmania parasites, as well as other trypanosomes, have unusual gene expression characteristics, such as polycistronic and constitutive transcription of protein-coding genes. Leishmania subtelomeric regions are even more unique because unlike these regions in other trypanosomes they are devoid of virulence genes. Given these peculiarities of Leishmania, we sought to investigate how telomeres are organized in the nucleus of Leishmania major parasites at both the human and insect stages of their life cycle. We developed a new automated and precise method for identifying telomere position in the three-dimensional space of the nucleus, and we found that the telomeres are organized in clusters present in similar numbers in both the human and insect stages. While the number of clusters remained the same, their distribution differed between the two stages. The telomeric clusters were found more concentrated near the center of the nucleus in the human stage than in the insect stage suggesting reorganization during the parasite's differentiation process between the two hosts. These data provide the first 3D analysis of Leishmania telomere organization. The possible biological implications of these findings are discussed

Trypanosome Lytic Factor, an Antimicrobial High-Density Lipoprotein, Ameliorates Leishmania Infection

Innate immunity is the first line of defense against invading microorganisms. Trypanosome Lytic Factor (TLF) is a minor sub-fraction of human high-density lipoprotein that provides innate immunity by completely protecting humans from infection by most species of African trypanosomes, which belong to the Kinetoplastida order. Herein, we demonstrate the broader protective effects of human TLF, which inhibits intracellular infection by Leishmania, a kinetoplastid that replicates in phagolysosomes of macrophages. We show that TLF accumulates within the parasitophorous vacuole of macrophages in vitro and reduces the number of Leishmania metacyclic promastigotes, but not amastigotes. We do not detect any activation of the macrophages by TLF in the presence or absence of Leishmania, and therefore propose that TLF directly damages the parasite in the acidic parasitophorous vacuole. To investigate the physiological relevance of this observation, we have reconstituted lytic activity in vivo by generating mice that express the two main protein components of TLFs: human apolipoprotein L-I and haptoglobin-related protein. Both proteins are expressed in mice at levels equivalent to those found in humans and circulate within high-density lipoproteins. We find that TLF mice can ameliorate an infection with Leishmania by significantly reducing the pathogen burden. In contrast, TLF mice were not protected against infection by the kinetoplastid Trypanosoma cruzi, which infects many cell types and transiently passes through a phagolysosome. We conclude that TLF not only determines species specificity for African trypanosomes, but can also ameliorate an infection with Leishmania, while having no effect on T. cruzi. We propose that TLFs are a component of the innate immune system that can limit infections by their ability to selectively damage pathogens in phagolysosomes within the reticuloendothelial system

Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers

https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd

Modyfikacja substratów stałych przez kontrolowaną adsorpcję makrojonów

Mechanisms of cationic macroion adsorption on negatively charged solid substrates comprising mica and silica were thoroughly discussed. Attention was focused on poly(allylamine hydrochloride) (PAH), poly(dimethyl-diallylammonium chloride) (PDDA) and poly-L-lysine (PLL) widely used in practice. The bulk physicochemical parameters controlling the macroion adsorption such as the diffusion coefficient, hydrodynamic diameter, intrinsic viscosity and electrophoretic mobility were discussed. The latter, experimentally accessible parameter, enables to determine the electrokinetic charge of macroion molecules, their isoelectric points and zeta potentials. On the other hand, the analysis of the hydrodynamic diameter and the intrinsic viscosity data confirmed a largely elongated shape of the molecules even for concentrated electrolyte solution. These results are used for a quantitative interpretation of macroion adsorption at solid substrates investigated using in situ streaming potential measurements. It is confirmed that the macroion mostly adsorb in the side-on orientation forming layers whose maximum coverage can be regulated by the ionic strength of the solution. This streaming potential method can also be used to determine the stability of the layers performing controlled desorption kinetic measurements. It is shown that at pH 7.4 the PDDA and PLL macroions form stable layers on solid substrates, which can be used for an efficient immobilization of negatively charged macroions and bioparticles comprising protein molecules and viruses

Contract theory and the optimal delivery of health care in presence of waiting times and waiting lists

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Abdellatif Laȃbi, Un autre Maroc. L’utopia di un progetto democratico

L'intellettuale marocchino realizza un lucido e impietoso ritratto della situazione sociopolitica in Marocco e prospetta la soluzione di una svolta democratica fondata sul rispetto dei diritti umani, sulla laicità e sulla totale libertà di pensiero ed espressione, che cancelli le ingiustizie e i soprusi perpetrati dal governo e dalla élite politica nei confronti della popolazione marocchina

pH-Induced Changes in Polypeptide Conformation : Force-Field Comparison with Experimental Validation

Microsecond-long all-atom molecular dynamics (MD) simulations, circular dichroism, laser Doppler velocimetry, and dynamic light-scattering techniques have been used to investigate pH-induced changes in the secondary structure, charge, and conformation of poly l-lysine (PLL) and poly l-glutamic acid (PGA). The employed combination of the experimental methods reveals for both PLL and PGA a narrow pH range at which they are charged enough to form stable colloidal suspensions, maintaining their α-helix content above 60%; an elevated charge state of the peptides required for colloidal stability promotes the peptide solvation as a random coil. To obtain a more microscopic view on the conformations and to verify the modeling performance, peptide secondary structure and conformations rising in MD simulations are also examined using three different force fields, i.e., OPLS-AA, CHARMM27, and AMBER99SB-ILDNP. Ramachandran plots reveal that in the examined setup the α-helix content is systematically overestimated in CHARMM27, while OPLS-AA overestimates the β-sheet fraction at lower ionization degrees. At high ionization degrees, the OPLS-AA force-field-predicted secondary structure fractions match the experimentally measured distribution most closely. However, the pH-induced changes in PLL and PGA secondary structure are reasonably captured only by the AMBER99SB-ILDNP force field, with the exception of the fully charged PGA in which the α-helix content is overestimated. The comparison to simulations results shows that the examined force fields involve significant deviations in their predictions for charged homopolypeptides. The detailed mapping of secondary structure dependency on pH for the polypeptides, especially finding the stable colloidal α-helical regime for both examined peptides, has significant potential for practical applications of the charged homopolypeptides. The findings raise attention especially to the pH fine tuning as an underappreciated control factor in surface modification and self-assembly.Peer reviewe