Narrow Results

The damage of DNA chains by environmental factors like radiation or chemical pollutants is a topic that has been frequently explored from an experimental and a theoretical perspective. Such damages, like the damage of the strands of a DNA chain, are toxic for the cell and can induce mutagenesis or apoptosis. Several models make strong assumptions for the distribution of damages; for instance a frequent supposition is that these damages are Poisson distributed. [L. Ma, J. J. Wagner, W. Hu, A. J. Levine and G. A. Stolovitzki, Proc. Natl. Acad. Sci.PNAS 102, 14266 (2005).] Only few models describe in detail the damage and the mechanisms associated to the formation and evolution of this damage distribution [H. Nikjoo, P. O'neill and D. T. Goodhead, Radiat. Res. 156, 577 (2001).] Nevertheless, such models do not include the repair processes which are continuously active inside the cell. In this work we present a novel model, based on a depolymerization process, describing the distribution of damages on DNA chains coupled to the dynamics associated to its repair processes. The central aim is not to give a final and comprehensive model, but a hint to represent in more detail the complex dynamics involved in the damage and repair of DNA. We show that there are critical parameters associated to this repair process, in particular we show how critical doses can be relevant in deciding whether the cell continues its repair process or starts apoptosis. We also find out that the damage concentration is related to the dose via a power law relation.

The editorial board discovered that the data points in several sections of the Mossbauer spectra as given in Figs. 3(a) and 3(b) are exactly identical. This is impossible and nonphysical for the measurement of two different samples (or for that matter not even for the same sample!). The only conclusion we can draw from this figure is that some of the data is fabricated. As a result, the results and conclusions as described in the paper are unacceptable. This article is retracted from its publication in Int. J. Mod. Phys. B.

In this paper, a synthesis of conducting polyaniline nanowires electrode junction (CPNEJ) has been reported. Conducting polyaniline nanowires electrode junction on Si/SiO₂ substrate (having 3 μm gap between two gold microelectrodes) is prepared. Polyaniline nanowires with diameter (ca. 140 nm to 160 nm) were synthesized by one step electrochemical polymerization using galvanostatic (constant current) technique to bridge this gap. The surface morphology of CPNEJ was studied by scanning electron microscope (SEM). The synthesized CPNEJ is an excellent platform for biosensor applications.

A technique is suggested to measure the threshold of two-photon initiated photopolymerization involving a Z-scan of a thin film of sensitive material along the focusing axis of the laser beam. A condition of reaching the threshold when scanning the sample along Z-direction is identified via interferometric effect. The technique is demonstrated for measurements employing Nd:YAG laser in nanosecond regime with fundamental frequency 1064 nm and its harmonic of 532 nm. Threshold data are presented for particular systems, indicating a threshold of 5 GW/cm² for a system based on Rose Bengal exposed by a 1064 nm nanosecond-pulsed radiation and 0.05 GW/cm² for Darocur initiators exposed to 532 nm.

UQ Researcher Receives $1000,000 Grand Challenges Explorations Grant.

UQ Scientist Receives AAS Honor.

Imperial College London Bestows its Highest Honor on A*STAR Chairman Lim Chuan Poh.

Three ansa-metallocenes (Me₂C)(Me₂Si)Cp₂TiCl₂(1), [(CH₂)₅C](Me₂Si)Cp₂TiCl₂(2) and (Me₂C)(Me₂Si)Cp₂ZrCl₂(3) with larger dihedral angles and longer distance from metal to the center of Cp planes were synthesized and used as catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). In the case of ethylene polymerization, compared the feature structures of unbridged metallocenes, singly bridged metallocenes and doubly bridged metallocenes 1, 2, 3, there exhibit the relationship between structural characteristics and the catalytic properties with behavior of polymers. And the view that the dimensions of the short dimethylsilylene and isopropylidene bridges of metallocene 3 do not match the co-ordination requirement of the larger zirconium atom can also explain the result for ethylene polymerization. Catalyzed by complexes 1 and 2 respectively, the copolymerizations of ethylene with 1-hexene, 1-octene, especially the long chain α-olefins (1-tetradecene, 1-hexadecene) were investigated, and showed high incorporations and comonomer effects in almost all the examples. The melting points of the copolymers are approximately 4%–31% below those of the homopolymers, and the enthalpies of fusion decrease greatly due to the lower crystallinity. The microstructures of the copolymer were analyzed with ¹³C-NMR to determine the comonomer sequence distributions and number–average sequence lengths. Comparison between results for the complexes 1 and 2 with different bridging groups respectively showed that the nature of the bridge has a significant effect on both the incorporation and sequence distribution of the α-olefin. Because of the bridges in ansa-metallocene complexes, the copolymerization behavior was different in using catalyst 1 and catalyst 2.

[t-BuNSiMe₂(2,7-t-Bu₂Flu)]ZrMe₂ and [t-BuNSiMe₂(3,6-t-Bu₂Flu)]ZrMe₂ were synthesized, and the solid structure of complex [t-BuNSiMe₂(2,7-t-₂Flu)]ZrMe₂ was elucidated by single crystal X-ray analysis. These complexes were applied for propylene polymerization using dried modified methylaluminoxane as a cocatalyst at 0°C and 20°C in toluene. Both systems did not show activity at 0°C, but they conducted the polymerization at 20°C. The introduction of t-butyl substituents to the fluorenyl ligand improved the activity more than six times regardless of the position of the substituents, and both systems gave low molecular weight polypropylenes (PP) with narrow molecular weight distribution. The introduction of t-butyl substituents also improved the syndiospecificity and [t-BuNSiMe₂(3,6-t-Bu₂Flu)]ZrMe₂ gave highly syndiotactic PP with the syndiotactic pentad of 0.91 and the melting point of 145°C.

A novel strategy for the synthesis of zinc thioporphyrazine nanospheres is presented. The uniform spheres were fabricated through a polymerization reaction without using any template or emulsifier, which result from the covalent links between zinc tetra(2,3-bis(pentenylthio)porphyrazine (ZnPz) possessing eight long flexible chains in periphery and each with one terminal olefin group. A possible mechanism to explain the self-assembly of ZnPz nanospheres was also illuminated through monitoring nanosphere formation by means of transmission electron microscopy (TEM). More importantly, ZnPz nanospheres can effectively activate dioxygen in aqueous media under simulated sunlight irradiation, and showed significantly improved photocatalytic activity for the degradation of Rhodamine B (RhB) as compared to monomeric ZnPz. Furthermore, the reactive oxygen species derived from ZnPz nanospheres under light irradiation were determined by electron paramagnetic resonance (EPR) technology, indicating that singlet oxygen (${}^{\mathrm{\text{1}}}$O${}_{\mathrm{\text{2}}})$ and hydroxyl radical (•OH) are the major reactive oxygen species. The facile synthetic methodology and the enhanced photocatalytic performance of the ZnPz nanospheres endow this novel material with the potential of being an efficient biomimetic photocatalyst for wastewater treatment.

Polymerization of C₆₀, Ce₂@C₈₀, and Lu₂@C₇₆ metallofullerenes induced by electron injection from a scanning tunneling microscope (STM) tip has been studied. C₆₀ polymerization has been observed only with C₆₀ multilayer on Au(111) and not with C₆₀ monolayer on Au(111). The Ce_2@C80 metallofullerene on Si(111)-7 × 7 also polymerizes by electron injection but has less polymerization reactivity than C₆₀. Interestingly, the Lu₂@C₇₆ metallofullerene on Si(111)-7 × 7 does not show any polymerization. Based on these STM observations on the tip-induced polymerization, the direction of the bond formation and the dependence of reactivity on the kind of fullerenes are discussed.

A novel ternary nanocomposite of nickel-manganese oxides/multi-walled carbon nanotubes (NMO/MWCNTs) coated with poly (3,4-ethylenedioxythiophene)(PEDOT) was prepared by chemical oxidation method. The filling of NMO particles inside MWCNTs and the uniform coating of NMO/MWCNTs with PEDOT intensified the capacitive behavior of MWCNTs. The lowest IR drop (0.1 V) and highest specific capacitance (SC) values of 526.55 F/g of NMO/MWCNTs/PEDOT imply it as highly efficient hybrid supercapacitor materials in 6 M KOH electrolyte.

A novel poly[($\epsilon$-CL)-co-(GA-alt-L-Asp)] with improved hydrophilicity was prepared. The monomer 3(S)-[(benzyloxycarbony)methyl]-1,4-dioxane-2,5-dione (BMD) was prepared from aspartic acid. The polymer was obtained by ring-opening polymerization of $\epsilon$-caprolactone ($\epsilon$-CL) and BMD. Poly[($\epsilon$-CL)-co-(GA-alt-L-Asp)] was synthesized by deprotection. The structure and properties of the polymer were characterized using ¹H nuclear magnetic resonance, gel permeation chromatography, and differential scanning calorimetry. The melting point and melting enthalpy of the polymer decreased with the increase of BMD. The structural regularity of polycaprolactone was destroyed by the BMD. A laminin-derived peptide [i.e., Arg-Gly-Asp (RGD)] was covalently tethered to the carboxyl groups and the peptide-grafted films. Results indicated that the addition of RGD had beneficial effects for cell growth, as shown by scanning electron microscopy.

We develop a systematic method to obtain spherically symmetric midisuperspace models with modifications inherited from loop quantum gravity. We obtain a family of effective constraints satisfying Dirac’s deformation algebra and show that holonomy corrections can be consistently implemented in the presence of matter with local degrees of freedom.

The current demand for more sustainable catalytic processes has seen a clear shift from the classical noble-metal-based catalysts to cheaper and abundant metals. The focus on earth-abundant transition-metal-based catalysts has been marred by synthetic and characterization challenges but is ultimately achieving the desired catalytic results. To extract the catalytic potential of earth-abundant transition-metal-based complexes, great care concerning the design of the supporting ligands is required. Under certain conditions, monoanionic bidentate chelates present a good strategy to tackle those goals. The 2-iminopyrrolyl framework is a good example of that: Its huge electronic and steric tuning potential has paved the way for diverse coordination chemistries of first-row transition metals, from manganese to copper. With such metal complexes in hand, several catalytic applications have been studied, namely polymerization, hydrofunctionalization and click chemistry. This chapter features the main catalytic achievements of complexes of earth-abundant metals bearing 2-iminopyrrolyl ligands and their respective mechanistic insights and structure–reactivity relationships.

The graft copolymerization of Styrene (ST), Methylmethacrylate (MMA)/Butylacrylate (BA) onto starch was carried chemically using ferrous ion-peroxide redox system. The combination of Starch with ST/MMA and ST/BA was used. The reaction condition was maintained at 60 °C and the monomer ratios were varied from 80/20, 50/50 and 20/80 for both the systems. The granular product of starch graft copolymer was made by spraying different concentrations of grafted starch emulsion on the native starch in the rapid mixer granulator. The resulted granules were dried in the Fluidized bed dryer. The resulted granular product was further analyzed for its physico-mechanical properties such as tensile strength, film strength and elongation at break and so on. The rheological properties of the resulting granular product as well as the starch graft copolymer emulsion were also studied. The viscosity of the granules measured at 28 °C which shows increase in the power law index with an increase in the grafting efficiency. The product finds huge potential as a sizing agent in the textile industry.

Several proteins can form ordered, protease-resistant fibrillar deposits, called amyloid, in the human body. Amyloid is associated with several different diseases, amyloidoses, including Alzheimer's disease. This progressive neurodegenerative disease affects around 1% of the population of the Western world. The disease is pathologically characterized by amyloid deposits composed of fibrils formed by the amyloid β-peptide, Aβ, and it has been suggested that compounds that interfere with Aβ-polymerization could be used for treatment of Alzheimer's disease. Several studies aimed at revealing the structure of Aβ in solution and in amyloid fibrils have been performed. Structural studies of Aβ and other amyloid proteins are problematic since these proteins have poor solubility and do not form crystals. However, with the help of a combination of several different, mostly spectroscopic, techniques the structure of Aβ is being resolved. Here, we will give an introduction to amyloid, Alzheimer's disease, Aβ and different techniques used for studying Aβ structure. Finally, we will look at Aβ-polymerization and how this process can be inhibited.

Multi-objective optimization (MOO) has received considerable attention from researchers in chemical engineering. Bhaskar et al. (2000a) have reviewed reported applications of MOO in chemical engineering until 2000. In this chapter, nearly hundred MOO applications in chemical engineering reported in journals from 2000 until mid 2007 are reviewed briefly. These are categorized into five groups: (1) process design and operation, (2) biotechnology and food industry, (3) petroleum refining and petrochemicals, (4) pharmaceuticals and other products/processes, and (5) polymerization. However, applications reported in this book are not included in this review.

To study the adhesion of absorbent resin, sodium polyacrylate/ diatomite composite was prepared by the aqueous solution polymerization with the main materials acrylic acid and diatomite, crosslinking agent and initiator. FT-IR was used to analyze the molecular structure of composite resin and it was also discussed the effect of the factors such as the neutralization degree, monomer concentration, the amount of initiator, crosslinking agent and the diatomite on adhesion properties.

Multi-objective optimization (MOO) has received considerable attention from researchers in chemical engineering. Bhaskar et al. (2000a) have reviewed reported applications of MOO in chemical engineering until 2000. In this chapter, nearly hundred MOO applications in chemical engineering reported in journals from 2000 until mid 2007 are reviewed briefly. These are categorized into five groups: (1) process design and operation, (2) biotechnology and food industry, (3) petroleum refining and petrochemicals, (4) pharmaceuticals and other products/processes, and (5) polymerization. Applications reported in this book are not included in this review.

This chapter focuses on applications of differential evolution (DE) in the field of polymerization reaction engineering. DE can be applied for modeling and for process optimization; it is being used in different variants, according to the specific characteristics of the system and the required accuracy. First, difficulties in modeling the polymerization processes are presented to justify the use of artificial intelligence tools, particularly artificial neural networks (ANN) and DE. These difficulties are related to the complexity of the reaction medium, lack of complete knowledge of the reaction mechanism, problems in developing and solving phenomenological models, their accuracy and/or potential for inclusion in on-line control procedures. Neuro-evolutive techniques are recommended methodologies for modeling and optimizing such complex polymerization processes. A special section is dedicated to general aspects of how DE can be used in combination with ANN for developing optimal neural models and for determining optimal operating conditions. Two applications: synthesis of polyacrylamide based hydrogels and of siloxane-siloxane copolymers, are discussed in detail.

Boscovich provided a unified theory of point-particles, and this served as basis for Modern quantum mechanics. Applications of Boscovich’s theory to quantum problems, such as to Modern chemistry will be considered based on the work of Dragoslav Stoiljkovich. The works of Stoiljkovich having not been published very much in English, and thus has not been more widely known among English-speaking scientists. This author is now engaged in translating these works in corroboration with Stoiljkovich; works that highlight the modern work that is still being pursued based on Boscovich’s unified field theory. Also, briefly the work of Augustus Prince will be dealt with.