Search

We have probed under high pressure the C–H hydrogen bonds formed by N,N′-disubstituted imidazolium ions having PF6- and Br- counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds. The appearance of a signal for the free-NH unit (or weakly bonded N–H...F unit) in the infrared spectrum of the PF6- salt indicates that conventional N–H...O and N–H...N hydrogen bonds do not fully dominate the packing. It is likely that the charge-enhanced C2–H...F interactions, combined with other weak hydrogen bonds, disturb the formation of N–H hydrogen bonds in the PF6- salt. This finding is consistent with the pressure-dependent results, which reveal that the C2–H...F interaction is enhanced upon increasing the pressure. In contrast to the PF6- salt, the imidazolium C–H bonds of the Br- salt have low sensitivity to high pressure. This finding suggests that the hydrogen bonding patterns are determined by the relative hydrogen bond acceptor strengths of the Br- and PF6- ions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: To monitor the bioactivity change of a hydrogen fermentor, this work presents a novel bioelectrochemical method equipped with a polyviologen modified glassy carbon as a working electrode and with ferricyanide as an electron mediator. Experimental results demonstrated that the ferricyanide can transfer electrons from hydrogen producing bacteria cells to electrode without significant inhibition on cell growth. To protect the electrode from fouling by protein and bacteria during bioassay, polyviologen film was applied to modify the working electrode, and stabilized the responding current compared to the use of bare electrode. The amperometric bioassay provided the bioactivity information for indicating the statue of the fermentor and helping draw up the operation strategy when the fermentor was operated under abnormal conditions, including stop-feeding and re-feeding. The results of bioactivity monitoring suggested an interesting phenomenon that the activity of hydrogen producing bacteria transiently increased during the unsteady period and then decreased. [Copyright &y& Elsevier]