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228 results on '"Davis, Thomas"'

4. Consistent experimental and theoretical evidence for long-lived intermediate radicals in living free radical polymerization

Author

Feldermann, Achim, Coote, Michelle L., Stenzel, Martina H., Davis, Thomas P., and Barner-Kowollik, Christopher

Subjects
Styrene -- Chemical properties, Molecular orbitals -- Research, Polymerization -- Methods, Chemistry
Abstract

Kinetic experiments and high-level ab initio molecular orbital calculations were used to study the cumyl dithiobenzoate (CDB)-mediated reversible addition fragmentation chain-transfer (RAFT) polymerization of styrene at 30 degree Celsius. The kinetic data indicates the delayed onset of steady-state behavior.

Published
2004

6. Engineering Polymers via Understanding the Effect of Anchoring Groups for Highly Stable Liquid Metal Nanoparticles.

Author

Huang, Xumin, Xu, Tianhong, Shen, Ao, Davis, Thomas P., Qiao, Ruirui, and Tang, Shi-Yang

Abstract

Liquid metal nanoparticles (LMNPs) have recently attracted much attention as soft functional materials for various biorelated applications. Despite the fact that several reports demonstrate highly stable LMNPs in aqueous solutions or organic solvents, it is still challenging to stabilize LMNPs in biological media with complex ionic environments. LMNPs grafted with functional polymers (polymers/LMNPs) have been fabricated for maintaining their colloidal and chemical stability; however, to the best of our knowledge, no related work has been conducted to systematically investigate the effect of anchoring groups on the stability of LMNPs. Herein, various anchoring groups, including phosphonic acids, trithiolcarbonates, thiols, and carboxylic acids, are incorporated into brush polymers via reversible addition-fragmentation chain transfer (RAFT) polymerization to graft LMNPs. Both the colloidal and chemical stability of such polymer/LMNP systems are then investigated in various biological media. Moreover, the influence of multidentate ligands is also investigated by incorporating different numbers of carboxylic or phosphonic acid into the brush polymers. We discover that increasing the number of anchoring groups enhances the colloidal stability of LMNPs, while polymers bearing phosphonic acids provide the optimum chemical stability for LMNPs due to surface passivation. Thus, polymers bearing multidentate phosphonic acids are desirable to decorate LMNPs to meet complex environments for biological studies. [ABSTRACT FROM AUTHOR]

Published
2022
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18. Star polymers reduce IAPP toxicity via accelerated amyloid aggregation

Author

Pilkington, Emily H., Lai, May, Ge, Xinwei, Stanley, William J., Wang, Bo, Wang, Miaovi, Kakinen, Aleksandr, Sani, Marc-Antonie, Whittaker, Michael R., Gurov, Esteban, Ding, Feng, Quinn, John F., Davis, Thomas P., and Ke, Pu Chun

Subjects
endocrine system, QD
Abstract

Protein aggregation into amyloid fibrils is a ubiquitous phenomenon across the spectrum of neurodegenerative disorders and type 2 diabetes. A common strategy against amyloidogenesis is to minimize the populations of toxic oligomers and protofibrils by inhibiting protein aggregation with small molecules or nanoparticles. However, melanin synthesis in nature is realized by accelerated protein fibrillation to circumvent accumulation of toxic intermediates. Accordingly, we designed and demonstrated the use of star-shaped poly(2-hydroxyethyl acrylate) (PHEA) nanostructures for promoting the aggregation while ameliorating the toxicity of human islet amyloid polypeptide (IAPP), the peptide involved in glycemic control and the pathology of type 2 diabetes. The binding of PHEA elevated the beta-sheet content in IAPP aggregates while rendered a new morphology of ‘stelliform’ amyloids originating from the polymers. Atomistic molecular dynamics simulations revealed that the PHEA arms served as rod-like scaffolds for IAPP binding and subsequently accelerated IAPP aggregation by increased local peptide concentration. The tertiary structure of the star nanoparticles was found to be essential to drive the specific interactions required to impel the accelerated IAPP aggregation. This study shed new light on the structure-toxicity relationship of IAPP and points to the potential of exploiting star polymers as a new class of therapeutic agents against amyloidogenesis.

Published
2017

23. Photochromic spirooxazines functionalized with oligomers: investigation of core-oligomer interactions and photomerocyanine isomer interconversion using NMR spectroscopy and DFT

Author

Yee, Lachlan H., Hanley, Tracey, Evans, Richard A., Davis, Thomas P., and Ball, Graham E.

Subjects
Methyl groups -- Spectra, Methyl groups -- Optical properties, Nuclear magnetic resonance spectroscopy -- Usage, Oligomers -- Spectra, Oligomers -- Optical properties, Biological sciences, Chemistry
Abstract

NMR spectroscopy at temperatures between 193 and 233 K before and after in situ exposure to UV irradiation is applied to monitor photochromic spirooxazines functionalized with poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) oligomers. The interaction of the oligomer side chain and core of the molecule is significantly enhanced by the permanent attachment, especially with the PDMS side chain and the 2D NMR spectra indicated the presence of exchange between the TTC (trans-s-trans-cis) and CTC (cis-s-trans-cis) isomers even at 193 K.

Published
2010

24. Bioapplications of RAFT polymerization

Author

Boyer, Cyrille, Bulmus, Volga, Davis, Thomas P., Ladmiral, Vincent, Jingquan Liu, and Perrier, Sebastien

Subjects
Amines -- Chemical properties, Biotin -- Chemical properties, Drug delivery systems -- Research, Esters -- Chemical properties, Polymerization -- Analysis, Drugs -- Vehicles, Drugs -- Research, Chemistry
Published
2009

25. Well-defined protein-polymer conjugates via in situ RAFT polymerization

Author

Boyer, Cyrille, Bulmus, Volga, Jingquan Liu, Davis, Thomas P., Stenzel, Martina H., and Barner-Kowollik, Christopher

Subjects
Serum albumin -- Analysis, Chemical synthesis -- Analysis, Polymerization -- Analysis, Chemistry
Abstract

A water-soluble reversible addition-fragmentation chain transfer polymerization (RAFT) agent is synthesized and used for in situ preparation of bovine serum albumin (BSA)-polymer conjugates in completely aqueous solutions. It is shown that the high retention of protein bioactivity and the absence of detectable free polymer traces in in situ-generated conjugates are vital for the RAFT method to generate well-defined protein-polymer conjugates without the requirement of postpolymerization purification steps.

Published
2007

45. Synthesis, multilayer film assembly, and capsule formation of macromolecularly engineered acrylic acid and styrene sulfonate block copolymers

Author

Yap, Heng Pho, Hao, Xiaojuan, Tjipto, Elvira, Gudipati, Chakravarthy, Quinn, John, Davis, Thomas, Barner-Kowollik, Christopher, Stenzel, Martina, Caruso, Frank, Yap, Heng Pho, Hao, Xiaojuan, Tjipto, Elvira, Gudipati, Chakravarthy, Quinn, John, Davis, Thomas, Barner-Kowollik, Christopher, Stenzel, Martina, and Caruso, Frank

Abstract

We report the use of copolymers synthesized with specific block ratios of weakly and strongly charged groups for the preparation of stable, pH-responsive multilayers. In this study, we utilized reversible addition-fragmentation chain transfer (RAFT) polymerization in the synthesis of novel pH-sensitive copolymers comprising block domains of acrylic acid (AA) and styrene sulfonate (SS) groups. The PAAX-b-SSy copolymers, containing 37%, 55%, and 73% of AA groups by mass (denoted as PAA37-b-SS63, PAA55-b-SS45, and PAA73-b-SS27, respectively), were utilized to perform stepwise multilayer assembly in alternation with poly(allylamine hydrochloride), PAH. The ratio of AA to SS groups, and the effect of the pH of both anionic and cationic adsorption solutions, on multilayer properties, were investigated using ellipsometry and atomic force microscopy. The presence of SS moieties in the PAA X-b-SSy copolymers, regardless of the precise composition, lead to films with a relatively consistent thickness. Exposure of these multilayers to acidic conditions postassembly revealed that these multilayers do not exhibit the characteristic large swelling that occurs with PAA/PAH films. The film stability was attributed to the presence of strongly charged SS groups. PAAx-b-SSy/PAH films were also formed on particle substrates under various adsorption conditions. Microelectrophoresis measurements revealed that the surface charge and isoelectric point of these core-shell particles are dependent on assembly pH and the proportion of AA groups in PAAx-b-SSy. These core-shell particles can be used as precursors to hollow capsules that incorporate weak polyelectrolyte functionality. The role of AA groups in determining the growth profile of these capsules was also examined. The multilayer films prepared may find applications in areas where pH-responsive films are required but large film swelling is unfavorable. © 2008 American Chemical Society.

Published
2008

47. Enhanced ionization in electrospray ionization mass spectrometry of labile end-group-containing polystyrenes using silver(I) tetrafluoroborate as doping salt

Author

Gruendling, Till, Hart-Smith, Gene, Davis, Thomas, Stenzel, Martina, Barner-Kowollik, Christopher, Gruendling, Till, Hart-Smith, Gene, Davis, Thomas, Stenzel, Martina, and Barner-Kowollik, Christopher

Abstract

The use of silver tetrafluoroborate as a doping salt to achieve efficient and soft desorption/ionization of labile end-group-carrying polystyrene during electrospray ionization is demonstrated. Polystyrene carrying a dithioester end group prepared via reversible addition fragmentation chain transfer (RAFT) chemistry (using the RAFT agent cumyl phenyldithioacetate) as well as a commercial polymer standard prepared by anionic polymerization serve as model compounds. By employing silver tetrafluoroborate as ionization agent, an increase in ion count of more than one order of magnitude was achieved compared to ionization with sodium iodide. Little loss of the end group occurred via elimination of the dithioacid to yield vinyl-terminated polymer. A possible mechanism is given for catalysis of the cleavage reaction in the presence of silver salts. Side-product formation due to thermal or collision induced loss of the dithioester was kept at a minimum under optimized source conditions. Thus, we introduce a novel soft ionization protocol for polystyrenes, which are often difficult to ionize. © 2008 American Chemical Society.

Published
2008

48. Reversible addition fragmentation chain transfer (RAFT) and hetero-Diels-Alder chemistry as a convenient conjugation tool for access to complex macromolecular designs

Author

Inglis, Andrew, Sinnwell, Sebastian, Davis, Thomas, Barner-Kowollik, Christopher, Stenzel, Martina, Inglis, Andrew, Sinnwell, Sebastian, Davis, Thomas, Barner-Kowollik, Christopher, and Stenzel, Martina

Abstract

The combination of RAFT chemistry and the hetero-Diels-Alder (HDA) cycloaddition was successfully utilized in the synthesis of poly(styrene) (PS) star polymers with up to 4 arms. This variant of the "coupling onto" method of star polymer synthesis was investigated for two different RAFT end groups (diethoxyphosphoryldithioformate and pyridin-2-yldithioformate) and coupling agents bearing 2, 3, or 4 diene functional groups. When a diethoxyphosphoryldithioformate terminated polymer was reacted with the 2-, 3-, and 4-fold functionalized coupling agents, the yields of 2-arm star, 3-arm star, and 4-arm star polymers were 81%, 77%, and 65%, respectively, and when a pyridin-2-yldithioformate terminated polymer was reacted with the same coupling agents, the yields of 2-arm star, 3-arm star and 4-arm star polymers were 91%, 86% and 82% respectively. The HDA coupling reaction was monitored via UV/vis spectroscopy from the perspective of the RAFT end group as well as by 1H NMR spectroscopy from the perspective of the diene functionality. The results of these investigations indicated that the phosphoryldiethoxydithioformate terminated polymer achieves 92% conversion within a 24 h time frame and the pyridin-2-yldithioformate terminated polymer achieves 96% conversion in 10 h. The 4-arm star polymers were also subjected to high-temperature environments, and GPC measurements indicated that complete cleavage of all 4 arms from the core was achieved in 24 h at 160 °C. © 2008 American Chemical Society.

Published
2008

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