Comparison of brown midrib-6 and -18 forage sorghum with conventional sorghum and corn silage in diets of lactating dairy cows

Total mixed rations containing conventional forage sorghum, brown midrib (bmr)-6 forage sorghum, bmr-18 forage sorghum, or corn silage were fed to Holstein dairy cows to determine the effect on lactation, ruminal fermentation, and total tract nutrient digestion. Sixteen multiparous cows (4 ruminally fistulated; 124 d in milk) were assigned to 1 of 4 diets in a replicated Latin square design with 4-wk periods (21-d adaptation and 7 d of collection). Diets consisted of 40% test silage, 10% alfalfa silage, and 50% concentrate mix (dry basis). Acid detergent lignin concentration was reduced by 21 and 13%, respectively, for the bmr-6 and bmr-18 sorghum silages when compared with the conventional sorghum. Dry matter intake was not affected by diet. Production of 4% fat-corrected milk was greatest for cows fed bmr-6 (33.7 kg/d) and corn silage (33.3 kg/d), was least for cows fed the conventional sorghum (29.1 kg/d), and was intermediate for cows fed the bmr-18 sorghum (31.2 kg/d), which did not differ from any other diet. Total tract neutral detergent fiber (NDF) digestibility was greatest for the bmr-6 sorghum (54.4%) and corn silage (54.1%) diets and was lower for the conventional (40.8%) and bmr-18 sorghum (47.9%) diets. In situ extent of NDF digestion was greatest for the bmr-6 sorghum (76.4%) and corn silage (79.0%) diets, least for the conventional sorghum diet (70.4%), and intermediate for the bmr-18 sorghum silage diet (73.1%), which was not different from the other diets. Results of this study indicate that the bmr-6 sorghum hybrid outperformed the conventional sorghum hybrid; the bmr-18 sorghum was intermediate between conventional and bmr-6 in most cases. Additionally, the bmr-6 hybrid resulted in lactational performance equivalent to the corn hybrid used in this study. There are important compositional differences among bmr forage sorghum hybrids that need to be characterized to predict animal response accurately.     

How donor-bridge-acceptor energetics influence electron tunneling dynamics and their distance dependences

Long-range electron transfer may occur via two fundamentally different mechanisms depending on the combination of electron donor, acceptor, and the bridging medium between the two redox partners. Activating the so-called hopping mechanism requires matching the energy levels of the donor and the bridge. If electrons from the donor can thermodynamically access bridge-localized redox states, the bridge may be temporarily reduced before the electron is forwarded to the acceptor. As a result, electron transfer rates may demonstrate an extremely shallow dependence on distance. When transient reduction of the bridging medium is thermodynamically impossible, a tunneling mechanism that exponentially depends on distance becomes important for electron transport. Fifty years ago, superexchange theory had already predicted that electron transfer rates should be affected by donor-bridge-acceptor energetics even in the tunneling regime, in which the energy gap (Δε) is too large for electrons to hop from the donor onto the bridge. However, because electron tunneling rates depend on many parameters and the influence of donor-bridge energy gaps is difficult to distinguish from other influences, direct experimental support for the theoretical prediction has been difficult to find. Because of remarkable progress, particularly in the past couple of years, researchers have finally found direct evidence for the long-sought but elusive tunneling-energy gap effect. After a brief introduction to the theory of the tunneling mechanism, this Account discusses recent experimental results describing the importance of the tunneling-energy gap. Experimental studies in this area usually combine synthetic chemistry with electrochemical investigations and time-resolved (optical) spectroscopy. For example, we present a case study of hole tunneling through synthetic DNA hairpins, in which different donor-acceptor couples attached to the same hairpins resulted in tunneling rates with significantly different dependences on distance. Recent systematic studies of conjugated molecular bridges have demonstrated the same result: The distance decay constant (β), which describes the steepness of the exponential decrease of charge tunneling rates with increasing donor-acceptor distance, is not a property of the bridge alone; rather it is a sensitive function of the entire donor-bridge-acceptor (D-b-A) combination. In selected cases, researchers have found a quantitative relationship between the experimentally determined distance decay constant (β) and the magnitude of the tunneling-energy gap (Δε). The rates and efficiencies of charge transfer reactions occurring over long distances are of pivotal importance in light-to-chemical energy conversion and molecular electronics. Tunneling-energy gap effects play an intriguing role in the formation of long-lived charge-separated states after photoexcitation: The kinetic stabilization of these charge-separated states frequently exploits the inverted driving-force effect. Recent studies indicate that tunneling-energy gap effects can differentiate the distance dependences of energy-storing charge-separation reactions from those of energy-wasting charge-recombination processes. Thus, the exploitation of tunneling-energy gap effects may provide an additional way to obtain long-lived charge-separated states.     

Thin water films and particle morphology evolution in nanocrystalline MgO

A key question in the field of ceramics and catalysis is how and to what extent residual water in the reactive environment of a metal oxide particle powder affects particle coarsening and morphology. With X‐ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), we investigated annealing‐induced morphology changes on powders of MgO nanocubes in different gaseous H₂O environments. The use of such a model system for particle powders enabled us to describe how adsorbed water that originates from short exposure to air determines the evolution of MgO grain size, morphology, and microstructure. While cubic nanoparticles with a predominant abundance of (100) surface planes retain their shape after annealing to T = 1173 K under continuous pumping with a base pressure of water p(H₂O) = 10^?5 mbar, higher water partial pressures promote mass transport on the surfaces and across interfaces of such particle systems. This leads to substantial growth and intergrowth of particles and simultaneously favors the formation of step edges and shallow protrusions on terraces. The mass transfer is promoted by thin films of water providing a two‐dimensional solvent for Mg²⁺ ion hydration. In addition, we obtained direct evidence for hydroxylation‐induced stabilization of (110) faces and step edges of the grain surfaces.