The role of charge in microdroplet redox chemistry

In charged water microdroplets, which occur in nature or in the lab upon ultrasonication or in electrospray processes, the thermodynamics for reactive chemistry can be dramatically altered relative to the bulk phase. Here, we provide a theoretical basis for the observation of accelerated chemistry by simulating water droplets of increasing charge imbalance to create redox agents such as hydroxyl and hydrogen radicals and solvated electrons. We compute the hydration enthalpy of OH- and H+ that controls the electron transfer process, and the corresponding changes in vertical ionization energy and vertical electron affinity of the ions, to create OH• and H• reactive species. We find that at ~ 20 - 50% of the Rayleigh limit of droplet charge the hydration enthalpy of both OH- and H+ have decreased by >50 kcal/mol such that electron transfer becomes thermodynamically favorable, in correspondence with the more favorable vertical electron affinity of H+ and the lowered vertical ionization energy of OH-. We provide scaling arguments that show that the nanoscale calculations and conclusions extend to the experimental microdroplet length scale. The relevance of the droplet charge for chemical reactivity is illustrated for the formation of H2O2, and has clear implications for other redox reactions observed to occur with enhanced rates in microdroplets

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

Simple and Accurate One-Body Energy and Dipole Moment Surfaces for Water and Beyond

Water is often the testing ground for new, advanced force fields. While advanced functional forms for intermolecular interactions have been integral to the development of accurate water models, less attention has been paid to a transferable model for intramolecular valence terms. In this work, we present a one-body energy and dipole moment surface model, named 1B-UCB, that is simple yet accurate and can be feasibly adapted for both standard and advanced potentials. 1B-UCB for water is comparable in accuracy to those with much more complex functional forms, despite having drastically fewer parameters. The parametrization protocol has been implemented as part of the Q-Force automated workflow and requires only a quantum mechanical Hessian calculation as reference data, hence allowing it to be easily extended to a variety of molecular systems beyond water, which we demonstrate on a selection of small molecules with different symmetries

Spontaneous Formation of Hydrogen Peroxide in Water Microdroplets

There is accumulating evidence that many chemical reactions are accelerated by several orders of magnitude in micrometer-sized aqueous or organic liquid droplets compared to their corresponding bulk liquid phase. However, the molecular origin of the enhanced rates remains unclear as in the case of spontaneous appearance of 1 μM hydrogen peroxide in water microdroplets. In this Letter, we consider the range of ionization energies and whether interfacial electric fields of a microdroplet can feasibly overcome the high energy step from hydroxide ions (OH-) to hydroxyl radicals (OH•) in a primary H2O2 mechanism. We find that the vertical ionization energies (VIEs) of partially solvated OH- ions are greatly lowered relative to the average VIE in the bulk liquid, unlike the case of the Cl- anion which shows no reduction in the VIEs regardless of solvation environment. Overall reduced hydrogen-bonding and undercoordination of OH- are structural features that are more readily present at the air-water interface, where the energy scale for ionization can be matched by statistically probable electric field values

Origin of Many-Body Vibrational Frequency Shifts in Water Clusters

We have demonstrated the application of many-body expansions to calculations of the anharmonic, local-mode, OH-stretching vibrational frequencies of water clusters. We focused on five low-lying isomers of the water hexamer and the DD*­(20,1) isomer of (H₂O)₂₁. Our approach provides accurate OH-stretching vibrational frequencies when treating one- and two-body interactions with the CCSD­(T)-F12 level of theory and the three- and four-body interactions with the DF-MP2-F12 level. Additionally, we have investigated the physical origin of the large contribution that two- and three-body interactions make to the shifts of vibrational frequencies using symmetry-adapted perturbation theory (SAPT). We conclude that while two-body vibrational frequency shifts can be correlated linearly with electrostatic energies, all strongly shifted three-body interactions can be correlated to the induction energy with a single regression coefficient of approximately 70 cm^–1 (kcal·mol^–1)⁻¹

Using Diffusion Maps to Analyze Reaction Dynamics for a Hydrogen Combustion Benchmark Dataset

We use local diffusion maps to assess the quality of two types of collective variables (CVs) for a recently published hydrogen combustion benchmark dataset1 that contains ab initio molecular dynamics (MD) trajectories and normal modes along minimum energy paths. This approach was recently advocated in2 for assessing CVs and analyzing reactions modeled by classical MD simulations. We report the effectiveness of this approach to molecular systems modeled by quantum ab initio MD. In addition to assessing the quality of CVs, we also use global diffusion maps to perform committor analysis as proposed in.2 We show that the committor function obtained from the global diffusion map allows us to identify transition regions of interest in several hydrogen combustion reaction channels

Mitigation of nitrogen mustard mediated skin injury by a novel indomethacin bifunctional prodrug

Described by Sir John Betjeman as 'the Grand Architectural Walk', Syon House and its 200 acre park is the London home of the Duke of Northumberland, whose family have lived here for over 400 years. Originally the site of a medieval abbey, Syon was named after Mount Zion in the Holy Land. At Syon House, London, between 1760 and 1769, Adam took a quadrangular Tudor nunnery with a later Jacobean long gallery, which had been somewhat adapted for greater aristocratic comfort, and transformed it into what Horace Walpole was to describe as ‘another Mount Palatine’. He created a series of rooms of varied and unusual shapes, partially derived from Roman Baths; these he ornamented with lively decoration, also reflecting Classical influences, ranging from apses screened by columns to statuary, grotesques and trophy panels. Responding to the demands of fashionable society, these were spaces intended for various functions that not only were appropriate for those functions but delighted the eye by their variation and ornamentation. This would have been carried even further had he been allowed to fill Syon’s interior courtyard with a great circular saloon, as he had intended (the cost was prohibitive).; Described by Sir John Betjeman as 'the Grand Architectural Walk', Syon House and its 200 acre park is the London home of the Duke of Northumberland, whose family have lived here for over 400 years. Originally the site of a medieval abbey, Syon was named after Mount Zion in the Holy Land. At Syon House, London, between 1760 and 1769, Adam took a quadrangular Tudor nunnery with a later Jacobean long gallery, which had been somewhat adapted for greater aristocratic comfort, and transformed it into what Horace Walpole was to describe as ‘another Mount Palatine’. He created a series of rooms of varied and unusual shapes, partially derived from Roman Baths; these he ornamented with lively decoration, also reflecting Classical influences, ranging from apses screened by columns to statuary, grotesques and trophy panels. Responding to the demands of fashionable society, these were spaces intended for various functions that not only were appropriate for those functions but delighted the eye by their variation and ornamentation. This would have been carried even further had he been allowed to fill Syon’s interior courtyard with a great circular saloon, as he had intended (the cost was prohibitive). Source: Grove Art Online; http://www.oxfordartonline.com/ (accessed 6/15/2009