PubMed · 14139220
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E A CHRISTENSEN. 1964-03-12. [RECENT STERILIZATION METHODS].. https://pubmed.ncbi.nlm.nih.gov/14139220/
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Ab initio conformational maps for beta-lactose in both the gas phase and in aqueous solution have been constructed at the HF/6-31G(d,p) level of calculation. The results of the gas-phase ab initio calculations allow us to conclude that a rigid conformational map is able to predict the regions of the minima in the potential energy surface of beta-lactose, in full agreement with those found in the relaxed conformational map. The solvation effects do not give rise to any new local minimum in the potential energy surface of beta-lactose, but just change the relative Boltzmann populations of the conformers found in the gas-phase calculations. The values obtained for heteronuclear spin coupling constant (3J(H,C)), using the seven most stable conformers in solution are in good agreement with the available experimental values. This is a good indication that ab initio rigid conformational maps can be reliably used to sort the most stable conformers of beta-lactose.
The gas phase reactions of protonated tryptophan have been examined in a quadrupole ion trap using a combination of collision induced dissociation, hydrogen-deuterium exchange, regiospecific deuterium labeling and molecular orbital calculations (at the B3LYP/6-31G* level of theory). The loss of ammonia from protonated tryptophan is observed as the primary fragmentation pathway, with concomitant formation of a [M + H - NH(3)](+) ion by nucleophilic attack from the C3 position of the indole side chain. Hydrogen-deuterium exchange and regiospecific deuterium labeling reveals that scrambling of protons in the C2 and C4 positions of the indole ring, via intramolecular proton transfer from the thermodynamically preferred site of protonation at the amino nitrogen, precedes ammonia loss. Molecular orbital calculations have been employed to demonstrate that the activation barriers to intramolecular proton transfer are lower than that for NH(3) loss.
A theory for a nanometer-scale pump based on the ratchet concept is presented. A lattice gas model with a set of moves that satisfy hydrodynamic equations is used to describe an asymmetric nanometer channel connecting two reservoirs of fluid. The channel, which is coupled to an external oscillatory (or stochastic) driving force, pumps fluid from one reservoir to the other. The frequency of the external driving force, the fluid density, and the channel dimensions are used to control the fluid flow. We observe a nonmonotonic behavior of the flow with respect to some model parameters and discuss the efficiency of the device.