Gas Transfer Controls Carbon Limitation During Biomass Production by Marine Microalgae.

This study presents the first in-depth analysis of CO2 limitation on the biomass productivity of the biofuel candidate marine microalga Nannochloropsis oculata. Net photosynthesis decreased by 60% from 125 to 50 μmol O2 L(-1)h(-1) over a 12 h light cycle as a direct result of carbon limitation. Continuous dissolved O2 and pH measurements were used to develop a detailed diurnal mechanism for the interaction between photosynthesis, gas exchange and carbonate chemistry in the photo-bioreactor.

Photodissociation of CH3I: a full-dimensional (9D) quantum dynamics study.

The photodissociation of methyl iodide in the A band is studied by full-dimensional (9D) wave packet dynamics calculations using the multiconfigurational time-dependent Hartree approach. The potential energy surfaces employed are based on the diabatic potentials of Xie et al. [J.

Trapping a diradical transition state by mechanochemical polymer extension.

Transition state structures are central to the rates and outcomes of chemical reactions, but their fleeting existence often leaves their properties to be inferred rather than observed. By treating polybutadiene with a difluorocarbene source, we embedded gem-difluorocyclopropanes (gDFCs) along the polymer backbone. We report that mechanochemical activation of the polymer under tension opens the gDFCs and traps a 1,3-diradical that is formally a transition state in their stress-free electrocyclic isomerization.

Locally optimized coordinates in modified Shepard interpolation.

An extension of the modified Shepard interpolation method is presented that allows expansions for the potential energy using different local coordinate sets to be used in a global interpolation. The coordinates used in a given Taylor expansion are determined using a training set of geometries at which the ab initio potential energy is known and that is built up during the construction of the interpolated potential energy surface. The method is applied to the bound state potential energy surface of methanol and a significant improvement in the rate of convergence of the interpolated potential energy surface to the ab initio potential energy is observed.

Calculating vibrational spectra using modified Shepard interpolated potential energy surfaces.

A potential energy interpolation approach based on modified Shepard interpolation and specifically designed for calculation of vibrational states is presented. The importance of the choice of coordinates for the rate of convergence is demonstrated. Studying the vibrational states of the water molecule as a test case, a coordinate system comprised of inverse bond distances and trigonometric functions of the bond angle is found to be particularly efficient.

Effect of the air-water interface on the structure of lysozyme in the presence of guanidinium chloride.

We report observations of the changes in the surface structure of lysozyme adsorbed at the air-water interface produced by the chemical denaturant guanidinium chloride. A primary result is the durability of the adsorbed surface layer to denaturation, as compared to the molecule in the bulk solution. Data on the surface film were obtained from X-ray and neutron reflectivity measurements and modeled simultaneously.

Interpolation of multidimensional diabatic potential energy matrices.

A method for constructing diabatic potential energy matrices by interpolation of ab initio quantum chemistry data is described and tested. This approach is applicable to any number of interacting electronic states, and relies on a formalism and a computational procedure that are more general than those presented previously for the case of two electronic states. The method is tested against an analytic model for three interacting electronic states of NH(3) (+).

Interpolation of diabatic potential-energy surfaces: quantum dynamics on ab initio surfaces.

A method for constructing diabatic potential-energy matrices from ab initio quantum chemistry data is described and tested for use in exact quantum reactive scattering. The method is a refinement of that presented in a previous paper, in that it accounts for the presence of the nonremovable derivative coupling. The accuracy of quantum dynamics on this type of diabatic potential is tested by comparison with an analytic model and for an ab initio description of the two lowest-energy states of H3.

Interpolation of diabatic potential energy surfaces.

A method is presented for constructing diabatic potential energy matrices from ab initio quantum chemistry data. The method is similar to that reported previously for single adiabatic potential energy surfaces, but correctly accounts for the nuclear permutation symmetry of diabatic potential energy matrices and other complications that arise from the derivative coupling of electronic states. The method is tested by comparison with an analytic model for the two lowest energy states of H(3).