Tip‐heating‐assisted Raman spectroscopy at elevated temperatures

We demonstrate tip‐heating‐assisted enhanced Raman spectroscopy to investigate the temperature dependence of the carbon nanotube G‐band with nanoscale resolution. The controllable and nanoscale heat generated at the tip apex was used to thermally perturb and characterize a small volume in a carbon nanotube sample that is precisely positioned underneath the tip. The dependence of tip enhancement with temperature was also experimentally examined, which is in good agreement with the enhancement calculated from the electromagnetic model of isolated spheroids. The technique presented may open up opportunities in the study of controlled heat‐assisted biochemical reactions and physical transformations of nanostructures. It can also be used for thermal characterization of various materials requiring site‐selective and controllable nanoscale heat source and could enable the realization of new photothermal devices. Copyright © 2010 John Wiley & Sons, Ltd.     

Fluorescence Properties and Exciplex Formation of Emissive Naphthyridine Derivatives: Application as Sensors for Amines

Water-soluble donor–acceptor-type fluorophore 15Nap-Cl having two trifluoromethyl groups and a Cl group on a 1,5-aminonaphthyridine framework was prepared. Fluorophore 15Nap-Cl showed strong solvatochromic fluorescence, and, as the solvent polarity increased, a bathochromic shift was observed accompanied by an increase in the fluorescence quantum yield. In addition, in the presence of amines such as ethylamine, diethylamine, and aniline, further considerable bathochromic shifts in the fluorescence were observed. Density functional calculations identified the source of the fluorescence behavior as exciplex formation between 15-Nap-Cl and the corresponding amine. The fluorescence behavior was exploited to fabricate a sensor that can identify various primary, secondary, and tertiary amines.     

Selective recognition and electrochemical sensing of dopamine using a ferrocene-based heteroditopic receptor

A redox-active ferrocene-based heteroditopic receptor bearing a boronic acid (as a catechol recognition site) and a benzo-18-crown-6-ether unit (as an ammonium ion recognition site) was synthesized. A 1:1 ditopic complex with dopamine was evidenced by mass spectrometry and NMR spectroscopy. Cyclic voltammetry measurements on the receptor in the presence of a series of organic guest species demonstrated the successful electrochemical sensing of dopamine through a distinct change in the ferrocene-centred redox-couple upon complex formation.     

Asymmetric intramolecular Cannizzaro reaction of anhydrous phenylglyoxal

The use of anhydrous phenylglyoxal provides a solution to the problem of low reactivity in the asymmetric intramolecular Cannizzaro reaction with alcohols. Double asymmetric induction was achieved in the reaction of anhydrous phenylglyoxal with d-(+)-menthol promoted by a (S,S)-t-BuBox·copper(II) hexafluoroantimonate complex.     

High-Spin and Reactive Fe13 Cluster with Exposed Metal Sites

Atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp*₄W₄Fe₁₃S₁₂ , displaying a Fe₁₃ core with M−M bonds that has precedent only in main group and late metal chemistry. M₁₃ clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp*₄W₄Fe₁₃S₁₂ displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.     

Module assembly for protein-surface recognition: geranylgeranyltransferase I bivalent inhibitors for simultaneous targeting of interior and exterior protein surfaces

Synthetic chemical probes designed to simultaneously targeting multiple sites of protein surfaces are of interest owing to their potential application as site specific modulators of protein-protein interactions. A new approach toward bivalent inhibitors of mammalian type I geranylgeranyltransferase (GGTase I) based on module assembly for simultaneous recognition of both interior and exterior protein surfaces is reported. The inhibitors synthesized in this study consist of two modules linked by an alkyl spacer; one is the tetrapeptide CVIL module for binding to the interior protein surface (active pocket) and the other is a 3,4,5-alkoxy substituted benzoyl motif that contains three aminoalkyl groups designed to bind to the negatively charged protein exterior surface near the active site. The compounds were screened by two distinct enzyme inhibition assays based on fluorescence spectroscopy and incorporation of a [(3)H]-labeled prenyl group onto a protein substrate. The bivalent inhibitors block GGTase I enzymatic activity with K(i) values in the submicromolar range and are approximately one order of magnitude and more than 150 times more effective than the tetrapeptide CVIL and the methyl benzoate derivatives, respectively. The bivalent compounds 6 and 8 were shown to be competitive inhibitors, suggesting that the CVIL module anchors the whole molecule to the GGTase I active site and delivers the other module to the targeting protein surface. Thus, our module-assembly approach resulted in simultaneous multiple-site recognition, and as a consequence, synergetic inhibition of GGTase I activity, thereby providing a new approach in designing protein-surface-directed inhibitors for targeting protein-protein interactions.     

Profiling and biomarker identification in plasma from different Zucker rat strains via high mass accuracy multistage mass spectrometric analysis using liquid chromatography/mass spectrometry with a quadrupole ion trap-time of flight mass spectrometer

High mass accuracy electrospray ionisation multistage tandem mass spectrometry (MS(n)) was applied to metabolite profiling studies on plasma samples derived from two strains of rat (the Zucker (fa/fa) obese strain and the normal wild type). Using a quadrupole ion trap time-of-flight (QIT-TOF) mass spectrometer, metabolite profiling software was applied to locate components of biological significance that could account for the differences between the two strains of rat and a formula prediction software tool was used to help identify individual components. The primary factor discriminating between the two populations was the concentration of endogenous lipids. In the Zucker (fa/fa) obese strain, the dominant ion signals and MS(n) spectra were in agreement with lysoglycerophosphocholine components such as palmitoyllysophosphatidylcholine, 1-oleoylglycerophosphocholine, 1-octadecyl-sn-glycero-3-phosphocholine and 1-stearoylglycerophosphocholine and these were found in relatively higher concentrations compared to the normal wild type. Components were identified using high mass accuracy MS(n) data, formula prediction software and by agreement with published mass spectra through internet databases, rather than using a conventional approach with authentic standards. This application shows that the use of high mass accuracy electrospray ionisation MS(n) together with a software tool can be used effectively to detect and characterise unknown analytes in complex matrices, and represents a promising approach for future profiling studies.     

Preparation and mechanical properties of bacterial cellulose nanocomposites loaded with silica nanoparticles

Bacterial cellulose (BC), which is produced by Gluconacetobacter xylinus (Ga. xylinus) in culture, is made up of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. In the current studies, we used two processes to prepare nanocomposites of BC filled with silica particles. In Process I, Ga. xylinus was incubated in medium containing silica sol Snowtex 0 (ST 0, pH 2–4) or Snowtex 20 (ST 20, pH 9.5–10.0). The elastic modulus at 20 °C was improved by keeping the amount of silica in the nanocomposites below 4% when ST 20 was used and below 8.7% when ST 0 was used. This process allowed incorporation of 50% silica in BC. Inclusion of higher amounts of silica reduced the modulus at 20 °C and the strength of the nanocomposites below that of BC. X-ray diffraction measurements revealed that the silica particles disturb the formation of ribbon-shaped fibrils and affect the preferential orientation of the ( ) plane. We also produced BC-silica nanocomposites by Process II, wherein the BC hydrogel was immersed in different concentrations of silica sols, allowing silica particles to diffuse into the BC hydrogel and lodge in the spaces between the ribbon-shaped fibrils. This method increased the modulus at 20°C and the strength compared to the BC matrix, but it was difficult to load the BC with more than 10% silica in this way.     

Enantioselective synthesis of silanol

An enantioselective nucleophilic substitution reaction of achiral dialkoxysilane has been developed. The reaction proceeds with efficient stereocontrol on the silicon chirality center to give the enantioenriched silyl ether, which can be converted to the silanol without loss of enantiopurity. We have analyzed the steric course of the reaction by using DFT calculations and propose a transition state model to explain the observed enantioselectivity.