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  1. Photothermally induced optical property changes of poly(N-isopropylacrylamide) microgel-based etalons [Download]

    Title: Photothermally induced optical property changes of poly(N-isopropylacrylamide) microgel-based etalons
    Creator: Islam, Molla R.
    Description: Poly(N-isopropylacrylamide) microgel-based optical devices were designed such that they can be stimulated to change their optical properties in response to light produced by a light-emitting diode (LED). The devices were fabricated by sandwiching the synthesized microgels between two Cr/Au layers all supported on a glass coverslip with gold nanoparticles (AuNPs) deposited. Here, we found that these devices can be stimulated to change their optical properties when exposed to green LED light, which excites the AuNPs and increases the local temperature, causing the thermoresponsive microgels to decrease in diameter, resulting in a change in the devices’ optical properties. We also found that the sensitivity of the devices to light was more pronounced as the environmental temperature approached the lower critical solution temperature (LCST) for the microgels, although the sensitivity of the devices to light exposure dropped off dramatically as the environmental temperature was increased above the LCST. This was a direct result of the microgels already being in their collapsed state and therefore unable to decrease in diameter any further due to light exposure. Finally, we found that the sensitivity of the devices to light exposure increased with increasing number of AuNP layers in the devices. We anticipate that these devices could be used for drug delivery applications; by using light to stimulate microgel collapse, the microgel-based devices can be stimulated to release small molecules on demand.
    Subjects: Poly(N-isopropylacrylamide) Microgels, Layer-By-Layer Assembly, Photothermal Effect, Light-Responsive Etalons, Responsive Polymers, Gold Nanoparticles
    Date Created: 2015
  2. Poly (N-isopropylacrylamide) microgel-based etalons for optical sensing [Download]

    Title: Poly (N-isopropylacrylamide) microgel-based etalons for optical sensing
    Creator: Hu, Liang
    Description: Poly (N-isopropylacrylamide) (pNIPAm) is one of the most completely studied “smart” polymers due to its unique reversible thermoresponsivity. That is, when pNIPAm in water is heated > ~31°C, it transits from a random coil to a globule conformation; this transition is reversed when T < ~31°C. This conformational change is accompanied by water exchange process. When pNIPAm undergoes the coil to globule transition, water is expelled, while water is “sorbed” when the polymer undergoes the opposite process.
    Subjects: Etalons, Sensors and Biosensors, Photonic Materials, Stimuli-Responsive Polymers, Poly (N-isopropylacrylamide)-Based Microgels
    Date Created: 2012
  3. Poly (N-isopropylacrylamide) microgel-based optical devices for sensing and biosensing [Download]

    Title: Poly (N-isopropylacrylamide) microgel-based optical devices for sensing and biosensing
    Creator: Islam, Molla R.
    Description: Responsive polymer-based materials have found numerous applications due to their ease of synthesis and the variety of stimuli that they can be made responsive to. In this review, we highlight the group’s efforts utilizing thermoresponsive poly (N-isopropylacrylamide) (pNIPAm) microgel-based optical devices for various sensing and biosensing applications.
    Subjects: Stimuli-Responsive Polymers, Poly (N-isopropylacrylamide)-Based Microgels, Sensors and Biosensors, Photonic Materials, Etalons
    Date Created: 2014
  4. Light switchable optical materials from azobenzene crosslinked poly(N-isopropylacrylamide)-based microgels [Download]

    Title: Light switchable optical materials from azobenzene crosslinked poly(N-isopropylacrylamide)-based microgels
    Creator: Zhang, Qiang M.
    Description: 4,40 -Di(acrylamido)-azobenzene was used as a crosslinker in poly(Nisopropylacrylamide)-based microgels. The microgels were subsequently used to fabricate microgel-based optical materials (etalons), which exhibited optical properties that were switchable upon exposure to UV irradiation. We also show that the extent of the response depended on the UV exposure time. These materials could find applications for controlled/triggered drug delivery, as well as in various optical applications.
    Subjects: Microarray, Switchable, Crosslinked Liquid-Crystalline Polymers, Molding
    Date Created: 2014
  5. Poly (N-isopropylacrylamide)-co-(acrylic acid) microgel/ag nanoparticle hybrids for the colorimetric sensing of H2O2 [Download]

    Title: Poly (N-isopropylacrylamide)-co-(acrylic acid) microgel/ag nanoparticle hybrids for the colorimetric sensing of H2O2
    Creator: Han, De-Man
    Description: Poly (N-isopropylacrylamide)-co-(acrylic acid) (pNIPAm-co-AAc) microgels composed of Ag nanoparticles (Ag NPs) have been synthesized and employed for the colorimetric sensing of H2O2. Each pNIPAmco-AAc microgel, which exhibited a diameter of ∼800 nm, contained multiple Ag NPs (diameter of ∼5 nm), and solutions of these hybrid materials showed a UV-vis absorption band at ∼400 nm. This is due to the excitation of the Ag NP surface plasmon. We go on to show that the intensity of this absorption band is dependent on the concentration of H2O2 in solution. Specifically, in the presence of H2O2 the magnitude of the absorption peak dramatically decreases in a linear fashion over the concentration range of 0.30 to 3.00 μM H2O2 (r 2 = 0.9918). We go on to show that the response is selective for H2O2 and can still function in complex mixtures, e.g., we showed that the response is still robust in milk samples. While Ag NPs themselves can exhibit similar responses, this system has many benefits including sample processing and long term stability – i.e., Ag NPs are destabilized in solutions of a certain pH, and aggregate readily. Our microgel/Ag NP hybrids have been shown to be extremely stable and are easily purified prior to use by simple centrifugation/washing protocols. This system is simple and straightforward to use, is low cost, and can be used in complex media, which makes it practical for analyzing complex biological and environmental samples.
    Subjects: Particles, Film, Electrode, Plasmon Resonance, Hydrogen-Peroxide Sensor, Probe, Silver Nanoparticles
    Date Created: 2015
  6. CO2-switchable poly (N-isopropylacrylamide) microgel-based etalons [Download]

    Title: CO2-switchable poly (N-isopropylacrylamide) microgel-based etalons
    Creator: Zhang, Qiang M.
    Description: A series of pyridine-functionalized poly (N-isopropylacrylamide)- based microgels were synthesized. Subsequently, a structured photonic device was fabricated by sandwiching the microgels between two thin Au layers, and their response to CO2 investigated. We show that devices show an optical response to CO2, which is reversible over many cycles.
    Subjects: Separation, Devices, Shape, pH, Size, Sheets, Release
    Date Created: 2015
  7. Stimuli-responsive polymers and their applications [Download]

    Title: Stimuli-responsive polymers and their applications
    Creator: Wei, Menglian
    Description: Responsive polymer-based materials are capable of altering their chemical and/or physical properties upon exposure to external stimuli. These materials have been intensively studied over the years for a diverse range of applications, e.g., for on-demand drug delivery, tissue generation/repair, biosensing, smart coatings, and artificial muscles. Here, we review recent advances in the areas of sensing and biosensing, drug delivery, and actuators. Specific examples are given in each of these areas, and we highlight our group's work on poly(N-isopropylacrylamide)-based microgels and assemblies.
    Subjects:
    Date Created: 2017
  8. Energetics of intermolecular hydrogen bonds in a hydrophobic protein cavity [Download]

    Title: Energetics of intermolecular hydrogen bonds in a hydrophobic protein cavity
    Creator: Liu, Lan
    Description: This work explores the energetics of intermolecular H-bonds inside a hydrophobic protein cavity. Kinetic measurements were performed on the gaseous deprotonated ions (at the −7 charge state) of complexes of bovine β-lactoglobulin (Lg) and three monohydroxylated analogs of palmitic acid (PA): 3-hydroxypalmitic acid (3-OHPA), 7-hydroxypalmitic acid (7-OHPA), and 16-hydroxypalmitic acid (16-OHPA). From the increase in the activation energy for the dissociation of the (Lg + X-OHPA)7– ions, compared with that of the (Lg + PA)7– ion, it is concluded that the –OH groups of the X-OHPA ligands participate in strong (5 – 11 kcal mol–1) intermolecular H-bonds in the hydrophobic cavity of Lg. The results of molecular dynamics (MD) simulations suggest that the –OH groups of 3-OHPA and 16-OHPA act as H-bond donors and interact with backbone carbonyl oxygens, whereas the –OH group of 7-OHPA acts as both H-bond donor and acceptor with nearby side chains. The capacity for intermolecular H-bonds within the Lg cavity, as suggested by the gas-phase measurements, does not necessarily lead to enhanced binding in aqueous solution. The association constant (Ka) measured for 7-OHPA [(2.3 ± 0.2) × 105 M–1] is similar to the value for the PA [(3.8 ± 0.1) × 105 M–1]; Ka for 3-OHPA [(1.1 ± 0.3) × 106 M–1] is approximately three-times larger, whereas Ka for 16-OHPA [(2.3 ± 0.2) × 104 M–1] is an order of magnitude smaller. Taken together, the results of this study suggest that the energetic penalty to desolvating the ligand –OH groups, which is necessary for complex formation, is similar in magnitude to the energetic contribution of the intermolecular H-bonds.
    Subjects: Hydrogen bonds, Kinetics energetics, Hydrophobic, Protein–ligand complexes
    Date Created: 2014
  9. Structural basis for antibody recognition in the receptor-binding domains of toxins A and B from Clostridium difficile [Download]

    Title: Structural basis for antibody recognition in the receptor-binding domains of toxins A and B from Clostridium difficile
    Creator: Murase, Tomohiko
    Description: Clostridium difficile infection is a serious and highly prevalent nosocomial disease in which the two large, Rho-glucosylating toxins TcdA and TcdB are the main virulence factors. We report for the first time crystal structures revealing how neutralizing and non-neutralizing single-domain antibodies (sdAbs) recognize the receptor-binding domains (RBDs) of TcdA and TcdB. Surprisingly, the complexes formed by two neutralizing antibodies recognizing TcdA do not show direct interference with the previously identified carbohydrate-binding sites, suggesting that neutralization of toxin activity may be mediated by mechanisms distinct from steric blockage of receptor binding. A camelid sdAb complex also reveals the molecular structure of the TcdB RBD for the first time, facilitating the crystallization of a strongly negatively charged protein fragment that has resisted previous attempts at crystallization and structure determination. Electrospray ionization mass spectrometry measurements confirm the stoichiometries of sdAbs observed in the crystal structures. These studies indicate how key epitopes in the RBDs from TcdA and TcdB are recognized by sdAbs, providing molecular insights into toxin structure and function and providing for the first time a basis for the design of highly specific toxin-specific therapeutic and diagnostic agents.
    Subjects: Mass Spectrometry (MS), Protein-Protein Interactions, X-ray Crystallography, Antibodies, Bacterial Toxins
    Date Created: 2014
  10. Exploiting bacterial glycosylation machineries for the synthesis of a Lewis antigen-containing glycoprotein [Download]

    Title: Exploiting bacterial glycosylation machineries for the synthesis of a Lewis antigen-containing glycoprotein
    Creator: Hug, Isabelle
    Description: Glycoproteins constitute a class of compounds of increasing importance for pharmaceutical applications. The manipulation of bacterial protein glycosylation systems from Gram-negative bacteria for the synthesis of recombinant glycoproteins is a promising alternative to the current production methods. Proteins carrying Lewis antigens have been shown to have potential applications for the treatment of diverse autoimmune diseases. In this work, we developed a mixed approach consisting of in vivo and in vitro steps for the synthesis of glycoproteins containing the Lewis x antigen. Using glycosyltransferases from Haemophilus influenzae, we engineered Escherichia coli to assemble a tetrasaccharide on the lipid carrier undecaprenylphosphate. This glycan was transferred in vivo from the lipid to a carrier protein by the Campylobacter jejuni oligosaccharyltransferase PglB. The glycoprotein was then fucosylated in vitro by a truncated fucosyltransferase from Helicobacter pylori. Diverse mass spectrometry techniques were used to confirm the structure of the glycan. The strategy presented here could be adapted in the future for the synthesis of diverse glycoproteins. Our experiments demonstrate that bacterial enzymes can be exploited for the production of glycoproteins carrying glycans present in human cells for potential therapeutic applications.
    Subjects: Bacterial Glycoproteins, Glycoengineering, Glycoprotein, Glycoconjugate, Fucosyltransferase, Helicobacter pylori, Glycosyltransferases, Glycosylation, Oligosaccharyltansferase
    Date Created: 2011