SERS from molecules bridging the gap of particle-in-cavity structures

We demonstrate that by combining silver nanoparticles and structured gold SSV surfaces the SERS for those molecules that bridge the nanoparticle-cavity gap is preferentially enhanced using 4-mercaptoaniline and 4-mercaptobenzoic acid as examples.     

Development and Initial Validation of the Beliefs About Reformed Science Teaching and Learning (BARSTL) Questionnaire

This article describes the development and the initial validation of an instrument that can be used to assess teachers' beliefs about science teaching and learning. The instrument, which is called the Beliefs About Reformed Science Teaching and Learning (BARSTL) questionnaire, draws on the current national science education reform efforts in order to define a traditional‐reformed teaching and learning belief continuum that can be used to map teachers' beliefs. The reliability and validity of the instrument were examined using a multiple perspective approach. The psychometric properties of the BARSTL suggest that it is a valid and reliable instrument for measuring prospective elementary teachers' beliefs about science education.     

Push it to the limit: comparing periodic and local approaches to density functional theory for intermolecular interactions

ABSTRACT

With the aim of systematically comparing two popular approaches to density functional theory – all-electron calculations with local basis sets, and periodic calculations employing plane wave basis sets and norm-conserving pseudopotentials – we have computed complete-basis binding energies across the S22 set of intermolecular interactions, a dataset consisting of noncovalent interactions of small- and medium-sized molecules containing first- and second-row atoms, using the Troullier-Martins norm-conserving pseudopotentials with SPW92, a local spin-density approximation; and PBE, a generalised gradient approximation. We have found that it is challenging to reach the basis set limit with these periodic calculations; for the methods and systems examined, a minimum vacuum distance of 30?Å between a system and its nearest images is necessary – unless some form of dipole correction is employed – as is a kinetic energy cutoff of at least 80 Ry. The trends in convergence with respect to vacuum size and kinetic energy cutoff are largely independent of the level of density functional approximation employed. A sense of the impact of each hyperparameter on basis set error provides a foundation for ensuring quality calculations in future studies and allows us to quantify the basis set errors incurred in existing studies on similar systems.     

Ligand‐Based Control of Single‐Site vs. Multi‐Site Reactivity by a Trichromium Cluster

The trichromium cluster (^tbsL)Cr₃(thf) ([^tbsL]^6?=[1,3,5‐C₆H₉(NC₆H₄‐o‐NSi^tBuMe₂)₃]^6?) exhibits steric‐ and solvation‐controlled reactivity with organic azides to form three distinct products: reaction of (^tbsL)Cr₃(thf) with benzyl azide forms a symmetrized bridging imido complex (^tbsL)Cr₃(μ³‐NBn); reaction with mesityl azide in benzene affords a terminally bound imido complex (^tbsL)Cr₃(μ¹‐NMes); whereas the reaction with mesityl azide in THF leads to terminal N‐atom excision from the azide to yield the nitride complex (^tbsL)Cr₃(μ³‐N). The reactivity of this complex demonstrates the ability of the cluster‐templating ligand to produce a well‐defined polynuclear transition metal cluster that can access distinct single‐site and cooperative reactivity controlled by either substrate steric demands or reaction media.     

Approximately Multiplicative Functionals on Algebras of Smooth Functions

Let be a bounded linear functional on A, where A is a commutativeBanach algebra, then the bilinear functional is defined as (a,b)= (ab)- (a) (b) for each a and b in A. If the norm of is small then is approximatelymultiplicative, and it is of interest whether or not |||| being small implies that is nearto a multiplicative functional. If this property holds for acommutative Banach algebra then A is an AMNM algebra (approximatelymultiplicative functionals are near multiplicative functionals).The main result of the paper shows that C^N [0,1]^M (the complexvalued functions defined on [0,1]^M with all Nth order partialderivatives continuous) is AMNM. It is also shown that a similarproof can be applied to certain Lipschitz algebras.     

A Solomon Link through an Interwoven Molecular Grid

A molecular Solomon link was synthesized through the assembly of an interwoven molecular grid consisting of four bis(benzimidazolepyridyl)benzthiazolo[5,4‐d]thiazole ligands and four zinc(II), iron(II), or cobalt(II) cations, followed by ring‐closing olefin metathesis. NMR spectroscopy, mass spectrometry, and X‐ray crystallography confirmed the doubly interlocked topology, and subsequent demetalation afforded the wholly organic Solomon link. The synthesis, in which each metal ion defines the crossing point of two ligand strands, suggests that interwoven molecular grids should be useful scaffolds for the rational construction of other topologically complex structures.     

Filling a Niche in “Ligand Space” with Bulky,Electron-Poor Phosphorus(III) Alkoxides

The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron-rich species. Many of the electron-poor P^III ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron-poor P^III ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of P^III ligands bearing highly fluorinated alkoxide groups of the general form PR_n(OR^F)_3−n, where R=Ph, R^F=C(H)(CF₃)₂ and C(CF₃)₃; n=1–3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron-poor ligands.     

Diastereoselective Control of Tetraphenylethene Reactivity by Metal Template Self-Assembly

The reaction of 4,4′,4′′,4′′′-(ethene-1,1,2,2-tetrayl)tetraaniline with 2-pyridinecarboxaldehyde and iron(II) chloride resulted, after aqueous workup, in the diastereoselective formation of an [Fe₂L₃]⁴⁺ triple-stranded helicate structure, irrespective of the stoichiometry employed. The helicate structure was characterized in solution by multinuclear NMR spectroscopy, and in the solid state by single-crystal X-ray crystallography. The reaction of iron(II) tetrafluoroborate or iron(II) bistriflimide with the tetraaniline and 2-pyridinecarboxaldehyde allowed the formation of an [Fe₈L₆]¹⁶⁺ cube when the appropriate stoichiometry was used, but these structures were unstable with respect to hydrolysis. The pendant amine groups on the helicate can be functionalized by reaction with acid chlorides or anhydrides, and the resulting functionalized tetraphenylethene (TPE) units were isolated by the reaction of the helicate with tris(2-aminoethyl)amine. The emission properties of the TPE units were studied in THF/water mixtures, and they were found by dynamic light scattering to self-assemble into large (av. diameter 250 nm) structures.