Synthesis and modification of terrylenediimides as high-performance fluorescent dyes

Two new synthetic approaches to terrylenediimides, highly photostable fluorescent dyes, are described. For the first time terrylenediimide has been synthesised in a straightforward procedure that makes large quantities available. The second route includes an efficient cross-coupling reaction followed by a cyclodehydrogenation. Monofunctionalisation of the imide structure allows terrylenediimides now to be coupled with a variety of compounds, for example, by Suzuki cross-coupling, which can lead to an array of terrylenediimides with new functional groups such as hydroxy, amino, or carboxy groups needed to link up with other molecules. The functionalisation in the bay region is used to tune the properties of terrylenediimides and extend the range of applications, for example, by introducing water solubility. These tetrasubstituted terrylenediimides offer, depending on the substituents used, exciting features such as good solubility in common organic solvents, water solubility, or NIR absorption.     

Electrochemical templating of metal nanoparticles and nanowires on single-walled carbon nanotube networks

The use of single-walled carbon nanotube (SWNT) networks as templates for the electrodeposition of metal (Ag and Pt) nanostructures is described. Pristine SWNTs, grown on insulating SiO2 surfaces using catalyzed chemical vapor deposition, served as the working electrode. In the simplest case, electrical contact was made by depositing a gold strip on the SWNT substrate (device 1). Deposition of Ag and Pt over extensive periods (30 s) resulted in a high density of particles on the SWNTs, with almost contiguous nanowire formation from the Au/SWNT boundary moving to isolated nanoparticles at further distances from the contact. For direct electrochemical studies of Ag and Pt nucleation, the assembly was coated in a resist layer and a small window opened up to expose only the electrically connected SWNTs to solution (device 2). In this case, the electrochemical signature in voltammetric and amperometric studies of metal deposition was due solely to processes at the SWNTs. Coupled with high-resolution microscopy measurements (atomic force microscopy and field emission scanning electron microscopy), this approach provided detail on the nucleation and growth mechanisms of Ag and Pt on SWNTs under electrochemical control. In particular, Ag growth was found to be rapid and progressive with an increasing nanoparticle density with time, whereas Pt deposition was characterized by lower nucleation densities and slower growth rates with a tendency for larger particles to be produced over long times.     

Diiodine complex of diferrocenyl(phenyl)phosphine sulfide: the structural and electrochemical behaviour of Fc2(Ph)PS · I2

The title compound, Fc₂(Ph)PS · I₂, has been prepared and characterised in both the solid state and solution. Single crystal X-ray crystallography reveals that the adduct adopts a molecular charge-transfer structure in the solid state. Mössbauer spectroscopy confirms the presence of low spin Fe²⁺ but also indicates the presence of ca. 24% of an Fe³⁺ species. The electrochemistry of Fc₂(Ph)PS · I₂, Fc₂(Ph)PS and Fc₂(Ph)P has been studied using a combination of cyclic voltammetry and differential pulse voltammetry. The data for Fc₂(Ph)PS · I₂ show two redox processes, consistent with the sequential oxidation of the ferrocenyl groups to ferrocenium species.     

Fluorimetric determination of danthron in pharmaceutical tablets and in urine

A simple, rapid determination is reported for danthron (1,8-dihydroxyanthraquinone) in pharmaceutical tablets. In a flow-injection system, danthron is reduced by sodium dithionite in $\text{1}\text{1}$ methanol/borate buffer to give a fluorescent complex. Linearity ranges from 30 μg ml^?1 to below 0.1 μg ml^?1. In urine samples, danthron is separated from other fluorescing species by reversed-phase high-performance liquid chromatography before its reduction by dithionite in a post-column reactor. Urine preparation requires no extraction. Spiked urine samples were studied in the working range of 0.02–2.0 μg ml^?1 danthron.     

Recent advances in the synthesis of well-defined glycopolymers

Glycopolymers are receiving increasing interest due to their application in areas, such as glycomics, medicine, biotechnology, sensors, and separation science. Consequently, new methods for their synthesis are constantly being developed, with an increasing emphasis on the preparation of well-defined polymers and on the production of complex macromolecular architectures such as stars. This review covers recent developments in the synthesis of glycopolymers, with a particular emphasis on (i) the use of controlled radical polymerization to prepare well-defined glycopolymers from unprotected monomers and (ii) postpolymerization modification strategies using reactive polymer precursors (including “click” reactions). Recent work on the production of glycosylated polypeptides, which are under investigation as mimics of naturally occurring glycoproteins, is also included. The authors offer some suggestions as to future developments and remaining challenges in this topical area of polymer chemistry. © 2007 Wiley Periodicals, Inc. J Polym Sci PartA: Polym Chem45: 2059–2072, 2007     

A cation-pi binding interaction with a tyrosine in the binding site of the GABAC receptor

GABA(C) (rho) receptors are members of the Cys-loop superfamily of neurotransmitter receptors, which includes nicotinic acetylcholine (nACh), 5-HT(3), and glycine receptors. As in other members of this family, the agonist binding site of GABA(C) receptors is rich in aromatic amino acids, but while other receptors bind agonist through a cation-pi interaction to a tryptophan, the GABA(C) binding site has tyrosine at the aligning positions. Incorporating a series of tyrosine derivatives at position 198 using unnatural amino acid mutagenesis reveals a clear correlation between the cation-pi binding ability of the side chain and EC(50) for receptor activation, thus demonstrating a cation-pi interaction between a tyrosine side chain and a neurotransmitter. Comparisons among four homologous receptors show variations in cation-pi binding energies that reflect the nature of the cationic center of the agonist.     

Capillary electrophoresis of cardiolipin with on-line dye interaction and spectrophotometric detection

Cardiolipin is an important phospholipid present in the mitochondrial inner membrane. It plays a key function in mitochondrial respiration by interacting with many enzymes or cofactors related to oxidative phosphorylation complexes. We have determined the concentration of cardiolipin using on-line 10-N-nonyl acridine orange (NAO) dye interaction capillary electrophoresis (CE) and spectrophotometric detection with a sample throughput of 3 min. In addition to the presence of 0.1 mM NAO, the background electrolyte (BGE) composition has been set at 80% methanol-10% acetonitrile-10% H(2)O (all v/v) to provide both good solubility and the maximum absorbance enhancement at 497 nm for the NAO-cardiolipin complex as compared to NAO alone. Sample consumption for each injection is about 57 nL. A calibration curve is established from 0.5 microM to 0.1 mM with R (2) = 0.9912 with a detection limit of 0.05 microM for cardiolipin. In a blind study, actual mitochondrial cell membrane samples in the microL range before or after UV light exposure were analyzed using the CE method. Cardiolipin concentration decreased in the different parts of the membrane sample upon UV photolysis of the cells. Support for the theory that UV light can induce cardiolipin translocation from the inner membrane (IM) to the outer membrane (OM) was indicated by a significant percentage increase of cardiolipin (as measured by the cardiolipin in the OM as compared to the sum total in the OM and IM) from 30.7 +/- 2.4% before UV light photolysis to 38.3 +/- 2.2% after UV irradiation.     

Cobalt Ion Incorporation into Periodic Mesoporous Organosilica Materials Synthesized by Co-condensation of 1,2-Bistrimethoxysilylethane with 3-Glycidoxypropyltriethoxysilane

Bifunctional periodic mesoporous organosilica materials with and without cobalt ion incorporation were synthesized by co-condensation of 1,2-bistrimethoxysilylethane (BTME) with 3-glycidoxypropyltriethoxysilane (GPTS) in the presence of cetyltrimethylammonium bromide. Nitrogen gas adsorption on samples with varying ratios of BTME:GPTS revealed that increasing the amount of GPTS affects pore size, surface area and pore volume as well as shapes of the isotherms and hysteresis loops. The hysteresis loops of the Type IV isotherms obtained for GPTS-modified ethane silica materials (without cobalt ion) change from Type H3 to Type H4 with increasing GPTS content. There is a tendency for pore sizes to change from mesopore to micropore when the amount of GPTS is increased. Isotherms of cobalt ion incorporated GPTS-modified ethane silica materials change from Type IV to Type I with increasing GPTS content. The surface area, pore volume and pore diameter decrease with increasing loading of GPTS as well as after cobalt ion incorporation. Thermogravimetric analysis and differential thermal analysis show that the surfactant is removed by solvent extraction. Cobalt ion incorporation is confirmed by powder X-ray diffraction and Raman spectroscopy.     

Kinetic and regiospecific interrogation of covalent intermediates in the nonribosomal peptide synthesis of yersiniabactin

For interrogation of enzyme-bound intermediates in nonribosomal peptide synthetases (NRPSs), mass spectrometry is used to read out the kinetics and substrate specificity of this medicinally important class of enzymes. The protein HMWP2 (230 kDa) catalyzes 11 chemical reactions, four of which could be resolved by fast quench approaches combined with mass spectrometry. The rate of complex intermediate accumulation at the PCP1 active site was observed to occur with a rate of 19 s(-1), with the rate of cysteine acylation faster than that of intermediate translocation. Use of alternative substrates for salicylic acid (at the ArCP carrier domain) and l-cysteine (at the PCP1 carrier domain) revealed a high penalty for omission of the salicyl alcohol. For some substrates, large discrepancies were found between prior adenylation assays and the current MS-based readouts. Indirect evidence for condensation via a thiolate attack (vs an amino group) was also accumulated. This is the first report to correlate the percent occupancy of multiple active sites in parallel with kinetic and structural resolution of intermediates and provides new evidence of interdomain and intermodule communication within thiotemplate assembly lines.     

SITE-DIRECTED MUTAGENESIS OF THE LH2 LIGHT-HARVESTING COMPLEX OF Rhodobacter sphaeroides: CHANGING βLys23 TO Gin RESULTS IN A SHIFT IN THE 850 nm ABSORPTION PEAK

The present study describes the construction of a Rhodobacter sphaeroides light-harvesting (LH2) mutant in which the charged residue βSLys23 is changed by site-directed mutagenesis to a Gin residue, and the characterization of the resulting mutant complex by a range of spectroscopic techniques. In the 77 K absorption spectrum of the mutant, the peak equivalent to the 850 nm peak in the wild-type membrane is blue-shifted by approximately 18 nm to 837 nm; except for this blue-shift, the 77 K. fluorescence excitation and emission spectra and the circular dichroism spectrum of the mutant are very similar to the equivalent spectra from the wild-type membranes, suggesting that the mutation βLys23 → Gin probably does not cause any major changes in the conformation or aggregation state of these membranes. Possible causes of the 18 nm blue-shift in the absorption spectrum are discussed.