Dynamics and self-assembly of bio-functionalized gold nanoparticles in solution: Reactive molecular dynamics simulations

The self-assembling properties, stability, and dynamics of hybrid nanocarriers (gold nanoparticles (AuNPs) functionalized with cysteine-based peptides) in solution are studied through a series of classical molecular dynamics simulations based on a recently parametrized reactive force field. The results reveal, at the atomic level, all the details regarding the peptide adsorption mechanisms, nanoparticle stabilization, aggregation, and sintering. The data confirm and explain the experimental findings and disclose aspects that cannot be scrutinized by experiments. The biomolecules are both chemisorbed and physisorbed; self-interactions of the adsorbates and formation of stable networks of interconnected molecules on the AuNP surfaces limit substrate reconstructions, protect the AuNPs from the action of the solvent, and prevent direct interactions of the gold surfaces. The possibility of agglomeration of the functionalized nanoparticles, compared with the sintering of the bare supports in a water solution, is demonstrated through relatively long simulations and fast steered dynamics. The analysis of the trajectories reveals that the AuNPs were well stabilized by the peptides. This prevented particle sintering and kept the particles far apart; however, part of their chains could form interconnections (crosslinks) between neighboring gold vehicles. The excellent agreement of these results with the literature confirm the reliability of the method and its potential application to the modeling of more complex materials relevant to the biomedical sector.

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Short- and long-term performance of the “Tecnaria” stud connector for timber-concrete composite beams

The paper presents the results of some experimental tests performed on the shear stud connection system for timber-concrete composite beams manufactured by the Tecnaria Ltd. Some push-out specimens constructed using both normal weight (NW) and light weight (LW) concrete were subjected to collapse and long-term creep tests. During the collapse test, the connector exhibited significant strength and stiffness. In the creep test performed in constant environmental conditions, delayed (creep) deformations took place mainly during the first days after loading. The next part of the creep test, conducted under cycles of environmental relative humidity, was characterized by an increase in delayed deformations (the so-called mechano-sorptive effect) due to the hygroscopic behaviour of timber around the connector. The amount of delayed deformation depended upon the cycle duration and was negligible for short period (less than one week) cycles. The use of LW concrete instead of␣NW concrete was found not to significantly affect␣the performance of the connection system␣neither in the long-term, nor in the collapse tests.     

Use of a chondroitin sulfate isomer as an effective and removable dispersant of single-walled carbon nanotubes

Three isomers of chondroitin sulfate (CS), i.e., CS-A, CS-B, and CS-C, are investigated as nanotube dispersants and are found to have vastly different abilities to disperse single-walled carbon nanotubes (SWNTs) in water due to their different intramolecular interactions. Only CS-A and CS-C effectively disperse SWNTs into small bundles or individual tubes while CS-B disperses SWNTs poorly. Computer simulation and circular dichrosim show that neat CS-A and CS-C have weak intramolecular hydrogen bonding and extended conformations in solution resulting in energetically more favorable interactions with nanotubes. CS-B has relatively strong intramolecular Coulombic interaction and more alpha-helical secondary structure in solution resulting in energetically less favorable interaction with the nanotubes. Atomic force microscopy images show helical wrappings of CS-A and CS-C around the SWNTs. Transmission electron microscopy corroborates the helical wrapping of CS-A. Different isomeric forms of a polymer can have vastly different dispersing power because of their different intramolecular interactions and conformations. The easy removability of CS-A from nanotubes is confirmed with X-ray photoelectron spectroscopy showing almost no detectable sulphur content after washing with water and by application of washed CS-A dispersed SWNTs in field-effect transistors.     

Daytime driving simulation performance and sleepiness in obstructive sleep apnoea patients

BACKGROUND: Sleepiness related car accidents are common in obstructive sleep apnoea syndrome (OSAS) patients. The objective measurements of sleepiness used in clinical setting quantify the tendency to fall asleep in quiet situations that are completely different from driving. METHODS: We studied 30 OSAS patients with subjective (subjective sleepiness scales) and objective (multiple sleep latency test, MSLT) sleepiness measurements, associated with driving simulation test (DST), previously validated in young healthy subjects. The results of subjective and objective sleepiness tests were compared with simulated driving performance in order to evaluate the suitability of our DST for measuring alertness. RESULTS: Subjective and objective sleepiness measurements were significantly correlated with driving performance on the simulator. The most significant correlates of sleepiness were the measures of the primary vehicle control task on the simulator: lane position variability and crash data. The comparison of DST and MSLT results suggested our driving simulated approach could be used to evaluate daytime sleepiness in the clinical setting of OSAS patients. CONCLUSIONS: Our DST is a suitable objective tool to detect sleepiness in OSAS patients, and could be useful in the clinical setting of sleep medicine and research.     

Air/Water Oxygen Transfer in a Biological Aerated Filter

The oxygen-transfer characteristics of an upflow biological aerated filter filled with angular clay media were determined over a wide range of gas and liquid flow rates. Liquid-side, oxygen-transfer coefficients (KLa) were measured using a nitrogen gas stripping method under abiotic conditions and were found to increase as both gas and liquid superficial velocity increases, with values ranging from 12 to 110?h?1 based on empty bed volume. The effect of gas and liquid velocity, wastewater to clean water ratio, and temperature dependence was correlated to within ±20% of the experimental KLa value. Stagnant gas holdup is roughly double in wastewater compared to clean water, but the dynamic gas holdup is the same. The oxygen-transfer coefficient is directly proportional to the dynamic gas holdup. Stagnant gas holdup does not influence the rate of oxygen transfer. The results suggest that dynamic gas holdup largely determines the specific interfacial area (a), whereas the interstitial liquid velocity largely controls the oxygen-transfer coefficient (KL).     

Attention remediation following traumatic brain injury in childhood and adolescence.

Traumatic brain injury (TBI) frequently affects both the basic and the superordinate components of attention; deficits vary according to patient age. This study evaluated the efficacy of a specific remediation intervention for attention. Sixty-five TBI patients (aged 6?18 years) with attention deficit were assessed at baseline and at 1-year follow-up: 40 patients received attention-specific neuropsychological training for 6 months, and the control group comprised 25 patients. Cognitive assessment included a Wechsler Intelligence Scale (e.g., A. Orsini, 1993) and the Continuous Performance Test II (CPT II; C. K. Conners, 2000). The Vineland Adaptive Behavior Scales (VABS; S. Sparrow, D. Balla & D. V. Cicchetti, 1984) was administered to assess the treatment's ecological validity. At baseline, all patients presented with a mild intellectual disability and pathological scores on the CPT II. At follow-up, significant differences were found between the 2 groups on the CPT II and VABS: The clinical group improved more than the control group. Specific remediation training for attention, including a combination of a process-specific approach and metacognitive strategies, significantly improved attention performance. Improvement in attention skills also affected adaptive skills positively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adsorption of Collagen Nanofibrils on Rough TiO2: A Molecular Dynamics Study

Classical molecular dynamics simulations of tropocollagen molecules on rough titania surfaces are presented. On the basis of plane rutile (100), two models for surface roughness have been adopted: (1 × 3) microfacets with dimensions of less than 14 Å had only minor influence on the adsorption of a triple helical structure with a diameter of about 16 Å. After increasing the roughness by terraces, steric hindrance of helix binding was observed. A model for telopeptide capping of the collagen triple helices was developed. The highly flexible telopeptide structures mediated adsorption on the surface and inserted into grooves of both surface models. The telopeptide β‐turn motifs at the C‐terminus of the tropocollagen interact with specific receptor regions of the triple helices. This intermolecular process seems to be entropy driven and may be the first step of assembling helices to ordered fibrils. Interaction between telopeptide and triple helix seems to be in competition with the rather enthalpy controlled surface adsorption of single collagen molecules.     

Functional Modification of Fibronectin by N‐Terminal FXIIIa‐Mediated Transamidation

A straightforward strategy is presented for the site‐specific incorporation of fluorophores or reactive probes into the extracellular matrix (ECM) protein fibronectin (Fn) by using the enzyme‐catalyzed transamidation by activated factor XIII. Characterization by SDS‐PAGE, western blotting, absorption measurements, mass spectrometry, and stepwise photobleaching for labeling quantification at the single‐molecule level showed that the labeling was efficient and restricted to the N‐terminal tails. The introduction of labels did not interfere with Fn fibrillogenesis, as verified by the incorporation of fluorescently labeled Fn into ECM and manually pulled Fn fibers. Site‐specific incorporation of an azide was used to create a template for bioorthogonal click chemistry reactions in a second bioconjugation step, thus offering versatile modification and application possibilities in the context of matrix biology and tissue engineering.