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1. Laser induced graphene-based glucose biofuel cell

   https://doi.org/10.1109/SENSORS47087.2021.9639554  

   Hossain, Md Faruk ; Slaughter, Gymama ( October 2021 , 2021 IEEE Sensors)

   A glucose biofuel cell is presented using laser induced 3D graphene (LIG) substrate integrated with catalytic active nanomaterials for harnessing the biochemical energy of glucose. The LIG anode comprised glucose dehydrogenase immobilized on reduced graphene oxide and multiwalled carbon nanotubes (RGO/MWCNTs) nanocomposite for glucose oxidation. The LIG cathode is modified with RGO/MWCNTs and silver oxide (Ag 2 O) nanocomposites for the reduction of oxygen. The assembled biofuel cell exhibited a linear peak power response up to 18 mM glucose with sensitivity of 0.63 μW mM -1 cm −2 and exhibited good linearity (r 2 = 0.99). The glucose biofuel cell showed an open-circuit voltage of 0.365 V, a maximum power density of 11.3 μW cm −2 at a cell voltage of 0.25 V, and a short-circuit current density of 45.18 μA cm −2 when operating in 18 mM glucose. Cyclic voltammetry revealed the bioanode exhibited similar linearity for the detection of glucose. These results demonstrate that LIG based bioelectrodes offer great promise for diverse applications in the development of hybrid biofuel cell and biosensor technology.
2. Structural Assessment of Polymer-Enzyme Complex Nanoparticle Stability

   Murthy, N. Sanjeeva ; Upadhya, Rahul ; Kosuri, Shashank ; Tamasi, Matthew ; Gormley, Adam J. ( April 2022 , Transactions of the Society for Biomaterials)

   Statement of Purpose Hybrid nanoparticles in which a polymer is used to stabilize the secondary structure of enzyme provide a means to preserve its activity in non-native environments. This approach is illustrated here with horseradish peroxidase (HRP), an important heme enzyme used in medical diagnostic, biosensing, and biotechnological applications. Polymer chaperones in these polymer-enzyme complex (PEC) nanoparticles can enhance the utility of enzymes in unfavorable environments. Structural analysis of the PECs is a crucial link in the machine-learning driven iterative optimization cycle of polymer synthesis and testing. Here, we discuss the utility of small-angle X-ray scattering (SAXS) and quartz crystal microbalance with dissipation (QCMD) for evaluating PECs. Materials and Methods Six polymers were synthesized by automated photoinduced electron/energy transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization directly in 96-well plates.1 Multiple molar ratios of enzyme:polymer (1:1, 1:5, 1:10, and 1:50) were characterized. HRP was mixed with the polymer and heated to 65 °C for 1 hr to form PECs. Enzyme assay and circular dichroism measurements were performed along with SAXS and QCMD to understand polymer-protein interactions. SAXS data were obtained at NSLS-II beamline 16-ID. Results and Discussion SAXS data were analyzed to determine the radius of gyration (Rg), Porod exponent and pair distancemore »distribution functions (P(r)) (Figure 1). Rg, which corresponds to the size of the PEC nanoparticles, is sensitive to the polydispersity of the solution and does not change significantly in the presence of the polymer GEP1. Notably, the maximal dimension does not change as significantly upon heating to denaturation in the case of the PEC as it does with HRP alone. The effect of denaturation induced by heating seems to depend on the molar ratio of the polymer to enzyme. The Porod exponent, which is related to roughness, decreased from about 4 to 3 upon complexation indicating polymer binding to the enzyme’s surface. These were confirmed by modeling the structures of the HRP, the polymer and the PEC were modeled using DAMMIF/DAMMIN and MONSA (ATSAS software). The changes observed in the structure could be correlated to the measured enzymatic activity. Figure 2 shows the evolution of the PEC when the polymer is deposited onto the enzyme immobilized on Figure 1. P(r) plots for PEC vs. HRP before and after heating, illustrating the increased enzymatic stability due to polymer additives. gold-coated QCM sensors. The plots show the changes in frequency (f) and dissipation (D) with time as HRP is first deposited and is followed by the adsorption of the polymer. Large f and D show that the polymer forms a complex with HRP. Such changes were not observed with negative controls, Pluronics and poly(ethylene glycol). Comparison of the data from free particles in solution with QCM data from immobilized enzymes, shows that the conformation of the complexes in solution and surface-bound HRP could be different. This way, we were able to explore the various states of complex formation under different conditions with different polymers. Figure 2. QCMD data showing the interaction between the immobilized HRP and the polymer. 3rd and 5th harmonics are plotted (blue -f; red-D). Conclusion SAXS and QCMD data show that stabilization of the enzyme activity by inhibiting the unraveling of the secondary structure as seen in size, surface roughness, pair distribution function and percent helicity. Acknowledgment This work was supported by NSF grant 2009942. References [1] Tamasi, M, et al. Adv Intell Syst 2020, 2(2): 1900126.« less
3. Immobilization of molecular catalysts on solid supports via atomic layer deposition for chemical synthesis in sustainable solvents

   https://doi.org/10.1039/D1GC02024B  

   Ayare, Pooja J. ; Gregory, Shawn A. ; Key, Ryan J. ; Short, Andrew E. ; Tillou, Jake G. ; Sitter, James D. ; Yom, Typher ; Goodlett, Dustin W. ; Lee, Dong-Chan ; Alamgir, Faisal M. ; et al ( November 2021 , Green Chemistry)

   Homogeneous molecular catalysts are valued for their reaction specificity but face challenges in manufacturing scale-up due to complexities in final product separation, catalyst recovery, and instability in the presence of water. Heterogenizing these molecular catalysts, by attachment to a solid support, could transform the practical utility of molecular catalysts, simplify catalyst separation and recovery, and prevent catalyst decomposition by impeding bimolecular catalyst interactions. Previous strategies to heterogenize molecular catalysts via ligand-first binding to supports have suffered from reduced catalytic activity and leaching (loss) of catalyst, especially in environmentally friendly solvents like water. Herein, we describe an approach in which molecular catalysts are first attached to a metal oxide support through acidic ligands and then “encapsulated” with a metal oxide layer via atomic layer deposition (ALD) to prevent molecular detachment from the surface. For this initial report, which is based upon the well-studied Suzuki carbon–carbon cross-coupling reaction, we demonstrate the ability to achieve catalytic performance using a non-noble metal molecular catalyst in high aqueous content solvents. The catalyst chosen exhibits limited catalytic reactivity under homogeneous conditions due to extremely short catalyst lifetimes, but when heterogenized and immobilized with an optimal ALD layer thickness product yields >90% can be obtained in primarilymore »aqueous solutions. Catalyst characterization before and after ALD application and catalytic reaction is achieved with infrared, electron paramagnetic resonance, and X-ray spectroscopies.« less
4. Heterogeneous catalysis by ultra-small bimetallic nanoparticles surpassing homogeneous catalysis for carbon–carbon bond forming reactions

   https://doi.org/10.1039/d0nr04105j  

   Norouzi, Nazgol ; Das, Mrinmoy K. ; Richard, Alexander J. ; Ibrahim, Amr A. ; El-Kaderi, Hani M. ; El-Shall, M. Samy ( October 2020 , Nanoscale)

   Palladium catalyzed cross-coupling reactions represent a significant advancement in contemporary organic synthesis as these reactions are of strategic importance in the area of pharmaceutical drug discovery and development. Supported palladium-based catalysts are highly sought-after in carbon–carbon bond forming catalytic processes to ensure catalyst recovery and reuse while preventing product contamination. This paper reports the development of heterogeneous Pd-based bimetallic catalysts supported on fumed silica that have high activity and selectivity matching those of homogeneous catalysts, eliminating the catalyst's leaching and sintering and allowing efficient recycling of the catalysts. Palladium and base metal (Cu, Ni or Co) contents of less than 1.0 wt% loading are deposited on a mesoporous fumed silica support (surface area SA BET = 350 m 2 g −1 ) using strong electrostatic adsorption (SEA) yielding homogeneously alloyed nanoparticles with an average size of 1.3 nm. All bimetallic catalysts were found to be highly active toward Suzuki cross-coupling (SCC) reactions with superior activity and stability for the CuPd/SiO 2 catalyst. A low CuPd/SiO 2 loading (Pd: 0.3 mol%) completes the conversion of bromobenzene and phenylboronic acid to biphenyl in 30 minutes under ambient conditions in water/ethanol solvent. In contrast, monometallic Pd/SiO 2 (Pd: 0.3 mol%) completes the samemore »reaction in three hours under the same conditions. The combination of Pd with the base metals helps in retaining the Pd 0 status by charge donation from the base metals to Pd, thus lowering the activation energy of the aryl halide oxidative addition step. Along with its exceptional activity, CuPd/SiO 2 exhibits excellent recycling performance with a turnover frequency (TOF) of 280 000 h −1 under microwave reaction conditions at 60 °C. Our study demonstrates that SEA is an excellent synthetic strategy for depositing ultra-small Pd-based bimetallic nanoparticles on porous silica for SCC. This avenue not only provides highly active and sintering-resistant catalysts but also significantly lowers Pd contents in the catalysts without compromising catalytic activity, making the catalysts very practical for large-scale applications.« less
5. Microfluidic Synthesis of Elastomeric Microparticles: A Case Study in Catalysis of Palladium-Mediated Cross-Coupling

   Bennett, Jeffrey A ; Genzer, Jan ; Abolhasani, Milad ( October 2018 , 2018 AIChE Annual Meeting)

   Metal-mediated cross-coupling reactions offer organic chemists a wide array of stereo- and chemically-selective reactions with broad applications in fine chemical and pharmaceutical synthesis.1 Current batch-based synthesis methods are beginning to be replaced with flow chemistry strategies to take advantage of the improved consistency and process control methods offered by continuous flow systems.2,3 Most cross-coupling chemistries still encounter several issues in flow using homogeneous catalysis, including expensive catalyst recovery and air sensitivity due to the chemical nature of the catalyst ligands.1 To mitigate some of these issues, a ligand-free heterogeneous catalysis reaction was developed using palladium (Pd) loaded into a polymeric network of a silicone elastomer, poly(hydromethylsiloxane) (PHMS), that is not air sensitive and can be used with mild reaction solvents (ethanol and water).4 In this work we present a novel method of producing soft catalytic microparticles using a multiphase flow-focusing microreactor and demonstrate their application for continuous Suzuki-Miyaura cross-coupling reactions. The catalytic microparticles are produced in a coaxial glass capillary-based 3D flow-focusing microreactor. The microreactor consists of two precursors, a cross-linking catalyst in toluene and a mixture of the PHMS polymer and a divinyl cross-linker. The dispersed phase containing the polymer, cross-linker, and cross-linking catalyst is continuously mixed and thenmore »formed into microdroplets by the continuous phase of water and surfactant (sodium dodecyl sulfate) introduced in a counter-flow configuration. Elastomeric microdroplets with a diameter ranging between 50 to 300 micron are produced at 25 to 250 Hz with a size polydispersity less than 3% in single stream production. The physicochemical properties of the elastomeric microparticles such as particle swelling/softness can be tuned using the ratio of cross-linker to polymer as well as the ratio of polymer mixture to solvent during the particle formation. Swelling in toluene can be tuned up to 400% of the initial particle volume by reducing the concentration of cross-linker in the mixture and increasing the ratio of polymer to solvent during production.5 After the particles are produced and collected, they are transferred into toluene containing palladium acetate, allowing the particles to incorporate the palladium into the polymer network and then reduce the palladium to Pd0 with the Si-H functionality present on the PHMS backbones. After the reduction, the Pd-loaded particles can be washed and dried for storage or switched into an ethanol/water solution for loading into a micro-packed bed reactor (µ-PBR) for continuous organic synthesis. The in-situ reduction of Pd within the PHMS microparticles was confirmed using energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and focused ion beam-SEM, and TEM techniques. In the next step, we used the developed µ-PBR to conduct continuous organic synthesis of 4-phenyltoluene by Suzuki-Miyaura cross-coupling of 4-iodotoluene and phenylboronic acid using potassium carbonate as the base. Catalyst leaching was determined to only occur at sub ppm concentrations even at high solvent flow rates after 24 h of continuous run using inductively coupled plasma mass spectrometry (ICP-MS). The developed µ-PBR using the elastomeric microparticles is an important initial step towards the development of highly-efficient and green continuous manufacturing technologies in the pharma industry. In addition, the developed elastomeric microparticle synthesis technique can be utilized for the development of a library of other chemically cross-linkable polymer/cross-linker pairs for applications in organic synthesis, targeted drug delivery, cell encapsulation, or biomedical imaging. References 1. Ruiz-Castillo P, Buchwald SL. Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions. Chem Rev. 2016;116(19):12564-12649. 2. Adamo A, Beingessner RL, Behnam M, et al. On-demand continuous-flow production of pharmaceuticals in a compact, reconfigurable system. Science. 2016;352(6281):61 LP-67. 3. Jensen KF. Flow Chemistry — Microreaction Technology Comes of Age. 2017;63(3). 4. Stibingerova I, Voltrova S, Kocova S, Lindale M, Srogl J. Modular Approach to Heterogenous Catalysis. Manipulation of Cross-Coupling Catalyst Activity. Org Lett. 2016;18(2):312-315. 5. Bennett JA, Kristof AJ, Vasudevan V, Genzer J, Srogl J, Abolhasani M. Microfluidic synthesis of elastomeric microparticles: A case study in catalysis of palladium-mediated cross-coupling. AIChE J. 2018;0(0):1-10.« less