Nanostructured Bimetallic Block Copolymers as Precursors to Magnetic FePt Nanoparticles

Phase-separated block copolymers (BCPs) that function as precursors to arrays of FePt nanoparticles (NPs) are of potential interest for the creation of media for the next-generation high-density magnetic data storage devices. A series of bimetallic BCPs has been synthesized by incorporating a complex containing Fe and Pt centers into the coordinating block of four different poly­(styrene-<i>b</i>-4-vinylpyridine)­s (PS-<i>b</i>-P4VPs, <b>P1–P4</b>). To facilitate phase separation for the resulting metalated BCPs (<b>PM1–PM4</b>), a loading of the FePt-bimetallic complex corresponding to ca. 20% was used. The bulk and thin-film self-assembly of these BCPs was studied by transmission electron microscopy (TEM) and atomic force microscopy, respectively. The spherical and cylindrical morphologies observed for the metalated BCPs corresponded to those observed for the metal-free BCPs. The products from the pyrolysis of the BCPs in bulk were also characterized by TEM, powder X-ray diffraction, and energy-dispersive X-ray spectroscopy, which indicated that the FePt NPs formed exist in an fct phase with average particle sizes of ca. 4–8 nm within a carbonaceous matrix. A comparison of the pyrolysis behavior of the metalated BCP (<b>PM3</b>), the metalated <b>P4VP</b> homopolymer (<b>PM5</b>), and the molecular model organometallic complex revealed the importance of using a nanostructured BCP approach for the synthesis of ferromagnetic FePt NPs with a smaller average NP size and a close to 1:1 Fe/Pt stoichiometric ratio

Recovery of cellulose fibers from oil palm empty fruit bunch for pulp and paper using green delignification approach

The aim of this work was to recover the cellulose fibers from EFB using low-transition-temperature-mixtures (LTTMs) as a green delignification approach. The hydrogen bonding of LTTMs observed in 1H NMR tends to disrupt the three-dimensional structure of lignin and further remove the lignin from EFB. Delignification process of EFB strands and EFB powder were performed using standard l-malic acid and cactus malic acid-LTTMs. The recovered cactus malic acid-LTTMs showed higher glucose concentration of 8.07 mg/mL than the recovered l-malic acid LTTMs (4.15 mg/mL). This implies that cactus malic acid-LTTMs had higher delignification efficiency which led to higher amount of cellulose hydrolyzed into glucose. The cactus malic acid-LTTMs-delignified EFB was the most feasible fibers for making paper due to its lowest kappa number of 69.84. The LTTMs-delignified EFB has great potential to be used for making specialty papers in pulp and paper industry

Immobilized enzyme/microorganism complexes for degradation of microplastics: A review of recent advances, feasibility and future prospects

Environmental prevalence of microplastics has prompted the development of novel methods for their removal, one of which involves immobilization of microplastics-degrading enzymes. Various materials including nanomaterials have been studied for this purpose but there is currently a lack of review to present these studies in an organized manner to highlight the advances and feasibility. This article reviewed more than 100 peer-reviewed scholarly papers to elucidate the latest advances in the novel application of immobilized enzyme/microorganism complexes for microplastics degradation, its feasibility and future prospects. This review shows that metal nanoparticle-enzyme complexes improve biodegradation of microplastics in most studies through creating photogenerated radicals to facilitate polymer oxidation, accelerating growth of bacterial consortia for biodegradation, anchoring enzymes and improving their stability, and absorbing water for hydrolysis. In a study, the antimicrobial property of nanoparticles retarded the growth of microorganisms, hence biodegradation. Carbon particle-enzyme complexes enable enzymes to be immobilized on carbon-based support or matrix through covalent bonding, adsorption, entrapment, encapsulation, and a combination of the mechanisms, facilitated by formation of cross-links between enzymes. These complexes were shown to improve microplastics-degrading efficiency and recyclability of enzymes. Other emerging nanoparticles and/or enzymatic technologies are fusion of enzymes with hydrophobins, polymer binding module, peptide and novel nanoparticles. Nonetheless, the enzymes in the complexes present a limiting factor due to limited understanding of the degradation mechanisms. Besides, there is a lack of studies on the degradation of polypropylene and polyvinyl chloride. Genetic bioengineering and metagenomics could provide breakthrough in this area. This review highlights the optimism of using immobilized enzymes/microorganisms to increase the efficiency of microplastics degradation but optimization of enzymatic or microbial activities and synthesis of immobilized enzymes/microorganisms are crucial to overcome the barriers to their wide application

Thermo-catalytic co-pyrolysis of palm kernel shell and plastic waste mixtures using bifunctional HZSM-5/limestone catalyst : Kinetic and thermodynamic insights

Kinetic and thermodynamic parameters of catalytic co-pyrolysis of palm kernel shell (PKS) and high-density polyethylene (HDPE) with three different catalysts (zeolite HZSM-5, limestone (LS) and bifunctional HZSM-5/LS) using thermogravimetric analyser via nitrogen environment were studied. The experiments were carried out at different heating rates ranging from 10 to 100 K/min within temperature range of 50–900 °C. Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and modified Distributed Activation Energy Model (DAEM) methods were employed in this current study. The average Ea for PKS, HDPE, PKS/HDPE (2:8) – HZSM-5, PKS/HDPE (2:8) – LS, PKS/HDPE (2:8) – HZSM-5/LS, PKS/HDPE (5:5) – HZSM-5/LS, PKS/HDPE (8:2) – HZSM-5/LS are 137.26–145.49, 247.73–250.45, 168.97–172.50, 149.74–152.79, 115.30–120.39, 124.36–129.41, 151.03–154.47 and 152.67–157.31 kJ mol−1, respectively. Among the different catalysts used, LS demonstrated the lowest average Ea (151.30–120.39 kJ mol−1) and ΔH (109.65–114.74 kJ mol−1). Positive values for ΔH and ΔG were found for the catalytic co-pyrolysis of PKS/HDPE mixtures which indicates the process is in endothermic reaction and possess non-spontaneous nature. The kinetic and thermodynamic analyses revealed the potential of PKS and HDPE as a potential feedstock for clean bioenergy production

Assisted reproduction in Hong Kong: Status in the 1990s

Information on assisted reproduction in Hong Kong for the period from January 1992 to December 1993 was collected from the three centres that offer assisted reproduction. Altogether, 912 treatment cycles of in vitro fertilisation and embryo transfer, 158 treatment cycles of gamete intrafallopian transfer, and 87 cycles of zygote intrafallopian transfer were initiated during this period. The delivery rates per cycle started were 8.4% for in vitro fertilisation, 29.1% for gamete intrafallopian transfer, and 13.8% for zygote intrafallopian transfer. During the same period, 233 cycles of replacement of frozen thawed embryos were completed with a delivery rate of 11.2% per cycle. Pregnancies were also achieved using oocyte donation and micromanipulation techniques.published_or_final_versio

Synergistic effects of catalytic co-pyrolysis Chlorella vulgaris and polyethylene mixtures using artificial neuron network: Thermodynamic and empirical kinetic analyses

The catalytic pyrolysis of Chlorella vulgaris, high-density polyethylene (Pure HDPE) and, their binary mixtures were conducted to analyse the kinetic and thermodynamic performances from 10 to 100 K/min. The kinetic parameters were computed by substituting the experimental and ANN predicted data into these iso-conversional equations and plotting linear plots. Among all the iso-conversional models, Flynn-Wall-Ozawa (FWO) model gave the best prediction for kinetic parameters with the lowest deviation error (2.28–12.76%). The bifunctional HZSM-5/LS catalysts were found out to be the best catalysts among HZSM-5 zeolite, natural limestone (LS), and bifunctional HZSM-5/LS catalyst in co-pyrolysis of binary mixture of Chlorella vulgaris and HDPE, in which the Ea of the whole system was reduced from range 144.93–225.84 kJ/mol (without catalysts) to 75.37–76.90 kJ/mol. With the aid of artificial neuron network and genetic algorithm, an empirical model with a mean absolute percentage error (MAPE) of 51.59% was developed for tri-solid state degradation system. The developed empirical model is comparable to the thermogravimetry analysis (TGA) experimental values alongside the other empirical model proposed in literatur

Solution Structures of the Acyl Carrier Protein Domain from the Highly Reducing Type I Iterative Polyketide Synthase CalE8

Biosynthesis of the enediyne natural product calicheamicins γ1I in Micromonospora echinospora ssp. calichensis is initiated by the iterative polyketide synthase (PKS) CalE8. Recent studies showed that CalE8 produces highly conjugated polyenes as potential biosynthetic intermediates and thus belongs to a family of highly-reducing (HR) type I iterative PKSs. We have determined the NMR structure of the ACP domain (meACP) of CalE8, which represents the first structure of a HR type I iterative PKS ACP domain. Featured by a distinct hydrophobic patch and a glutamate-residue rich acidic patch, meACP adopts a twisted three-helix bundle structure rather than the canonical four-helix bundle structure. The so-called ‘recognition helix’ (α2) of meACP is less negatively charged than the typical type II ACPs. Although loop-2 exhibits greater conformational mobility than other regions of the protein with a missing short helix that can be observed in most ACPs, two bulky non-polar residues (Met992, Phe996) from loop-2 packed against the hydrophobic protein core seem to restrict large movement of the loop and impede the opening of the hydrophobic pocket for sequestering the acyl chains. NMR studies of the hydroxybutyryl- and octanoyl-meACP confirm that meACP is unable to sequester the hydrophobic chains in a well-defined central cavity. Instead, meACP seems to interact with the octanoyl tail through a distinct hydrophobic patch without involving large conformational change of loop-2. NMR titration study of the interaction between meACP and the cognate thioesterase partner CalE7 further suggests that their interaction is likely through the binding of CalE7 to the meACP-tethered polyene moiety rather than direct specific protein-protein interaction

Isolation of bioactive compounds extracted from Eurycoma longifolia Jack old leaves, screening for anti-bacterial, anti-fungal and GSK-3beta inhibition

The plant Eurycoma longifolia Jack or known more commonly as Tongkat Ali has long been a source of traditional remedy curing infertility and also to treat mild illnesses like dysentery and rashes. In this study, the screening and isolation of compounds from Eurycoma longifolia Jack old leaves, by extraction using solvent-solvent method and chromatography methods, have been tested for anti-bacterial, antifungal and Glycogen Synthase Kinase-3beta inhibition activity. The separations of the phytochemicals were performed by liquid-liquid extraction to allow separation according to its classes and specific characteristics. It was determined from the test that the leaf extracts showed activity against Escherichia coli, Staphylococcus aureus and Candida krusei, but had no activity against Bacillus subtilis, Candida albicans or GSK-3beta The study includes isolation via Column Chromatography and verification by Thin Layer Chromatography. It was shown that the leaf extract possesses activity at possibly a single compound against E. coli, two possible compounds showing activity against C. krusei and 7 possible compounds against s.aureus. It was assumed that during isolation a single compound was collected at a specific time in these compound and further study in the future. The comparison of the leaf activity to the test performed using the root and the bark of the plant had also been performed and it was proved that the plant has no activity against GSK-3beta, but the leaf may have precursors in producing even more effective anti-microbial drugs. The experiment had proven that chemicals exhibiting anti-bacterial and antifungal exist in the plants and had been purified to a certain extent

Design and application of cyclic-di-GMP biosensors.

Cyclic‐di‐GMP is an important bacterial secondary messenger molecule that regulates motility, virulence and biofilm formation in many pathogenic bacteria. This messenger molecule is synthesized from cellular GTP by diguanylate cyclase (DGC) and hydrolyzed by phosphodiesterases (PDE) to form 5‐pGpG and GMP. In this dissertation, I have designed biosensors that can report the in vitro and in vivo changes of c‐di‐GMP concentration that can be used for elucidating the function of DGC and PDE proteins in the regulation of c‐di‐GMP that modulates the biofilm formation. The in vitro biosensor was designed using the catalytically inactive EAL domain of FimX (EALFimX) that binds to c‐di‐GMP at sub‐micromolar concentrations. Out of 6 different mutants designed for fluorescent dye labeled biosensor, the mutant Q484C‐MDCC showed to be the best performer. When titrated with c‐di‐GMP, this biosensor protein shown a disassociation constant (Kd) of 172 nM with a decrease in fluorescence by 46%. This biosensor was demonstrated to be highly specific to c‐di‐GMP and is able to report c‐di‐GMP concentration changes in real time. The biosensor was used to determine the steady‐state kinetics of AxDGC2 and RocR. Screening of nucleotide library revealed that AxDGC2 is inhibited by Rp‐GTP‐α‐S and GDP. The IC50 value of Ca2+ as an inhibitor of RocR was calculated to be at 141 μM. This demonstrates that the Q484C‐MDCC was able to report changes in c‐di‐GMP concentrations resulting from DGC and PDE activities and can be used to screen for inhibitors effective against these catalytically active proteins. The FRET in vivo biosensors were designed by flanking PilZ domain proteins, VCA0042 and MrkH with fluorescent proteins mCerulean and mVenus. By measuring the FRET activity, we were able to observe cellular fluctuations of c‐di‐GMP when bacteria cells expressing these sensors were treated with biofilm triggering antibiotic and biofilm dispersing factors. The treatment of E. coli Bl21(DE3) and wild type UTI89 with antibiotics that target cell wall synthesis and ribosomal activity at sub‐MIC shown to up‐regulate c‐di‐GMP, whilst treatment with biofilm dispersal factors causes a down‐regulation of c‐di‐GMP levels. It was also observed that when these E. coli cells were engulfed by murine macrophage cells, the antimicrobial agents secreted for digestion of these xiv bacterial cells down‐regulates the c‐di‐GMP concentrations. This proves that the FRET biosensors are capable of reporting changes in c‐di‐GMP concentrations in E. coli cells and can be used for testing different drugs to promote or disperse biofilms. The polyketide synthase (PKS) are a group of multi-domain proteins involved in synthesizing the various polyketide chains that makes up the majority of drugs today. We have described the optimization of the expression conditions for 2 groups of these large sized proteins. These proteins are the SalA-SalB hybrid system and the PKS8 from Salinospora tropica and Saccharopolyspora erythraea respectively.​Doctor of Philosophy (SBS