Modeling the properties of self-assembled monolayers terminated by carboxylic acids

Self-assembled monolayers of long-chain carboxylic acids are often used as substrates to promote the growth of oriented crystals. Recent work has shown that the length of the chain (odd or even number of carbon atoms) determines whether oriented growth is observed. We use molecular dynamics simulations to investigate whether the configuration of the headgroups is significantly different in the two cases. We conclude that there are differences between odd- and even-length chains, even at 300 K and in the presence of water for some packings of the monolayer. We discuss whether these differences are large enough to account for the different behavior.     

Hydrogen bonding and the conformations of poly(alkyl acrylamides)

The conformations of poly(alkyl acrylamide) oligomers in nonpolar solvents were studied using molecular dynamics techniques. Poly(methyl acrylamide) was found to collapse to a globule-like conformation at low temperatures; however, excluded volume effects inhibited the collapse of poly(octadecyl acrylamide). A high density of structured units, characterized by a trans-gauche-trans-trans-gauche-trans torsional sequence along the backbone, was noted in all simulations. Such units were found to create a particularly stable set of intramolecular hydrogen bonds. An oligomer constructed with these stable units was found to have significantly lower minimized energy than both the all-trans and the helical backbone conformations. The constructed conformation had lower Coulomb energy (more hydrogen bonds) than the all-trans conformation and lower dihedral energy (less backbone distortion) than the helical conformation. The propensity for poly(octadecyl acrylamide) to form hydrogen bonds introduced significant disorder into the orientation of the alkyl side chains. This disorder would inhibit crystallization and restrict the ability of such polymers to form epitaxial seeds for nucleating paraffin crystals.     

Direct observation of the multisheet Fermi surface in the strongly correlated transition metal compound ZrZn2

The existence of flat areas of a Fermi surface (FS), predicted by electronic structure calculations and used in models of both magnetically mediated and phonon-mediated Fulde-Ferrell-Larkin-Ovchinnikov superconducting states, is reported in the paramagnetic phase of the ferromagnetic superconductor ZrZn2 using positron annihilation. The strongly mass-renormalized FS sheet, dominating the Fermi level density of states, is seen for the first time. The delocalization of the magnetization is studied using measured and calculated magnetic Compton profiles.     

The impact of preventive voice care programs for training teachers: A longitudinal study

The teaching profession puts vocal health at a higher risk than other professions, causing what is referred to as "occupational dysphonia." There is a need for primary prevention of "occupational dysphonia" among the teaching profession, where good vocal health is promoted before a problem occurs. To investigate the primary prevention of occupational dysphonia among teachers, this study uses a sample population of 55 training teachers, in the postgraduate certificate of education (PGCE) course at the University of Ulster, Northern Ireland, who were randomly assigned to three training groups: control, indirect, and direct. The vocal performance of the three groups was measured at two points over the year of the PGCE course: first before any teaching or training began, and again after the first teaching practice. The training for the indirect and direct groups was provided before the teaching practices. Acoustic and self-perceptual measurements were used to assess the multidimensional outcomes. The results demonstrate interesting trends, that although not found to be significant, are approaching significance. Their voices will be reevaluated at a third point of measurement. The acoustic measurement reflects deterioration from time 1 to time 2 for the control group, improvement for the direct group, and no change for the indirect group, indicating that the training has proved beneficial. The self-rating scores vary in agreement with the acoustic results, presenting interesting findings. The findings of this study will be of benefit to teachers, their educators, voice therapists, health promoters, and human resource personnel.     

A conductometric device for monitoring of enzyme-catalyzed reactions

A new conductometric device is described for measurement of conductance changes during enzyme-catalyzed reactions. The use of platinum resistances inside the cell allows temperature regulation to be obtained without circulating water. Solutions are introduced and removed from the cell with a peristaltic pump. The device is evaluated by assaying serum urea concentrations down to 40 nM. The results correlate well with a spectrophotometric method based on biacetylmonoxime (r=0.997).     

The structure and properties of the stepped surfaces of MgO and NiO

The static lattice computer simulation method has been used to study the structure and properties of high index faces of MgO and NiO. The (10_n) series of faces can be considered as stepped (001) surfaces and have been studied for both materials. In addition, the (403) and (302) faces which can be considered as stepped (101) surfaces have been studied for NiO. The calculated energies for steps on the (001) face are 3.72×10^?10 and 3.62×10^?10 J m^?1 for MgO and NiO respectively. The NiO energy also requires correction for the crystal field splitting. The energy of steps on the (101) surface is at least an order of magnitude lower. The interaction between the steps is repulsive but of short range. The large variation of surface energy with angle indicates that torque terms cannot be neglected in the analysis of thermal grooving experiments. The step structure is modified by substantial ionic displacements leading to an obtuse step angle. The structure is qualitatively similar for both NiO and MgO. The large distortions are likely to modify the step properties from those deduced by consideration of only the ideal geometry.     

Self-assembly of 10-microm-sized objects into ordered three-dimensional arrays

This paper describes the self-assembly of small objects--polyhedral metal plates with largest dimensions of 10 to 30 microm--into highly ordered, three-dimensional arrays. The plates were fabricated using photolithography and electrodeposition techniques, and the faces of the plates were functionalized to be hydrophobic or hydrophilic using self-assembled monolayers (SAMs). Self-assembly occurs in water through capillary interactions between thin films of a hydrophobic liquid (a liquid prepolymer adhesive) coated onto the hydrophobic faces of the plates; coalescence of the adhesive films reduces the interfacial free energy of the system and drives self-assembly. By altering the size and surface-patterning of the plates, the external morphologies of the aggregates were varied. Curing the adhesive furnished mechanically stable aggregates that were characterized by scanning electron microscopy (SEM). For assemblies formed by plates partially composed of a sacrificial material, a subsequent etching step furnished fully open, three-dimensional microstructures. This work validates the use of capillary interactions for three-dimensional mesoscale self-assembly in the 10-microm-size regime and opens new avenues for the fabrication of complex, three-dimensional microscructures.     

The role of the hydrolysis and zirconium concentration on the structure and anticorrosion performances of a hybrid silicate sol-gel coating

In sol-gel chemistry, hydrolysis is the key step in the formation of the reactive hydroxide groups that are responsible for the formation of inorganic networks via the occurrence of condensation reactions. Though previous studies have investigated the effect of the hydrolysis conditions on the structure of organically modified silicates (ormosils), no study, to our knowledge, has investigated this variable on the structure of hybrid materials prepared by combinations of an ormosil and a transition metal (TM). Here, we propose to investigate this effect in a hybrid material composed of 3-trimethoxysilylpropylmethacrylate and a zirconium complex. To also highlight the effects of the precursor’s concentrations on the hydrolysis and condensation reactions of the hybrid materials, their relative content was altered along with the hydrolysis degree. The anticorrosion barrier properties were identified by characterisation of coatings deposited on AA2024-T3 substrates and correlation between the structure and the anticorrosion properties of the coatings were performed based on results obtained from structural characterisations (DLS, FTIR, ²⁹Si-NMR, DSC, AFM and SEM) and corrosion testing (EIS and NSS). It is demonstrated that competition in the formation of siloxane and Si-O-Zr bonds takes place and can be controlled by the degree of hydrolysis and the concentration of the zirconium complex. This effect was found to dramatically alter the morphology of the coatings and their subsequent anticorrosion performances. At short-term exposure times, it is found that the most condensed materials exhibited a higher corrosion resistance while over longer periods the performances were found to level. This article highlighted the critical impact of the hydrolysis degree and zirconium concentration on the connectivity of hybrid sol-gel coatings and the impact this has on corrosion performances.

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CycloPs: generating virtual libraries of cyclized and constrained peptides including nonnatural amino acids

We introduce CycloPs, software for the generation of virtual libraries of constrained peptides including natural and nonnatural commercially available amino acids. The software is written in the cross-platform Python programming language, and features include generating virtual libraries in one-dimensional SMILES and three-dimensional SDF formats, suitable for virtual screening. The stand-alone software is capable of filtering the virtual libraries using empirical measurements, including peptide synthesizability by standard peptide synthesis techniques, stability, and the druglike properties of the peptide. The software and accompanying Web interface is designed to enable the rapid generation of large, structurally diverse, synthesizable virtual libraries of constrained peptides quickly and conveniently, for use in virtual screening experiments. The stand-alone software, and the Web interface for evaluating these empirical properties of a single peptide, are available at http://bioware.ucd.ie .