scholarly journals Following Molecular Mobility During Chemical Reactions: No Evidence for Active Propulsion

2021 ◽  
Author(s):  
Lucy Fillbrook ◽  
Jan-Philipp Günther ◽  
Günter Majer ◽  
Daniel O'Leary ◽  
William Price ◽  
...  
Keyword(s):  
Diffusion Coefficients ◽  
Density Functional ◽  
Click Reaction ◽  
Copper Catalyst ◽  
Critical Role ◽  
Accurate Determination ◽  
Valuable Insight ◽  
Relaxation Rates ◽  
Diffusion Nmr ◽  
Paramagnetic Ions

The measured changes in self-diffusion of small molecules during reactions have been attributed “boosted mobility”. We demonstrate the critical role of changing concentrations of paramagnetic ions on nuclear magnetic resonance (NMR) signal intensities, which lead to erroneous measurements of diffusion coefficients. We present simple methods to overcome this problem. The use of shuffled gradient amplitudes allows accurate diffusion NMR measurements, even with time-dependent relaxation rates caused by changing concentrations of paramagnetic ions. The addition of a paramagnetic relaxation agent allows accurate determination of both diffusion coefficients and reaction kinetics during a single experiment. We analyze a copper-catalyzed azide-alkyne cycloaddition ‘click’ reaction, for which boosted mobility has been claimed. With our methods, we accurately measure the diffusive behavior of solvent, starting materials and product, and find no global increase in diffusion coefficients during the reaction. We overcome NMR signal overlap using an alternative reducing agent to improve the accuracy of the diffusion measurements. The alkyne reactant diffuses slower as the reaction proceeds, due to binding to the copper catalyst during the catalytic cycle. The formation of this intermediate was confirmed by complementary NMR techniques and density functional theory calculations. Our work calls into question recent claims that molecules actively propel or swim during reactions, and establishes that time-resolved diffusion NMR measurements can provide valuable insight into reaction mechanisms.

Accurate determination of band gaps within density functional formalism

2013 ◽  
Vol 87 (23) ◽  
Author(s):  
Prashant Singh ◽  
Manoj K. Harbola ◽  
Biplab Sanyal ◽  
Abhijit Mookerjee
Keyword(s):  
Density Functional ◽  
Accurate Determination ◽  
Band Gaps ◽  
Functional Formalism

scholarly journals A Multi-Scale Modelling of Aggregation of TiO2 Nanoparticle Suspensions in Water

2021 ◽  
Author(s):  
Giulia Mancardi ◽  
Matteo Alberghini ◽  
Neus Aguilera-Porta ◽  
Monica Calatayud ◽  
Pietro Asinari ◽  
...  
Keyword(s):  
Titanium Dioxide ◽  
Density Functional ◽  
Large Scale ◽  
Molecular Descriptors ◽  
Titanium Dioxide Nanoparticles ◽  
Accurate Determination ◽  
Multi Scale ◽  
Spherical Bead ◽  
Living Organisms ◽  
Dynamics Simulations

Titanium dioxide nanoparticles have risen concerns about their possible toxicity and the European Food Safety Authority recently banned the use of TiO2 nano-additive in food products. Following the intent of relating nanomaterials atomic structure with their toxicity without having to conduct large scale experiments on living organisms, we investigate the aggregation of titanium dioxide nanoparticles using a multi-scale technique: starting from ab initio Density Functional Theory to get an accurate determination of the energetics and electronic structure, we switch to classical Molecular Dynamics simulations to calculate the Potential of Mean Force for the connection of two identical nanoparticles in water; the fitting of the latter by a set of mathematical equations is the key for the upscale. Lastly, we perform Brownian Dynamics simulations where each nanoparticle is a spherical bead. This coarsening strategy allows studying the aggregation of a few thousand nanoparticles. Applying this novel procedure, we find three new molecular descriptors, namely, the aggregation free energy and two numerical parameters used to correct the observed deviation from the aggregation kinetic described by the Smoluchowski theory. Molecular descriptors can be fed into QSAR models to predict the toxicity of a material knowing its physicochemical properties, without having to conduct large scale experiments on living organisms.

scholarly journals Assessing the Performance of Density Functional Theory Methods on the Prediction of Low-Frequency Vibrational Spectra

2020 ◽  
Author(s):  
Peter Banks ◽  
Zihui Song ◽  
Michael Ruggiero
Keyword(s):  
Density Functional Theory ◽  
Vibrational Spectra ◽  
Density Functional ◽  
Low Frequency ◽  
Intermolecular Forces ◽  
State Density ◽  
Basis Set ◽  
Valuable Insight ◽  
Great Success ◽  
Functional Theory

The low-frequency (terahertz) dynamics of condensed phase materials provide valuable insight into numerous bulk phenomena. However, the assignment and interpretation of experimental results requires computational methods due to the complex mode-types that depend on weak intermolecular forces. Solid-state density functional theory has been used in this regard with great success, yet the selection of specific computational parameters, namely the chosen basis set and density functional, has a profound influence on the accuracy of predicted spectra. In this work, the role of these two parameters is investigated in a series of organic molecular crystals, in order to assess the ability of various methods to reproduce intermolecular forces, and subsequently experimental terahertz spectra. Specifically, naphthalene, oxalic acid, and thymine were chosen based on the varied intermolecular interactions present in each material. The results highlight that unconstrained geometry optimizations can be used as an initial proxy for the accuracy of interatomic forces, with errors in the calculated geometries indicative of subsequent errors in the calculated low-frequency vibrational spectra, providing a powerful metric for the validation of theoretical results. Finally, the origins of the observed shortcomings are analyzed, providing a basic framework for further studies on related materials.

scholarly journals Identification of different oxygen species in oxide nanostructures with 17O solid-state NMR spectroscopy

2015 ◽  
Vol 1 (1) ◽  
pp. e1400133 ◽  
Author(s):  
Meng Wang ◽  
Xin-Ping Wu ◽  
Sujuan Zheng ◽  
Li Zhao ◽  
Lei Li ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Strong Dependence ◽  
Critical Role ◽  
Oxygen Species ◽  
Structure Property ◽  
Diverse Range ◽  
Oxygen Ions ◽  
Surface Sites ◽  
Nanostructured Oxides

Nanostructured oxides find multiple uses in a diverse range of applications including catalysis, energy storage, and environmental management, their higher surface areas, and, in some cases, electronic properties resulting in different physical properties from their bulk counterparts. Developing structure-property relations for these materials requires a determination of surface and subsurface structure. Although microscopy plays a critical role owing to the fact that the volumes sampled by such techniques may not be representative of the whole sample, complementary characterization methods are urgently required. We develop a simple nuclear magnetic resonance (NMR) strategy to detect the first few layers of a nanomaterial, demonstrating the approach with technologically relevant ceria nanoparticles. We show that the 17O resonances arising from the first to third surface layer oxygen ions, hydroxyl sites, and oxygen species near vacancies can be distinguished from the oxygen ions in the bulk, with higher-frequency 17O chemical shifts being observed for the lower coordinated surface sites. H217O can be used to selectively enrich surface sites, allowing only these particular active sites to be monitored in a chemical process. 17O NMR spectra of thermally treated nanosized ceria clearly show how different oxygen species interconvert at elevated temperature. Density functional theory calculations confirm the assignments and reveal a strong dependence of chemical shift on the nature of the surface. These results open up new strategies for characterizing nanostructured oxides and their applications.

scholarly journals Racial Uplift? Intra‐Racial Class Conflict and the Economic Revitalization of Harlem and Bronzeville

2006 ◽  
Vol 5 (1) ◽  
pp. 71-92 ◽  
Author(s):  
Derek S. Hyra
Keyword(s):  
African American ◽  
Middle Class ◽  
Critical Role ◽  
Community Change ◽  
Urban Neighborhoods ◽  
Economic Transformation ◽  
Class Conflict ◽  
Black Middle Class ◽  
Valuable Insight ◽  
Racial Uplift

The study of revitalizing African American urban neighborhoods is needed to understand how race, class, and politics influence community development. While numerous investigations of urban neighborhoods stress inter‐racial conflict, few explore intra‐racial class discord. Class antagonism within black America is a controversial and debated topic. Several scholars claim that the common experience of racism has led to social and political unity among African Americans. However, others predict that with greater economic differentiation, shared feelings of social and political commonality will decrease. The economic transformation of Harlem in New York City and Bronzeville in Chicago, two historic African American communities, provides valuable insight into the importance of class conflict to community change. After decades of economic abandonment, these areas are experiencing a resurgence of residential and commercial investments, triggered, in part, by the return of the black middle class. Based on a 4‐year, comparative ethnographic investigation, using extensive participant observation, interviews, and archival data, this study reveals the conflict between lower‐ and upper‐income residents. I highlight the process by which members of the black middle class translate their preferences for community improvement, through local organizations, by advocating for the removal of the poor from these once low‐income neighborhoods. I argue that intra‐racial class antagonism plays a critical role in the economic development of these communities, and assess whether the redevelopment of Harlem and Bronzeville can be considered “racial uplift.” This study supports the notion that class conflict is essential for understanding community change and the black experience in urban America.

Hydrocarbon-Phase Behaviors in Shale Nanopore/Fracture Model: Multiscale, Multicomponent, and Multiphase

SPE Journal ◽  
2019 ◽  
Vol 24 (06) ◽  
pp. 2526-2540 ◽  
Author(s):  
Yinuo Zhao ◽  
Zhehui Jin
Keyword(s):  
Oil Recovery ◽  
Density Functional ◽  
Critical Role ◽  
Volume Ratio ◽  
Phase Region ◽  
Bulk Phase ◽  
Two Phase ◽  
Well Productivity ◽  
Pressure Drops ◽  
Shale Reservoirs

Summary Hydrocarbon recovery from shale subformations has greatly contributed to the global energy supply and has been constantly reshaping the energy sector. Oil production from shale is a complex process in which multicomponent–fluid mixtures experience multiphase transitions in multiscale volumes (i.e., nanoscale pores are connected to fractures/macropores). Understanding such complicated phenomena plays a critical role in the estimation of ultimate oil recovery, well productivity, and reserves estimation, and ultimately in policy making. In this work, we use density–functional theory (DFT) to explicitly consider fluid/surface interactions, inhomogeneous–density distributions in nanopores, volume partitioning in nanopores, and connected macropores/natural fractures to study the complex multiphase transitions of multicomponent fluids in multiscale volumes. We found that vapor–like and liquid–like phases can coexist in nanopores when pressure is between the bubblepoint and dewpoint pressures of nanoconfined fluids, both of which are much lower than those of the originally injected hydrocarbon mixtures. As the volume ratio of the bulk at the initial condition to pores decreases, both the bubblepoint and the dewpoint in nanopores increase and the pore two–phase region expands. Within the pore two–phase region, both C1 and C3 are released from the nanopores to the bulk phase as pressure declines. Meanwhile, both liquid and vapor phases become denser as pressure drops. By further decreasing pressure below the dewpoint of confined fluids, C3 in the nanopore can be recovered. Throughout the process, the bulk–phase composition varies, which is in line with the field observation. Collectively, this work captures the coupled complexity of multicomponent and multiphase fluids in multiscale geometries that is inherent to shale reservoirs and provides a theoretical foundation for reservoir simulation, which is significant for the accurate prediction of well productivity and ultimate oil recovery in shale reservoirs.

scholarly journals Silver-catalysed azide–alkyne cycloaddition (AgAAC): assessing the mechanism by density functional theory calculations

2016 ◽  
Vol 3 (9) ◽  
pp. 160090 ◽  
Author(s):  
Biswadip Banerji ◽  
K. Chandrasekhar ◽  
Sunil Kumar Killi ◽  
Sumit Kumar Pramanik ◽  
Pal Uttam ◽  
...  
Keyword(s):  
Density Functional ◽  
Click Reaction ◽  
Cycloaddition Reaction ◽  
Triazole Ring ◽  
Density Functional Theory Calculations ◽  
Dipolar Cycloaddition ◽  
Reaction Conditions ◽  
Functional Theory ◽  
Click Reactions ◽  
Counter Ions

‘Click reactions’ are the copper catalysed dipolar cycloaddition reaction of azides and alkynes to incorporate nitrogens into a cyclic hydrocarbon scaffold forming a triazole ring. Owing to its efficiency and versatility, this reaction and the products, triazole-containing heterocycles, have immense importance in medicinal chemistry. Copper is the only known catalyst to carry out this reaction, the mechanism of which remains unclear. We report here that the ‘click reactions’ can also be catalysed by silver halides in non-aqueous medium. It constitutes an alternative to the well-known CuAAC click reaction. The yield of the reaction varies on the type of counter ion present in the silver salt. This reaction exhibits significant features, such as high regioselectivity, mild reaction conditions, easy availability of substrates and reasonably good yields. In this communication, the findings of a new catalyst along with the effect of solvent and counter ions will help to decipher the still obscure mechanism of this important reaction.

The Cognitive Component of Elite High Jumpers’ Preperformance Routines

2020 ◽  
Vol 34 (2) ◽  
pp. 99-110
Author(s):  
Thomas Gretton ◽  
Lindsey Blom ◽  
Dorice Hankemeier ◽  
Lawrence Judge
Keyword(s):  
Thematic Analysis ◽  
Critical Role ◽  
Valuable Insight ◽  
Psychological Skills ◽  
Cognitive Content ◽  
Successful Performance ◽  
Cognitive Component ◽  
Inductive Thematic Analysis ◽  
Insight Into

Preperformance routines are microlevel performance processes utilized by athletes to facilitate the attainment of an optimal state and enhance the chance for successful performance. Despite continued examination of these routines, only a small proportion of research has been directed toward the cognitive component of these routines. This study explored the cognitive component of elite high jumpers’ preperformance routines, and specifically the consistency of the cognitive content (i.e., psychological skills and strategies). Data were acquired over an 8-week high-jump season and subjected to inductive thematic analysis. Results revealed the consistent implementation of the cognitive content (e.g., visualization) but an inconsistent design of this content (i.e., the content of the visualization). Furthermore, results underline the critical role of high-jump coaches and an athlete’s need to be adaptable and competent in utilizing various types of preperformance routine. This study offers valuable insight into the complexities and inconsistencies of the cognitive component of high jumpers’ preperformance routines.

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