Water exchange of a ProHance MRI contrast agent: isomer-dependent free-energy landscapes and mechanisms

The water-exchange reaction in two diastereoisomers of the clinical magnetic resonance imaging contrast agent [Gd(HP-DO3A)(H(2)O)] (also known as ProHance) has been studied using ab initio simulations. On the basis of the molecular-level details of the mechanism derived from these simulations in aqueous solution, we unravel the underlying difference in the free energies and mechanisms of water exchange in the two diastereoisomers. These findings reveal the crucial role played by hydrogen-bonding dynamics and thus suggest their appropriate control in tailoring improved gadolinium-based constrast agents.     

Assessment and prediction of thermal transport at solid-self-assembled monolayer junctions

Self-assembled monolayers (SAMs) have recently garnered much interest due to their unique electrical, chemical, and thermal properties. Several studies have focused on thermal transport across solid-SAM junctions, demonstrating that interface conductance is largely insensitive to changes in SAM length. In the present study, we have investigated the vibrational spectra of alkanedithiol-based SAMs as a function of the number of methylene groups forming the molecular backbone via Hartree-Fock methods. In the case of Au-alkanedithiol junctions, it is found that despite the addition of nine new vibrational modes per added methylene group, only one of these modes falls below the maximum phonon frequency of Au. In addition, the alkanedithiol one-dimensional density of normal modes (modes per unit energy per unit length) is nearly constant regardless of chain length, explaining the observed insensitivity. Furthermore, we developed a diffusive transport model intended to predict interface conductance at solid-SAM junctions. It is shown that this predictive model is in an excellent agreement with prior experimental data available in the literature.     

Enantioselective palladium-catalyzed [3 + 2] cycloadditions of trimethylenemethane with nitroalkenes

Nitroalkenes readily undergo palladium-catalyzed [3 + 2] cycloaddition with trimethylenemethane to generate nitrocyclopentanes in excellent yield and enantioselectivity. Furthermore, the products thus formed are highly versatile synthetic intermediates and provide convenient access to both cyclopentylamines and cyclopentenones.     

Theoretical studies of Pt-Ti nanoparticles for potential use as PEMFC electrocatalysts

A theoretical investigation is presented of alloying platinum with titanium to form binary Pt-Ti nanoalloys as an alternative to the expensive pure platinum catalysts commonly used for Proton Exchange Membrane Fuel Cell cathode electrocatalysts. Density Functional Theory calculations are performed to investigate compositional effects on structural properties as well as Oxygen Reduction Reaction kinetics and poisoning effects. High symmetry A(32)-B(6) clusters are studied to investigate structural properties. From these structures binding energies of hydroxyl and carbon monoxide are studied on a range of sites on the surface of the clusters. Promising results are obtained suggesting that the bimetallic Pt-Ti nanoalloys may exhibit enhanced properties compared to pure platinum catalysts.     

Mathematical literacy in undergraduates: role of gender,emotional intelligence and emotional self-efficacy

This empirical study explores the roles that Emotional Intelligence (EI) and Emotional Self-Efficacy (ESE) play in undergraduates’ mathematical literacy, and the influence of EI and ESE on students’ attitudes towards and beliefs about mathematics. A convenience sample of 93 female and 82 male first-year undergraduates completed a test of mathematical literacy, followed by an online survey designed to measure the students’ EI, ESE and factors associated with mathematical literacy. Analysis of the data revealed significant gender differences. Males attained a higher mean test score than females and out-performed the females on most of the individual questions and the associated mathematical tasks. Overall, males expressed greater confidence in their mathematical skills, although both males’ and females’ confidence outweighed their actual mathematical proficiency. Correlation analyses revealed that males and females attaining higher mathematical literacy test scores were more confident and persistent, exhibited lower levels of mathematics anxiety and possessed higher mathematics qualifications. Correlation analyses also revealed that in male students, aspects of ESE were associated with beliefs concerning the learning of mathematics (i.e. that intelligence is malleable and that persistence can facilitate success), but not with confidence or actual performance. Both EI and ESE play a greater role with regard to test performance and attitudes/beliefs regarding mathematics amongst female undergraduates; higher EI and ESE scores were associated with higher test scores, while females exhibiting higher levels of ESE were also more confident and less anxious about mathematics, believed intelligence to be malleable, were more persistent and were learning goal oriented. Moderated regression analyses confirmed mathematics anxiety as a negative predictor of test performance in males and females, but also revealed that in females EI and ESE moderate the effects of anxiety on test performance, with the relationship between anxiety and test performance linked more to emotional management (EI) than to ESE.     

Convergent, stereoselective synthesis of the GHIJ fragment of brevetoxin A

[reaction: see text] A stereoselective synthesis of the GHIJ fragment of brevetoxin A utilizing a convergent assembly strategy is described. Glycolate alkylation, ring-closing metathesis, and Hosomi-Sakurai reactions were central operations in the construction of the G ring and J ring subunits, which were united through a Horner-Wadsworth-Emmons coupling. Subsequent dehydrative cyclization produced an endocyclic enol ether that was further elaborated to the tetracyclic GHIJ fragment of brevetoxin A.     

Fate of vacancy-induced supersolidity in 4He

The supersolid state of matter, exhibiting nondissipative flow in solids, has been elusive for 35 years. The recent discovery of a nonclassical moment of inertia in solid 4He by Kim and Chan provided the first experimental evidence, although the interpretation in terms of supersolidity of the ideal crystal phase remains a subject to debate. Using quantum Monte Carlo methods we investigate the long-standing question of vacancy-induced superflow and find that vacancies in a 4He crystal phase separate instead of forming a supersolid. On the other hand, nonequilibrium vacancies relaxing on defects of polycrystalline samples could provide an explanation for the experimental observations.     

Rapid conversion of hindered arylsulfonates to alkyl chlorides with retention of configuration

Arylsulfonates of hindered secondary alcohols are converted to the corresponding alkyl chlorides very rapidly and in good yields in the presence of titanium tetrachloride at low temperatures. These reactions proceed with exclusive retention of configuration.     

Comparison of mixed-mode anion-exchange performance of N-vinylimidazole-divinylbenzene sorbent

A newly synthesized copolymer based on N-vinylimidazole-divinylbenzene (NVIm-DVB) was evaluated as a mixed-mode anion-exchange sorbent for SPE, since the NVIm monomer apart from its hydrophilic properties can be protonated at a certain pH, and then performs as an anion-exchanger. To investigate the behavior of the NVIm-based sorbent, the SPE performance was evaluated under reversed-phase (RP), weak anion-exchange, and strong anion-exchange conditions. The results for the NVIm-DVB sorbent were also compared to commercial reference sorbents from each group: Oasis HLB, Oasis WAX, and Oasis MAX, respectively. SPE results from this evaluation showed that NVIm-DVB can be used as an RP material, compared to Oasis HLB. It also has the potential to act as a strong anion-exchange sorbent, compared to Oasis MAX, since under the proper conditions it was able to fraction and quantitatively recover a group of selected solutes.