Toward the Control of the Creation of Mixed Monolayers on Glassy Carbon Surfaces by Amine Oxidation.

A versatile and simple methodology for the creation of mixed monolayers on glassy carbon (GC) surfaces was developed, using an osmium-bipyridyl complex and anthraquinone as model redox probes. The work consisted in the electrochemical grafting on GC of a mixture of mono-protected diamine linkers in varying ratios which, after attachment to the surface, allowed orthogonal deprotection. After optimisation of the deprotection conditions, it was possible to remove one of the protecting groups selectively, couple a suitable osmium complex and cap the residual free amines. The removal of the second protecting group allowed the coupling of anthraquinone. The characterisation of the resulting surfaces by cyclic voltammetry showed the variation of the surface coverage of the two redox centres in relation to the initial ratio of the linking amine in solution.

Synthesis and evaluation of a (3R,6S,9S)-2-oxo-1-azabicyclo[4.3.0]nonane scaffold as a mimic of Xaa-trans-Pro in poly-L-proline type II helix conformation.

We describe the development of a small-molecule mimic of Xaa-trans-Pro dipeptide in poly-l-proline type II helix conformation, based upon a (3R,6S,9S)-2-oxo-1-azabicyclo[4.3.0]nonane core structure. Stereoselective synthesis of the mimic from l-pyroglutamic acid is achieved in twelve linear steps and 9.9% yield. Configurational and conformational analyses are conducted using a combination of (1)H NMR spectroscopy, X-ray crystallography and circular dichroism spectroscopy; and evaluation of the mimic as a promising surrogate dipeptide, in a protein-protein interaction between the SH3 domain of human Fyn kinase (Fyn SH3) and peptidomimetics of its biological ligand, are conducted by (1)H-(15)N HSQC NMR titration experiments.

Design of maleimide-functionalised electrodes for covalent attachment of proteins through free surface cysteine groups.

Mixed two-component monolayers on glassy carbon are prepared by electrochemical oxidation of N-(2-aminoethyl)acetamide and mono-N-Boc-hexamethylenediamine in mixed solution. Subsequent N-deprotection, amide coupling and solid-phase synthetic steps lead to electrode-surface functionalisation with maleimide, with controlled partial coverage of this cysteine-binding group at appropriate dilution for covalent immobilisation of a model redox-active protein, cytochrome c, with high coverage (≈7.5 pmol cm(-2) ).

High-throughput synthesis and electrochemical screening of a library of modified electrodes for NADH oxidation.

We report the combinatorial preparation and high-throughput screening of a library of modified electrodes designed to catalyze the oxidation of NADH. Sixty glassy carbon electrodes were covalently modified with ruthenium(II) or zinc(II) complexes bearing the redox active 1,10-phenanthroline-5,6-dione (phendione) ligand by electrochemical functionalization using one of four different linkers, followed by attachment of one of five different phendione metal complexes using combinatorial solid-phase synthesis methodology. This gave a library with three replicates of each of 20 different electrode modifications. This library was electrochemically screened in high-throughput (HTP) mode using cyclic voltammetry. The members of the library were evaluated with regard to the surface coverage, midpeak potential, and voltammetric peak separation for the phendione ligand, and their catalytic activity toward NADH oxidation. The surface coverage was found to depend on the length and flexibility of the linker and the geometry of the metal complex. The choices of linker and metal complex were also found to have significant impact on the kinetics of the reaction between the 1,10-phenanthroline-5,6-dione ligand and NADH. The rate constants for the reaction were obtained by analyzing the catalytic currents as a function of NADH concentration and scan rate, and the influence of the surface molecular architecture on the kinetics was evaluated.

Mass transport controlled oxygen reduction at anthraquinone modified 3D-CNT electrodes with immobilized Trametes hirsuta laccase.

Carbon nanotubes covalently modified with anthraquinone were used as an electrode for the immobilization of Trametes hirsuta laccase. The adsorbed laccase is capable of oxygen reduction at a mass transport controlled rate (up to 3.5 mA cm(-2)) in the absence of a soluble mediator. The storage and operational stability of the electrode are excellent.

Selective anticancer activity of a hexapeptide with sequence homology to a non-kinase domain of Cyclin Dependent Kinase 4.

BACKGROUND: Cyclin-dependent kinases 2, 4 and 6 (Cdk2, Cdk4, Cdk6) are closely structurally homologous proteins which are classically understood to control the transition from the G1 to the S-phases of the cell cycle by combining with their appropriate cyclin D or cyclin E partners to form kinase-active holoenzymes. Deregulation of Cdk4 is widespread in human cancer, CDK4 gene knockout is highly protective against chemical and oncogene-mediated epithelial carcinogenesis, despite the continued presence of CDK2 and CDK6; and overexpresssion of Cdk4 promotes skin carcinogenesis. Surprisingly, however, Cdk4 kinase inhibitors have not yet fulfilled their expectation as 'blockbuster' anticancer agents. Resistance to inhibition of Cdk4 kinase in some cases could potentially be due to a non-kinase activity, as recently reported with epidermal growth factor receptor. RESULTS: A search for a potential functional site of non-kinase activity present in Cdk4 but not Cdk2 or Cdk6 revealed a previously-unidentified loop on the outside of the C'-terminal non-kinase domain of Cdk4, containing a central amino-acid sequence, Pro-Arg-Gly-Pro-Arg-Pro (PRGPRP). An isolated hexapeptide with this sequence and its cyclic amphiphilic congeners are selectively lethal at high doses to a wide range of human cancer cell lines whilst sparing normal diploid keratinocytes and fibroblasts. Treated cancer cells do not exhibit the wide variability of dose response typically seen with other anticancer agents. Cancer cell killing by PRGPRP, in a cyclic amphiphilic cassette, requires cells to be in cycle but does not perturb cell cycle distribution and is accompanied by altered relative Cdk4/Cdk1 expression and selective decrease in ATP levels. Morphological features of apoptosis are absent and cancer cell death does not appear to involve autophagy. CONCLUSION: These findings suggest a potential new paradigm for the development of broad-spectrum cancer specific therapeutics with a companion diagnostic biomarker and a putative functional site for kinase-unrelated activities of Cdk4.

Dimeric self-assembly of pyridyl guanidinium carboxylates in polar solvents.

A series of pyridyl guanidinium-carboxylates has been prepared and the dimeric self-assembly of these studied in H(2)O/DMSO mixtures, principally using dilution isothermal calorimetry. Compounds 5 and 6, incorporating an aromatic ring in the "tethering" region between the guanidinium and carboxylate groups, demonstrate the strongest dimerisation in neat DMSO. X-ray crystal structures of 5 and 6 reveal two different dimerisation architectures in the solid-state, but both involve carboxylate-guanidinium salt bridges as anticipated, and π-π interactions. Compounds 10-16 incorporating peptidic fragments between the guanidinium and carboxylate groups, showed reduced dimerisation strength with increased amino acid content, but also sustained dimerisation under increasingly aqueous conditions, up to 50% H(2)O/DMSO in the case of 14 and 15. The extent of our study in H(2)O/DMSO mixtures was determined by substrate solubility of 10-16, and not the limit of self-assembly.

Dimeric supramolecular motifs of two carboxylate-guanidinium compounds.

The structures of N-benzyl-N'-{6-[(4-carboxylatobenzyl)aminocarbonyl]-2-pyridylmethyl}guanidinium, C(23)H(23)N(5)O(3), (I), and N-[2-(benzylaminocarbonyl)ethyl]-N'-{6-[(4-carboxylatobenzyl)aminocarbonyl]-2-pyridylmethyl}guanidinium monohydrate, C(26)H(28)N(6)O(4).H(2)O, (II), both form three-dimensional supramolecular hydrogen-bonded networks based on a dimeric primary synthon involving carboxylate-guanidinium linkages. The differences in the geometries and hydrogen-bonding connectivities are driven by the additional methylpropionamide group and water of crystallization of (II).

Monolayer anthracene and anthraquinone modified electrodes as platforms for Trametes hirsuta laccase immobilisation.

Surface modification techniques are essential to the construction of enzyme based elements of biofuel cells and biosensors. In this article we report on the preparation and characterisation of modified carbon electrodes which were used as supports for the immobilisation of laccase from Trametes hirsuta. The electrodes were electrochemically modified with diamine or diazonium linkers followed by attachment of either anthracene or anthraquinone head groups using solid phase chemical methodology. These well defined surfaces were found to effectively bind laccase and to provide direct electrical contact to the enzyme active site, as evidenced by XPS, EIS and voltammetry, respectively. The influence of the type of linker and head group on enzyme binding and bioelectrocatalytic activity are evaluated.

Identification of major phenolic compounds from Nephelium lappaceum L. and their antioxidant activities.

Nephelium lappaceum is a tropical fruit whose peel possesses antioxidant properties. Experiments on the isolation and identification of the active constituents were conducted, and on their antioxidant activity using a lipid peroxidation inhibition assay. The methanolic extract of N. lappaceum peels exhibited strong antioxidant properties. Sephadex LH-20 chromatography was utilized in the isolation of each constituent and the antioxidant properties of each was studied. The isolated compounds were identified as ellagic acid (EA) (1), corilagin (2) and geraniin (3). These compounds accounted for 69.3% of methanolic extract, with geraniin (56.8%) as the major component, and exhibited much greater antioxidant activities than BHT in both lipid peroxidation (77-186 fold) and DPPH* (42-87 fold) assays. The results suggest that the isolated ellagitannins, as the principal components of rambutan peels, could be further utilized as both a medicine and in the food industry.

Synthesis of dihydrodehydrodiconiferyl alcohol: the revised structure of lawsonicin.

Structural revision of lawsonicin, a natural product of Lawsonia alba, is reported based upon comparison of its spectral data with that of the naturally occurring dihydrobenzo[b]furan neolignan (rac)-trans-dihydrodehydrodiconiferyl alcohol, which is found to be identical. A concise synthesis of dihydrodehydrodiconiferyl alcohol, via Rh(2)[S-DOSP](4)-catalysed intramolecular C-H insertion, is described.

Covalent modification of glassy carbon surfaces by using electrochemical and solid-phase synthetic methodologies: application to bi- and trifunctionalisation with different redox centres.

Glassy carbon electrodes functionalised with two redox centres have been prepared by using electrochemical and solid-phase synthetic methodologies. Initially the individual coupling of anthraquinone, nitrobenzene and dihydroxybenzene to a glassy carbon electrode bearing an ethylenediamine linker was optimised by using different coupling agents and conditions. Bifunctionalisation was then carried out, either simultaneously, with a mixture of nitrobenzene and dihydroxybenzene, or sequentially, with anthraquinone then nitrobenzene and with anthraquinone then dihydroxybenzene. Characterisation of these electrodes by cyclic voltammetry and differential pulse voltammetry clearly proved the attachment of the pairs of redox centres to the glassy carbon electrode. Their partial surface coverages can be controlled by varying the coupling agent or by controlling the substrate concentration during the solid-phase coupling process. Trifunctionalisation was also realised according to this methodology.

Electrochemical and solid-phase synthetic modification of glassy carbon electrodes with dihydroxybenzene compounds and the electrocatalytic oxidation of NADH.

We report the preparation, using electrochemical and solid-phase synthesis, and characterisation of a 26 member library of 13 dihydroxybenzene derivatives covalently attached to glassy carbon through ethylenediamine (EDA) and C(6)H(4)CH(2)NH linkers. First, Boc-protected EDA or Boc-NHCH(2)C(6)H(4) were electrochemically attached to the GC surface. After Boc-deprotection, dimethoxybenzoyl chlorides were coupled to the EDA and C(6)H(4)CH(2)NH linkers using solid-phase synthesis followed by deprotection of the methoxy groups to give the corresponding dihydroxybenzene compounds. Surface coverage and electrochemical parameters of the dihydroxybenzene modified electrodes were evaluated in parallel using cyclic voltammetry. The mid-peak potentials, E(mp), and surface coverages for the 13 dihydroxybenzene derivatives were found to be independent of the choice of linker. The mid-peak potentials of the immobilised dihydroxybenzene derivatives varied between 0.0 and 260 mV vs. SCE and their surface coverages varied between 0.07 and 1.1 nmol cm(-2), depending on the pattern of substitution of the dihydroxybenzene ring. The electrocatalytic activities of the library were evaluated for mediation of NADH oxidation, and the ortho-dihydroxybenzene derivatives were found to have higher catalytic activity.

Selective binding of L-glutamate derivative in aqueous solvents.

A chiral bisguanidinium macrocycle binds N-Boc-L-glutamate in a 1 : 1 stoichiometry with significant selectivity in competitive solvent (DMSO-H(2)O).

Covalent tethering of organic functionality to the surface of glassy carbon electrodes by using electrochemical and solid-phase synthesis methodologies.

Organic linkers such as (N-Boc-aminomethyl)phenyl (BocNHCH2C6H4) and N-Boc-ethylenediamine (Boc-EDA) have been covalently tethered onto a glassy carbon surface by employing electrochemical reduction of BocNHCH2C6H4 diazonium salt or oxidation of Boc-EDA. After removal of the Boc group, anthraquinone as a redox model was attached to the linker by a solid-phase coupling reaction. Grafting of anthraquinone to electrodes bearing a second spacer such as 4-(N-Boc-aminomethyl)benzoic acid or N-Boc-beta-alanine was also performed by following this methodology. The surface coverage, stability and electron transfer to/from the tethered anthraquinone redox group through the linkers were investigated by cyclic voltammetry. The effects of pH and scan rate were studied, and the electron-transfer coefficient and rate constant were determined by using Laviron's equation for the different types of linker. The combination of electrochemical attachment of protected linkers and subsequent modifications under the conditions of solid-phase synthesis provides a very versatile methodology for tailoring a wide range of organic functional arrangements on a glassy carbon surface.

Carboxylate binding in polar solvents using pyridylguanidinium salts.

A series of thiourea and guanidinium derivatives have been prepared and their ability to bind a carboxylate group has been investigated. Guanidinium 33, featuring two additional amides and a pyridine moiety, proved to be the most potent carboxylate binding site and was able to bind acetate in aqueous solvent systems (K(ass) = 480 M(-1) in 30% H(2)O-DMSO). The pyridine moiety is critical to obtaining strong binding, and comparison with the binding properties of analogous compounds in which the pyridine is replaced by a benzene ring provides a striking example of enthalpy-entropy compensation.

A combined computational and experimental approach for the analysis of the enantioselective potential of a new macrocyclic receptor for N-protected alpha-amino acids.

A new macrocyclic receptor incorporating a thiourea moiety has been synthesised. Crystal structures of the macrocycle showed that the receptor has a rigid backbone but the thiourea moiety can orientate itself to bind to a DMSO solvent molecule. Force-field (MMFFs) calculations were performed to model the macrocycle and its binding properties with respect to N-protected amino acids, which were measured experimentally by NMR titration. Binding free energies were calculated by using the mode integration algorithm (MINTA) or free-energy perturbation (FEP). Excellent qualitative agreement with experiment was obtained. To further exploit the accuracy of the free-energy predictions for this system, the faster free-energy algorithm MINTA was used as a prediction tool to test the binding affinity of the macrocycle towards a series of several other amino acid derivatives, which speeded up considerably the screening process and reduced laboratory costs.

Pyridyl thioureas as switchable anion receptors.

The binding selectivity of simple pyridyl thioureas in acetonitrile can be completely switched by protonation; hence the neutral thiourea binds acetate, but not chloride or bromide, whereas the protonated thiourea binds strongly to chloride or bromide, but is deprotonated by acetate.

Synthesis of unsymmetrical tweezer receptor libraries and identification of receptors for lys-D-ala-D-ala in aqueous solution.

Libraries of "unsymmetrical" tweezer receptors, featuring a guanidinium head group as a carboxylate binding site and two independently synthesized peptidic arms, have been prepared and screened to identify receptors for the N-Ac-Lys-D-Ala-D-Ala tripeptide sequence. The binding properties of one such receptor structure, with dye-labeled N-Ac-Lys-D-Ala-D-Ala, were investigated. These studies demonstrated that when attached to the solid-phase, the receptor binds dye-labeled N-Ac-Lys-D-Ala-D-Ala, in buffered aqueous media, with mM binding affinity.

Novel enantioselective receptors for N-protected glutamate and aspartate.

A series of chiral bisthiourea macrocycles 1-4 have been prepared and their binding properties with various dicarboxylate salts have been examined by using NMR titration and isothermal calorimetry experiments. Macrocycle 1, in particular, favours the 1:1 binding of N-protected L-glutamate and aspartate, but favours 1:2 binding of the corresponding D-amino acids in polar solvents (dimethyl sulfoxide and acetonitrile). The macrocycles, however, do not bind carboxylates at all in the less competitive solvent chloroform. The binding properties of these macrocyles are sensitive to small structural changes as demonstrated by the altered binding properties of macrocycles 2-4 compared with 1.