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Molecular Engineering of Biological and Chemical Systems (MEBCS)

Mostrando recursos 1 - 20 de 106

  1. Template Synthesis of Tubular Sn-Based Nanostructures for Lithium Ion Storage

    Wang, Yong; Zeng, Hua Chun; Lee, Jim Yang
    We report herewith the preparation of SnO₂ nanotubes with very good shape and size control, and with and without a carbon nanotube overlayer, The SnO₂-core/carbon-shell nanotubes are excellent reversible Li ion storage compounds combining the best features of carbon (cyclability) and SnO₂ (capacity) to deliver a high specific capacity (~540-600 mAh/g) simultaneous with good cyclability (0.0375% capacity loss per cycle).

  2. Targeted Stimuli-Responsive Dextran Conjugates for Doxorubicin Delivery to Hepatocytes

    Zaman, Noreen T.; Tan, Fred E.; Joshi, Shilpa M.; Ying, Jackie Y.
    A targeted, stimuli-responsive, polymeric drug delivery vehicle has been developed to help alleviate the severe side-effects caused by narrow therapeutic window drugs. Doxorubicin, a commonly used chemotherapeutic agent has been conjugated to dextran by two different techniques. In the first method, doxorubicin and hepatocyte-targeting galactosamine were attached to dextran through amine bonds. Conjugation efficiency based on the amount loaded of each reactant varied from 1% to 50% for doxorubicin and from 2% to 20% for galactosamine, depending on various synthesis parameters. For the second conjugate, doxorubicin was attached to dextran through an acid-labile hydrazide bond. Fluorescence quenching indicated that all...

  3. Synthesis and Self-assembly of [60]Fullerene Containing Sulfobetaine Polymer in Aqueous Solution

    Ravi, P.; Dai, S.; Tam, K. C.
    A series of well-defined stimuli responsive water soluble [60]fullerene (C₆₀) containing polymers such as polyelectrolytes (polyacids and polybases), polyampholyte and polyzwitterionic polymers were synthesized using atom transfer radical polymerization. The aqueous solution properties of these polymers with respective external stimuli such as pH, temperature and salt were studied using potentiometric and conductivity titration, light transmittance, laser light scattering and transmission electron microscopic techniques. The influence of polymer concentration, temperature, pH and electrolyte on the hydrodynamic radius (Rh), radius of gyration (Rg) and aggregation number (Nagg) of the particles were investigated in detail to elucidate the morphology of the particles. The...

  4. Study of GDNF-Family Receptor Alpha 2 And Inhibitory Activity of GDNF-Family Receptor Alpha 2b (GFRα2b) Isoform

    Yoong, Li Foong; Too, Heng-Phon
    The glial cell-line derived neurotrophic factor (GDNF) and neurturin (NTN) belong to a structurally related family of neurotrophic factors. NTN exerts its effect through a multi-component receptor system consisting of the GDNF family receptor alpha 2 (GFRα2), proto-oncogene RET and/or NCAM. GFRα2 is spliced into at least three isoforms, GFRα2a, GFRα2b and GFRα2c. The present study investigated the expression and functional differences of GFRα2 isoforms. These receptor isoforms are differentially expressed in specific human brain regions. Using Neuro2A model, GDNF and NTN promote neurite outgrowth via GFRα2a and GFRα2c, but not GFRα2b. These GFRα2 isoforms regulate different early response genes...

  5. Rare-Earth Doped LaF₃ Nanocrystals for Upconversion Fluorescence

    Yi, Guang-Shun; Chow, Gan-Moog
    Upconversion fluorescent nanocrystals, Yb-Er, Yb-Ho and Yb-Tm co-doped LaF₃ were chemically synthesized. The average particle size was 4.4 nm with a narrow size distribution of ± 0.3 nm. Under the 980 nm NIR excitation, the green, red and blue emission bands from these nanocrystals were observed, respectively. These nanocrystals have potential applications as bio-probes and displays.

  6. Photo- and Thermoinduced Sol-Gel Transitions in Blends of Azobenzene Copolymers and Pluronic Surfactants

    Deshmukh, Smeet; Bromberg, Lev; Hatton, T. Alan
    Novel self-assembling copolymers of 4-Methacryloyloxyazobenzene and NN-dimethylacrylamide (MOAB-DMA) exhibiting a pronounced photoviscosity effects in water are described. An optimum polymer architecture corresponding to maximum contents of the azobenzene moieties that allowed for the aqueous solubility of the MOAB-DMA copolymer at ambient temperature was observed at a molar fraction of the MOAB moieties in the copolymer of 0.2. When blended with Pluronic F127 copolymers, the MOAB-DMA solutions become both irradiation- and temperature-sensitive and capable of sol-gel transitions depending on the MOAB-DMA content. Effect of the MOAB-DMA copolymer addition to concentrated Pluronic F127 solutions was studied by controlled stress rheology. The presence...

  7. Molecular Engineering of Conjugated Polymers for Sensor Applications

    Vetrichelvan, Muthalagu; Valiyaveettil, Suresh
    In recent years, the application of fluorescent conjugated polymers for sensing chemical and biological analytes has received much attention from many researchers. A promising development in this direction was the fabrication of conducting polymer-based sensors for the detection of metal ions, small organic molecules and biomolecules. Herein, we have designed, synthesized and studied a series of copolymers containing alternate phenylene and 2,5- or 2,6-substituted pyridine rings. The basic N-atom of the pyridine ring and the adjacent –OH group from the phenyl ring provide binding sites for metal ions. Another series of water-soluble conjugated polymers with propoxy sulfonate side chains are...

  8. Machine Learning Approaches to Modeling the Physiochemical Properties of Small Peptides

    Jensen, Kyle; Styczynski, Mark; Stephanopoulos, Gregory
    Peptide and protein sequences are most commonly represented as a strings: a series of letters selected from the twenty character alphabet of abbreviations for the naturally occurring amino acids. Here, we experiment with representations of small peptide sequences that incorporate more physiochemical information. Specifically, we develop three different physiochemical representations for a set of roughly 700 HIV–I protease substrates. These different representations are used as input to an array of six different machine learning models which are used to predict whether or not a given peptide is likely to be an acceptable substrate for the protease. Our results show that,...

  9. Fabrication of Micro and Nanoparticles of Paclitaxel-loaded Poly L Lactide for Controlled Release using Supercritical Antisolvent Method: Effects of Thermodynamics and Hydrodynamics

    Lee, Lai Yeng; Smith, Kenneth A.; Wang, Chi-Hwa
    This paper presents the fabrication of controlled release devices for anticancer drug paclitaxel using supercritical antisolvent method. The thermodynamic and hydrodynamic effects during supercritical antisolvent process on the particle properties obtained were investigated. Scanning electron microscopy was employed to study particle sizes and morphologies achieved. It was observed that increasing supercritical pressure improves the surface morphology of particles obtained, and increasing the flow rate of the organic solution jet reduces the particle sizes obtained. A modified Supercritical Antisolvent with Enhanced Mass transfer setup was developed to produce monodispersed nanoparticles with high recovery yield. High performance liquid chromatography was used to...

  10. Dynamic Surface Tension Behaviour in a Photoresponsive Surfactant System

    Cicciarelli, Bradley A.; Smith, Kenneth A.; Hatton, T. Alan
    We report on the surface properties of a photoresponsive surfactant that incorporates the light-sensitive azobenzene group into its tail. Cis-trans photo-isomerization of this group alters the ability of the surfactant to pack into adsorbed monolayers at an air-water interface or into aggregates in solution, causing a significant variation in bulk and surface properties upon changes in the illumination conditions. NMR studies indicate that a solution left in the dark for an extended period of time contains trans isomer almost exclusively, while samples exposed to light of fixed wavelength eventually reach a photostationary equilibrium with significant amounts of both isomers present....

  11. Discrimination of Alternative Spliced Isoforms by Real-Time PCR Using Locked Nucleic Acid (LNA) Substituted Primer

    Wan, Guoqiang; Too, Heng-Phon
    Determination of quantitative expression levels of alternatively spliced isoforms provides an important approach to the understanding of the functional significance of each isoform. Real-time PCR using exon junction overlapping primers has been shown to allow specific detection of each isoform. However, this design often suffers from severe cross amplification of sequences with high homology at the exon junctions. We used human GFRα2b as a model to evaluate the specificity of primers substituted with locked nucleic acids (LNAs). We demonstrate here that single LNA substitutions at different positions of 3’ terminus could improve the discrimination of the primers against GFRα2a template,...

  12. Design, Fabrication and Functional Analysis of a New Protein Array Based on ssDNA-based Assembly

    Ajikumar, Parayil Kumaran; Ng, Jin Kiat; Tang, Yew Chung; Lee, Jim Yang; Stephanopoulos, Gregory; Too, Heng-Phon
    In the post genomic era, proteomics has enormous potential in biology and medicine. Among the various bioanalytical tools developed, protein microarray is one of the recent advancements which offer high throughput profiling of cellular proteins to provide insights into the mechanisms of biological processes. Fundamentally, the protein microarray involves the immobilization of interacting elements, proteins, on a few square microns of a solid support and in principle, it is capable of detecting analytes with a higher sensitivity than conventional macroscopic immunoassays. Here in the present report we delineates the design, fabrication and functional analysis of protein microarray using semi-synthetic ssDNA...

  13. Correlating Gene Transfection Efficiency and the Physical Properties of Various Cationic Poly(methacrylate) Systems

    Tan, J. F.; Too, Heng-Phon; Hatton, T. Alan; Tam, K. C.
    Transfection efficiencies of several polymeric gene carriers were compared and correlated quantitatively to the amounts of cellular accumulation of plasmid DNA and to the expression of mRNA by quantitative real time PCR. Three cationic methacrylate polymer systems with similar chemical structure were used in this study, namely: poly(dimethylamino)ethyl methacrylate (PDMA) homopolymer, PEO-b-PDMA copolymer and PEO-b-poly(diethylamino)ethyl methacrylate (PEO-b-PDEA) copolymer. Despite their similar chemical structures, their transfection efficiencies were significantly different. PEO-b-PDEA copolymer was significantly less efficient as gene carrier compared to both PDMA and PEO-b-PDMA systems. Results from quantitative real-time polymerase chain reaction (real-time PCR), cytotoxicity and Zeta potential measurements showed...

  14. CIRP Expression on Growth and Productivity of CHO Cells

    Tan, Hong-Kiat; Yap, Miranda G.S.; Wang, Daniel I.C.
    Mammalian cell culture is typically operated at the physiological temperature of 37°C. Low temperature cell culture at 30-33°C, in particular for CHO cells, increased the specific productivity of many recombinant proteins amongst many other benefits. However, the cell density is lower, thus reducing the total protein yield. Of the 17 mammalian cold-stress genes reported to be up- or down-regulated at low temperature, CIRP shows potential as a gene target for improving recombinant protein production, as its expression levels were reported to affect both growth and specific productivity. In this study, it was shown that over-expression of the cold-stress gene CIRP...

  15. Bioinformatics and Handwriting/Speech Reconition: Uncoventional Applications of Similarity Search Tools

    Jensen, Kyle; Stephanopoulos, Gregory
    This work introduces two unconventional applications for sequence alignment algorithms outside the domain of bioinformatics: handwriting recognition and speech recognition. In each application we treated data samples, such as the path of a and written pen stroke, as a protein sequence and use the FastA sequence alignment tool to classify unknown data samples, such as a written character. That is, we handle the handwriting and speech recognition problems like the protein annotation problem: given a sequence of unknown function, we annotate the sequence via sequence alignment. This approach achieves classification rates of 99.65% and 93.84% for the handwriting and speech...

  16. A Computational Study to Understand the Surface Reactivity of Gold Nanoparticles with Amines and DNA

    Pong, Boon-Kin; Lee, Jim Yang; Trout, Bernhardt L.
    We conducted a computational adsorption study of methylamine on various surface-models of gold nanoparticle which is facetted by multiple {111} and {100} planes. In addition to these flat surfaces, our models include the stepped surfaces (ridges) formed along the intersections of these planes. Binding on the flat surface was fairly weak, but substantially stronger on the ridges by an average of 4.4 kcal/mol. This finding supports the idea that ssDNA’s interaction with gold nanoparticles occurs through the amines on the purine/pyrrimidine rings. Also, this typically undesirable interaction between DNA and gold nanoparticles is expected to increase as the particle size...

  17. Active Hypothermic Growth: A Novel Means For Increasing Total Interferon-γ Production by Chinese Hamster Ovary Cells

    Stephen R., Fox; Yap, Mei Xia; Yap, Miranda G.S.; Wang, Daniel I.C.
    When grown under hypothermic conditions, Chinese Hamster Ovary (CHO) cells become growth arrested in the G₀/G₁ phase of the cell cycle and also often exhibit increased recombinant protein production. In this study, we have validated this hypothesis by stimulating hypothermic growth using basic fibroblast growth factor and fetal bovine serum supplementation. This method led to 7.7- and 4.9-fold increase in total production compared to the 37°C and 32°C control cultures, respectively. This proof-of-concept study will motivate the creation of cell lines capable of growing at low temperatures for use in industrial processes.

  18. Effect of Gas Sparging in Mammalian Cell Bioreactors

    Wang, Daniel I.C.; Orton, Dawn
    One of the major problems in the operations of mammalian cell bioreactors is the detrimental effect of gas sparging. Since the most convenient way to oxygenate any bioreactor is by gas sparging, this adverse effect has often been one of the limiting oxygen transport problems in both laboratory and industrial mammalian cell bioreactors. When one examines the literature on the effect of gas sparging on the death of mammalian cells, a great deal of confusions has been reported. It is not clear from the published literature as to the leading cause for gas-sparged related cell death. These confusions prevent the...

  19. Study on Granular Dynamics in Vertically Vibrated Beds using Tracking Technique

    Wong, Yee Sun; Gan, Chee Hong; Wang, Chi-Hwa
    The study of granular material is of great interest to many researchers in both engineering and science communities. The importance of such a study derives from its complex rheological character and also its significant role in a wide range of industrial applications, such as coal, food, plastics, pharmaceutical, powder metallurgy and mineral processing. A number of recent reports have been focused on the physics of non-cohesive granular material submitted to vertical vibration in either experimental or theoretical approaches. Such a kind of system can be used to separate, mix and dry granular materials in industries. It exhibits different instability behaviour...

  20. Molecular computations for reactions and phase transitions: applications to protein stabilization, hydrates and catalysis

    Anderson, Brian J.; Baynes, Brian M.; Lo, Cynthia S.; Chu, Jhih-Wei; Pan, Bin; Wang, Daniel I.C.; Trout, Bernhardt L.
    In this work we have made significant contributions in three different areas of interest: therapeutic protein stabilization, thermodynamics of natural gas clathrate-hydrates, and zeolite catalysis. In all three fields, using our various computational techniques, we have been able to elucidate phenomena that are difficult or impossible to explain experimentally. More specifically, in mixed solvent systems for proteins we developed a statistical-mechanical method to model the thermodynamic effects of additives in molecular-level detail. It was the first method demonstrated to have truly predictive (no adjustable parameters) capability for real protein systems. We also describe a novel mechanism that slows protein association...

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