R-3 Repository :: Browsing by Author "Martí, Angel A."

Browsing by Author "Martí, Angel A."

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Adverse Effect of PTFE Stir Bars on the Covalent Functionalization of Carbon and Boron Nitride Nanotubes Using Billups–Birch Reduction Conditions
(American Chemical Society, 2019) de los Reyes, Carlos A.; Smith McWilliams, Ashleigh D.; Hernández, Katharyn; Walz-Mitra, Kendahl L.; Ergülen, Selin; Pasquali, Matteo; Martí, Angel A.
The functionalization of nanomaterials has long been studied as a way to manipulate and tailor their properties to a desired application. Of the various methods available, the Billups–Birch reduction has become an important and widely used reaction for the functionalization of carbon nanotubes (CNTs) and, more recently, boron nitride nanotubes. However, an easily overlooked source of error when using highly reductive conditions is the utilization of poly(tetrafluoroethylene) (PTFE) stir bars. In this work, we studied the effects of using this kind of stir bar versus using a glass stir bar by measuring the resulting degree of functionalization with 1-bromododecane. Thermogravimetric analysis studies alone could deceive one into thinking that reactions stirred with PTFE stir bars are highly functionalized; however, the utilization of spectroscopic techniques, such as Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, tells otherwise. Furthermore, in the case of CNTs, we determined that using Raman spectroscopy alone for analysis is not sufficient to demonstrate successful chemical modification.
Bifunctional Luminomagnetic Rare-Earth Nanorods for High-Contrast Bioimaging Nanoprobes
(Springer Nature, 2016) Gupta, Bipin Kumar; Singh, Satbir; Kumar, Pawan; Lee, Yean; Kedawat, Garima; Narayanan, Tharangattu N.; Vithayathil, Sajna Antony; Ge, Liehui; Zhan, Xiaobo; Gupta, Sarika; Martí, Angel A.; Vajtai, Robert; Ajayan, Pulickel M.; Kaipparettu, Benny Abraham
Nanoparticles exhibiting both magnetic and luminescent properties are need of the hour for many biological applications. A single compound exhibiting this combination of properties is uncommon. Herein, we report a strategy to synthesize a bifunctional luminomagnetic Gd2−xEuxO3 (x = 0.05 to 0.5) nanorod, with a diameter of ~20 nm and length in ~0.6 μm, using hydrothermal method. Gd2O3:Eu3+ nanorods have been characterized by studying its structural, optical and magnetic properties. The advantage offered by photoluminescent imaging with Gd2O3:Eu3+ nanorods is that this ultrafine nanorod material exhibits hypersensitive intense red emission (610 nm) with good brightness (quantum yield more than 90%), which is an essential parameter for high-contrast bioimaging, especially for overcoming auto fluorescent background. The utility of luminomagnetic nanorods for biological applications in high-contrast cell imaging capability and cell toxicity to image two human breast cancer cell lines T47D and MDA-MB-231 are also evaluated. Additionally, to understand the significance of shape of the nanostructure, the photoluminescence and paramagnetic characteristic of Gd2O3:Eu3+ nanorods were compared with the spherical nanoparticles of Gd2O3:Eu3+.
Carbon Based Nanomaterials for Electrochemical Energy Storage Applications
(2015-04-22) Li, Lei; Tour, James M.; Ajayan, Pulickel; Martí, Angel A.
Ever-growing energy needs, limited energy resources, and the need to decrease soaring greenhouse gas emissions have brought about an urgent demand on the pursuit of energy alternatives, includ¬ing both renewable energy sources and sustainable storage technologies. Electrochemical capacitors (ECs) and reversible lithium ion batteries (LIBs) are two promising energy storage technologies that are well positioned to satisfy this need in a green energy future. However, their large-scale deployment has been significantly hindered by several major technological barriers, such as high cost, intrinsically poor safety characteristic, limited life, and low energy density and/or power density. One promising solution is to develop advanced electrodes materials for these devices. In this thesis, various nanomaterials and nanostructures have been developed to improve the electrochemical performance of ECs and LIBs. My thesis begins with the introduction of energy storage systems of ECs and LIBs in Chapter 1. Chapter 2 to 4 discuss the synthesis of nitrogen-doped carbonized cotton, brush-like structured nanocomposites of polyaniline nanorods-graphene nanoribbons, laser induced graphene-MnO2, and laser induced graphene-polyaniline and their applications in ECs. All of them demonstrated excellent performance in energy storage, showing high potential applications as electrode materials in ECs. Chapter 5 to 8 discuss a graphene wrapping strategy designed to synthesize graphene-metal oxide/sulfide-graphene nanoribbons, including graphene-MnO2-GNRs, graphene-NiO-rGONRs, graphene-Fe3O4-GNRs, and graphene-FeS-GNRs. This sandwich structure mitigated the pulverization of these anode materials from their conversion reactions during extended cycling, leading to a large improvement in the cycling stability of anodes in LIBs. To address the volume change of SnO2-based anode materials, a facile and cost-effective approach was developed to prepare a thin layer SnO2 on reduced graphene oxide nanoribbons. Chapter 9 discusses how this nanocomposite demonstrated excellent cycling stability with high capacity. For LIBs cathode materials, a hierarchical polyaniline matrix was designed to reduce the dissolution of the intermediate lithium polysulfide into the electrolyte as shown in Chapter 10. This material showed great improvement in cycling stability with high capacity.
Deconvoluting binding sites in amyloid nanofibrils using time-resolved spectroscopy
(Royal Society of Chemisty, 2023) Jiang, Bo; Umezaki, Utana; Augustine, Andrea; Jayasinghe-Arachchige, Vindi M.; Serafim, Leonardo F.; He, Zhi Mei Sonia; Wyss, Kevin M.; Prabhakar, Rajeev; Martí, Angel A.
Steady-state fluorescence spectroscopy has a central role not only for sensing applications, but also in biophysics and imaging. Light switching probes, such as ruthenium dipyridophenazine complexes, have been used to study complex systems such as DNA, RNA, and amyloid fibrils. Nonetheless, steady-state spectroscopy is limited in the kind of information it can provide. In this paper, we use time-resolved spectroscopy for studying binding interactions between amyloid-β fibrillar structures and photoluminescent ligands. Using time-resolved spectroscopy, we demonstrate that ruthenium complexes with a pyrazino phenanthroline derivative can bind to two distinct binding sites on the surface of fibrillar amyloid-β, in contrast with previous studies using steady-state photoluminescence spectroscopy, which only identified one binding site for similar compounds. The second elusive binding site is revealed when deconvoluting the signals from the time-resolved decay traces, allowing the determination of dissociation constants of 3 and 2.2 μM. Molecular dynamic simulations agree with two binding sites on the surface of amyloid-β fibrils. Time-resolved spectroscopy was also used to monitor the aggregation of amyloid-β in real-time. In addition, we show that common polypyridine complexes can bind to amyloid-β also at two different binding sites. Information on how molecules bind to amyloid proteins is important to understand their toxicity and to design potential drugs that bind and quench their deleterious effects. The additional information contained in time-resolved spectroscopy provides a powerful tool not only for studying excited state dynamics but also for sensing and revealing important information about the system including hidden binding sites.
Exploring the Photophysical Properties of UiO-67 MOF Doped with Rhenium Carbonyl Complexes
(Elsevier, 2022) Ling, Kexin; Ogle, Meredith M.; Flores, Erick; Godoy, Fernando; Martí, Angel A.
Directly coordinating transition metal catalysts to the linkers of stable metal organic frameworks (MOFs) is a sleek solution to increasing the longevity of the catalyst. Photoluminescence metal complexes incorporated in MOFs have risen in interest lately. Particularly, Re(bpydc)(CO)3Cl (bpydc = 2,2’-bipyridine-5,5’-dicarboxylic acid) doped zirconium-based MOFs (Re-UiO-67) and their use in the photocatalytic reduction of CO2 have attracted considerable attention. Nonetheless, the photophysical characteristics of Re-UiO-67 as a function of loading have not been well explored. Here we analyzed the structural and compositional properties of Re-UiO-67 and showed that the photoluminescence properties of rhenium doped MOFs, including emission intensity, maximum, and lifetime, can be tuned by changing the rhenium loading. The photoluminescence of the film made of Re-UiO-67 exposed to different vapors also exhibited vapoluminescence, luminescence vapochromism, and vapotemporism. Understanding of photophysical properties of the Re-doped MOFs material could provide guidance for further photocatalytic, solar energy conversion and sensing applications.
Fluorinated h-BN as a magnetic semiconductor
(American Association for the Advancement of Science, 2017) Radhakrishnan, Sruthi; Das, Deya; Samanta, Atanu; de los Reyes, Carlos A.; Deng, Liangzi; Alemany, Lawrence B.; Weldeghiorghis, Thomas K.; Khabashesku, Valery N.; Kochat, Vidya; Jin, Zehua; Sudeep, Parambath M.; Martí, Angel A.; Chu, Ching-Wu; Roy, Ajit; Tiwary, Chandra Sekhar; Singh, Abhishek K.; Ajayan, Pulickel M.
We report the fluorination of electrically insulating hexagonal boron nitride (h-BN) and the subsequent modification of its electronic band structure to a wide bandgap semiconductor via introduction of defect levels. The electrophilic nature of fluorine causes changes in the charge distribution around neighboring nitrogen atoms in h-BN, leading to room temperature weak ferromagnetism. The observations are further supported by theoretical calculations considering various possible configurations of fluorinated h-BN structure and their energy states. This unconventional magnetic semiconductor material could spur studies of stable two-dimensional magnetic semiconductors. Although the high thermal and chemical stability of h-BN have found a variety of uses, this chemical functionalization approach expands its functionality to electronic and magnetic devices.
High-Throughput Discovery of Input Stimuli of Bacterial Two-Component Systems
(2021-07-22) Brink, Kathryn Renee; Tabor, Jeffrey J.; Martí, Angel A.
Two-component systems (TCSs) are the largest class of biological signal transduction pathways and an important class of bacterial sensors. In their native contexts, TCSs enable bacteria to sense and respond to changes in their environment. TCSs are also a major source of novel biosensors for medical, environmental, and industrial applications. In the first portion of this work, we use TCS engineering and chemical input screens to characterize TCSs of unknown function from Shewanella oneidensis. Through these screens, we discover a pH-responsive TCS, which we apply to detect acidification of intestinal tissues in a mouse model of inflammatory bowel disease. In the second portion of this work, we develop a high-throughput screening approach for characterizing peptide-TCS interactions. We screen PhoPQ, a virulence-regulating TCS from Salmonella Typhimurium, against 117 human antimicrobial peptides (AMPs). We discover 13 novel activators of PhoPQ comprising diverse sequences, structures, and biological functions and identify subdomains and peptide biophysical features responsible for PhoPQ activation. Finally, we find that PhoPQ homologs exhibit distinct AMP response profiles, suggesting a role for evolutionary adaptation in AMP sensing. The engineering approaches developed here enable high-throughput discovery and characterization of TCS inputs, which could provide important insights into bacterial stimulus response and reveal novel biosensors with applications across a wide range of sectors.
Luminogenic iridium azide complexes
(Royal Society of Chemistry, 2015) Ohata, Jun; Vohidov, Farrukh; Aliyan, Amirhossein; Huang, Kewei; Martí, Angel A.; Ball, Zachary T.
The synthesis and characterization of luminogenic, bioorthogonal iridium probes is described. These probes exhibit long photoluminescence lifetimes amenable to time-resolved applications. A simple, modular synthesis via 5-azidophenanthroline allows structural variation and allows optimization of cell labeling.
Photoactive metal complexes for studying amyloid-β aggregates
(2017-08-11) Aliyan, Amirhossein; Martí, Angel A.
Amyloid-β is a short peptide produced in the brain, which self-assembles into large aggregates. This process is known to be involved in the development of Alzheimer’s disease. Because of this link, there is a significant interest in developing probes that are capable of sensing and reporting on this structural conversion. Previous work in our lab by Dr. Nate Cook showed that [Ru(bpy)2(dppz)]2+ exhibits a photoluminescence light-switching response for the formation of Aβ fibrils. This thesis focuses on studying of the interaction of a rhenium dipyridophenazine complex, [Re(CO)3(dppz)(Py)]+, with Aβ aggregates. Chapter 1 is an overview of the probes that have been developed for in vitro, in vivo, and Ex vivo detection of Amyloid monomers, oligomers, and fibrils. Chapter 2 details the light-switching of [Re(CO)3(dppz)(Py)]+ in the presence of Aβ fibrils, and more importantly, explains the unique photo-induced oxidation capability of this complex, which is coupled with an unexpected light-switching enhancement (secondary light-switching effect). The application of this secondary light-switching effect is explained by utilizing it in detecting Aβ aggregation with enhanced sensitivity. Chapter 3 focuses on the characterization of the binding between the [Re(CO)3(dppz)(Py)]+ and Aβ fibrils, as well as identifying the oxidation site. Due to the fact that the oxidation is a chemical modification on the peptide, it is used as a chemical footprint of the probe binding site on the Aβ fibril. This is of significant importance as it provides empirical support for the proposed simulated binding site. Binding and Job-plot assays along with several experiments were performed to provide further empirical information about the interaction, which were shown to be consistent with the proposed binding site. Chapter 4 describes the development of a photoluminescence anisotropy method using a ruthenium always-on probe, [Ru(bpy)2(dpqp)]2+, to track the formation of toxic oligomeric species, which are challenging to detect using other techniques. Optimization were performed to find proper experimental conditions, and the probe was shown to track the formation of fibril, oligomer, and low molecular-weight aggregates in real-time. The assay was analyzed with gel electrophoresis to further support the capability of this probe. MTT assaying of N2a cell line showed that the detected species were indeed toxic.
Recent advances and perspective on boron nitride nanotubes: From synthesis to applications
(Springer Nature, 2022) Jakubinek, Michael B.; Kim, Keun Su; Kim, Myung Jong; Martí, Angel A.; Pasquali, Matteo; The Smalley-Curl Institute; The Carbon Hub
Boron nitride nanotubes (BNNTs) are emerging nanomaterials with analogous structures and similarly impressive mechanical properties to carbon nanotubes (CNTs), but unique chemistry and complimentary multifunctional properties, including higher thermal stability, electrical insulation, optical transparency, neutron absorption capability, and piezoelectricity. Over the past decade, advances in synthesis have made BNNTs more broadly accessible to the nanomaterials and other research communities, removing a major barrier to their utilization and research. Therefore, the field is poised to grow rapidly and see the emergence of BNNT applications ranging from electronics to aerospace materials. A key challenge, that is being gradually overcome, is the development of manufacturing processes to make “neat” BNNT materials. This overview highlights the history and current status of the field, providing both an introduction to this Focus Issue—BNNTs: Synthesis to Applications—as well as a perspective on advances, challenges, and opportunities for this emerging material.
Synthesis and Photostability of Unimolecular Submersible Nanomachines: Toward Single-Molecule Tracking in Solution
(American Chemical Society, 2016) García-López, Víctor; Jeffet, Jonathan; Kuwahara, Shunsuke; Martí, Angel A.; Ebenstein, Yuval; Tour, James M.; NanoCarbon Center
The synthesis and photophysical properties of a series of photostable unimolecular submersible nanomachines (USNs) are reported as a first step toward the analysis of their trajectories in solution. The USNs have a light-driven rotatory motor for propulsion in solution and photostable cy5-COT fluorophores for their tracking. These cy5-COT fluorophores are found to provide an almost 2-fold increase in photostability compared to the previous USN versions and do not affect the rotation of the motor.
Unimolecular Submersible Nanomachines. Synthesis, Actuation, and Monitoring
(America Chemical Society, 2015) García-López, Víctor; Chiang, Pinn-Tsong; Chen, Fang; Ruan, Gedeng; Martí, Angel A.; Kolomeisky, Anatoly B.; Wang, Gufeng; Tour, James M.; Center for Theoretical Biological Physics
Unimolecular submersible nanomachines (USNs) bearing light-driven motors and fluorophores are synthesized. NMR experiments demonstrate that the rotation of the motor is not quenched by the fluorophore and that the motor behaves in the same manner as the corresponding motor without attached fluorophores. No photo or thermal decomposition is observed. Through careful design of control molecules with no motor and with a slow motor, we found using single molecule fluorescence correlation spectroscopy that only the molecules with fast rotating speed (MHz range) show an enhancement in diffusion by 26% when the motor is fully activated by UV light. This suggests that the USN molecules give ?9 nm steps upon each motor actuation. A non-unidirectional rotating motor also results in a smaller, 10%, increase in diffusion. This study gives new insight into the light actuation of motorized molecules in solution.

Browsing by Author "Martí, Angel A."

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