Understanding the chemistry of dental erosion.

Dental erosion is caused by repeated short episodes of exposure to acids. Dental minerals are calcium-deficient, carbonated hydroxyapatites containing impurity ions such as Na(+), Mg(2+) and Cl(-). The rate of dissolution, which is crucial to the progression of erosion, is influenced by solubility and also by other factors. After outlining principles of solubility and acid dissolution, this chapter describes the factors related to the dental tissues on the one hand and to the erosive solution on the other. The impurities in the dental mineral introduce crystal strain and increase solubility, so dentine mineral is more soluble than enamel mineral and both are more soluble than hydroxyapatite. The considerable differences in structure and porosity between dentine and enamel influence interactions of the tissues with acid solutions, so the relative rates of dissolution do not necessarily reflect the respective solubilities. The rate of dissolution is further influenced strongly by physical factors (temperature, flow rate) and chemical factors (degree of saturation, presence of inhibitors, buffering, pH, fluoride). Temperature and flow rate, as determined by the method of consumption of a product, strongly influence erosion in vivo. The net effect of the solution factors determines the overall erosive potential of different products. Prospects for remineralization of erosive lesions are evaluated.

Highlights in Analytical Chemistry in Switzerland: OMA & OPA - A Software Tool for Mass Spectrometric Sequencing of Nucleic Acids

Oligonucleotides comprising unnatural building blocks, which interfere with the translation machinery, have gained increased attention for the treatment of gene-related diseases (e.g. antisense, RNAi). Due to structural modifications, synthetic oligonucleotides exhibit increased biostability and bioavailability upon administration. Consequently, classical enzyme-based sequencing methods are not applicable to their sequence elucidation and verification. Tandem mass spectrometry is the method of choice for performing such tasks, since gas-phase dissociation is not restricted to natural nucleic acids. However, tandem mass spectrometric analysis can generate product ion spectra of tremendous complexity, as the number of possible fragments grows rapidly with increasing sequence length. The fact that structural modifications affect the dissociation pathways greatly increases the variety of analytically valuable fragment ions. The gas-phase dissociation of oligonucleotides is characterized by the cleavage of one of the four bonds along the phosphodiester chain, by the accompanying loss of nucleases, and by the generation of internal fragments due to secondary backbone cleavage. For example, an 18-mer oligonucleotide yields a total number of 272’920 theoretical fragment ions. In contrast to the processing of peptide product ion spectra, which nowadays is highly automated, there is a lack of tools assisting the interpretation of oligonucleotide data. The existing web-based and stand-alone software applications are primarily designed for the sequence analysis of natural nucleic acids, but do not account for chemical modifications and adducts. Consequently, we developed a software to support the interpretation of mass spectrometric data of natural and modified nucleic acids and their adducts with chemotherapeutic agents.

Cytotoxic peptide conjugates of dinuclear arene ruthenium trithiolato complexes

In order to improve the water-solubility of dinuclear thiolato-bridged arene ruthenium complexes, a new series was synthesized by conjugating octaarginine, octalysine, and cyclo[Lys-Arg-Gly-Asp-D-Phe] using chloroacetyl thioether (ClAc) ligation, resulting in cytotoxic conjugates against A2780 human ovarian cancer cells (IC50 = 2–8 μM) and against the cisplatin resistant line A2780cisR (IC50 = 7–15 μM). These metal complexes represent, to the best of our knowledge, the most cytotoxic ruthenium bioconjugates reported so far.

Shakespeare, the Middle Ages and the Luck of the British: Medievalism and National Identity in The Hollow Crown (2012)

Images of the medieval past have long been fertile soil for the identity politics of subsequent periods. Rather than “authentically” reproducing the Middle Ages, medievalism therefore usually tells us more about the concerns and ideological climate of its own time and place of origin. To dramatise the nascent nation, Shakespeare resorts to medievalism in his history plays. Centuries later, the BBC-produced television mini-serial The Hollow Crown – adapting Shakespeare’s second histories tetralogy – revamps this negotiation of national identity for the “Cultural Olympiad” in the run-up to the 2012 London Olympics. In this context of celebratory introspection, The Hollow Crown weaves a genealogical narrative consisting of the increasingly “glorious” medieval history depicted and “national” Shakespearean heritage in order to valorise 21st-century “Britishness”. Encouraging a reading of the histories as medieval history, the films construct an ostensibly inclusive, liberal-minded national identity grounded in this history. Moreover, medieval kingship is represented in distinctly sentimentalising and humanising terms, fostering emotional identification especially with the no longer ambivalent Hal/Henry V and making him an apt model for present-day British grandeur. However, the fact that the films in return marginalise female, Scottish, Irish and Welsh characters gives rise to doubts as to whether this vision of Shakespeare’s Middle Ages really is, as the producers claimed, “for everybody”.

Syntheses, characterization and crystal structures of a new functionalised TTF derivative and its Ni(II) complex

The new ligand 4,5-bis (2-pyridylmethylsulfanyl)-4',5'-bis(cyanoethylthio)tetrathiafulvalene (BPM-BCET-TTF) and its nickel(II) complex have been prepared and crystallographically characterized. The Ni(II) complex shows octahedral geometry around the metal ion with the coordination site occupied by the pyridyl nitrogen atoms, the thioether sulfur atoms of the ligand and cis coordination of the halide ions.

Structural Studies of Transition Metal Complexes with 4,5-Bis(2-pyridylmethylsulfanyl)-4‘,5‘-ethylenedithiotetrathiafulvalene: Probing Their Potential for the Construction of Multifunctional Molecular Assemblies

Three divalent transition metal complexes of 4,5-bis(2-pyridylmethylsulfanyl)-4‘,5‘-ethylenedithiotetrathiafulvalene have been prepared and crystallographically characterized. The isostructural Co(II) and the Ni(II) complexes show octahedral geometries around the metal ions with the coordination sites occupied by the pyridyl nitrogen atoms and the thioether sulfur atoms of the ligand and cis coordination of the halide ions. Cyclic voltammetry reveals that the complexation leads to a small anodic shift in the first oxidation potential of the TTF system.

A short, efficient synthesis of 2'-deoxypseudoisocytidine based on Heck-chemistry

A novel synthesis of 2'-deoxypseudoisocytidine as well as of its phosphoramidite building block for oligonucleotide synthesis is presented. The synthesis is based on Heck-coupling between N-protected pseudoisocytosine and a silyl protected furanoid glycal. With this procedure the corresponding phosphoramidite building block is obtained in 5 steps and an overall yield of 28%.

Chemistry of pyrrocorphins: methylative opening of the macrocycle between rings A and D, a side reaction in the peripheral C-methylation of a 20-methyl-pyrrocorphinate

One of the minor products from the previously described peripheral -methylation of a magnesium()-20-methyl--pyrrocorphinate is a C-19-methylated 19,20-seco-corphinoid derivative which, on complexation with nickel() acetate, recyclizes to a nickel()-tetradehydro-corrinate.

Chemistry of pyrrocorphins: C-methylations at the periphery of pyrrocorphins and related corphinoid ligand systems

Various corphinoid model systems bearing a methyl group at the position C-20 have been found to undergo regioselective chemical -methylation at the ligand periphery, mimicking enzymic -methylation occurring in vitamin-B biosynthesis.