Julio César Azcárate

2024

1. Catalytic Performance in Nitroarene Reduction of Nanocatalyst Based on Noble Metal Nanoparticles Supported on Polymer/s-Layer Protein Hybrids

   Sofia Huggias, María De Los Ángeles Serradell, Julio C. Azcárate, Mónica L. Casella, Pablo J. Peruzzo, and Patricia A. Bolla

   J. Phys. Chem. B, Apr 2024

2022

1. Magnetic Nanoparticle–Polymer Composites Loaded with Hydrophobic Sensitizers for Photodegradation of Azoic Dyes

   María Belén Rivas Aiello, Gabriel C. Lavorato, Julio C. Azcárate, Juan M. Orozco-Henao, Pedro Mendoza Zélis, Carlos J. Cobos, Mariano H. Fonticelli, Daniel O. Mártire, and Carolina Vericat

   ACS Appl. Nano Mater., May 2022

2021

1. Photothermal therapy with silver nanoplates in HeLa cells studied by \textitin situ fluorescence microscopy

   María Belén Rivas Aiello, Julio C. Azcárate, Eugenia Zelaya, Pedro David Gara, Gabriela N. Bosio, Thomas Gensch, and Daniel O. Mártire

   Biomater. Sci., May 2021

   0 citations (Crossref) [2021-05-10]

   Abs

   Low power femtosecond-pulsed NIR irradiation kills HeLa cells incubated with Ag nanoplates by both photothermal effect and optical breakdown leading to plasma formation that spreads fast through the cell. , Photothermal therapy (PTT) is a noninvasive treatment for cancer relying on the incorporation of NIR-light absorbing nanomaterials into cells, which upon illumination release heat causing thermally induced cell death. We prove that irradiation of aqueous suspensions of poly(vinylpyrrolidone)-coated silver nanoplates (PVPAgNP) or PVPAgNP in HeLa cells with red or NIR lasers causes a sizeable photothermal effect, which in cells can be visualized with the temperature sensing fluorophore Rhodamine B (RhB) using spinning disk confocal fluorescence microscopy or fluorescence lifetime imaging. Upon red-light irradiation of cells that were incubated with both, RhB and PVPAgNP at concentrations with no adverse effects on cell viability, a substantial heat release is detected. Initiation of cell death by photothermal effect is observed by positive signals of fluorescent markers for early and late apoptosis. Surprisingly, a new nanomaterial-assisted cell killing mode is operating when PVPAgNP-loaded HeLa cells are excited with moderate powers of fs-pulsed NIR light. Small roundish areas are generated with bright and fast (\textless1 ns) decaying emission, which expand fast and destroy the whole cell in seconds. This characteristic emission is assigned to efficient optical breakdown initiation around the strongly absorbing PVPAgNP leading to plasma formation that spreads fast through the cell.

2. Hydrophilization of magnetic nanoparticles with an amphiphilic polymer revisited: Roles of nanoparticle capping density and polymer structure

   Gabriel C. Lavorato, Julio C. Azcárate, Maria Belen Rivas Aiello, Juan Manuel Orozco Henao, Pedro Mendoza Zélis, Marcelo Ceolin, Elin Winkler, Mariano H. Fonticelli, and Carolina Vericat

   Applied Surface Science, Dec 2021

   Abs

   Amphiphilic comb polymers, like poly(maleic anhydride-alt-1-octadecene) (PMAO), are frequently used to transfer hydrophobic magnetic nanoparticles (NPs) into aqueous media. While it is accepted that the hydro­ philization is based on the interdigitation of the hydrocarbon chains from the polymer and the NP capping, the factors that determine the success of such process are still not fully understood. In this paper, some key aspects of the formation of water-soluble NP-PMAO assemblies from oleate-capped iron oxide NPs, not considered in previous works, are discussed thoroughly. We have found that the process is notably hindered when the chemisorbed oleates coverage decreases from 2.9 to 1.5 molecules/nm2, revealing the importance of the capping packing density in the assembly mechanism. Combined results from small-angle x-ray scattering and electron microscopy show that, for polymer concentrations ranging from 10 to 200 monomer units/nm2, the NPs are individually covered by polymer chains, although forming rather planar NP-PMAO assemblies which contain several NPs. Both the minimum polymer concentration needed for a successful hydrophilization (0.7 gPMAO/L) and the geometry of the assemblies suggest that intermolecular structures typical of comb polymers act as templates in the assembly process. Finally, we show that the magnetic properties are modulated by the polymer loading.

3. Unraveling the Radiation Damage of \textitn -Dodecanethiol Self-Assembled Monolayers on Au(100) and Au(111): A Prerequisite to Understand the Oriented Attachment of Au Nanoparticles

   Natalia D. Aagaard, Eugenia Zelaya, Mariano H. Fonticelli, and Julio C. Azcárate

   J. Phys. Chem. C, Dec 2021

   Abs

   We present a quantitative X-ray photoelectron spectroscopy study on the electron-induced degradation of selfassembled monolayers of n-dodecanethiol on Au(100) and Au(111). This study is motivated by the lack of mechanistic explanations of the oriented attachment of n-dodecanethiolateprotected nanoparticles exposed to irradiation during imaging by transmission electron microscopy. The coalescence of these nanoparticles preferentially occurs through the encounter of the (100) faces. It could be hypothesized that thiolate desorption from the Au(100) faces is faster than that on Au(111), which would overcome the steric hindrance for the encounter of the (100) metallic surfaces. Nevertheless, we found that the organic material desorbs at comparable rates and extension from both singlecrystalline surfaces, despite the fact that the most abundant damaging products are different on these surfaces. Furthermore, although RS−R′ prevails on Au(111) while RS−SR is formed on Au(100), complete moieties derived from dodecanethiolate are the main desorption products from both SAMs. In addition, we provided arguments based on the reaction mechanism to describe the crosslinking of hydrocarbon chains and to explain why sulfur-containing species desorbs at the same rate from both single-crystalline surfaces.

2020

1. Mechanistic Framework for the Formation of Different Sulfur Species by Electron Irradiation of n -Dodecanethiol Self-Assembled Monolayers on Au(111) and Au(100)

   Natalia D. Aagaard, Julio C. Azcárate, Jimena Olmos-Asar, Marcelo M. Mariscal, José Solla-Gullón, Eugenia Zelaya, and Mariano H. Fonticelli

   J. Phys. Chem. C, Dec 2020
2. HRTEM Characterization and Simulation of Ag Nanoplates

   Natalia D. Aagaard, Julio C. Azcárate, and Eugenia Zelaya

   In Microscopy and Microanalysis, Mar 2020

   Issue: S1
3. Sodium Hexametaphosphate: An Inexpensive Inorganic Polyelectrolyte “Primer” For Upconverting Nanoparticles/Mesoporous Silica Core‐Shell Synthesis

   María Fernanda Torresan, Loreiny Parra‐Florez, Cecilia Sorbello, Julio César Azcárate, Roberto Etchenique, and Alejandro Wolosiuk

   ChemistrySelect, May 2020
4. Noble metal nanoparticles-based heterogeneous bionano-catalysts supported on S-layer protein/polyurethane system

   Sofía Huggias, Patricia A. Bolla, Julio C. Azcarate, María A. Serradell, Mónica L. Casella, and Pablo J. Peruzzo

   Catalysis Today, Sep 2020

   1 citations (Crossref) [2021-01-25]

   Abs

   This work presents the synthesis of platinum and silver nanoparticles obtained on a support composed of the Slayer protein (SLP) isolated from Lactobacillus kefiri and polyurethane particles (PU). The support was obtained by adsorption of the protein on the polymer particles in aqueous dispersion. After combining the support with the platinum or silver salts and subsequently reducing with hydrogen, noble metal-based heterogeneous bio­ nanocatalysts were obtained. Platinum or silver nanoparticles with diameters dn = 4.9 nm (ds = 4.9 nm; dv/dn = 1.05) or dn = 8.0 nm (ds = 10.6 nm; dv/dn = 1.63), respectively, were observed by TEM on the surface of the protein/polymer supports. Both nanocatalysts showed excellent catalytic activity in the reduction of p-nitro­ phenol with NaBH4 at room temperature, with conversions of 100% and 97% for platinum and silver bio­ nanocatalysts, respectively. Noteworthy, both bionanocatalysts maintain their activity until 4 reuse cycles, being the platinum-based system the one showing the best performance. These results demonstrated that the developed bionanocatalysts are promising and emerging alternatives in the field of supported noble metal nanoparticlebased heterogeneous catalysts.

2019

1. Atomic Sulfur Formation Mechanism on 3-Mercaptopropanoic Acid Derivative Self-Assembled Monolayers: Understanding the C–S Bond Cleavage

   Julio C. Azcárate, Natalia D. Aagaard, Guillermo Zampieri, Eugenia Zelaya, and Mariano H. Fonticelli

   J. Phys. Chem. C, Oct 2019

   Publisher: American Chemical Society (ACS)

   Abs

   Self-assembled monolayers (SAMs) of ω-carboxylic acid thiols are very important in the surface modification of metals, especially on gold surfaces. Indeed, the 3-mercaptopropanoic acid (MPA) and its ester or amide derivatives are widely used for SAM-based sensor design. It was already shown that MPA does not suffer C–S bond scission when adsorbed on Au. On the other hand, in this work we demonstrate that its simplest derivative, methyl 3-mercapto propionate (Me-MPA), is prone to form significant amounts of atomic sulfur when adsorbed on Au. The MPA derivatives are more sensible than MPA itself to alkaline solutions, and its SAM-based sensors will rapidly degrade given atomic sulfur. In this work, we study the simplest MPA derivative Me-MPA SAMs on preferentially oriented Au(111) surfaces by XPS and electrochemical measurements. It was found that the desulfuration of Me-MPA depends on its preparation conditions (grown from ethanol or toluene solution) and on its post-treatment with alkaline solution. In order

2018

1. Photodynamic Therapy in HeLa Cells Incubated with Riboflavin and Pectin-coated Silver Nanoparticles

   María Belén Rivas Aiello, Daniel Castrogiovanni, Julieta Parisi, Julio C. Azcárate, Fernando S. García Einschlag, Thomas Gensch, Gabriela N. Bosio, and Daniel O. Mártire

   Photochemistry and Photobiology, Nov 2018

2017

1. Radiation Damage Mechanisms of Monolayer-Protected Nanoparticles via TEM Analysis

   Julio C. Azcárate, Mariano H. Fonticelli, and Eugenia Zelaya

   J. Phys. Chem. C, Nov 2017

   Abs

   In this work, it is shown that thiol-protected Au nanoparticles (AuNPs@SR) of approximately 3.4 nm size suffered unexpectedly high radiation damage under standard transmission electron microscopy (TEM) operating conditions. For metallic systems (conducting sample), it is expected that the greatest contribution to the damage comes from knock-on displacement, but radiolysis is the most probable radiation damage mechanism for organic samples. The radiation damage of the electron beam produces huge changes in AuNPs’ structure, leading to coalescence of the Au cores when their {100} surfaces are facing each other. The complete coalescence process involve thiol desoprtion, AuNPs’ reorientation, and surface diffusion of Au adatoms, which produce the oriented attachment of the Au cores. The knock-on displacement cannot explain by itself the time taken by the entire process. Through a rigorous analysis, we rationalize the results considering that because of the small size of AuNPs they have a lower electron density than the bulk material which favors radiolytic damage.

2014

1. Estudio sobre la modificación de nanopartículas metálicas para el desarrollo de sensores fluorescentes fotomodulables

   Julio César Azcárate

   Nov 2014
2. Surface Chemistry of Thiomalic Acid Adsorption on Planar Gold and Gold Nanoparticles

   Julio C. Azcárate, María Alejandra Floridia Addato, Aldo Rubert, Gastón Corthey, Germán S. Kürten Moreno, Guillermo Benítez, Eugenia Zelaya, Roberto C. Salvarezza, and Mariano H. Fonticelli

   Langmuir, Feb 2014