Publications

RATIONALE The nanostructure‐initiator mass spectrometry based enzyme assay (Nimzyme) provides a rapid method for screening glycan modifying reactions. However, this approach cannot resolve stereospecific reactions which are common in glycobiology and are typically assayed using lower‐throughput methods (gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis) often in conjunction with stable isotopically labeled reactants. However, in many applications, library size necessitates the development of higher‐throughput screening approaches of stereospecific reactions from crude sample preparations. Therefore, here we test the approach of utilizing Nimzyme linkers with unique masses to encode substrate identity such that this assay can resolve stereospecific reactions. METHODS We utilize the nanostructure‐initiator mass spectrometry (NIMS) enzyme assay in conjuction with an accurate mass tagging approach where each reactant is tagged with a unique perfluoronated tail. Mass spectrometric analysis was conducted using conventional MALDI‐TOF instrumentation. RESULTS Stereospecific reaction pathways of three stereoisomers (maltose, lactose and cellobiose) to afford the same product glucose were resolved simutaneously due to the presence of unique fluorous tags on both reactants and products. Not only purified enzymes, but also crude cell lysates can be used in this assay. CONCLUSIONS The Nimzyme assay with accurate mass tagging provides a rapid method for screening for targeted stereospecific reactions using mass spectrometry and may be useful for high‐throughput screening and functional annotation of a wide range of glycan‐modifying enzymes. Copyright © 2012 John Wiley & Sons, Ltd.

Abstract The selective functionalization of one C−H bond over others in nearly identical steric and electronic environments can facilitate the construction of complex molecules. We report site‐selective functionalizations of C−H bonds, differentiated solely by remote substituents, catalyzed by artificial metalloenzymes (ArMs) that are generated from the combination of an evolvable P450 scaffold and an iridium‐porphyrin cofactor. The generated systems catalyze the insertion of carbenes into the C−H bonds of a range of phthalan derivatives containing substituents that render the two methylene positions in each phthalan inequivalent. These reactions occur with site‐selectivity ratios of up to 17.8:1 and, in most cases, with pairs of enzyme mutants that preferentially form each of the two constitutional isomers. This study demonstrates the potential of abiotic reactions catalyzed by metalloenzymes to functionalize C−H bonds with site selectivity that is difficult to achieve with small‐molecule catalysts.

As an alternative to Li-based technologies to develop stationary energy storage systems, Na-ion batteries have attracted substantial interest. Unlike the Li-ion, layered sodium transition metal oxide (NaTMO 2 ) cathodes can diversify their redox centers from expensive Co to cheap Mn and Fe to achieve high energy density, offering a wide variety of chemistry selection to design low-cost, high-performance batteries. 1 These cathode materials often undergo discontinuous, yet reversible, phase transitions upon Na intercalation due to complex interatomic interactions, which result in multiple plateau-like features in their voltage profiles. However, large desodiation of Fe-containing Na-ion cathodes often leads to an unclarified, irreversible phase transition at high voltage, hindering the full use of Fe redox. 2 In this talk, we will discuss how transition metal selection affects the thermodynamic stability of desodiated structures of NaTMO 2 . First, we demonstrate this insight by comparing two prototypical compositions, NaNi 0.5 Co 0.5 O 2 and NaNi 0.5 Fe 0.5 O 2 , with detailed experimental and computational investigation. 3 The Na intercalation processes of the two compounds are carefully investigated by electrochemical methods and in situ X-ray diffraction. We confirm that although the two materials share the same Ni 3+ /Ni 4+ redox, their structural changes are very different from each other. Na x Ni 0.5 Co 0.5 O 2 goes through multiple phase transitions including three different O3-type and three different P3-type structures. In contrast, Na x Ni 0.5 Fe 0.5 O 2 only undergoes a generic O3-P3 transition with no sign of monoclinicity, leading to a smoothly increasing voltage profile. Second, our recent findings on a quaternary transition metal system, NaTi 0.25 Fe 0.25 Co 0.25 Ni 0.25 O 2 , 4 will be underlined. We will present structural evidence and characterization of the highly-desodiated, high-voltage phase that exhibits peculiar oxygen stacking. This phase consists of alternating octahedral and prismatic Na layers, namely OP2 stacking, in which formation is afforded by distortion-tolerant Ti and Jahn-Teller-active Fe. Moreover, we will demonstrate that this new phase participates in redox reaction reversibly, fundamentally distinct from inactive high-voltage phases in many Na-ion cathodes. Finally, a strategy to stabilize Fe-containing NaTMO 2 materials to create layered cathodes with high reversible Na capacity will be briefly discussed. Our results demonstrate that we can manipulate the redox reaction and associated structure change by transition metal mixing. References Yabuuchi, K. Kubota, M. Dahbi, and S. Komaba, Chem. Rev. , 2014, 114, 11636−11682 Jeong, H. Lee, J. Yoon, and W.-S. Yoon, J. Power Sources , 2019, 439, 227064 Vassilaras, D.-H. Kwon, S. T. Dacek, T. Shi, D. -H. Seo, G. Ceder, and J. C. Kim, J. Mater. Chem. A , 2017, 5, 4596–4606 Vassilaras, S. T. Dacek, H. Kim, T. T. Fister, S. Kim, G. Ceder, and J. C. Kim, J. Electrochem. Soc. , 164, 2017, A3484–A3486

A study of electronic factors governing the thermodynamics of C-H and N-H bond addition to Ir(I) complexes was conducted. DFT calculations were performed on an extensive series of trans-(PH3)2IrXL complexes (L = NH3 and CO; X = various monodentate ligands) to parametrize the relative σ- and π-donating/withdrawing properties of the various ligands, X. Computed energies of oxidative addition of methane to a series of three- and four-coordinate Ir(I) complexes bearing an ancillary ligand, X, were correlated with the resulting (σ(X), π(X)) parameter set. Regression analysis indicates that the thermodynamics of addition of methane to trans-(PH3)2IrX are generally strongly disfavored by increased σ-donation from the ligand X, in contradiction to widely held views on oxidative addition. The trend for oxidative addition of methane to four-coordinate Ir(I) was closely related to that observed for the three-coordinate complexes, albeit slightly more complicated. The computational analysis was found to be consistent with the rates of reductive elimination of benzene from a series of isoelectronic Ir(III) phenyl hydride complexes, measured experimentally in this work and previously reported. Extending the analysis of ancillary ligand energetic effects to the oxidative addition of ammonia to three-coordinate Ir(I) complexes leads to the conclusion that increasing σ-donation by X also disfavors oxidative addition of N-H bonds to trans-(PH3)2IrX. However, coordination of NH3 to the Ir(I) center is disfavored even more strongly by increasing σ-donation by X, which explains why the few documented examples of H-NH2 oxidative addition to transition metals involve complexes with strongly σ-donating ligands situated trans to the site of addition. An orbital-based rationale for the observed results is presented.

The liberalization of marijuana policies, including the legalization of medical and recreational marijuana, is sweeping the United States and other countries. Marijuana cultivation can have significant negative collateral effects on the environment that are often unknown or overlooked. Focusing on the state of California, where by some estimates 60%-70% of the marijuana consumed in the United States is grown, we argue that (a) the environmental harm caused by marijuana cultivation merits a direct policy response, (b) current approaches to governing the environmental effects are inadequate, and

In this paper, we present BlinkDB, a massively parallel, sampling-based approximate query engine for running ad-hoc, interactive SQL queries on large volumes of data. The key insight that BlinkDB builds on is that one can often make reasonable decisions in the absence of perfect answers. For example, reliably detecting a malfunctioning server using a distributed collection of system logs does not require analyzing every request processed by the system. Based on this insight, BlinkDB allows one to trade-off query accuracy for response time, enabling interactive queries over massive data by running queries on data samples and presenting results annotated with meaningful error bars. To achieve this, BlinkDB uses two key ideas that differentiate it from previous work in this area: (1) an adaptive optimization framework that builds and maintains a set of multi-dimensional, multi-resolution samples from original data over time, and (2) a dynamic sample selection strategy that selects an appropriately sized sample based on a query's accuracy and/or response time requirements. We have built an open-source version of BlinkDB and validated its effectiveness using the well-known TPC-H benchmark as well as a real-world analytic workload derived from Conviva Inc. Our experiments on a 100 node cluster show that BlinkDB can answer a wide range of queries from a real-world query trace on up to 17 TBs of data in less than 2 seconds (over 100\times faster than Hive), within an error of 2 - 10%.

Correction for ‘Dicopper( i ) complexes of a binucleating, dianionic, naphthyridine bis(amide) ligand’ by Laurent Sévery et al. , Dalton Trans. , 2025, https://doi.org/10.1039/d5dt00034c.