Investigations of adsorption behavior and anti-inflammatory activity of glycine functionalized Al12N12 and Al12ON11 fullerene-like cages.

The adsorption behavior of the amino acid, glycine (Gly), via the carboxyl, hydroxyl, and amino groups onto the surfaces of Al12N12 and Al16N16 fullerene-like cages were computationally evaluated by the combination of density functional theory (DFT) and molecular docking studies. It was found that Gly can chemically bond with the Al12N12 and Al16N16 fullerene-like cages as its amino group being more favorable to interact with the aluminum atoms of the adsorbents compared to carboxyl and hydroxyl groups. Oxygen and carbon doping were reported to reduce steric hindrance for Glycine interaction at Al site of Al12ON11/Gly and Al12CN11/Gly complexes. Interaction was further enhanced by oxygen doping due to its greater electron withdrawing effect. Herein, the Al12ON11/Gly complex where two carbonyl groups of Gly are bonded to the aluminum atoms of the Al12N12 fullerene-like cage is the most stable interaction configuration showing ∆adsH and ∆adsG values of -81.74 kcal/mol and -66.21 kcal/mol, respectively. Computational studies also revealed the frequency shifts that occurred due to the interaction process. Molecular docking analysis revealed that the Al12N12/Gly (-11.7 kcal/mol) and the Al12ON11/Gly (-9.2 kcal/mol) complexes have a good binding affinity with protein tumor necrosis factor alpha (TNF-α). TNF-α was implicated as a key cytokine in various diseases, and it has been a validated therapeutic target for the treatment of rheumatoid arthritis. These results suggest that the Al12N12/Gly complex in comparison with the Al16N16/Gly, Al12ON11/Gly, and the Al12CN11/Gly complexes could be efficient inhibitors of TNF-α.

Serine adsorption through different functionalities on the B12N12 and Pt-B12N12 nanocages.

The present work reports the adsorption of serine in the neutral and zwitterionic forms on the pure and Pt-decorated B12N12 fullerenes by means of density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The binding energy of serine over the fullerene has been studied through its hydroxyl (-OH), carboxyl (-COOH), and amine (-NH2) functional groups. Based on our analysis, the binding energy of serine in zwitterionic form (F: -1.52 eV) on B12N12 fullerene is less stable than that of the neutral form (C: -1.61 eV) using the M06-2X functional. Our results indicated that the most stable chemisorption state for serine is through its amine group (I: -2.49 eV) interacting with the Pt-decorated B12N12 fullerene in comparison with the carbonyl group (J: -1.92 eV). The conductivity of the B12N12 and Pt-decorated B12N12 fullerenes is influenced by the energy band gap variation when serine is adsorbed upon the outer surface of fullerenes. Understanding the adsorption of serine on B12N12 and Pt-decorated B12N12 fullerenes provide fundamental knowledge for future applications in biomolecules and metal surfaces.

Bactericidal activity of self-assembled palmitic and stearic fatty acid crystals on highly ordered pyrolytic graphite.

The wings of insects such as cicadas and dragonflies have been found to possess nanostructure arrays that are assembled from fatty acids. These arrays can physically interact with the bacterial cell membranes, leading to the death of the cell. Such mechanobactericidal surfaces are of significant interest, as they can kill bacteria without the need for antibacterial chemicals. Here, we report on the bactericidal effect of two of the main lipid components of the insect wing epicuticle, palmitic (C16) and stearic (C18) fatty acids. Films of these fatty acids were re-crystallised on the surface of highly ordered pyrolytic graphite. It appeared that the presence of two additional CH2 groups in the alkyl chain resulted in the formation of different surface structures. Scanning electron microscopy and atomic force microscopy showed that the palmitic acid microcrystallites were more asymmetric than those of the stearic acid, where the palmitic acid microcrystallites were observed to be an angular abutment in the scanning electron micrographs. The principal differences between the two types of long-chain saturated fatty acid crystallites were the larger density of peaks in the upper contact plane of the palmitic acid crystallites, as well as their greater proportion of asymmetrical shapes, in comparison to that of the stearic acid film. These two parameters might contribute to higher bactericidal activity on surfaces derived from palmitic acid. Both the palmitic and stearic acid crystallite surfaces displayed activity against Gram-negative, rod-shaped Pseudomonas aeruginosa and Gram-positive, spherical Staphylococcus aureus cells. These microcrystallite interfaces might be a useful tool in the fabrication of effective bactericidal nanocoatings. STATEMENT OF SIGNIFICANCE: Nanostructured cicada and dragonfly wing surfaces have been discovered to be able physically kill bacterial cells. Here, we report on the successful fabrication of bactericidal three-dimensional structures of two main lipid components of the epicuticle of insect wings, palmitic (C16) and stearic (C18) acids. After crystallisation onto highly ordered pyrolytic graphite, both the palmitic and stearic acid films displayed bactericidal activity against both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus cells. The simplicity of the production of these microcrystallite interfaces suggests that a fabrication technique, based on solution deposition, could be an effective technique for the application of bactericidal nanocoatings.

Antibacterial Nerol Cinnamates from the Australian Plant Eremophila longifolia.

Two new antimicrobial agents, neryl ferulate (1) and neryl p-coumarate (2), were identified using bioassay-guided isolation from the leaves of Eremophila longifolia, which is a medicinal plant used by some Australian Aboriginal communities. Although gradual autoxidation of the nerol subunit hindered the initial attempts to purify and characterize 1 and 2, it was found that the autoxidation could be stopped through storage under argon at -20 °C. Biological evaluation showed that neryl ferulate (1) had moderate activity against various Gram-positive bacteria, while neryl p-coumarate (2) was active only against Enterococcus faecium.

Electrochemistry of Iodide, Iodine, and Iodine Monochloride in Chloride Containing Nonhaloaluminate Ionic Liquids.

The electrochemical behavior of iodine remains a contemporary research interest due to the integral role of the I(-)/I3(-) couple in dye-sensitized solar cell technology. The neutral (I2) and positive (I(+)) oxidation states of iodine are known to be strongly electrophilic, and thus the I(-)/I2/I(+) redox processes are sensitive to the presence of nucleophilic chloride or bromide, which are both commonly present as impurities in nonhaloaluminate room temperature ionic liquids (ILs). In this study, the electrochemistry of I(-), I2, and ICl has been investigated by cyclic voltammetry at a platinum macrodisk electrode in a binary IL mixture composed of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2mim][NTf2]). In the absence of chloride (e.g., in neat [C2mim][NTf2]), I(-) is oxidized in an overall one electron per iodide ion process to I2 via an I3(-) intermediate, giving rise to two resolved I(-)/I3(-) and I3(-)/I2 processes, as per previous reports. In the presence of low concentrations of chloride ([Cl(-)] and [I(-)] are both <30 mM), an additional oxidation process appears at potentials less positive than the I3(-)/I2 process, which corresponds to the oxidation of I3(-) to the interhalide complex anion [ICl2](-), in an overall two electron per iodide ion process. In the presence of a large excess of Cl(-) ([I(-)] ≈ 10 mM and [Cl(-)] ≈ 3.7 M), I(-) is oxidized in an overall two electron per iodide ion process to [ICl2](-) via an [I2Cl](-) intermediate (confirmed by investigating the voltammetric response of ICl and I2 under these conditions). In summary, the I(-)/I2/I(+) processes in nonhaloaluminate ILs involve a complicated interplay between multiple electron transfer pathways and homogeneous chemical reactions which may not be at equilibrium on the voltammetric time scale.

Bacterial patterning at the three-phase line of contact with microtextured alkanes.

Aliphatic crystallites, characteristic of the eicosane and docosane components of naturally occurring lipids, were found to form microtextures that were structured by specific interactions with ordered graphite (HOPG) used as the underlying substratum, as confirmed by scanning electron microscopy (SEM) and fast Fourier transform (FFT) analysis. Confocal scanning laser microscopy (CLSM) showed highly directed bacterial alignment for two bacterial species (spherical and rod-shaped), reflecting the preferential orientation of the crystallite-air-water interfaces to give linear and triangular bacterial patterning. The mechanisms of bacterial attachment are demonstrated in terms of the balance between effective radial adhesional forces and the capillary forces resulting from the water contact angle of the bacteria at the three-phase line (TPL) of the lipid surface. It is suggested that these microtextured surfaces, which exhibit the ability to limit bacterial adhesion to a precise patterning at the lipid TPL, could be used as a means of controlling bacterial colonization.

Controlled release of retinyl acetate from ß-cyclodextrin functionalized poly(vinyl alcohol) electrospun nanofibers.

Retinyl acetate (RA) was effectively incorporated into electrospun nanofibers of poly(vinyl alcohol) (PVA) containing ß-cyclodextrin (ß-CD) in order to form inclusion complexes for encapsulation to prolong shelf life and thermal stability. The physical and thermal properties of encapsulated RA were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The nanofibers of PVA/RA and PVA/RA/ß-CD exhibited bead free average fiber diameters of 264 ± 61 and 223 ± 49 nm, respectively. The surface chemistry of the functional nanofibers was investigated by X-ray photoelectron spectroscopy (XPS). Thermogravimetric analysis (TGA) demonstrated different thermal stabilities between the bioactive and the polymer, with and without ß-CD. Square-wave voltammogram peak current changes were used to follow the release kinetics of RA from the nanofibers. Results indicate that RA coated inside PVA/ß-CD nanofibers was protected against oxidation much better than RA in PVA nanofibers and should extend the shelf life. In addition, RA encapsulated in the PVA/ß-CD had better thermal stability than PVA nanofibers.

Natural insect and plant micro-/nanostructsured surfaces: an excellent selection of valuable templates with superhydrophobic and self-cleaning properties.

Insects and plants are two types of organisms that are widely separated on the evolutionary tree; for example, plants are mostly phototrophic organisms whilst insects are heterotrophic organisms. In order to cope with environmental stresses, their surfaces have developed cuticular layers that consist of highly sophisticated structures. These structures serve a number of purposes, and impart useful properties to these surfaces. These two groups of organisms are the only ones identified thus far that possess truly superhydrophobic and self-cleaning properties. These properties result from their micro- and nano-scale structures, comprised of three-dimensional wax formations. This review analyzes the surface topologies and surface chemistry of insects and plants in order to identify the features common to both organisms, with particular reference to their superhydrophobic and self-cleaning properties. This information will be valuable when determining the potential application of these surfaces in the design and manufacture of superhydrophobic and self-cleaning devices, including those that can be used in the manufacture of biomedical implants.

Amylase production by Preussia minima, a fungus of endophytic origin: optimization of fermentation conditions and analysis of fungal secretome by LC-MS.

BACKGROUND: Environmental screening programs are used to find new enzymes that may be utilized in large-scale industrial processes. Among microbial sources of new enzymes, the rationale for screening fungal endophytes as a potential source of such enzymes relates to the hypothesised mutualistic relationship between the endophyte and its host plant. There is a need for new microbial amylases that are active at low temperature and alkaline conditions as these would find industrial applications as detergents. RESULTS: An α-amylase produced by Preussia minima, isolated from the Australian native plant, Eremophilia longifolia, was purified to homogeneity through fractional acetone precipitation and Sephadex G-200 gel filtration, followed by DEAE-Sepharose ion exchange chromatography. The purified α-amylase showed a molecular mass of 70 kDa which was confirmed by zymography. Temperature and pH optima were 25°C and pH 9, respectively. The enzyme was activated and stabilized mainly by the metal ions manganese and calcium. Enzyme activity was also studied using different carbon and nitrogen sources. It was observed that enzyme activity was highest (138 U/mg) with starch as the carbon source and L-asparagine as the nitrogen source. Bioreactor studies showed that enzyme activity was comparable to that obtained in shaker cultures, which encourages scale-up fermentation for enzyme production. Following in-gel digestion of the purified protein by trypsin, a 9-mer peptide was sequenced and analysed by LC-ESI-MS/MS. The partial amino acid sequence of the purified enzyme presented similarity to α-amylase from Magnaporthe oryzae. CONCLUSIONS: The findings of the present study indicate that the purified α-amylase exhibits a number of promising properties that make it a strong candidate for application in the detergent industry. To our knowledge, this is the first amylase isolated from a Preussia minima strain of endophytic origin.

Applications of convolution voltammetry in electroanalytical chemistry.

The robustness of convolution voltammetry for determining accurate values of the diffusivity (D), bulk concentration (C(b)), and stoichiometric number of electrons (n) has been demonstrated by applying the technique to a series of electrode reactions in molecular solvents and room temperature ionic liquids (RTILs). In acetonitrile, the relatively minor contribution of nonfaradaic current facilitates analysis with macrodisk electrodes, thus moderate scan rates can be used without the need to perform background subtraction to quantify the diffusivity of iodide [D = 1.75 (±0.02) × 10(-5) cm(2) s(-1)] in this solvent. In the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, background subtraction is necessary at a macrodisk electrode but can be avoided at a microdisk electrode, thereby simplifying the analytical procedure and allowing the diffusivity of iodide [D = 2.70 (±0.03) × 10(-7) cm(2) s(-1)] to be quantified. Use of a convolutive procedure which simultaneously allows D and nC(b) values to be determined is also demonstrated. Three conditions under which a technique of this kind may be applied are explored and are related to electroactive species which display slow dissolution kinetics, undergo a single multielectron transfer step, or contain multiple noninteracting redox centers using ferrocene in an RTIL, 1,4-dinitro-2,3,5,6-tetramethylbenzene, and an alkynylruthenium trimer, respectively, as examples. The results highlight the advantages of convolution voltammetry over steady-state techniques such as rotating disk electrode voltammetry and microdisk electrode voltammetry, as it is not restricted by the mode of diffusion (planar or radial), hence removing limitations on solvent viscosity, electrode geometry, and voltammetric scan rate.

Optimization of protease production by endophytic fungus, Alternaria alternata, isolated from an Australian native plant.

Endophytes are recognised as potential sources of novel secondary metabolites, including enzymes and drugs, with applications in medicine, agriculture and industry. There is a growing need for new enzymes, including proteases, for use in industry that can function under a variety of conditions. In this study, three fungal endophytes (Alternaria alternata, Phoma herbarum and an unclassified fungus), were isolated from the Australian native plant, Eremophilia longifolia, and assessed for production of proteases. The lyophilised growth media obtained after fungal fermentation were analysed for protease production using enzyme activity assays. Protease production was optimised by assessing the effects of temperature, pH, carbon source and nitrogen source on activity. A. alternata showed the greatest protease activity in a wide range of pH (3-9). The broadest activity between 9 and 50 °C was observed at pH 7, suggesting a neutral protease. Overall, the optimum conditions were 37 °C and pH 7 with a maximum specific activity value of 69.86 BAEE units/mg. The characteristics demonstrated by this fungal endophyte showed that it is a potential source of an enzyme with particular application in the dairy industry. However, further studies of the tolerance to higher temperatures and pH will indicate whether the enzyme is suitable to such applications.

Unexpected complexity in the electro-oxidation of iodide on gold in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

The electro-oxidation of iodide on a gold electrode in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been investigated using transient cyclic voltammetry, linear-sweep semi-integral voltammetry, an electrochemical quartz crystal microbalance technique, and coulometry/electrogravimetry. Two oxidation processes are observed, with an electron stoichiometry of 1:1, compared with the well-known 2:1 electron stoichiometry observed on other commonly used electrode materials, such as platinum, glassy carbon, and boron-doped diamond, under identical conditions. Detailed mechanistic information, obtained in situ using an electrochemical quartz crystal microbalance, reveals that this unusual observation can be attributed to the dissolution of the gold electrode in the presence of iodide. Coulometric/electrogravimetric analysis suggests that the oxidation state of the soluble gold species is +1 and that diiodoaurate, [AuI2](-), is the likely intermediate. A proportionally smaller amount of triiodide intermediate is also detected by means of UV-vis spectroscopy. On this basis, it is proposed that iodide oxidation on gold occurs via two parallel pathways: predominantly via a diiodoaurate intermediate 2I(-) + Au ⇌ [AuI2](-) + e(-) and [AuI2](-) ⇌ I2 + Au + e(-) and to a lesser extent via a triiodide intermediate 3I(-) ⇌ I3(-) + 2e(-) and I3(-) ⇌ 3/2I2 + e(-). This proposed mechanism was further supported by voltammetric investigations with an authentic sample of the anionic [AuI2](-) complex.

Molecular organization of the nanoscale surface structures of the dragonfly Hemianax papuensis wing epicuticle.

The molecular organization of the epicuticle (the outermost layer) of insect wings is vital in the formation of the nanoscale surface patterns that are responsible for bestowing remarkable functional properties. Using a combination of spectroscopic and chromatographic techniques, including Synchrotron-sourced Fourier-transform infrared microspectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) depth profiling and gas chromatography-mass spectrometry (GCMS), we have identified the chemical components that constitute the nanoscale structures on the surface of the wings of the dragonfly, Hemianax papuensis. The major components were identified to be fatty acids, predominantly hexadecanoic acid and octadecanoic acid, and n-alkanes with even numbered carbon chains ranging from C14 to C30. The data obtained from XPS depth profiling, in conjunction with that obtained from GCMS analyses, enabled the location of particular classes of compounds to different regions within the epicuticle. Hexadecanoic acid was found to be a major component of the outer region of the epicuticle, which forms the surface nanostructures, and was also detected in deeper layers along with octadecanoic acid. Aliphatic compounds were detected throughout the epicuticle, and these appeared to form a third discrete layer that was separate from both the inner and outer epicuticles, which has never previously been reported.

Toward rational design of organic dye sensitized solar cells (DSSCs): an application to the TA-St-CA dye.

A computer aided rational design has been performed on TA-St-CA dye sensitizer in order to improve the desirable properties for new organic dye sensitized solar cell (DSSC). A number of electron-donating (ED) and electron-withdrawing (EW) units based on Dewar's rules are substituted into the π-conjugated oligo-phenylenevinylene bridge of the reference TA-St-CA dye. The effects of these alternations on the molecular structures and the electron absorption spectra are calculated using time-dependant density functional theory (TDDFT). It is found that chemical modifications using electron donating (ED) substitutions exhibit advantages over the electron withdrawing (EW) substitutes to reduce the HOMO-LUMO energy gap as well as the electron distribution of the frontier orbitals of the new dyes. Dewar's rule is a useful guideline for rational design of new dye sensitizers with desired HOMO-LUMO gap. The impact on the optical spectra of new dyes are, however, less significant.

Endophytes from an Australian native plant are a promising source of industrially useful enzymes.

Endophytes are microorganisms that live within plant tissues that are potential sources of novel bioactive compounds, including enzymes. We have identified endophytes of the Australian native plant Eremophilia longifolia which were screened for the production of industrially useful enzymes. Seventeen fungal endophytes were isolated from the leaves of E. longifolia and enzyme production was investigated within a range of pH (3.5, 5.5, 7 and 9) and temperatures (9, 25, 37 and 50 °C). Amylase was the most common enzyme encountered with numerous isolates showing production throughout the temperature and pH ranges. Protease production was also seen over the conditions tested but was more dominant at lower pH and temperature. Activity was not observed for other enzymes including ligninase, xylanase and cellobiohydrolase. Enzymes from isolates of Preussia minima, Alternaria sp. and an unclassified fungus, which showed highest activity in screening assays, were investigated further. Enzyme production was verified by zymography and the amylase activity of P. minima was found to be significantly greater than that of Aspergillus oryzae particularly in alkaline conditions and low temperature which are desirable properties for the detergent industry. This work shows that enzymes with potential use in industry can be readily identified in fungal endophytes.

Advantages available in the application of the semi-integral electroanalysis technique for the determination of diffusion coefficients in the highly viscous ionic liquid 1-methyl-3-octylimidazolium hexafluorophosphate.

While it is common to determine diffusion coefficients from steady-state voltammetric limiting current values, derived from microelectrode/rotating disk electrode measurements or transient peak currents at macroelectrodes, application of these methods is problematic in highly viscous ionic liquids. This study shows that the semi-integral electroanalysis technique is highly advantageous under these circumstances, and it has allowed the diffusion coefficient of cobaltocenium, [Co(Cp)(2)](+) (simple redox process), and iodide, I(-) (complex redox mechanism), to be determined in the highly viscous ionic liquid 1-methyl-3-octylimidazolium hexafluorophosphate (viscosity = 866 cP at 20 °C) from transient voltammograms obtained using a 1.6 mm diameter Pt electrode. In such a viscous medium, a near-steady-state current is not attainable with a 10 µm diameter microdisk electrode or a 3 mm diameter Pt rotating disk electrode, while peak currents at a macrodisk are subject to ohmic drop problems and the analysis is hampered by difficulties in modeling the processes involved in the oxidation of iodide. The diffusion coefficients of [Co(Cp)(2)](+) and I(-) were determined to be 9.4 (±0.3) × 10(-9) cm(2) s(-1) and 7.3 (±0.3) × 10(-9) cm(2) s(-1), respectively. These results highlight the utility of the semi-integral electroanalysis technique for quantifying the diffusivity of electroactive species in high viscosity media, where the use of steady-state techniques and transient peak currents is often limited.

Simulations of cyclic voltammetric and chronoamperometric electrode responses at a disk electrode using combinations of spherical and cylindrical electrode geometries.

Using geometric models based on one-dimensional transport at spheres and cylinders, three methods for improving the simulation of voltammetric behavior of a disk electrode have been explored. One method is based on the common assumption of equivalency between the limiting currents for a disk and a hemisphere under steady-state diffusion conditions. The second method involves the use of a partial-sphere geometry which is a better approximation that is suitable at the extreme diffusional limits achievable at a disk electrode of fully planar and steady-state transport. The third method, which is generally applicable, is a further refinement that uses a combination of appropriate one-dimensional spherical and cylindrical geometries. The results demonstrate that reasonably accurate approximations of disk behavior for several reaction mechanisms can be achieved in a fraction of the time required to compute the more rigorous two-dimensional model. We propose that the approximation serve primarily as a fast way to explore system behavior and establish approximate values of the relevant parameters. More accurate computations can then be performed using the two-dimensional model.

Diffusion-controlled chronoamperometry at a disk electrode.

An accurate formula exists for describing the decay of the current following the imposition of extreme concentration polarization on a disk electrode under diffusion-controlled conditions. It has been amply validated by diverse simulations and is presented here in a more compact form than hitherto. The formula finds application beyond the realm of potential-step chronoamperometry.

Synthesis, electrochemistry, and bioactivity of the cyanobacterial calothrixins and related quinones.

The calothrixins are quinone-based natural products isolated from Calothrix cyanobacteria which show potent antiproliferative properties against several cancer cell lines. Preliminary mechanistic studies suggest that the biological mode of action of the calothrixins may be linked to their ability to undergo redox cycling. In this study we compare the bioactivities of the calothrixins with those of structurally related quinones in order to identify the structural features in the calothrixins essential for biological activity. In particular, the reduction potentials of the calothrixins and some related quinones were measured electrochemically. Our studies indicate that while there is no direct correlation between the reduction potentials and biological activities of the studied compounds, in all cases quinones with EC(50) values <1.6 microM undergo reduction to their respective semiquinones readily, with their E(1/2) values being more positive than -0.5 V versus the standard hydrogen electrode (SHE).