Influence of Functional Groups on Charge Transport in Molecular Junctions

Using density functional theory (DFT), we analyze the influence of five classes of functional groups, as exemplified by NO2, OCH3, CH3, CCl3, and I, on the transport properties of a 1,4-benzenedithiolate (BDT) and 1,4-benzenediamine (BDA) molecular junction with gold electrodes. Our analysis demonstrates how ideas from functional group chemistry may be used to engineer a molecule's transport properties, as was shown experimentally and using a semiempirical model for BDA [Nano Lett. 7, 502 (2007)]. In particular, we show that the qualitative change in conductance due to a given functional group can be predicted from its known electronic effect (whether it is pi/sigma donating/withdrawing). However, the influence of functional groups on a molecule's conductance is very weak, as was also found in the BDA experiments. The calculated DFT conductances for the BDA species are five times larger than the experimental values, but good agreement is obtained after correcting for self-interaction and image charge effects.Comment: 6 pages, 3 figures, J. Chem. Phys (in press

Decision Support Systems to Support International Students: Potential for Practice?

International students now comprise a significant group within Australian higher education but many must overcome difficulties related to initial acceptance by the institution of their choice and enrolment in an appropriate course. The need to extend visas to permit completion or the application process for permanent resident status may also be important to the individual student. Decision support systems (DSS) for customer relationship management (CRM) have been suggested as a means of utilising information technologies for admission procedures in higher education (McClea & Yen 2005). This paper will consider whether students may be defined as customers and reflect upon the possible introduction of a decision support system to facilitate the admission and satisfactory progress of international students through their courses. It will focus upon the experiences of international students and academic staff in the School of Computer and Information Science of Edith Cowan University

Neuroconductor: an R platform for medical imaging analysis

Neuroconductor (https://neuroconductor.org) is an open-source platform for rapid testing and dissemination of reproducible computational imaging software. The goals of the project are to: (i) provide a centralized repository of R software dedicated to image analysis, (ii) disseminate software updates quickly, (iii) train a large, diverse community of scientists using detailed tutorials and short courses, (iv) increase software quality via automatic and manual quality controls, and (v) promote reproducibility of image data analysis. Based on the programming language R (https://www.r-project.org/), Neuroconductor starts with 51 inter-operable packages that cover multiple areas of imaging including visualization, data processing and storage, and statistical inference. Neuroconductor accepts new R package submissions, which are subject to a formal review and continuous automated testing. We provide a description of the purpose of Neuroconductor and the user and developer experience

Conformational photoswitching of a synthetic peptide foldamer bound within a phospholipid bilayer

The dynamic properties of foldamers, synthetic molecules that mimic folded biomolecules, have mainly been explored in free solution.We report on the design, synthesis, and conformational behavior of photoresponsive foldamers bound in a phospholipid bilayer akin to a biological membrane phase. These molecules contain a chromophore, which can be switched between two configurations by different wavelengths of light, attached to a helical synthetic peptide that both promotes membrane insertion and communicates conformational change along its length. Light-induced structural changes in the chromophore are translated into global conformational changes, which are detected by monitoring the solid-state 19 F nuclear magnetic resonance signals of a remote fluorine-containing residue located 1 to 2 nanometers away. The behavior of the foldamers in the membrane phase is similar to that of analogous compounds in organic solvents

Mechanism of stabilization of helix secondary structure by constrained Cα-tetrasubstituted alpha-amino acids

The theoretical basis behind the ability of constrained C\u3b1-tetrasubstituted amino acids (CTAAs) to induce stable helical conformations has been studied through Replica Exchange Molecular Dynamics Potential of Mean Force Quantum Theory of Atoms In Molecules calculations on Ac-l-Ala-CTAA-l-Ala-Aib-l-Ala-NHMe peptide models. We found that the origin of helix stabilization by CTAAs can be ascribed to at least two complementary mechanisms limiting the backbone conformational freedom: steric hindrance predominantly in the (+x,+y,\u2013z) sector of a right-handed 3D Cartesian space, where the z axis coincides with the helical axis and the C\u3b1 of the CTAA lies on the +y axis (0,+y,0), and the establishment of additional and relatively strong C\u2013H\ub7\ub7\ub7O interactions involving the CTAA

Reversible Capture and Release of a Ligand Mediated by a Long-Range Relayed Polarity Switch in a Urea Oligomer

[Image: see text] Ethylene-bridged oligoureas characterized by a continuous, switchable chain of hydrogen bonds and carrying a binding site (an N,N′-disubstituted urea) for a hydrogen-bond-accepting ligand (a phosphine oxide) were synthesized. These oligomers show stronger ligand binding when the binding site is located at the hydrogen-bond-donating terminus than when the same binding site is at the hydrogen-bond-accepting terminus. An acidic group at the terminus remote from the binding site allows hydrogen bond polarity, and hence ligand binding ability, to be controlled remotely by a deprotonation/reprotonation cycle. Addition of base induces a remote conformational change that is relayed through up to five urea linkages, reducing the ability of the binding site to retain an intermolecular association to its ligand, which is consequently released into solution. Reprotonation returns the polarity of the oligomer to its original directionality, restoring the function of the remote binding site, which consequently recaptures the ligand. This is the first example of a synthetic molecular structure that relays intermolecular binding information, and these “dynamic foldamer” structures are prototypes of components for chemical systems capable of controlling chemical function from a distance

Cutting the Lawn - Natural Burial and its Contribution to the Delivery of Ecosystem Services in Urban Cemeteries

This article investigates the impact of natural burial on the delivery of ecosystem services (ESs) in urban cemeteries in England that are owned and managed by local authorities. Local authority natural burial sites have received far less attention from researchers than independent sites developed by farmers, charitable trusts, funeral directors and land owners. Here we argue that the local authority hybrid cemeteries that combine natural burial with traditional graves may have a far greater impact in delivering regulatory and cultural ecosystem services than the much larger and frequently more environmentally ambitious natural burial grounds developed by the independent sector. The article presents three case studies of cemeteries, each of which represents a different interpretation of natural burial. Two have retrofitted natural burial into an existing cemetery landscape. The third is a new cemetery where natural burial was included with traditional burial in the original design brief and planning application. The research reveals how natural burial is transforming the traditional cemetery, with its focus on an intensively managed lawn aesthetic, towards a more habitat rich and spatially complex landscape with its own distinctive identity. The research also reveals how natural burial (within the unique constraints of UK burial culture that does not permit the recycling of burial space) is increasing the burial capacity of urban cemeteries by accessing land and grave space that might not be suitable or appropriate for more traditional forms of burial

Tilt-angle landscapes and temperature dependence of the conductance in biphenyl-dithiol single-molecule junctions

Using a density-functional-based transport method we study the conduction properties of several biphenyl-derived dithiol (BPDDT) molecules wired to gold electrodes. The BPDDT molecules differ in their side groups, which control the degree of conjugation of the pi-electron system. We have analyzed the dependence of the low-bias zero-temperature conductance on the tilt angle phi between the two phenyl ring units, and find that it follows closely a cos^2(phi) law, as expected from an effective pi-orbital coupling model. We show that the tilting of the phenyl rings results in a decrease of the zero-temperature conductance by roughly two orders of magnitude, when going from a planar conformation to a configuration in which the rings are perpendicular. In addition we demonstrate that the side groups, apart from determining phi, have no influence on the conductance. All this is in agreement with the recent experiment by Venkataraman et al. [Nature 442, 904 (2006)]. Finally, we study the temperature dependence of both the conductance and its fluctuations and find qualitative differences between the examined molecules. In this analysis we consider two contributions to the temperature behavior, one coming from the Fermi functions and the other one from a thermal average over different contact configurations. We illustrate that the fluctuations of the conductance due to temperature-induced changes in the geometric structure of the molecule can be reduced by an appropriate design.Comment: 9 pages, 6 figures; submitted to Phys. Rev.

Hydantoin-bridged medium ring scaffolds by migratory insertion of urea-tethered nitrile anions into aromatic C-N bonds

Bicyclic or tricyclic nitrogen-containing heterocyclic scaffolds were constructed rapidly by intramolecular nucleophilic aromatic substitution of metallated nitriles tethered by a urea linkage to a series of electronically unactivated heterocyclic precursors. The substitution reaction constitutes a ring expansion, enabled by the conformationally constrained tether between the nitrile and the heterocycle. Attack of the metallated urea leaving group on the nitrile generates a hydantoin that bridges the polycyclic products. X-ray crystallography reveals ring-dependant strain within the hydantoin