Kaitlin M. Bratlie

Bio: Kaitlin M. Bratlie is an academic researcher from Iowa State University. The author has contributed to research in topics: Self-healing hydrogels & Catalysis. The author has an hindex of 26, co-authored 73 publications receiving 3155 citations. Previous affiliations of Kaitlin M. Bratlie include Harvard University & Massachusetts Institute of Technology.

Platinum Nanoparticle Shape Effects on Benzene Hydrogenation Selectivity

Abstract: Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-H...Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 +/- 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and cyclohexene production are 8.3 +/- 0.2 and 12.2 +/- 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnover rates are three times higher than those obtained with single-crystal Pt surfaces.

Combinatorial hydrogel library enables identification of materials that mitigate the foreign body response in primates

Abstract: The foreign body response is an immune-mediated reaction that can lead to the failure of implanted medical devices and discomfort for the recipient. There is a critical need for biomaterials that overcome this key challenge in the development of medical devices. Here we use a combinatorial approach for covalent chemical modification to generate a large library of variants of one of the most widely used hydrogel biomaterials, alginate. We evaluated the materials in vivo and identified three triazole-containing analogs that substantially reduce foreign body reactions in both rodents and, for at least 6 months, in non-human primates. The distribution of the triazole modification creates a unique hydrogel surface that inhibits recognition by macrophages and fibrous deposition. In addition to the utility of the compounds reported here, our approach may enable the discovery of other materials that mitigate the foreign body response.

A Reactive Oxide Overlayer on Rhodium Nanoparticles during CO Oxidation and Its Size Dependence Studied by In Situ Ambient-Pressure X-ray Photoelectron Spectroscopy

Abstract: Carbon monoxide oxidation is one of the most studied heterogeneous reactions, being scientifically and industrially important, particularly for removal of CO from exhaust streams and preferential oxidation for hydrogen purification in fuel-cell applications. The precious metals Ru, Rh, Pd, Pt, and Au are most commonly used for this reaction because of their high activity and stability. Despite the wealth of experimental and theoretical data, it remains unclear what is the active surface for CO oxidation under catalytic conditions for these metals. Herein we utilize in situ synchrotron ambient pressure X-ray photoelectron spectroscopy (APXPS) to monitor the oxidation state at the surface of rhodium nanoparticles (Rh NPs) during CO oxidation and demonstrate that the active catalyst is a surface oxide, the formation of which is dependent on particle size. The amount of oxide formed and the reaction rate both increase with decreasing particle size. Many single-crystal CO oxidation studies over rhodium suggest that the reaction is structure-insensitive and that the oxide formation decreases the reaction rate. However, recent advances in synthetic techniques and in-situ experimentation have revealed that the oxidation state and stoichiometry of the surface oxide greatly affects CO oxidation rates. At low temperatures or low O2/CO ratios, CO strongly adsorbs onto the catalyst surface and inhibits O2 adsorption. At high temperatures or high O2/CO ratios, the catalyst surface becomes saturated with oxygen atoms and the reaction proceeds more rapidly. It has been demonstrated that small palladium nanoparticles are more active for CO oxidation than larger particles and single crystals, whereas the opposite is reported for platinum. For Rh NPs, no particle size effect was observed for supported rhodium catalysts, but a strong particle size dependence was observed for CO desorption, dissociation, and transient CO oxidation over electron-beam-prepared Rh NPs that were precovered with oxygen. For this investigation we have prepared small, polymerstabilized Rh NPs with a narrow size distribution and studied CO oxidation; polymer stabilized NP syntheses enable control of NP size, shape, and/or composition for reaction studies. The turnover frequency (TOF) for CO oxidation at 200 8C increases five-fold, and the apparent activation energy decreases from 27.9 kcalmol 1 to 19.0 kcalmol 1 as the particle size decreases from 11 nm to 2 nm. APXPS of 2 nm and 7 nm Rh NP films during CO oxidation at about 1 Torr provides the first in-situ measurement of the oxidation state of Rh NPs during CO oxidation and demonstrates that smaller particles are more oxidized than larger particles during reaction at 150–200 8C. A surface oxygen species is also observed during CO oxidation that is not present when heating in O2 alone, possibly indicating a unique active oxide phase on Rh NPs. This oxide phase may alter the relative bonding geometries of CO and/or oxygen on the rhodium surface, thereby lowering the activation energy for the reaction. The synthesis of monodisperse Rh NPs by polyol reduction using poly(vinylpyrrolidone) (PVP) as a capping agent and [Rh(acac)3] as a rhodium precursor [17] was extended to smaller sizes by the addition of sodium citrate. Using this approach, Rh NPs of 3.5 nm (3.6 0.5 nm), 2.5 nm (2.5 0.4 nm), and 2 nm (1.9 0.3 nm) were formed by increasing the amount of sodium citrate. Monolayer films of these particles were then prepared in a Langmuir–Blodgett (LB) trough and characterized with transmission electron microscopy (TEM) and XPS. Figure 1a–c shows TEM images of the NPs, with insets of size distribution histograms taken from 100 particles. Figure 1 f shows X-ray photoelectron spectra for the Rh 3d peak of the as-synthesized (no pretreatment) particles after LB deposition onto a silicon wafer. The ratio of oxidized rhodium to reduced rhodium clearly increases as the particle size decreases. The three samples of small Rh NP (2, 2.5, and 3.5 nm) LB films and two previously synthesized samples, 7 nm (7.1 [*] M. E. Grass, D. R. Butcher, Dr. J. Y. Park, Dr. Y. Li, Dr. H. Bluhm, Dr. K. M. Bratlie, Dr. T. Zhang, Prof. G. A. Somorjai Department of Chemistry; University of California, Berkeley Chemical and Materials Sciences Divisions Lawrence Berkeley National Laboratory; Berkeley, CA 94720 (USA) Fax: (+1) 510-643-9668 E-mail: Somorjai@berkeley.edu

Combinatorial hydrogel library enables identification of materials that mitigate the foreign body response in primates

Abstract: The foreign body response is an immune-mediated reaction that can lead to the failure of implanted medical devices and discomfort for the recipient There is a critical need for biomaterials that overcome this key challenge in the development of medical devices Here we use a combinatorial approach for covalent chemical modification to generate a large library of variants of one of the most widely used hydrogel biomaterials, alginate We evaluated the materials in vivo and identified three triazole-containing analogs that substantially reduce foreign body reactions in both rodents and, for at least 6 months, in non-human primates The distribution of the triazole modification creates a unique hydrogel surface that inhibits recognition by macrophages and fibrous deposition In addition to the utility of the compounds reported here, our approach may enable the discovery of other materials that mitigate the foreign body response

Core-Shell Hydrogel Microcapsules for Improved Islets Encapsulation

Abstract: Islets microencapsulation holds great promise to treat type 1 diabetes. Currently used alginate microcapsules often have islets protruding outside capsules, leading to inadequate immuno-protection. A novel design of microcapsules with core-shell structures using a two-fluid co-axial electro-jetting is reported. Improved encapsulation and diabetes correction is achieved in a single step by simply confining the islets in the core region of the capsules.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Abstract: Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Abstract: Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction

Abstract: Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. We synthesized Pd-Pt bimetallic nanodendrites consisting of a dense array of Pt branches on a Pd core by reducing K2PtCl4 with L-ascorbic acid in the presence of uniform Pd nanocrystal seeds in an aqueous solution. The Pt branches supported on faceted Pd nanocrystals exhibited relatively large surface areas and particularly active facets toward the oxygen reduction reaction (ORR), the rate-determining step in a proton-exchange membrane fuel cell. The Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst.

Designing hydrogels for controlled drug delivery.

Abstract: Hydrogel delivery systems can leverage therapeutically beneficial outcomes of drug delivery and have found clinical use. Hydrogels can provide spatial and temporal control over the release of various therapeutic agents, including small-molecule drugs, macromolecular drugs and cells. Owing to their tunable physical properties, controllable degradability and capability to protect labile drugs from degradation, hydrogels serve as a platform in which various physiochemical interactions with the encapsulated drugs control their release. In this Review, we cover multiscale mechanisms underlying the design of hydrogel drug delivery systems, focusing on physical and chemical properties of the hydrogel network and the hydrogel-drug interactions across the network, mesh, and molecular (or atomistic) scales. We discuss how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation. We also collect experimental release data from the literature, review clinical translation to date of these systems, and present quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.