Robert C. Mawhinney

An ab initio and TD-DFT study of solvent effect contributions to the electronic spectrum of Nile Red

A CIS and TD-DFT study using a polarizable continuum solvent model has been conducted to assess non-specific solvent effects on the spectral shifts in Nile Red (NR). The results in this paper show that the electronic band shifts of Nile Red are a consequence of both a field effect on the transition energy and an effect due to a solvent induced geometry change. The S0-->S1 transition experiences a large red-shift with increasing solvent polarity but is relatively insensitive to geometric change. The TD-B3LYP assessment of the S0-->S2 transition yields a blue shift with increasing solvent polarity but a red shift due to the solvent induced geometry change. Ground state dipole moments and polarizabilities are also shown to increase with solvent polarity. CIS optimization of the first excited state of NR is reported, but the solvent effects suggest a locally excited state may have been obtained. Further studies are needed to assess the role of a TICT state.

The electronic structure of nitrilimines revisitedElectronic supplementary information (ESI) available: Optimized structures and absolute energies of all stationary points. See http://www.rsc.org/suppdata/cc/b4/b407302a/

A combination of density-functional theory and natural resonance theory has been used to show that a complete description of the electronic structure of nitrilimines, R(1)CNNR(2), requires four resonance structures (propargylic, allenic, 1,3-dipolar and carbenic); appropriate substituents were shown to enhance the carbene character of nitrilimines to the point where they may be considered stable carbenes.

Competition between coordination bonds and hydrogen bonds: the nitrile-silver(I) interaction using dicyanobithiophene as ligand

Reactions of the ligand 5,5′-dicyano-2,2′-bithiophene (T2CN2) with a variety of silver(I) salts are presented. In most cases, the ligand precipitates by itself without incorporating the silver(I) metal. However, when the counterion is triflate, in benzene or THF, a coordination compound is formed. The crystal structure of the species grown from benzene, a double-stranded one-dimensional polymer, is reported. In this structure, the bithiophene ligand is twisted into the uncommon syn orientation. The reasons for the lack of reactivity of the ligand are discussed by comparing the relative strengths of the interligand hydrogen bond with the ligand–metal bond.

Assessment of density functional theory for the prediction of the nature of the oxirene stationary point

Abstract The nature of the stationary point of oxirene, cyclic C 2 H 2 O, has been examined using selected GGA and hybrid functionals in combination with a number of basis sets. All GGA functionals (BLYP, BP91, PBE, HCTH, HCTH147, and HCTH407) predict the stationary point to be a transition state and show very little basis set dependence. The hybrid functionals (B3LYP, B3P91, PBE0, B97, B97-1, and B3P86), on the other hand, show more basis set dependence and predict oxirene to be a minimum in a number of cases. However, these parameterized hybrid functionals are not consistent in their characterization of oxirene. The theoretically derived hybrid functional PBE0 predicts oxirene to be a minimum with 11 of the 12 basis sets used and results with the largest basis set are in good agreement with earlier predictions with the high level correlated method, CCSD(T).

Using the nitro group to induce π-stacking in terthiophenes

A new synthetic route to mononitrated oligothiophenes is described, as well as the preparation of halogenated derivatives (Br, I) thereof. An unusual deep red colour is observed and explained, with...

Identification of a Mammalian Silicon Transporter

Silicon (Si) has long been known to play a major physiological and structural role in certain organisms, including diatoms, sponges, and many higher plants, leading to the recent identification of multiple proteins responsible for Si transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding about the biochemical pathways that enable Si homeostasis. Here we report the identification of a mammalian efflux Si transporter, namely Slc34a2 (also termed NaPiIIb), a known sodium-phosphate cotransporter, which was upregulated in rat kidney following chronic dietary Si deprivation. Normal rat renal epithelium demonstrated punctate expression of Slc34a2, and when the protein was heterologously expressed in Xenopus laevis oocytes, Si efflux activity (i.e., movement of Si out of cells) was induced and was quantitatively similar to that induced by the known plant Si transporter OsLsi2 in the same expression system. Interestingly, Si efflux appeared saturable over time, but it did not vary as a function of extracellular HPO42− or Na+ concentration, suggesting that Slc34a2 harbors a functionally independent transport site for Si operating in the reverse direction to the site for phosphate. Indeed, in rats with dietary Si depletion-induced upregulation of transporter expression, there was increased urinary phosphate excretion. This is the first evidence of an active Si transport protein in mammals and points towards an important role for Si in vertebrates and explains interactions between dietary phosphate and silicon.

5,5′-Dicyano-2,2′-bithiophene and 3,3′-dicyanobiphenyl: off-axis rod-like ligands for silver(I)

The two ligands 3,3′-dicyanobiphenyl (3) and 5,5′-dicyano-2,2′-bithiophene (4) are geometrically similar but give rise to different coordination compounds when reacted with silver(I) salts. The crystal structures of 3·AgClO4 and 3·AgBF4 have 1 : 1 ligand : cation ratios, while 42·ClO4 and 42·BF4 have 2 : 1 ligand : cation ratios. These ratios for the solid-state materials were constant, even when different stoichiometric ratios were used in the reaction vessels. The structures of these four coordination compounds are presented and the reasons for the difference in the coordination environments discussed with reference to IR spectroscopic and DFT computational results.