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pt.3 (1807

Conformational Sampling by Ab Initio Molecular Dynamics Simulations Improves NMR Chemical Shift Predictions

Car–Parrinello molecular dynamics simulations were performed for <i>N</i>-methyl acetamide as a small test system for amide groups in protein backbones, and NMR chemical shifts were calculated based on the generated ensemble. If conformational sampling and explicit solvent molecules are taken into account, excellent agreement between the calculated and experimental chemical shifts is obtained. These results represent a landmark improvement over calculations based on classical molecular dynamics (MD) simulations especially for amide protons, which are predicted too high-field shifted based on the latter ensembles. We were able to show that the better results are caused by the solute–solvents interactions forming shorter hydrogen bonds as well as by the internal degrees of freedom of the solute. Inspired by these results, we propose our approach as a new tool for the validation of force fields due to its power of identifying the structural reasons for discrepancies between the experimental and calculated data

Citizenship: Annual Program Improvement And Assessment Report, 2015-2016

University of New England (UNE) College of Arts and Sciences (CAS) core curriculum assessment document

Polyglycidol-Based Prepolymers to Tune the Nanostructure of Microgels

The use of prepolymers for microgel synthesis via miniemulsification allows predefining the chemical functionality and the nanostructure of microgels. We report on tailor-made polyglycidol-based prepolymers using three protected glycidol monomers (allyl glycidyl ether, AGE; ethoxy ethyl glycidyl ether, EEGE; and <i>tert</i>-butyl glycidyl ether, tBGE). AGE with its pendant double bonds serves as site for cross-linking or functionalization, whereas the EEGE and tBGE building blocks represent precursors for hydroxyl functionalities. Following the prepolymer approach, we design statistical and block copolymers to control the nanostructure of the microgel. Cross-linking of the prepolymers is achieved in miniemulsions under UV irradiation in a thiol–ene click type reaction addressing the allyl groups with 2,2′-(ethylenedioxy)­diethanethiol. Analysis with cryo-TEM reveals that microgels derived from poly­(glycidol)-<i>block</i>-poly­(AGE) show larger hydrophobic domains than microgels derived from statistical copolymers. Additionally, the cross-linking of pH responsive tBGE/AGE prepolymers with different microstructures leads to microgels with nanostructures differing in local charge distributions

Microgel-Based Adaptive Hybrid Capsules with Tunable Shell Permeability

In the present work, we demonstrate the preparation of adaptive hybrid capsules with microgel/SiO₂ composite walls. During the first stage of the capsule synthesis process, microgel particles stabilize the oil droplets in water and become self-assembled on the oil/water interface. At the second stage, microgels are subsequently glued by the sol–gel reaction of a silica precursor-hyperbranched polyethoxysiloxane (PEOS) which occurs at the oil/water interface. Consequently, hybrid capsules consisting of silica shell with embedded microgels are obtained. Responsive microgels present in the capsule wall act as transportation channels for different encapsulated materials. The use of smart microgels allows us to design capsules with controlled size, morphology, and wall permeability able to operate in both water and organic solvents

Surfactant-Free Synthesis of Polystyrene Nanoparticles Using Oligoglycidol Macromonomers

We investigate the synthesis of functional polystyrene/oligoglycidol particles by surfactant-free emulsion polymerization. Oligoglycidol macromonomers with linear and branched oligoglycidol structure and variable oligoglycidol chain lengths were synthesized. These macromonomers were used as surfmers (surfactants and comonomers) in emulsion polymerization of styrene. Monodisperse colloidally stable polystyrene particles were obtained, decorated with oligoglycidol chains with diameters between 100 and 600 nm. The increase of the macromonomer concentration induced a decrease of the particle size and broadening of the particle size distribution. The macromonomers with branched architecture were more effective and produced monodisperse particles even at low concentrations. Due to the steric stabilization provided by the hydrophilic oligoglycidol layer on the particle surface, the emulsion of polystyrene/oligoglycidol particles obtained exhibited very good resistance against electrolytes. The chemical and enzyme catalyzed grafting polymerization of ε-caprolactone from the polystyrene/oligoglycidol particle surface was demonstrated along with formation of composite particles

Correlated Morphological Changes in the Volume Temperature Transition of Core–Shell Microgels

PVCL and PNIPMAAm core–shell components in microgel particles are shown to have different volume phase temperature transition behavior than the respective homopolymer microgel particles due to confinement effects. A combination of dynamic light scattering (DLS) data that gives access to the temperature dependence of hydrodynamic radius and modified Flory–Rehner theory in the presence of networks confinement allowed obtaining information about correlated morphological changes of components inside of core–shell microgels. The core–shell components individual temperature behavior is analyzed by modifying the Flory–Rehner transition theory in order to account for core–shell morphology and the existence of an interaction force between core and shell. Describing the dependence on temperature of the radial scale parameter, the ratio between the radius of the core and the hydrodynamic radius, we gain access to the swelling behavior of the core and shell components irrespective of the swelling behavior of the total hydrodynamic radius. Furthermore, the theoretical description of volume phase temperature transition permits the development of scenarios for the correlated changes in the core and shell radial dimensions for the two microgels with reversed morphologies. The fact that the theoretical model is appropriate for the treatment of core–shell microgels is proved <i>a posteriori</i> by obtaining a temperature dependence of the components that is in accordance with the expected physical behavior. Novel core–shell microgel systems of PVCL (poly­(<i>N</i>-vinylcaprolactam))-core/PNIPMAAm (poly­(<i>N</i>-isopropylmethacrylamide))-shell and PNIPMAAm-core/PVCL-shell, with a double volume phase temperature transition due to the thermoresponsive components, were used for this study

Diffusion of Gold Nanorods Functionalized with Thermoresponsive Polymer Brushes

Understanding the diffusion of gold nanorods (AuNRs) and their composites in dispersion is important at fundamental level and in fields as diverse as material science, nanobiotechnology to drug delivery. The translational and rotational diffusion of AuNRs decorated with thermoresponsive poly­(<i>N</i>-isopropylacrylamide) brushes having hydrophilic and hydrophobic end groups was investigated in the dilute regime by dynamic light scattering. The same series of functionalized AuNRs were studied in the isotropic concentrated dispersions by high-resolution NMR diffusometry. The dependence of translational and rotational diffusivity upon molecular weight and polymer end group were measured as a function of temperature in the region of the brush phase transition. The effective hydrodynamic radius of AuNR composites proved to be the most sensitive quantity to the temperature-induced phase transition of brushes, allowing the evaluation of the brush thickness in the swollen and collapsed states