Well-defined Metal Nanostructures as Platform for Chemical Characterization and Catalytic Applications.

Metal nanostructures with controlled sizes and shapes possess interesting optical, electronic and catalytic properties, making them suitable for a wide range of applications. The objectives of this dissertation were to 1) exploit the optical properties of the metal nanostructures to achieve selective molecular sensing using surface enhanced Raman spectroscopy (SERS) and high selectivity towards the desired product in heterogeneous catalysis, and 2) improve the stability of the metal nanostructures of controlled shape under catalytic reaction conditions. The optical properties of silver (Ag) nanostructures can be controlled by changing their shape. We have demonstrated that this effect can be employed to control the degree to which the Ag nanostructures enhance different vibrational bands of a molecule in SERS. We have shown that Ag nanocube and Ag nanosphere substrates with surface plasmon resonance peaks near 600 and 560 nm could be used to selectively detect species with 2100-2200 cm-1 and 900–1000 cm-1 Raman vibrational bands, respectively. This approach gives new insights in the design of plasmonic substrates for the selective molecular species detection. We have also demonstrated that the optical properties of copper (Cu) nanoparticles can be exploited under propylene oxidation conditions to favor the formation of the desired product, propylene oxide. We find that Cu nanocatalysts exhibit a sharp increase in selectivity to propylene oxide from ~20% to ~50% when illuminated with visible light. This increase in the selectivity is accompanied by light-induced change in the oxidation state of the surface Cu atoms from Cu-oxide (light off) to Cu metal (light on). This design principle gives new insights to control the reaction rate and product selectivity in heterogeneous catalysis. Finally, we have demonstrated a pretreatment method to improve the stability of metal nanostructures of controlled shape under catalytic reaction conditions. Ag nanocube catalysts pretreated at high temperature (400 °C) in oxygen atmosphere to remove the polymeric capping agent (polyvinylpyrrolidone) exhibit ~20% loss in activity under ethylene oxidation at 230 °C during the reaction time of 20 hours. However, we demonstrate that Ag nanocube catalysts pretreated with polysulfide solution at room temperature can exhibit stable activity for similar reaction conditions.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/100007/1/andmar_1.pd

Tuning Catalytic Activity and Selectivity in Photocatalysis on Dielectric Cuprous Oxide Particles

Dye degradation has been for more than forty years in the scientific community. All these studies have primarily focused on breaking various dyes using catalysts driven by either light or heat. Most studies started to focus on metal-oxides after the discovery of water-splitting by TiO2. Among the many catalysts used plasmonic metal nanostructures have been explored significantly in recent times due to their special property called localized surface plasmon resonances (LSPR). However, facing multiple problems of heat losses and instability, people started to focus on dielectric medium-to-high refractive indexed materials for photonic applications. Most of these dielectric materials have been studied from a physics point of view and less from chemistry. In this work, we have focused on how these materials can be used for tuning selectivity through wavelength-dependent studies by performing methylene blue (MB) dye degradation.Comment: Main draft & SI - 15 page

Canonical Wnt pathway gene expression and their clinical correlation in oral squamous cell carcinoma

Aim: The aim of this study is to explore the prognostic significance and clinicopathological correlations of the Wnt pathway genes in a cohort of surgically treated patients with oral squamous cell carcinoma (OSCC) patients. Settings and Design: A prospective genetic study on patients with OSCC was carried out during the period from July 2014 to January 2016. Informed consent from patients and institutional ethical approval for the study was obtained and the guidelines were strictly followed for collection of samples. Subjects and Methods: Clinical data and mRNA expression analysis of ten genes in the canonical Wnt pathway were evaluated and their relationships with clinical and demographic variables were studied in 58 tissue samples. Wnt-3a, β-catenin, secreted frizzled-related proteins sFRP-1, sFRP-2, sFRP-4, sFRP-5, Wnt inhibitory factor 1, dickkopf-1, c-MYC, and cyclin-D1 from cancer (n = 29) and normal (n = 29) tissue samples were investigated using quantitative reverse transcription-polymerase chain reaction. Statistical Analysis: Descriptive statistics were used to summarize the sample characteristics and clinical variables. If the data were normal, then parametric tests were used; otherwise, nonparametric alternatives were used. All the analyses were carried out using SPSS version 23.0 (IBM SPSS Inc., USA). Results: Expression of sFRP-1, sFRP-2, and sFRP-5 in control samples and expression of c-MYC and cyclin D1 in cancer samples showed statistical significance. Significant expression of Wnt3A was observed among patients who had recurrence and were deceased. Conclusion: Wnt3A, β-catenin, and cyclin D1 are recognized as key components of Wnt/β-catenin signaling. However, in this study, there was no significant expression of all the three genes in OSCC. The proto-oncogene c-MYC showed statistically significant upregulation in cancer tissue samples suggesting that the OSCC among South Indian population is primarily not mediated by the canonical Wnt signaling pathway

Structure-Property-Performance Relationships of Dielectric Nanostructures for Mie Resonance-Enhanced Dye-Sensitization

Dye-sensitized photocatalytic (DSP) approach is considered as one of the promising approaches for developing visible light- and near-infrared light-responsive photocatalysts. DSP systems are still affected by significant drawbacks, such as low light absorption efficiency. Recently, it has been demonstrated that the plasmonic metal nanostructures can be used to enhance the light absorption efficiency and the overall dye-sensitization rate of DSP systems through the plasmonic Mie resonance-enhanced dye-sensitization approach. In this contribution, we report an alternate and novel approach, dielectric Mie resonance-enhanced dye sensitization. Specifically, we demonstrate that the dielectric Mie resonances in cuprous oxide (Cu2O) spherical and cubical nanostructures can be used to enhance the dye-sensitization rate of methylene blue dye. The Cu2O nanostructures exhibiting dielectric Mie resonances exhibit up to an order of magnitude higher dye-sensitization rate as compared to Cu2O nanostructures not exhibiting dielectric Mie resonances. Our model system developed from finite-difference time-domain simulation predicts a volcano-type relationship between the dye sensitization rate and the size of Cu2O nanostructures. The predicted structure-property-performance relationship is experimentally verified and the optimal size ranges of Cu2O nanospheres and nanocubes are identified. Although we demonstrate the dielectric Mie resonance-enhanced dye-sensitization approach using Cu2O nanostructures, the proposed approach can be used to design a wide range of DSP systems, including CeO2, {\alpha}-Fe2O3, and TiO2 nanostructures-based DSP systems

Structure-Property-Performance Relationships of Cuprous Oxide Nanostructures for Dielectric Mie Resonance-Enhanced Photocatalysis

Nanostructured metal oxides, such as Cu2O, CeO2, {\alpha}-Fe2O3, and TiO2 can efficiently mediate photocatalysis for solar-to-chemical energy conversion and pollution remediation. In this contribution, we report a novel approach, dielectric Mie resonance-enhanced photocatalysis, to enhance the catalytic activity of metal oxide photocatalysts. Specifically, we demonstrate that Cu2O nanostructures exhibiting dielectric Mie resonances can exhibit up to an order of magnitude higher photocatalytic rate as compared to Cu2O nanostructures not exhibiting dielectric Mie resonances. Our finite-difference time-domain (FDTD) simulation and experimental results predict a volcano-type relationship between the photocatalytic rate and the size of Cu2O nanospheres and nanocubes. Using transient absorption measurements, we reveal that a coherent electronic process associated with dielectric Mie resonance-mediated charge carrier generation is dominant in Cu2O nanostructures that exhibit higher photocatalytic rates. Although we experimentally demonstrate dielectric Mie resonance-enhanced photocatalysis using Cu2O particles here, based on our FDTD simulations, we anticipate the same can be achieved with other metal oxide photocatalysts, including CeO2, {\alpha}-Fe2O3, and TiO2

Mitigating the Risk of Coprecipitation of Pinacol during Isolation from Telescoped Miyaura Borylation and Suzuki Couplings Utilizing Boron Pinacol Esters: Use of Modeling for Process Design

Process definition and optimization of a telescoped Miyaura borylation and Suzuki coupling reaction employing bis­(pinacolato)­diboron (BisPin), used in the developmental synthesis of an intermediate for Abemaciclib, led to the unexpected coprecipitation of pinacol during the isolation. Thermodynamic phase separation, distillation, and pinacol phase diagram models were used to guide the design of a modified process to maintain pinacol fully soluble. A Quality by Design (QbD) approach was used to illustrate the control strategy and provide a maximally flexible process for manufacturing to maintain high purity of the intermediate. Different possible representations of the design space to mitigate pinacol precipitation are discussed and compared. The risk of pinacol precipitation may not be unique to the system of study and could have broad implication to the development of this class of reactions