Description: This article discusses oxygen atom transfer energetics. Several density functional methods, the semiempirical methods AM1 and PM3, Hartree-Fock, and Gaussian3 theories were applied to compute the oxygen atom transfer enthalpies for 14 X/XO couples (inorganic and organic systems, charged and neutral species, light and heavy main group element containing molecules). The calculated reaction enthalpies were compared to available experimental data. The G3 method alone was found to perform within the experimental error, while the popular B3LYP and BLYP functionals provided inadequate results. Solvent effects were estimated for 19 neutral and anionic X/XO couples by using the conductor-like polarizable continuum model and several cavity models coupled with the B3LYP/6-31++G-(2d,2p) level of theory. Surprisingly, the magnitude of the aqueous solvent correction was found to vary significantly for different solute cavity models, occasionally giving larger errors than the gas-phase calculation.

Description: This article discusses pediatric functional magnetic resonance neuroimaging. Background: Neuroimaging technology has afforded advances in our understanding of normal and pathological brain function and development in children and adolescents. However, noncompliance involving the inability to remain in the magnetic resonance imaging (MRI) scanner to complete tasks is one common and significant problem. Task noncompliance is an especially significant problem in pediatric functional magnetic resonance imaging (fMRI) research because increases in noncompliance produces a greater risk that a study sample will not be representative of the study population. Method: In this preliminary investigation, the authors describe the development and application of an approach for increasing the number of fMRI tasks children complete during neuroimaging. Twenty-eight healthy children ages 9-13 years participated. Generalization of the approach was examined in additional fMRI and event-related potential investigations with children at risk for depression, children with anxiety and children with depression (N = 120). Essential features of the approach include a preference assessment for identifying multiple individualized rewards, increasing reinforcement rates during imaging by pairing tasks with chosen rewards and presenting a visual 'road map' listing tasks, rewards and current progress. Results: Our results showing a higher percentage of fMRI task completion by healthy children ...

Description: This article discusses the performance of density functional theory for 3d transition metal-containing complexes. The performance of 44 density functionals used in conjunction with the correlation consistent basis sets (ccpVnZ where n = T and Q) has been assessed for the gas-phase enthalpies of formation at 298.15 K of 3d transition metal (TM) containing systems. Nineteen molecules were examined: ScS, VO, VO₂, Cr(CO)₆, MnS, MnCl₂, Mn(CO)₅Cl, FeCl₃, Fe(CO)₅, CoH(CO)₄, NiCl₂, Ni(CO)₄, CuH, CuF, CuCl, ZnH, ZnO, ZnCl, and Zn(CH₃)₂. Of the functionals examined, the functionals that resulted in the smallest mean absolute deviation (MAD, in parentheses, kcal molˉ¹) from experiment were B97-1(6.9), PBE1KCIS (8.1), TPSS1KCIS (9.6), B97-2(9.7), and B98(10.7). All five of these functionals include some degree of Hartree-Fock (HF) exchange. The impact of increasing the basis set from cc-pVTZ to cc-pVQZ was found to be slight for the generalized gradient approximation (GGA) and meta-GGA (MGGA) functionals studied, indicating basis set saturation at the triple-ζ level. By contrast, for most of the generalized gradient exchange (GGE), hybrid GGA (HGGA), and hybrid meta-GGA (HMGGA) functionals considered, improvements in the average MAD of 2-3 kcal molˉ¹ were seen upon progressing to a quadruple-ζ level basis set. Overall, it was found that the ...

Description: This article discusses a periodic and molecular modeling study. Supramolecular stacked materials (dbbpy)Pt(tdt)•TENF and [Pt(dbbpy)(tdt)]₂•TENF are built from (dbbpy)Pt(tdt) donors (D) with TENF acceptors (A) (TENF = 2,4,5,7-tetranitro-9-fluorenone; dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt = 3,4-toluenedithiolate). Simulations using extended Hückel tight binding (EHTB) and plane-wave DFT methods are performed. From EHTB analysis, the density of states (DOS) of D/A and DD/A stacks exhibit metallic behavior with a large contribution from TENF π in the valence band mixed with more significant Pt character in the D/A than in the DD/A stacks. DOS modification and charge transfer are estimated via analysis of the stacking sequences. Theoretical results from plane-wave DFT calculations give evidence of semimetallic behavior for the D/A material (gap < 0.1 eV) and metallic behavior for DD/A. Fragment analysis was performed, and similarities and differences between EHTB and DFT were noted. Molecular DFT computations suggest that the close (~3.6 Å) D-A distances are sufficient to allow some intermolecular donor-to-acceptor charge transfer and high interaction energy in DD/A than in D/A units, consistent with the periodic calculations for the solid-state stacks. Calculations of metric data via modeling of a (dbbpy)Pt(tdt)•TENF cluster as well as neutral, cationic, and anionic TENF are used to assess ...

Description: This article discusses phase transition enthalpy measurements of organic and organometallic compounds. A compendium of phase change enthalpies published within the period 1880-2010 is reported. Phase change enthalpies including fusion, vaporization, and sublimation are included for organic, organometallic, and a few inorganic compounds. This compendium is a combination of three previous series focusing on phase change enthalpies updated to 2009. Sufficient data are presently available for some compounds to permit thermodynamic cycles to be constructed, an important manner of evaluating the reliability of the measurements. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T = 298.15 K, are briefly discussed and a protocol for doing so is illustrated.