A theory of nonvertical triplet energy transfer in terms of accurate potential energy surfaces: the transfer reaction from pi,pi* triplet donors to 1,3,5,7-cyclooctatetraene

Triplet energy transfer (TET) from aromatic donors to 1,3,5,7-cyclooctatetraene (COT) is an extreme case of "nonvertical" behavior, where the transfer rate for low-energy donors is considerably faster than that predicted for a thermally activated (Arrhenius) process. To explain the anomalous TET of COT and other molecules, a new theoretical model based on transition state theory for nonadiabatic processes is proposed here, which makes use of the adiabatic potential energy surfaces (PES) of reactants and products, as computed from high-level quantum mechanical methods, and a nonadiabatic transfer rate constant. It is shown that the rate of transfer depends on a geometrical distortion parameter gamma=(2g(2)/kappa(1))(1/2) in which g stands for the norm of the energy gradient in the PES of the acceptor triplet state and kappa(1) is a combination of vibrational force constants of the ground-state acceptor in the gradient direction. The application of the model to existing experimental data for the triplet energy transfer reaction to COT from a series of pi,pi(*) triplet donors, provides a detailed interpretation of the parameters that determine the transfer rate constant. In addition, the model shows that the observed decrease of the acceptor electronic excitation energy is due to thermal activation of C=C bond stretchings and C-C bond torsions, which collectively change the ground-state COT bent conformation (D(2d)) toward a planar triplet state (D(8h)).     

Determination of the free activation energy for the breaking of the P---Ag bond in [(η-p-cymene)Ru(μ-pz)3Ag(PPh3)]

The Arrhenius equation corresponding to the process P---Ag+P*---Ag*→---P---Ag*+P*---Ag has been determined for [(η⁶-p-cymene)Ru(μ-pz)₃Ag(PPh₃)] (1) by complete line-shape analysis of the ³¹P NMR spectra between −40°C and +30°C. It has the form K = 10^11.8± e^{(−46±5 kJ mol−1/RT)}. The preexponential term, log A = 11.8 corresponds to a small activation entropy, whereas the activation energy, 46 kJ mol⁻¹ is comparable to those determined for other phosphorus—metal compounds.     

A Note on the Subcritical Two Dimensional Keller-Segel System

The existence of solution for the 2D-Keller-Segel system in the subcritical case, i.e. when the initial mass is less than 8π, is reproved. Instead of using the entropy in the free energy and free energy dissipation, which was used in the proofs (Blanchet et al. in SIAM J. Numer. Anal. 46:691–721, 2008; Electron. J. Differ. Equ. Conf. 44:32, 2006 (electronic)), the potential energy term is fully utilized by adapting Delort’s theory on 2D incompressible Euler equation (Delort in J. Am. Math. Soc. 4:553–386, 1991).     

A theoretical investigation of the mechanism of formation of a simplified analog of the green fluorescent protein (GFP) from a peptide model

Theoretical calculations at the B3LYP/6-311++G(d,p) level have been carried out on the reaction path connecting a dipeptide to an imidazolinone as a model for the formation of GFP. In addition, we have studied the hydration effects on the processes, adding a water molecule to assist the cyclization. The solvent effects have been taken into account by introducing the monohydrated molecules into a solvent cavity with a polarized continuum model. Significant reductions of the energy barriers for the reaction path can be observed within the water-assisted processes. The solvent effects account for a barrier lowering of 4–5 kJ mol^?1.     

Is the US stock market becoming weakly efficient over time? Evidence from 80-year-long data

We propose a degree of market efficiency in terms of entropy concepts. The relative efficiency for the US stock market varies over time from 1929 to 2012, with a slight decline in the past 10 years.     

Metal Oxide Assisted Preparation of Core–Shell Beads with Dense Metal–Organic Framework Coatings for the Enhanced Extraction of Organic Pollutants

Dense and homogeneous metal–organic framework (MOF) coatings on functional bead surfaces are easily prepared by using intermediate sacrificial metal oxide coatings containing the metal precursor of the MOF. Polystyrene (PS) beads are coated with a ZnO layer to give ZnO@PS core–shell beads. The ZnO@PS beads are reactive in the presence of 2‐methylimidazole to transform part of the ZnO coating into a porous zeolitic imidazolate framework‐8 (ZIF‐8) external shell positioned above the internal ZnO precursor shell. The obtained ZIF‐8@ZnO@PS beads can be easily packed in column format for flow‐through applications, such as the solid‐phase extraction of trace priority‐listed environmental pollutants. The prepared material shows an excellent permeance to flow when packed as a column to give high enrichment factors, facile regeneration, and excellent reusability for the extraction of the pollutant bisphenol A. It also shows an outstanding performance for the simultaneous enrichment of mixtures of endocrine disrupting chemicals (bisphenol A, 4‐tert‐octylphenol and 4‐n‐nonylphenol), facilitating their analysis when present at very low levels (<1 μg L^?1) in drinking waters. For the extraction of the pollutant bisphenol A, the prepared ZIF‐8@ZnO@PS beads also show a superior extraction and preconcentration capacity to that of the PS beads used as precursors and the composite materials obtained by the direct growth of ZIF‐8 on the surface of the PS beads in the absence of metal oxide intermediate coatings.     

Multinuclear magnetic resonance studies of five silver(I) trinuclear pyrazolate complexes

Structural Chemistry - Experimental multinuclear determination of the chemical shifts, especially 15N and 109Ag, of five silver(I) trinuclear pyrazolate complexes, (PzAg)3, coupled with ZORA...