Martin R. Johnston

Ruthenium Porphyrin Functionalized Single-Walled Carbon Nanotube Arrays-A Step Toward Light Harvesting Antenna and Multibit Information Storage

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays have been prepared using coordination of the axial position of the metal ion onto 4-aminopyridine preassembled single-walled carbon nanotubes directly anchored to a silicon(100) surface (SWCNTs-Si). The formation of these ruthenium porphyrin functionalized single-walled carbon nanotube array electrodes (RuTPP-SWCNTs-Si) has been monitored using infrared spectroscopy (IR), differential pulse voltammetry (DPV), atomic force microscopy (AFM), laser desorption time-of-flight mass spectroscopy (LDI-TOF-MS), UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Electrochemical results show two successive one-electron reversible redox waves. The surface concentration of the ruthenium porphyrin molecules is 3.44 x 10 (-8) mol cm (-2). Optical results indicate that the immobilization of ruthenium porphyrin enhances the light absorption of SWCNTs-Si surfaces in the visible light region. Moreover mixed assembly of ferrocene/porphyrin onto carbon nanotube arrays has been achieved by altering the ratio of two redox-active species in the deposition solution. These results suggest the ruthenium porphyrin modified electrodes are excellent candidates for molecular memory devices and light harvesting antennae.

Observation of the keto tautomer of d-fructose in D2O using 1H NMR spectroscopy

D-Fructose was analysed by NMR spectroscopy and previously unidentified (1)H NMR resonances were assigned to the keto and α-pyranose tautomers. The full assignment of shifts for the various fructose tautomers enabled the use of (1)H NMR spectroscopy in studies of the mutarotation (5-25°C) and tautomeric composition at equilibrium (5-50°C). The mutarotation of β-pyranose to furanose tautomers in D(2)O at a concentration of 0.18 M was found to have an activation energy of 62.6 kJmol(-1). At tautomeric equilibrium (20°C in D(2)O) the distribution of the β-pyranose, β-furanose, α-furanose, α-pyranose and the keto tautomers was found to be 68.23%, 22.35%, 6.24%, 2.67% and 0.50%, respectively. This tautomeric composition was not significantly affected by varying concentrations between 0.089 and 0.36 M or acidification to pH 3. Upon equilibrating at 6 temperatures between 5 and 50°C there was a linear relationship between the change in concentration and temperature for all forms.

Direct attachment of well-aligned single-walled carbon nanotube architectures to silicon (100) surfaces : a simple approach for device assembly

A new approach for the attachment of vertically-aligned shortened carbon nanotube architectures to a silicon (100) substrate by chemical anchoring directly to the surface has been demonstrated for the first time. The ordered assembly of single-walled carbon nanotubes (SWCNTs) was accomplished by hydroxylating the silicon surface followed by a condensation reaction with carboxylic acid functionalised SWCNTs. This new nanostructure has been characterised by X-ray photoelectron, Raman and Fourier transform infrared (FTIR) spectroscopy as well as scanning electron and atomic force microscopy. The assembly behaviour of SWCNTs onto the silicon surface shows a fast initial step producing isolated functionalised carbon nanotubes or nanotube bundles anchored to the silicon surface followed by a slower step where the adsorbed nanotubes grow into larger aggregates via van der Waals interactions between adsorbed and solvated nanotubes. The electrochemical and optical properties of the SWCNTs directly attached to silicon have also been investigated. These new nanostructures are excellent electrochemical electrodes. They also fluoresce in the wavelength range 650-800 nm. The successful attachment of the SWCNTs directly to silicon provides a simple, new avenue for fabrication and development of silicon-based nanoelectronic, nano-optoelectronic and sensing devices. Compared to existing techniques, this new approach has several advantages including low operating temperature, low cost and the possibility of further modification.

Photoinduced electron transfer in bisporphyrin - diimide complexes

The bisporphyrin host ZnH was synthesized, and its complexation with two aromatic diimide guest molecules, bis(pyridyl)naphthalenediimide NIN and bis(pyridyl)phenyldiimide PIN, was investigated by (1)H NMR and UV/Vis spectroscopy. The diimide guests were complexed simultaneously with both metalloporphyrins of the host, with association constants on the order of 10(8)M(-1). The processes occurring in the complex after excitation of the porphyrinic host were studied by steady-state and time-resolved emission and transient absorption spectroscopy. Complexation alters the photophysical properties of the host ZnH; the luminescence bands shift to the red by 30 nm in the complexed forms, while the emission quantum yield and the lifetime decrease. Comparison of a complex between ZnH and a model guest unable to undergo photoinduced processes allowed us to establish that, in the diimide complexes, quenching of the porphyrinic luminescence occurs with a rate of 1.1 x 10(10)s(-1). The process is identified as an electron transfer from the excited singlet of the porphyrinic host to the imide guest, which yields charge-separated states with a lifetime of 710 ps for ZnH(+)-NIN(-) and 260 ps for ZnH(+)-PIN(-).

Synthesis, structure, and biological applications of α-fluorinated β-amino acids and derivatives.

This review gives a broad overview of the state of play with respect to the synthesis, conformational properties, and biological activity of α‐fluorinated β‐amino acids and derivatives. General methods are described for the preparation of monosubstituted α‐fluoro‐β‐amino acids (Scheme 1). Nucleophilic methods for the introduction of fluorine predominantly involve the reaction of DAST with alcohols derived from α‐amino acids, whereas electrophilic sources of fluorine such as NFSI have been used in conjunction with ArndtEistert homologation, conjugate addition or organocatalyzed Mannich reactions. α,α‐Difluoro‐β‐amino acids have also been prepared using DAST; however, this area of synthesis is largely dominated by the use of difluorinated Reformatsky reagents to introduce the difluoro ester functionality (Scheme 9). α‐Fluoro‐β‐amino acids and derivatives analyzed by X‐ray crystal and NMR solution techniques are found to adopt preferred conformations which are thought to result from stereoelectronic effects associated with F located close to amines, amides, and esters (Figs. 2–6). α‐Fluoro amide and β‐fluoro ethylamide/amine effects can influence the secondary structure of α‐fluoro‐β‐amino acid‐containing derivatives including peptides and peptidomimetics (Figs. 7–9). α‐Fluoro‐β‐amino acids are also components of a diverse range of bioactive anticancer (e.g., 5‐fluorouracil), antifungal, and antiinsomnia agents as well as protease inhibitors where such fluorinated analogs have shown increased potency and spectrum of activity.

Analysis of the hydrolysis of inulin using real time 1H NMR spectroscopy

The hydrolysis of various carbohydrates was investigated under acidic conditions in real time by (1)H NMR spectroscopy, with a focus on the polysaccharide inulin. Sucrose was used as a model compound to illustrate the applicability of this technique. The hydrolysis of sucrose was shown to follow pseudo first order kinetics and have an activation energy of 107.0 kJ mol(-1) (SD 1.7 kJ mol(-1)). Inulin, pullulan and glycogen also all followed pseudo first order kinetics, but had an initiation phase at least partially generated by the protonation of the glycosidic bonds. It was also demonstrated that polysaccharide chain length has an effect on the hydrolysis of inulin. For short chain inulin (DPn 18, SD 0.70) the activation energy calculated for the hydrolytic cleavage of glucose was similar to sucrose at 108.5 kJ mol(-1) (SD 0.60). For long chain inulin (DPn 30, SD 1.3) the activation energy for the hydrolytic cleavage of glucose was reduced to 80.5 kJ mol(-1) (SD 2.3 kJ mol(-1)). This anomaly has been attributed to varied conformations for the two different lengths of inulin chain in solution.

Morphine Glucuronidation and Glucosidation Represent Complementary Metabolic Pathways That Are Both Catalyzed by UDP-Glucuronosyltransferase 2B7: Kinetic, Inhibition, and Molecular Modeling Studies

Morphine 3-β-D-glucuronide (M3G) and morphine 6-β-D-glucuronide (M6G) are the major metabolites of morphine in humans. More recently, morphine-3-β-d-glucoside (M-3-glucoside) was identified in the urine of patients treated with morphine. Kinetic and inhibition studies using human liver microsomes (HLM) and recombinant UGTs as enzyme sources along with molecular modeling were used here to characterize the relationship between morphine glucuronidation and glucosidation. The M3G to M6G intrinsic clearance (CLint) ratio (∼5.5) from HLM supplemented with UDP-glucuronic acid (UDP-GlcUA) alone was consistent with the relative formation of these metabolites in humans. The mean CLint values observed for M-3-glucoside by incubations of HLM with UDP-glucose (UDP-Glc) as cofactor were approximately twice those for M6G formation. However, although the M3G-to-M6G CLint ratio remained close to 5.5 when human liver microsomal kinetic studies were performed in the presence of a 1:1 mixture of cofactors, the mean CLint value for M-3-glucoside formation was less than that of M6G. Studies with UGT enzyme-selective inhibitors and recombinant UGT enzymes, along with effects of BSA on morphine glycosidation kinetics, were consistent with a major role of UGT2B7 in both morphine glucuronidation and glucosidation. Molecular modeling identified key amino acids involved in the binding of UDP-GlcUA and UDP-Glc to UGT2B7. Mutagenesis of these residues abolished morphine glucuronidation and glucosidation. Overall, the data indicate that morphine glucuronidation and glucosidation occur as complementary metabolic pathways catalyzed by a common enzyme (UGT2B7). Glucuronidation is the dominant metabolic pathway because the binding affinity of UDP-GlcUA to UGT2B7 is higher than that of UDP-Glc.

Synthesis and modelling of novel rigid rods derived from a simple pentacyclic bis-norbornene [1]

Abstract New rigid rods with 4σ, 6σ, 10σ, 12σ, and 16σ bond separations have been prepared from the pentacyclic diene 3 using ACE (alkene plus cyclobutene epoxide) and s-tetrazine coupling techniques and their shapes evaluated using AM1 calculations. The X-ray structure of the 6σ-rod 5 is reported.

Photoinduced electron transfer in a non-covalently linked donor–acceptor system: a bis-porphyrinic host and a naphthalene diimide guest

Complexation of the two pyridyl residues of a naphthalene imide guest by a V-shaped bis-porphyrinic host occurs with an association constant of the order of 108 M−1 and results in the quenching of the porphyrin luminescence with a rate of 1.2 × 1010 s−1, assigned to electron transfer.

Porphyrin [2]catenanes—dynamic control through protonation

Protonation of the previously reported porphyrin [2]catenanes in strongly acidic solutions results in electrostatic repulsion of their two components, and conformational reorientations and changes in rotation rates, which are dependent on the structural flexibility of the molecules.