A two-stage approach to automatic determination of 1H NMR coupling constants

(1)H NMR scalar coupling constants are a rich source of information on molecular structure, but their extraction from spectra can be less than straightforward. Previous approaches to J extraction include methods proposed by Hoye, Golotvin, and the 'modified J-doubling' method. Here we describe the ACCA method, currently implemented in the NMR package MestReC, which allows a high degree of automation in the extraction of coupling patterns even in the case of complex multiplets with sublinewidth splitting. The new approach is illustrated by application to strychnine, for which it has detected previously unreported couplings.     

The Reactivity of Cr‐Te Superlattice Reactants and of Co‐deposited Cr‐Te Films: Studies with in‐situ X‐ray Diffractometry

The reactivity of a Cr‐Te multilayer film consisting of 326 Cr/Te double‐layers with about 88(3) at% Te was investigated with in‐situ X‐ray diffraction. The occurrence of a superstructure reflection caused by the multilayer system is observed. During the annealing procedure between 80 and 90 °C the layer‐by‐layer arrangement is destroyed and elemental Te crystallizes. After 6 h isothermal annealing at 140 °C CrTe₃ starts to crystallize. The amount and the crystal size of CrTe₃ increase with raising temperature and Te is consumed during the growth process. At 220 °C the formation of crystalline Cr₂Te₃ is observed and between 220 and 260 °C CrTe₃ is completely decomposed into Cr₂Te₃. The two Cr tellurides grow as highly textured materials. The size of CrTe₃ crystals is significantly larger than that of Cr₂Te₃. For a co‐deposited Cr‐Te film with composition 77(3) at% Te the tri‐telluride and elemental Te crystallize simultaneously. The texture of CrTe₃ is less pronounced and different reflections of the tri‐telluride occur besides the (h00)‐reflections. Up to 160 °C a pronounced increase of the crystallite size is observed and the crystals are significantly larger than those obtained with the multifilm sample. At 130 °C the crystallization kinetics seem to be controlled by nucleation.     

Predicting the shape and structure of face-centered cubic gold nanocrystals smaller than 3 nm.

Although a number of computational studies have examined the relative stability of icosahedral and decahedral gold clusters from 1 to 3 nm in size, few studies have focussed on the variety of face-centered cubic (fcc) nanoparticles in this size regime. In most cases small fcc gold particles are assumed to adopt the truncated octahedral shape, but in light of the fact that the shape and structure of gold nanoparticles is known to vary, the relative stability of fcc polyhedra may change with size. Presented here are results of first-principles calculations investigating the preferred shape of gold particles less than 3 nm in size. Our results indicate that the equilibrium shape of fcc gold nanoparticles less than 1 nm is the cuboctahedron, but this shape rapidly becomes energetically unstable with respect to the truncated octahedron, octahedron and truncated cube shapes as the size increases.     

Analytical assays based on detecting conformational changes of single molecules.

One common strategy for the detection of biomolecules is labeling either the target itself or an antibody that binds to it. Herein, a different approach, based on detecting the conformational change of a probe molecule induced by binding of the target is discussed. That is, what is being detected is not the presence of the target or the probe, but the conformational change of the probe. Recently, a single-molecule sensor has been developed that exploits this mechanism to detect hybridization of a single DNA oligomer to a DNA probe, as well as specific binding of a single protein to a DNA probe. Biomolecular recognition often involves large conformational changes of the molecules involved, and therefore this strategy may be applicable to other assays.     

Determination of Nonsteroidal Anti‐inflammatory Drugs in Serum by Microchip Capillary Electrophoresis with Electrochemical Detection

A simple and rapid method has been developed for the analysis of four nonsteroidal anti‐inflammatory drugs (NSAIDs) in serum using microchip capillary electrophoresis with pulsed amperometric detection. The selected NSAIDs (salicylic acid, acetaminophen, diflunisal, and diclofenac) are among the most commonly used drugs to treat fever, inflammation, and pain. Used above the therapeutic levels, these drugs can cause a wide variety of adverse effects and their fast analysis could have a significant impact in treatment and recovery of the patients. Several conditions, including separation potential, pH, and concentration of the electrolyte solution were studied to optimize the separation and detection. In this study, salicylic acid, acetaminophen, diflunisal, and diclofenac were separated in less than 2 minutes using a 5 mM borate buffer at pH 11.5 and a separation potential of +1200 V. Linear relationships were obtained between the concentration and peak current in the 0.5–15.3 μg/mL range and detection limits around 0.26 μg/mL. After 30 consecutive injections, the stability of both the response and migration time of the analytes showed relative related deviations of less than 4.6% and 1.0%, respectively. The potential of this method was verified by spiking a bovine serum sample with the four NSAIDs and analyzing the recovery ratio.     

Search of ligands for the amyloidogenic protein beta2-microglobulin by capillary electrophoresis and other techniques

Beta2-microglobulin (beta2-m) is a small amyloidogenic protein normally present on the surface of most nucleated cells and responsible for dialysis-related amyloidosis, which represents a severe complication of long-term hemodialysis. A therapeutic approach for this amyloidosis could be based on the stabilization of beta2-m through the binding to a small molecule, and consequent inhibition of protein misfolding and amyloid fibril formation. A few compounds have been described to weakly bind beta2-m, including the drug suramin. The lack of a binding site for nonpolypeptidic ligands on the beta2-m structure makes it difficult for both the identification of functional groups responsible for the binding and the search of hits to be optimized. The characterization of the binding properties of suramin for beta2-m by using three different techniques (surface plasmon resonance, affinity CE (ACE), ultrafiltration) is here described and the results obtained are compared. The common features of the chemical structures of the compounds known to bind the protein led us to select 200 sulfonated/suramin-like molecules from a wider chemical library on the basis of similarity rules, so as to possibly single out some interesting hits and to gain more information on the functional groups involved in the binding. The development of screening methods to test the compounds by using ultrafiltration and ACE is described.     

Synthesis of macrocyclic aliphatic disulfide oligomers from dithiols by oxidative coupling with oxygen using a copper‐amine catalyst

A new effective method is provided for the synthesis of macrocyclic aliphatic disulfide oligomers by catalytic oxidation of aliphatic dithiols with oxygen in the presence of a copper‐amine catalyst. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis,Characterization, and Crystal Structure of Thallium(I) Complex containing Monodeprotonated 2,6‐Pyridinedicarboxylic Acid

The reaction of an ethanolic solution 2,6‐pyridinedicarboxylic acid ( 1 , LH₂) with TlNO₃ in the presence of triethylamine led to the coordination polymer [Tl(LH)]_n ( 2 ). The complex was characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction. Crystal data for 2 at –80 °C: monoclinic, space group I2/a, a = 696.1(1), b = 1190.6(2), c = 931.0(2) pm, β = 103.28(1)°, Z = 4, R₁ = 0.0256.     

Insoluble eggshell matrix proteins--their peptide mapping and partial characterization by capillary electrophoresis and high-performance liquid chromatography

Avian eggshell matrix proteins were studied by two analytical approaches. Peptide mapping was done by trypsin and pepsin followed by collagenase cleavage; analyses were carried out by capillary electrophoresis and reversed-phase high-performance liquid chromatography (HPLC). Comparison of peptide maps obtained by both methods revealed a complex mixture of peptides in the insoluble layers of the eggshell; it was concluded that there are at least three different insoluble protein/peptide layers in the avian eggshell (cuticle, palisade, and mammillary layer). Partial characterization of peptides in each layer was made by HPLC-mass spectrometry analysis. There is an evidence that the eggshell insoluble proteins contain species susceptible to collagenase cleavage, however, the sequences split by this enzyme probably are not those typical for the main triple-helical core of collagenous proteins. It is proposed that the action of collagenase upon eggshell proteins is caused by the side effect of collagenase described previously with synthetic peptides. Some of the proteins present are probably glycosylated. Fatty acid content in the insoluble eggshell layers (after decalcification) was in the range of 2-4% (which reflected both lipid and lipoproteins bound fatty acids). Porphyrin pigments are dominant in the cuticle layer.     

Fabrication and Properties of Conducting Polypyrrole/SWNT‐PABS Composite Films and Nanotubes

We report the electropolymerization and characterization of polypyrrole films doped with poly(m‐aminobenzene sulfonic acid (PABS) functionalized single‐walled nanotubes (SWNT) (PPy/SWNT‐PABS). The negatively charged water‐soluble SWNT‐PABS served as anionic dopant during the electropolymerization to synthesize PPy/SWNT‐PABS composite films. The synthetic, morphological and electrical properties of PPy/SWNT‐PABS films and chloride doped polypyrrole (PPy/Cl) films were compared. Characterization was performed by cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. SEM and AFM images revealed that the incorporation of SWNT‐PABS significantly altered the morphology of the PPy. Cyclic voltammetry showed improved electrochemical properties of PPy/SWNT‐PABS films as compared to PPy/Cl films. Raman Spectroscopy confirmed the presence of SWNT‐PABS within composite films. Field effect transistor (FET) and electrical characterization studies show that the incorporation of the SWNT‐PABS increased the electronic performance of PPy/SWNT‐PABS films when compared to PPy/Cl films. Finally, we fabricated PPy/SWNT‐PABS nanotubes which may lead to potential applications to sensors and other electronic devices.