The generation of surrogate potential energy functions (PEF) that are orders of magnitude faster to compute but as accurate as the underlying training data from high-level electronic structure ...methods is one of the most promising applications of fitting procedures in chemistry. In previous work, we have shown that transition state force fields (TSFFs), fitted to the functional form of MM3* force fields using the quantum guided molecular mechanics (Q2MM) method, provide an accurate description of transition states that can be used for stereoselectivity predictions of small molecule reactions. Here, we demonstrate the applicability of the method for fit TSFFs to the well-established Amber force field, which could be used for molecular dynamics studies of enzyme reaction. As a case study, the fitting of a TSFF to the second hydride transfer in Pseudomonas mevalonii 3-hydroxy-3-methylglutaryl coenzyme A reductase (PmHMGR) is used. The differences and similarities to fitting of small molecule TSFFs are discussed.
Realtime time-dependent density-functional theory (RT-TDDFT) is one of the most practical techniques available to simulate electronic dynamics of molecules and materials. Promising applications of ...RT-TDDFT to study nonlinear spectra and energy transport demand simulations of large solvated systems over long time scales, which are computationally quite costly. In this paper, we apply an embedding technique developed for ground-state SCF methods by Manby and Miller to accelerate realtime TDDFT. We assess the accuracy and speed of these approximations by studying the absorption spectra of solvated and covalently split chromophores. Our embedding approach is also compared with less accurate, less costly QM/MM charge embeddings. We find that by mixing levels of detail the embedded mean-field theory scheme is a simple, accurate, and effective way to accelerate RT-TDDFT simulations.
A phosphorus(III)-mediated dearomatization of ortho-substituted dianiline squaraine dyes results in an unusual skeletal rearrangement to provide exotic, highly conjugated benzofuranone and oxindole ...scaffolds bearing a C3 side chain comprised of a linear conflagration of an enol, a phosphorus ylide, and 2,4-disubstituted aniline. Employing experimental and computational analysis, a mechanistic evaluation revealed a striking dependence on the acidity of the aniline ortho substituent. Notably, the rearrangement adducts underwent rapid and complete reversion to the parent squaraine in the presence of a Brønsted acid.
Phytase enzymes are a crucial component of the natural phosphorus cycle, as they help make phosphate bioavailable by releasing it from phytate, the primary reservoir of organic phosphorus in grain ...and soil. Phytases also comprise a significant segment of the agricultural enzyme market, used primarily as an animal feed additive. At least four structurally and mechanistically distinct classes of phytases have evolved in bacteria and eukaryotes, and the natural diversity of each class is explored here using advances in protein structure prediction and functional annotation. This graphical review aims to provide a succinct description of the major classes of phytase enzymes across phyla, including their structures, conserved motifs, and mechanisms of action.
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•An overview of phytases across phyla, building on recent advances in protein structure prediction and function annotation.•Key examples across all four major classes of phytases, including a description of their respective reaction mechanisms.•Utilized recently published tools to conduct a structure-based survey of phytases and related phosphatases.
We examine contagion in earnings management using 2,376 restatements announced during the years 1997–2008. Controlling for industry and firm characteristics, firms are more likely to begin managing ...earnings after the public announcement of a restatement by another firm in their industry or neighborhood. Such contagion is absent when the restating firm is disciplined by the SEC or class action lawsuits, suggesting deterrent effects of enforcement activity. Contagion among peers is observed (1) in the same account as the one restated by the target firm, or (2) when larger target firms restate or the restatement is prominently disclosed, or (3) when the target firm's restatement is less severe. Contagion stops during the years 2003–2005, possibly due to the enforcement associated with the Sarbanes-Oxley Act (SOX), but reappears during 2006–2008, perhaps because the sting associated with SOX has worn off. In sum, peers' actions appear to affect a firm's earnings management decisions.
In this study, I investigate the impact of managerial reputation, as proxied by high‐profile awards to CEOs, on financial reporting practices and firm performance. Using a sample of 269 awards given ...to 189 celebrity CEOs (CEOs who win awards) from 1987 to 2003, I compare within‐firm changes in financial reporting practices and firm performance before and after each CEO wins their first award. I find that celebrity CEOs engage in more conservative accounting practices and are less likely to engage in opportunistic earnings management to meet short‐term earnings benchmarks. In addition, firm performance improves after celebrity CEOs win awards.
Fluctuations in cytosolic Ca2+ are crucial for a variety of cellular processes including many aspects of development. Mobilization of intracellular Ca2+ stores via the production of inositol ...trisphosphate (IP3) and the consequent activation of IP3-sensitive Ca2+ channels is a ubiquitous means by which diverse stimuli mediate their cellular effects. Although IP3 receptors have been well studied at fertilization, information regarding their possible involvement during subsequent development is scant. In the present study we examined the role of IP3 receptors in early development of the zebrafish. We report the first molecular analysis of zebrafish IP3 receptors which indicates that, like mammals, the zebrafish genome contains three distinct IP3 receptor genes. mRNA for all isoforms was detectable at differing levels by the 64 cell stage, and IP3-induced Ca2+ transients could be readily generated (by flash photolysis) in a controlled fashion throughout the cleavage period in vivo. Furthermore, we show that early blastula formation was disrupted by pharmacological blockade of IP3 receptors or phospholipase C, by molecular inhibition of the former by injection of IRBIT (IP3 receptor-binding protein released with IP3) and by depletion of thapsigargin-sensitive Ca2+ stores after completion of the second cell cycle. Inhibition of Ca2+ entry or ryanodine receptors, however, had little effect. Our work defines the importance of IP3 receptors during early development of a genetically and optically tractable model vertebrate organism.
With increasing stakeholders' demand for information on corporate social responsibility (CSR) performance and a growing number of firms issuing standalone CSR reports, this study examines the ...relation between CSR performance and the quantity and quality of CSR disclosures. Drawing on signaling and political legitimacy theories of information disclosure and using a US sample of 2774 standalone CSR reports from 2003 to 2015, we find better CSR performing firms issue longer CSR reports and provide incremental information in their CSR reports relative to their annual financial reports. Furthermore, the textual content in their CSR reports is less focused on short‐term issues, reflecting higher disclosure quality. In contrast, poor CSR performing firms tend exhibit lower disclosure quality as their CSR reports use more uncertain words. Our study contributes to the understanding of how CSR performance affect stakeholder engagement through the characteristics of textual content in standalone CSR reports.
We investigate the consequences of the “revolving door” for trial lawyers at the SEC’s enforcement division. If future job opportunities motivate SEC lawyers to develop and/or showcase their ...enforcement expertise, then the revolving door phenomenon will promote more aggressive regulatory activity (the “human capital” hypothesis). In contrast, SEC lawyers can relax enforcement efforts in order to develop networking skills and/or curry favor with prospective employers at private law firms (the “rent seeking” hypothesis”). We collect data on the career paths of 336 SEC lawyers that span 284 SEC civil cases against accounting misrepresentation over the period 1990–2007. Our overall evidence is consistent with the “human capital” hypothesis. However, we find some evidence of “rent seeking” when SEC lawyers are based in Washington DC and when defense firms employ more former SEC lawyers. The revolving door likely impacts numerous aspects of SEC regulation setting and enforcement. This study examines accounting-related civil cases and is not able to study administrative or non-accounting enforcement cases. Further, the study does not address the choice of which cases to pursue, the incentives of employees other than trial lawyers, or how the revolving door affects rule making. Subject to these caveats, our study provides an important first look into the effects of revolving door incentives on the SEC’s enforcement process and lays the groundwork for future research.
We conjecture that corporate social responsibility (CSR) can be indicative of managerial ethics and integrity and examine whether equity investors and financial analysts consider CSR performance when ...they assess firms' disclosures of actual and forecasted earnings. We find that only adverse CSR performance affects investors' assessments of these disclosures. In contrast, we find that both positive and adverse CSR performance affect analysts' forecast revisions in response to firms' disclosures. We also find that firms with adverse CSR performance exhibit lower disclosure quality and earnings persistence, but do not find that firms with positive CSR performance exhibit higher levels of both measures. This asymmetric result is consistent with investors', but not analysts', assessments of the effect of CSR performance on corporate disclosures. Our results are robust to using a three-stage least squares approach to address endogeneity concerns and to a battery of robustness and sensitivity analyses. Overall, our findings suggest that investors and analysts consider CSR when assessing the information in earnings-related corporate disclosures.
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