Retroracemization using new forms of Belokon's original ligand: ­intermediate NiII complexes of N‐({2‐[N‐(S)‐alkylprolylamino]phenyl}phenylmethylene)‐(S)‐phenylalanine (alkyl is 2‐picolyl, 3‐picolyl or ethyl)

In the title compounds, [N‐(phenyl{2‐[N‐(S)‐(2‐picolyl)­prolyl­amino]­phenyl}methyl­ene)‐(S)‐phenyl­alaninato]­nickel(II), [Ni(C₃₃H₃₀N₄O₃)], (I), [N‐(phenyl{2‐[N‐(S)‐(3‐picolyl)­prolyl­amino]­phenyl}methyl­ene)‐(S)‐phenyl­alaninato]­nickel(II) hemihydrate, [Ni(C₃₃H₃₀N₄O₃)]·0.5H₂O, (II), and [N‐({2‐[N‐(S)‐ethyl­prolyl­amino]­phenyl}phenyl­methyl­ene)‐(S)‐phenyl­ala­nin­ato]­nickel(II), [Ni(C₂₉H₂₉N₃O₃)], (III), the Ni^II centres have approximate square‐planar coordination geometries from N₃O donor sets. The picolyl N atoms in (I) and (II) are too remote from the metal centres to interact significantly, but the metal coordination geometries experience tetrahedral distortion and/or displacement of the metal centre from the N₃O plane. These are linked to conformational differences between the ligands of the symmetry‐independent complexes (Z′ = 2), which in turn are related to molecular packing. In (III), where a less sterically demanding ethyl group replaces the picolyl substituents, there are none of the distortions or displacements seen in (I) and (II).     

Thiaminase I (42 kDa) heterogeneity,sequence refinement,and active site location from high-resolution tandem mass spectrometry

Thiaminase I (E.C. 2.5. 1.2) from Bacillus thiaminolyticus catalyzes the degradation of thiamin (vitamin B₁). Unexpected mass heterogeneity (MW 42,127, 42,197, and 42,254; 1:2:1) in recombinant thiaminase I from Escherichia coli was detected by electrospray ionization Fourier-transform mass spectrometry, resolving power 7×10⁴. Nozzle-skimmer fragmentation data reveal an extra Ala (+71.02; 71.04=theory) and GlyAla (+128.04; 128.06=theory) on the N-terminus, in addition to the fully processed enzyme. However, the fragment ion masses were consistent only with this sequence through 330 N-terminal residues; resequencing of the last 150 bps of the thiaminase I gene yields a sequence consistent with the molecular weight values and all 61 fragment ion masses. Covalently labeling the active site with a 108-Da pyrimidine moiety via mechanism-based inhibition produces a corresponding molecular weight increase in all three thiaminase I components, which indicates that they are all enzymatically active. Inspection of the fragment ions that do and do not increase by 108 Da indicates that the active site nucleophile is located between Pro⁷⁹ and Thr¹⁷⁷ in the 379 amino acid enzyme.     

MnRe(CO)10: A review of the chemical and physical properties of a simple heterobimetallic non-bridged dimer

A review of the chemical and physical properties of MnRe(CO)₁₀ and its derivatives has been undertaken. This heterobimetallic complex is one of the simplest complexes known which contains a bond between two different metals and does not contain bridging groups. The review has revealed that high yield synthetic strategies are known for this complex and the synthetic strategies have bearing for the synthesis of other bimetallic complexes. Kinetic data suggest that information available on monometallic fragments can provide information on the reactivity trends expected for the dimer. However, the second metal is not a neutral spectator and provides a site forsecondary reactions eg for CO substitution. Data on the physical properties of the dimer are sparse and definitive statements ond _Mn-Re·v _Mn-Re, H_Mn-Re etc. cannot be made. This has significant implications for studies on related simple and complex dimer and cluster complexes.     

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.