Synthesis, structure, and properties of azatriangulenlenium salts

A general synthetic route to novel nitrogen-bridged heterocyclic carbenium ions of the acridinium and triangulenium type has been developed and investigated. The synthetic method is based on nucleophilic aromatic substitution (SNAr) on the tris(2,6-dimethoxyphenyl)carbenium ion (1) with primary amines and, by virtue of its stepwise and irreversible nature, provides a powerful tool for the preparation of a wide variety of new heterocyclic carbenium salts. Several derivatives of the three new oxygen- and/or nitrogen-bridged triangulenium salts, azadioxa- (6), diazaoxa- (7), and triazatriangulenium (4), have been synthesized and their physicochemical properties have been investigated. Crystal structures for compounds 2 b-PF6, 2 d-PF6, 4b-BF4, 4c-BF4, 6e-BF4, and 8 are reported. The different packing modes found for the triazatriagulenium salts are discussed in relation to the electrostatic and space-filling requirements of the ions. The stabilities of the cations 6a, 7b, and 4a, as expressed by their pKR+ values, have been determined in strongly basic nonaqueous solution by use of the C_ acidity function; the values obtained were 14.5, 19.4, and 23.7, respectively. This study further implied that the C_ scale in its present form is unsuitable for the precise determination of pKR+ values beyond 22.     

A novel electrosynthesized polymer applied to molecular imprinting technology

Poly(2-macaptobenzimidazole) (PMBI) films are prepared at the gold electrode surface by electropolymerization using imprinting technology and the target analyte cholesterol is used as the template. A cholesterol-selective sensor based on PMBI film was employed in conjunction with differential pulse voltammetry (DPV) and ferricyanide as mediator. Concentration of cholesterol up to 100 μM could be detected with a linear determination range up to 20 μM and a detection limit of 0.7 μM. The molecular imprinting approach offers a relatively nice selectivity for the sensor toward cholesterol with respect to common coexisting substances. The method is simple and the stability of the electrode prepared is satisfactory. The results of this research show the feasibility of using molecular imprinting methodology for preparing sensing devices for analytes that are electrochemically inactive.     

Qualitative and quantitative analysis of a thermoset polymer, poly(benzoxazine), by pyrolysis-gas chromatography

The chemical composition of a poly(benzoxazine) thermoset polymer (a copolymer of bisphenol-A benzoxazine and tert.-butylphenol benzoxazine) has been studied by pyrolysis-gas chromatography (Py-GC). Major pyrolysates have been identified and the possible degradation pathways have been investigated. A specific pyrolysate was identified for quantitative analysis after carefully proving the linear relationship between the pyrolysate signal intensity and monomer concentration over a wide range of compositions. A method to determine the concentration of the monomer that potentially acts as a cross-linking unit has been developed. In this study, Py-GC was shown to be an excellent analytical technique for the qualitative and quantitative analysis of thermoset polymers.     

Total structural assignment and absolute configuration of terreinol by 13C and 1H NMR

The carbon-carbon connectivity of terreinol, a new metabolite isolated from Aspergillus terreus, and its previous (13)C assignments were confirmed by a two-dimensional INADEQUATE experiment using a few milligrams of the compound with natural (13)C abundance. The carbon-carbon correlations were determined by computational analysis (with >99% probability) of this experiment. Additionally, the absolute configuration of terreinol was achieved indirectly via its corresponding secondary alcohol by the modified Mosher method allied to conformational analysis. The shielding effect of the phenyl group of methoxytrifluoromethylphenylacetic acid (MTPA) on the substituents of the carbonylic centre gave a fully regular Deltadelta(SR) sign distribution, allowing reliable assignment of the R configuration for terreinol.     

The measurement of the fluorescence detected circular dichroism (FDCD) from a chiral Eu(III) system

The first measurement of the fluorescence detected circular dichroism (FDCD) from a chiral Eu(III) system, made possible by use of a variable liquid crystal circular polarizer, is reported.     

Single-molecule surface enhanced resonance Raman spectroscopy of the enhanced green fluorescent protein

In the present contribution, we demonstrated that surface-enhanced resonance Raman scattering spectra from single green fluorescent proteins (GFPs) were obtained. The most important findings are the direct detection of the conversion between a deprotonated and a protonated form of the chromophore at the single-molecule level via the corresponding vibrational fingerprints, and the fact that the enhanced green fluorescent protein (EGFP) also shows a high surface enhanced resonance Raman scattering (SERRS) signal. Our findings show the potential of the technique to study structural dynamics of protein molecules at a single-molecule level.     

Water-Soluble Ln<Superscript>3+</Superscript>-Doped LaF<Subscript>3</Subscript> Nanoparticles: Retention of Strong Luminescence and Potential as Biolabels

The use of optically robust, luminescent lanthanide-based particles is becoming an area of interest for biolabel-related chemistry, due to their long lifetimes and range of non-overlapping absorption and emission lines from the visible to the near-infrared. We report the synthesis and optical properties of water-soluble, luminescent Ln³⁺-doped nanoparticles (NPs) coordinated with a hydrophilic (RO)PO₃²⁻ ligand that facilitates the stabilization of the NPs in aqueous conditions, and that regulates particle growth to the nanometer range. The use of lanthanide ions as dopants, in particular Eu³⁺ and Er³⁺ ions, yields optically robust particles with narrow emission lines in the visible (591 nm) and in the near-infrared (1530 nm), respectively. Luminescent lifetimes range from the microsecond to the millisecond for Er³⁺ and Eu³⁺ ions, respectively, and the NPs are not expected to be susceptible to photo-bleaching due to the fact that the emissions arise from intra-4f transitions of the lanthanide ions.